Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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PCT Patent Application
Series Fans with Flow Modification Element
Inventor: Howard Harrison
November 12, 2004
Priority
This application claims priority from US 60/520,678 (High performance Series
Fan
Configurations, filed November 18, 2003) and US 60/520,676 (Dual Redundant
Cooling
Fan Sinks and Trays, filed November 18, 2003)
Field of the Invention
This invention relates to a unique series fan configuration intended for
cooling
electronics. The configuration is modular, extremely compact, fault tolerant,
and uses
readily available low cost axial fans. A display panel may be configured to
alert the user
regarding a failed fan, which may then be replaced (or "hot swapped") without
shutting
down the system being cooled.
Acknowledgement of Prior Art
The need for highly reliable, fault tolerant, and hot swappable cooling fans
has increased
as the mission critical use of high performance electronics becomes more and
more
prevalent. In many cases a loss of cooling for more than a brief moment could
damage
the underlying electronic components.
This has driven a tremendous amount of inventive activity in the field as
evidenced by
numerous recent patents including US patent 6,247,898 issued June 19, 2001 to
Henderson, et al (assigned to Micron Electronics), US Patent 6,108,203 issued
Aug. 22,
2000 to Dittus, et al (as"signed to IBM), US patent 6,101,459 issued Aug. 8,
2000 to
Tavallaei, et al (assigned to Compaq Computer), US patent 6,061,237 issued May
9,
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2000 to Sands, et al (assigned to Dell Computer), US patent 6,040,987 issued
Mar. 21,
2000 to Schmitt, et al (assigned to Dell), US patent 6,031,717 issued Feb. 29,
2000 to
Baddour, et al (assigned to Dell Computer), US patent 6,021,042 issued Feb. 1.
2000 to
Anderson, et al (assigned to Intel Corporation), US patent 6,005,770 issued
Dec. 21,
1999 to Schmitt (assigned to Dell Computer), US patent 5,572,403 issued Nov.
5, 1996
to Mills, et al (assigned to Dell Computer), and US patent 5,562,410 issued
Oct. 8, 1996
to Sachs, et al (assigned to EMC Corporation),
Most of these patents, including US Patent 6,108,203 assigned to IBM, US
patent
6,101,459 assigned to Compaq, US patent 6,061,237 assigned to Dell, US patent
6,031,717 assigned to Dell, US 6,021,042 assigned to Intel, and US patent
6,005,770
assigned to Dell teach redundant fans operating in parallel. Of these, US
6,108,203, US
6,061, 237, US 6,031,717, US 6,021,042, and US 6,005,770 all teach various
types of
baffling to prevent the reverse flow of air through the defective fan, and the
ensuing loss
of cooling air pressure within the cabinet. US 6,101,459 teaches that this
reverse flow of
air may be prevented by placing a second, back-up, fan in series with each of
the
parallel fans. However it must be noted that this same patent also teaches
that the back-
up fans remain idle until required. These patents also suggest various ways to
ease the
process of replacing the defective fan(s). US 6,061, 237 teaches that two
parallel fans
may be placed at an angle to save space.
Only two of these patents, US 6,101,459 assigned to Compaq and US 5,572,403
assigned to Dell, suggest a series configuration for the cooling fans. Of
these, US
6,101,459 teaches that the second fan in the series is for back-up purposes
only, and
will remain idle until required as previously noted. US 5,572, 403 does teach
that the
series configured fans run simultaneously, in counter-rotating fashion, and
further
teaches that a plenum bypass be used to reduce impedance and increase airflow
in the
event of a fan failure. However this approach requires specialized fans and
also requires
further baffling within the cabinet to accommodate the plenum bypass flow when
required.
An additional two of these patents, US 6,040,981 assigned to Dell and US
5,562,410
assigned to EMC address the issues of easy fan removal and hot swappable fans.
US
6,040,981 teaches a removable fan with camming handle that aligns the fan and
re-
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connects power in a single operation. US 5,562,410 teaches a self aligning hot-
pluggable fan assembly, primarily to complement the fault tolerant
characteristic of RAID
based disk arrays.
Finally, US 6,247,898 teaches a method of controlling the speed of a plurality
of fans
connected in parallel fashion.
Summary of the invention
As taught by prior art, a currently accepted solution is to install dual fans
(or blowers) in
a parallel configuration such that one fan has the capacity to cool the entire
cabinet, at
least on a minimal cooling basis. In this manner, the failure of one fan can
be tolerated
without damaging the equipment. While this approach works, the parallel
installation has
the following associated problems; (1) mounting two fans side by side requires
twice as
much cabinet wall space, and increases the potential for Electro-Magnetic (EM)
leakage
through the fan opening, (2) the fail over mechanism must contain sufficient
baffling to
prevent air from escaping (or entering) through the defective fan, a complex
and bulky
approach, (3) further baffling is required to ensure that the air stream is
directed
consistently regardless of which fan is operating, and (4) the system may need
to be
shut down before replacing the defective fan.
There are benefits to mounting the fans in series rather than in parallel -
i.e. place one
fan behind the other rather than one fan beside the other. However the problem
with this
approach has been that two fans in series do not perform well because the
airflow
produced by the primary fan contains swirl, and this does not match the ideal
input
conditions for the secondary fan. The secondary fan must have a substantially
reduced
level of swirl at its input to operate efficiently.
Despite this drawback, the series configuration solves many of the problems
associated
with the parallel configuration; (1) a series configuration takes less cabinet
wall space
than a parallel configuration, and therefore reduces the potential EM leakage,
(2) no
baffling is required to prevent air from escaping through the defective fan -
in fact air
must flow through the defective fan in order for the series configuration to
work, (3) no
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further baffling is required to ensure that the air is consistently directed
since the two
fans are mounted on the same or similar axis, and (4) a defective fan may be
safely
replaced or "hot swapped" without shutting down the system or components being
cooled.
Accordingly the present invention discloses a method of reducing the swirl
between the
two fans by placing a flow modification element, or diffuser element, between
the two
fans, so that the above benefits can be realized. The present invention also
discloses
several additional features that will contribute to functionality, ease of
use, ease of
maintenance, and lower cost such as; (1) an integrated filter / flow control
element, (2) a
user interface panel to show the status of both fans and the integrated filter
element, (3)
the ability to replace the filter element or the defective fan from outside
the cabinet while
the system is running, and (4) a very compact and modular device that can be
installed
between two industry standard fans to create a high performance series fan
configuration. Further, the present invention discloses many applications for
high
performance series fans such as for the cooling of components, heat sinks,
system
cabinets, and enclosures.
It is commonly known that an axial fan works best if it sees laminar flow on
the input
side. This condition is met with a single fan since there is nothing on the
input side to
generate swirl. However this is not the case with a series configuration since
the output
of the primary fan, as in the case of all axial fans, contains swirl.
The present invention discloses that this problem may be resolved by placing a
diffuser
element between the two fans. The result of placing a diffuser element between
the two
fans is to substantially reduce the swirl produced by the primary fan before
the airflow
enters the secondary fan, thereby increasing the efficiency of the secondary
fan.
The use of an intermediate diffuser element will not affect the primary
inherent
advantages of a series fan configuration - the airflow will always be in the
same
direction, even during a fan failure, and no baffling changes will be required
within the
cabinet to re-direct the flow during a fan failure. In the event of a primary
(or input) fan
failure, the secondary (or output) fan will continue to "pull" air through the
diffuser
element and move it in the same direction. Likewise air will continue to flow
in the same
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direction if the secondary fan fails, except that the primary fan will "push"
rather than
"pull" air through the diffuser element.
Although the direction of airflow will remain consistent in a series fan
configuration with a
single fan failure, the volume of airflow will be reduced if the remaining fan
continues to
operate at the same speed. This is an acceptable situation only if the volume
of airflow
does not fall below the minimum required to dissipate the heat generated by
the
components being cooled. The present invention teaches that a control system
may be
configured to sense the fan failure and adjust the remaining fan speed
accordingly, in
order to ensure that this minimum requirement is met until the defective fan
can be
replaced. This type of control may be easily implemented since (1) many fans
today are
available with fault sensors to indicate an impending failure / total failure
and (2) fan
speed can be easily controlled by controlling the input parameters such as
voltage, in
the case of DC fans, or through pulse width modulation.
The efficiency of the series fan configuration, while in single fan failure
mode, may be
increased by allowing the diffuser element to swing or slide out of the air
flow, for
example by splitting the diffuser element down the middle and allowing each
half to
swing out of the flow, or otherwise partially or completely removing the
diffuser element
from the air flow until the defective fan may be replaced. Further, the
efficiency of the
series fan configuration, while in a single fan failure mode, may be increased
by partially
or completely removing the failed fan from the configuration until such time
as it may be
replaced. Further, the efficiency of the series fan configuration, while in a
single fan
failure mode, may be increased by providing a diffuser element bypass channel
configured to allow the free flow of air past the diffuser element while in
failure mode.
Should a fan fail, the present invention teaches that it may be replaced
without having to
shut down the system or components being cooled. High performance series fans
may
be configured as a "sliding drawer" that can be pulled away from the cabinet
without
interrupting the airflow. The defective fan may be replaced while the drawer
is in the
"open" position, and then the drawer may be returned to the "closed" position
without
affecting system operation or necessitating a system shut down. The control
system will
detect the new fan, and adjust speeds accordingly.
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In some cases it may be possible to enhance the functionality of the diffuser
element by
configuring it as a combined filter / diffuser element, to reduce swirl and
prevent particles
from entering the system being cooled, a combined heat exchanger / diffuser
element, to
reduce swirl while adding or removing heat from the airflow, a combined
Electro-
Magnetic (EM) shield / diffuser element, to reduce swirl while maintaining the
integrity of
the EM shield in the fan opening, or other possible combinations. In larger
applications
the diffuser element may be active rather than passive so that the flow
control
parameters may be adjusted and optimized while the high performance series fan
configuration is operating.
Various configurations are possible including a tightly coupled or modular
arrangement,
or a loosely coupled or push / pull arrangement. In a tightly coupled
arrangement a
primary fan and a secondary fan may be mounted at opposite ends of an air
channel, in
a substantially coaxial configuration, such that the air channel contains the
diffuser
element, and directs the airflow from the output of the primary fan, through
the diffuser
element, and into the secondary fan. In a loosely coupled or push / pull
arrangement a
primary fan blows air into an enclosed space and a secondary fan blows air out
of the
same enclosed space, and the components within the enclosed space act as a
type of
diffuser element to remove swirl from the airflow as it moves from the primary
to the
secondary fan. In some loosely coupled configurations a diffuser element may
also be
installed on the input side of the secondary fan to further reduce the swirl
and improve
the efficiency of the secondary fan, and baffling may be added to improve the
efficiency
of the airflow within the enclosed space.
The performance of the secondary fan may be enhanced by increasing the
residual
momentum and reducing the swirl component of the airflow at its input, as
previously
described. The primary fan contributes to this enhanced performance, since it
increases
the residual momentum of the airflow entering the secondary fan, however it
also
introduces a swirl component that is counter-productive. An optimized high
performance
series fan configuration retains a maximum level of residual momentum while
reducing
swirl to an ideal level before the airflow enters the secondary fan.
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The total output of a series fan configuration, relative to the theoretical
output of a non-
optimized series fan configuration (generally considered to generate two times
the static
pressure for any given CFM output), may be expressed, in simple terms, as
follows;
(1) OutputT = (2 x Outputs) + M - S
Where OutputT = Total output
OutputS = Output from single fan
M Momentum Factor (at secondary fan)
S Swirl Factor (at secondary fan)
The momentum factor will naturally decay as the distance between the primary
and
secondary fans is increased, and as more restrictions, e.g. a diffuser
element, are
placed in the airflow. From this perspective the most effective series fan
configurations
will have the least possible distance between the primary and secondary fans,
the
closest co-axial alignment between the two fans, and the least number of
restrictions
between the two fans.
The swirl component will also naturally decay as the distance between the
primary and
secondary fans is increased, and from this perspective the most effective
series fan
configurations will have the greatest possible distance between the primary
and
secondary fans. The present invention teaches that this distance may be
substantially
reduced by installing a diffuser element between the primary and secondary
fans to
force a more rapid decay of swirl, as previously described. In a loosely
coupled series
fan configuration the components to be cooled may serve as a type of diffuser
element,
as in the case of a computer system where the primary and secondary fans are
located
at opposite ends of the cabinet and the air flowing between them must pass
over the
electronic components. Alternatively the diffuser element may be a purpose
built
component placed strategically between the two fans, or in front of the
secondary fan. In
either case the flow straightening element(s) will have both a positive and a
negative
effect since will it reduce the swirl component while at the same time
increasing drag.
Based on this information the, model may be re-constructed as follows;
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(2) OutputT = (2 x Outputs) + M - S + (SR - D)
Where SR = Swirl reduction factor
D = Drag introduced by swirl reducing components
Equation (2) may be re-written as follows to separate the behaviour of the
primary and
secondary fans, and associate this behaviour with the most closely aligned
correction
factor, as observed;
(3) OutputT = (Outputsp - D) + (Outputss + M - (S - SR))
Where Outputsp = Output of a single primary fan
OutputsS = Output of a single secondary fan
It is important to note that Outputsp and Outputss both represent the output
of single fans
operating in independent fashion. It follows that OutputSP and Outputss will
be the same
for a symmetrical series fan configuration, where the primary and secondary
fans have
identical specifications, and that Outputsp and OutputsS will be different for
an
asymmetrical series fan configuration, where the primary and secondary fans
may have
different specifications.
Clearly, then, the optimization objectives are to simultaneously maximize the
momentum
of airflow as it enters the secondary fan (M), minimize the swirl component of
the airflow
as it enters the secondary fan (S - SR), and minimize the drag introduced by
the swirl
reducing components (D). In fact the output of the secondary fan may be
enhanced, in
this manner, to the extent that it exceeds Outputss, i.e. it exceeds the
output of a single
secondary fan operating in independent fashion with input conditions that meet
design
specifications. It follows that the total output of a high performance series
fan
configuration with a diffuser element may exceed the theoretical output of two
single
fans as long as the following optimum condition exists;
(4) M > ((S - SR) - D)
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It has been found that an optimal condition may achieved by (1) mounting the
primary
and secondary fans coaxially at either end of a sealed air conducting tube or
connecting
sleeve, adapted with internal features such as longitudinal grooves or
octagonal corners
to induce natural swirl decay while maintaining the maximum level of momentum
as the
air flows between the two fans, and (2) by placing the diffuser element at a
distance from
the primary fan such that a substantial amount of natural swirl decay will
have occurred
before the airflow enters the diffuser element, as depicted in Figure 24 (with
reference to
the following components and corresponding numbers for Figure 24 only);
Component No. Component No.
Primary Fan 200 Secondary Fan 202
Diffuser Element 204 Seal 206
Airflow 208 Integrated Stator 210
Acoustic Gap 212
The diffuser element may be further optimized to remove substantially all of
the
remaining swirl while introducing a minimal level of incremental drag, thereby
"straightening" the airflow while maintaining its momentum at the highest
possible level
as it leaves the diffuser element, and converting swirl energy to kinetic
energy with the
highest possible efficiency. The diffuser element may be placed immediately
before or in
close proximity to the secondary fan in order to maintain this momentum as the
airflow
enters the secondary fan, recognizing that a small gap may be required between
the
diffuser element and secondary fan to reduce the acoustical noise produced by
the
overall configuration. The diffuser element and the air conducting tube may be
combined
and further adapted in various ways to provide further optimization and
enhanced
performance.
Further optimization may be achieved by controlling the combined momentum and
swirl
at the input to the secondary fan such that the momentum vector(s) drive the
secondary
fan to achieve greater efficiency and performance. Such optimization may
require a
more complex diffuser element design, optimized for efficient swirl energy to
kinetic
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energy conversion, directional control of the momentum vector(s), reduced
drag, and so
on.
Further optimization may also be achieved by using a primary fan with an
integrated
stator on the output side. In this case OutputsP will have less swirl (due to
the
straightening effect of the stator) and a lower flow rate (due to the drag
effects of the
stator) relative to a similar primary fan that does not have an integrated
stator. These
attributes can be used to enhance the performance of, and reduce the overall
length of,
a high performance series fan configuration with diffuser element since the
requirement
for swirl reduction in the area between the two fans will have been reduced by
the
integrated stator on the primary fan. However the reduced level of drag
produced by the
shorter air conducting tube between the two fans, and the smaller diffuser
element, may
be offset by the Incremental drag produced by the integrated stator on the
primary fan.
A closely coupled high performance series fan with diffuser element, or dual
redundant
fan module, is ideally suited for the cooling of cabinets and other
enclosures. Further,
the excellent single stream performance under high static pressures makes it
ideal for
the impingement cooling of CPUs and other electronic components, as well as
the
impingement cooling of power heat sinks. The latter configuration may be
referred to as
a high performance series fan sink.
A loosely coupled or "push / pull" series configuration is depicted in Figure
25 (with
reference to the following components and corresponding numbers for Figure 25
and
Figure 26 only);
Component No. Component No.
Primary Fan 300 Secondary Fan 302
Air Flow In 304 Electronic Components 306
System Cabinet 308 Air Flow Out 310
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A loosely coupled series configuration may be designed to incorporate some of
these
operating parameters, however it will likely deliver sub-optimal performance
relative to a
closely coupled configuration using similar fans. A loosely coupled series
configuration
has a much larger distance and a much less efficient duct between the primary
and
secondary fans, as illustrated below. The result is a substantial loss of
momentum
before the airflow reaches the secondary fan.
The practice of relying on the electronic and other components to remove swirl
may work
to some degree, however it would be extremely difficult to lay out the
components for the
optimization of this function, and doing so may introduce volumetric
inefficiencies in the
design. Further, it would be extremely difficult to configure the components
such that
substantially all of the swirl will have been removed just as the airflow
enters the
secondary fan. Further, the optimized design, if it could be achieved, would
change with
the addition or modification of a single component within the air space
between the two
fans.
In contrast, a tightly coupled or modular series fan configuration operates
with an
optimized design that remains the same regardless of component layout within
the
system cabinet being cooled. While a change in components may affect the
static
pressure or load conditions, it will not affect the optimized design of the
high
performance series fan configuration. In other words the performance curve
(i.e. static
pressure / flow curve) for the high performance series fan configuration will
remain the
same regardless of the change in load curves - it is just the intersection of
these curves
(i.e. the operating point) that will change. The fact that the output of an
optimized high
performance series fan configuration may be plotted as a standard performance
curve
greatly eases the thermal design task since the operating point may be readily
determined in the same way that one would determine the operating point for a
single
fan.
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It is possible to combine some of the benefits of a tightly coupled series
configuration
with a loosely coupled series configuration by placing a diffuser element
immediately
prior to the secondary fan as depicted in Figure 26 (with reference to the
following
components and corresponding numbers for Figure 25 and Figure 26 only);
Component No. Component No.
Primary Fan 300 Secondary Fan 302
Air Flow In 304 Electronic Components 306
System Cabinet 308 Air Flow Out 310
Diffuser Element 312
The installation of a diffuser element at this point in the loosely coupled
configuration will
serve to remove substantially all of the swirl before the air enters the
secondary fan,
providing an increase in efficiency as described above.
A further analysis of equation (3) above reveals that the configuration may be
more
responsive to an increased level of power applied to the secondary fan
relative to the
primary fan. This is due to the fact that the impact of any incremental power
applied to
the secondary fan is enhanced beyond what one would normally expect from a
single
independent fan because of the increased momentum of the air entering the
secondary
fan. When operating independently, the momentum of the air flowing into and
out of the
secondary fan is completely generated by the secondary fan. When operating in
a series
configuration, however, the air flowing through the secondary fan has a
residual
momentum that has already been generated by the primary fan. This increases
the
efficiency of the secondary fan beyond that of an independent fan.
A further observed effect is that the primary fan is more sensitive (than the
secondary
fan) to the drag introduced by the diffuser element as noted in equation (3).
This also
indicates that the series configuration may be more responsive to increased
power
applied to the secondary fan rather than the primary fan.
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It is therefore possible to take advantage of these effects, and increase the
efficiency of
the overall series fan configuration, by re-balancing the distribution of
power such that
more power is applied to the secondary fan than the primary fan. The result
will be an
increased output relative to an equal distribution of the same total power
between the
two fans. This principle may be applied to tightly coupled or loosely coupled
series fan
configurations. In practice it may be implemented by supplying a higher
voltage to the
secondary fan than the primary fan, or by utilizing a higher performance
secondary fan
and applying the same voltage to both fans, or through some other means.
It is important to note that although the preceding discussion has been
limited to high
performance series fan configurations with two fans, the principles taught
herein may
also be applied to configurations of three or more fans in various series
combinations.
As an example, a tightly coupled serial fan module may replace the primary fan
in a
loosely coupled configuration, resulting in a three (3) fan configuration with
enhanced
performance.
Further, multiple high performance series fan modules may be installed in
parallel for
greater airflow capacity and / or to provide multiple fault tolerant airflows.
It has been
previously noted that parallel single fan installations are not inherently
fault tolerant since
the failed fan presents an air leak that quickly disperses the pressure and
airflow
produced by the remaining fan(s). In contrast, a parallel installation of two
or more high
performance series fan modules is fault tolerant because each one of the
series fan
modules is inherently fault tolerant. The module that contains the failed fan
will still
continue to produce airflow and pressure, thereby preventing the leakage of
air that is
normally associated with a parallel fan installation. As an added benefit, the
failed fan
may be replaced on a scheduled rather than an urgent basis.
Parallel high performance series fan modules are ideal for many applications
including
system cabinet cooling and rack mount enclosure cooling. The former is
particularly well
suited for very low profile 1 U and 2U (approximately 44mm and 88mm in height,
respectively) server formats where the installation of larger diameter fans is
impossible
and performance and fault tolerance are essential. The latter configuration
may be used
to replace the parallel single fans commonly installed on a fan tray to form a
high
performance series fan tray.
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A high performance series fan configuration operates in fault mode when one
fan fails,
and the remaining fan continues to create airflow. A controller may be
configured to
recognize and respond to this situation by increasing the power supplied to
the
remaining fan, thereby increasing the output during failure mode. In some
applications
that demand improved fault mode performance a unique offset series
configuration
provides a supplementary air inlet or air outlet that may be opened in the
event of a fan
failure to improve the efficiency of the remaining fan, while maintaining a
consistent
direction and rate of flow
Finally, the principles taught herein may be applied to larger fans and
propellers to
develop high performance fault tolerant automotive fans, e.g. for cooling and
turbo-
charging, innovative consumer products, such as vertical pole fans to de-
stratify the air
within a room, high performance fault tolerant industrial fans, e.g. for large
air moving
systems, propulsion systems, where the safety associated with a fault tolerant
configuration cannot be underestimated, and other applications that may become
obvious when the principles are understood. Further, the principles taught
herein may
also be applied to other gasses and fluids, e.g. for the development of pumps
and
marine propulsion systems, and other applications that may becomes obvious
when the
principles are understood.
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Embodiments
Embodiments of the invention are described by way of example with reference to
the
drawings in which:
Figure 1 illustrates an inefficient series fan configuration,
Figure 2 illustrates an efficient series fan configuration with diffuser
elements,
Figure 3 provides an overview of a high performance series fan configuration,
Figure 4 provides a side view of a high performance series fan configuration,
Figure 5 provides a side view of a high performance series fan in normal
operation,
Figure 6 provides a front view of a high performance series fan with a control
panel,
Figure 7 illustrates how a high performance series fan drawer may be withdrawn
from a
cabinet,
Figure 8 details the replacement of one of the series fans,
Figure 9 shows how two high performance series fan modules may be mounted in
parallel,
Figure 10 shows a high performance series fan module with a supplementary air
inlet
and outlet,
Figure 11 provides a connection diagram for a high performance series fan
controller,
Figure 12 illustrates a control algorithm for a high performance series fan
controller in
flow chart format,
Figure 13 provides a perspective view of a high performance series fan sink,
Figure 14 provides a section view of a high performance series fan sink,
Figure 15 illustrates a high performance series fan sink with the primary fan
being
replaced,
Figure 16 illustrates a high performance series fan sink with the secondary
fan being
replaced,
Figure 17 provides a perspective view of a high performance series fan tray,
Figure 18 provides a second perspective view of a high performance series fan
tray
showing further details of one of the high performance series fan modules,
Figure 19 illustrates a high performance series fan tray with the primary fan
being
replaced,
Figure 20 illustrates a high performance series fan tray with the secondary
fan being
replaced,
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Figure 21 illustrates a high performance series fan tray controller operating
in a fan
failure mode,
Figure 22 illustrates a method for monitoring airflow through a high
performance series
fan module, and:
Figure 23 provides a perspective view of an alternatively configured high
performance
series fan tray.
FIG. 1 illustrates an inefficient series fan configuration with three
independent axial
cooling fans mounted such that the output from one fan becomes the input to
the next
fan in the series. In this case the output from primary fan 8 becomes the
input to
secondary fan 16, and in like manner the output from secondary fan 16 becomes
the
input to tertiary fan 17. Basic series fan configurations may be comprised of
two or more
axial fans configured in this manner.
An axial fan works best if it sees a substantially laminar flow, i.e. a flow
with no or a
controlled level of swirl, on the input side. This condition is met with a
single fan since
there is nothing on the input side to generate swirl. However this is not the
case with a
basic series configuration since the outputs of the primary fan 8 and
secondary fan 16
(as with all axial fans) contain swirl as depicted by airflow with swirl 10
and second
airflow with swirl 11. Therefore a basic series configuration is inefficient
because the
secondary, tertiary, and all subsequent fans will have a substantial swirl
component in
the input airflow.
In contrast, FIG. 2 illustrates an efficient series fan configuration with
diffuser element 14
and second diffuser element 15 inserted between primary fan 8 and secondary
fan 16,
and secondary fan 16 and tertiary fan 17, respectively.
The result of inserting diffuser element 14 between primary fan 8 and
secondary fan 16
is to convert the input seen by secondary fan 16 from airflow with swirl 10 to
reduced
swirl airflow 12, thereby increasing the efficiency of secondary fan 16 to a
level
approaching that of primary fan 8. Likewise, second diffuser element 15 will
convert the
input seen by tertiary fan 17 from second airflow with swirl 11 to second
reduced swirl
airflow 13, thereby improving the efficiency of tertiary fan 17.
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Diffuser element 14 and second diffuser element 15 may be comprised, for
example, of
filter material or a number of vanes or tubes mounted in the path of the air
and
configured to reduce swirl and direct the airflow into downstream fan, as
illustrated by
alternative second diffuser element 15a. Further, the vanes or tubes may be
configured
to leave a certain level of residual swirl in the airflow in order to (1) flow
more easily past
the stationary fan blades of a the downstream fan and/or (2) create a set of
input
conditions that would allow the downstream fan to operate more efficiently, at
above
design conditions, rotating faster than normal for a given input power level.
In certain
applications it may be beneficial to combine diffuser element 14 and second
diffuser
element 15 with other functions such as a heat exchanger to add or remove heat
from
the airflow, or an Electro-Magnetic (EM) shield to substantially prevent the
passage of
EM waves through the fan opening. While the number of different diffuser
element
designs and their related efficiencies and functionalities is vast, the
principle of reducing
swirl to improve the efficiency of the secondary or downstream fan remains the
same.
While diffuser element 14 and second diffuser element 15 may be primarily
designed to
reduce swirl, they will also add an impedance to the airflow that will add to
the system
head and reduce the efficiency of the system. This becomes a trade-off that
must be
balanced against the positive effects of installing a diffuser element between
two fans in
series. In general, however, the overall effect of installing a diffuser
element is positive
since the impact of the reduced swirl far outweighs the incremental system
head. In
some applications the pressure drop across the diffuser element may be
monitored and
used to measure the airflow through the diffuser element.
FIG. 2 also illustrates the impact of a fan failure. If primary fan 8 fails,
then secondary fan
16 and tertiary fan 17 will continue to draw air through the assembly and
"push" it in the
same direction, i.e. combined airflow 22 will continue to flow in the same
direction, and
no external baffling changes will be required. A similar result will occur if
secondary fan
16 or tertiary fan 17 fails. This ability to continue to provide airflow in
the same direction
despite the loss of a fan is the primary inherent advantage of a series fan
configuration.
In the event of a primary fan 8 failure, the fan blades may continue to rotate
or they may
remain fixed or "locked" - depending on the nature of the failure. However, in
the case of
primary fan with variable pitch blades 8a, primary fan blade 9 will remain in
an oblique
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position during normal operation (i.e. while rotating in the direction defined
by arrow 7)
and then return to coaxial position 9a in the event of a failure. Since
coaxial position 9a
aligns the fan blade with the airflow, it will present a far lower input
impedance as seen
by secondary fan 16, therefore contributing to increased efficiency during a
primary fan
with variable pitch blades 8a failure relative to an primary fan 8 (i.e. fixed
fan blade)
failure. It follows that a secondary fan 16 with similar variable pitch blades
would also
contribute to greater efficiency during the failure mode as it would present a
lower output
impedance as seen by primary fan 8.
Although the direction of airflow will remain consistent in a series fan
configuration with a
single fan failure, the volume of airflow will be reduced if the remaining
fan(s) continue to
operate at the same speed. This is an acceptable situation only if the volume
of airflow
does not fall below the minimum required to dissipate the heat generated in
the cabinet
or by the components being cooled. In practice a control system may be
required to
sense the fan failure and adjust the remaining fan speed accordingly, in order
to ensure
that this minimum airflow requirement is met until the defective fan can be
replaced. This
type of control can be easily implemented since (1) many fans today are
available with
fault sensors to indicate an impending failure I total failure and (2) fan
speed can be
easily controlled by varying the input voltage, at least for DC fans, or by
using some
other type of fan speed controller.
During normal operation, primary fan 8, secondary fan 16, and tertiary fan 17
may all be
operating at less than full rpm to produce the required combined airflow 22.
The lower
rpm will reduce the noise produced by each fan and also extend the life of
each fan.
Should the controller sense an impending or actual failure in one of these
fans, then the.
The user may then be alerted to replace the defective fan on a scheduled
rather than an
urgent basis. Similarly, if the airflow is impeded by a clogged air filter or
some other
obstacle, then the power applied to the fans may be increased to the point
where
combined airflow 22 remains the same.
A series configuration of "n +1" fans configured with intermediate diffuser
elements, as
described above, will be tolerant to the failure of one fan where "n" is the
total number of
fans whose combined flow is required to meet the cooling requirements of the
system or
component(s) being cooled. FIG. 2 illustrates an example where "n" = 2, and "n
+ 1" = 3
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fans in total. Actual configurations may include 2, 3 or more fans depending
on cooling
requirements. The remainder of this document will deal with high performance
series
fans with diffuser elements configured with two fans for reasons of
simplicity, however it
should always be noted that additional fans may be added to these
representative series
configurations. Further, it should be noted that multiple fans could be added
to provide
increased performance while preserving an n + 1 redundancy and providing a
fault
tolerant configuration.
It is also possible that multiple series fans with diffuser or flow
modification elements
may be installed in parallel to meet demanding cooling requirements. In this
case, there
is no need for the movable baffles normally associated with parallel
configurations since
each independent high performance series fans with diffuser element assembly
is fault
tolerant and will not allow the back flow or "leakage" of air in the event of
a fan failure.
These configurations may be used to meet very high airflow requirements, to
produce
independently directed airflow streams, or where space considerations limit
the number
of fans that may be mounted in a series.
Series fans with flow modification element, or high performance series fans,
may be
configured to allow a defective fan to be replaced without having to shut down
the
system or components being cooled - commonly referred to as "hot swapping" the
fans.
This is made possible by the fact that high performance series fans 1 may be
configured
to fit in a sliding "drawer" that can be pulled away from the cabinet without
interrupting
the airflow, as illustrated in FIG. 3. In this case secondary fan 16 is being
replaced while
sliding drawer 2 is in the "out" position. Sliding drawer 2 may then be
returned to the "in"
position without affecting system operation or necessitating a system shut
down. A
control system may be configured to detect the fan failure, alert the user,
detect the
presence of a new and fully functional secondary fan 16, adjust the power
applied to
both primary fan 8 and secondary fan 16 to maintain a controlled airflow
throughout the
process, and then reset the lights on control panel 30 to reflect normal
operation. Note
that diffuser element 14 could also be replaced while the sliding drawer 2 is
in the "out"
position, again without affecting system operation. Finger guard 6 has been
added to the
configuration for safety reasons.
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FIG. 4 provides further detail in a side view of high performance series fans
1 mounted
in sliding drawer 2. Primary fan 8 and secondary fan 16 are mounted co-axially
in sliding
drawer 2 such that the air flowing from primary fan 8 flows through diffuser
element 14
and directly into secondary fan 16. Sliding drawer 2 slides into and out of
internal sleeve
3 as depicted by drawer movement arrow 18. Sliding drawer 2 requires a minimum
opening in cabinet 4, taking less cabinet wall space than a parallel
configuration and
making it easier to maintain the integrity of an EM shield. In certain
applications diffuser
element 14 may be configured as an integral part of the EM shield.
Internal sleeve 3 has at least five distinct functions; (1) to provide a means
to mount
sliding drawer 2, and therefore high performance series fans with diffuser
element 1, on
cabinet 4, (2) to provide a means to allow sliding drawer 2 to slide "in" or
"out", (3) to
support sliding drawer 2 whilst in the "in" or "out" position, (4) to provide
baffling such
that combined airflow 22 only exits the assembly through the open end of
internal sleeve
3, and (5) to provide, in combination with sliding drawer 2, a contained
channel for the
air flowing through high performance series fans 1.
The latter function is particularly important since the length and geometry of
the
contained air channel between primary fan 8 and diffuser element 14 may be
configured
to provide a pre-determined level of natural decay of swirl in the airflow
before it enters
diffuser element 14. This natural decay of swirl may be enhanced by providing
multiple
corners within this portion of the contained air channel, for example by
configuring the air
channel with a square or hexagonal cross section. In certain applications, in
particular
those using a primary fan 8 having stator blades, the this portion of the
contained air
channel may be shortened while providing the same overall effect since some of
the
swirl will have already been removed by the stator blades.
Similarly the length and geometry of the contained air channel between primary
fan 8
and diffuser element 14, and diffuser element 14 and secondary fan 16, may be
configured to reduce the acoustical noise produced by high performance series
fans 1.
As an example, a short contained air channel with smooth walls between
diffuser
element 14 and secondary fan 16 may be configured to reduce acoustical noise,
even
though it may not necessarily be required to further reduce swirl in this
region.
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Flange 21 may be used to secure internal sleeve 3 to cabinet 4 with machine
screws, or
through some other suitable means. Latch 19 may be used to hold and seal tab
20
against flange 21, i.e. to hold sliding drawer 2 in the "in" position, until
released. Back lip
extends outward from the normal geometry of sliding drawer 2 to prevent the
5 accidental removal of sliding drawer 2 by coming to rest against an extended
portion of
flange 21, when sliding drawer 2 is in the full "out" position. A means may be
provided to
completely remove sliding drawer 2 from internal sleeve 3, when and if
required.
In some applications diffuser element 14 may be configured as a diffuser, to
reduce swirl
in the airflow leaving primary fan 8, and as a filter, to substantially remove
unwanted
particulate from the airflow. In these cases diffuser element 14 should be
selected to
optimize both functions, in combination with the length and geometry of the
contained air
channel between primary fan 8 and diffuser element 14, as described above,
while
introducing a minimal incremental system head.
Alternatively, an air filter optimized for removing particulates may be
mounted between
finger guard 6 and primary fan 8, leaving the diffuser element 14 to be fully
optimized for
the reduction of swirl. In these configurations diffuser element 14 may be a
screen, a
laminar flow element consisting of a number of round, square, hexagonal, or
alternatively shaped tubes mounted co-axially with the fans, a series of flow
directing
vanes, or some combination thereof. Further, diffuser element 14 may be
configured
with an air funnel at the entry point to each tube, and with the funnel
openings directed /
skewed towards the source of the air as it comes off the blades of primary fan
8.
Regardless of configuration, the flow related objective of diffuser element 14
is, in
combination with the length and geometry of the contained air channel between
primary
fan 8 and diffuser element 14, to reduce swirl in the airflow leaving primary
fan 8, and
before it enters secondary fan 16, while introducing a minimum amount of
incremental
back pressure, thereby contributing to the overall efficiency of the high
performance
series fans 1.
Primary fan 8 and secondary fan 16 may rotate in the same or different
directions. This
aspect of the configuration will be somewhat dependent on the cost,
performance, and
acoustical objectives associated with a given application, as a pair of
standard fans that
rotate in the same direction may be less expensive than a pair of counter-
rotating fans,
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or a counter-rotating fan module. Also, any efficiency gained by having
counter-rotating
fans should be weighed against the service cost of stocking two types of
spares.
FIG. 5 shows high performance series fans 1 in operation. In this case sliding
drawer 2
has been moved "in" such that finger guard 6 is flush with the outside of
cabinet 4.
Sliding drawer 2 slides within the internal sleeve with sliding interfaces at
flange 21 and
back lip 5. Alternatively, sliding drawer 2 may be configured to slide on
rails or some
other suitable means.
Sliding drawer 2 is prevented from moving farther into cabinet 4 by tab 20
(top and
bottom) when it interfaces with the outer edge of flange 21.Sliding drawer 2
is then held
in place by latch 19. In some cases an aesthetic cover may be configured to
snap onto
the outside of sliding drawer 2, once in place, to improve the appearance of
the cooling
module. Further, the aesthetic cover would provide visual access to the
control panel so
that the operation of high performance series fans 1 could still be easily
monitored.
As in FIG. 4, cooling air flows efficiently through primary fan 8, diffuser
element 14, and
secondary fan 16 to provide combined airflow 22. It is important to note that
the direction
of combined airflow 22 remains consistent whether one or both of primary fan 8
and
secondary fan 16 is / are operational. This precludes the requirement for any
incremental baffling to ensure that the direction of combined airflow 22
remains
consistent in the event of a fan failure.
In the event of a primary fan 8 failure, combined airflow 22 will continue to
flow through
primary fan 8 and into secondary fan 16 - i.e. the airflow will not escape
through
primary fan 8. Likewise, in the event of an secondary fan 16 failure, combined
airflow 22
will continue to flow through secondary fan 16 and into cabinet 4 - i.e. the
airflow will not
escape through secondary fan 16. This precludes the requirement for specialize
baffling
to prevent combined airflow 22 from escaping through the defective fan.
The last two paragraphs highlight a very important characteristic of the
series fan
configuration - no baffling is required to accommodate a failed fan scenario.
This
contrasts sharply with the parallel fan configuration where substantial
baffling is required
to prevent the loss of air through the defective fan and to keep the direction
of airflow
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consistent in the event of a fan failure. As a result, high performance series
fans are very
compact, and they may be configured as a stand-alone cooling module that does
not
requires any further baffling.
Primary fan 8 may need to be rated at a higher capacity than secondary fan 16
to
compensate for the added backpressure introduced by diffuser element 14 and
secondary fan 16, if and when secondary fan 16 is defective and I or
stationary.
Conversely stated, secondary fan 16 may be rated at a lower capacity than
primary fan 8
because it will not "see" the same incremental causes of backpressure. In
practice both
fans may be of the same rating, but should they be so configured that the
ratings match
the higher rating required by primary fan 8. This will ensure that combined
airflow 22 will
always exceed the minimum required regardless of whether one or both fans is /
are
operational.
During normal operation primary fan 8 and secondary fan 16 may run at less
than full
rpm as long as combined airflow 22 meets the cooling requirements for the
application at
hand. Further, the total power applied to the system may be re-balanced
asymmetrically,
with more power being applied to the secondary fan in order to take advantage
of the
fact that secondary fan 16 runs more efficiently than primary fan 8, therefore
improving
the overall efficiency of the system. The configuration will be very
responsive to a fan
failure since the remaining fan is already running, albeit at a lower rpm, and
it is much
faster to ramp up from partial to full rpm than it is to go from stopped to
full rpm.
It can be deduced from FIG. 5 that the size of the opening in cabinet 4 will
be only
slightly larger than the size of primary fan 8. In a parallel configuration
the opening
would be approximately twice this size since the two fans would be mounted
side-by-
side. Further the volume of space required in cabinet 4 will be much smaller
than a
parallel configuration since no extra internal baffling will be required. This
2:1 reduction
in the size of the opening combined with the much smaller internal volume
requirement
represents a major benefit of the series configuration from a system
designer's
perspective.
In simple configurations, high performance series fans 1 may be implemented
without a
controller by using two fans, each of which is capable of providing the full
combined
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airflow 22 required for the application at hand. Under normal operating
conditions
combined airflow 22 will actually exceed the minimum requirement, keeping the
load
cooler than necessary. A fan failure can be tolerated since the remaining fan
will already
be running, and is capable of carrying the load. As described above, no
further baffling is
required since the fans are in series. A simple indicator light will flag the
operator to
replace the defective fan.
In other configurations, where power consumption, precise cooling, and / or
acoustic
management are important requirements, a controller may be used to provide a
controlled airflow during normal operation and in the event of a fan failure.
The controller
may be installed behind control panel 30, as shown in FIG. 6. This drawing
also
illustrates the full extent of tab 20 as seen around the perimeter of the
unit, and the front
face of finger guard 6. Control panel 30 contains indicator lights 32 to alert
the user
regarding the operation of primary fan 8, secondary fan 16, and diffuser
element 14
(reference FIG. 5). The controller may also be adapted to communicate with
other
systems for remote monitoring and control.
An aesthetic cover may be affixed over the entire front face of high
performance series
fan 1, providing that airflow is not impeded to the degree that it will affect
cooling
performance. In most cases indicator lights 32 will need to be visible through
the
aesthetic cover so that the operator can respond to a fan problem, however
this may not
be an absolute requirement in situations where the operator may be initially
alerted
through some other means, for example through software and a remote monitor.
In the
latter case the operator, once alerted to the problem, could remove the
aesthetic cover
and visually inspect indicator lights 32 to determine which fan is defective.
Fans are readily available with sensors for failure, or degradation in
performance that
might indicate imminent failure. This information may be used to inform the
controller to
increase the speed of the other fan in order to continue to provide the
required airflow.
The controller can also use the same information to illuminate the appropriate
indicator
lights 32, alerting the operator to take action. Indicator lights 32 may be
activated in
several different modes, e.g. steady, flashing, red yellow or green, to
communicate
certain information and the level of severity of the problem to the user.
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Under normal operation each fan may be running at less than maximum rpm to
extend
life, reduce noise, and to allow for an immediate increase in speed should the
other fan
fail. It is possible that one fan may be left idle (i.e. not running) during
normal operation,
however in practice it may be better to leave both fans running to some extent
in order to
(1) continually ensure that they are both operational (2) minimize any "ramp
up" time in
the event of a failure and (3) reduce any unnecessary static loads or sources
of
backpressure during normal operation.
FIG. 7 illustrates how high performance series fans 1 may be withdrawn from
cabinet 4
to allow for the inspection and / or replacement of a faulty component. Note
that finger
guard 6 has been removed in this diagram for illustrative purposes only, and
that this
would not normally be the case when servicing the unit.
FIG. 8 provides a top view of high performance series fans 1, and illustrates
the method
of replacing a defective fan without shutting down the system, commonly
referred to as
"hot swapping" the fans. In this scenario secondary fan 16 is defective, and
this
information would have been conveyed to the user through indicator lights 32.
The first step in replacing defective secondary fan 16 is to pull out sliding
drawer 2 until it
is fully extended, as depicted by drawer extension arrow 42. At this point
back lip 5 will
rest against the internal edge of flange 21 to prevent further forward
movement of sliding
drawer 2. Internal indicator lights 33 may be used as a secondary check to
ensure that
the correct (faulty) fan is being removed.
Once sliding drawer 2 is in the fully extended position, secondary fan 16 may
be
removed by sliding it sideways, to the right, and disconnecting internal power
and control
cable 44 from internal power and control receptacle 46. FIG. 8 shows secondary
fan 16
partially removed with approximately 30% of its width already beyond the right
side of
sliding drawer 2. Note that secondary fan 16 is completely outside of and can
slide clear
of cabinet 4. It can be seen that diffuser element 14 and primary fan 8 could
be similarly
removed without interfering with cabinet 4.
Primary fan 8 remains running as secondary fan 16 is being removed and
replaced, and
may be running at a higher RPM, as determined by controller 40, so that
combined
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airflow 22 remains at or above the minimum airflow required to cool the
components
contained within cabinet 4. Note that the direction of combined airflow 22
will not
change, as it remains contained and directed by internal sleeve 3, precluding
the need
for any change in baffling when running with only one fan. It can be seen from
FIG. 8
that diffuser element 14 and primary fan 8 may be similarly removed without
affecting
the direction of the combined airflow 22. All of these operations can be
completed
without shutting down the system contained in cabinet 4.
Referring back to the scenario at hand, a new secondary fan 16 may be set in
place in
sliding drawer 2, and the internal power and control cable 44 may be re-
connected to
internal power and control receptacle 46. Controller 40 may be configured to
recognize
that secondary fan 16 has been replaced, and that it is operational, and to
adjust the
speed of primary fan 8 and secondary fan 16 accordingly. Sliding drawer 2 can
then be
pushed back into cabinet 4 such that finger guard 6 and control panel 30 are
flush with
the outside of cabinet 4. Indicator lights 32 may then be monitored by the
operator for
further problems. Indicator lights 32 and controller 40 may also be interfaced
with the
system in cabinet 4 to alert the operator through other means such as a remote
system
monitor.
Sliding drawer 2 may be configured to accommodate standard sized fans
available from
a variety of manufacturers, e.g. 120 mm, 92mm, or 40 mm fans. These fans are
readily
available in a variety of thicknesses that loosely correspond to a range of
CFM ratings,
i.e. the thicker fans generally have a higher CFM rating for a given fan
diameter. It
follows that sliding drawer 2 may be configured to accept the thickest fan in
a particular
size range, and that slimmer or lower capacity fans may be accommodated by
installing
the fan in conjunction with a "shim" ring that takes up the extra space and
holds the fan
securely in place. This approach allows a standard size sliding drawer 2 to
accommodate a variety of fan capacities, and also provides a convenient
upgrade path
since the shims may be removed or replaced with thinner shims to allow the
installation
of higher capacity fans. This approach can be used to provide additional
cooling, when
required, without replacing the entire cooling subsystem.
In some applications it may be necessary to provide a fixed baffle 48 inside
cabinet 4 to
ensure that re-directed combined airflow 49 is appropriate for the
application. This fixed
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baffle 48 will need to interface with internal sleeve 3 to prevent air
leakage, however it
will remain fixed in the event of a fan failure.
FIG. 9 shows how two high performance series fan modules may be mounted in
parallel
for increased airflow. Parallel baffle 50 may be configured to interface with
top inner
sleeve 3a and bottom inner sleeve 3b to contain the output from both compact
series fan
assemblies, and produce total combined airflow 54. Sealing cap 52 may be
positioned
between the two assemblies to improve the airflow and to prevent any leakage
of air in
this area. Sealing cap 52 may be configured with a cone shaped cap that
protrudes
downstream, or some other feature, to increase the efficiency of the airflow.
It is important to note that even though this is a parallel configuration of
series fan
assemblies, it does not require any of the specialized baffling normally
associated with
this type of installation. This is because each one of the high performance
series fans
with diffuser element assemblies is independently fault tolerant, and prevents
the back
flow of air in the event of a fan failure. In other words, each series fan
assembly will
always contribute to total combined airflow 54, and will not allow a portion
of combined
airflow 54 to leak back out to the ambient air around cabinet 4, even in the
event of a
single fan failure.
The parallel configuration of high performance series fan modules also
provides more
flexibility in the event of a fan failure. In this case a controller may be
configured to
speed up three additional fans, rather than just one in a non-parallel
installation, to
maintain a constant total combined airflow 54. It follows that parallel
configurations with
more than two high performance series fans with diffuser element assemblies
will have
an even greater ability to respond to a single fan failure.
FIG. 10 shows a high performance series fan module configured with a
supplementary
air inlet and outlet to improve airflow in the event of a fan failure.
Under normal operation, air inlet baffle 70 and air outlet baffle 72 will
direct the output
from primary fan 8 and diffuser element 14 through secondary fan 16 to form
combined
airflow 22, as previously described. Combined airflow 22 is further directed
through air
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funnel 74 which may have an opening size that approximates the opening size of
the
fans.
In the event of a primary fan 8 failure, air inlet baffle 70 may be moved to
position 70a to
reduce the input impedance seen by, and therefore increase the flow of air
into,
secondary fan 16. Outlet baffle 72 may remain in place to ensure that no air
leaks from
the output side to the input side of secondary fan 16. Combined airflow 22
will be
comprised solely of the output from secondary fan 16, part of which will flow
through the
defective primary fan 8 and another part of which will flow through the open
inlet baffle
70a.
Conversely, in the event of an secondary fan 16 failure, air outlet baffle 72
may be
moved to position 72a to reduce the output impedance seen by, and therefore
increase
the flow of air out of, primary fan 8. In this case inlet baffle 70 will
remain in place to
ensure that no air leaks from the output side to the input side of primary fan
8. Combined
airflow 22 will be comprised solely of the output from primary fan 8, part of
which will flow
through the defective secondary fan 16 and another part of which will flow
through the
open outlet baffle 72a.
Inlet baffle 70 and outlet baffle 72 may be configured to operate
automatically, based on
pressure differentials, or to be controlled by controller 40 (reference FIG.
8). In the
former case a higher relative pressure between primary fan 8 and secondary fan
16
would cause outlet baffle 72 to move to position 72a, and a lower relative
pressure
between the same fans would cause inlet baffle 70 to over to position 70a. In
the latter
case controller 40 may be used to control the position of the baffles in
response to a
failing or defective fan. In all cases the action taken serves to relieve the
pressure
differential and improve the flow of air through the configuration. However
the use of the
controller provides greater flexibility and does allow for certain load
sharing scenarios
between the two fans that might cause temporary pressure differentials between
the
fans that might otherwise be interpreted as a defective fan situation.
It is important to note that air inlet baffle 70 and air outlet baffle 72 may
be configured, in
conjunction with air funnel 74 and controller 40 (reference FIG. 8), such that
the direction
and rate of combined airflow 22 will remain constant even in the event of a
fan failure.
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This precludes the requirement for any further baffle changes within cabinet 4
in the
event of a fan failure, meaning that the configuration may still be supplied
as a
standalone module that provides fault tolerant cooling.
It is also important to note that the use of air inlet baffle 70 and air
outlet baffle 72 still
allows for the replacement of a defective fan or filter element / diffuser
while the system
is running. This is because air inlet baffle 70 and air outlet baffle 72 have
been
configured to not interfere with the normal removal and replacement of the fan
and filter
element / diffuser element while sliding drawer 2 is in the "out" position as
previously
described.
Primary fan 8 and secondary fan 16 may both be mounted with axis parallel to
combined
airflow 22 as shown in FIG. 10. Alternatively, primary fan 8 and secondary fan
16 may
both be mounted at a slight angle to the desired combined airflow 22, and not
necessarily in a coaxial fashion, in order to improve the smooth flow of air
between
primary fan 8 and secondary fan 16. In this case inner sleeve 3 and air funnel
may be
adaptively re-configured to ensure that combined airflow 22 flows in the
desired
direction.
FIG. 11 provides a connection diagram for high performance series fan
controller 40.
Controller 40 may be configured to receive its primary input from cooled
component(s)
62, upon which the output of high performance cooling fan module 1, i.e.
combined
airflow 22, impinges. This primary input may be comprised of information such
as the
temperature of cooled component(s) 62, the rate of airflow around cooled
component(s)
62, and the current and / or anticipated workload on cooled component(s) 62.
Information regarding the anticipated workload on cooled component(s) 62 would
allow
controller 40 to proactively respond to a corresponding change in heat
dissipation
requirements by changing the speed of primary fan 8 and / or secondary fan 16.
Controller 40 may also be configured to receive input from airflow sensor 60.
Airflow
sensor 60 provides information regarding the rate of combined airflow 22, and
this
information may be used by controller 40 to test for appropriate responses to
changes in
input to primary fan 8 and / or secondary fan 16. A non-appropriate response
to such an
input may be used by controller 40 to determine that there may be a fault with
diffuser
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element 14 or one of the fans. For example, controller 40 may determine that
combined
airflow 22 cannot be maintained above a threshold level and may deduce that
(1) this
problem may be caused by a seriously clogged diffuser element 14, especially
if it has a
secondary function as a filter, or, in the worst case, that (2) both fans may
have failed or
are failing simultaneously. The user would be alerted to take immediate action
in either
case, and a graceful shutdown procedure could be initiated if either situation
persists for
an unacceptable period of time.
Controller 40 may also be configured to receive input from position sensors
64, which
inform controller 40 regarding the correct installed position of primary fan
8, diffuser
element 14, and secondary fan 16. In the case of the fans, this information
may be
combined with input from combined control and monitor wires 66 to determine
that the
fans are installed correctly and operating efficiently. The combined control
and monitor
wires may be used to supply a control voltage to the fans, monitor current
draw, and in
some cases monitor other information such as rpm, output temperature, or
output flow
rate.
Position sensors 64 may further contain a physical feature that precludes the
incorrect
installation of primary fan 8 and secondary fan 16, i.e. prevents an
accidental installation
that would cause air to flow in the wrong direction. Such an incorrect
installation could
cause immediate damage to the components being cooled.
The information provided by combined monitor and control wires 66 may be used
by
controller 40 as leading indicators of potential fan failure. As an example, a
drop in rpm
for a given voltage input may indicate that a bearing is failing. Controller
40 may initially
respond by increasing the voltage input to that fan, and alerting the user to
the problem.
Controller 40 may ultimately respond by shutting down the defective fan and
changing
the load over to the alternative fan if the problem persists. Most
importantly, the
information allows the controller to make proactive responses to an impending
problem
before cooled component(s) 62 becomes overheated.
Controller 40 may communicate with the user through control panel 30,
containing
indicator lights 32a, 32b, and 32c, which may be used to indicate the status
of primary
fan 8, diffuser element 14, and secondary fan 16 respectively. Any commonly
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understood indicator algorithm may be used, for example green meaning normal
operation, yellow meaning that a component should be replaced due to sub-
optimal
performance or impending failure, and red or flashing red used to indicate
that a
component has failed. Note that a failed fan does not mean that high
performance
cooling fan module 1 is not operating; it simply means that the system is only
running
with one fan and has no ability to respond to a further fan failure. Therefore
the failed
component must be replaced immediately to avoid potential problems.
As an example, controller 40 may be used to monitor the amount of time that
diffuser
element 14 is in use, and to activate the appropriate indicator light 32
should the "in use"
time exceed a recommended maximum. This will alert the operator to replace
diffuser
element 14. The appropriate position sensor 64 in may be used to automatically
reset
the "in use" timer back to zero. This algorithm would be particularly useful
in applications
where diffuser element 14 is configured as a combined filter / diffuser
element.
Controller 40 may also communicate with the user through a second redundant
set of
internal indicator lights 33 (reference FIG. 8). These lights may be more
visible to the
user or service technician when the fans are being replaced, and therefore
they will
serve as a safeguard to prevent the accidental removal of a correctly
operating fan.
Such a mistake would leave only the defective fan in place, potentially
causing
immediate damage to cooled component(s) 62. Controller 40 may use an audible
emergency signal to instantly warn the user of such a dangerous situation.
FIG. 12 presents a control algorithm for a high performance series fan
controller, in flow
chart format.
The fundamental purpose of the controller is to keep cooled component(s) 62
(reference
FIG. 11) within a defined control temperature range, despite changes on
workload that
might affect the heat dissipated by cooled component(s) 62. Therefore the
first task in
each control cycle is to check for anticipated changes in workload as outlined
in first
decision triangle 80. This information may come from the operating system
associated
with cooled component(s) 62. An increase in workload would cause the
controller to
increase the output CFM control point, and a decrease in workload would cause
the
controller to decrease the output CFM control point, perhaps after some delay
period, as
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indicated by first control box 86. The controller would proceed directly to
second decision
triangle 82 should there be no anticipated changes in workload.
At second decision triangle 82 the controller will check to ensure that cooled
component(s) 62 (reference FIG. 11) is operating within its defined control
temperature
range. Should this not be the case, then the controller will adjust the output
CFM control
point to raise or lower the temperature of cooled component(s) 62 as required.
However
under normal operation, when no adjustment is required, the controller will
proceed
directly to third decision triangle 84.
At third decision triangle 84, the controller checks to ensure that the output
CFM, i.e.
combined airflow 22 (reference FIG. 11), is at the output CFM control point.
Should there
be a discrepancy that lies outside of the acceptable control range, then the
controller will
immediately investigate to determine the cause of the problem. As an example,
secondary fan 16 (reference FIG. 11) may have suffered a drop in rpm given the
same
input parameters, a possible leading indicator of impending fan failure. The
controller
would then proceed to take corrective action by adjusting the inputs to
secondary fan 16
and notifying the user through indicator lights 32 (reference FIG. 11).
Under normal circumstances the output of the high performance cooling fan
module will
be at the required constant output CFM control point and no corrective action
will be
required. In this case the controller loops back to first decision triangle 80
to repeat the
above control cycle once again.
While operating normally, the controller may actually change the speed of both
fans
slightly on a regular timed basis. These subtle changes in rpm will prevent
any lasting
beat frequencies that might occur if the fans are left running at a constant
rpm for any
length of time.
Interrupts may be used at any time to alert the controller regarding a
situation that
requires immediate attention. Examples may include a locked rotor ("0" rpm
with a full
normal input) or perhaps a dislodged fan. In these cases the controller must
take
immediate action to preserve a constant CFM output, thus keeping the cooled
component(s) at the required operating temperature.
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FIG. 13 provides a perspective view of high performance series fan sink 100.
Primary
fan 8 and secondary fan 16 are configured in series to draw inlet airflow 108
into high
performance series fan module 106, and push it into heat sink 102 where it
divides into
right outlet airflow 110 and left outlet airflow 112. Primary fan 8 and
secondary fan 16
may be obliquely mounted on heat sink 102 at a variety of angles such the
diagonal of
the fans substantially covers the width of heat sink 102 and provides airflow
through
substantially all of the channels within heat sink 102. Air is retained within
the confines of
heat sink 102, such that it flows through and only exits at the open ends of
heat sink
102, by baffle 104.
Baffle 104 may be configured to hold high performance series fan module 106 at
a
distance above heat sink 102, while preventing the leakage of air at the
interface
between baffle 104 and high performance series fan module 106, to improve the
dispersion of air throughout heat sink 102. Further, baffle 104 may be
configured to
expand the opening of high performance series fan module 106 such that covers
substantially all of the width of heat sink 102, allowing smaller series fan
modules 106 to
be used effectively with larger heat sinks 102.
Inlet airflow 108 is drawn through finger guard 122, into primary fan 8,
through diffuser
element 14, into secondary fan 16, and then pushed through heat sink 102 and
exhausted as right outlet airflow 110 and left outlet airflow 112.
Alternatively, the
direction of airflow may be reversed such that right outlet airflow 110 and
left outlet
airflow 112 become the inlet airflows, and the air is exhausted through finger
guard 122
at inlet airflow 108, which becomes the exhaust. However the former
configuration, as
illustrated in FIG. 13, provides for an impingement air flow on heat sink 102,
and this can
be directed at the area of maximum heat flux on heat sink 102 for enhanced
cooling
efficiency.
Control module 120 controls the operation of high performance series fan sink
100.
Primary fan indicator light 122 and secondary fan indicator light 124 indicate
the
operating status of primary fan 8 and secondary fan 16 respectively. Control
module 120
may be configured to sense the failure of primary fan 8 or secondary fan 16
and
increase the power to secondary fan 16 or primary fan 8, respectively, to
maintain a
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relatively constant right outlet airflow 110 and left outlet airflow 112
during a single fan
failure. Further, control module 120 may be configured to be responsive to a
range of
different backpressures to provide a relatively constant right outlet airflow
110 and left
outlet airflow 112 over a range of operating conditions, or for a variety of
heat sinks 102.
FIG. 14 provides a section view of high performance series fan sink 100. High
performance series fan module 106 contains primary fan 8, diffuser element 14,
and
secondary fan 16. High performance series fan module 106 may be configured as
a
module that contains all of these components and holds them at the appropriate
location, or alternatively as a standardized sub-assembly that only contains
diffuser
element 14 and is adapted to be bolted or otherwise fastened between two
industry
standard fans of similar geometry, e.g. two 120 mm or 40 mm fans.
Primary fan 8 is separated from diffuser element 14 by a first distance, and
diffuser
element 14 is further separated from secondary fan 16 by a second distance.
The
purpose of the first distance between primary fan 8 and diffuser element 14 is
to reduce
the swirl component of the airflow exiting from primary fan 8 through natural
swirl decay,
with a longer channel generally resulting in an increased level of natural
swirl decay. The
first distance may be reduced by configuring the internal geometry of the
airflow channel
to increase the rate of natural swirl decay, e.g. by using a square or
octagonal internal
cross section and/or by incorporating ridges, spines, or other surface
features along the
interior walls of the airflow channel, thereby reducing the overall length of
high
performance series fan module 106. The first distance may be further reduced
by
selecting a primary fan 8 having an integrated stator on the outlet side,
thereby providing
some level of swirl decay before the airflow leaves primary fan 8.
The purpose of diffuser element 14 is to complement the natural swirl decay
accomplished within the first distance, i.e. between primary fan 8 and
diffuser element
14, by further reducing the swirl component of the airflow before it enters
secondary fan
16. This will increase the efficiency of secondary fan 16.
The purpose of the second distance between diffuser element 14 and secondary
fan 16
is to reduce the acoustical noise produced by high performance series fan
module 106.
The small gap between the two components also provides sufficient space to
mount a
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pressure sensor, and this signal may be compared to the signal produced by
another
pressure sensor located on the upstream side of diffuser element 14 to provide
an
indication of flow rate through high performance series fan module 106.
Thermal load 130 may be in thermal communication with the bottom of heat sink
102,
and may be optimally positioned such that area of highest heat flux (i.e. the
hottest
portio0n of heat sink 102) is immediately below the impinging airflow. Heat
may then be
removed through forced convection as the air flows through heat sink 102 and
exits as
right outlet airflow 110 and left outlet airflow 112, as previously described.
Control
module 120 may be configured to maintain a constant temperature of thermal
load 130,
a constant right outlet airflow 110 and left outlet airflow 112, or some
combination of
these and / or other control parameters.
FIG. 15 illustrates high performance series fan sink 100 as primary fan 8 is
being
replaced. A defective primary fan 8 may be removed while thermal load 130
(reference
FIG. 14) remains active since control module 120 may be configured to increase
the
power applied to secondary fan 16 during the primary fan 8 outage, and until
primary fan
8 has been replaced, in order to maintain a relatively constant right outlet
airflow 110
and left outlet airflow 112 (reference FIG 14). Control module 120 may also be
configured to detect the re-insertion of a new primary fan 8, and may then re-
apply
power to both fans in a controlled fashion to optimize the performance of high
performance series fan module 106, as previously described.
FIG. 16 illustrates high performance series fan sink 100 with secondary fan 16
being
replaced. A defective secondary fan 16 may be removed while thermal load 130
(reference FIG. 14) remains active since control module 120 will increase the
power
applied to primary fan 8 during the secondary fan 16 outage, and until
secondary fan 16
has been replaced, in order to maintain a relatively constant right outlet
airflow 110 and
left outlet airflow 112 (reference FIG 14). Control module 120 may also be
configured to
detect the re-insertion of a new secondary fan 18, and may then re-apply power
to both
fans in a controlled fashion to optimize the performance of high performance
series fan
module 106, as previously described.
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FIG. 17 provides a perspective view of high performance series fan tray 200,
which may
be configured with a single row of high performance series fan modules, as
shown, or
multiple rows of high performance series fan modules. Further, a single row of
high
performance series fan modules may be configured as a partial fan tray that
may be
mounted from the front of a rack system, and possibility combined with a
similar fan tray
mounted from the back of the same system to provide flexible and expandable
cooling
solutions. Further, high performance series fan trays 200 may be may be
mounted
horizontally to produce a vertical airflow, or vertically to produce a
horizontal airflow.
Finally, one or more high performance series fan modules may be added to an
existing
fan tray, using a traditional array of single axial fans in parallel, to
increase performance
and add a measure of fault tolerance to an existing installation.
Each high performance series fan module within high performance series fan
tray 200
may be configured independently. For example, one module may be configured
with a
duct to provide direct cooling for one or more components within the system,
and
another module may be configured to actively exhaust air from the same or
different
component(s). Other modules may be configured to provide a more general flow
of air
within the system.
The high performance series fan tray 200 depicted in FIG. 17 includes three
high
performance series fan modules, 106a, 106b, and 106c, that draw inlet airFlows
108a,
108b, and 108c, respectively, to produce outlet airflows 110a, 110b, and 110c,
respectively. Control module 120 may be configured to monitor and control high
performance series fan modules 106a, 106b, and 106c, and outlet airflows 110a,
110b,
and 110c
FIG. 18 provides a second perspective view of high performance series fan tray
200,
showing further details of high performance series fan module 106a (reference
FIG. 17),
which contains primary fan 8, diffuser element 14, and secondary fan 16, and
operates
as previously described. High performance series fan module 106a further
contains
primary fan indicator light 122a and secondary fan indicator light 124a.
It may be seen from FIG. 18 that control module 120 may contain Cubic Feet per
Minute
(CFM) or temperature display 126, increase increment button 130, decrease
increment
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button 128, and power switch 132. The CFM, temperature, or other set point may
be
increased or decreased by pressing increase increment button 130 or decrease
increment button 128, respectively, causing control module 120 to adjust the
power
applied to high performance series fan modules 106a, 106b, and 106c (reference
FIG.
17) accordingly. CFM or temperature display 126 may then be used to monitor
the
changing parameter as it moves towards, and then reaches, the new set point.
FIG. 19 illustrates high performance series fan tray 200 with primary fan 8c
being
replaced. Primary fan 8c may be removed while the thermal load within the
cabinet or
system being cooled remains active since control module 120 will increase the
power
applied to secondary fan 16c, and high performance series fan modules 106a and
106b
(reference FIG. 17), during the primary fan 8c outage, and until primary fan
8c has been
replaced, in order to maintain a relatively constant combined outlet airflow,
comprised of
output airflows 110a, 110b, and 110c (reference FIG. 17). Control module 120
may also
be configured to detect the re-insertion of a new primary fan 8c, and then re-
apply power
to high performance series fan modules 106a, 106b, and 106c in a balanced
fashion in
order to optimize the performance of high performance series fan tray 100, as
previously
described.
FIG. 20 illustrates high performance series fan tray 200 with secondary fan
16c being
replaced. Secondary fan 16c may be removed while the thermal load within the
cabinet
or system being cooled remains active since control module 120 will increase
the power
applied to primary fan 8c, and high performance series fan modules 106a and
106b
(reference FIG. 17), during the secondary fan 16c outage, and until secondary
fan 16c
has been replaced, in order to maintain a relatively constant combined outlet
airflow,
comprised of output airflows 110a, 110b, and 110c (reference FIG. 17). Control
module
120 may also be configured to detect the re-insertion of a new secondary fan
16c, and
then to re-apply power to high performance series fan modules 106a, 106b, and
106c in
a balanced fashion in order to optimize the performance of high performance
series fan
tray 100, as previously described.
FIG. 21 illustrates control module 120 operating in fan failure mode. Control
module 120
is in communication with, and controls the power delivered to, primary fan
modules 8a,
8b, and 8c, and secondary fan modules 16a, 16b, and 16c (reference FIG.
18,19,20),
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and their respective indicator lights. Control module 120 may be configured to
sense that
secondary fan module 16b has failed, and to illuminate secondary fan module
indicator
light 124b accordingly. Controller module 120 may then adjust the power
applied to
cooling fan modules 106a, 106b, and 106c such that adjusted inlet airflows
138a and
138c are greater than normal inlet airflow 108 (shown here for reference
only), and
adjusted inlet airflow 138b, solely generated by primary fan module 114b, is
as close to
normal inlet air 108 as possible. Inlet flows 138a, 138b, and 138c may be
adjusted in this
manner such that the combined outlet airflow will be substantially equal to
the sum of
combined normal outlet airflows 110a, 110b, and 110c, and the thermal load
within the
system or cabinet being cooled will experience the same degree of forced
convection
cooling as with normal operation. Control module 120 may be configured to
compensate
for multiple fan module failures in a similar manner, however at some point
the
remaining fans may not be able to generate the full replacement airflow during
the
outage situation. Further, control module 120 may be configured to re-adjust
power
delivered to the cooling fan modules to normal levels once the defective
fan(s) have
been replaced, and turn off the indicator lights accordingly.
FIG. 22 illustrates a method for monitoring the airflow through high
performance series
fan module 106 using first pressure sensor 142 and second pressure sensor 144.
Control module 120 may be in communication with both sensors, and may be
configured
to monitor the output from both sensors to determine the differential pressure
between
first pressure sensor 142 and second pressure sensor 144, as caused by the
flow of air
through diffuser element 14. Control module 120 may then use the differential
pressure
information to determine the rate of flow of air through diffuser element 14,
and may
further use the flow rate information as a feedback signal for an internal
flow rate control
algorithm. The power applied to primary fan 8 and secondary fan module 16 may
be
adjusted by control module 120 to compensate for any detected difference
between the
measured flow rate and the flow set point for high performance series fan
module 106. A
power adjustment that does not generate the predicted response, or does not
generate a
response that falls within normal guidelines, may indicate to the controller
that primary
fan 8 or secondary fan 16 is failing or has failed. Control module 120 may
complete
further tests, in like manner, to determine which fan has a problem, to
determine the
extent of that problem, and to determine an appropriate response.
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FIG. 22 also illustrates swirl gap 140 between primary fan 8 and diffuser
element 14.
The swirl component of the flow produced by primary fan 8 will decay at an
initial rate,
and then decay at an ever decreasing rate as the distance from primary fan 8
increases.
Swirl gap 140 allows sufficient space for some decay of swirl prior to
diffuser element 14.
This increases the effectiveness of diffuser element 14 since the swirl
component at the
inlet side of diffuser element 14 will have been reduced by some amount, and
the net
swirl decay caused by swirl gap 140 combined with diffuser element 14 will be
greater
than that caused by a diffuser element 14 placed immediately downstream from
primary
fan 8. The location and physical characteristics of diffuser 14 may be
configured such
that the swirl and other flow parameters meet or exceed the design
specifications for
secondary fan 16 as the flow enters secondary fan 16.
A small gap may be introduced between diffuser element 14 and secondary fan
module
118 to reduce the acoustical noise produced high performance series fan module
106,
and to allows sufficient space for second pressure sensor 144. This gap may be
eliminated if second pressure sensor 144 is placed within diffuser element 14
116, at
some distance from first pressure sensor 142, and if acoustic management is
not an
overriding design consideration.
Although diffuser element 14 has a very positive effect on the efficiency and
performance of high performance series fan module 106, as previously
described, it
does introduce a small flow restriction and a corresponding pressure drop.
Although this
is acceptable during normal operation, it does limit the maximum achievable
flow rate
when only one of primary fan 8 or secondary fan module 16 is operational.
Therefore in
some applications diffuser element 14 may be configured to slide out of the
way, swing
out of the way, or otherwise be partially or completely removed from the flow
in order to
maximize the achievable flow rate during an outage situation.
Accordingly, diffuser element 14 may be configured to be removable from the
flow by
splitting it in the middle, and allowing each half to swing towards primary
fan module 8.
The right half of diffuser element 14 and the left half of diffuser element 14
may be
configured to swing along the right and left sides of high performance series
fan module
106, respectively, and lie along the sides of the airflow channel in the area
normally
defined as swirl gap 140 during a fan outage situation. The sides of swirl gap
140 may
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be configured to accommodate the right and left sides of diffuser element, so
positioned,
such that they present a minimum restriction to the flow. Control module 120
may be
configured to release the right and left sides of diffuser element 14 during a
fan outage,
such that they must be manually returned to normal position when the defective
fan has
been replaced, and held there with a retaining mechanism controlled by control
module
120, or to move the right and left sides of diffuser element 14 in a
controlled fashion both
during the outage and after it has been resolved.
FIG. 23 provides a perspective view of an alternatively configured high
performance
series fan tray with high performance series fan modules 106a and 106b mounted
obliquely to provide a relatively even airflow over the maximum width possible
with only
two high performance cooling fan modules. Further, the primary and secondary
cooling
fans located within high performance series fan modules 106a and 106b, so
mounted,
may be conveniently removed by sliding them in the direction defined by
removal arrows
156 and 154, respectively. Multiple high performance series fan modules may be
configured obliquely, in this manner, and at various angles, to provide a
relatively even
airflow over a maximum possible width with the fewest possible number of high
performance series fan modules. Further, this configuration offers fault
tolerance with the
fewest possible number of high performance series fan modules.
The present invention may be embodied in other specific forms without
departing from
the spirit or essential characteristics thereof. Certain adaptations and
modifications of
the invention will be obvious to those skilled in the art. Therefore, the
above-discussed
embodiments are considered to be illustrative and not restrictive, the scope
of the
invention being indicated by the appended claims rather than the foregoing
description,
and all changes which come within the meaning and range of equivalency of the
claims
are therefore intended to be embraced therein.
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