Note: Descriptions are shown in the official language in which they were submitted.
CA 02733413 2011-02-07
WO 2010/018398 PCT/GB2009/050996
-1-
EQUIPMENT COOLING
This invention relates to cooling for equipment, in particular but not
exclusively to the use of an open cell foam-filled ducting for convection
cooling
of electronic and other heat-generating equipment.
From a first aspect the present invention resides in an equipment cooling
apparatus, comprising a structure formed at least in part by an open cell foam
of
a thermally conducting material, wherein the structure is arranged to enable a
coolant to pass through the foam for removing heat conducted into the foam
from equipment to be cooled.
The use of an open cell foam in such a cooled structure has been found
to be particularly advantageous in that it provides a large surface area in
contact with the coolant and the open cell nature of the material enables
coolant
to flow relatively easily through the structure.
An open cell foam structure may be formed or cut to any desired shape
due to the structurally homogeneous nature of the open cell foam. For example
the structure may be shaped to at least partially enclose or to fit closely to
the
surface of a piece of equipment to be cooled.
In one convenient implementation, the structure comprises a panel of the
open cell foam arranged to provide a duct for the passage of the coolant. In a
preferred embodiment, one or more such panels may be used to form walls or
parts of a wall of a cooled equipment box, or they may be detached from the
walls of the box to provide supplemental equipment cooling within the box.
Alternatively, or in addition, the equipment box may further comprise a
chimney,
detached from the walls of the box, formed using the open cell foam to provide
a supplementary passage for the coolant and for removing heat from equipment
thermally linked to it.
In a further preferred embodiment, a panel of the open cell foam may be
provided with one or more fans for propelling air through the panel, so
forming a
self-contained cooled panel for equipment thermally linked to it.
CA 02733413 2011-02-07
WO 2010/018398 PCT/GB2009/050996
-2-
In designing a heat management solution, there are situations where
cooling provided by structures according to this first aspect of the present
invention may be insufficient, at least for short periods of time. Preferably,
therefore, in the cooling apparatus according to this first aspect of the
present
invention, the structure further comprises an enclosed section formed using
the
open cell foam and containing a latent heat thermal storage material to
provide
a heat storage body, thermally linked to that portion of the structure
arranged to
pass the coolant. In this way, short term demands for higher levels of heat
removal may be accommodated with help from the heat storage body while,
during times of cooler operation, the cooled portion of the structure may be
used to remove heat from the heat storage body. The heat storage body may
contain a phase change material such as wax in which the wax would be
allowed to set during a cooling phase. However, other types of latent heat
thermal storage material may be used in the heat storage body, including
solids
such as metal hydrides, for example.
The open cell foam may be made using metals, such as aluminium or
copper, or other materials with good thermal conductivity. The choice of
material may depend upon weight considerations, required levels of thermal
conductivity, expansion properties and mechanical robustness, to name but a
few considerations. Furthermore, the size of the cells in the foam may be
adjusted on the same or similar bases, taking account also of the nature of
the
coolant and the required rate of flow of the coolant through the open cell
foam.
The coolant itself may take a number of different forms. Typically, air
may be pumped or allowed to flow freely through the structure. However, other
types of gas and various types of liquid may be used as coolants according to
the particular cooling application.
Preferred embodiments of the present invention will now be described in
more detail and with reference to the accompanying drawings, of which:
Figure 1 is a perspective view of a portion of a cooled electronics
equipment box according to a first preferred embodiment of the present
invention;
CA 02733413 2011-02-07
WO 2010/018398 PCT/GB2009/050996
-3-
Figure 2 provides two sectional views through a cooled electronics
equipment box according to a second preferred embodiment of the present
invention;
Figure 3 provides a perspective view of a self-contained cooling panel
according to a third preferred embodiment of the present invention;
Figure 4 provides a perspective view and a cross-sectional view of a
cooling structure for at least partially enclosing a heat source such as an
electric
motor, according to a fourth preferred embodiment of the present invention;
and
Figure 5 provides a plan view of an equipment box combining cooled
panels with heat storage panels according to a fifth preferred embodiment of
the
present invention.
Preferred features according to a first embodiment of the present
invention will now be described, with reference to Figure 1, in the context of
a
cooled electronic equipment box.
Referring to Figure 1, a perspective view is provided of a portion of a
cooled electronics equipment box 100 comprising a hollow base plenum
chamber 105 having a coolant inlet 110 and a coolant outlet 115, and four
walls
120, 125, 130 and 135 fixed to a mounting surface of the plenum chamber 105.
Each of the walls 120-135 comprises one or more panels of an open cell
aluminium foam, clad in aluminium on those faces forming the inner and outer
faces of the box 100. The open-cell nature of the aluminium foam panels allows
for the flow of air, or other types of coolant such as water, through selected
sections of the walls 120-135. Coolant is able to flow from the plenum chamber
105 into selected panels through holes or slots (not shown in Figure 1) formed
in the mounting surface of the plenum chamber 105 and, after flowing through
the selected panels, may emerge into a lid (not shown in Figure 1) comprising
a
similar plenum chamber into which the coolant may flow through corresponding
holes or slots. The cladding on the faces of each panel ensures that the
panels
act as foam-filled ducts through which the coolant may flow without entering
the
box 100 itself.
CA 02733413 2011-02-07
WO 2010/018398 PCT/GB2009/050996
-4-
Cladding or other types of divider may be provided between panels
within or between walls 120-135 of the box 100 to direct or to increase the
flow
rate of coolant to selected panels, in particular to those having heat-
producing
components mounted thereon or otherwise thermally linked thereto. The relative
positioning of holes or slots in the mounting surface of the base 105 and of
dividers between panels may be arranged to provide for any desired route
through the panels for coolant to flow. Coolant may for example enter one
panel
from the plenum chamber 105 and flow through that and an adjacent panel
before emerging from the adjacent panel into a lid.
Sources of heat in an electronic circuit, e.g. power transistors 140, are
shown in Figure 1 fixed directly to the inner walls of panels 145 and 150 of
the
box 100. Those panels 145, 150 in particular have been arranged to receive a
flow of coolant from the plenum chamber 105. In an alternative arrangement, a
heat source may be attached to a heat path of high thermal conductivity, made
using metal encapsulated anisotropic graphite or another high-conductivity
material, arranged to conduct heat to the inner wall of such a panel 145, 150
for
removal.
Omitted from the view provided in Figure 1 is a plenum chamber lid
arranged to receive and remove coolant emerging from selected ones of the
wall panels 120-135. In the box 100 shown in Figure 1, the open cell structure
of one panel in each of the walls 130 and 135 has been exposed (155) to allow
coolant to emerge from those panels and to flow into the plenum chamber lid
when mounted on the box 100.
In the particular example of a box 100 in Figure 1, each of the walls 120-
135 is constructed from aluminium foam panels of substantially the same
thickness and hence of volume. However, according to the heat management
requirements for the electronics intended for mounting in the box 100, one or
more of the panels may be of greater thickness than the others, or some of the
panels may comprise only aluminium sheeting of appropriate thickness with no
convection cooling duct provided. An example of this is shown in sectional
views through an alternative electronic equipment box in Figure 2 according to
a
second preferred embodiment of the present invention.
CA 02733413 2011-02-07
WO 2010/018398 PCT/GB2009/050996
-5-
Referring to Figure 2a and to Figure 2b, a plan view and a cross-
sectional view, respectively, are provided through an electronic equipment box
200. Figure 2a shows the box 200 in section through a plane parallel to a
plenum chamber base 260 of the box 200. Figure 2b provides a cross-sectional
view through the same box in a plane indicated by A-A in Figure 2a,
perpendicular to the plenum chamber base 260 of the box 200.
The box 200 is provided with one wall 205 comprising two open cell
aluminium foam panels 210, 215 of differing thicknesses; the panel 215 having
a greater thickness and hence of volume of open cell aluminium foam than the
panel 210. A wall 220 of the box 200 is also provided with an open cell
aluminium foam panel 225 similar in thickness to the panel 210, but the
remainder of the wall 220 comprises a section 230 of aluminium sheeting, as do
the other two walls 235 and 240 of the box 200. Four power transistors 245 are
shown mounted on the inner wall of the panel 215 and three circuit boards 250
are shown in position within the box 200 with their mounting edges in thermal
contact with the panels 210 and 225.
Whereas open cell aluminium foam panels have been shown to provide
both walls and coolant channels in an electronic equipment box 200, further
cooling may be provided by inserting an appropriately clad, open cell
aluminium
foam chimney 275 through the equipment box 200, as shown in section in
Figure 2a and 2b. As with the panels 210, 215, 225, coolant may flow through
the open cell foam of the chimney 275. The profile of the chimney 275 may be
tapered, as in a conventional chimney, to improve the ducting of coolant
through the chimney. Heat sources 280 may be mounted or otherwise thermally
linked to the chimney 275 in the same way as for a wall panel 210, 215, 225.
Referring in particular to Figure 2b, the sectional view A-A though the
box 200 shows the plenum chamber base 260 and lid 265 in place on the box
200 with the panel 215 and the aluminium wall section 230 shown in position
mounted between them. Holes or slots 270 are provided in the mounting
surfaces of the base 260 and the lid 265 to enable coolant to flow between the
base 260 and the lid 265 through the open cell aluminium foam of the panel 215
CA 02733413 2011-02-07
WO 2010/018398 PCT/GB2009/050996
-6-
and the chimney 275, in either direction, to remove heat from the power
transistors 245 and heat sources 280 respectively.
The increased surface area of open cell thermally conducting foams in
comparison with alternative heat transfer features such as fins or pins placed
in
the path of a flowing coolant, makes for a more effective heat transfer device
while providing high structural rigidity in a lightweight electronics
equipment box.
The open cell foam is suitable for use with air coolants or with liquid
coolants
such as water, although increased attention to the effective sealing of joints
is
required if liquid coolants are to be used, as would be apparent to a person
of
ordinary skill in the relevant art.
In situations where an equipment box is not required, but a more self-
contained cooling arrangement is required, for example in the form of panel, a
arrangement according to a third embodiment of the present invention may be
used. This arrangement will now be described with reference to Figure 3.
Referring to Figure 3, a perspective view is provided of a self-contained
cooled panel 300 having heat-producing components 305 mounted thereon.
The panel 300 comprises an open cell aluminium foam panel clad on both main
faces and on two of the four edges, leaving one edge 310 open to the
atmosphere and the opposite edge open for the mounting of three low voltage
motorised fans 315 to blow air through the panel and out of the exposed edge
310, so carrying heat away from the mounted components 305. The panel 300
may be changed in size and shape, in all three dimensions, and the number
and type of fans may be changed to suit different applications as required,
without departing from the scope of the present invention as regards this
third
preferred embodiment. Furthermore, if a liquid coolant is used, the fans are
replaced by one or more pumps.
A further application of open cell thermally conducting foam to the
removal of heat from equipment will now be described with reference to Figure
4 according to a fourth preferred embodiment of the present invention.
Referring to Figure 4a and to Figure 4b, a perspective and a cross-
sectional view are provided, respectively, of an enclosing structure
comprising a
body 400 of open cell aluminium foam through which a hole has been formed to
CA 02733413 2011-02-07
WO 2010/018398 PCT/GB2009/050996
-7-
accommodate an electric motor 405. The foam has been clad in aluminium on
all the exposed surfaces. A coolant inlet 410 and a coolant outlet 415 are
provided such that coolant may flow through the enclosing open cell foam
structure to remove heat from the electric motor 405. The volume of the
enclosing structure may be adjusted, for example according to the amount of
heat likely to be generated by the electric motor, the flow rate of the
coolant
through the structure and the available space. The external shape of the
enclosing foam structure 400 does not need to correspond to that of the
equipment being enclosed and cooled.
Of course, any shape of enclosure may be provided to completely or
partially surround a source of heat with a structure functionally equivalent
to that
shown in Figure 4, clad as required to contain the coolant as it flows through
the
open cell foam enclosure from one or more inlets to one or more outlets. The
body 400 may be changed in size and shape, to suit the object to be cooled. In
the case of the coolant being air, the foam may be unclad in suitable
locations,
so that the air can enter and exit the foam without needing to fabricate the
inlet
410 and outlet 415 as physical entities.
Whereas preferred embodiments of the present invention have been
described as using open cell aluminium foam in particular, other metals and
other materials, having good thermal conductivity, may be used for the foam
and the cladding. For all embodiments, the choice of material (foam or
cladding)
may be varied to achieve different mechanical or thermo-mechanical properties
such as strength, stiffness, coefficient of thermal expansion, etc. according
to
particular requirements of the application. For example, copper may be used
where weight is not as critical. Furthermore, the cell structure may be
altered to
provide larger or smaller cell sizes according to the available surface area
required for the transfer of heat to the coolant, the type and the required
flow
rate of coolant through the open cell structure and the resultant weight of
the
structure.
In providing a heat management solution, besides providing enhanced
convention cooling by the techniques described above, it may be advantageous
to incorporate one or more heat storage bodies into a cooling arrangement. A
CA 02733413 2011-02-07
WO 2010/018398 PCT/GB2009/050996
-8-
heat storage body, based for example upon a phase change material such as
wax, may be used to accommodate short term higher levels of heat which may
be beyond the capability of the convection cooling structure to handle without
an undesirable increase in temperature of the cooled equipment.
Improved heat storage bodies have been developed by the present
Applicant, making use of an open cell foam structure similar to that used in
preferred embodiments of the present invention to spread heat more effectively
through the phase change material. Such improved heat storage bodies are
described in a co-pending patent application by the present Applicant.
Conveniently, a structure comprising thermally linked sections of open
cell foam may be made initially without needing to decide which portions will
carry a coolant for convection cooling and which portions will be filled with
wax
for heat storage. Having established the position of heat sources to be
cooled, a
corresponding arrangement of convection cooling and heat storage portions of
the cooling structure may be designed and easily implemented. For example,
an equipment box with walls made from isolated panels of open cell aluminium
foam may be easily adapted to a particular application by using one or more
panels as heat storage bodies and others as convection cooling ducts. One
particular example of such an equipment box will now be described with
reference to Figure 5, according to a fifth preferred embodiment of the
present
invention.
Referring to Figure 5, a plan view is provided showing a cross-section
through an equipment box 500 similar in configuration to that shown in Figure
1
in that the walls of the box 500 comprise eight discrete panels 505-540, each
formed using an open cell aluminium foam clad in aluminium on its largest
faces
and on the upstanding internal and external edges. Any of the panels 505-540
may be linked to a plenum chamber in a base and a lid or the box 500 (not
shown in Figure 5) for the passage of a coolant by means of holes of slots as
required. Similarly, any of the panels may contain a phase change material
such as wax and be used as a heat storage body. In the particular example
shown in Figure 5, two of the panels 510 and 530 contain wax and the
remaining panels 505, 515, 520, 525, 535 and 540 remain open and available
CA 02733413 2011-02-07
WO 2010/018398 PCT/GB2009/050996
-9-
for the passage of a coolant. Each of the wax-filled panels 510, 530 abuts and
is preferably thermally bonded to two panels 505, 515, 525, 535 carrying
coolant so that, during a cooling phase, heat from the wax-filled panels 510,
530
may be transferred to and carried away by the coolant.
In addition to the walls of the box 500, further structures are provided
within the box 500 to supplement the cooling provided by the walls 505-540. In
particular, an additional panel 545 has been provided for the passage of
coolant
and a square-sectioned heat storage body 550 has been provided comprising
an enclosure containing two portions 555 of open cell aluminium foam
containing wax. The heat storage body 550 has been thermally bonded to the
internal face of the panel 540 so that during a cooling phase of the heat
storage
body 550, heat may be conducted away by the cooled panel 540.
In principle, and as would be apparent to a person of ordinary skill in the
relevant art, a cooled equipment box may comprise any desired combination of
heat storage panels and coolant panels, with different panels having different
sizes if required. Any combination of additional coolant carrying structures
and
heat storage bodies may be provided within the box, such as those (545, 550)
shown in Figure 5. Such structures are not limited to panel-like structures
and
may be shaped according to available space or to the shape of the equipment
to be cooled.
While the use of cooled structures in combination with heat storage
bodies, both formed using open cell foams of thermally conducting material,
has
been described in the context of an equipment box in this preferred embodiment
of the present invention, any other type or shape of structure may be formed
using such foam materials, appropriately enclosed, according to the physical
requirements of the equipment to be cooled and overall heat management
requirements. Structures such as that described above with reference to Figure
4 may comprise one or more partitioned but thermally linked sections to be
made into heat storage portions, containing a suitable latent heat thermal
storage material. Conveniently, the heat storage portions of such a structure
may closely resemble the coolant conducting portions as regards their physical
structure, so simplifying the manufacture of such structures. Preferably, a
CA 02733413 2011-02-07
WO 2010/018398 PCT/GB2009/050996
-10-
structure may be provided in which the choice of coolant carrying and heat
storage portions need not be made at the time of manufacture. The structure
may be adapted to suit a particular application by filling selected portions
with a
phase change material such as wax. The porous nature of the structure enables
this to be achieved easily at any time prior to use.
