Note: Descriptions are shown in the official language in which they were submitted.
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"Electric fluid heater and method of electrically heating fluid"
Cross-Reference to Related Applications
The present application claims priority from International Patent Application
No.
PCT/AU2011/000016, filed on 7 January 2011, the entire content of which is
incorporated herein by reference.
Technical Field
Embodiments generally relate to electric fluid heaters, methods for heating
fluid and
systems employing such heaters and heating methods.
Background
Rapid heating of fluid substances is desirable in a range of fields, including
automotive,
marine, aeronautical and aerospace. For instance, battery performance in cold
climates
is an ongoing concern for hybrid electric vehicles. It is therefore necessary
to warm up
the batteries in hybrid electric vehicles in order to achieve acceptable power
and energy
performance from the batteries. In an especially cold environment, both the
battery and
the hybrid electric vehicle's engine are cold. To avoid sluggish engine
performance, it
is desirable to preheat the engine block. In other situations it is the air in
a
compartment of the vehicle which requires heating for the comfort of
passengers.
A heater core or heat exchange system is typically used in heating fluids or
gasses. As
an example, heated engine coolant, heated by a vehicle's engine, is passed
through a
heat exchanger of a heater core installed in the vehicle. Air is forced past
the heat
exchanger by a fan and receives heat from the heat exchanger that is derived
from the
heated engine coolant. The heated air is then directed into the passenger
compartment
for the comfort of occupants, or may be directed to the windscreen for
demisting or de-
icing.
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In some applications where heated fluid is needed, space can be quite
restricted, for
example in coffee machines and other heated fluid dispensers. Conventional
heaters
can be too bulky or, if they are small, can be too inefficient.
It is desired to address or ameliorate one or more shortcomings or
disadvantages
associated with prior heating techniques, or to at least provide a useful
alternative to
such techniques.
Throughout this specification the word "comprise", or variations such as
"comprises" or
"comprising", will be understood to imply the inclusion of a stated element,
integer or
step, or group of elements, integers or steps, but not the exclusion of any
other element,
integer or step, or group of elements, integers or steps.
Summary
Some embodiments relate to an electric fluid heater comprising:
a body having a fluid inlet and a fluid outlet and defining a fluid passage
between the fluid inlet and the fluid outlet; and
at least two heating assemblies disposed in the body and arranged in parallel,
each heating assembly comprising at least two electrodes configured to heat
fluid by
passing alternating electric current through the fluid;
wherein the at least two heating assemblies are arranged in the body so that
fluid
flowing through the fluid passage flows simultaneously through the at least
two heating
assemblies.
The electric fluid heater may comprise at least three heating assemblies. At
least one of
the heating assemblies comprises at least one segmented electrode, each
segmented
electrode comprising a plurality of electrically separable electrode segments.
Each
segmented electrode may be controllable by selectively activating one or more
of the
electrode segments such that upon application of a voltage to the segmented
electrode,
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current drawn by the segmented electrode depends on an effective active area
of the
selected one or more electrode segments.
The heater may further comprise a controller operable to optimise power
applied to
heat the fluid by selectively activating or deactivating electrode segments of
the one or
more segmented electrodes. The controller may be further operable to
repeatedly
measure the fluid temperature at outputs of each of the heating assemblies and
compare
the measured temperature outputs with calculated output temperature values.
The at least two heating assemblies may be arranged so that fluid passing from
the fluid
inlet to the fluid outlet must pass through at least one of the at least two
heating
assemblies.
The body may have a volume less than about 0.1 m3 and optionally about 0.05
m3, for
example. The at least two heating assemblies may be arranged equally spaced
about a
central axis of the body. The body may be substantially cylindrical or
substantially
rectangular, at least in part. The at least two electrodes of each heating
assembly may
be substantially concentric. The surface area of the concentrically arranged
electrodes
in each heating assembly is such that the correct amount of energy is passed
to the
water. The surface areas of the electrodes in each of the concentric parallel
heating
assemblies may be different.
The at least two electrodes of each heating assembly may be formed of an inert
electrically conductive material. The inert electrically conductive material
may
comprise one of a electrically conductive plastic material, a carbon-
impregnated
material and a carbon-coated material, but are not limited to these materials.
Some embodiments relate to a heat generator to heat a substance, the heat
generator
comprising:
the electric fluid heater described herein; and
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a fluid receptacle to receive heated fluid from the electric fluid heater and
to
transfer heat from the heated fluid to a substance, wherein the substance to
be heated is
in proximity to the receptacle that contains the heated fluid.
The fluid heated by the heater may be one of water, ethylene glycol, propylene
glycol,
a mineral or synthetic oil and a nanofluid. The heater and the fluid
receptacle may form
part of a closed loop fluid path within which the fluid travels. The heat
generator may
further comprise a pump to cause fluid to travel through the heater and into
the fluid
receptacle.
Some embodiments relate to a heating method comprising:
passing fluid through a body having a fluid inlet and a fluid outlet and
defining a
fluid passage between the fluid inlet and the fluid outlet; and
heating the fluid using at least two heating assemblies disposed in the body
and
arranged in parallel, each heating assembly comprising at least two electrodes
configured to heat fluid by passing alternating electric current through the
fluid;
wherein the at least two heating assemblies are arranged in the body so that
fluid
flowing through the fluid passage flows simultaneously through the at least
two heating
assemblies.
The method may further comprise pumping heated fluid from the body into a
fluid
receptacle, wherein the fluid receptacle transfers heat from the heated fluid
to a
substance which is in proximity to the fluid receptacle. The fluid receptacle
may be
within a heat exchanger and the method further comprises passing the substance
through the heat exchanger. The fluid receptacle, heat exchanger and the body
together
may form part of a closed fluid loop and the method further comprises
circulating the
fluid through the closed loop.
The method may further comprise controlling the temperature of the heated
fluid in
order to control the temperature of the heated substance.
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The at least two heating assemblies may comprise at least first, second and
third
parallel heating assemblies positioned in the fluid passage. The at least two
heating
assemblies may be arranged so that fluid passing from the fluid inlet to the
fluid outlet
must pass through at least one of the at least two heating assemblies.
5
The method may further comprise: measuring fluid conductivity, set flow rate
and fluid
temperature at the fluid inlet; and from the measured fluid conductivity, flow
rate and
temperature, determining a required power to be delivered to the fluid via the
electrodes to heat the fluid to a set temperature.
The method may further comprise selectively activating or deactivating
segmented
electrode elements of the at least two electrodes. This may allow optimisation
of power
transferred to the fluid.
The at least two electrodes of each heating assembly may comprise a segmented
electrode, and the heating may comprise selectively activating one or more
electrode
segments of the segmented electrode such that upon application of a voltage to
the
segmented electrode, current drawn by the segmented electrode depends on an
effective
active area of the selected one or more electrode segments.
Some embodiments relate to a method to generate heat to heat a substance, the
method
comprising:
pumping fluid to an electric fluid heater;
the electric fluid heater heating the fluid by passing alternating electric
current
through the fluid, which by virtue of the fluid's electrical resistive
properties the fluid
will heat up; and
pumping heated fluid from the electric fluid heater into a fluid receptacle
wherein the fluid receptacle transfers heat from the heated fluid to a
substance, the
substance being in proximity to the fluid receptacle that contains the heated
fluid.
Some embodiments relate to a heat generator to heat a substance, the heat
generator
comprising:
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an electric fluid heater operable to receive fluid and to heat the fluid by
passing
alternating electric current through the fluid, which by virtue of the fluid's
electrical
resistive properties the fluid will heat up; and
a fluid receptacle within a heat exchanger to receive heated fluid from the
electric fluid heater and to transfer heat from the heated fluid to a
substance via the heat
exchanger, wherein the substance to be heated is in proximity to the heat
exchanger.
This method of heating a substance uses the heat generated by a fluid that is
being
electrically energised in a controlled fashion. The heat from the fluid can be
passed to
the substance requiring heating by any means available. Typically the
substance to be
heated will be positioned or passed in very close proximity to or in direct
contact with
the fluid receptacle containing the heated fluid. In this way heat exchange
will occur
and the substance to be heated will heat up. The temperature of the heated
substance is
controlled by maintaining accurate control of the temperature of the heated
fluid.
The fluid receptacle forms a closed loop with the electric fluid heater. In
such an
embodiment the method comprises circulating the fluid throughout the closed
loop. The
fluid will typically be circulated in the fluid receptacle which may be either
in very
close proximity to, or in direct contact with the substance to be heated.
The electric fluid heater operates on electrical power, which may be
alternating current
(AC) or direct current (DC) power from an electrical source. If a DC source is
used, it
must be converted to an alternating current and then supplied to the
electrodes.
The heat generator is not limited to the specific type of fluid heated by the
electric fluid
heater though it should be appreciated that it will be one that is
electrically and
thermally conductive. The selection of the fluid used in any system will in
part depend
on the desired temperature to be obtained and the application in which the
heated
substance is to be used. The thermally conductive fluid may be selected from,
but not
limited to water, ethylene glycol, propylene glycol, mineral or synthetic oils
and
nanofluids. These fluids are suited for use in heat exchange applications as
described
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herein. In applications where the heated fluid is to be dispensed rather than
used for
heat exchange, other fluids may be used.
The heat generator is not limited to the form of the fluid receptacle, the
configuration of
which will depend on the type of substance to be heated and the particular
fluid heating
application selected. Described fluid heating embodiments have wide
application to a
number of fluid heating needs.
The fluid receptacle may form a component of a heat exchanger. In one
embodiment
the substance to be heated may be air and a heat exchanger in the form of a
radiator
may be provided. In such an embodiment the radiator may transfer heat from the
heated
fluid to the air (substance) as it flows through the radiator. In other
embodiments the
fluid receptacle may form a component of a heat exchanger or the like for
deployment
of a diverse range of applications including polymer curing, autoclave
operation, de-
icing of windscreens, heating of batteries, and engine preheating.
The electric fluid heater may heat the electrically resistive fluid by passing
the fluid
along a flow path from an inlet to an outlet. The flow path may comprise at
least first
and second heating assemblies positioned in parallel along the flow path such
that fluid
passing the first heating assembly passes the second heating assembly in
parallel, each
heating assembly comprising at least one pair of electrodes between which the
electrically resistive fluid is passed, which, by virtue of its electrical
resistance will
draw electric current as it passes through the fluid passage along the flow
path.
The flow path may comprise at least first, second and third parallel heating
assemblies
positioned along the flow path such that fluid passes through all three or
more heating
assemblies in parallel.
The electric fluid heater may be further operable to measure fluid
conductivity, flow
rate and fluid temperature at the inlet and outlet. From the measured fluid
conductivity,
flow rate and temperature the electric fluid heater may determine the required
power to
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be delivered to the fluid by the first, second, third and/or nth parallel
heating assemblies
to raise the fluid temperature the desired amount.
In certain embodiments, at least one of the heating assemblies of the electric
fluid
heater may comprise at least one segmented electrode, the segmented electrode
comprising a plurality of electrically separable electrode segments allowing
an
effective active area of the segmented electrode to be controlled by
selectively
activating the segments such that upon application of a voltage to the
segmented
electrode current drawn will depend upon the effective active area of the
selected one
or more segments. Further, electrode segment selection may be carried out in a
manner
to ensure peak current limits are not exceeded. In such embodiments, the
measurement
of inlet conductivity permits the controller to determine whether the current
to be
supplied would exceed the current limits and to prevent operation of the
electrodes if
such current limits will not safely be met.
In certain embodiments, variations in fluid conductivity are substantially
continually
accommodated in response to measurements of incoming fluid conductivity. Fluid
conductivity may be determined by reference to the current drawn upon
application of a
voltage across one or more electrodes of one or more heating assemblies.
Further embodiments utilise the measured fluid conductivity to ensure that no
violation
occurs of a predetermined range of acceptable fluid conductivity within which
the heat
generator is designed to operate.
Moreover, by providing a plurality of parallel heating assemblies, each
heating
assembly is able to be operated in a manner that allows for changes in
electrical
conductivity of the fluid with increasing fluid temperature. For example,
water
conductivity increases with temperature, on average by around 2% per degree
Celsius.
Where fluid is to be heated by scores of degrees Celsius, for example from
room
temperature to 60 degrees Celsius or 90 degrees Celsius, inlet fluid
conductivity can be
substantially different to outlet fluid conductivity.
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Electrically energizing the fluid while passing through the parallel heating
assemblies
along the flow path allows each heating assembly to operate within a defined
temperature range. Thus, each heating assembly may apply the appropriate power
that
is applicable to the fluid conductivity within that defined temperature range
rather than
attempting to apply power in respect of a single or averaged conductivity
value across
the entire temperature range.
One or more of the embodiments may further comprise a downstream fluid
temperature
sensor to measure fluid temperature at the heater outlet, to permit feedback
control of
the fluid heating.
In some embodiments, each heating assembly may comprise substantially planar
electrodes between which the fluid flow path passes. Alternatively, each
heating
assembly may comprise substantially coaxial cylindrical or curved members with
the
heating assembly defining an approximately annular volume or channel for fluid
flow.
The heating assemblies may together define a plurality of parallel flow paths
for the
fluid.
In some embodiments, the heat generator may comprise three or more heating
assemblies, each assembly having an inlet and an outlet, the assemblies being
connected in parallel and the control means initially selecting electrode
segments in
accordance with the measured incoming fluid conductivity, the control means
controlling power to an electrode pair of each assembly in accordance with the
required
fluid temperature which is determined by measuring the system inlet and outlet
temperatures.
The volume of fluid passing between any set of electrodes may be determined by
a
determination of the dimensions of the passage within which the fluid is
exposed to the
electrodes taken in conjunction with fluid flow.
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The time for which a given volume of fluid will receive electrical power from
the
electrodes may be determined by reference to the flow rate of fluid through
the system.
The temperature increase of the fluid is proportional to the amount of
electrical power
applied to the fluid. The amount of electrical power required to raise the
temperature
5 of the fluid a known amount, is proportional to the mass (volume) of the
fluid being
heated and the fluid flow rate through the flow path. The measurement of
electrical
current flowing through the fluid can be used as a measure of the electrical
conductivity, or the specific conductance of that fluid, and hence allows
selection of
electrode segments to be activated together with system control and management
10 required to keep the applied electrical power constant or at a desired
level. The
electrical conductivity, and hence the specific conductance of the fluid being
heated
will change with rising temperature, thus causing a specific conductance
gradient along
the path of fluid flow.
The energy required to increase the temperature of a body of fluid may be
determined
by combining two relationships:
Energy = Specific Heat Capacity x Density x Volume x Temp-Change
The energy per unit of time required to increase the temperature of a body of
fluid may
be determined by the relationship:
Power (P) = Specific Heat Capacity(SHC) x Density x Vol (V) x Temp-Change (Dt)
Time (T)
For analysis purposes where water is concerned, the specific heat capacity of
water, for
example, may be considered as a constant between the temperatures of Odeg
Celsius
and 100 deg Celsius. The density of water being equal to 1, may also be
considered
constant. Therefore, the specific heat or amount of energy required to change
the
temperature of a unit mass of water, 1 deg Celsius in 1 second is considered
as a
constant and can be labelled "k". Volume/Time is the equivalent of flow rate
(Fr).
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Thus, the energy per unit of time required to increase the temperature of a
body of fluid
may be determined by the relationship:
Power (P) = k x Flow rate (Fr) x Temp-Change (Dt)
Time (T)
Thus if the required temperature change is known, the flow rate can be
determined and
the power required can be calculated.
In a non-limiting example where the substance to be heated is the air in a
vehicle's
cabin, a controller input component on the vehicle instrument panel or a
remote control
device is operated when a user requires heated air. This operation input may
be
detected by or passed to the electric fluid heater and cause the initiation of
a heating
sequence. The temperature of the inlet fluid may be measured and compared with
a
preset desired temperature for fluid output from the system. From these two
values, the
required change in fluid temperature from inlet to outlet may be determined by
the
controller.
The temperature of the inlet fluid to the electrode assemblies may be
repeatedly
measured over time and, as the value for the measured inlet fluid temperature
changes,
the calculated value for the required temperature change from inlet to outlet
of the
electrode assemblies can be adjusted accordingly.
Similarly, with changing
temperature, mineral content and the like, changes in electrical conductivity
and
therefore specific conductance of the fluid may occur over time. Accordingly,
the
current passing through the fluid may change, causing the resulting power
applied to
the fluid to change, and this may be managed by selectively activating or
deactivating
elements of the segmented electrode(s). Repeatedly measuring the temperature
outputs
of the heating sections over time and comparing these with the calculated
output
temperature values will enable repeated calculations to continually optimise
the power
applied to the fluid.
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In some embodiments, a computing means provided by the microcomputer-
controlled
management system is used to determine the electrical power that should be
applied to
the fluid passing between the electrodes, by determining the value of
electrical power
that will effect the desired temperature change between the heating assembly
inlet and
outlet, measuring the effect of changes to the specific conductance of the
water and
thereby selecting appropriate activation of electrode segments and calculating
the
power that needs to be applied for a given flow rate.
In some embodiments, the electrical current flowing between the electrodes
within each
heating assembly, and hence through the fluid, is measured. The heating
embodiment
input and output temperatures are also measured. Measurement of the electrical
current
and temperature allows the computing means of the microcomputer-controlled
management system to determine the power required to be applied to the fluid
in each
heating assembly to increase the temperature of the fluid by a desired amount.
In some embodiments, the computing means provided by the microcomputer-
controlled
management system determines the electrical power that should be applied to
the fluid
passing between the electrodes of each heating assembly, selects which
electrode
segments should be activated in each segmented electrode, and calculates the
power
that needs to be applied to effect the desired temperature change.
As part of the initial heating sequence, the applied voltage may be controlled
in such a
way so as to determine the initial specific conductance of the fluid passing
between the
electrodes. The application of voltage to the electrodes will cause current to
be drawn
through the fluid passing there-between, thus enabling determination of the
specific
conductance of the fluid, being directly proportional to the current drawn
there-through.
Accordingly, management of the electrical power that should be supplied to the
fluid
flowing between the electrodes in each heating assembly can be correctly
applied, in
order to increase the temperature of the fluid flowing between the electrodes
in each
heating assembly by the required amount. The instantaneous current being drawn
by
the fluid may be continually monitored for change along the length of the
fluid flow
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path. Any change in instantaneous current drawn at any position along the
passage is
indicative of a change in electrical conductivity or specific conductance of
the fluid.
The varying values of specific conductance apparent in the fluid passing
between the
electrodes in the heating assemblies effectively defines the specific
conductivity
gradient along the heating path.
Various operational parameters of the heater and heat generator are
continuously
monitored and calculations continuously performed to determine the electrical
power
that should be supplied to the fluid in order to raise the temperature of the
fluid to a
preset desired temperature in a given period.
Brief Description of the Drawings
Embodiments are described in further detail below, by way of example and with
reference to the accompanying drawings, in which:
Figure 1 illustrates a heat generator to heat a substance according to some
embodiments;
Figure 2 illustrates a heat generator to heat a substance according to some
embodiments; and
Figure 3 illustrates an electric fluid heater, which can be used with the heat
generator shown in Fig. 1 or Figure 2 and which has a parallel arrangement of
three
heating assemblies, each assembly having a pair of electrodes, one of each of
which are
segmented into two electrode segments; and
Figure 4 illustrates an electric fluid heater, which can be used with the heat
generator shown in Fig. 1, Figure 2 or Figure 3 and which has a parallel
arrangement of
three heating assemblies, where the electrodes are arranged concentrically.
Detailed Description
Embodiments relate generally to electric fluid heaters and heating methods.
Some
heater and fluid heating embodiments may be employed with a heat generator or
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heating system to transfer heat from the heated fluid to another substance,
such as
another fluid, like air or a liquid, like water. The fluid heater and heating
method
embodiments employ a parallel arrangement of multiple fluid heating assemblies
to
efficiently and rapidly heat water within a small volume. This parallel
arrangement
allows the heating device to be contained within a surprisingly small housing
for its
heating efficiency and power consumption.
Figure 1 illustrates some embodiments of a heat generator 10 to heat a target
substance,
which may be a gas, such as air, or a liquid, such as water or a beverage
liquid, for
example. The heat generator 10 shows an electric fluid heater 22 controlled by
an
electronic controller 24 and coupled to a fluid receptacle which forms a
component of a
conditioning/heat exchanger 20. Various possible configurations of the heat
exchanger
may be used. The embodiments illustrated in Figure 1 provide for the electric
fluid
heater 22 to effectively be thermally coupled to the substance being heated
via the heat
15 exchanger 20. The electric fluid heater 22 is used to heat fluid that is
circulated
between the electric fluid heater 22 and the heat exchanger 20 using a small
pump 26.
The heat exchanger 20 is used to transfer heat from the heated fluid to the
substance
being heated. The level of heat transferred is controlled by the electric
fluid heater 22
and electronic controller 24.
In this, or similar embodiments, the electric fluid heater 22 uses multiple
parallel (and
optionally concentric) electrode elements, and heats fluid through the direct
application
of electrical energy, in the form of alternating current, into the fluid from
the electrodes
to cause heating within the fluid itself under electronic control. This
application of
alternating current to the electrodes is intended to substantially avoid the
occurrence of
electrolysis of the fluid (other than at an instantaneous level for each
successive
opposite polarity current pulse). The provision if electrical energy to the
fluid is thus
controlled to minimise chemical interference with the properties of the fluid
other than
to increase the thermal (kinetic) energy of the fluid.
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The electric fluid heater voltage is provided by an electrical power source,
such as
mains power or a battery. The heater 22 controls fluid flow therethrough to
generally
achieve a set fluid flow rate and, where applicable, to account for changes in
fluid
conductivity, for example due to temperature changes. Being a closed loop
continuous
5 flow fluid heater, with fluid flow facilitated via a pump 26, the
electric fluid heater 22
operates within constrained ranges of variation of temperature and
conductivity.
Figure 2 illustrates further embodiments of a heat generator 15 to heat a
target
substance, with like numbers illustrating like components as between the
embodiments.
10 In this example, the electric fluid heater 22 is used to heat motor vehicle
engine
coolant. In this context, the term coolant is used to mean a temperature
transmission
medium, rather than necessarily performing a cooling function. The heated
engine
coolant is pumped through an existing fluid receptacle within a heat exchanger
20 that
is used to heat the air being transferred into the motor vehicle interior. In
effect, the
15 heated fluid is circulated in a closed loop between the electric fluid
heater 22 and the
heat exchanger 20 using a small pump 26. The solenoids 28 in line with the
heat
exchanger 20 supply/return engine coolant to be heated. The heat exchanger 20
may be
used to heat air to be transferred into the vehicle cabin. When the running
engine
coolant is sufficiently hot enough to allow air to be effectively heated by
the heat
exchanger 20, the electric fluid heater 22 is isolated using the solenoids 28.
Figure 3 and Figure 4 are schematic diagrams of embodiments of an electric
fluid
heater 100, which may be used as the fluid heater 22 for the heat generator 10
or 15 to
heat a substance by heat transfer from a heated fluid. Figure 3 illustrates
embodiments
where the electrodes are arranged in a planar configuration, and Figure 4
illustrates
embodiments where the electrodes are arranged in a concentric configuration.
The
surface areas of the electrodes in each of the concentric parallel heating
assemblies may
be different or, in some embodiments may be substantially the same. The fluid
to be
heated, which may include water, ethylene glycol, propylene glycol, a mineral
or
synthetic oil and a nanofluid, for example, is caused to flow through a body
112 of the
electric fluid heater 100.
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The body 112 is preferably made from a material that is electrically non-
conductive and
thermally non- or minimally conductive, such as a synthetic plastic material.
However,
depending on the application, the body 112 may be connected to metallic fluid
pipe,
such as aluminium pipe, that is electrically conductive. Accordingly, earth
mesh grids
114 shown in Figure 3 are included at the inlet and outlet of the body 112 so
as to
electrically earth any metal tubing connected to the apparatus 100. The earth
grids 114
would ideally be connected to an electrical earth of the electrical
installation in which
the heater 100 is installed. As the earth mesh grids 114 may draw current from
an
electrode through water passing through the apparatus 100, activation of an
earth
leakage protection within the control system may be effected. The system
preferably
includes earth leakage circuit protective devices.
In operation, fluid flows into a fluid inlet at one end of the body 112 and
out of a fluid
outlet at an opposite end, with fluid passing through a fluid passage defined
by the
body 112, with the direction of flow indicated by flow path arrows 102.
The body 112 may house three heating sections comprising respective parallel
heating
assemblies 116, 117 and 118, which together defines the fluid flow path of
fluid
passing from the inlet to the outlet. The heating assemblies 116, 117 and 118
are
arranged within the body 112 so that fluid passing from the inlet to the
outlet must pass
through at least one of the heating assemblies 116, 117 and 118. In some
embodiments, two, four, five, six, seven, eight, nine, ten or more such
heating
assemblies may be employed instead of the three illustrated in Figure 3.
However, for
purposes of illustration, embodiments having three heating assemblies are
shown and
described.
The electrode material of electrodes in the heating assemblies 116, 117 and
118 may be
any suitable inert electrically conductive material or a non-metallic
conductive material
such as a conductive plastics material, carbon impregnated, coated material or
the like.
It is important that the electrodes are selected of a material to minimise
chemical
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reaction and/or electrolysis. These electrodes are arranged in pairs, with one
electrode
of the pair being segmented into at least two electrodes segments
The segmented electrode of each electrode pair, being segmented electrodes
116a, 117a
and 118a, is connected to a common switched path via separate voltage supply
power
control devices Q 1, Q2, Q3 to the live side 124 of the AC electrical supply,
while the
other of each electrode pair 116b and 117b is connected to the return side
voltage
supply 121. The separate voltage supply power control devices Ql, Q2, Q3
switch the
live electrical supply 124 in accordance with the power management control
provided
by microprocessor control system 141. The total electrical current supplied to
each
individual heating assembly 116, 117 and 118 is measured by a current
measuring
device 129. The current measurements are supplied as an input signal via input
interface 133 to microprocessor control system 141 which acts as a power
supply
controller for the heating assemblies.
The microprocessor control system 141 has access to a memory (not shown)
storing
executable program code that, when executed, causes the microprocessor control
system 141 (also called a controller herein) to receive data inputs from the
measuring
devices/sensors, to process that data to make calculations and determinations
as
described herein and to provide control outputs to the various electrical and
fluid
control components described herein.
The microprocessor control system 141 also receives signals via input
interface 133
from a flow switch device 104 located in the body 112 near the inlet. The
volume of
fluid passing between any set of electrode segments may be accurately
determined by
measuring ahead of time the dimensions of the passage within which the fluid
is
exposed to the electrode segments taken in conjunction with fluid flow.
Similarly, the
time for which a given volume of fluid will receive electrical power from the
electrode
segments may be determined by measuring the flow rate of fluid through the
passage.
The temperature increase of the fluid is proportional to the amount of
electrical power
applied to the fluid. The amount of electrical power required to raise the
temperature
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of the fluid a known amount is proportional to the mass (or volume for a known
fluid
density) of the fluid being heated and the fluid flow rate through the
passage. The
measurement of electrical current flowing through the fluid can be used as a
measure of
the electrical conductivity or the specific conductance of that fluid and
hence allows
determination by the microprocessor control system 141 of the change in
applied power
management required to keep the applied electrical power constant. The
electrical
conductivity, and hence the specific conductance of the fluid being heated,
will change
with rising temperature, thus causing a specific conductance gradient along
the path of
fluid flow.
The microprocessor control system 141 also receives signals via signal input
interface
133 from an input temperature measurement device 135 near the inlet to measure
the
temperature of input fluid to the body 112, an output temperature measurement
device
136 measuring the temperature of fluid exiting the body 112.
The fluid heating device 100 is further capable of adapting to variations in
fluid
conductivity, whether arising from the particular location at which the device
is
installed or occurring from time to time at a single location. Variations in
fluid
conductivity will cause changes in the amount of electrical current drawn by
each
electrode for a given applied voltage. This embodiment monitors such
variations and
ensures that the device draws a desired level of current by using the measured
conductivity value to initially select a commensurate combination of electrode
segments before allowing the system to operate.
One electrode of each electrode pair 116, 117 and 118 may be segmented into
two
electrode segments, 116a and 116ai, 117a and 117ai, 118a and 118ai. For each
respective electrode, the ai segment may be fabricated to form about 40% of
the active
area of the electrode and the a segment may be fabricated to form about 60% of
the
active area of the electrode, for example. More than two segments may be used
and
different proportions of active areas may be used for the segments, however.
Selection
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of appropriate electrode segments or appropriate combinations of electrode
segments
thus allows the appropriate electrode surface area to be selected.
For highly conductive fluid, a smaller electrode area may be selected, so that
for a
given voltage, the current drawn by the electrode is prevented from rising
above
desired or safe levels. Conversely, for poorly conductive fluid, a larger
electrode area
may be selected, so that for the same given voltage, adequate current will be
drawn to
effect the desired power transfer to the fluid. Selection of segments can be
simply
effected by switching the power switching devices Q1,..., Q3 in or out as
appropriate.
The combined surface area of the selected electrode segments is specifically
calculated
to ensure that the rated maximum electrical current values of the system are
not
exceeded.
The microprocessor control system 141 receives the various monitored inputs
and
performs necessary calculations with regard to electrode active area selection
and
desired electrode pair power to provide a calculated power amount to be
supplied to the
fluid flowing through the body 112. The microprocessor control system 141
controls
the (alternating) pulsed supply of voltage from electric supply connected to
each of the
heating assemblies 116, 117, 118. Each pulsed voltage supply is separately
controlled
by the separate control signals from the microprocessor control system 141 to
the
power switching devices Ql, ..., Q3.
Based upon the various parameters for which the microprocessor control system
141
receives representative input signals, a computing means under the control of
software
code executed by the microprocessor control system 141 calculates the control
pulses
required by the power switching devices in order to supply a required
electrical power
to impart the required temperature change in the fluid flowing through the
body 112 so
that heated fluid is emitted from the outlet of the body 112 at or very close
to the
desired temperature.
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The microprocessor control system 141 may have (or have access to in the
memory) a
stored defined maximum temperature which represents the maximum temperature
value above which the fluid may not be heated. The fluid heater 100 may be
designed
so that, if for any reason, the temperature sensed by the output temperature
sensor 136
5 were greater than the defined maximum temperature, provision of power to the
electrodes would be immediately shut off and the fluid pump 26 would be
deactivated.
Microprocessor control system 141 may remain active in such a situation,
however, in
order to be able to provide an indication of the nature of the shutdown, for
example.
10 The microprocessor control system 141 repeatedly performs a series of
checks to
ensure that:
(a) the fluid temperature at the outlet does not exceed the maximum
allowable
temperature;
(b) leakage of current to earth has not exceeded a predetermined set value;
and
15 (c) system current does not exceed a preset current limit of the
system.
These checks are repeatedly performed while the unit is operational and if any
of the
checks reveals a breach of the controlling limits, at least the electrodes and
pump are
immediately deactivated. When the initial system check is satisfactorily
completed, a
20 calculation is performed to determine the required power that must be
applied to the
fluid flowing through the body 112 in order to change its temperature by the
desired
amount. The calculated power is then applied to heating assemblies 116, 117,
118 so
as to quickly increase the fluid temperature to the desired temperature as it
flows
through the body 112 in a single pass.
As the fluid flowing through the body 112 increases in temperature from the
inlet end
of the body, the conductivity changes in response to increased temperature.
The input
temperature measuring device 135 and output temperature measuring device 136
measure the temperature differential in the three heating assemblies in the
body 112
containing the heating assemblies 116, 117, 118. The power applied to the
respective
heating assemblies 116, 117, 118 can then be managed to take account of the
changes
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in fluid conductivity to ensure that an even temperature rise occurs along the
length of
the body 112, to maintain a substantially constant power input to each of the
heating
assemblies 116, 117, 118 and to ensure greatest efficiency and stability in
fluid heating
between the input temperature measurement at 135 and the output temperature
measurement at 136. The power supplied to the flowing fluid is changed by
managing
the control pulses supplied by the activated power switching devices Q 1 ...Q3
commensurate with the power required. This serves to increase or decrease the
power
supplied by individual heating assemblies 116, 117, 118 to the fluid.
The fluid heater 100 repeatedly monitors the fluid for changes in conductivity
by
referring to the current measuring device 129, and the temperature measurement
devices 135 and 136. Any changes in the values for fluid conductivity within
the
system resulting from changes in fluid temperature increases, changes in fluid
constituents as detected along the length of the body 112 or changes in the
detected
currents drawn by the fluid cause the computing means to calculate revised
average
power values to be applied to the heating assemblies 116, 117 and 118.
Changes in incoming fluid conductivity cause the microprocessor control system
141 to
selectively activate changed combinations of electrode segments 116a and
116ai, 117a
and 117ai, 118a and 118ai. Constant closed loop monitoring of such changes to
the
system current, individual electrode currents and electrode segment fluid
temperature
allows recalculation of the power to be applied to the individual heating
assemblies to
enable the system to supply relatively constant and stable power to the fluid
flowing
through the fluid heater 100. The changes in specific conductance of the fluid
passing
through the separate segmented heating assemblies can be managed separately in
this
manner. Therefore the fluid heater 100 is able to effectively control and
manage the
resulting specific conductance gradient across fluid in the body 112.
Embodiments thus provide compensation for a change in the electrical
conductivity of
the fluid caused by varying temperatures and varying concentrations of
dissolved
chemical constituents, and through the heating of the fluid, by altering the
power to
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accommodate for changes in specific conductance when increasing the fluid
temperature by the desired amount.
It will be appreciated that any suitable number of electrode heating
assemblies may be
used in the performance of described embodiments. Thus, while the embodiments
described show three heating sections for heating the fluid flowing through
body 112,
the number of heating assemblies in the passage may be altered in accordance
with
individual requirements or applications specific for fluid heating. If the
number of
heating assemblies is increased to, for example, six pairs, each individual
heating
assembly may be individually controlled with regards to power in the same way
as is
described in relation to the embodiments herein. Similarly, the number of
electrode
segments into which a single electrode is segmented may be different to two.
For
example, segmentation of an electrode into four segments having active areas
in a ratio
of 1:2:4:8 provides 15 values of effective area which may be selected by the
microprocessor control system 141.
It is to be appreciated that by utilising heating assemblies which cause
current to flow
through the fluid itself such that heat is generated from the resistivity of
the fluid itself,
the embodiments obviate the need for electrical resistance heating elements,
thus
ameliorating the problems associated with element scaling or failure. Further
the
compact arrangement of the parallel heating assemblies allows the fluid heater
to be
quite space efficient relative to prior heating systems.
Some portions of this detailed description are presented in terms of
algorithms and
symbolic representations of operations on data bits within a computer memory.
These
algorithmic descriptions and representations are the means used by those
skilled in the
data processing arts to most effectively convey the substance of their work to
others
skilled in the art. An algorithm is here, and generally, conceived to be a
self-consistent
sequence of steps leading to a desired result. The steps are those requiring
physical
manipulations of physical quantities. Usually, though not necessarily, these
quantities
take the form of electrical or magnetic signals capable of being stored,
transferred,
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combined, compared, and otherwise manipulated. It has proven convenient at
times,
principally for reasons of common usage, to refer to these signals as bits,
values,
elements, symbols, characters, terms, numbers, or the like.
Described acts and operations, which are at times referred to as being
computer-
executed, include the manipulation by the processing unit of the computer of
electrical
signals representing data in a structured form. This manipulation transforms
the data or
maintains it at locations in the memory system of the computer, which
reconfigures or
otherwise alters the operation of the computer in a manner well understood by
those
skilled in the art. The data structures where data is maintained are physical
locations of
the memory that have particular properties defined by the format of the data.
However,
while embodiments are described in the foregoing context, it is not meant to
be limiting
as those of skill in the art will appreciate that various of the acts and
operations
described may also be implemented in hardware.
It should be borne in mind, however, that all of these and similar terms are
to be
associated with the appropriate physical quantities and are merely convenient
labels
applied to these quantities. Unless specifically stated otherwise as apparent
from the
description, it is appreciated that throughout the description, discussions
utilizing terms
such as "processing" or "computing" or "calculating" or "determining" or
"displaying"
or the like, refer to the action and processes of a computer system, or
similar electronic
computing device, that manipulates and transforms data represented as physical
(electronic) quantities within the computer system's registers and memories
into other
data similarly represented as physical quantities within the computer system
memories
or registers or other such information storage, transmission or display
devices.
Numerous variations and/or modifications may be made to the embodiments
without
departing from the scope of the invention as broadly described. The present
embodiments are, therefore, to be considered in all respects as illustrative
and not
restrictive.
