U.S. patent application number 12/680323 was filed with the patent office on 2011-08-18 for heat transfer system and method.
Invention is credited to Pei Fan Florence Ng, Kim Tiow Ooi, Tiew Toon Phay, Yong Liang Teh.
Application Number | 20110197609 12/680323 |
Document ID | / |
Family ID | 40567648 |
Filed Date | 2011-08-18 |
United States Patent
Application |
20110197609 |
Kind Code |
A1 |
Ooi; Kim Tiow ; et
al. |
August 18, 2011 |
HEAT TRANSFER SYSTEM AND METHOD
Abstract
A heat transfer system and method for maintaining or controlling
a temperature of a device under test (DUT) with heat generating
capability. The heat transfer system comprises a temperature
control unit (TCU) for thermal coupling to the DUT, the TCU
arranged for flow of a heat transfer medium therethrough; an
automatic expansion valve disposed upstream of the TCU; a
flow-regulating valve disposed downstream of the TCU; and a
controller coupled to the TCU for receiving an input signal
representative of a temperature of the DUT; wherein the controller
is further coupled to the flow-regulating valve to change a flow
area of the flow-regulating valve based on the signal
representative of the temperature of the DUT.
Inventors: |
Ooi; Kim Tiow; (Maplewoods,
SG) ; Teh; Yong Liang; (Singapore, SG) ; Phay;
Tiew Toon; (Singapore, SG) ; Florence Ng; Pei
Fan; (singapore, SG) |
Family ID: |
40567648 |
Appl. No.: |
12/680323 |
Filed: |
April 28, 2008 |
PCT Filed: |
April 28, 2008 |
PCT NO: |
PCT/SG08/00143 |
371 Date: |
August 24, 2010 |
Current U.S.
Class: |
62/222 |
Current CPC
Class: |
F25B 2700/1933 20130101;
F25B 41/22 20210101; F25D 2700/16 20130101; F25B 41/385 20210101;
F25B 2400/16 20130101; F25B 2600/2513 20130101 |
Class at
Publication: |
62/222 |
International
Class: |
F25B 41/04 20060101
F25B041/04; F25B 1/00 20060101 F25B001/00 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 16, 2007 |
MY |
PI20071780 |
Claims
1-14. (canceled)
15. A heat transfer system for maintaining or controlling a
temperature of a device under test (DUT) with heat generating
capability, the heat transfer system comprising: a temperature
control unit (TCU) for thermal coupling to the DUT, the TCU
arranged for flow of a heat transfer medium therethrough; an
automatic expansion valve disposed upstream of the TCU; a
flow-regulating valve disposed downstream of the TCU; and a
controller coupled to the TCU for receiving an input signal
representative of a temperature of the DUT; wherein the controller
is further coupled to the flow-regulating valve to change a flow
area of the flow-regulating valve based on the signal
representative of the temperature of the DUT.
16. The system as claimed in claim 15, wherein a predetermined
downstream pressure of the automatic expansion valve is adjustable
by adjusting a pressure differential across the automatic expansion
valve for changing a range of a cooling capacity adjustment of the
heat transfer system.
17. The system as claimed in claim 16, further comprising a
receiver reservoir upstream from the automatic expansion valve for
maintaining a substantially constant pressure upstream of the
automatic expansion valve.
18. The system as claimed in claim 15, comprising a plurality of
TCUs, each TCU in fluid connection with one associated upstream
automatic expansion valve and one associated downstream
flow-regulating valve, the TCUs coupled to a single variable speed
compressor, wherein the controller is coupled to each of the TCUs
and to each of the flow-regulating valves for changing the flow
areas of the respective flow-regulating valves based on signals
representative of the temperatures of respective DUTs.
19. The system as claimed in claim 18, further comprising an
accumulator in fluid connection with each of the flow-regulating
valves at an input of the accumulator, and to the compressor for
the heat transfer medium at an output of the accumulator, for
de-coupling the flow-regulating valves from the compressor.
20. The system as claimed in claim 18, wherein the controller is
further coupled to the accumulator for receiving a signal
representative of a pressure in the accumulator, and the controller
is further coupled to the compressor for adjusting a speed of the
compressor based on the signal representative of the pressure in
the accumulator.
21. The system as claimed in claim 15, further comprising a
condenser for dissipating heat from the heat transfer medium.
22. The system as claimed in claim 15, wherein the controller
further comprises a set-point adjustment unit for adjusting a
set-point of the DUT.
23. The system as claimed claim 22, wherein the controller changes
the flow area of the flow-regulating device based on a comparison
of the signal representative of the temperature of the DUT and the
set-point.
24. The system as claimed in claim 23, wherein, in an active
operation mode, the set-point is changed whereby a cooling capacity
of the heat transfer system is changed as a result of said
comparison, resulting in a change of the temperature of the
DUT.
25. A method of heat transfer for maintaining or controlling a
temperature of a device under test (DUT) with heat generating
capability, the method comprising the steps of: thermally coupling
a temperature control unit (TCU) to the DUT, the TCU arranged for
flow of a heat transfer medium therethrough; disposing an automatic
expansion valve upstream of the TCU; disposing a flow-regulating
valve downstream of the TCU; receiving an input signal
representative of a temperature of the DUT; and changing a flow
area of the flow-regulating valve based on the signal
representative of the temperature of the DUT.
26. The method as claimed in claim 25, wherein a predetermined
downstream pressure of the automatic expansion valve is adjusted by
adjusting a pressure differential across the automatic expansion
valve for changing a range of a cooling capacity adjustment of the
heat transfer system.
27. The method as claimed in claim 26, further comprising
maintaining a substantially constant pressure upstream of the
automatic expansion valve.
28. The method as claimed in claim 25, comprising providing a
plurality of TCUs, each TCU in fluid connection with one associated
upstream automatic expansion valve and one associated downstream
flow-regulating valve, coupling the TCUs to a single variable speed
compressor, wherein the controller is coupled to each of the TCUs
and to each of the flow-regulating valves for changing the flow
areas of the respective flow-regulating valves based on signals
representative of the temperatures of respective DUTs.
Description
FIELD OF INVENTION
[0001] The present invention relates broadly to a heat transfer
system and to a method of heat transfer for maintaining or
controlling a temperature of a device under test with heat
generating capability.
BACKGROUND
[0002] Typically, high-performance electronic devices are subjected
to a 100% functional test prior to being shipped by a manufacturer.
For example, high power microprocessor devices are typically
subjected to a classification test to determine an effective
operating speed of the devices. During the classification test, it
is important to keep a temperature of a die of the microprocessor
device at a single prescribed temperature while the power of the
device is varied from about 0% to about 100% of the power rating in
a predetermined test sequence.
[0003] A thermal control unit (TCU) is usually used to facilitate
heat exchange between the device and the heat transfer medium such
that the die temperature of the device can be subjected to a
prescribed thermal cycle. The heating process of the device can be
achieved by installing heaters within the TCU. For the cooling
process, the TCU is coupled to a closed loop system whereby a heat
transfer medium in fluid form is delivered through the TCU to
remove heat generated by the devices such as the
microprocessors.
[0004] During the cooling process, the heat transfer medium can
exist in either a single phase or a two-phase flow condition. The
single phase flow removes heat by forced convection without
changing the state of the heat transfer medium while the two-phase
flow experiences a phase change of state from liquid to vapour to
remove heat largely by acquiring the latent heat of vaporization.
For better cooling efficiency, the latter heat removal process is
desired.
[0005] A system that is widely known to employ phase change of
fluid in promoting heat transfer is a vapour-compression system.
This system is widely used in the existing refrigeration system. A
thermostatic expansion valve is positioned upstream of the
evaporator to reduce the condensing pressure to the evaporating
pressure of the fluid. The thermostatic expansion valve operates
its flow regulating function by sensing the superheat temperature
of the refrigerant at the downstream of the evaporator. Thus, when
the amount of heat absorbed by the evaporator varies, the
thermostatic expansion valve restores the required superheat
temperature but does not necessarily maintain a desired temperature
of the heat source at the evaporator. Therefore, accurate control
of the temperature of the heat source may not be achieved. As it is
widely known, temperature control at the evaporator employing a
conventional thermostatic expansion valve is usually achieved via a
compressor, either by start-stop control or speed variation.
Therefore, with a conventional vapour-compression system as
described, it is difficult if not impossible to provide a system
comprising of a single compressor yet having multiple TCUs with
individual temperature control of each TCU.
[0006] Hence, there is a need to provide a heat transfer system
which seeks to address at least one of the above-mentioned
problems.
SUMMARY
[0007] In accordance with a first aspect of the present invention
there is provided a heat transfer system for maintaining or
controlling a temperature of a device under test (DUT) with heat
generating capability, the heat transfer system comprising a
temperature control unit (TCU) for thermal coupling to the DUT, the
TCU arranged for flow of a heat transfer medium therethrough; an
automatic expansion valve disposed upstream of the TCU; a
flow-regulating valve disposed downstream of the TCU; and a
controller coupled to the TCU for receiving an input signal
representative of a temperature of the DUT; wherein the controller
is further coupled to the flow-regulating valve to change a flow
area of the flow-regulating valve based on the signal
representative of the temperature of the DUT.
[0008] A predetermined downstream pressure of the automatic
expansion valve may be adjustable by adjusting a pressure
differential across the automatic expansion valve for changing a
range of a cooling capacity adjustment of the heat transfer
system.
[0009] The system may further comprise a receiver reservoir
upstream from the automatic expansion valve for maintaining a
substantially constant pressure upstream of the automatic expansion
valve.
[0010] The system may comprise a plurality of TCUs, each TCU in
fluid connection with one associated upstream automatic expansion
valve and one associated downstream flow-regulating valve, the TCUs
coupled to a single variable speed compressor, wherein the
controller is coupled to each of the TCUs and to each of the
flow-regulating valves for changing the flow areas of the
respective flow-regulating valves based on signals representative
of the temperatures of respective DUTs.
[0011] The system may further comprise an accumulator in fluid
connection with each of the flow-regulating valves at an input of
the accumulator, and to the compressor for the heat transfer medium
at an output of the accumulator, for de-coupling the
flow-regulating valves from the compressor.
[0012] The controller may further be coupled to the accumulator for
receiving a signal representative of a pressure in the accumulator,
and the controller is further coupled to the compressor for
adjusting a speed of the compressor based on the signal
representative of the pressure in the accumulator.
[0013] The system may further comprise a condenser for dissipating
heat from the heat transfer medium.
[0014] The controller may further comprise a set-point adjustment
unit for adjusting a set-point of the DUT.
[0015] The controller may change the flow area of the
flow-regulating device based on a comparison of the signal
representative of the temperature of the DUT and the set-point.
[0016] In an active operation mode, the set-point may be changed
whereby a cooling capacity of the heat transfer system is changed
as a result of said comparison, resulting in a change of the
temperature of the DUT.
[0017] In accordance with a second aspect of the present invention
there is provided a method of heat transfer for maintaining or
controlling a temperature of a device under test (DUT) with heat
generating capability, the method comprising the steps of thermally
coupling a temperature control unit (TCU) to the DUT, the TCU
arranged for flow of a heat transfer medium therethrough; disposing
an automatic expansion valve upstream of the TCU; disposing a
flow-regulating valve downstream of the TCU; receiving an input
signal representative of a temperature of the DUT; and changing a
flow area of the flow-regulating valve based on the signal
representative of the temperature of the DUT.
[0018] A predetermined downstream pressure of the automatic
expansion valve may be adjusted by adjusting a pressure
differential across the automatic expansion valve for changing a
range of a cooling capacity adjustment of the heat transfer
system.
[0019] The method may further comprise maintaining a substantially
constant pressure upstream of the automatic expansion valve.
[0020] The method may comprise providing a plurality of TCUs, each
TCU in fluid connection with one associated upstream automatic
expansion valve and one associated downstream flow-regulating
valve, coupling the TCUs to a single variable speed compressor,
wherein the controller is coupled to each of the TCUs and to each
of the flow-regulating valves for changing the flow areas of the
respective flow-regulating valves based on signals representative
of the temperatures of respective DUTs.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] Embodiments of the invention will be better understood and
readily apparent to one of ordinary skill in the art from the
following written description, by way of example only, and in
conjunction with the drawings, in which:
[0022] FIG. 1 shows a schematic diagram of a single thermal control
unit (ICU) system.
[0023] FIG. 2 shows a schematic diagram of a multi-TCU system.
[0024] FIG. 3 shows a flow-chart illustrating a method of heat
transfer for maintaining or controlling the temperature of a device
under test (DUT), with heat generating capability, according to an
example embodiment.
DETAILED DESCRIPTION
[0025] FIG. 1 shows a schematic diagram of a single thermal control
unit (TCU) system 100. The single TCU system 100 is a
vapour-compression system, which makes use of a phase change
cooling process for heat removal. The single TCU system 100 firstly
comprises a compressor 102 for driving a heat transfer medium in
fluid form, a condenser 104 for dissipating heat to a heat
reservoir, for example, the environment, and a heat transfer device
in the form of a thermal control unit (ICU) 106 which absorbs heat
from a heat generating device, thus performing the function of an
evaporator. The TCU 106 may be provided in different designs and
configurations, but generally includes a thermally conducting main
body which is in thermal contact with a device under test (DUT)
(not shown), and having the heat transfer medium flowing through
one or more passages provided in the TCU 106.
[0026] The ends of the passage(s) of the TCU 106 are coupled to an
automatic expansion valve 108 and a flow-regulating valve 110,
respectively. The automatic expansion valve 108 is disposed at the
upstream of the TCU 106. The automatic expansion valve 108 creates
the pressure difference required to set the conditions for heat
absorption at the TCU 106 and heat discharge at the condenser 104.
The flow-regulating valve 110 is disposed at the downstream of the
TCU 106. The flow-regulating valve 110 is coupled to the compressor
102, the compressor 102 is coupled to the condenser 104 and the
condenser 104 is coupled to the automatic expansion valve 108 to
form a closed loop system. A controller 112 is coupled to the TCU
106 and the flow-regulating valve 110. The controller 112 controls
the flow-regulating valve 110 through feedbacks from TCU.
[0027] During a steady operation mode, the TCU 106 absorbs a
certain amount of heat generated by a device under test (not shown)
and dissipates the heat to the environment through the condenser
104. The automatic expansion valve 108 maintains a steady flow area
according to a set pressure difference across the automatic
expansion valve 108. By having a receiver 118 upstream of the
automatic expansion valve 108, the pressure upstream can be easily
maintained constant and thus the automatic expansion valve 108 is
able to maintain a constant pressure downstream at the TCU 106. The
accumulator 120 downstream of the flow-regulating valve 110 also
assists in maintaining a constant pressure at the receiver 118 and
thus at the TCU 106. The flow-regulating valve 110 also maintains a
constant flow area for enabling a steady flow across the TCU 106.
The temperature of the device under test remains constant at a
user-defined temperature during this steady operation mode. The
user-defined temperature is also known as a set-point.
[0028] During a transient operation mode, e.g. when the heat
generated by the device under test increases, there is an increase
in the temperature of the device under test. The temperature of the
device under test is detected by a temperature sensor, e.g. a
thermocouple 113, which sends an electrical signal 114 in the form
of voltage or current to the controller 112. The controller 112
then sends an output signal 116 to the flow-regulating valve 110 to
increase the flow area at the flow-regulating valve 110, resulting
in a larger flow rate across the TCU 106. At the same time, the
pressure at the downstream of the automatic expansion valve 108
decreases. The automatic expansion valve 108 increases its flow
area to increase the flow rate across the automatic expansion valve
108. The fluid pressure at the downstream of the automatic
expansion valve 108 returns to the initial pressure corresponding
to the initial set pressure difference across the automatic
expansion valve 108. The combined action of the flow regulating
valve 110 and the automatic expansion valve 108 results in an
increased flow rate of the heat transfer medium across the TCU 106
and this sequence of event also increases the cooling capacity of
the TCU 106. Thus, an additional amount of heat generated by the
device under test is removed and the temperature of the device
under test is thus maintained at the set-point.
[0029] When there is a decrease in heat generated by the device
under test, the opposite happens. The flow areas at the
flow-regulating valve 110 and the automatic expansion valve 108 are
reduced, resulting in a lower flow rate of the heat transfer medium
across the TCU 106 and reducing the cooling capacity of the TCU 106
to maintain the temperature of the device under test at the
set-point.
[0030] The above describes a passive type of operation in which the
function of the system 100 is to maintain the temperature of the
device under test constant at the user-defined temperature. The
system 100 can be advantageously arranged without additional
complexities to implement an active type of operation, e.g.
dynamically cause variations in the temperature of the device under
test. For example, the reliability of the device under test imposed
by thermal shocks such as when a particular surface of the device
under test is subjected to a sudden drop in temperature can be
investigated by decreasing the set-point of the device under test
fast enough to cause the desired rate of decrease in the
temperature. When the set-point of the device under test is lowered
using an adjustment element, for example output signal 116, the
system 100 responds in a manner similar to that when an increase in
the temperature of the device under test is detected as described
above. In consequence, the cooling capacity of the TCU increases
and the temperature of the device under test decrease rapidly to
simulate the occurrence of a thermal shock.
[0031] Further, although there is a change in the flow rate of the
heat transfer medium during the transient operation mode, the
temperature of the heat transfer medium which also affects the
cooling capacity of the TCU 106 remains unaltered by using the
automatic expansion valve 108 disposed upstream of the TCU 106.
Therefore, the overall range of the cooling capacity which the TCU
106 is capable of operating as a result of the control of the
flow-regulating valve 110 can be changed by selecting a different
fluid pressure downstream of the automatic expansion valve 108 by
selecting a corresponding pressure difference across the automatic
expansion valve 108. In other words, by pre-selecting the pressure
downstream of the automatic expansion valve 108, which typically
involves a manual adjustment of the automatic expansion valve 108,
the absolute values of the cooling capacity within the variable
range as a result of the control of the flow-regulating valve 110
can be adjusted, for example moving from a range from 10 Watt to 20
Watt, to a range of 20 Watt to 200 Watt.
[0032] The system 100 advantageously provides ease of control of
the cooling capacity at the TCU 106, which only requires a single
input signal (i.e. signal representative of the temperature of the
device under test in the example embodiment) and a single output
signal (i.e. flow area control of the flow-regulating valve in the
example embodiment). Active variation of cooling capacities can be
advantageously achieved by changing the set-point of the device
under test. The single TCU system 100 advantageously allows a
testing process to be conducted on a single device at any one time.
It is noted that for the single TCU system 100, the compressor 102
may be operated at a constant, optimized speed, chosen so as to be
capable of handling the range of flows controlled using the
flow-regulating valve 110 (and the automatic expansion valve 108)
in the example embodiment.
[0033] For better productivity, it is preferred that several TCUs
can be employed in a single main circuit having a compressor and a
condenser with the capability of achieving individual control of
each TCU. The single TCU system 100 can be advantageously modified
into a multi-TCU system.
[0034] FIG. 2 shows a schematic diagram of a multi-TCU system 200.
The multi-TCU system comprises a receiver 202, an accumulator 204,
multiple TCU lines 206, a condenser 208 and a variable speed
compressor 210. Each TCU line 206 comprises an automatic expansion
valve 212, a TCU 214 and a flow-regulating valve 216. The ends of
the TCU 214 are coupled to the automatic expansion valve 212 and
the flow-regulating valve 216 respectively. The automatic expansion
valve 212 is disposed at the upstream of the TCU 214 and the
flow-regulating valve 216 is disposed at the downstream of the TCU
214. Each TCU line 206 is coupled to the receiver 202 and the
accumulator 204. The receiver 202 is disposed at the upstream of
each TCU line 206 and the accumulator 204 is disposed at the
downstream of each TCU line 206. The accumulator 204 is a reservoir
for the heat transfer medium flowing through each TCU 214. The
accumulator 204 is coupled to the compressor 210, the compressor
coupled to the condenser 208 and the condenser coupled to the
receiver 202. A controller 218 is coupled to the TCUs 214, the
flow-regulating valves 216, the accumulator 204, the condenser 208
and the compressor 210. The pressure at the accumulator 204 is
monitored by the controller 218 to ensure sufficient flow of
refrigerant through each TCU 214.
[0035] When the heat absorbed by any one of the TCU(s) 214
increases, the flow areas at the respective flow-regulating valves
216 and the respective automatic expansion valves 212 are
increased, resulting in an increase in the flow rate of the heat
transfer medium across the relevant TCU(s) 214. Thus, there is a
larger amount of heat transfer medium flowing into the accumulator
204, which results in an increase in the pressure in the
accumulator 204. The increase in the pressure in the accumulator
204 is detected by a transducer 217, e.g. a piezo-electric or
resistive pressure transducer, and the controller 218 sends a
signal to the variable speed compressor 210 to drive the compressor
210 faster. Hence, more heat transfer medium is drawn out of the
accumulator 204 and the prescribed pressure in the accumulator 204
is restored. Correspondingly, more heat is dissipated at the
condenser 208 as the heat transfer medium channelling out of the
compressor 210 increases. It is noted that the accumulator 204
advantageously avoids a situation where, if the flow-regulating
valves 216 were each in direct fluid communication with the
compressor 210, variation of the drive speed of the compressor 210
would affect the heat transfer medium flow in each of the TCUs 214.
Thus, the accumulator 204 in the described example embodiment
advantageously functions as a "buffer" which de-couples the
compressor 210 from the flow-regulating valves 216. In a further
modification of the embodiment shown in FIG. 2, the controller 218
may further be coupled to the condenser 208, for control of e.g. a
fan speed of the condenser, depending on the speed the variable
speed compressor 210 set under the control of the controller
218.
[0036] The increased heat transfer medium eventually flows into the
receiver 202, which is subsequently supplied to the respective TCUs
214. The additional heat generated by the device(s) under test is
removed and the temperature of the device(s) under test is
maintained at the set-point. The cooling capacity of each TCU 214
is independently controlled by the combined action of the
flow-regulating valve 216 and the automatic expansion valve 218 as
described above. Also, as described above, the absolute range of
the cooling capacity in the respective TCUs 214 can be adjusted by
selecting the desired pressure downstream of the respective
automatic expansion valves 212. Thus, even in a single multi-TCU
system, the overall range of cooling capacity for each TCU can be
individually selected, independent of other TCUs in the entire
system.
[0037] When there is a decline in heat absorption by any one or
more of the TCU(s) 214, the opposite happens. The flow areas at the
respective flow-regulating valves 216 and the respective automatic
expansion valves 212 are reduced, resulting in a lower flow rate of
the heat transfer medium across the relevant TCU(s) 214. Thus,
there is a smaller amount of heat transfer medium flowing into the
accumulator 204, which results in a decrease in the pressure in the
accumulator 204. The decrease in pressure is detected, and the
controller 218 sends a signal to the variable speed compressor 210
to drive the compressor slower. Less heat transfer medium is drawn
out of the accumulator 204 and the prescribed pressure in the
accumulator 204 is restored. Thus, the temperature of the device(s)
under test is maintained at the set-point.
[0038] The multi-TCU system 200 advantageously provides independent
control of each TCU 214. The use of a pressure set-point at the
accumulator 204 means that one does not need to physically monitor
and control the main flow circuit as changes are automatically made
to ensure the proper operating conditions. In addition, the control
algorithm is easy to implement as the control of the main flow
circuit and the individual evaporator lines are uncoupled. This
advantageously provides controllability of the individual TCUs 214
with accuracy and short response time, as changes made to the main
circuit do not have to correspond with control of the individual
TCU lines. Further, the system 200 can advantageously accommodate a
large number of the TCU lines as pressure fluctuations at the
accumulator is less likely to be affected by individual changes at
the TCUs 214. Various individual different prescribed thermal
conditions required at each TCU of the multi-TCU system 200 can be
advantageously provided. The multi-TCU system 200 is simple and
reliable and can be effective for all kinds of cooling
processes.
[0039] FIG. 3 shows a flow-chart 300 illustrating a method of heat
transfer for maintaining or controlling a temperature of a device
under test (DUT) with heat generating capability, according to an
example embodiment. At step 302, a thermal control unit (TCU) is
thermally coupled to the DUT, the TCU arranged for flow of a heat
transfer medium therethrough. At step 304, an automatic expansion
valve is disposed upstream of the TCU. At step 306, a
flow-regulating valve is disposed downstream of the TCU. At step
308, an input signal representative of a temperature of the DUT is
received. At step 310, a flow area of the flow-regulating valve is
changed based on the signal representative of the temperature of
the DUT.
[0040] The components used to implement the control of the TCU(s)
in the example embodiments described above are available standard
components. Few components are required for the embodiments.
Individual control of different thermal cycles of different heat
loads is advantageously provided. Further, the designs of the
embodiments are compact, which advantageously makes it easy to
integrate the embodiments into a test handler system. The
embodiments can be advantageously used in cooling applications.
[0041] It will be appreciated by a person skilled in the art that
numerous variations and/or modifications may be made to the present
invention as shown in the specific embodiments without departing
from the spirit or scope of the invention as broadly described. The
present embodiments are, therefore, to be considered in all
respects to be illustrative and not restrictive.
* * * * *