U.S. patent application number 14/236116 was filed with the patent office on 2014-10-02 for personal cooling unit using phase change material.
This patent application is currently assigned to University of Tasmania. The applicant listed for this patent is Teen Onn Law. Invention is credited to Teen Onn Law.
Application Number | 20140290301 14/236116 |
Document ID | / |
Family ID | 47436366 |
Filed Date | 2014-10-02 |
United States Patent
Application |
20140290301 |
Kind Code |
A1 |
Law; Teen Onn |
October 2, 2014 |
PERSONAL COOLING UNIT USING PHASE CHANGE MATERIAL
Abstract
A personal cooling unit, comprising: an air inlet for receiving
input air; at least one heat pump having a first surface and a
second surface, and being configured to extract heat from the input
air at the first surface to generate cooled output air and to
transport heat to the second surface; a phase change material in
thermal contact with the second surface of the heat pump; and means
for conveying the cooled output air to the exterior of the
unit;--wherein the phase change material undergoes a
temperature-driven phase change from a first phase to a second
phase, so that when at least a portion of the phase change material
is in the first phase, the phase change material absorbs heat from
the second surface until all of the phase change material has
changed to the second phase; and wherein the phase change material
has a phase transition temperature which is at least about
28.degree. C.
Inventors: |
Law; Teen Onn; (Launceston,
AU) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Law; Teen Onn |
Launceston |
|
AU |
|
|
Assignee: |
University of Tasmania
Sandy Bay, Tasmania
AU
|
Family ID: |
47436366 |
Appl. No.: |
14/236116 |
Filed: |
June 27, 2012 |
PCT Filed: |
June 27, 2012 |
PCT NO: |
PCT/AU2012/000757 |
371 Date: |
June 4, 2014 |
Current U.S.
Class: |
62/404 |
Current CPC
Class: |
F25B 21/02 20130101;
F24F 5/0021 20130101; F25D 17/04 20130101; F25B 2321/025 20130101;
Y02E 60/14 20130101; F24F 2221/38 20130101; F24F 5/0042 20130101;
Y02E 60/147 20130101; F28D 20/02 20130101 |
Class at
Publication: |
62/404 |
International
Class: |
F25D 17/04 20060101
F25D017/04 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 1, 2011 |
AU |
2011902620 |
Claims
1. A personal cooling unit, comprising: an air inlet for receiving
input air; at least one heat pump having a first surface and a
second surface, and being configured to extract heat from the input
air at the first surface to generate cooled output air and to
transport heat to the second surface; a phase change material in
thermal contact with the second surface of the heat pump; and means
for conveying the cooled output air to the exterior of the unit;
wherein the phase change material undergoes a temperature-driven
phase change from a first phase to a second phase, so that when at
least a portion of the phase change material is in the first phase,
the phase change material absorbs heat from the second surface
until all of the phase change material has changed to the second
phase; and wherein the phase change material has a phase transition
temperature which is at least about 28.degree. C.
2. A personal cooling unit according to claim 1, wherein the phase
change material is selected on the basis of an expected ambient air
temperature range for a predetermined location over a predetermined
time period, the phase change material having a phase transition
temperature which is higher than a maximum of the expected ambient
air temperature range.
3. A personal cooling unit according to claim 1, wherein the phase
transition temperature is at least about 40.degree. C.
4. A personal cooling unit according to claim 1, wherein the phase
change material comprises paraffin wax.
5. A personal cooling unit according to claim 1, comprising a
filtering system for at least partially removing at least one of
moisture and contaminants from the input air.
6. A personal cooling unit according to claim 5, comprising at
least one of a dehumidification component, a particulate matter
filtration component, and a gas filtration component.
7. A personal cooling unit according to claim 5, wherein the
filtering system is partly or fully removable.
8. A personal cooling unit according to claim 1, comprising an air
sanitization system for at least one of partially removing and
killing microbial contaminants.
9. A personal cooling unit according to claim 8, wherein the air
sanitization system is in fluid communication with at least one of
the air inlet and an air outlet of the unit.
10. A personal cooling unit according to claim 8, wherein the air
sanitisation system comprises at least one of: a UV-C light source;
a photocatalytic component; and a negative ion generator.
11. A personal cooling unit according to claim 1, wherein a vessel
containing the phase change material at least partly surrounds each
of the at least one heat pump.
12. A personal cooling unit according to claim 11, wherein each of
the at least one heat pump is concentric with the vessel.
13. A personal cooling unit according to claim 1, further including
a heat exchanger in thermal contact with the first surface of each
of the at least one heat pump.
14. A personal cooling unit according to claim 13, wherein the heat
exchanger comprises a plurality of planar members.
15. A personal cooling unit according to claim 14, wherein the
planar members form a honeycomb structure.
16. A personal cooling unit according to claim 1, wherein the
vessel comprises at least one heat sink in thermal contact with the
second surface of each of the at least one heat pump.
17. A personal cooling unit according to claim 16, wherein each of
the at least one heat sink comprises a plurality of extrusions.
18. (canceled)
19. A personal cooling unit according to claim 1, further
comprising means for adjusting a voltage across each of the at
least one heat pump
20. An air-conditioning method, comprising steps of: determining an
expected ambient air temperature range for a specified location
over a specified time period; selecting, on the basis of the
expected ambient air temperature range, a phase change material
having a phase transition temperature which is higher than a
maximum of the expected ambient air temperature range; and
providing a personal cooling unit comprising: an air inlet for
receiving input air; at least one heat pump having a first surface
and a second surface, the second surface being in thermal contact
with the phase change material, the heat pump being configured to
extract heat from the input air at the first surface to generate
cooled output air and to transport heat to the second surface; and
means for conveying the cooled output air to the exterior of the
unit; wherein the phase change material undergoes a
temperature-driven phase change from a first phase to a second
phase, so that when at least a portion of the phase change material
is in the first phase, the phase change material absorbs heat from
the second surface until all of the phase change material has
changed to the second phase.
Description
TECHNICAL FIELD
[0001] The present invention relates to personal cooling
devices.
BACKGROUND
[0002] In indoor spaces of office buildings and the like, it is
usual to seek to improve the comfort of persons within the building
by the use of air-conditioning apparatus. The air-conditioning
system is installed within the walls of the building and ducts are
provided to release cooled or heated air at particular locations,
usually the rooms or offices of the building. It is difficult to
control, with any precision, the temperature of the air in an
individual office using such systems.
[0003] Personalised heating or cooling units which could partially
address the individual needs of persons within the building are
known. For example, it is known to provide small electric fans
which can provide a localised cooling effect due to wind chill
(convective heat loss). However, in hot and humid environments, to
supply sufficient cooling for thermal comfort, the fan may need to
be operated at speeds such that excessive draft is induced.
[0004] An alternative type of personalised heating or cooling
device is described in U.S. Pat. No. 6,481,213. The apparatus
therein described incorporates an inlet fan which draws air towards
a heat exchanger. The heat exchanger is in thermal contact with and
is cooled by a heat pump in the form of a thermoelectric device.
The heat removed from the air by the heat pump is delivered to a
thermal store heat exchanger to be absorbed by a thermal mass in
the form of ice. Rather than reject the heat from the input air,
and waste heat from the heat pumping process, to the surrounding
local environment, the heat is at least partially stored in the
thermal mass as latent heat due to melting of the ice.
[0005] Whilst overcoming some of the disadvantages of the prior
art, the device described in U.S. Pat. No. 6,481,213 has several
disadvantages of its own: [0006] Prior to use, the device must be
"re-charged" by freezing the ice, and this may require the use of a
timer such that the re-charging process is commenced sufficiently
early relative to the time of intended use. The device therefore
may not be suitable in situations where the demand is difficult to
predict beforehand. [0007] If a number of devices in, for example,
an office space is set to charge at the end of a working day, this
would result in simultaneous rejection of heat into the space from
the devices, possibly causing discomfort to anyone remaining in the
office at the scheduled charge time. [0008] The ice must be
insulated, for example by polystyrene which consumes space, or by a
high R-value material such as polyurethane/silicone which adds
substantial cost. There is a need to provide a personal cooling
device which alleviates one or more of the above disadvantages, or
at least provides a useful alternative.
SUMMARY OF THE INVENTION
[0009] The present invention provides, in a first aspect, a
personal cooling unit, comprising: [0010] an air inlet for
receiving input air; [0011] at least one heat pump having a first
surface and a second surface, and being configured to extract heat
from the input air at the first surface to generate cooled output
air and to transport heat to the second surface; [0012] a phase
change material in thermal contact with the second surface of the
heat pump; and [0013] means for conveying the cooled output air to
the exterior of the unit; [0014] wherein the phase change material
undergoes a temperature-driven phase change from a first phase to a
second phase, so that when at least a portion of the phase change
material is in the first phase, the phase change material absorbs
heat from the second surface until all of the phase change material
has changed to the second phase; and [0015] wherein the phase
change material has a phase transition temperature which is at
least about 28.degree. C.
[0016] The present invention also provides an air-conditioning
method, comprising steps of: [0017] determining an expected ambient
air temperature range for a specified location over a specified
time period; [0018] selecting, on the basis of the expected ambient
air temperature range, a phase change material having a phase
transition temperature which is higher than a maximum of the
expected ambient air temperature range; and [0019] providing a
personal cooling unit comprising: [0020] an air inlet for receiving
input air; [0021] at least one heat pump having a first surface and
a second surface, the second surface being in thermal contact with
the phase change material, the heat pump being configured to
extract heat from the input air at the first surface to generate
cooled output air and to transport heat to the second surface; and
[0022] means for conveying the cooled output air to the exterior of
the unit; [0023] wherein the phase change material undergoes a
temperature-driven phase change from a first phase to a second
phase, so that when at least a portion of the phase change material
is in the first phase, the phase change material absorbs heat from
the second surface until all of the phase change material has
changed to the second phase.
[0024] The present applicant has surprisingly found that phase
change materials with a relatively high (greater than 28.degree.
C.) transition temperature, as opposed to the low transition
temperatures of the prior art, are particularly effective in
providing cooling of localised spaces such as those around persons
in an office or home environment. By using a phase change material
with a phase transition temperature (for example, melting
temperature) above an expected ambient air temperature, it is
possible to provide a cooling unit which automatically recharges
when not in use. That is, the phase change material begins
passively undergoing the reverse phase change from the second phase
to the first phase once the heat pump is switched off and the phase
change material is exposed to ambient air at a temperature below
its transition temperature. The need for a timing mechanism, and
for pre-charging the unit, is thereby obviated.
[0025] In certain embodiments, the phase change material is
selected on the basis of an expected ambient air temperature range
for a predetermined location over a predetermined time period, the
phase change material having a phase transition temperature which
is higher than a maximum of the expected ambient air temperature
range.
[0026] Phase change materials having a transition temperature
around 28.degree. C. or more may be particularly suitable when the
unit is to be used as supplementary cooling in a space which is
already air-conditioned, for example, while materials with even
higher transition temperatures (above 40.degree. C. or more, for
example) may be useful when the unit is to be the primary source of
localised cooling.
[0027] The heat pump may be a thermoelectric device, for example a
Peltier module. In other embodiments, the heat pump may be a device
which transports heat by means of thermotunnelling or the
electro-calorific effect.
[0028] In certain embodiments, a suitable phase change material
comprises a paraffin wax and has a melting point temperature of
about 40.degree. C. However, other phase change materials having a
melting temperature greater than 40.degree. C. may be used. In
other embodiments, the phase change material may comprise a
paraffin wax having a melting point temperature of greater than
about 28.degree. C. Paraffin waxes are preferred due to their ease
of containment, non-toxicity and non-causticity.
[0029] In certain embodiments, the unit includes a filtering system
for at least partially removing moisture and/or contaminants from
the input air. The filtering system may be located adjacent the air
inlet, for example. The filtering system may include one or more of
a dehumidification component, a particulate matter filtration
component, or a gas filtration component. The filtering system may
be partly or fully removable. For example, individual components of
the filtering system may be individually removable, and may be
user-maintainable.
[0030] The unit may include an air sanitisation system for at least
partially removing or killing microbial contaminants. The air
sanitisation system may be in fluid communication with the air
inlet and/or an air outlet of the unit. For example, the air
sanitisation system may include one or more of: a UV-C light
source; a photocatalytic component, such as a photocatalytic
coating which may be applied to internal surfaces of the unit; or a
negative ion generator.
[0031] In one embodiment, the vessel containing the phase change
material at least partly surrounds the or each heat pump. The or
each heat pump may be concentric with the vessel.
[0032] In some embodiments, the unit further includes a heat
exchanger in thermal contact with the first surface of the or each
heat pump. The heat exchanger may comprise a plurality of planar
members, which may form, for example, a honeycomb structure.
[0033] The vessel preferably comprises at least one heat sink in
thermal contact with the second surface of the or each heat pump.
The or each heat sink may comprise a plurality of fins.
[0034] If the unit includes a heat exchanger as described above,
the heat exchanger may be polygonal in cross-section, for example
having rectangular or hexagonal cross-section, with each side of
the heat exchanger being in thermal contact with a first surface of
one of the heat pumps.
[0035] The unit, in some embodiments, further comprises means for
adjusting the voltage across the or each heat pump.
BRIEF DESCRIPTION OF THE DRAWINGS
[0036] Some embodiments of the invention will now be described, by
way of non-limiting example only, with reference to the
accompanying figures in which:
[0037] FIG. 1 is a schematic block diagram of a personal cooling
unit according to an embodiment of the invention;
[0038] FIG. 2 shows an exploded and partially cut-away view of a
personal cooling unit according to another embodiment of the
invention;
[0039] FIG. 3 is a front perspective view of an alternative
embodiment of a personal cooling unit;
[0040] FIG. 4 is a rear perspective view of the personal cooling
unit of FIG. 3;
[0041] FIG. 5 is a perspective view of a phase change
material-containing vessel for use with the cooling unit of FIGS. 3
and 4;
[0042] FIG. 6 is a schematic sectional view of the phase change
material-containing vessel of FIG. 5; and
[0043] FIG. 7 shows a further alternative embodiment of a personal
cooling unit.
DETAILED DESCRIPTION
[0044] Referring initially to FIG. 1, there is shown in schematic
form a personal cooling unit 10 having a housing 12 which houses
components including a filtering system 30, a heat exchanger 40, a
heat pump 50, vessel containing phase change material 60, an air
sanitisation system 75, and fan 15. Defined within the housing 12
is a channel 35 delimited by inlet 20 and outlet 80 for flow and
cooling of air therebetween in a manner which will be described
below.
[0045] The unit 10 accepts input air 90 at ambient temperature at
inlet 20. The input air passes through a filtering system 30, which
in a presently preferred embodiment is located adjacent the inlet
20 and in fluid communication therewith. Other locations of the
filtering system 30 are possible. The filtering system 30,
depending on its particular configuration, may perform a number of
functions including, without limitation, dehumidification,
particulate matter filtration, or gas filtration.
[0046] For example, the filtering system 30 may dehumidify input
air using a dehumidification component which comprises at least one
desiccant bed or desiccant impregnated honeycomb structure of any
suitable type known in the art. The dehumidification component may
be removable by a user of the unit 10, and able to be regenerated
by heating in a microwave oven to expel the absorbed moisture, for
example.
[0047] Alternatively, or in addition, the filtering system may
comprise a particulate matter filtration component. The particulate
matter filtration component may comprise a single stage (MERV 13)
air filter; a double stage air filter (MERV 8 pre-filter and MERV
13 final filter); or an electrostatic filtration module.
[0048] As a further alternative, the filtering system 30 may
comprise a gas filtration component, such as a molecular sieve or
activated carbon honeycomb structure, for removing volatile organic
compounds (VOCs) and odour-causing gases.
[0049] The filtering system 30 may be partly or fully removable.
For example, individual components (as mentioned above) of the
filtering system may be individually removable, and may be
user-maintainable.
[0050] The filtered input air flows along channel 35 in the
direction indicated by the arrows. The channel 35 is in thermal
contact with heat exchanger 40. Heat exchanger 40 is in thermal
contact with a first surface of heat pump 50, and a second surface
of heat pump 50 is in turn in thermal contact with the phase change
material 60. Phase change material 60 has a melting temperature
which is higher than the ambient air temperature. As input air
flows along the channel 35, heat is drawn therefrom by heat
exchanger 40/heat pump 50 and into phase change material 60. The
cooled air is drawn by the action of fan 15 through an air
sanitisation system 75 to the outlet 80 such that cooled, sanitised
output air 95 exits the unit 10. Exemplary configurations of heat
exchanger 40 and heat pump 50 for achieving the cooling action will
be described below.
[0051] The air sanitisation system 75 serves to at least partially
remove or kill any microbial contaminants which may be present in
input air 90, and may take a number of forms. For example, the air
sanitisation system may include one or more of a UV-C light source
for irradiating bacteria and viruses; a photocatalytic component,
such as a photocatalytic coating which may be applied to internal
surfaces of the unit, for example an internal surface of channel
35; or a negative ion generator. Although shown adjacent the outlet
80 of the unit 10, it will be appreciated that the sanitisation
system 75 may instead be located near inlet 20, or may extend along
the channel 35. For example, a series of UV-C light sources may be
placed along channel 35, and/or a titanium dioxide or other
photocatalytic coating may be applied along the length of the
channel 35.
[0052] It will be appreciated that, while depicted as substantially
linear in FIG. 1, the channel 35 may take any number of forms, and
may follow a path which is curved or serpentine in at least some
portions, for example.
[0053] Turning now to FIG. 2, there is shown a personal cooling
unit, generally indicated by 100, comprising a vessel 110
containing a phase change material that has a melting temperature
above the ambient air temperature. The phase change material used
in the presently described embodiments is a paraffin wax, although
it will be appreciated that in other embodiments, different phase
change materials may be used.
[0054] The vessel 110 is concentric with a heat exchanger in the
form of a honeycomb structure 102, and is also concentric with
thermoelectric heat pumps (Peltier modules) 104. The Peltier
modules each have a first surface 105 which is in thermal contact
with the heat exchanger 102, and a second surface 106 which is in
thermal contact with one of the heat sinks 112. The heat sinks 112
include a plurality of extrusions in the form of fins, and are
immersed in, and therefore in thermal contact with, the phase
change material in the vessel 110.
[0055] The heat exchanger 102 particularly shown in FIG. 1 is of
substantially rectangular cross-section, and is in thermal contact
with one of four Peltier modules 104 at each of its faces. It will
also be appreciated by the skilled person that other
cross-sectional shapes for the heat exchanger 102 may be chosen.
For example, the heat exchanger 102 could have a hexagonal
cross-section, in which case six Peltier modules could be employed,
one for each side of the hexagon.
[0056] The cooling unit 100 includes means for conveying cooled
output air to its exterior, in the form of a fan 115. After input
air is received at ambient temperature at an air inlet (not shown)
and cooled on passage through heat exchanger 102, fan 115 moves the
cooled output air towards controller/vent 120 where it is dispersed
through diffuser 130.
[0057] The operation of the cooling unit is controlled by the
controller/vent unit 120. Controller 120 may have a number of
functions including powering the unit on and off, adjusting the
speed of fan 115 (via fan speed knob 122), and adjusting the
voltage across Peltier modules 104, and hence the amount of heat
drawn from the input air (via voltage knob 124). Power to the
cooling unit will generally be supplied by mains power, but in some
circumstances could be supplied by a generator or battery. If mains
power is used, then a regulated power supply including a rectifier
may be used in order to supply an adjustable DC voltage to the
Peltier modules 104.
[0058] The Peltier modules 104 are configured such that their
inward-facing (first) surfaces 105 are the "cold" side, and the
outward-facing (second) surfaces 106 are the "hot side". The
difference between the temperatures of the two sides is sufficient
to produce a "cold" side temperature which is less than the ambient
air temperature, and a "hot" side temperature which is greater than
or equal to the melting temperature of the phase change material. A
Peltier module 104 will thus extract heat at its first surface 105
from input air which is at ambient temperature, and transport it to
its second surface 106 and then (via the heat sink 112) to the
phase change material where it will be stored.
[0059] The cooling unit preferably includes a condensate pan 140 to
catch any water droplets which might form, for example on days of
high humidity.
[0060] The cooling unit 100 shown in FIG. 2 is suitable for
installation at an office workstation, for example with the
controller/vent unit 120 lying above a desk surface 150 and the
remainder of the cooling unit 100 lying below the desk surface and
out of view once the unit 100 is installed. For example, the
controller/vent unit 120 may have formed in its lower surface a
channel or bore (not shown) for receiving an annular projection 126
of a plate 128. During installation, a circular aperture sized to
accommodate projection 126 may be formed in the desk surface 150.
The components which are to remain below desk surface 150 may be
assembled, and once complete, the projection 126 fitted to
controller/vent unit 120 such that the desk surface 150 is
effectively sandwiched between the controller/vent unit 120 and the
plate 128.
[0061] Referring now to FIGS. 3 and 4, there is shown an
alternative embodiment of a personal cooling unit 200 which is
portable and which can be placed directly on a desktop without
installation, for example.
[0062] The cooling unit 200 includes a heat exchanger 202 which is
seated under a vessel 210 containing a phase change material. The
unit may be connected to a rechargeable battery (not shown) which
provides power to the Peltier modules 204 by means of terminals 240
seated in the top of the unit's casing.
[0063] The upper surface of heat exchanger 202 is in thermal
contact with a first surface of one or more Peltier modules 204
(FIG. 6), and the second, upper surfaces of Peltier modules 204 are
in thermal contact with the vessel 210.
[0064] FIGS. 5 (in which the phase change material has been omitted
for clarity) and 6 depict the internal structure of the vessel 210
of cooling unit 200. The vessel 210 contains a paraffin wax, which
is shown (during phase change) partly in solid (218) and liquid
(219) form. The vessel 210 includes a heat sink, generally
indicated by reference numeral 212. The heat sink 212 includes two
plates 214 and 215 having substantially L-shaped cross section,
which sit one on top of the other so that the short limbs of the
respective `L` shapes form the ends of the heat sink 212, and fins
213 extend upwardly between the two ends and penetrate through the
upper surface of the paraffin. The plates 214 and 215 and
extrusions (fins) 213 are preferably formed of a highly thermally
conductive material such as aluminium.
[0065] The double-walled configuration shown in FIG. 6, in which a
relatively thick layer of aluminium is presented at the base of the
vessel 210, has been found to be particularly advantageous in
directing heat from the upper (hot) surfaces of Peltier modules 204
to the solid paraffin 218. In particular, the extruded profile of
the fins 213 presents an increased surface area such that more of
the solid paraffin 218 is in contact with the heated aluminium. In
the absence of fins 213, the unmelted paraffin 218 tends to remain
buoyant, and thus out of thermal contact with the hot surface of
Peltier modules 204, thereby decreasing the effectiveness of the
cooling unit 200. By contrast, when fins 213 penetrating through
the upper surface of the paraffin are installed, relatively thin
sections of solid paraffin 218 sink towards the base of the vessel
210 through the liquid paraffin 219, so that solid paraffin 218 is
continually fed towards the hot surface of Peltier modules 204 by
gravity.
[0066] Turning now to FIG. 7, there is shown a further embodiment
of a personal cooling unit 300. The unit 300 has a housing 312
which contains a tank 360 of a phase change material which is in
thermal contact with a heat pump (not shown), the heat pump being
interposed between the tank 360 and a heat exchanger 340. The heat
pump may be in the form of a series of Peltier modules, as
described above for example. The heat exchanger 340 comprises a
series of cooling fins and is located near the bottom of the
housing. In use, input air is drawn through intake 320 and
subsequently through a filtering system located at 330 and then
through heat exchanger 340 by operation of a centrifugal fan 315.
The filtering system 330 may comprise any of the components
mentioned above.
[0067] The unit 300 includes an output channel generally indicated
by dotted outline at 372. Output channel 372 may include an air
sanitisation system 375, for example along the lines of air
sanitisation system 75 discussed previously. Cooled and sanitised
output air is expelled from outlets 380, which may be connected to
respective ducts for conveying cooled air to different respective
locations. For example, each outlet 380 may be connected to a duct
which terminates at a controller/vent unit similar to
controller/vent unit 120 discussed previously, respective
controller/vent units 120 being located at different locations.
[0068] In certain embodiments, the unit 300 includes insulation
365, for example a column of an insulating material having
dimensions to suit those of the tank 360, the housing 312 and the
output channel 372, interposed between the phase change material
tank 360 and the output channel 372 to reduce or substantially
prevent transfer of heat from the tank 360 to the cooled air in
output channel 372. The unit 300 may also include a fan power
control dial 314 (for controlling the speed of fan 315) and a
cooling power control dial 316 (for controlling the operation of
the heat pump, for example by adjusting the voltage across the
Peltier modules).
[0069] The filtering system 330 may be housed in a removable tray
332 located adjacent to the intake 320, the tray having a recessed
handle 335 for ease of removal. The tray 332 may be removably
mounted in the housing 312 in any suitable manner known in the art,
for example by means of guide rails configured to mate with
corresponding channels or grooves in the housing 312.
[0070] Many modifications of the embodiments described above will
be apparent to those skilled in the art without departing from the
scope of the present invention. For example, while the phase change
material employed in the embodiments presently described is a
paraffin wax having a melting temperature of about 40.degree. C.,
it will be appreciated that other phase change materials having the
required thermal characteristics can be used in other embodiments.
For example, if the personal cooling unit 100 is to be used to
provide supplementary cooling in a space which is already
air-conditioned, a phase change material with a lower melting
temperature, of about 28.degree. C. or more, could be used. A phase
change material having a melting temperature of this order is
advantageous as it requires a lower voltage to be applied across
the thermoelectric heat pump in order to achieve the desired
cooling. In addition, while the heat sinks described above employ
extrusions in the form of substantially planar fins, it may be
advantageous in some circumstances to replace the fins with
elongate members such as pins or spikes.
[0071] An exemplary class of alternative phase change materials
includes encapsulated hydrated salts. An exemplary hydrated salt is
hydrated sodium sulphate which has a melting temperature of about
32.degree. C. The encapsulated hydrated salt may be submerged in a
bath.
[0072] Throughout this specification and the claims which follow,
unless the context requires otherwise, the word "comprise", or
variations such as "comprises" or "comprising", will be understood
to imply the inclusion of a stated integer or step or group of
integers or steps but not the exclusion of any other integer or
step or group of integers or steps.
[0073] The reference in this specification to any prior publication
(or information derived from it), or to any matter which is known,
is not, and should not be taken as an acknowledgment or admission
or any form of suggestion that that prior publication (or
information derived from it) or known matter forms part of the
common general knowledge in the field of endeavour to which this
specification relates.
* * * * *