U.S. patent application number 14/384611 was filed with the patent office on 2015-02-12 for method of fabricating a component of a solar energy system.
The applicant listed for this patent is ENDLESS SOLAR CORPORATION LTD. Invention is credited to Michael Dennis.
Application Number | 20150040399 14/384611 |
Document ID | / |
Family ID | 49160150 |
Filed Date | 2015-02-12 |
United States Patent
Application |
20150040399 |
Kind Code |
A1 |
Dennis; Michael |
February 12, 2015 |
METHOD OF FABRICATING A COMPONENT OF A SOLAR ENERGY SYSTEM
Abstract
The present disclosure provides a method of fabricating a
component of a solar energy system. The method comprises the step
of providing a tube. The tube comprises a material that deforms
when at least a length of the tube is exposed to a suitable
difference in pressure between an interior portion of the length of
the tube and an exterior portion of the length of the tube. The
method also comprises providing a die having a cavity arranged to
receive the length of the tube. The cavity defines a shape that is
related to that of the component of the solar energy system.
Further, the method comprises positioning the length of the tube in
the cavity of the die. The method also comprises increasing a
relative pressure of a fluid within the interior portion of the
length of the tube relative to a pressure within the cavity and
outside the interior portion of the length of the tube such that at
least a portion of the length of the tube expands at to a shape
that is related to that of the component of the solar energy
system.
Inventors: |
Dennis; Michael; (Melbourne,
AU) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
ENDLESS SOLAR CORPORATION LTD |
Melbourne, Victoria |
|
AU |
|
|
Family ID: |
49160150 |
Appl. No.: |
14/384611 |
Filed: |
March 14, 2013 |
PCT Filed: |
March 14, 2013 |
PCT NO: |
PCT/AU2013/000248 |
371 Date: |
September 11, 2014 |
Current U.S.
Class: |
29/890.053 |
Current CPC
Class: |
B29C 49/04 20130101;
B21D 51/16 20130101; Y10T 29/49391 20150115; F25B 1/06 20130101;
B21D 26/041 20130101; Y02E 10/40 20130101; B21D 26/033 20130101;
F25B 27/005 20130101; B29C 2049/4658 20130101; F24S 90/00
20180501 |
Class at
Publication: |
29/890.053 |
International
Class: |
B21D 51/16 20060101
B21D051/16; B21D 26/041 20060101 B21D026/041 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 14, 2012 |
AU |
2012901003 |
Claims
1-17. (canceled)
18. A method of fabricating an ejector of a solar energy system,
the method comprising the steps of: providing a tube, the tube
comprising a metallic material that deforms when at least a length
of the tube is exposed to a suitable difference in pressure between
an interior portion of the length of the tube and an exterior
portion of the length of the tube; providing a die having a cavity
arranged to receive the length of the tube, the cavity defining a
shape that is related to that of the ejector; positioning the
length of the tube in the cavity of the die; heating the length of
the tube to a temperature above a transition temperature at which
the material changes from a brittle state to a ductile state; and
increasing a relative pressure of a fluid within the interior
portion of the heated length of the tube relative to a pressure
within the cavity and outside the interior portion of the length of
the tube such that at least a portion of the length of the tube
expands to a shape that is related to that of the ejector.
19. The method of claim 18 comprising the step of controlling a
temperature of the fluid.
20. The method of claim 18 wherein the step increasing the relative
pressure of the fluid within the interior portion the of the length
of the tube relative to a pressure within the cavity and outside
the interior portion of length of the tube comprises increasing the
pressure within the interior portion of the tube.
21. The method of claim 18 wherein the step of providing the tube
comprises shaping the tube and wherein the method comprises locally
reducing the exterior diameter of the tube such that the tube has a
non-uniform exterior diameter.
22. The method of claim 21 wherein the exterior diameter of the
tube is selected and reducing the external diameter of the tube is
conducted such that the step of increasing the relative pressure
within an interior portion of the tube results in less expansion
compared to the use of a tube having a uniform and smaller exterior
diameter
23. The method of claim 18 wherein the step of providing the tube
comprises pre-forming or pre-machining tube material such that an
additional amount of the tube material is located at a region of
the length of the tube that is subjected to more expansion than
another region of the length of the tube.
24. The method of claim 18 comprising the step of heating the
length of the tube prior or during the step of increasing the
relative pressure.
25. The method of claim 18 comprising the step of exposing the
length of the tube to an axial compression during expansion of the
length of the tube.
26. The method of claim 18 comprising the step of disposing a
lubricant between the length of the tube and the die.
27. The method of claim 18 wherein the shape that is related to
that of the ejector or the component of the solar energy system
comprises the shape of a compressor portion of the ejector.
28. The method of claim 27 wherein the shape also comprises a
nozzle housing of the ejector such that the compressor portion and
the nozzle housing are formed integrally.
29. The method of claim 18 wherein the fluid is a liquid and the
method comprises the step of charging an interior portion of the
length of the tube with the liquid.
30. The method of claim 18 wherein the die is arranged and the tube
material is selected such that the tube slightly contracts in
diameter when the relative pressure within the interior portion of
the length of the tube is reduced.
31. The method of claim 30 comprising controlling the temperature
of the fluid such that the tube material is exposed to rapid
cooling after expansion of the length of the tube.
32. The method of claim 18 comprising the step of determining a
temporal pressure profile of the fluid.
33. The method of claim 32 comprising determining a rate of
relative pressure increase of the interior portion of the length of
the tube and a rate of subsequent relative pressure decrease of the
interior portion of the length of the tube.
34. The method of claim 32 wherein the step of increasing the
relative pressure is defined at least in part by the determined
temporal pressure profile.
Description
TECHNICAL FIELD
[0001] The present invention relates to a method of fabricating a
component of a solar energy system, and relates particularly,
though not exclusively to a method of fabricating an ejector of a
solar energy system, such as a solar cooling system.
BACKGROUND
[0002] Cooling systems such as air conditioning and refrigeration
units require considerable amounts of electrical energy that is
often generated from fossil fuels associated with emission of
pollutants and greenhouse gases.
[0003] Photovoltaic solar panels may be used to convert sunlight
into electricity that subsequently powers a compressor of a cooling
system. This may reduce the consumption of fossil fuels but the
efficiency is relatively low and the capital cost is relatively
high.
[0004] Steam-driven ejector heat pump cooling systems have been
used for air conditioning of very large spaces within buildings
that are equipped with fossil fuel powered steam boilers. The
application of ejector heat pump cooling systems outside of
large-scale niche applications, however, has not been a commercial
success, at least in part because efficient and inexpensive large
scale production of suitable ejectors has proved to be a
challenge.
SUMMARY OF THE INVENTION
[0005] In accordance with a first aspect of the present invention
there is provided a method of fabricating a component of a solar
energy system, the method comprising the steps of: [0006] providing
a tube, the tube comprising a material that deforms when at least a
length of the tube is exposed to a suitable difference in pressure
between an interior portion of the length of the tube and an
exterior portion of the length of the tube; [0007] providing a die
having a cavity arranged to receive the length of the tube, the
cavity defining a shape that is related to that of the component of
the solar energy system; [0008] positioning the length of the tube
in the cavity of the die; and [0009] increasing a relative pressure
of a fluid within the interior portion of the length of the tube
relative to a pressure within the cavity and outside the interior
portion of the length of the tube such that at least a portion of
the length of the tube expands to a shape that is related to that
of the component of the solar energy system.
[0010] The component of the solar energy system may be an ejector
and may be arranged for pumping a fluid. The ejector may be a
refrigeration ejector suitable for solar cooling applications.
[0011] Embodiments of the present invention facilitate fabrication
of ejectors at a relatively fast rate and typically with reduced
energy consumption. Material wastage may also be reduced compared
with known methods.
[0012] In accordance with a second aspect of the present invention
there is provided a method of fabricating at an ejector of a solar
energy system, the method comprising the steps of: [0013] providing
a tube, the tube comprising a material that deforms when at least a
length of the tube is exposed to a suitable difference in pressure
between an interior portion of the length of the tube and an
exterior portion of the length of the tube; [0014] providing a die
having a cavity arranged to receive the length of the tube, the
cavity defining a shape that is related to that of the ejector;
[0015] positioning the length of the tube in the cavity of the die;
and [0016] increasing a relative pressure of a fluid within the
interior portion of the length of the tube relative to a pressure
within the cavity and outside the interior portion of the length of
the tube such that at least a portion of the length of the tube
expands to a shape that is related to that of the ejector.
[0017] The ejector typically is arranged for pumping a fluid and
may be a refrigeration ejector suitable for solar cooling
applications.
[0018] The following introduces features that embodiments of the
first and second aspects of the present invention may have.
[0019] In one embodiment the step of increasing the relative
pressure is conducted such that at least the portion of the length
of the tube expands until that portion of the length of the tube is
in contact with the cavity of the die.
[0020] The step of increasing the relative pressure of the fluid
within the interior portion the tube relative to a pressure within
the cavity and outside the interior portion of the tube may
comprise increasing the pressure within the interior portion of the
tube. Alternatively, the step of increasing the relative pressure
of the fluid within the interior portion the tube relative to a
pressure within the cavity and outside the interior portion of the
tube may comprise reducing the pressure of a fluid within the
cavity and outside the interior portion of the tube.
[0021] In one specific embodiment the step of providing the tube
comprises shaping the tube. For example, the tube may initially
have an exterior diameter that larger than that of a portion of the
ejector, such as a throat portion of the ejector. The method may
comprise locally reducing the exterior diameter of the tube such
that the tube has a non-uniform exterior diameter that may be
profiled. For example, the method may comprise locally reducing the
exterior diameter of the tube at a throat portion of the ejector.
Reducing the external diameter of the tube may comprise any
suitable process, such as rotary swaging. The exterior diameter of
the tube typically is selected and reducing the external diameter
of the tube typically is conducted such that the step of increasing
the relative pressure within an interior portion of the tube
results in less expansion compared to the use of a tube having a
uniform and smaller exterior diameter. Consequently, likelihood of
overstretching and tearing of tube material as a consequence of the
expansion is reduced.
[0022] Further, the step of providing the tube may comprise
pre-forming or pre-machining tube material such that an additional
amount of the tube material is located at a region of the length of
the tube that is subjected to more expansion than another region of
the length of the tube. Consequently, likelihood of overstretching
and tearing of tube material as a consequence of the expansion is
further reduced.
[0023] The method typically also comprises the step of heating the
length of the tube prior or during the step of increasing the
relative pressure. Heating of the length of the tube may relieve
work hardening of the material. In one example the tube comprises a
metallic material and at least the length of the tube may be heated
to a temperature above a transition temperature at which the
material changes from a brittle state to a ductile state. The tube
material may also be provided in the form of an annealed material
and the method may comprise heat treating the tube material after
formation of the ejector to improve material properties.
[0024] In an embodiment, the step of increasing the relative
pressure is conducted such that a hoop stress is induced in at
least the portion of the length of the tube and the hoop stress is
greater than a yield strength of at least the portion of the length
of the tube.
[0025] The tube may not necessarily comprise a metallic material,
but may alternatively comprise another suitable material. For
example, the tube may comprise a polymeric material, a ceramic or
glass. Examples of suitable metallic materials include steel,
copper, aluminium, brass, carbon steel, an alloy, and high
elongation steel that may have a relatively low carbon content.
[0026] In an embodiment, the method comprises the step of exposing
the length of the tube to an axial compression during expansion of
the length of the tube. Exposing the length of the tube to an axial
compression during expansion may reduce the risk of tearing of the
tube material. The method may further comprise the step of
disposing a lubricant between the length of the tube and the die.
The lubricant may reduce friction between the tube and the die. The
lubricant may comprise molybdenum disulphide, although any suitable
lubricant may be used as appropriate. Suitable alternative
lubricants may comprise graphite, boron nitride, chalk, calcium
fluoride, cerium fluoride and tungsten disulphide.
[0027] The shape that is related to that of the ejector may
comprise the shape of a compressor portion of the ejector. The
shape that is related to that of the ejector may also comprise a
nozzle housing of the ejector such that the compressor portion and
the nozzle housing are formed integrally.
[0028] The fluid within the interior portion of the length of the
tube typically is a liquid and the method may comprise the step of
charging an interior portion of the length of the tube with the
fluid. The fluid typically is selected such that the fluid can be
heated to a temperature that is appropriate for heat treatment of
the tube material without suffering any substantial deleterious
effects. The fluid typically is selected such that the fluid will
not vapourise when the fluid is pressurised and/or when the tube is
released from the die. The fluid typically is not flammable. For
example, the fluid may be a silicone oil.
[0029] In one embodiment of the present invention the die is
arranged and the tube material is selected such that the tube
slightly contracts ("springs back") in diameter when the relative
pressure within the interior portion of the length of the tube is
reduced. This may facilitate separation of the length of the tube
from the die. It will be appreciated that this contraction in
diameter is dependent on the tube material and not all materials
show such a contraction.
[0030] The method may also comprise the step of locally or globally
controlling the temperature of the fluid, which may provide a
number of advantages. For example, moderate heating temperatures
may be used to assist in reducing or preventing local stresses in
the tube material. In a further example, controlling the
temperature of the fluid may also comprise exposing the tube
material to rapid cooling after expansion of the length of the
tube.
[0031] In an embodiment the method comprises the step of
determining a temporal pressure profile of the fluid, which may
comprise determining a rate of relative pressure increase of the
interior portion of the length of the tube and a rate of subsequent
relative pressure decrease of the interior portion of the length of
the tube. The step of increasing the relative pressure may be
defined at least in part by the determined temporal pressure
profile.
[0032] The invention will be more fully understood from the
following description of specific embodiments of the invention. The
description is provided with reference to the accompanying
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0033] FIG. 1 is a flow chart illustrating a method of forming an
ejector in accordance with an embodiment of the present
invention;
[0034] FIG. 2 is a schematic cross-sectional representation of an
ejector fabricated in accordance with an embodiment of the present
invention;
[0035] FIG. 3 is a perspective view of a schematic (wire frame)
representation of a compressor portion of an ejector fabricated in
accordance with an embodiment of the present invention;
[0036] FIG. 4 is a perspective view of a solid representation of
the compressor portion of FIG. 2;
[0037] FIG. 5 is a side view of the compressor portion of FIG.
2;
[0038] FIG. 6 is a cross-sectional view of two portions of a die
used to fabricate the compressor portion of FIG. 2 in accordance
with an embodiment of the present invention;
[0039] FIG. 7 is the die of FIG. 6 positioned around a tube from
which the compressor portion of FIG. 2 is fabricated in accordance
with an embodiment of the present invention; and
[0040] FIG. 8 is a schematic diagram of one embodiment of an
ejector cooling system circuit in accordance with an embodiment of
the present invention.
DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS
[0041] Embodiments of the present invention relate a method of
fabricating a component of a solar energy system, such as an
ejector.
[0042] Referring initially to FIG. 1, a method 10 in accordance
with an embodiment of the present invention is now described.
Further details of the method will be described further below with
reference to FIGS. 2 to 8.
[0043] The method 10 comprises the initial step 12 of providing a
tube, such as tube composed of copper or another suitable material.
The tube material is selected such that the tube material deforms
when the tube is exposed to a suitable difference in pressure
between an interior portion of the tube and an exterior portion of
the tube. As will be described further below in more detail, the
tube may comprise a portion that is processed such that a diameter
of the tube is locally reduced. Step 14 provides a die that has a
cavity arranged to receive the length of the tube. The cavity
defines a shape that is related to that of the component of the
solar energy system.
[0044] Step 16 positions the length of the tube in the cavity of
the die. Step 18 increases a relative pressure of a fluid within
the interior portion of the length of the tube relative to a
pressure within the cavity and outside the interior portion of the
length of the tube such that at least a portion of the length of
the tube expands to a shape that is related to that of the
component of the solar energy system.
[0045] Referring now to FIG. 2 an embodiment of the present
invention is described in further detail. FIG. 2 shows an ejector
20 that was formed using a method in accordance with the present
invention. The ejector 20 may be operated to drive a heat pump
refrigeration cycle, in which case, the ejector may be used in
place of an electrically driven compressor. The ejector 20 has no
moving parts and is suitable for widespread commercial and domestic
use. The ejector 20 uses thermal energy rather than electrical
energy to generate a compression effect. FIG. 8 shows an example of
a solar cooling system 200 comprising a solar panel 204 that
supplies thermal energy to the ejector 20.
[0046] In the example illustrated in FIG. 2 the ejector 20
comprises a hollow body 22 that has a partially closed end 25 and
an open end 29. The ejector 20 is often cylindrical, and in this
embodiment is substantially symmetric around a central axis 36. The
hollow body 22 has a nozzle housing 42 attached to a compressor
portion 34. A nozzle 30 penetrates the end 25 of the hollow body
22. The nozzle 30 has an inlet 38 external of the hollow body 22
and an outlet 40 interior of the hollow body 22. The nozzle 30 has
a constriction 31 intermediate the inlet 38 and the outlet 40.
[0047] It will be appreciated that other designs are envisaged. For
example, both ends 25, 29 may be open and the ejector 20 may be
arranged such that evaporator flow is in an axial direction through
open end 25 and a nozzle 30 may enter the hollow body 22 of the
ejector 20 through a side portion of the nozzle housing 42. It will
also be appreciated that designs comprising an annular shaped
nozzle and/or multiple nozzles are envisaged.
[0048] The nozzle housing 42 defines an entry chamber 24. A wall 32
of the entry chamber 24 has an entrained flow inlet formed therein.
The compressor portion 44 defines a mixing chamber 26 in
communication with the entry chamber 24. The compressor portion 44
also defines a diffusing chamber 28, and an intermediate chamber 27
in communication with and intermediate of the mixing and diffusing
chambers. The intermediate chamber is restricted relative to the
mixing and diffusing chamber. FIGS. 3 to 5 show views of the
compression portion 44 of the ejector 20.
[0049] An embodiment of a method of manufacturing the compressor
portion 44 will now be described with reference to the FIGS. 6 and
7. FIG. 6 shows a cross-sectional view of die 100. The die 100 is
typically cylindrical and comprises a die portions 101 and 102 that
are initially spaced apart from each other. The die 100 is formed
when the portions 101 and 102 are brought together. The die 100 is
configured with an internal space that has a shape that is
complementary to that of a portion of an ejector, for example the
ejector 20 illustrated in FIG. 2.
[0050] Prior to inserting a tube 104 for forming an ejector portion
into the die 100, the tube 104 is sometimes deformed or machined.
In this example the tube 104 has initially an exterior diameter
that larger than that of a narrow throat portion of the ejector 20.
The method may comprise locally reducing the exterior diameter at
the throat portion of the tube 104 such that the tube 104 has a
non-uniform exterior diameter (not shown in FIGS. 6 and 7). In this
example the exterior diameter of the tube 104 is locally reduced
using rotary swaging. The exterior diameter of the tube 104 is
selected and reducing of the external diameter of the tube 104 is
conducted such that an expansion required for formation of the
ejector portion is reduced. Consequently, likelihood of tearing of
material of the tube 104 as a consequence of the expansion is also
reduced.
[0051] Further, tube 104 may also be pre-machined such that an
additional amount of the tube material is located at a region of
the tube that is subjected to more expansion than another region of
the tube.
[0052] The tube 104 is then inserted between the spaced apart die
portions 101, 102. A fluid 110 is then introduced into a first end
112 the tube. The fluid may be a silicone oil, and preferably a
fluid that is able to be heated to temperatures that are
appropriate for annealing the tube without the fluid suffering any
deleterious effects. It is also be preferable for the fluid to not
vapourise when the fluid is heated or de-pressurised, and
particularly when the tube is released from the die. It is also
preferable that the fluid not be flammable. The second end 114 of
the tube may be pinched closed or capped, for example. The pressure
of the fluid 110 in the tube is then increased using a suitable
pump. In this embodiment, the pump is a piston type pump, however
other embodiments may use any suitable pump, examples of which
include but are not limited to a rotary type positive displacement
pump, a reciprocating type positive displacement pump (such as a
piston or diaphragm pump), and a linear type positive displacement
pump (such as a rope pump or chain pump).
[0053] The increased fluid pressure within the tube induces a hoop
stress of the tube which is greater than the hoop strength of the
tube to plastically deform the tube 104 into contact with the
internal walls 106, 108 of the die portions 101, 102,
respectively.
[0054] Generally, but necessarily, during the increase of the fluid
pressure the die portions 106,108 may be held in a mechanical
press, for example a clamp or vice.
[0055] The tube 104 may be composed of any suitable material. In
the examples of FIGS. 4 to 7, the tube 104 is a copper or stainless
steel tube. Further examples of the tube material include a high
elongation steel with a low carbon content. In some examples, the
tube may comprise a non metallic material such as a polymeric
material, glass or ceramic.
[0056] An axial compression is applied to the tube 104 when the
fluid pressure is being increased to compensate for thinning of a
wall of the tube that may occur as the wall is urged outwardly by
the pressure of the fluid. For example, the tube 104 may be grasped
at two points of either side of the die 100 by jaws which are then
urged to move together by a hydraulic piston, rack and pinion, or
other suitable compression means. Generally, the axial tension that
is applied to the tube 104 is determined prior to its application.
This may be determined using computational finite element analysis
of the process. During the fabrication the tube 104 is expanded
into the die 100 which may result in localised thinning of the
material. This may possibly lead to rupture of the tube. Applying
an axial tension may relieve this unwanted side effect.
[0057] A lubricant is disposed between the tube 104 and the die
portions 106, 108. The lubricant may be, for example, molybdenum
disulphide although any suitable lubricant may be used. Lubrication
is favourable during the application of an axial compression to the
tube.
[0058] The tube 104 is heated before expansion above a material
brittle-to-ductile transition temperature. The method should also
be carried out below the melting temperature of the tube material,
around 1085.degree. C. for a copper tube. It will be appreciated
that the values of the transition and melting temperatures vary
from material to material. The material of the tube 104 may also be
provided in annealed form.
[0059] The fluid pressure is then increased until the tube 104
expands within the die 104 such that an exterior surface of the
tube 104 is in contact with the entire die surfaces 106 and 108.
The pressure is then realised and the die 100 is configured such
that at least for some suitable tube materials) the tube 104
contracts ("springs back") when the pressure of the fluid is
reduced.
[0060] The formed portion of the ejector 20 is then machined and
processed using known techniques to form the ejector 20.
[0061] The temperature of the fluid may be controlled to improve
the method. The step of controlling the temperature of the fluid
may provide a number of advantages. For example, moderate heating
temperatures may be used to assist in preventing local stresses in
the material that might otherwise lead to rupturing of the tube. In
some cases, the tube material may be exposed to rapid and this may
be achieved by admitting cool fluid into the tube. Further,
admitting a cool fluid after hydroforming may cause the tube to
shrink sufficiently to facilitate its removal from the die.
[0062] The temporal pressure profile may be determined prior to
placing the tube in the die. This may be determined by, for
example, computational finite element analysis of the method. The
pressure of the fluid may be increased and/or decreased as defined
by the output of the analysis.
[0063] After the tube has been deformed by the increased pressure
therein to form the compressor portion, the vice or press is
released and the die portions 106 and 108 are separated. The fluid
is drained from the formed compression portion and the tube is
subsequently removed from the die and cleaned. The compressor
portion 44 may then be machined or trimmed if required, and then
may be attached to the nozzle housing 42 by any suitable means
including but not limited to brazing, wielding or by use of an
adhesive. In one embodiment, complementary threads are formed on
the compressor portion 44 and the nozzle housing 42 which are then
engaged to attach the nozzle housing 42 to the compressor portion
44.
[0064] Alternatively, the die may be configured so as to facilitate
formation of the nozzle housing 42 such that the compressor portion
34 and the nozzle housing 42 are formed integrally.
[0065] The operation of the ejector 20 may be generally understood
with reference to FIGS. 3 and 8. A source of vapour is coupled to
the exterior end 38 of the nozzle 30. The vapour passes through the
nozzle 30 and leaves the nozzle through the interior end 40. The
passage of the vapour through the ejector 20 causes a reduction in
pressure at the entrained flow inlet 34. Entrained flow inlet 34 is
in communication with a vessel having a fluid in the form of a
refrigerant, examples of which include but are not limited to
hydrofluorocarbons, hydrocarbons, alcohols and water. In the
embodiment of FIG. 8, the vessel is contained in an evaporator 208.
The relatively low pressure at the entrained flow inlet 34 causes
evaporation of the refrigerant which in turn cools the remaining
refrigerant in the vessel. The cooled refrigerant may then be used
for subsequent cooling applications such as air conditioning.
[0066] The heat pump refrigeration cycle may consist of high 210
and low 212 temperature sub cycles. In the high temperature sub
cycle, heat that is transferred to the ejector from the heat source
(such as a solar collector 204) through a vapour generator causing
vaporisation of the ejector cycle working fluid in the generator at
a temperature slightly above the saturation temperature of the
refrigerant. Vapour then flows to the ejector where it is
accelerated through the nozzle 30.
[0067] A pump 201 may be required to generate a pressure difference
for the ejector 20 to operate, but since liquid is being
compressed, the electricity required may be relatively small. All
other components in the heat pump circuit 202 may be, but may not
be, conventional.
[0068] Since much of the vapour enthalpy may be converted to
kinetic energy, conservation of energy suggests that the vapour
temperature and pressure within the inlet housing 22 may be very
low. The low pressure within the inlet housing may act to draw
vapour flow from the evaporator.
[0069] The generator and evaporator flows may then mix in the
ejector and the combined flow may undergo a compression shock. Thus
thermal compression may replace the electrical compressor in a
conventional heat pump. Further compression may take place in the
diffusing chamber such that a subsonic stream emerging from the
ejector then flows into the condenser 206.
[0070] At the condenser 206, heat is rejected from the working
fluid (refrigerant) to the surroundings, resulting in a condensed
refrigerant liquid at the condenser exit. The ejector 20 needs to
provide sufficient exit pressure such that the saturation
temperature of the refrigerant at this point is greater than the
condenser cooling medium, otherwise heat cannot be rejected and the
cycle ceases to operate. This is the malfunction mode of the
ejector, caused by excessive condensing backpressure. Malfunction
can be overcome by supplying greater generator pressure and
temperature, for example from a generator 214.
[0071] Liquid refrigerant leaving the condenser is then divided
into two streams; one enters the evaporator 208 after a pressure
reduction through the expansion valve, the other is routed back
into the generator after undergoing a pressure increase through the
refrigerant pump 201. The refrigerant fluid is evaporated in the
evaporator, absorbing heat from the environment that is being
cooled, and then it is entrained back into the ejector 20
completing the cycle.
[0072] The ejector heat pump cycle may benefit from sub cooling
prior to evaporation and from minimising superheating through
compression.
[0073] The ejector mechanism may offer freedom of choice of
refrigerant and is not complicated by the need for compressor
lubricant compatibility. Also, the ejector is tolerant of liquid
slugging since both generator and evaporator ports are essentially
open tubes.
[0074] There are a number of means to model the performance of an
ejector. Modelling may be based on thermodynamic compressible flow
theory with minor corrections for non-ideal behaviour, or
numerically derived using computational fluid dynamics and/or
finite element analysis. Modelling may be aided with reference to:
[0075] Eames, I W, Aphornratana, S & Haider, H 1995, `A
theoretical and experimental study of a small-scale steam jet
refrigerator`, International Journal of Refrigeration, vol. 18, no.
6, pp. 378-86. [0076] Huang B., Petrenko V., Chang J, Lin C., Hu
S., `A combined cycle refrigeration system using ejector cooling
cycle as bottoming cycle`, International Journal of Refrigeration
24 (2001) 391-399. [0077] Zhu C., Wen L., Shock Circle method for
ejector performance evaluation, Energy Conversion and Management,
Vol 48, pp 2533-2541, 2007. [0078] Eames I., `A new prescription
for the design of supersonic jet pumps: the constant rate of
momentum change method`, Applied Thermal Engineering, Vol 22, pp
121-131, 2002.
[0079] Computational Fluid Dynamics (CFD) has matured over the last
decade with the advance in hardware computational capability. This
is allowing researchers to investigate the ejector processes in
greater detail including supersonic shock effects, real gas
behaviour, metastable refrigerant states, boundary layer flow, flow
separation and the like. Due to the complexity of highly turbulent
supersonic compressible flow involving a real gas model, only
highly developed CFD packages maybe suitable for ejector modelling.
Ejector modellers may use Fluent or ANSYS CFD, or any other
suitable softonne.
[0080] The selection of a turbulence model is required for CFD
modelling. The standard .kappa.-.epsilon. turbulence model may not
be adequate. In particular, the hybrid .kappa.-.omega.-sst model
seems to offer good result, as described by Bartosiewicz Y., Aidoun
Z., Desevaux P., Mercadier Y., CFD experiments integration in the
evaluation of six turbulence models for supersonic ejector
modelling, Proceedings of Integrating CFD and Experiments, Glasgow,
2003.
[0081] Insights into real ejector flows may be provided by advanced
visualisation techniques involving transparent ejectors.
[0082] It will be appreciated that numerous variations and/or
modifications may be made to the disclosed embodiments. The present
embodiments are, therefore, to be considered in all respects as
illustrative and not restrictive. For example, the component of the
ejector may be formed by reducing a pressure at a region that is
exterior to the tube 104 resulting in an increase in relative
pressure within an interior region of the tube 104.
[0083] Reference that is made to prior publication is not an
admission that the prior publication are part of the common general
knowledge of a skilled person in Australia or any other
country.
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