U.S. patent application number 16/186262 was filed with the patent office on 2020-01-23 for low pressure refrigerant system.
The applicant listed for this patent is Carrier Corporation. Invention is credited to Zissis A. Dardas, Yinshan Feng, Rajiv Ranjan, Parmesh Verma.
Application Number | 20200025429 16/186262 |
Document ID | / |
Family ID | 64267683 |
Filed Date | 2020-01-23 |
![](/patent/app/20200025429/US20200025429A1-20200123-D00000.png)
![](/patent/app/20200025429/US20200025429A1-20200123-D00001.png)
![](/patent/app/20200025429/US20200025429A1-20200123-D00002.png)
![](/patent/app/20200025429/US20200025429A1-20200123-D00003.png)
United States Patent
Application |
20200025429 |
Kind Code |
A1 |
Ranjan; Rajiv ; et
al. |
January 23, 2020 |
LOW PRESSURE REFRIGERANT SYSTEM
Abstract
Disclosed is a refrigeration system including a heat transfer
fluid circulation loop configured to allow a refrigerant to
circulate therethrough, a purge outlet from the heat transfer fluid
circulation loop, and at least one gas permeable membrane having a
first side in communication with the purge outlet. The membrane
includes a porous inorganic material with pores of a size to allow
passage of contaminants through the membrane and restrict passage
of the refrigerant through the membrane. A retentate return flow
path connects the first side of the membrane to the heat transfer
fluid circulation loop.
Inventors: |
Ranjan; Rajiv; (South
Windsor, CT) ; Feng; Yinshan; (Manchester, CT)
; Verma; Parmesh; (South Windsor, CT) ; Dardas;
Zissis A.; (Worcester, MA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Carrier Corporation |
Palm Beach Gardens |
FL |
US |
|
|
Family ID: |
64267683 |
Appl. No.: |
16/186262 |
Filed: |
November 9, 2018 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
62584012 |
Nov 9, 2017 |
|
|
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
F25B 43/043 20130101;
F25B 41/06 20130101; F25B 43/00 20130101; F25B 41/043 20130101;
F25B 13/00 20130101 |
International
Class: |
F25B 41/04 20060101
F25B041/04; F25B 13/00 20060101 F25B013/00; F25B 41/06 20060101
F25B041/06 |
Claims
1. A refrigeration system comprising a heat transfer fluid
circulation loop configured to allow a refrigerant to circulate
therethrough; a purge outlet from the heat transfer fluid
circulation loop; at least one gas permeable membrane comprising a
porous inorganic material with pores of a size to allow passage of
contaminants through the membrane and restrict passage of the
refrigerant through the membrane, said membrane having a first side
in communication with the purge outlet; and a retentate return flow
path from the first side of the membrane to the heat transfer fluid
circulation loop.
2. The refrigeration system of claim 1, wherein the heat transfer
fluid circulation loop comprises a compressor, a heat rejection
heat exchanger, an expansion device, and a heat absorption heat
exchanger, connected together in order by conduit.
3. The refrigeration system of claim 1, wherein the retentate
return flow path includes a control device.
4. The refrigeration system of claim 1, wherein the purge system is
configured for continuous operation.
5. The refrigeration system of claim 1, further comprising a prime
mover configured to move gas from a second side of the membrane to
an exhaust port leading outside the refrigeration system, and a
controller configured to operate the refrigeration system in
response to a cooling demand signal, and to operate the prime mover
in response to a purge signal.
6. The refrigeration system of claim 5, wherein the retentate
return flow path includes a control device, and the controller is
further configured to operate the control device in response to the
purge signal.
7. The refrigeration system of claim 1, wherein the prime mover
comprises a vacuum pump in communication with the second side of
the membrane.
8. The refrigeration system of claim 1, further comprising a purge
gas collector between the purge outlet and the membrane.
9. The refrigeration system of claim 3, wherein the control device
comprises an expansion device and returns retentate to the fluid
circulation loop to the heat absorption heat exchanger or to the
compressor inlet.
10. The refrigeration system of claim 1, wherein the at least one
gas permeable membrane comprises a plurality of gas permeable
membranes in serial or parallel communication between the purge
outlet and the exhaust port.
11. The refrigeration system of claim 10, comprising a retentate
return flow path operably coupling the first side of each of
plurality of membranes to the fluid circulation loop.
12. (canceled)
13. The refrigeration system of claim 5, wherein the system further
comprises a pressure sensor operably coupled to the fluid
circulation loop, and the controller generates the purge signal in
response to output from the pressure sensor.
14. (canceled)
15. The refrigeration system of claim 5, wherein the system further
comprises a temperature sensor operably coupled to the fluid
circulation loop, and the controller generates the purge signal in
response to output from the temperature sensor.
16. (canceled)
17. The refrigeration system of claim 5, wherein the system further
comprises a refrigerant gas detection sensor operably coupled to
second side of the membrane, and the controller generates the purge
signal in response to output from the refrigerant gas detection
sensor.
18. The refrigeration system of claim 5, wherein the controller is
configured to generate the purge signal based at least in part on a
timer setting.
19. (canceled)
20. The refrigeration system of claim 6, wherein the controller is
configured, in response to the purge signal, to operate the control
device to provide a varying flow rate or pressure drop through the
control device, or to vary prime mover pressure in coordination
with varying the control device setting, or to operate the control
device to provide a varying flow rate or pressure drop through the
control device and vary prime mover pressure in coordination with
varying the control device setting.
21. The refrigeration system of claim 20, wherein the control
device includes a control valve, and the controller is configured,
in response to the purge signal, to alternately operate the prime
mover with the control valve closed and suspend operation of the
prime mover with the control valve open.
22. (canceled)
23. (canceled)
24. The refrigeration system of claim 1, wherein the purge outlet
is operably coupled to the condenser.
25. A method of operating the refrigeration system of claim 5,
comprising circulating the refrigerant through the vapor
compression heat transfer fluid circulation loop in response to the
cooling demand signal under conditions in which the refrigerant is
at a pressure less than atmospheric pressure in at least a portion
of the fluid circulation loop; and operating the prime mover and
the control device, if present, with the controller as configured.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the benefit of Provisional
Application 62/584,012 filed Nov. 9, 2017, which is incorporated
herein by reference in its entirety.
BACKGROUND
[0002] This disclosure relates generally to chiller systems used in
air conditioning systems, and more particularly to a purge system
for removing contaminants from a refrigeration system.
[0003] Chiller systems such as those utilizing centrifugal
compressors may include sections that operate below atmospheric
pressure. As a result, leaks in the chiller system may draw air
into the system, contaminating the refrigerant. This contamination
degrades the performance of the chiller system. To address this
problem, existing low pressure chillers include a purge unit to
remove contamination. Existing purge units use a vapor compression
cycle to separate non-condensable contaminant gas from the
refrigerant. Existing purge units are complicated and lose
refrigerant in the process of removing contamination.
BRIEF DESCRIPTION
[0004] Disclosed is a refrigeration system including a heat
transfer fluid circulation loop configured to allow a refrigerant
to circulate therethrough, a purge outlet from the heat transfer
fluid circulation loop, and at least one gas permeable membrane
having a first side in communication with the purge outlet. The
membrane includes a porous inorganic material with pores of a size
to allow passage of contaminants through the membrane and restrict
passage of the refrigerant through the membrane. A retentate return
flow path connects the first side of the membrane to the heat
transfer fluid circulation loop.
[0005] In some embodiments, the enclosure includes a vapor
compression heat transfer fluid circulation loop including a
compressor, a heat rejection heat exchanger, an expansion device,
and a heat absorption heat exchanger, connected together in order
by conduit and having the refrigerant disposed therein. In an
operational state, the refrigerant is at a pressure less than
atmospheric pressure in at least a portion of the fluid circulation
loop.
[0006] In any one or combination of the foregoing embodiments, the
retentate return flow path includes a control device.
[0007] In any one or combination of the foregoing embodiments, the
system is configured for continuous purge operation.
[0008] In any one or combination of the foregoing embodiments, the
system further includes a prime mover configured to move gas from a
second side of the membrane to an exhaust port leading outside the
refrigeration system, and a controller configured to operate the
refrigeration system in response to a cooling demand signal, and to
operate the prime mover in response to a purge signal.
[0009] In any one or combination of the foregoing embodiments
including a control device, the controller is further configured to
operate the control device in response to the purge signal.
[0010] In some embodiments, the prime mover includes a vacuum pump
in communication with the second side of the membrane.
[0011] In any one or combination of the foregoing embodiments, the
system further includes a purge gas collector between the purge
outlet and the membrane.
[0012] In any one or combination of the foregoing embodiments, the
retentate return flow path includes an expansion device and returns
retentate to the fluid circulation loop to the heat absorption heat
exchanger or to the compressor inlet.
[0013] In any one or combination of the foregoing embodiments, the
at least one gas permeable membrane includes a plurality of gas
permeable membranes in serial or parallel communication between the
purge outlet and the exhaust port. In some embodiments, the system
includes a retentate return flow path operably coupling the first
side of each of plurality of membranes to the fluid circulation
loop
[0014] In any one or combination of the foregoing embodiments, the
contaminants includes nitrogen, oxygen, or water.
[0015] In any one or combination of the foregoing embodiments, the
system further includes a pressure sensor operably coupled to the
fluid circulation loop, and the controller generates the purge
signal in response to output from the pressure sensor.
[0016] In any one or combination of the foregoing embodiments, the
pressure sensor is operably coupled to the condenser or to the
outlet of the compressor.
[0017] In any one or combination of the foregoing embodiments, the
system further includes a temperature sensor operably coupled to
the fluid circulation loop, and the controller generates the purge
signal in response to output from the temperature sensor.
[0018] In any one or combination of the foregoing embodiments, the
temperature sensor is operably coupled to the condenser or
evaporator.
[0019] In any one or combination of the foregoing embodiments, the
system further includes a refrigerant gas detection sensor operably
coupled to second side of the membrane, and the controller
generates the purge signal in response to output from the
refrigerant gas detection sensor.
[0020] In any one or combination of the foregoing embodiments, the
controller is configured to generate the purge signal based at
least in part on a timer setting.
[0021] In any one or combination of the foregoing embodiments, the
controller is configured to, in response to the purge signal,
operate the control device to provide a varying flow rate or
pressure drop through the control device.
[0022] In any one or combination of the foregoing embodiments, the
controller is configured to, in response to the purge signal, vary
prime mover pressure in coordination with varying control device
setting. In some embodiments, the control device includes a control
valve, and the controller is configured to, in response to the
purge signal, alternately operate the prime mover with the control
valve closed and suspend operation of the prime mover with the
control valve open.
[0023] In any one or combination of the foregoing embodiments, the
controller is configured, in response to the purge signal, to
operate the prime mover at a constant pressure.
[0024] In any one or combination of the foregoing embodiments, the
controller is configured, in response to the purge signal, to
operate the prime mover at a varying pressure.
[0025] In any one or combination of the foregoing embodiments, the
purge outlet is operably coupled to the condenser.
[0026] Also disclosed is a method of operating the refrigeration
system of any one or combination of the foregoing embodiments,
including circulating the refrigerant through the vapor compression
heat transfer fluid circulation loop in response to the cooling
demand signal under conditions in which the refrigerant is at a
pressure less than atmospheric pressure in at least a portion of
the fluid circulation loop, and operating the prime mover and the
control device with the controller as configured.
BRIEF DESCRIPTION OF THE DRAWINGS
[0027] The following descriptions should not be considered limiting
in any way. With reference to the accompanying drawings, like
elements are numbered alike:
[0028] FIG. 1 is a schematic depiction of a vapor compression heat
transfer refrigerant fluid circulation loop;
[0029] FIG. 2 is schematic depiction of an example embodiment of a
purge system and relevant components of a vapor compression heat
transfer refrigerant fluid circulation loop, with membrane unit
retentate directed to the system evaporator;
[0030] FIG. 3 is schematic depiction of another example embodiment
of a purge system and relevant components of a vapor compression
heat transfer refrigerant fluid circulation loop, with membrane
retentate directed to the condenser;
[0031] FIG. 4 is a schematic depiction of another example
embodiment of a purge system and relevant components of a vapor
compression heat transfer refrigerant fluid circulation loop, with
membrane units in a cascade configuration; and
[0032] FIG. 5 is a schematic depiction of another example
embodiment of a purge system and relevant components of a vapor
compression heat transfer refrigerant fluid circulation loop, with
condenser pressure-based control.
DETAILED DESCRIPTION
[0033] A detailed description of one or more embodiments of the
disclosed apparatus and method are presented herein by way of
exemplification and not limitation with reference to the
Figures.
[0034] With reference to FIG. 1, a refrigerant enclosure in the
form of a heat transfer fluid circulation loop is shown in block
diagram form in FIG. 1. As shown in FIG. 1, a compressor 10
pressurizes heat transfer fluid in its gaseous state, which both
heats the fluid and provides pressure to circulate it throughout
the system. In some embodiments, the heat transfer fluid, or
refrigerant, comprises an organic compound. In some embodiments,
the refrigerant comprises a hydrocarbon or substituted hydrocarbon.
In some embodiments, the refrigerant comprises a
halogen-substituted hydrocarbon. In some embodiments, the
refrigerant comprises a fluoro-substituted or
chloro-fluoro-substituted hydrocarbon. The hot pressurized gaseous
heat transfer fluid exiting from the compressor 10 flows through
conduit 15 to heat exchanger condenser 20, which functions as a
heat exchanger to transfer heat from the heat transfer fluid to the
surrounding environment, resulting in condensation of the hot
gaseous heat transfer fluid to a pressurized moderate temperature
liquid. The liquid heat transfer fluid exiting from the condenser
20 flows through conduit 25 to expansion valve 30, where the
pressure is reduced. The reduced pressure liquid heat transfer
fluid exiting the expansion valve 30 flows through conduit 35 to
heat exchanger evaporator 40, which functions as a heat exchanger
to absorb heat from the surrounding environment and boil the heat
transfer fluid. Gaseous heat transfer fluid exiting the evaporator
40 flows through conduit 45 to the compressor 10, thus completing
the heat transfer fluid loop. The heat transfer system has the
effect of transferring heat from the environment surrounding the
evaporator 40 to the environment surrounding the condenser 20. The
thermodynamic properties of the heat transfer fluid must allow it
to reach a high enough temperature when compressed so that it is
greater than the environment surrounding the condenser 20, allowing
heat to be transferred to the surrounding environment. The
thermodynamic properties of the heat transfer fluid must also have
a boiling point at its post-expansion pressure that allows the
temperature surrounding the evaporator 40 to provide heat to
vaporize the liquid heat transfer fluid.
[0035] With reference now to FIG. 2, there is shown an example
embodiment of a purge system connected to a vapor compression heat
transfer fluid circulation loop such as FIG. 1 (not all components
of FIG. 1 shown). As shown in FIG. 2, a purge collector 66 receives
purge gas comprising refrigerant gas and contaminants (e.g.,
nitrogen, oxygen) from a purge connection 52 connected to the
condenser 20. The purge gas is directed from the purge collector 66
to a first side of a membrane 56 in a membrane separator 54. A
prime mover such as a vacuum pump 58 connected to the membrane
separator 54 provides a driving force to pass the contaminant
molecules through the membrane 56 and exit the system from a second
side of the membrane 56 through an outlet. In some embodiments, the
prime mover can be in the fluid loop, e.g., a refrigerant pump or
compressor. Retentate comprising refrigerant gas (and optionally
other components including but not limited to oil(s) or other
contaminants that did (e.g., nitrogen, gas remains on the first
side of the membrane 56 and returns to the fluid circulation loop
through a connection 67 that bypasses the condenser 20. A
controller 50 receives system data (e.g., pressure, temperature,
mass flow rates) and system or operator control (e.g., on/of,
receipt of cooling demand signal), and utilizes electronic control
components (e.g., a microprocessor) to control system components
such as various pumps, valves, switches.
[0036] In some embodiments, the connection of the purge connection
52 to the condenser can be made at a high point of the condenser
structure. In some embodiments, the purge collector 66 can provide
a technical effect of promoting higher concentrations of
contaminants at the membrane separator 54, which can promote more
effective mass transfer and separation. This effect can occur
through a stratification of gas in the purge collector 66 in which
lighter contaminants concentrate toward the top of the purge
collector 66 and heavier refrigerant gas concentrates toward the
bottom of the purge collector 66. In some embodiments, the purge
collector 66 can be any kind of vessel or chamber with a volume or
cross-sectional open space to provide for collection of purge gas
and for a low gas velocity during operation of the purge system
vacuum pump 58 to promote stratification. Stratification can also
occur at any time when the purge system is not operating (including
during operation of the refrigeration system fluid circulation
loop), as the purge collector 66 remains in fluid communication
with the purge connection 52 with essentially stagnant gas in the
purge collector 66. Other embodiments can also be employed to
promote higher concentrations of contaminants at the membrane
separator 54, as discussed in more detail below.
[0037] With reference again to FIG. 2, the connection 67 returns
retentate gas from the first side of membrane 56 to the refrigerant
fluid circulation loop at the evaporator 40, through a control
device such as expansion valve 68 utilized to accommodate the
pressure differential between the first side of the membrane 56
(which is close to the pressure at the condenser 20) and pressure
at the evaporator 40. It should be noted that the control device
can control either or both flow through or pressure drop across the
control device, and expansion valve 68 is shown as an integrated
control device unit that performs both functions for ease of
illustration, but could be separate components such as a control
valve and an expansion orifice. Other types of expansion devices
can also be used, including but not limited to capillaries,
solenoids, thermostatic, or electronic expansion devices. In some
embodiments, utilization of a bypass refrigerant return can provide
a technical effect of promoting greater concentrations of
contaminants at the first side of membrane 56 by removing gas at
the membrane 56 that is concentrated with refrigerant after removal
of contaminant molecules through the membrane 56, so that
refrigerant-concentrated gas can be displaced with gas from the
purge collector 66 that has a higher concentration of contaminants.
In alternative embodiments as shown in FIG. 3, the connection 67
can return retentate gas to the colder side of the condenser 20 or
the inlet of the compressor 10, in which case an expansion device
may not be needed due to lower pressure differential compared to
that of a bypass return to the evaporator 40. In such as case, the
connection 67 can utilize a control device such as a control or
shut-off valve 69 that does not provide gas expansion.
[0038] The membrane 56 comprises a porous inorganic material.
Examples of porous inorganic materials can include ceramics such as
metal oxides or metal silicates, more specifically aluminosilicates
(e.g., Chabazite Framework (CHA) zeolite, Linde type A (LTA)
zeolite, porous carbon, porous glass, clays (e.g., Montmorillonite,
Halloysite). Porous inorganic materials can also include porous
metals such as platinum and nickel. Hybrid inorganic-organic
materials such as a metal organic framework (MOF) can also be used.
Other materials can be present in the membrane such as a carrier in
which a microporous material can be dispersed, which can be
included for structural or process considerations.
[0039] Metal organic framework materials are well-known in the art,
and comprise metal ions or clusters of metal ions coordinated to
organic ligands to form one-, two- or three-dimensional structures.
A metal-organic framework can be characterized as a coordination
network with organic ligands containing voids. The coordination
network can be characterized as a coordination compound extending,
through repeating coordination entities, in one dimension, but with
cross-links between two or more individual chains, loops, or
spiro-links, or a coordination compound extending through repeating
coordination entities in two or three dimensions. Coordination
compounds can include coordination polymers with repeating
coordination entities extending in one, two, or three dimensions.
Examples of organic ligands include but are not limited to
bidentate carboxylates (e.g., oxalic acid, succinic acid, phthalic
acid isomers, etc.), tridentate carboxylates (e.g., citric acid,
trimesic acid), azoles (e.g., 1,2,3-triazole), as well as other
known organic ligands. A wide variety of metals can be included in
a metal organic framework. Examples of specific metal organic
framework materials include but are not limited to zeolitic
imidazole framework (ZIF), HKUST-1.
[0040] In some embodiments, pore sizes can be characterized by a
pore size distribution with an average pore size from 2.5 .ANG. to
10.0 .ANG., and a pore size distribution of at least 0.1 .ANG.. In
some embodiments, the average pore size for the porous material can
be in a range with a lower end of 2.5 .ANG. to 4.0 .ANG. and an
upper end of 2.6 .ANG. to 10.0 .ANG.. A. In some embodiments, the
average pore size can be in a range having a lower end of 2.5
.ANG., 3.0 .ANG., 3.5 .ANG., and an upper end of 3.5 .ANG., 5.0
.ANG., or 6.0 .ANG.. These range endpoints can be independently
combined to form a number of different ranges, and all ranges for
each possible combination of range endpoints are hereby disclosed.
Porosity of the material can be in a range having a lower end of
5%, 10%, or 15%, and an upper end of 85%, 90%, or 95% (percentages
by volume). These range endpoints can be independently combined to
form a number of different ranges, and all ranges for each possible
combination of range endpoints are hereby disclosed.
[0041] The above microporous materials can be can be synthesized by
hydrothermal or solvothermal techniques (e.g., sol-gel) where
crystals are slowly grown from a solution. Templating for the
microstructure can be provided by a secondary building unit (SBU)
and the organic ligands. Alternate synthesis techniques are also
available, such as physical vapor deposition or chemical vapor
deposition, in which metal oxide precursor layers are deposited,
either as a primary microporous material, or as a precursor to an
MOF structure formed by exposure of the precursor layers to
sublimed ligand molecules to impart a phase transformation to an
MOF crystal lattice.
[0042] In some embodiments, the above-described inorganic or MOF
membrane materials can provide a technical effect of promoting
separation of contaminants (e.g., nitrogen, oxygen, water) from
refrigerant gas, which is condensable. Other microporous materials,
such as porous polymers can be subject to solvent interaction with
the matrix material, which can interfere with effective separation.
In some embodiments, the capabilities of the materials described
herein can provide a technical effect of promoting the
implementation of a various example embodiments of refrigeration
systems with purge, as described in more detail with reference to
the example embodiments below.
[0043] The membrane material can be self-supporting or it can be
supported, for example, as a layer on a porous support or
integrated with a matrix support material. In some embodiments,
thickness of a support for a supported membrane can range from 50
nm to 1000 nm, more specifically from 100 nm to 750 nm, and even
more specifically from 250 nm to 500 nm. In the case of tubular
membranes, fiber diameters can range from 100 nm to 2000 nm, and
fiber lengths can range from 0.2 m to 2 m.
[0044] In some embodiments, the microporous material can be
deposited on a support as particles in a powder or dispersed in a
liquid carrier using various techniques such as spray coating, dip
coating, solution casting, etc. The dispersion can contain various
additives, such as dispersing aids, rheology modifiers, etc.
Polymeric additives can be used; however, a polymer binder is not
needed, although a polymer binder can be included and in some
embodiments is included such as with a mixed matrix membrane
comprising a microporous inorganic material (e.g., microporous
ceramic particles) in an organic (e.g., organic polymer) matrix.
However, a polymer binder present in an amount sufficient to form a
contiguous polymer phase can provide passageways in the membrane
for larger molecules to bypass the molecular sieve particles.
Accordingly, in some embodiments a polymer binder is excluded. In
other embodiments, a polymer binder can be present in an amount
below that needed to form a contiguous polymer phase, such as
embodiments in which the membrane is in series with other membranes
that may be more restrictive. In some embodiments, particles of the
microporous material (e.g., particles with sizes of 0.01 .mu.m to
10 mm, or in some embodiments from 0.5 .mu.m to 10 .mu.m, can be
applied as a powder or dispersed in a liquid carrier (e.g., an
organic solvent or aqueous liquid carrier) and coated onto the
support followed by removal of the liquid. In some embodiments, the
application of solid particles of microporous material from a
liquid composition to the support surface can be assisted by
application of a pressure differential across the support. For
example a vacuum can be applied from the opposite side of the
support as the liquid composition comprising the solid microporous
particles to assist in application of the solid particles to the
surface of the support. A coated layer of microporous material can
be dried to remove residual solvent and optionally heated to fuse
the microporous particles together into a contiguous layer. Various
membrane structure configurations can be utilized, including but
not limited to flat or planar configurations, tubular
configurations, or spiral configurations.
[0045] In some embodiments, the microporous material can be
configured as nanoplatelets such as zeolite nanosheets. Zeolite
nanosheet particles can have thicknesses ranging from 2 to 50 nm,
more specifically 2 to 20 nm, and even more specifically from 2 nm
to 10 nm. The mean diameter of the nanosheets can range from 50 nm
to 5000 nm, more specifically from 100 nm to 2500 nm, and even more
specifically from 100 nm to 1000 nm. Mean diameter of an
irregularly-shaped tabular particle can be determined by
calculating the diameter of a circular-shaped tabular particle
having the same surface area in the x-y direction (i.e., along the
tabular planar surface) as the irregularly-shaped particle. Zeolite
such as zeolite nanosheets can be formed from any of various
zeolite structures, including but not limited to framework type
MFI, MWW, FER, LTA, FAU, and mixtures of the preceding with each
other or with other zeolite structures. In a more specific group of
exemplary embodiments, the zeolite such as zeolite nanosheets can
comprise zeolite structures selected from MFI, MWW, FER, LTA
framework type. Zeolite nanosheets can be prepared using known
techniques such as exfoliation of zeolite crystal structure
precursors. For example, MFI and MWW zeolite nanosheets can be
prepared by sonicating the layered precursors (multilamellar
silicalite-1 and ITQ-1, respectively) in solvent. Prior to
sonication, the zeolite layers can optionally be swollen, for
example with a combination of base and surfactant, and/or
melt-blending with polystyrene. The zeolite layered precursors are
typically prepared using conventional techniques for preparation of
microporous materials such as sol-gel methods.
[0046] The above embodiments are examples of specific embodiments,
and other variations and modifications may be made. For example, a
single membrane is depicted for ease of illustration in the
above-discussed Figures. However, multiple membranes (or membrane
separation units) can be utilized, either in cascaded or parallel
configurations. An example embodiment of a cascaded configuration
is schematically depicted in FIG. 4. As shown in FIG. 4, membrane
separation units 54a and 54b (with membranes 56a and 56b) are
disposed in a cascaded configuration in which permeate from the
separation unit 54a is fed to the first side of the second
separation unit 54b. Retentate from the first side of the membranes
56a and 56b is routed through connections 67a and 67b to the
refrigerant fluid circulation loop at the evaporator 40, with
expansion valves 68a and 68b utilized to accommodate the pressure
differential between the first side of the membrane 56 (which is
close to the pressure at the condenser 20) and pressure at the
evaporator 40. Other system variations such as centrifugal
separators or chilling coils integrated with a purge chamber,
pumped recycle of permeate back to the retentate (upstream) side of
the membrane, cascaded multiple membranes, or alternative prime
movers such as a thermal prime mover or a pump or compressor in the
fluid circulation loop, are described in more detail in U.S. patent
application Ser. No. 15/808,837, entitled "Refrigeration Purge
System", filed on Nov. 9, 2017, the disclosure of which is
incorporated herein by reference in its entirety.
[0047] As mentioned above, the system includes a controller such as
controller 50 for controlling the operation of the heat transfer
refrigerant flow loop and the purge system. As mentioned above, a
refrigeration or chiller system controller can operate the
refrigerant heat transfer flow loop in response to a cooling demand
signal, which can be generated externally to the system by a master
controller or can be entered by a human operator. Some systems can
be configured to operate the flow loop continuously for extended
periods. The controller can also be configured to also operate the
control device in the retentate return flow path, or the prime
mover, or both the control device and the prime mover, in response
to a purge signal. The purge signal can be generated from various
criteria. In some embodiments, the purge signal can be in response
to elapse of a predetermined amount of time (e.g., simple passage
of time, or tracked operating hours) tracked by the controller
circuitry. In some embodiments, the purge signal can be in response
to human operator input. In some embodiments, the purge signal can
be in response to measured parameters of the refrigerant fluid flow
loop. For example, as shown in FIG. 5, a pressure sensor 80 at the
condenser 20 (e.g., a condenser discharge pressure sensor) can
provide a pressure signal to the controller 50, based on which the
controller can generate a purge signal control the expansion valve
68 and/or the vacuum pump 58.
[0048] Various control schemes can be utilized for operating the
vacuum pump 58 (or other prime mover) and the expansion valve 68
(or other control device). For example, in some embodiments, the
controller 50 can be configured to operate the control device to
provide a varying flow rate through the connection 67 during purge.
In some embodiments, the controller 50 can be configured to operate
a vacuum pump 58 or other prime mover at a constant pressure during
purge. In some embodiments, the controller 50 can be configured to
operate the vacuum pump 58 or other prime mover at varying pressure
during purge. In some embodiments, the controller 50 can be
configured to vary vacuum pressure or on/off status (with "off"
including a vacuum shut-off valve (not shown)) during purge in
coordination with varying settings of the control valve 68 or other
control device. For example, in some embodiments, the controller 50
can be configured to alternately operate the vacuum pump 58 or
other prime mover with the expansion valve 68 or other control
device closed and suspend operation of the vacuum pump 58 or other
prime mover with the expansion valve 68 or other control device
open. In some embodiments, the expansion valve 68 or other control
device can be left open while the vacuum pump 58 or other prime
mover is cycled on or off or with varying output. In some
embodiments, the vacuum pump 58 or other prime mover can be
operated continuously or at constant pressure while the expansion
valve 68 or other control device is cycled open and closed or to
vary the flow rate or pressure drop across the control device.
[0049] The term "about", if used, is intended to include the degree
of error associated with measurement of the particular quantity
based upon the equipment available at the time of filing the
application. For example, "about" can include a range of .+-.8% or
5%, or 2% of a given value.
[0050] The terminology used herein is for the purpose of describing
particular embodiments only and is not intended to be limiting of
the present disclosure. As used herein, the singular forms "a",
"an" and "the" are intended to include the plural forms as well,
unless the context clearly indicates otherwise. It will be further
understood that the terms "comprises" and/or "comprising," when
used in this specification, specify the presence of stated
features, integers, steps, operations, elements, and/or components,
but do not preclude the presence or addition of one or more other
features, integers, steps, operations, element components, and/or
groups thereof.
[0051] While the present disclosure has been described with
reference to an exemplary embodiment or embodiments, it will be
understood by those skilled in the art that various changes may be
made and equivalents may be substituted for elements thereof
without departing from the scope of the present disclosure. In
addition, many modifications may be made to adapt a particular
situation or material to the teachings of the present disclosure
without departing from the essential scope thereof. Therefore, it
is intended that the present disclosure not be limited to the
particular embodiment disclosed as the best mode contemplated for
carrying out this present disclosure, but that the present
disclosure will include all embodiments falling within the scope of
the claims.
* * * * *