U.S. patent application number 13/121486 was filed with the patent office on 2011-07-21 for liquid vapor separation in transcritical refrigerant cycle.
This patent application is currently assigned to CARRIER CORPORATION. Invention is credited to Yu H. Chen, Jason Scarcella.
Application Number | 20110174014 13/121486 |
Document ID | / |
Family ID | 42074150 |
Filed Date | 2011-07-21 |
United States Patent
Application |
20110174014 |
Kind Code |
A1 |
Scarcella; Jason ; et
al. |
July 21, 2011 |
LIQUID VAPOR SEPARATION IN TRANSCRITICAL REFRIGERANT CYCLE
Abstract
A refrigerant vapor compression system includes a flash tank
disposed in the refrigerant circuit intermediate a refrigerant heat
rejection heat exchanger and a refrigerant heat absorption heat
exchanger. The flash tank has a shell defining an interior volume
having an upper chamber, a lower chamber and a middle chamber. A
first fluid passage establishes fluid communication between the
middle chamber and the upper chamber and a second fluid passage
establishing fluid communication between the middle chamber and the
lower chamber. An inlet port opens to the middle chamber. A first
outlet port opens to the upper chamber and a second outlet port
opens to the lower chamber.
Inventors: |
Scarcella; Jason; (Cicero,
NY) ; Chen; Yu H.; (Manlius, NY) |
Assignee: |
CARRIER CORPORATION
Farmington
CT
|
Family ID: |
42074150 |
Appl. No.: |
13/121486 |
Filed: |
September 29, 2009 |
PCT Filed: |
September 29, 2009 |
PCT NO: |
PCT/US09/58732 |
371 Date: |
March 29, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61101792 |
Oct 1, 2008 |
|
|
|
Current U.S.
Class: |
62/510 ; 62/498;
62/512 |
Current CPC
Class: |
F25B 2700/1933 20130101;
F25B 41/39 20210101; F25B 2700/195 20130101; F25B 2700/21151
20130101; F25B 43/006 20130101; F25B 2400/13 20130101; F25B
2309/061 20130101; F25B 2400/23 20130101; F25B 2400/0411 20130101;
F25B 1/10 20130101; F25B 2600/0261 20130101; F25B 31/008 20130101;
F25B 2700/2109 20130101; F25B 2700/21163 20130101; F25B 2700/2113
20130101; F25B 9/008 20130101 |
Class at
Publication: |
62/510 ; 62/498;
62/512 |
International
Class: |
F25B 1/10 20060101
F25B001/10; F25B 1/00 20060101 F25B001/00; F25B 43/00 20060101
F25B043/00 |
Claims
1. A transport refrigeration refrigerant vapor compression system
operating in a transcritical refrigeration cycle comprising: a
compression device for compressing a refrigerant vapor to a
supercritical refrigerant pressure, a gas cooler operating at a
supercritical refrigerant pressure, and an evaporator operating at
a subcritical refrigerant pressure, said compression device, said
gas cooler and said evaporator connected in refrigerant flow
communication in a refrigerant circuit; a primary expansion device
disposed in said refrigerant circuit between said gas cooler and
said evaporator; a secondary expansion device disposed in said
refrigerant circuit between said gas cooler and said primary
expansion device; a flash tank disposed in the refrigerant circuit
upstream with respect to refrigerant flow of said primary expansion
device and downstream with respect to refrigerant flow of said
secondary expansion device, said flash tank having: a shell
defining an interior volume, said interior volume divided into an
upper chamber, a lower chamber and a middle chamber; a first fluid
passage establishing fluid communication between the middle chamber
and the upper chamber; a second fluid passage establishing fluid
communication between the middle chamber and the lower chamber; an
inlet port in fluid communication with the middle chamber for
receiving the refrigerant flow having traversed the secondary
expansion device; a first outlet port in fluid communication with
the upper chamber for discharging a vapor phase of the refrigerant
flow from said flash tank separator; and a second outlet port in
fluid communication with the lower chamber for discharging a liquid
phase of the refrigerant flow from said flash tank into the
refrigerant circuit.
2. The transport refrigeration refrigerant vapor compression system
as recited in claim 1 further comprising: a refrigerant vapor
injection line establishing refrigerant flow communication between
the first outlet port in fluid communication with the upper chamber
of said flask tank and an intermediate pressure stage of said
compression device.
3. The transport refrigeration refrigerant vapor compression system
as recited in claim 1 further comprising: a refrigerant liquid
injection line establishing refrigerant flow communication between
the second outlet port in fluid communication with the lower
chamber of said flash tank and an intermediate pressure stage of
said compression device.
4. The transport refrigerant vapor compression system as recited in
claim 1 wherein said flash tank further comprises: a lower plate
and an upper plate disposed in spaced relationship within the
interior volume defined by said shell, each of said lower plate and
said upper plate extending across the interior volume thereby
sectioning the interior volume into the lower chamber, the middle
chamber and the lower chamber; a first opening extending through
said upper plate and forming the first fluid passage establishing
fluid communication between said middle chamber and said upper
chamber; and a second opening extending through said lower plate
and forming the second fluid passage establishing fluid
communication between said middle chamber and said lower
chamber.
5. The transport refrigerant vapor compression system as recited in
claim 1 wherein said flash tank further comprises: an elongated
support tube extending along a central vertical axis of said shell,
said support tube defining a conduit establishing fluid
communication between said lower chamber and said upper chamber;
and a helical spiral member extending about said vertical support
tube and defining a continuous spiral fluid flow passage, a first
portion of said continuous helical passage forming the first fluid
passage establishing fluid communication between the middle chamber
and the upper chamber and a second portion of said continuous
helical passage forming the second fluid passage establishing fluid
communication between the middle chamber and the lower chamber.
6. A refrigerant vapor compression system as recited in claim 1
wherein the refrigerant comprises carbon dioxide.
7. A refrigerant vapor compression system as recited in claim 1
wherein said compression device comprises a single compressor
having at least a first relatively lower pressure compression stage
and a second relatively higher pressure compression stage.
8. A refrigerant vapor compression system as recited in claim 1
wherein said compression device comprises a first compressor and a
second compressor disposed in said refrigerant circuit in series
refrigerant flow relationship with a discharge outlet of said first
compressor in refrigerant flow communication with a suction inlet
of said second compressor.
9. A refrigerant vapor compression system as recited in claim 5
further comprising: an upper equalization hole passing through said
support tube and located near an upper end of said support tube,
said upper equalization hole establishing fluid communication
between an upper region of said conduit and an upper region of said
continuous helical passage; and a lower equalization hole passing
through said support tube and located near a lower end of said
support tube, said lower equalization hole establishing fluid
communication between a lower region of said conduit and a lower
region of said continuous helical passage.
10. A flash tank separator comprising: a shell defining an interior
volume; a lower plate and an upper plate disposed in spaced
relationship within the interior volume defined by said shell, each
of said lower plate and said upper plate extending across the
interior volume thereby sectioning the interior volume into the
lower chamber, the middle chamber and the lower chamber; a first
opening extending through said upper plate and establishing fluid
communication between said middle chamber and said upper chamber; a
second opening extending through said lower plate and establishing
fluid communication between said middle chamber and said lower
chamber; an inlet port in fluid communication with the middle
chamber for receiving a flow of a mixed liquid phase and vapor
phase fluid; a first outlet port in fluid communication with the
upper chamber for discharging a vapor phase of the refrigerant flow
from the upper chamber; and a second outlet port in fluid
communication with the lower chamber for discharging a liquid phase
from the lower chamber.
11. The flash tank separator as recited in claim 10 wherein the
first opening in said upper plate and the second opening in said
lower plate are disposed remotely from each other.
12. The flash tank separator as recited in claim 10 further
comprising an inlet tube penetrating said shell and having a fluted
outlet defining said inlet port.
13. A flash tank separator comprising: a shell defining an interior
volume having an upper chamber, a middle chamber and a lower
chamber; an elongated support tube extending along a central
vertical axis of said shell between the lower chamber and the upper
chamber; a helical spiral member extending about said vertical
support tube and defining a continuous spiral fluid flow passage, a
first portion of said continuous helical passage establishing fluid
communication between the middle chamber and the upper chamber and
a second portion of said continuous helical passage establishing
fluid communication between the middle chamber and the lower
chamber; an upper equalization hole passing through said support
tube and located near an upper end of said support tube, said upper
equalization hole establishing fluid communication between an upper
region of said conduit and an upper region of said continuous
helical passage; a lower equalization hole passing through said
support tube and located near a lower end of said support tube,
said lower equalization hole establishing fluid communication
between a lower region of said conduit and a lower region of said
continuous helical passage; an inlet port in fluid communication
with the middle chamber for receiving the refrigerant flow having
traversed the secondary expansion device; a first outlet port in
fluid communication with the upper chamber for discharging a gas
phase of the refrigerant flow from said flash tank separator; and a
second outlet port in fluid communication with the lower chamber
for discharging a liquid phase of the refrigerant flow from said
flash tank into the refrigerant circuit.
14. The flash tank separator as recited in claim 13 further
comprising an inlet tube penetrating said shell and having a outlet
defining said inlet port for directing an incoming flow of a mixed
liquid phase and vapor phase fluid to pass circumferentially along
an inner wall of said shell.
Description
FIELD OF THE INVENTION
[0001] This invention relates generally to refrigerant vapor
compression systems and, more particularly, to improving the
separation of a two-phase refrigeration flow into a liquid portion
and a vapor portion in a refrigerant vapor compression system
having a flash tank economizer and operating in a transcritical
cycle.
BACKGROUND OF THE INVENTION
[0002] Refrigerant vapor compression systems are well known in the
art and commonly used in transport refrigeration systems for
refrigerating air or other gaseous fluid supplied to a temperature
controlled cargo space of a truck, trailer, container or the like
for transporting perishable/frozen items by truck, rail, ship or
intermodal. Refrigerant vapor compression systems used in
connection with transport refrigeration systems are generally
subject to stringent operating conditions due to the wide range of
operating load conditions and the wide range of outdoor ambient
conditions over which the refrigerant vapor compression system must
operate to maintain product within the cargo space at a desired
temperature. The desired temperature at which the cargo needs to be
stored during transport can also vary over a wide range depending
on the nature of cargo to be preserved. The refrigerant vapor
compression system must not only have sufficient capacity to
rapidly pull down the temperature of product loaded into the cargo
space at ambient temperature, but also operate efficiently at low
load when maintaining a stable product temperature during
transport. Additionally, transport refrigerant vapor compression
systems are subject to vibration and movements not experienced by
stationary refrigerant vapor compression systems. Transport
refrigeration systems are also subject to size restrictions due to
limitations on available space not generally associated with
stationary refrigerant vapor compression systems, such as air
conditioners and heat pumps.
[0003] Traditionally, conventional refrigerant vapor compression
systems used in transport refrigeration applications commonly
operate at subcritical refrigerant pressures and typically include
a compressor, a condenser, and an evaporator, and expansion device,
commonly an expansion valve, disposed upstream, with respect to
refrigerant flow, of the evaporator and downstream of the
condenser. These basic refrigerant system components are
interconnected by refrigerant lines in a closed refrigerant
circuit, arranged in accord with known refrigerant vapor
compression cycles, and operated in the subcritical pressure range
for the particular refrigerant in use. Refrigerant vapor
compression systems operating in the subcritical range are commonly
charged with fluorocarbon refrigerants such as, but not limited to,
hydrochlorofluorocarbons (HCFCs), such as R22, and more commonly
hydrofluorocarbons (HFCs), such as R134a, R410A, R404A and
R407C.
[0004] In today's market, greater interest is being shown in
"natural" refrigerants, such as carbon dioxide, for use in air
conditioning and transport refrigeration systems instead of HFC
refrigerants. However, because carbon dioxide has a low critical
temperature and a low liquid phase density to vapor phase density
ratio, most refrigerant vapor compression systems charged with
carbon dioxide as the refrigerant are designed for operation in the
transcritical pressure regime. In refrigerant vapor compression
systems operating in a subcritical cycle, both the condenser and
the evaporator heat exchangers operate at refrigerant temperatures
and pressures below the refrigerant's critical point. However, in
refrigerant vapor compression systems operating in a transcritical
cycle, the heat rejection heat exchanger, which functions as a gas
cooler rather than a condenser, operates at a refrigerant
temperature and pressure in excess of the refrigerant's critical
point, while the evaporator operates at a refrigerant temperature
and pressure in the subcritical range. Thus, for a refrigerant
vapor compression system operating in a transcritical cycle, the
difference between the refrigerant pressure within the gas cooler
and refrigerant pressure within the evaporator is
characteristically substantially greater than the difference
between the refrigerant pressure within the condenser and the
refrigerant pressure within the evaporator for a refrigerant vapor
compression system operating in a subcritical cycle.
[0005] It is also common practice to incorporate an economizer into
the refrigerant circuit. So equipped, the refrigerant vapor
compression system may be selectively operated in an economized
mode to increase the capacity of the refrigerant vapor compression
system. In some refrigerant vapor compression systems operating in
a transcritical mode, a flash tank economizer is incorporated into
the refrigerant circuit between the gas cooler and the evaporator.
In such case, the refrigerant vapor leaving the gas cooler is
expanded through an expansion device, such as a thermostatic
expansion valve or an electronic expansion valve, prior to entering
the flash tank wherein the expanded refrigerant separates into a
liquid refrigerant component and a vapor refrigerant component. The
vapor component of the refrigerant is thence directed from the
flash tank into an intermediate pressure stage of the compression
process. The liquid component of the refrigerant is directed from
the flash tank through the system's main expansion valve prior to
entering the evaporator. U.S. Pat. No. 6,385,980 discloses a
transcritical refrigerant vapor compression system incorporating a
flash tank economizer in the refrigerant circuit between the gas
cooler and the evaporator.
SUMMARY OF THE INVENTION
[0006] A transport refrigeration refrigerant vapor compression
system operating in a transcritical refrigeration cycle includes: a
compression device for compressing a refrigerant vapor to a
supercritical refrigerant pressure, a gas cooler operating at a
supercritical refrigerant pressure, and an evaporator operating at
a subcritical refrigerant pressure connected in refrigerant flow
communication in a refrigerant circuit; a primary expansion device
disposed in the refrigerant circuit between the gas cooler and the
evaporator; a secondary expansion device disposed in the
refrigerant circuit between the gas cooler and the primary
expansion device; and a flash tank disposed in the refrigerant
circuit upstream with respect to refrigerant flow of the primary
expansion device and downstream with respect to refrigerant flow of
the secondary expansion device.
[0007] The flash tank has a shell defining an interior volume
having an upper chamber, a lower chamber and a middle chamber; a
first fluid passage establishing fluid communication between the
middle chamber and the upper chamber; a second fluid passage
establishing fluid communication between the middle chamber and the
lower chamber; an inlet port in fluid communication with the middle
chamber for receiving the refrigerant flow having traversed the
secondary expansion device; a first outlet port in fluid
communication with the upper chamber for discharging a gas phase of
the refrigerant flow from the flash tank separator; and a second
outlet port in fluid communication with the lower chamber for
discharging a liquid phase of the refrigerant flow from the flash
tank into the refrigerant circuit.
[0008] In an embodiment, the flash tank further includes: a lower
plate and an upper plate disposed in spaced relationship within the
interior volume defined by the shell, each of which extends across
the interior volume thereby sectioning the interior volume into the
lower chamber, the middle chamber and the lower chamber; a first
opening extending through the upper plate and forming the first
fluid passage establishing fluid communication between the middle
chamber and the upper chamber; and a second opening extending
through the lower plate and forming the second fluid passage
establishing fluid communication between the middle chamber and the
lower chamber.
[0009] In an embodiment, the flash tank includes: an elongated
support tube extending along a central vertical axis of its shell
and defining a conduit establishing fluid communication between the
lower chamber and the upper chamber; and a helical spiral member
extending about the vertical support tube and defining a continuous
spiral fluid flow passage. A first portion of the continuous
helical passage forms the first fluid passage establishing fluid
communication between the middle chamber and the upper chamber. A
second portion of the continuous helical passage forms the second
fluid passage establishing fluid communication between the middle
chamber and the lower chamber. An upper equalization hole passing
through the support tube near an upper end thereof may be provided
to establish fluid communication between the upper region of the
conduit defined by the support tube and the upper chamber, and a
lower equalization hole passing through the support tube near a
lower end thereof may be provided to establish fluid communication
between the lower region of the conduit defined by the support tube
and the lower chamber.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] For a further understanding of the invention, reference will
be made to the following detailed description of the invention
which is to be read in connection with the accompanying drawing,
where:
[0011] FIG. 1 is a schematic diagram illustrating a first exemplary
embodiment of a refrigerant vapor compression system operating in a
transcritical cycle;
[0012] FIG. 2 is a schematic diagram illustrating a second
exemplary embodiment of a refrigerant vapor compression system
operating in a transcritical cycle;
[0013] FIG. 3 is a sectioned perspective view of a first exemplary
embodiment of the flash tank of the refrigerant vapor compression
system shown in FIG. 1; and
[0014] FIG. 4 is a sectioned perspective view of a first exemplary
embodiment of the flash tank of the refrigerant vapor compression
system shown in FIG. 2.
DETAILED DESCRIPTION OF THE INVENTION
[0015] Referring now to FIGS. 1 and 2, there are depicted therein
exemplary embodiments of a refrigerant vapor compression system 100
suitable for use in a transport refrigeration system for
refrigerating the air or other gaseous atmosphere within the
temperature controlled cargo space 200 of a truck, trailer,
container or the like for transporting perishable/frozen goods. The
refrigerant vapor compression system 100 is particularly adapted
for operation in a transcritical cycle with a low critical
temperature refrigerant, such as for example, but not limited to,
carbon dioxide. The refrigerant vapor compression system 100
includes a multi-step compression device 20, a refrigerant heat
rejecting heat exchanger 40 and a refrigerant heat absorbing heat
exchanger 50, also referred to herein as an evaporator, with
refrigerant lines 2, 4 and 6 connecting the aforementioned
components in refrigerant flow communication in a refrigerant
circuit. A primary expansion device 55, such as for example an
electronic expansion valve, operatively associated with the
evaporator 50 is disposed in the refrigerant circuit in refrigerant
line 4 between the refrigerant heat rejection heat exchanger 40 and
the evaporator 50. A secondary expansion device 65, such as for
example an electronic expansion valve, is disposed in the
refrigerant circuit in refrigerant line 4 between the refrigerant
heat rejecting heat exchanger 40 and the primary expansion device
55. Additionally, a flash tank 10A, 10B is disposed in refrigerant
line 4 of the primary refrigerant circuit downstream with respect
to refrigerant flow of the secondary expansion device 65 and
upstream of the primary expansion device 55. Thus, the flash tank
10A, 10B is position in the refrigerant circuit downstream with
respect to refrigerant flow of the refrigerant heat rejecting heat
exchanger 40 and upstream with respect to refrigerant flow of the
evaporator 50.
[0016] In a refrigerant vapor compression system operating in a
transcritical cycle, the refrigerant heat rejecting heat exchanger
40 operates at a pressure above the critical point of the
refrigerant and therefore functions to cool supercritical
refrigerant vapor passing therethrough in heat exchange
relationship with a cooling medium, such as for example, but not
limited to ambient air or water, and may be also be referred to
herein as a gas cooler. In the depicted embodiments, the
refrigerant heat rejecting heat exchanger 40 includes a finned tube
heat exchanger 42, such as for example a fin and round tube heat
exchange coil or a fin and mini-channel flat tube heat exchanger,
through which the refrigerant passes in heat exchange relationship
with ambient air being drawn through the finned tube heat exchanger
42 by the fan(s) 44 associated with the gas cooler 40.
[0017] The refrigerant heat absorption heat exchanger 50 serves an
evaporator wherein refrigerant liquid is passed in heat exchange
relationship with a fluid to be cooled, most commonly air or an air
and inerting gas mixture, drawn from and to be returned to a
temperature controlled environment 200, such as the cargo box of a
refrigerated transport truck, trailer or container. In the depicted
embodiments, the refrigerant heat absorbing heat exchanger 50
comprises a finned tube heat exchanger 52 through which refrigerant
passes in heat exchange relationship with air drawn from and
returned to the refrigerated cargo box 200 by the evaporator fan(s)
54 associated with the evaporator 50. The finned tube heat
exchanger 52 may comprise, for example, a fin and round tube heat
exchange coil or a fin and mini-channel flat tube heat
exchanger.
[0018] The compression device 20 functions to compress the
refrigerant to a supercritical pressure and to circulate
refrigerant through the primary refrigerant circuit as will be
discussed in further detail hereinafter. The compression device 20
may comprise a single multiple-stage refrigerant compressor, such
as for example a scroll compressor, a screw compressor or a
reciprocating compressor, disposed in the primary refrigerant
circuit and having a first compression stage 20a and a second
compression stage 20b, such as illustrated in FIG. 1. The first and
second compression stages are disposed in series refrigerant flow
relationship with the refrigerant leaving the first compression
stage passing directly to the second compression stage for further
compression. Alternatively, the compression device 20 may comprise
a pair of independent compressors 20a and 20b, connected in series
refrigerant flow relationship in the primary refrigerant circuit
via a refrigerant line 8 connecting the discharge outlet port of
the first compressor 20a in refrigerant flow communication with the
suction inlet port of the second compressor 20b, such as
illustrated in FIG. 2. In the independent compressor embodiment,
the compressors 20a and 20b may be scroll compressors, screw
compressors, reciprocating compressors, rotary compressors or any
other type of compressor or a combination of any such
compressors.
[0019] In operation, high temperature, supercritical pressure
refrigerant vapor discharged from the second compression stage or
second compressor 20b of the compression device is cooled to a
lower temperature as it traverses the heat exchanger 42 of the gas
cooler 40 before traversing the secondary expansion device 65. In
traversing the secondary expansion device 65, the supercritical
pressure refrigerant vapor is expanded to a lower subcritical
pressure sufficient to establish a two-phase mixture of refrigerant
vapor and refrigerant liquid prior to entering the flash tank
10.
[0020] Referring now to FIGS. 3 and 4 in particular, flash tank
10A, 10B has a shell 120 that encloses an interior volume having an
upper chamber 122, a middle chamber 124 and a lower chamber 126.
The two-phase refrigerant flow having traversed the secondary
expansion device 65 passes into the central chamber 124 through an
inlet 125 opening in fluid communication with the middle chamber
124. The two-phase refrigerant flow received within the middle
chamber 124 separates into a vapor phase which migrates upwardly
into the upper chamber 122 and a liquid phase which migrates
downwardly into the lower chamber 126 of the shell 120 of the flash
tank 10A, 10B. The flash tank 10A, 10B also includes a first outlet
127 in fluid communication with the lower chamber 126 and a second
outlet 129 in fluid communication with the upper chamber 122.
[0021] The liquid phase refrigerant, which is typically saturated
liquid, passes from the lower chamber 126 of the flash tank 10A,
10B through a first outlet 127 in fluid communication with the
lower chamber 126 into refrigerant line 4 of the refrigerant
circuit. In one mode of operation, all of the liquid phase
refrigerant passing from the lower chamber 126 of the flash tank
10A, 10B traverses the primary refrigerant circuit expansion device
55 interdisposed in refrigerant line 4 upstream with respect to
refrigerant flow of the evaporator 50. As this liquid refrigerant
traverses the primary expansion device 55, it expands to a lower
pressure and temperature before entering the evaporator 50. The
evaporator 50 constitutes a refrigerant evaporating heat exchanger
through which expanded refrigerant passes in heat exchange
relationship with the air to be cooled, whereby the refrigerant is
vaporized and typically superheated. As in conventional practice,
the primary expansion device 55 meters the refrigerant flow through
the refrigerant line 4 to maintain a desired level of superheat in
the refrigerant vapor leaving the evaporator 50 to ensure that no
liquid is present in the refrigerant leaving the evaporator. The
low pressure refrigerant vapor leaving the evaporator 50 returns
through refrigerant line 6 to the suction port of the first
compression stage or first compressor 20a of the compression device
20.
[0022] In an embodiment, a refrigerant bypass line 5 may be
provided to permit bypass of all or a portion of the liquid phase
refrigerant passing through refrigerant line 4 from the lower
chamber 126 of the flash tank around the primary expansion device
55. The refrigerant bypass line 5 taps into refrigerant line 4 at a
first location upstream with respect to refrigerant flow of the
primary expansion device 55 and downstream with respect to
refrigerant flow of the flash tank 10A, 10B and at a second
location downstream with respect to refrigerant flow of the primary
expansion device 55 and upstream with respect to refrigerant flow
of the evaporator 50. A flow control device 57, such as for example
a solenoid valve having an open position and a closed position, may
be interdisposed in the refrigerant bypass line 5 for selectively
opening and closing the bypass flow passage to refrigerant flow
therethrough.
[0023] The refrigerant vapor compression system 100 also includes a
refrigerant vapor injection line 14 that establishes refrigerant
flow communication between the upper chamber 122 of the interior
volume defined within the shell 120 of the flash tank 10A, 10B via
the second outlet 129 of the flash tank 10A, 10B and an
intermediate stage of the compression process. The refrigerant
vapor compression system 100 may also include a refrigerant liquid
injection line 18 that establishes refrigerant flow communication
the lower chamber 126 of the interior volume defined within the
shell 120 of the flash tank 10A, 10B, typically via tapping
refrigerant line 4 at a location downstream with respect to
refrigerant flow of the flash tank 10A, 10B and upstream with
respect to refrigerant flow of the primary expansion valve 55, and
between an intermediate stage of the compression process. In the
exemplary embodiment of the refrigerant vapor compression system
100 depicted in FIG. 1, injection of refrigerant vapor or
refrigeration liquid into the intermediate pressure stage of the
compression process would be accomplished by injection of the
refrigerant vapor or refrigerant liquid into the refrigerant
passing from the first compression stage 20a into the second
compression stage 20b of a single compressor. In the exemplary
embodiment of the refrigerant vapor compression system 100 depicted
in FIG. 2, injection of refrigerant vapor or refrigeration liquid
into the intermediate pressure stage of the compression process
would be accomplished by injection of the refrigerant vapor or
refrigerant liquid into the refrigerant passing through refrigerant
line 8 from the discharge outlet of the first compressor 20a to the
suction inlet of the second compressor 20b.
[0024] The refrigerant vapor compression system 100 may also
include a compressor unload refrigerant line 16 that establishes
refrigerant flow communication between an intermediate pressure
stage of the compression device and the suction pressure portion of
the refrigerant circuit, i.e. refrigerant line 6 extending between
the outlet of the evaporator 50 and the suction inlet of the first
stage 20a of the compression device 20, as depicted in the FIG. 1
embodiment, or the suction inlet of the first compressor 20a, as
depicted in the FIG. 2 embodiment. Each of the refrigerant vapor
injection line 14 and the refrigerant liquid injection line 18 may
open in refrigerant flow communication with the compressor unload
refrigerant line 16, whereby the compressor unload refrigerant line
16 forms a downstream portion of both the refrigerant vapor
injection line 14 and the refrigerant liquid injection line 18. In
this manner, refrigerant vapor may pass through the refrigerant
vapor injection line 14 to be selectively injected either into an
intermediate stage of the compression process or into the suction
pressure portion of the refrigerant circuit. Similarly, refrigerant
liquid may pass through the refrigerant liquid injection line 18 to
be selectively injected either into an intermediate stage of the
compression process or into the suction pressure portion of the
refrigerant circuit. Additionally, to unload the compression
device, all or a portion of the refrigerant discharging from the
first stage 20a or the first compressor 20a may be passed through
the compressor unload refrigerant line 16 to the suction pressure
portion of the refrigerant circuit.
[0025] The refrigerant vapor compression system 100 may further
include a control system including a controller 70. In an
embodiment, the controller 70 may comprise a microprocessor
controller such as, by way of example, but not limitation, a
MicroLink.TM. controller available from Carrier Corporation of
Syracuse, N.Y., USA. The controller 70 is configured to operate the
refrigeration unit to maintain a predetermined thermal environment
within the enclosed interior volume 200, i.e. the cargo box,
wherein the product being transported is stored. The controller 70
maintains the predetermined environment by selectively controlling
the operation of the compressor 20, the condenser fan(s) 34
associated with the condenser heat exchanger coil 32, the
evaporator fan(s) 44 associated with the evaporator heat exchanger
coil 42, and a plurality of refrigerant flow control devices
operatively associated with the control 70. The plurality of flow
control devices operatively associated with the controller 70 may
include a flow control device 53 interdisposed in refrigerant line
18 for controlling the flow of liquid refrigerant passing
therethrough from the lower chamber 126 of the flash tank 10A, 10B,
and a flow control device 73 interdisposed in refrigerant line 14
for controlling the flow of vapor phase refrigerant therethrough
from the upper chamber 122 of the flask tank 10A, 10B. The
plurality of flow control devices operatively associated with the
controller 70 may also include a flow control device 93
interdisposed in the refrigerant line 16 for controlling the flow
of refrigerant therethrough to a suction portion of the refrigerant
circuit. Each of the aforementioned flow control devices 53, 73, 93
may comprise a flow control valve selectively positionable between
an open position wherein refrigerant flow may pass through the
refrigerant line in which the flow control valve is interdisposed
and a closed position wherein refrigerant flow is blocked through
the refrigerant line in which the flow control valve is
interdisposed. In an embodiment, each of the flow control valves
53, 73, 93 may comprise a two-position solenoid valve of the type
selectively positionable between a first open position and a second
closed position. The plurality of flow control devices operatively
associated with the controller 70 may also include the primary
expansion valve 55, the secondary expansion valve 65, and the flow
control device 57. In operation, the controller 70 may selectively
open and close various of these flow control devices operatively
associated therewith for selectively directing refrigerant flow
through the primary refrigerant circuit, as well as refrigerant
lines 5, 14, 16 and 18, as desired.
[0026] To facilitate control of the refrigeration system 100, the
controller 70 also monitors operating parameters at various points
in the refrigeration system through a plurality of sensors disposed
at selected locations throughout the system 100. Among the sensors
that may be provided include, among others not specifically shown:
an ambient air temperature sensor 90 which inputs into the
controller 70 a variable resistance value indicative of the ambient
air temperature in front of the condenser 30; a return air
temperature sensor 92 which inputs into the controller 70 a
variable resistance value indicative of the temperature of the air
leaving the evaporator 50 to return to the cargo box 200; a box air
temperature sensor 94 which inputs into the controller 70 a
variable resistance value indicative of the temperature of the air
within the cargo box 200, i.e. the product storage temperature; a
flash tank temperature sensor 101 which inputs into the controller
70 a variable resistance value indicative of the refrigerant
temperature entering the flash tank 10A, 10B; a flask tank pressure
sensor 102 which inputs a variable voltage indicative of the
refrigerant pressure entering the flash tank 10A, 10B; a compressor
suction temperature sensor 103 which inputs into the controller 70
a variable resistance value indicative of the refrigerant suction
temperature; a compressor suction pressure sensor 104 which inputs
into the controller 70 a variable voltage indicative of the
refrigerant suction pressure; a compressor discharge temperature
sensor 105 which inputs into the controller 70 a variable
resistance value indicative of the compressor discharge refrigerant
temperature; a compressor discharge pressure sensor 106 which
inputs into the controller 70 a variable voltage indicative of the
compressor discharge refrigerant pressure; a gas cooler temperature
sensor 107 which inputs into the controller 70 a variable
resistance value indicative of the refrigerant temperature having
traversed the gas cooler 40; a gas cooler pressure sensor 108 which
inputs a variable voltage indicative of the refrigerant pressure
having traversed the gas cooler 40. The pressure sensors 102, 104,
106, 108 may be conventional pressure sensors, such as for example,
pressure transducers, and the temperature sensors 90, 92, 94, 101,
103, 105, 107 may be conventional temperature sensors, such as for
example, thermocouples or thermistors. The aforementioned sensors
are merely examples of some of the various sensors that may be
associated with the system 100, and are not meant to limit the type
of sensors or transducers that may be provided.
[0027] The refrigerant vapor compression system 100 may be operated
in selected operating modes depending upon load requirements and
ambient conditions, such as for example, but not limited to, a box
temperature pull down mode, a deep frozen box temperature
maintenance mode, and a refrigerated product box temperature
maintenance mode. The controller 100 determines the desired mode of
operation based upon ambient conditions, box conditions, and
various sensed system controls and then positions the various flow
control valves accordingly.
[0028] As noted previously, a flash tank 10A, 10B is disposed in
refrigerant line 4 of the refrigerant circuit upstream with respect
to refrigerant flow of the primary expansion device 55 and
downstream with respect to refrigerant flow of the secondary
expansion device 65. Referring now to FIGS. 3 and 4 in particular,
as noted hereinbefore, the flash tank 10A, 10A includes a shell 120
defining an interior volume having an upper chamber 124, a lower
chamber 126 and a middle chamber 122. The shell 120 has a generally
cylindrical central portion 120-1 extending between an upper end
cap 120-2 and a lower end cap 120-3. The upper and lower end caps
120-2, 120-3 are attached in such a manner, for example by welding
or brazing or the like, as to form a sealed enclosure defining the
interior volume of the flash tank.
[0029] The flash tank 10A, 10B further includes an inlet port 125,
a first outlet port 127 and a second outlet port 129. The inlet
port 125 is in fluid communication with the middle chamber 124 for
receiving the refrigerant flow having traversed the secondary
expansion device. The inlet port 125 may be defined by the outlet
opening of a tube 160 that penetrates through the shell 120 and is
in fluid communication at its inlet end with refrigerant line 4 on
the upstream side (with respect to refrigerant flow) of the flash
tank. The second outlet port 129 is in fluid communication with the
upper chamber 122 for discharging a gas phase of the refrigerant
flow from the flash tank 10A, 10B. The second outlet port 129 may
be defined by the inlet opening of a tube 162 that penetrates
through the shell 120 and is in fluid flow communication at its
outlet end with refrigerant line 14. The first outlet port 127 is
in fluid communication with the lower chamber 126 for discharging a
liquid phase of the refrigerant flow from the flash tank 10A, 10B
into the refrigerant circuit. The first outlet port 127 may be
defined by the inlet opening of a tube 164 that penetrates through
the shell 120 and is in fluid flow communication at its outlet end
with refrigerant line 4 on the downstream side (with respect to
refrigerant flow) of the flash tank.
[0030] Referring now to FIG. 3, in the exemplary embodiment
depicted therein, the flash tank 10A includes a lower plate 130 and
an upper plate 140 disposed in spaced relationship within the
interior volume defined by the shell 120. Each of the plates 130,
140 extends across the interior volume and sealingly abuts the
inner wall of the generally cylindrical central portion 120-1 of
the shell 120 thereby sectioning the interior volume of the shell
120 into three separate chambers: the middle chamber 124 between
the two spaced apart plates 130, 140; the upper chamber 122 between
the upper plate 140 and the upper end cap 120-2; and the lower
chamber 126 between the lower plate 130 and the lower end cap
120-3. In this embodiment, a first fluid passage 142 is provided in
and extends through the upper plate 140 thereby establishing fluid
communication between the middle chamber 124 and the upper chamber
122, and a second fluid passage 132 is provided in and extends
through the lower plate 130 thereby establishing fluid
communication between the middle chamber 124 and the lower chamber
126.
[0031] In operation, the two-phase refrigerant flow passing into
the flash tank 10A through the inlet tube 160 into the middle
chamber 124 through the inlet port 125. Within the middle chamber
124, the two-phase flow separates due the density differential
existing between the liquid phase and the vapor phase. The vapor
phase refrigerant passes upwardly through the first fluid passage
142 to enter the upper chamber 122. The liquid phase refrigerant
passes downwardly through the second fluid passage 132 to enter the
lower chamber 126. The outlet portion of the inlet tube 160 may be
fluted whereby the two phase refrigerant flow passing through the
inlet port 125 decelerates as it enters the middle chamber 124. The
resulting deceleration enhances separation of the vapor and liquid
phases thereby reducing carryover of liquid refrigerant in the
vapor phase refrigerant flow passing upwardly through the first
passage 142 and the carry under of vapor phase refrigerant in the
liquid phase refrigerant flow passing downwardly through the second
fluid flow passage 132. Additionally, the first fluid passage 142
and the second fluid passage 132 may be located diametrically
opposite each other to further reduce the potential for carryover.
Also, the outlet end of the inlet tube 160 may extend into the
middle chamber 122 sufficiently that the inlet port 125 is
juxtaposed opposite the upper surface of the lower plate 130 and
the first fluid passage 142 in the upper plate 140 may be located
vertically above the fluted portion of the inlet tube 160 as
illustrated in FIG. 3. So located, a portion of the vapor phase
refrigeration would tend to flow upwardly along the fluted contour
of the outlet end of the inlet tube 160 to pass through the first
fluid passage 142, while almost all of the liquid phase of the
incoming refrigerant flow would spread out horizontally along the
upper surface of the lower plate 130. In this arrangement, the
second fluid passage 132 in the second plate 130 would be located
diametrically opposite the first fluid passage 142 and thus away
from the turbulent zone beneath the inlet port 125.
[0032] Referring now to FIG. 4, in the exemplary embodiment
depicted therein, the flash tank 10B includes a helical spiral
member 150 that extends about a vertical support tube 152 disposed
along the central axis of the shell 120. The radially outward edge
of the helical spiral member 150 sealingly abuts the inner wall of
the generally cylindrical central portion 120-1 of the shell 120.
The helical spiral member 150 thereby defines a continuous spiral
passage from extending between the lower chamber 126 and the upper
chamber 122. The inlet tube 160 opens into the continuous spiral
passage at a location between the upper chamber 124 and the lower
chamber 126, which is referred to in this embodiment as the middle
chamber 124. In an embodiment, the inlet tube 160 may be arranged
such that the two-phase refrigerant flow passing into the middle
chamber 124 through the inlet 125 enters tangentially along the
inner wall of the generally cylindrical central member 120-1 of the
shell 120. Due to the density differential between the vapor phase
and the liquid phase, the vapor phase refrigerant in the entering
two-phase flow will tend to flow generally upwardly through the
continuous spiral passage defined by the helical spiral member 150,
while the liquid phase of the two-phase flow will tend to flow
generally downwardly through the continuous spiral passage defined
by the helical spiral member 150. The central support tube 152 that
supports the helical spiral member 150 also defines an elongated
conduit 155 that extends along the central vertical axis of the
shell 120 thereby establishing fluid communication between the
upper chamber 122 and the lower chamber 126.
[0033] An upper equalization hole 154 and a lower equalization hole
156 opening through the wall of the tube 152 near the upper and
lower ends, respectively, of the tube 152. The upper equalization
hole 154 provides fluid communication between the upper chamber 122
and the conduit 155, while the lower equalization hole 156 provides
fluid communication between the lower chamber 126 and the conduit
155. The fluid path established between the upper equalization hole
154 and the lower equalization hole 156 via the conduit 155 permits
the fluid level in the conduit 155 defined within the support tube
152 to be equal to the fluid level within the continuous helical
passage defined between the outer wall of the central support tube
152 and the inner wall of the central portion 120-1 of the shell
120. This fluid path also provides for a relatively stagnant
refrigerant flow within the conduit 155 which enhances the
opportunity for improved phase separation.
[0034] Unlike flash tanks used in stationary refrigeration systems,
in transport refrigeration applications, the refrigerant vapor
compression system is subject to vibration and movement due to the
travel along roads, rail and sea. Consequently, refrigerant is the
flash tank 10A, 10B would be subject to sloshing, which tends to
increase intermixing if the vapor and liquid phases of the
refrigerant within the flash tank. The presence of the plates 130,
140 or the helical spiral member 150 serve to lessen the degree of
sloshing resulting from vibration and movement of the transport
refrigeration system. Additionally, the flash tanks 10A, 10B
include internal components that substantially improve separation
of the liquid phase and the vapor phase introduced into in the
flash tank, thereby maximizing the enthalpy difference of the
refrigerant across the evaporator which allows for limiting the
size of system components while optimizing the coefficient of
performance, COP, and energy efficiency rating, EER, of the system.
Additionally, the improved quality of the refrigerant vapor
withdrawn from the upper chamber of the flask tank 10A, 10B and
injected into the intermediate-stage of the compression process,
results in increased capacity of the refrigeration system. It is to
be understood that either embodiment of the flash tanks 10A, 10B
may be used in either the FIG. 1 embodiment or the FIG. 2
embodiment of the refrigerant vapor compression system 100.
[0035] Those skilled in the art will recognize that many variations
may be made to the particular exemplary embodiments described
herein. For example, the refrigerant vapor compression system may
also be operated in a subcritical cycle, rather than in a
transcritical cycle as described hereinbefore. While the present
invention has been particularly shown and described with reference
to the exemplary embodiments as illustrated in the drawings, it
will be understood by one skilled in the art that various changes
in detail may be effected therein without departing from the spirit
and scope of the invention as defined by the claims.
* * * * *