U.S. patent application number 11/816327 was filed with the patent office on 2009-01-22 for refrigeration circuit with improved liquid/vapour receiver.
Invention is credited to Neelkanth S. Gupte.
Application Number | 20090019878 11/816327 |
Document ID | / |
Family ID | 34993425 |
Filed Date | 2009-01-22 |
United States Patent
Application |
20090019878 |
Kind Code |
A1 |
Gupte; Neelkanth S. |
January 22, 2009 |
REFRIGERATION CIRCUIT WITH IMPROVED LIQUID/VAPOUR RECEIVER
Abstract
Refrigeration circuit comprising a compressor, a heat-rejecting
heat exchanger an expansion valve, a receiver (3), and a further
expansion valve/evaporator to provide cooling. A second heat
exchanger (24) is arranged in an upper gas portion of the receiver
and/or a third heat exchanger (34) is arranged in a lower liquid
portion of the receiver. A better liquid/vapour separation of the
refrigerant and/or sub-cooling of the liquid refrigerant are
achieved.
Inventors: |
Gupte; Neelkanth S.; (Katy,
TX) |
Correspondence
Address: |
CARLSON, GASKEY & OLDS, P.C.
400 WEST MAPLE ROAD, SUITE 350
BIRMINGHAM
MI
48009
US
|
Family ID: |
34993425 |
Appl. No.: |
11/816327 |
Filed: |
February 18, 2005 |
PCT Filed: |
February 18, 2005 |
PCT NO: |
PCT/US05/05411 |
371 Date: |
April 15, 2008 |
Current U.S.
Class: |
62/335 ;
62/56 |
Current CPC
Class: |
F25B 2400/075 20130101;
F25B 2400/053 20130101; F25B 2400/13 20130101; F25B 2400/23
20130101; F25B 41/39 20210101; F25B 40/02 20130101; F25B 1/10
20130101; F25B 2309/061 20130101; F25B 9/008 20130101 |
Class at
Publication: |
62/335 ;
62/56 |
International
Class: |
F25B 7/00 20060101
F25B007/00; F25D 3/00 20060101 F25D003/00 |
Claims
1. Refrigeration circuit for circulating a refrigerant in a
predetermined flow direction, comprising in flow direction a first
compressor device, a heat-rejecting heat exchanger, a first
expansion device, a receiver having in its interior an upper
portion, being in flow communication with the first expansion
device, and a lower portion, a second expansion device being in
flow communication with the lower portion of the receiver, and a
first evaporator; and comprising a further flow path between the
upper portion of the receiver and the suction side of a compressor,
the pressure side of which is in flow communication with the
entrance of said heat-rejecting heat exchanger; wherein at least
one element of the group consisting of the following elements (a)
and (b) is provided: (a) a second heat exchanger is arranged in
said upper portion of said receiver, the entrance of the second
heat exchanger being in flow communication with the exit of said
heat-rejecting heat exchanger and the exit of the second heat
exchanger being in flow communication with the entrance of said
first expansion device, (b) said further flow path comprises a
third expansion device and, downstream thereof, a third heat
exchanger arranged in said lower portion of said receiver.
2. Refrigeration circuit according to claim 1, wherein said
compressor connected to said further flow path is part of said
first compressor device.
3. Refrigeration circuit according to any one of claims 1 to 2,
wherein said refrigerant is CO.sub.2.
4. Refrigeration circuit according to any one of claims 1 to 3,
wherein said first compressor device comprises a parallel group of
several compressors.
5. Refrigeration circuit according to any one of claims 1 to 4,
further comprising a branch circuit, branching off from a location
located in a section of said circuit which section extends from
said lower portion of said receiver to the entrance of said second
expansion device; the branch circuit comprising in flow direction a
fourth expansion device, a second evaporator, and a second
compressor device; and the branch circuit, at its downstream end,
being in flow communication with the suction side of said first
compressor device.
6. Refrigeration circuit according to any one of claims 1 to 5,
wherein several parallel first evaporators are provided.
7. Refrigeration apparatus comprising a refrigeration circuit as
specified in any one of claims 1 to 6.
8. Refrigeration method, comprising: (a) circulating a refrigerant
in a refrigeration circuit comprising, in flow direction, a first
compressor device, a heat-rejecting heat exchanger, a first
expansion device, a receiver having in its interior an upper
portion, being in flow communication with the first expansion
device, and a lower portion, a second expansion device being in
flow communication with the lower portion of the receiver, and a
first evaporator; (b) the refrigeration circuit further comprising
a further flow path provided between the upper portion of the
receiver and the suction side of a compressor, the pressure side of
which is in fluid communication with the entrance of said
heat-rejecting heat exchanger; (c) said refrigeration method
comprising at least one step of the group of steps consisting of
(i) operating a heat source in said upper portion of said receiver,
(ii) operating a heat sink in said lower portion of said
receiver.
9. Refrigeration method according to claim 8, wherein the
refrigerant is CO.sub.2.
Description
[0001] This invention relates to a refrigeration circuit comprising
a first compressor device, a heat-rejecting heat exchanger, a first
expansion device, a receiver having an upper portion and a lower
portion, a second expansion device, and a first evaporator. The
refrigeration circuit further comprises a flow path between the
upper portion of the receiver and a compressor, the pressure side
of which is in flow communication with the entrance of the
heat-rejecting heat exchanger.
[0002] The refrigeration circuit preferably is of the type designed
for CO.sub.2 as a refrigerant, but is not limited thereto.
[0003] The refrigeration circuit is of the two stage expansion
type, wherein the refrigerant first is expanded in first stage
expansion. The first stage expansion provides cooling to complete
condensation of the refrigerant in the receiver. Furthermore, the
section of the refrigeration circuit extending from the receiver to
the compressor device is at a substantially lower pressure level
than the remaining section of the refrigeration circuit extending
from the compressor device to first expansion device.
[0004] It is an object of the invention to provide a refrigeration
circuit with an improved receiver.
[0005] It is a further object of the invention to provide a
refrigeration circuit with a receiver outputting from its upper
portion flash gas having substantially no liquid droplets
therein.
[0006] It is a still further object of the invention to provide a
refrigeration circuit with a receiver outputting a sub-cooled
liquid refrigerant.
[0007] In accordance with one embodiment of the invention there is
provided a refrigeration circuit for circulating a refrigerant in a
predetermined flow direction, comprising in flow direction a first
compressor device, a heat-rejecting heat exchanger, a first
expansion device, a receiver having in its interior an upper
portion, being in flow communication with the first expansion
device, and a lower portion, a second expansion device being in
flow communication with the lower portion of the receiver, and a
first evaporator; and comprising a further flow path between the
upper portion of the receiver and the suction side of a compressor,
the pressure side of which is in flow communication with the
entrance of said heat-rejecting heat exchanger; wherein at least
one element of the group consisting of the following elements (a)
and (b) is provided: (a) a second heat exchanger is arranged in
said upper portion of said receiver, the entrance of the second
heat exchanger being in flow communication with the exit of said
heat-rejecting heat exchanger and the exit of the second heat
exchanger being in flow communication with the entrance of said
first expansion device, (b) said further flow path comprises a
third expansion device and, downstream thereof, a third heat
exchanger arranged in said lower portion of said receiver.
[0008] The second heat exchanger arranged in the upper portion of
the receiver exchanges heat against the vapour contained in the
upper portion of the receiver. Any liquid droplets that may be
present in the upper portion of the receiver will be evaporated and
entrained into the further flow path.
[0009] The third expansion device and the third heat exchanger
arranged in lower portion of the receiver provide sub-cooling the
liquid in the lower portion of the receiver. Such sub-cooled liquid
refrigerant results in more efficient cooling effect by the first
evaporator and reduces the formation of refrigerant vapour in the
section of the circuit extending from the receiver to the second
expansion device.
[0010] All in all the improved receiver provides for a more perfect
separation into a gaseous phase of the refrigerant having
substantially no content of liquid droplets, and a liquid phase
that is sub-cooled and has less tendency to vapour formation.
[0011] The first compressor device may be a single compressor or a
parallel group of several compressors. The compressor device may be
of the type comprising a control of its performance, for example by
way of controlling its rotational speed dependent on the pressure
level of the compressed gaseous refrigerant to be achieved.
[0012] The compressor associated to the further flow path starting
from the upper portion of the receiver, may be a further
compressor. The suction side of such further compressor may be at a
higher pressure level than the suction side of the first-mentioned
compressor device, or may be a substantially the same pressure
level as the first-mentioned compressor device. It is possible to
combine the compressor, that is associated to the further flow
path, with the first-mentioned compressor device, either by using
one and the same compressor for compressing the gaseous refrigerant
coming from the second expansion device as well as the gaseous
refrigerant coming from the upper portion of the receiver, or by
combining the further compressor, that is associated to the further
flow path, into a parallel group of compressors forming the first
compressor device.
[0013] In accordance with an embodiment of the invention, the
refrigeration circuit further comprises a branch circuit, branching
off from a location located in a section of said circuit which
section extends from said lower portion of said receiver to the
entrance of said second expansion device; the branch circuit
comprising in flow direction a fourth expansion device, a second
evaporator, and a second compressor device; and the branch circuit,
at its downstream end, being in flow communication with the suction
side of said first compressor device.
[0014] In such embodiment, the branch circuit provides low
temperature cooling, for example for deep-freezing purposes. As
compared to such low temperature cooling, the second expansion
device and the first evaporator provide for medium temperature
cooling, for example for keeping food and beverages at a
temperature level of 0 to 10.degree. C.
[0015] The refrigeration circuit may comprise one or several second
expansion devices/first evaporators, arranged in parallel, and one
or several fourth expansion devices/second evaporators, arranged in
parallel, if any.
[0016] The refrigerant in the refrigeration circuit may be a
one-component refrigerant or a multiple-components refrigerant.
[0017] In the preceding description, reference has been made to
various expansion devices. It should be stressed that expansion
devices of various constructions and designs may be provided. A
quite common form of expansion device is an expansion valve. The
expansion device may be a throttling device or a throttle valve.
The expansion device, depending on its location, the temperature
level, and the pressure level, may serve to expand liquid
refrigerant to gaseous refrigerant or may expand gaseous
refrigerant from a higher pressure level to a lower pressure
level.
[0018] This invention further relates to a refrigeration apparatus
comprising a refrigeration circuit as disclosed in the present
application.
[0019] The refrigeration apparatus of this invention may be
provided as a heat pump. The technical elements of cooling
apparatus and heat pumps are the same. With the cooling apparatus,
the purpose of cooling is the primary purpose, and the related
generation of heat is normally a side effect. With heat pumps, the
generation of heat is the desired purpose, whereas the related
cooling effect of the evaporator(s) is normally considered a less
useful side effect. This invention also discloses a heat pump
having a circuit as disclosed in the present application. Such
circuit may be designated a refrigeration circuit because it
contains a refrigerant undergoing condensation and evaporation.
Some times people prefer to use the term working fluid rather than
to use the term refrigerant when describing a heat pump.
[0020] A refrigeration circuit containing CO.sub.2 as a refrigerant
may be a circuit operated in transcritical cycle, or may be a
circuit operated in subcritical cycle, or may be a circuit operable
in transcritical cycle or in subcritical cycle depending on
parameters such as environmental temperature and pressure level
after the compressor device. In typical applications such as
cooling temperature sensitive products, deep-freezing, cooling
buildings, the refrigeration circuit does not reach a subcritical
temperature level at the heat-rejecting heat exchanger, at least in
summer time season; the circuit is operated in transcritical cycle.
In such a situation the heat-rejecting heat exchanger operates as a
gas cooler. In case of a subcritical cycle, the heat-rejecting heat
exchanger operates as a combined gas cooler and condenser.
[0021] The main functions of the receiver are to permanently keep
available a sufficient quantity of liquid refrigerant and to
provide a separation between liquid refrigerant and gaseous
refrigerant (vapour). In case of transcritical cycle, the
condensation of refrigerant by means of flash cooling provided by
the first expansion device is a further function.
[0022] The refrigeration apparatus/heat pump of this invention has
a number of preferred fields of application. The most important are
cooling food and beverages in shops, restaurants or other locations
of storage; cooling other temperature-sensitive products such as
pharmaceuticals; deep-freezing; cooling buildings of any sort;
cooling cars and any other type of vehicles in the broad sense,
such as aircrafts, ships, railway cars etc.
[0023] This invention further relates to a refrigeration method. In
an embodiment of the invention the refrigeration method comprises
at least one step of the group of steps consisting of (i) operating
a heat source in said upper portion of said receiver, (ii)
operating a heat sink in said lower portion of said receiver.
[0024] An exemplary embodiment of the invention will be described
in the following. The features of such embodiment are preferred
features of the refrigeration circuit of this invention:
[0025] FIG. 1 shows a diagram of a refrigeration circuit for
elucidating the basic configuration of such a circuit;
[0026] FIG. 2 shows a receiver/separator on a larger scale, which
may be incorporated in the refrigeration circuit of FIG. 1.
[0027] The total refrigeration circuit shown in FIG. 1 comprises a
first-described (basic) circuit, a second-described further flow
path, and a third-described branch circuit, and some additional
elements.
[0028] The basic circuit, when beginning with a compressor device 6
and progressing in flow direction of the CO.sub.2-refrigerant,
comprises the following elements: [0029] compressor device 6 or 6
and 6'; [0030] conduit 7; [0031] heat-rejecting heat exchanger 1
(gas cooler and/or condenser); [0032] conduit 2; [0033] first
expansion valve a; [0034] receiver 3; [0035] conduit 4; [0036] two
parallel second expansion valves b and c; [0037] two parallel
evaporators E2 and E3; [0038] conduit 5 back to compressor device
6.
[0039] The compressor device 6 comprises three parallel compressors
and a further compressor 6' to be described in more detail further
below. The suction sides of the three compressors are supplied by a
common supply space 20. Typically, the compressor device 6
compresses the supplied gaseous CO.sub.2 to a pressure in the range
of 50 to 120 bar, whereby the temperature of the gaseous compressed
CO.sub.2 is increased to about 50 to 150.degree. C. In subcritical
operation the pressure of the compressed gaseous CO.sub.2 would
typically be in the range of 40 to 70 bar.
[0040] The heat-rejecting heat exchanger removes heat from the
CO.sub.2. In subcritical operation, the CO.sub.2 is typically
cooled to 10 to 30.degree. C. and condensed in the heat-rejecting
heat exchanger 1; in this case heat exchanger 1 works as a combined
gas cooler and condenser. In transcritical operation, the CO.sub.2
is typically cooled to a temperature of 25 to 45.degree. C.,
without condensation of a substantial part of the CO.sub.2, in the
heat-rejecting heat exchanger; in this case it works as a gas
cooler. In order to remove heat from the CO.sub.2, the heat
exchanger 1 is gas cooled or liquid (water) cooled.
[0041] The vapour or liquid/vapour mixture or liquid CO.sub.2 in
subcritical operation, is expanded by the expansion valve a
provided next to the receiver 3, thereby providing flash gas in an
upper portion of the receiver 3. Typically, the pressure level in
the interior of the receiver 3 is 30 to 40 bar. A lower portion of
the receiver 3 contains liquid CO.sub.2. The receiver 3 also acts
as a separator of liquid CO.sub.2 and CO.sub.2 vapour.
[0042] By the expansion valves b and c the liquid CO.sub.2 is
expanded to typically a temperature of minus 15 to 0.degree. C.,
resulting in a pressure level of typically 20 to 35 bar. The
evaporators E2 and E3 next to the expansion valves b and c serve to
allow for a complete evaporation of the CO.sub.2 and provide large
cool surfaces, from where the cooling proper originates, typically
by air moving by the "cool air is heavier than warm air" principle
or moving by forced ventilation.
[0043] The compressor device 6 and the receiver 3 are typically
mounted in a common metal frame, also supporting the control
equipment of the refrigeration apparatus. The (first) heat
exchanger 1, that is a heat-rejecting heat exchanger, normally
stands some distance away from the compressor device 6 and the
receiver 3 and the expansion valve 8, for example outside a
building, where it can be cooled best. It is important to note that
only the section of the basic circuit extending from the pressure
side of the compressor device 6 to the exit side of the expansion
valve 8 is at the high pressure level of typically 50 to 120 bar.
The remaining section of the basic circuit extending from the exit
side of the expansion valve a to the suction side of the compressor
device 6 is at two substantially lower pressure levels, namely
typically 30 to 40 bar in front of the expansion valves b and c and
typically 25 to 30 bar in front of the compressor device 6. As a
consequence, the second-mentioned section of the basic circuit may
be designed for such lower pressure levels, i.e. by using tubes
having thinner walls, by using less sophisticated connections where
CO.sub.2 is flowing, and by using evaporators adapted to the
relatively low pressure level.
[0044] There is a further flow path, starting at an exit side of
the upper portion (vapour portion) of the receiver 3 with a conduit
12 and containing an expansion valve e or throttle valve, and
finally leading to the entrance side of the compressor device 6 via
a conduit 11. The expansion valve e serve to reduce the pressure of
the gaseous CO.sub.2 to the level existing at the suction side of
the compressor device 6.
[0045] As an alternative, the expansion valve e may be dispensed
with, and there is just a conduit 12, 15 from the upper portion of
the receiver 3 to the further compressor 6'. The suction side of
such further compressor 6' is at a higher pressure level that the
suction side 20 of the compressor device 6. The pressure sides of
all the compressors 6 and 6' have the same pressure level. Rather
than providing the further compressor 6', it is possible to feed
from line 15 into one or several of the compressors of the
compressor device 6, but at a stage after a first compression
stage, so that the flash gas is fed into the compressor device 6 at
the right pressure level of the compressors.
[0046] Furthermore, FIG. 1 shows a branch circuit comprising the
following: A conduit 8 branches off from the conduit 4 upstream of
the expansion valves b and c; a (fourth) expansion valve d; a
second evaporator E4; a conduit 9; a second compressor device 10,
and a conduit 11 providing fluid flow connection with the suction
side of the first compressor device 6. The expansion valve d and
the second evaporator E4 are designed to provide an expansion of
the liquid CO.sub.2 to a lower pressure level than existing at the
suction side 20 of the compressor device 6. The temperature level
reached at the evaporator E4 is lower than the temperature level
reached at the evaporators E2 and E3, thereby providing means for
deep-freezing or storing at deep-freezing temperature. Typical
values are 7 to 15 bar and minus 50 to minus 25.degree. C. in the
evaporator E4.
[0047] Finally, FIG. 1 shows a conduit 13 branching off the conduit
2 (that leads from the first heat exchanger 1 to the first
expansion valve a) to a heat exchanger E1, an expansion valve f
being provided in such conduit 13. A conduit 14 leads from the heat
exchanger E1 to the suction side of the further compressor 6'. The
heat exchanger E1 exchanges heat against the CO.sub.2 flowing
through the conduit 2. Since the expansion valve f provides cool
gaseous CO.sub.2, the CO.sub.2 flowing through the conduit 2 is
cooled, thereby either assisting in condensation of CO.sub.2 or in
sub-cooling of liquid CO.sub.2.
[0048] FIG. 2 shows a schematically sectional view of the receiver
3 at a larger scale than in FIG. 1. The receiver 3 has in its
interior an upper portion 3a and a lower portion 3b. A quantity of
liquid CO.sub.2 is contained in the receiver 3, filling the
interior of the receiver 3 up to a level 22. Depending on the
operational conditions of the refrigeration circuit, the level 22
may be higher or lower than shown in FIG. 2.
[0049] The line 2 (providing a fluid flow connection between the
exit of the heat exchanger 1 and the expansion valve a, cf. FIG. 1)
extends into the receiver 3 and is connected to a second heat
exchanger 24 arranged in the upper portion 3a of the receiver 3.
There is a further conduit 26, extending outside the receiver 3 and
connecting the downstream end of the second heat exchanger 24 to
the interior of the upper portion 3a of the receiver 3, an
expansion valve 28 being provided in such conduit 26. The expansion
valve 28 produces flash gas in the upper portion 3a, which as a
consequence is at a lower temperature level than the CO.sub.2
flowing through the second heat exchanger 24. Any droplets of
liquid CO.sub.2 that may be present in the upper portion 3a, are
evaporated. This minimizes the potential for erosion of the
expansion valve 34 described in the following paragraph.
[0050] The expansion valve 28 has the same function as the
expansion valve a shown in FIG. 1. The difference is that the
conduit 2 does not lead directly to the expansion valve 28, but
there is the second heat exchanger 24 upstream of the expansion
valve 28. By means of the second heat exchanger 24, the gaseous
CO.sub.2 exiting the upper portion 3a contains less condensed
CO.sub.2 than without the provision of the second heat exchanger
24.
[0051] There is a further conduit 30 leading, outside the receiver
3, from the upper portion 3a to a third heat exchanger 32 arranged
in the lower portion 3b of the receiver 3, an expansion valve 34
being provided in such conduit 30. The downstream end of the third
heat exchanger 32 is connected by a conduit 36 to the suction side
20 of the compressor device 6. In other words, the expansion valve
34 replaces the expansion valve e shown in FIG. 1, and the third
heat exchanger 32 is provided in addition.
[0052] By passing through the expansion valve 34 the CO.sub.2
becomes cooler, and the third heat exchanger 32 provides
sub-cooling of the liquid CO.sub.2 accumulated in the lower portion
3b of the receiver 3. The liquid, sub-cooled CO.sub.2 exits the
lower portion 3b via conduit 4, as shown in FIG. 1.
[0053] The gaseous CO.sub.2 flowing through the third heat
exchanger 32 gets a certain overheating which reduces the risk of
entrainment of liquid CO.sub.2 into the compressor device 6.
* * * * *