U.S. patent application number 13/453503 was filed with the patent office on 2013-10-24 for heat exchanger.
This patent application is currently assigned to AAF-MCQUAY INC.. The applicant listed for this patent is Kazushige KASAI, Mitsuharu NUMATA. Invention is credited to Kazushige KASAI, Mitsuharu NUMATA.
Application Number | 20130277020 13/453503 |
Document ID | / |
Family ID | 48045086 |
Filed Date | 2013-10-24 |
United States Patent
Application |
20130277020 |
Kind Code |
A1 |
NUMATA; Mitsuharu ; et
al. |
October 24, 2013 |
HEAT EXCHANGER
Abstract
A heat exchanger is adapted to be used in a vapor compression
system, and includes a shell, a distributing part, a tube bundle
and a trough part. The shell has a longitudinal center axis
extending generally parallel to a horizontal plane. The
distributing part is configured and arranged to distribute a
refrigerant. The tube bundle includes a plurality of heat transfer
tubes disposed below the distributing part so that the refrigerant
discharged from the distributor is supplied onto the tube bundle.
The heat transfer tubes extend generally parallel to the
longitudinal center axis. The trough part extends generally
parallel to the longitudinal center axis under at least one of the
heat transfer tubes to accumulate the refrigerant therein. The
trough part at least partially overlaps with the at least one of
the heat transfer tubes when viewed along a horizontal direction
perpendicular to the longitudinal center axis.
Inventors: |
NUMATA; Mitsuharu;
(Plymouth, MN) ; KASAI; Kazushige; (Minnetonka,
MN) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
NUMATA; Mitsuharu
KASAI; Kazushige |
Plymouth
Minnetonka |
MN
MN |
US
US |
|
|
Assignee: |
AAF-MCQUAY INC.
Minneapolis
MN
|
Family ID: |
48045086 |
Appl. No.: |
13/453503 |
Filed: |
April 23, 2012 |
Current U.S.
Class: |
165/157 |
Current CPC
Class: |
F28F 25/04 20130101;
F25B 39/028 20130101; F28D 5/02 20130101; F28F 25/08 20130101; F28F
25/02 20130101; F28D 7/1607 20130101 |
Class at
Publication: |
165/157 |
International
Class: |
F28D 7/00 20060101
F28D007/00 |
Claims
1. A heat exchanger adapted to be used in a vapor compression
system, comprising: a shell with a longitudinal center axis
extending generally parallel to a horizontal plane; a distributing
part disposed inside of the shell, and configured and arranged to
distribute a refrigerant; a tube bundle including a plurality of
heat transfer tubes disposed inside of the shell below the
distributing part so that the refrigerant discharged from the
distributor is supplied onto the tube bundle, the heat transfer
tubes extending generally parallel to the longitudinal center axis
of the shell; and a trough part extending generally parallel to the
longitudinal center axis of the shell under at least one of the
heat transfer tubes to accumulate the refrigerant therein, the
trough part at least partially overlapping with the at least one of
the heat transfer tubes when viewed along a horizontal direction
perpendicular to the longitudinal center axis of the shell.
2. The heat exchanger according to claim 1, wherein the tube bundle
includes a falling film region and an accumulating region arranged
below the falling film region, and the at least one of the heat
transfer tubes is disposed in the accumulating region.
3. The heat exchanger according to claim 2, wherein the heat
transfer tubes in the falling film region are arranged in a
plurality of columns extending parallel to each other when viewed
along the longitudinal center axis of the shell.
4. The heat exchanger according to claim 3, wherein the heat
transfer tubes in the accumulating region are arranged in a
plurality of rows extending parallel to each other when viewed
along the longitudinal center axis of the shell, and the trough
part includes a plurality of trough sections disposed respectively
below the rows of the heat transfer tubes in the accumulating
region.
5. The heat exchanger according to claim 2, wherein the trough part
continuously extends under two or more of the heat transfer tubes
disposed in the accumulating region.
6. The heat exchanger according to claim 4, wherein at least one of
the trough sections continuously extends under all of the heat
transfer tubes in at least one of the rows in the accumulating
region.
7. The heat exchanger according to claim 4, wherein a number of the
rows of the heat transfer tubes in the accumulating region is
smaller than a number of the heat transfer tubes in each of the
columns in the falling film region.
8. The heat exchanger according to claim 7, wherein a ratio between
the number of rows of the heat transfer tubes in the accumulating
region and the number of the heat transfer tubes in each of the
columns in the falling film region is about 1:9 to about 2:8.
9. The heat exchanger according to claim 3, wherein an outermost
one of the heat transfer tubes in the accumulating region is
positioned outwardly of an outermost one of the columns of the heat
transfer tubes in the falling film region with respect to a
transverse direction when viewed along the longitudinal center axis
of the shell.
10. The heat exchanger according to claim 2, wherein the heat
transfer tubes are arranged in a plurality of columns extending
parallel to each other when viewed along the longitudinal center
axis of the shell with at least one of the heat transfer tubes in
each of the columns being disposed in the accumulating region.
11. The heat exchanger according to claim 10, wherein the trough
part includes a plurality of trough sections respectively disposed
below the at least one of the heat transfer tubes in each of the
columns.
12. The heat exchanger according to claim 11, wherein a number of
the heat transfer tubes disposed in the accumulating region in each
of the columns is smaller than a number of the heat transfer tubes
disposed in the falling film region in each of the columns.
13. The heat exchanger according to claim 12, wherein a ratio
between the number of the heat transfer tubes disposed in the
accumulating region in each of the columns and the number of the
heat transfer tubes disposed in the falling film region in each of
the columns is about 1:9 to about 2:8.
14. The heat exchanger according to claim 1, further comprising a
supply conduit fluidly connected to the distributing part to supply
the refrigerant to the distributing part, and a recirculation
conduit fluidly connected to an opening formed on a bottom surface
of the shell to recirculate the refrigerant accumulated in a bottom
portion of the shell into the supply conduit.
15. The heat exchanger according to claim 14, further comprising a
bypass conduit fluidly connected to the trough part to discharge a
fluid accumulated in the trough part toward outside of the
shell.
16. A heat exchanger adapted to be used in a vapor compression
system, comprising: a shell with a longitudinal center axis
extending generally parallel to a horizontal plane; a distributing
part disposed inside of the shell, and configured and arranged to
distribute a refrigerant; a tube bundle including a plurality of
heat transfer tubes disposed inside of the shell below the
distributing part so that the refrigerant discharged from the
distributor is supplied onto the tube bundle, the heat transfer
tubes extending generally parallel to the longitudinal center axis
of the shell; and a trough part extending generally parallel to the
longitudinal center axis of the shell under at least one of the
heat transfer tubes to accumulate the refrigerant therein such that
at least a part of the at least one of the heat transfer tubes is
submerged in the refrigerant accumulated in the trough part when
the heat exchanger operates under normal conditions.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] This invention generally relates to a heat exchanger adapted
to be used in a vapor compression system. More specifically, this
invention relates to a heat exchanger including a trough part
extending under at least one of the heat transfer tubes to
accumulate the refrigerant therein.
[0003] 2. Background Information
[0004] Vapor compression refrigeration has been the most commonly
used method for air-conditioning of large buildings or the like.
Conventional vapor compression refrigeration systems are typically
provided with an evaporator, which is a heat exchanger that allows
the refrigerant to evaporate from liquid to vapor while absorbing
heat from liquid to be cooled passing through the evaporator. One
type of evaporator includes a tube bundle having a plurality of
horizontally extending heat transfer tubes through which the liquid
to be cooled is circulated, and the tube bundle is housed inside a
cylindrical shell. There are several known methods for evaporating
the refrigerant in this type of evaporator. In a flooded
evaporator, the shell is filled with liquid refrigerant and the
heat transfer tubes are immersed in a pool of the liquid
refrigerant so that the liquid refrigerant boils and/or evaporates
as vapor. In a falling film evaporator, liquid refrigerant is
deposited onto exterior surfaces of the heat transfer tubes from
above so that a layer or a thin film of the liquid refrigerant is
formed along the exterior surfaces of the heat transfer tubes. Heat
from walls of the heat transfer tubes is transferred via convection
and/or conduction through the liquid film to the vapor-liquid
interface where part of the liquid refrigerant evaporates, and
thus, heat is removed from the water flowing inside of the heat
transfer tubes. The liquid refrigerant that does not evaporate
falls vertically from the heat transfer tube at an upper position
toward the heat transfer tube at a lower position by force of
gravity. There is also a hybrid falling film evaporator, in which
the liquid refrigerant is deposited on the exterior surfaces of
some of the heat transfer tubes in the tube bundle and the other
heat transfer tubes in the tube bundle are immersed in the liquid
refrigerant that has been collected at the bottom portion of the
shell.
[0005] Although the flooded evaporators exhibit high heat transfer
performance, the flooded evaporators require a considerable amount
of refrigerant because the heat transfer tubes are immersed in a
pool of the liquid refrigerant. With recent development of new and
high-cost refrigerant having a much lower global warming potential
(such as R1234ze or R1234yf), it is desirable to reduce the
refrigerant charge in the evaporator. The main advantage of the
falling film evaporators is that the refrigerant charge can be
reduced while ensuring good heat transfer performance. Therefore,
the falling film evaporators have a significant potential to
replace the flooded evaporators in large refrigeration systems.
[0006] U.S. Pat. No. 5,839,294 discloses a hybrid falling film
evaporator that has a section that operates in a flooded mode and a
section that operates in a falling film mode. More specifically,
the evaporator disclosed in this publication includes an outer
shell through which passes a plurality of horizontal heat transfer
tubes in a tube bundle. A distribution system is provided in
overlying relationship with the upper most level of the heat
transfer tubes in the tube bundle so that refrigerant which enters
into the shell is dispensed onto the top of the tubes. The liquid
refrigerant forms a film along an exterior wall of each of the heat
transfer tubes where part of the liquid refrigerant evaporates as
the vapor refrigerant. The rest of the liquid refrigerant collects
in the lower portion of the shell. In steady state operation, the
level of liquid refrigerant within the outer shell is maintained at
a level such that at least twenty-five percent of the horizontal
heat transfer tubes near the lower end of the shell are immersed in
liquid refrigerant. Therefore, in this publication, the evaporator
operates with the heat transfer tubes in the lower section of the
shell operating in a flooded heat transfer mode, while the heat
transfer tubes which are not immersed in liquid refrigerant operate
in a falling film heat transfer mode.
[0007] U.S. Pat. No. 7,849,710 discloses a falling film evaporator
in which liquid refrigerant collected in a lower portion of an
evaporator shell is recirculated. More specifically, the evaporator
disclosed in this publication includes the shell having a tube
bundle with a plurality of heat transfer tubes extending
substantially horizontally in the shell. Liquid refrigerant that
enters in the shell is directed from a distributor to the heat
transfer tubes. The liquid refrigerant creates a film along an
exterior wall of each of the heat transfer tubes where part of the
liquid refrigerant evaporates as the vapor refrigerant. The rest of
the liquid refrigerant collects in a lower portion of the shell. In
this publication, a pump or an ejector is provided to draw the
liquid refrigerant collected in the lower portion of the shell to
recirculate the liquid refrigerant from the lower portion of the
shell to the distributor.
SUMMARY OF THE INVENTION
[0008] The hybrid falling film evaporator disclosed in U.S. Pat.
No. 5,839,294 as mentioned above still presents a problem that it
requires a relatively large amount of refrigerant charge because of
the existence of the flooded section at the bottom portion of the
shell. On the other hand, with the evaporator disclosed in U.S.
Pat. No. 7,849,710, which recirculates the collected liquid
refrigerant from the bottom portion of the shell to the
distributor, an excess amount of circulated refrigerant is required
in order to rewet dry patches on the heat transfer tubes in case
such dry patches are formed due to fluctuation in performance of
the evaporator. Moreover, when a compressor in the vapor
compression system utilizes lubrication oil (refrigerant oil), the
oil migrated from the compressor into the refrigeration circuit of
the vapor compression system tends to accumulate in the evaporator
because the oil is less volatile than the refrigerant. Thus, with
the refrigerant recirculation system as disclosed in U.S. Pat. No.
7,849,710, the oil is recirculated within the evaporator along with
the liquid refrigerant, which causes a high concentration of the
oil in the liquid refrigerant circulating in the evaporator.
Therefore, performance of the evaporator is degraded.
[0009] In view of the above, one object of the present invention is
to provide a heat exchanger that can reduce the amount of
refrigerant charge while ensuring good performance of the heat
exchanger.
[0010] Another object of the present invention is to provide a heat
exchanger that accumulates refrigerant oil migrated from a
compressor into a refrigeration circuit of a vapor compression
system and discharges the refrigerant oil outside of the
evaporator.
[0011] A heat exchanger according to one aspect of the present
invention is adapted to be used in a vapor compression system, and
includes a shell, a distributing part, a tube bundle and a trough
part. The shell has a longitudinal center axis extending generally
parallel to a horizontal plane. The distributing part is disposed
inside of the shell, and configured and arranged to distribute a
refrigerant. The tube bundle includes a plurality of heat transfer
tubes disposed inside of the shell below the distributing part so
that the refrigerant discharged from the distributor is supplied
onto the tube bundle. The heat transfer tubes extend generally
parallel to the longitudinal center axis of the shell. The trough
part extends generally parallel to the longitudinal center axis of
the shell under at least one of the heat transfer tubes to
accumulate the refrigerant therein. The trough part at least
partially overlaps with the at least one of the heat transfer tubes
when viewed along a horizontal direction perpendicular to the
longitudinal center axis of the shell.
[0012] A heat exchanger according to another aspect of the present
invention is adapted to be used in a vapor compression system, and
includes a shell, a distributing part, a tube bundle and a trough
part. The shell has a longitudinal center axis extending generally
parallel to a horizontal plane. The distributing part is disposed
inside of the shell, and configured and arranged to distribute a
refrigerant. The tube bundle includes a plurality of heat transfer
tubes disposed inside of the shell below the distributing part so
that the refrigerant discharged from the distributor is supplied
onto the tube bundle. The heat transfer tubes extend generally
parallel to the longitudinal center axis of the shell. The trough
part extends generally parallel to the longitudinal center axis of
the shell under at least one of the heat transfer tubes to
accumulate the refrigerant therein such that at least a part of the
at least one of the heat transfer tubes is submerged in the
refrigerant accumulated in the trough part when the heat exchanger
operates under normal conditions.
[0013] These and other objects, features, aspects and advantages of
the present invention will become apparent to those skilled in the
art from the following detailed description, which, taken in
conjunction with the annexed drawings, discloses preferred
embodiments.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] Referring now to the attached drawings which form a part of
this original disclosure:
[0015] FIG. 1 is a simplified, overall perspective view of a vapor
compression system including a heat exchanger according to a first
embodiment of the present invention;
[0016] FIG. 2 is a block diagram illustrating a refrigeration
circuit of the vapor compression system including the heat
exchanger according to the first embodiment of the present
invention;
[0017] FIG. 3 is a simplified perspective view of the heat
exchanger according to the first embodiment of the present
invention;
[0018] FIG. 4 is a simplified perspective view of an internal
structure of the heat exchanger according to the first embodiment
of the present invention;
[0019] FIG. 5 is an exploded view of the internal structure of the
heat exchanger according to the first embodiment of the present
invention;
[0020] FIG. 6 is a simplified longitudinal cross sectional view of
the heat exchanger according to the first embodiment of the present
invention as taken along a section line 6-6' in FIG. 3;
[0021] FIG. 7 is a simplified transverse cross sectional view of
the heat exchanger according to the first embodiment of the present
invention as taken along a section line 7-7' in FIG. 3;
[0022] FIG. 8 is an enlarged schematic cross sectional view of heat
transfer tubes and a trough part disposed in region X in FIG. 7
illustrating a state in which the heat exchanger is in use
according to the first embodiment of the present invention;
[0023] FIG. 9 is an enlarged cross sectional view of the heat
transfer tubes and one of trough sections of a trough part
according to the first embodiment of the present invention;
[0024] FIG. 10 is a partial side elevational view of the heat
transfer tubes and the trough section according to the first
embodiment of the present invention as seen in a direction along an
arrow 10 in FIG. 9;
[0025] FIG. 11A is a graph of an overall heat transfer coefficient
versus an overlapping distance between the trough part and the heat
transfer tube according to the first embodiment of the present
invention, and FIGS. 11B to 11D are simplified cross sectional
views of the samples used to plot the graph shown in FIG. 11A;
[0026] FIG. 12 is a simplified transverse cross sectional view of
the heat exchanger illustrating a first modified example for an
arrangement of a tube bundle and a trough part according to the
first embodiment of the present invention;
[0027] FIG. 13 is a simplified transverse cross sectional view of
the heat exchanger illustrating a second modified example for an
arrangement of a tube bundle and a trough part according to the
first embodiment of the present invention;
[0028] FIG. 14 is a simplified transverse cross sectional view of
the heat exchanger illustrating a third modified example for an
arrangement of a tube bundle and a trough part according to the
first embodiment of the present invention;
[0029] FIG. 15 is a simplified transverse cross sectional view of
the heat exchanger illustrating a fourth modified example for an
arrangement of a tube bundle and a trough part according to the
first embodiment of the present invention;
[0030] FIG. 16 is an enlarged schematic cross sectional view of the
heat transfer tubes and trough sections disposed in region Y in
FIG. 15 illustrating a state in which the heat exchanger is in use
according to the first embodiment of the present invention;
[0031] FIG. 17 is a simplified transverse cross sectional view of
the heat exchanger illustrating a fifth modified example for an
arrangement of a tube bundle and a trough part according to the
first embodiment of the present invention;
[0032] FIG. 18 is a simplified transverse cross sectional view of
the heat exchanger illustrating a sixth modified example for an
arrangement of a tube bundle and a trough part according to the
first embodiment of the present invention;
[0033] FIG. 19 is a simplified transverse cross sectional view of a
heat exchanger according to a second embodiment of the present
invention;
[0034] FIG. 20 is a simplified transverse cross sectional view of a
heat exchanger according to a third embodiment of the present
invention;
[0035] FIG. 21 is a simplified transverse cross sectional view of a
heat exchanger illustrating a first modified example for an
arrangement of a tube bundle and a trough part according to the
third embodiment of the present invention;
[0036] FIG. 22 is a simplified transverse cross sectional view of a
heat exchanger illustrating a second modified example for an
arrangement of a tube bundle and a trough part according to the
third embodiment of the present invention;
[0037] FIG. 23 is a simplified transverse cross sectional view of a
heat exchanger illustrating a third modified example for an
arrangement of a tube bundle and a trough part according to the
third embodiment of the present invention;
[0038] FIG. 24 is a simplified transverse cross sectional view of a
heat exchanger according to a fourth embodiment of the present
invention; and
[0039] FIG. 25 is a simplified longitudinal cross sectional view of
the heat exchanger according to the fourth embodiment of the
present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0040] Selected embodiments of the present invention will now be
explained with reference to the drawings. It will be apparent to
those skilled in the art from this disclosure that the following
descriptions of the embodiments of the present invention are
provided for illustration only and not for the purpose of limiting
the invention as defined by the appended claims and their
equivalents.
[0041] Referring initially to FIGS. 1 and 2, a vapor compression
system including a heat exchanger according to a first embodiment
will be explained. As seen in FIG. 1, the vapor compression system
according to the first embodiment is a chiller that may be used in
a heating, ventilation and air conditioning (HVAC) system for
air-conditioning of large buildings and the like. The vapor
compression system of the first embodiment is configured and
arranged to remove heat from liquid to be cooled (e.g., water,
ethylene, ethylene glycol, calcium chloride brine, etc.) via a
vapor-compression refrigeration cycle.
[0042] As shown in FIGS. 1 and 2, the vapor compression system
includes the following four main components: an evaporator 1, a
compressor 2, a condenser 3 and an expansion device 4.
[0043] The evaporator 1 is a heat exchanger that removes heat from
the liquid to be cooled (in this example, water) passing through
the evaporator 1 to lower the temperature of the water as a
circulating refrigerant evaporates in the evaporator 1. The
refrigerant entering the evaporator 1 is in a two-phase gas/liquid
state. The liquid refrigerant evaporates as the vapor refrigerant
in the evaporator 1 while absorbing heat from the water.
[0044] The low pressure, low temperature vapor refrigerant is
discharged from the evaporator 1 and enters the compressor 2 by
suction. In the compressor 2, the vapor refrigerant is compressed
to the higher pressure, higher temperature vapor. The compressor 2
may be any type of conventional compressor, for example,
centrifugal compressor, scroll compressor, reciprocating
compressor, screw compressor, etc.
[0045] Next, the high temperature, high pressure vapor refrigerant
enters the condenser 3, which is another heat exchanger that
removes heat from the vapor refrigerant causing it to condense from
a gas state to a liquid state. The condenser 3 may be an air-cooled
type, a water-cooled type, or any suitable type of condenser. The
heat raises the temperature of cooling water or air passing through
the condenser 3, and the heat is rejected to outside of the system
as being carried by the cooling water or air.
[0046] The condensed liquid refrigerant then enters through the
expansion device 4 where the refrigerant undergoes an abrupt
reduction in pressure. The expansion device 4 may be as simple as
an orifice plate or as complicated as an electronic modulating
thermal expansion valve. The abrupt pressure reduction results in
partial evaporation of the liquid refrigerant, and thus, the
refrigerant entering the evaporator 1 is in a two-phase gas/liquid
state.
[0047] Some examples of refrigerants used in the vapor compression
system are hydrofluorocarbon (HFC) based refrigerants, for example,
R-410A, R-407C, and R-134a, hydrofluoro olefin (HFO), unsaturated
HFC based refrigerant, for example, R-1234ze, and R-1234yf, natural
refrigerants, for example, R-717 and R-718, or any other suitable
type of refrigerant.
[0048] The vapor compression system includes a control unit 5 that
is operatively coupled to a drive mechanism of the compressor 2 to
control operation of the vapor compression system.
[0049] It will be apparent to those skilled in the art from this
disclosure that conventional compressor, condenser and expansion
device may be used respectively as the compressor 2, the condenser
3 and the expansion device 4 in order to carry out the present
invention. In other words, the compressor 2, the condenser 3 and
the expansion device 4 are conventional components that are well
known in the art. Since the compressor 2, the condenser 3 and the
expansion device 4 are well known in the art, these structures will
not be discussed or illustrated in detail herein. The vapor
compression system may include a plurality of evaporators 1,
compressors 2 and/or condensers 3.
[0050] Referring now to FIGS. 3 to 5, the detailed structure of the
evaporator 1, which is the heat exchanger according to the first
embodiment, will be explained. As shown in FIGS. 3 and 6, the
evaporator 1 includes a shell 10 having a generally cylindrical
shape with a longitudinal center axis C (FIG. 6) extending
generally in the horizontal direction. The shell 10 includes a
connection head member 13 defining an inlet water chamber 13a and
an outlet water chamber 13b, and a return head member 14 defining a
water chamber 14a. The connection head member 13 and the return
head member 14 are fixedly coupled to longitudinal ends of a
cylindrical body of the shell 10. The inlet water chamber 13a and
the outlet water chamber 13b are partitioned by a water baffle 13c.
The connection head member 13 includes a water inlet pipe 15
through which water enters the shell 10 and a water outlet pipe 16
through which the water is discharged from the shell 10. As shown
in FIGS. 3 and 6, the shell 10 further includes a refrigerant inlet
pipe 11 and a refrigerant outlet pipe 12. The refrigerant inlet
pipe 11 is fluidly connected to the expansion device 4 via a supply
conduit 6 (FIG. 7) to introduce the two-phase refrigerant into the
shell 10. The expansion device 4 may be directly coupled at the
refrigerant inlet pipe 11. The liquid component in the two-phase
refrigerant boils and/or evaporates in the evaporator 1 and goes
through phase change from liquid to vapor as it absorbs heat from
the water passing through the evaporator 1. The vapor refrigerant
is drawn from the refrigerant outlet pipe 12 to the compressor 2 by
suction.
[0051] FIG. 4 is a simplified perspective view illustrating an
internal structure accommodated in the shell 10. FIG. 5 is an
exploded view of the internal structure shown in FIG. 4. As shown
in FIGS. 4 and 5, the evaporator 1 basically includes a
distributing part 20, a tube bundle 30, and a trough part 40. The
evaporator 1 preferably further includes a baffle member 50 as
shown in FIG. 7 although illustration of the baffle member 50 is
omitted in FIGS. 4-6 for the sake of brevity.
[0052] The distributing part 20 is configured and arranged to serve
as both a gas-liquid separator and a refrigerant distributor. As
shown in FIG. 5, the distributing part 20 includes an inlet pipe
part 21, a first tray part 22 and a plurality of second tray parts
23.
[0053] As shown in FIG. 6, the inlet pipe part 21 extends generally
parallel to the longitudinal center axis C of the shell 10. The
inlet pipe part 21 is fluidly connected to the refrigerant inlet
pipe 11 of the shell 10 so that the two-phase refrigerant is
introduced into the inlet pipe part 21 via the refrigerant inlet
pipe 11. The inlet pipe part 21 includes a plurality of openings
21a disposed along the longitudinal length of the inlet pipe part
21 for discharging the two-phase refrigerant. When the two-phase
refrigerant is discharged from the openings 21a of the inlet pipe
part 21, the liquid component of the two-phase refrigerant
discharged from the openings 21a of the inlet pipe part 21 is
received by the first tray part 22. On the other hand, the vapor
component of the two-phase refrigerant flows upwardly and impinges
the baffle member 50 shown in FIG. 7, so that liquid droplets
entrained in the vapor are captured by the baffle member 50. The
liquid droplets captured by the baffle member 50 are guided along a
slanted surface of the baffle member 50 toward the first tray part
22. The baffle member 50 may be configured as a plate member, a
mesh screen, or the like. The vapor component flows downwardly
along the baffle member 50 and then changes its direction upwardly
toward the outlet pipe 12. The vapor refrigerant is discharged
toward the compressor 2 via the outlet pipe 12.
[0054] As shown in FIGS. 5 and 6, the first tray part 22 extends
generally parallel to the longitudinal center axis C of the shell
10. As shown in FIG. 7, a bottom surface of the first tray part 22
is disposed below the inlet pipe part 21 to receive the liquid
refrigerant discharged from the openings 21a of the inlet pipe part
21. In the first embodiment, the inlet pipe part 21 is disposed
within the first tray part 22 so that no vertical gap is formed
between the bottom surface of the first tray part 22 and the inlet
pipe part 21 as shown in FIG. 7. In other words, in the first
embodiment, a majority of the inlet pipe part 21 overlaps the first
tray part 22 when viewed along a horizontal direction perpendicular
to the longitudinal center axis C of the shell 10 as shown in FIG.
6. This arrangement is advantageous because an overall volume of
the liquid refrigerant accumulated in the first tray part 22 can be
reduced while maintaining a level (height) of the liquid
refrigerant accumulated in the first tray part 22 relatively high.
Alternatively, the inlet pipe part 21 and the first tray part 22
may be arranged such that a larger vertical gap is formed between
the bottom surface of the first tray part 22 and the inlet pipe
part 21. The inlet pipe part 21, the first tray part 22 and the
baffle member 50 are preferably coupled together and suspended from
above in an upper portion of the shell 10 in a suitable manner.
[0055] As shown in FIGS. 5 and 7, the first tray part 22 has a
plurality of first discharge apertures 22a from which the liquid
refrigerant accumulated therein is discharged downwardly. The
liquid refrigerant discharged from the first discharge apertures
22a of the first tray part 22 is received by one of the second tray
parts 23 disposed below the first tray part 22.
[0056] As shown in FIGS. 5 and 6, the distributing part 20 of the
first embodiment includes three identical second try parts 23. The
second tray parts 23 are aligned side-by-side along the
longitudinal center axis C of the shell 10. As shown in FIG. 6, an
overall longitudinal length of the three second tray parts 23 is
substantially the same as a longitudinal length of the first tray
part 22 as shown in FIG. 6. A transverse width of the second tray
part 23 is set to be larger than a transverse width of the first
tray part 22 so that the second tray part 23 extends over
substantially an entire width of the tube bundle 30 as shown in
FIG. 7. The second tray parts 23 are arranged so that the liquid
refrigerant accumulated in the second tray parts 23 does not
communicate between the second tray parts 23. As shown in FIGS. 5
and 7, each of the second tray parts 23 has a plurality of second
discharge apertures 23a from which the liquid refrigerant is
discharged downwardly toward the tube bundle 30.
[0057] It will be apparent to those skilled in the art from this
disclosure that structure and configuration of the distributing
part 20 are not limited to the ones described herein. Any
conventional structure for distributing the liquid refrigerant
downwardly onto the tube bundle 30 may be utilized to carry out the
present invention. For example, a conventional distributing system
utilizing spraying nozzles and/or spray tree tubes may be used as
the distributing part 20. In other words, any conventional
distributing system that is compatible with a falling film type
evaporator can be used as the distributing part 20 to carry out the
present invention.
[0058] The tube bundle 30 is disposed below the distributing part
20 so that the liquid refrigerant discharged from the distributing
part 20 is supplied onto the tube bundle 30. The tube bundle 30
includes a plurality of heat transfer tubes 31 that extend
generally parallel to the longitudinal center axis C of the shell
10 as shown in FIG. 6. The heat transfer tubes 31 are made of
materials having high thermal conductivity, such as metal. The heat
transfer tubes 31 are preferably provided with interior and
exterior grooves to further promote heat exchange between the
refrigerant and the water flowing inside the heat transfer tubes
31. Such heat transfer tubes including the interior and exterior
grooves are well known in the art. For example, Thermoexel-E tubes
by Hitachi Cable Ltd. may be used as the heat transfer tubes 31 of
this embodiment. As shown in FIG. 5, the heat transfer tubes 31 are
supported by a plurality of vertically extending support plates 32,
which are fixedly coupled to the shell 10. In the first embodiment,
the tube bundle 30 is arranged to form a two-pass system, in which
the heat transfer tubes 31 are divided into a supply line group
disposed in a lower portion of the tube bundle 30, and a return
line group disposed in an upper portion of the tube bundle 30. As
shown in FIG. 6, inlet ends of the heat transfer tubes 31 in the
supply line group are fluidly connected to the water inlet pipe 15
via the inlet water chamber 13a of the connection head member 13 so
that water entering the evaporator 1 is distributed into the heat
transfer tubes 31 in the supply line group. Outlet ends of the heat
transfer tubes 31 in the supply line group and inlet ends of the
heat transfer tubes 31 of the return line tubes are fluidly
communicated with a water chamber 14a of the return head member 14.
Therefore, the water flowing inside the heat transfer tubes 31 in
the supply line group is discharged into the water chamber 14a, and
redistributed into the heat transfer tubes 31 in the return line
group. Outlet ends of the heat transfer tubes 31 in the return line
group are fluidly communicated with the water outlet pipe 16 via
the outlet water chamber 13b of the connection head member 13.
Thus, the water flowing inside the heat transfer tubes 31 in the
return line group exits the evaporator 1 through the water outlet
pipe 16. In a typical two-pass evaporator, the temperature of the
water entering at the water inlet pipe 15 may be about 54 degrees
F. (about 12.degree. C.), and the water is cooled to about 44
degrees F. (about 7.degree. C.) when it exits from the water outlet
pipe 16. Although, in this embodiment, the evaporator 1 is arranged
to form a two-pass system in which the water goes in and out on the
same side of the evaporator 1, it will be apparent to those skilled
in the art from this disclosure that the other conventional system
such as a one-pass or three-pass system may be used. Moreover, in
the two-pass system, the return line group may be disposed below or
side-by-side with the supply line group instead of the arrangement
illustrated herein.
[0059] The detailed arrangement for a heat transfer mechanism of
the evaporator 1 according to the first embodiment will be
explained with reference to FIG. 7. FIG. 7 is a simplified
transverse cross sectional view of the evaporator 1 taken along a
section line 7-7' in FIG. 3.
[0060] As described above, the refrigerant in a two-phase state is
supplied through the supply conduit 6 to the inlet pipe part 21 of
the distributing part 20 via the inlet pipe 11. In FIG. 7, the flow
of refrigerant in the refrigeration circuit is schematically
illustrated, and the inlet pipe 11 is omitted for the sake of
brevity. The vapor component of the refrigerant supplied to the
distributing part 20 is separated from the liquid component in the
first tray section 22 of the distributing part 20 and exits the
evaporator 1 through the outlet pipe 12. On the other hand, the
liquid component of the two-phase refrigerant is accumulated in the
first tray part 22 and then in the second tray parts 23, and
discharged from the discharge apertures 23a of the second tray part
23 downwardly towards the tube bundle 30.
[0061] As shown in FIG. 7, the tube bundle 30 of the first
embodiment includes a falling film region F and an accumulating
region A. The heat transfer tubes 31 in the falling film region F
are configured and arranged to perform falling film evaporation of
the liquid refrigerant. More specifically, the heat transfer tubes
31 in the falling film region F are arranged such that the liquid
refrigerant discharged from the distributing part 20 forms a layer
(or a film) along an exterior wall of each of the heat transfer
tubes 31, where the liquid refrigerant evaporates as vapor
refrigerant while it absorbs heat from the water flowing inside the
heat transfer tubes 31. As shown in FIG. 7, the heat transfer tubes
31 in the falling film region F are arranged in a plurality of
vertical columns extending parallel to each other when seen in a
direction parallel to the longitudinal center axis C of the shell
10 (as shown in FIG. 7). Therefore, the refrigerant falls
downwardly from one heat transfer tube to another by force of
gravity in each of the columns of the heat transfer tubes 31. The
columns of the heat transfer tubes 31 are disposed with respect to
the second discharge openings 23a of the second tray part 23 so
that the liquid refrigerant discharged from the second discharge
openings 23a is deposited onto an uppermost one of the heat
transfer tubes 31 in each of the columns. In the first embodiment,
the columns of the heat transfer tubes 31 in the falling film
region F are arranged in a staggered pattern as shown in FIG. 7. In
the first embodiment, a vertical pitch between two adjacent ones of
the heat transfer tubes 31 in the falling film region F is
substantially constant. Likewise, a horizontal pitch between two
adjacent ones of the columns of the heat transfer tubes 31 in the
falling film region F is substantially constant.
[0062] The liquid refrigerant that did not evaporate in the falling
film region F continues falling downwardly by force of gravity into
the accumulating region A, where the trough part 40 is provided as
shown in FIG. 7. The trough part 40 is configured and arranged to
accumulate the liquid refrigerant flowing from above so that the
heat transfer tubes 31 in the accumulating region A are at least
partially immersed in the liquid refrigerant that is accumulated in
the trough part 40. A number of rows of the heat transfer tubes 31
in the accumulating region A, to which the trough part 40 is
provided, is preferably about 10% to about 20% of a total number of
rows of the heat transfer tubes 31 of the tube bundle 30. In other
words, a ratio between the number of rows of the heat transfer
tubes 31 in the accumulating region A and the number of the heat
transfer tubes 31 in one of the columns in the falling film region
F is preferably about 1:9 to about 2:8. Alternatively, when the
heat transfer tubes 31 is arranged in an irregular pattern (e.g.,
the number of heat transfer tubes in each of the columns is
different), a number of heat transfer tubes 31 disposed in the
accumulating region A (i.e., at least partially immersed in the
liquid refrigerant accumulated in the trough part 40) is preferably
about 10% to about 20% of a total number of the heat transfer tubes
in the tube bundle 30. In the example shown in FIG. 7, the trough
part 40 is provided to two rows of the heat transfer tubes 31 in
the accumulating region A, while each of the columns of the heat
transfer tubes 31 in the falling film region F includes ten rows
(i.e., the total number of rows in the tube bundle 30 is twelve).
It will be apparent to those skilled in the art from this
disclosure that, when the evaporator has a larger capacity and
includes a larger number of heat transfer tubes, the number of
columns of the heat transfer tubes in the falling film region F
and/or the number of rows of the heat transfer tubes in the
accumulating region A also increase.
[0063] As shown in FIG. 7, the trough part 40 includes a first
trough section 41 and a pair of second trough sections 42. As seen
in FIG. 6, the first trough section 41 and the second trough
sections 42 extend generally parallel to the longitudinal center
axis C of the shell 10 over a longitudinal length that is
substantially the same as a longitudinal length of the heat
transfer tubes 31. The first trough section 41 and the second
trough sections 42 of the trough part 40 are spaced apart from an
interior surface of the shell 10 when viewed along the longitudinal
center axis C as seen in FIG. 7. The first trough section 41 and
the second trough sections 42 may be made of a variety of materials
such as metal, alloy, resin, etc. In the first embodiment, the
first trough section 41 and the second trough sections 42 are made
of metallic material, such as a steel plate (steel sheet). The
first trough section 41 and the second trough sections 42 are
supported by the support plates 32. The support plates 32 include
openings (not shown) disposed at positions corresponding to an
internal region of the first trough section 41 so that all segments
of the trough section 41 are in fluid communication along the
longitudinal length of the first trough section 41. Therefore, the
liquid refrigerant accumulated in the first trough section 41
fluidly communicates via the openings in the support plates 32
along the longitudinal length of the trough section 41. Likewise,
openings (not shown) are provided in the support plates 32 at
positions corresponding to an internal region of each of the second
trough sections 42 so that all segments of the second trough
section 42 are in fluid communication along the longitudinal length
of the second trough section 42. Therefore, the liquid refrigerant
accumulated in the trough section 42 fluidly communicates via the
openings in the support plates 32 along the longitudinal length of
the second trough section 42.
[0064] As shown in FIG. 7, the first trough section 41 is disposed
below the lowermost row of the heat transfer tubes 31 in the
accumulating region A while the second trough sections 42 are
disposed below the second lowermost row of the heat transfer tubes
31. As shown in FIG. 7, the second lowermost row in of the heat
transfer tubes 31 in the accumulating region A is divided into two
groups, and each of the second trough sections 42 is respectively
disposed below each of the two groups. A gap is formed between the
second trough sections 42 to allow an overflow of the liquid
refrigerant from the second trough sections 42 toward the first
trough section 41.
[0065] In the first embodiment, the heat transfer tubes 31 in the
accumulating region A are arranged so that an outermost one of the
heat transfer tubes 31 in each row of the accumulating region A is
disposed outwardly of an outermost column of the heat transfer
tubes 31 in the falling film region F on each side of the tube
bundle 30 as shown in FIG. 7. Since the flow of liquid refrigerant
tends to flare outwardly as it progresses toward the lower region
of the tube bundle 30 due to vapor flow within the shell 10, it is
preferable to provide at least one heat transfer tube in each row
of the accumulating region A, which is disposed outwardly of the
outermost column of the heat transfer tubes 31 in the falling film
region F as shown in FIG. 7.
[0066] FIG. 8 shows an enlarged cross sectional view of the region
X in FIG. 7 schematically illustrating a state in which the
evaporator 1 is in use under normal conditions. Water flowing
inside the heat transfer tubes 31 is not illustrated in FIG. 8 for
the sake of brevity. As shown in FIG. 8, the liquid refrigerant
forms films along the exterior surfaces of the heat transfer tubes
31 in the falling film region F and part of the liquid refrigerant
evaporates as the vapor refrigerant. However, an amount of the
liquid refrigerant falling along the heat transfer tubes 31
decreases as it progresses toward the lower region of the tube
bundle 30 while the liquid refrigerant evaporates as the vapor
refrigerant. Moreover, if distribution of the liquid refrigerant
from the distributing part 20 is not be even, there is more chance
of formation of dry patches in the heat transfer tubes 31 disposed
in a lower region of the tube bundle 30, which is detrimental to
heat transfer. Thus, in the first embodiment of the present
invention, the trough part 40 is provided in the accumulating
region A, which is disposed in the lower region of the tube bundle
30, to accumulate the liquid refrigerant flowing from above and to
redistribute the accumulated refrigerant along the longitudinal
direction of the shell C. Therefore, all of the heat transfer tubes
31 in the accumulating region A are at least partially immersed in
the liquid refrigerant collected in the trough part 40 according to
the first embodiment. Thus, formation of dry patch in the lower
region of the tube bundle 30 can be prevented, and good heat
transfer efficiency of the evaporator 1 can be ensured.
[0067] For example, as shown in FIG. 8, when the heat transfer
tubes 31 marked "1" receive little refrigerant, the heater transfer
tubes 31 marked "2", which are disposed immediately below the ones
marked "1," do not receive the liquid refrigerant from above.
However, the liquid refrigerant is accumulated in the second trough
sections 42 as the liquid refrigerant flows along the other heat
transfer tubes 31. Therefore, the heat transfer tubes 31
immediately above the second trough sections 42 are at least
partially immersed in the liquid refrigerant accumulated in the
second trough sections 42. Moreover, even when the heat transfer
tubes 31 are only partially immersed in the liquid refrigerant
accumulated in the second trough section 42 (i.e., a part of each
of the heat transfer tubes 31 is exposed), the liquid refrigerant
accumulated in the trough sections 42 rises up along exposed
surfaces of the exterior walls of the heat transfer tubes 31 as
indicated by the arrows shown in FIG. 8 due to capillary action.
Therefore, the liquid refrigerant accumulated in the second trough
sections 42 boils and/or evaporates while absorbing heat from the
water passing through the heat transfer tubes 31. Moreover, the
second trough sections 42 are designed to allow the liquid
refrigerant to overflow from the second trough sections 42 onto the
first trough section 41. In order to readily receive the liquid
refrigerant overflowed from the second trough section 42, outer
edges of the first trough section 41 are disposed outwardly of
outer edges of the second trough sections 42 as shown in FIGS. 7
and 8. The heat transfer tubes 31 that are disposed immediately
above the first trough section 41 are at least partially immersed
in the liquid refrigerant accumulated in the first trough section
41 as shown in FIG. 8. Moreover, even when the heat transfer tubes
31 are only partially immersed in the liquid refrigerant
accumulated in the second trough section 41 (i.e., a part of each
of the heat transfer tubes 31 is exposed), the liquid refrigerant
in the trough section 41 rises up along exposed surfaces of the
exterior walls of the heat transfer tubes 31 that are at least
partially immersed in the accumulated refrigerant due to capillary
action. Therefore, the liquid refrigerant accumulated in the first
trough section 41 boils and/or evaporates while absorbing heat from
the water passing inside the heat transfer tubes 31. Accordingly,
heat transfer effectively takes place between the liquid
refrigerant and the water flowing inside the heat transfer tubes 31
in the accumulating region A.
[0068] With reference to FIGS. 9 and 10, the detailed structure of
the first trough section 41 and the second trough sections 42, and
an arrangement of the first trough section 41 and the second trough
sections 42 with respect to the heat transfer tubes 31 will be
explained using one of the second trough sections 42 as an example.
As seen in FIG. 9, the second trough section 42 includes a bottom
wall portion 42a and a pair of side wall portions 42b extending
upwardly from transverse ends of the bottom wall portion 42a.
Although the side wall portions 42b have an upwardly tapered
profile in the first embodiment, the shape of the second trough
section 42 is not limited to this configuration. For example, the
side wall portions 42b of the second trough section 42 may extend
parallel to each other (see, FIGS. 11B to 11D).
[0069] The bottom wall portion 42a and the side wall portions 42b
form a recess in which the liquid refrigerant is accumulated so
that the heat transfer tubes 31 are at least partially immersed in
the liquid refrigerant accumulated in the second trough section 42
when the evaporator 1 is operated under normal conditions. More
specifically, the side wall portions 42b of the second trough part
42 partially overlap with the heat transfer tubes 31 disposed
directly above the second trough part 42 when viewed along a
horizontal direction perpendicular to the longitudinal center axis
C of the shell 10. FIG. 10 shows the trough section 42 and the heat
transfer tubes 31 when viewed along the horizontal direction
perpendicular to the longitudinal center axis C of the shell 10. An
overlapping distance D1 between the side wall portions 42b and the
heat transfer tubes 31 disposed immediately above the second trough
section 42 as viewed along the horizontal direction perpendicular
to the longitudinal center axis C of the shell 10 is set such that
the heat transfer tubes 31 are at least partially immersed in the
liquid refrigerant accumulated in the second trough section 42. The
overlapping distance D1 is also set so that the liquid refrigerant
reliably overflows from the second trough section 42 when the
evaporator 1 runs under normal conditions. Preferably, the
overlapping distance D1 is set to be equal to or greater than
one-half of a height (outer diameter) D2 of the heat transfer tube
31 (D1/D2.gtoreq.0.5). More preferably, the overlapping distance D1
is set to be equal to or greater than three-quarters of the height
(outer diameter) of the heat transfer tube 31 (D1/D2.gtoreq.0.75).
In other words, the second trough section 42 is arranged such that,
when the second trough section 42 is filled with the liquid
refrigerant to the brim, at least one-half (or, more preferably, at
least three-quarters) of the height (outer diameter) of each of the
heat transfer tubes 31 are immersed in the liquid refrigerant. The
overlapping distance D1 may be equal to or greater than the height
D2 of the heat transfer tube 31. In such a case, the heat transfer
tubes 31 are completely immersed in the liquid refrigerant
accumulated in the second trough section 42. However, since the
amount of refrigerant charge increases as the capacity of the
second trough section 42 increases, it is preferable that the
overlapping distance D1 is substantially equal to or smaller than
the height D2 of the heat transfer tube 31.
[0070] A distance D3 between the bottom wall portion 42a and the
heat transfer tubes 31 and a distance D4 between the side wall
portion 42b and the heat transfer tube 31 are not limited to any
particular distance as long as a sufficient space is formed between
the heat transfer tubes 31 and the second trough section 42 to
allow the liquid refrigerant flow between the heat transfer tubes
31 and the second trough section 42. For example, each of the
distance D3 and the distance D4 may be set to about 1 mm to about 4
mm. Moreover, the distance D3 and the distance D4 may be the same
or different.
[0071] The first trough section 41 includes the similar structure
as the second trough section 42 as described above except that the
height of the first trough section 41 may be the same or different
from the height of the second trough section. Since the first
trough section 41 is disposed below the lowermost row of the heat
transfer tubes 31, it is not necessary to overflow the liquid
refrigerant from the first trough section 41. Therefore, an overall
height of the first trough section 41 may be set to be higher than
that of the second trough section 42. In any event, it is
preferable that the overlapping distance D1 between the first
trough section 41 and the heat transfer tubes 31 is set to be equal
to or greater than one-half (or, more preferably, three-quarters)
of the height (outer diameter) D2 of the heat transfer tube 31 as
explained above.
[0072] FIG. 11A is a graph of an overall heat transfer coefficient
versus the overlapping distance D1 between a trough section and the
heat transfer tube 31 according to the first embodiment. In the
graph shown in FIG. 11A, the vertical axis indicates the
overlapping heat transfer coefficient (kw/m.sup.2K) and the
horizontal axis indicates the overlapping distance D1 as expressed
by a proportion of the height D2 of the heat transfer tube 31. An
experiment was conducted to measure the overall heat transfer
coefficient by using three samples shown in FIG. 11B to 11D. In the
first sample shown in FIG. 11B, the overlapping distance D1 between
a trough part 40' and the heat transfer tube 31 was equal to the
height D2 of the heat transfer tube 31, and thus, the overlapping
distance expressed by a proportion of the height of the heat
transfer tube 31 was 1.0. In the second sample shown in FIG. 11C,
the overlapping distance D1 between a trough part 40'' and the heat
transfer tube 31 was equal to three-quarters (0.75) of the height
D2 of the heat transfer tube 31. In the third sample shown in FIG.
11D, the overlapping distance D1 between a trough part 40''' and
the heat transfer tube 31 was equal to one-half (0.5) of the height
D2 of the heat transfer tube 31. In the first to third samples
shown in FIGS. 11B to 11D, a distance D3 between the bottom wall of
the trough section and the heat transfer tube 31 and a distance D4
between the side wall of the trough section and the heat transfer
tube 31 were about 1 mm. The first to third samples were filled
with the liquid refrigerant (R-134a) to the brim, and the overall
heat transfer coefficient was measured under different heat flux
levels (30 kw/m.sup.2, 20 kw/m.sup.2, and 15 kw/m.sup.2).
[0073] As shown in the graph of FIG. 11A, the overall heat transfer
coefficient in the second sample with the overlapping distance of
0.75 (FIG. 11C) was substantially the same as the overall heat
transfer coefficient of the first sample with the overlapping
distance of 1.0 (FIG. 11B) under all heat flux levels. Moreover,
the overall heat transfer coefficient in the third sample with the
overlapping distance of 0.5 (FIG. 11D) was about 80% of the overall
heat transfer coefficient as the first sample (FIG. 11B) under the
higher heat flux level (30 kw/m.sup.2), and the overall heat
transfer coefficient in the third sample (FIG. 11D) was about 90%
of the overall heat transfer coefficient of the first sample (FIG.
11B) under the lower heat flux level (20 kw/m.sup.2). In other
words, there was no drastic decrease in performance even when the
overlapping distance D1 was one-half (0.5) of the height of the
heat transfer tube 31. Accordingly, the overlapping distance D1 is
preferably set to be equal to or greater than one-half (0.5), and
more preferably equal to or greater than three-quarters (0.75), of
the height of the heat transfer tube 31.
[0074] With the evaporator 1 according to the first embodiment, the
liquid refrigerant is accumulated in the trough part 40 in the
accumulating region A so that the heat transfer tubes 31 disposed
in a lower region of the tube bundle 30 are at least partially
immersed in the liquid refrigerant accumulated in the trough part.
Therefore, even when the liquid refrigerant is not evenly
distributed from above, formation of dry patches in the lower
region of the tube bundle 30 can be readily prevented. Moreover,
with the evaporator 1 according to the first embodiment, since the
trough part 40 is disposed adjacent to the heat transfer tubes 31
and spaced apart from the interior surface of the shell 10, the
amount of refrigerant charge can be greatly reduced as compared to
a conventional hybrid evaporator including a flooded section, which
forms a pool of refrigerant at a bottom portion of an evaporator
shell, while ensuring good heat transfer performance.
[0075] The arrangements for the tube bundle 30 and the trough part
40 are not limited to the ones illustrated in FIG. 7. It will be
apparent to those skilled in the art from this disclosure that
various changes and modifications can be made herein without
departing from the scope of the invention. Several modified
examples will be explained with reference to FIGS. 12 to 18.
[0076] FIG. 12 is a simplified transverse cross sectional view of
an evaporator 1A illustrating a first modified example for an
arrangement of a tube bundle 30A and a trough part 40A according to
the first embodiment. The evaporator 1A is basically the same as
the evaporator 1 illustrated in FIGS. 2 to 7 except that the
outermost one of the heat transfer tubes 31 in the accumulating
region A in each row is vertically aligned with the outermost
column of the heat transfer tubes 31 in the falling film region F
on each side of the tube bundle 30A as shown in FIG. 12. In such a
case too, since outermost ends of second trough sections 42A extend
outwardly, the liquid refrigerant can be readily received by the
second trough sections 42A even when the flow of liquid refrigerant
flares outwardly as it progresses toward the lower region of the
tube bundle 30A.
[0077] FIG. 13 is a simplified transverse cross sectional view of
an evaporator 1B illustrating a second modified example for an
arrangement of a tube bundle 30B and a trough part 40B according to
the first embodiment. The evaporator 113 is basically the same as
the evaporator 1A shown in FIG. 12 except that the heat transfer
tubes 31 of the tube bundle 30B in the falling film region F are
arranged not in a staggered pattern, but in a matrix as shown in
FIG. 13.
[0078] FIG. 14 is a simplified transverse cross sectional view of
an evaporator 1C illustrating a third modified example for an
arrangement of a tube bundle 30C and a trough part 40C according to
the first embodiment. The evaporator 1C is basically the same as
the evaporator 1B shown in FIG. 13 except that the trough part 40C
includes a single second trough section 42C that extends
continuously in the transverse direction. In such a case too, the
liquid refrigerant accumulated in the second trough section 42C
overflows from both transverse sides of the second trough section
42C towards a first trough section 41C.
[0079] FIG. 15 is a simplified transverse cross sectional view of
an evaporator 1D illustrating a fourth modified example for an
arrangement of a tube bundle 30D and a trough part 40D according to
the first embodiment. In the example shown in FIG. 15, the trough
part 40D includes a plurality of individual trough sections 43 that
are disposed respectively below the heat transfer tubes 31 in the
accumulating region A. FIG. 16 is an enlarged schematic cross
sectional view of the heat transfer tubes 31 and the trough
sections 43 disposed in region Y in FIG. 15 illustrating a state in
which the evaporator 1D is in use. The liquid refrigerant
accumulated in the trough sections 43 in the uppermost row in the
accumulating region A overflows towards the trough sections 43
disposed downwardly as shown in FIG. 16. Therefore, all of the heat
transfer tubes 31 in the accumulating region A are at least
partially immersed in the liquid refrigerant accumulated in the
trough sections 43. Accordingly, the liquid refrigerant evaporates
as the vapor refrigerant as heat transfer takes place between the
liquid refrigerant and the water flowing inside the heat transfer
tubes 31.
[0080] The shape of the trough section 43 is not limited to the
configuration illustrated in FIGS. 15 and 16. For example, a cross
section of the trough section 43 may have C-shape, V-shape, U-shape
or the like. Similarly to the example discussed above, the
overlapping distance between the trough section 43 and the heat
transfer tube 31 disposed directly above the trough section 43 is
preferably set to be equal to or greater than one-half (0.5), and
more preferably equal to or greater than three-quarters (0.75), of
the height of the heat transfer tube 31 as viewed along the
horizontal direction perpendicular to the longitudinal center axis
C.
[0081] FIG. 17 is a simplified transverse cross sectional view of
an evaporator 1E illustrating a fifth modified example for an
arrangement of a tube bundle 30E and a trough part 40E according to
the first embodiment. The evaporator 1E is basically the same as
the evaporator 1D illustrated in FIG. 16 except that the outermost
one of the heat transfer tubes 31 in the accumulating region A in
each row is vertically aligned with the outermost column of the
heat transfer tubes 31 in the falling film region F on each side of
the tube bundle 30E as shown in FIG. 17.
[0082] FIG. 18 is a simplified transverse cross sectional view of
an evaporator 1F illustrating a sixth modified example for an
arrangement of a tube bundle 30F and a trough part 40F according to
the first embodiment. The evaporator 1A is basically the same as
the evaporator 1 illustrated in FIGS. 2 to 7 except for an
arrangement pattern of the heat transfer tubes 31 in the falling
film region F. More specifically, in the example shown in FIG. 18,
the heat transfer tubes 31 in the falling film region F are
arranged so that a vertical pitch between two adjacent ones of the
heat transfer tubes 31 in each column is larger in an upper region
of the falling film region F than in a lower region of the falling
film region F. Moreover, the heat transfer tubes 31 in the falling
film region F are arranged so that a horizontal pitch between two
adjacent columns of the heat transfer tubes is larger in a
transverse center region of the falling film region F than in an
outer region of the falling film region F.
[0083] An amount of vapor flow in the shell 10 tends to be larger
in the upper region of the falling film region F than in the lower
region of the falling film region F. Likewise, the amount of vapor
flow in the shell 10 tends to be larger in the transverse center
region of the falling film region F than in the outer region of the
falling film region F. Therefore, the vapor velocity in the upper
region and the outer region of the falling film region F often
become very high. As a result, the transverse vapor flow causes
disruption of the vertical flow of the liquid refrigerant between
the heat transfer tubes 31. Moreover, the liquid refrigerant may be
carried over by the high velocity vapor flow to the compressor 2,
and the entrained liquid refrigerant may damage the compressor 2.
Accordingly, in the example shown in FIG. 18, the vertical pitch
and the horizontal pitch of the heat transfer tubes 31 are adjusted
to enlarge cross sectional areas of vapor passages formed between
the heat transfer tubes 31 in the upper region and the outer region
of the falling film region F. Accordingly, the velocity of the
vapor flow in the upper region and the outer region of the falling
film region F can be decreased. Therefore, disruption of vertical
flow of the liquid refrigerant and occurrence of entrained liquid
refrigerant by the vapor flow can be prevented.
Second Embodiment
[0084] Referring now to FIG. 19, an evaporator 101 in accordance
with a second embodiment will now be explained. In view of the
similarity between the first and second embodiments, the parts of
the second embodiment that are identical to the parts of the first
embodiment will be given the same reference numerals as the parts
of the first embodiment. Moreover, the descriptions of the parts of
the second embodiment that are identical to the parts of the first
embodiment may be omitted for the sake of brevity.
[0085] The evaporator 101 according to the second embodiment is
basically the same as the evaporator 1 of the first embodiment
except that the evaporator 101 of the second embodiment is provided
with a refrigerant recirculation system. A trough part 140 of the
second embodiment is basically the same as the trough part 40 of
the first embodiment. In the first embodiment as described above,
if the liquid refrigerant is distributed from the distributing part
20 over the tube bundle 30 relatively uniformly (e.g., .+-.10%),
the refrigerant charge can be set to a prescribed amount with which
almost all the liquid refrigerant evaporates in the falling film
region F or the accumulating region A. In such a case, there is
little liquid refrigerant that overflows from the first trough
section 41 towards the bottom portion of the shell 10. However,
when distribution of the liquid refrigerant from the distributing
part 20 over the tube bundle 30 is significantly uneven (e.g.,
.+-.20%), there is a greater chance of dry patches being formed in
the tube bundle 30. Therefore, in such a case, more than the
prescribed amount of refrigerant needs to be supplied to the system
in order to prevent formation of the dry patches. Thus, in the
second embodiment, the refrigerant recirculation system is provided
to the evaporator 101 for recirculating the liquid refrigerant,
which has overflowed from the trough part 140 and accumulated in a
bottom portion of a shell 110. The shell 110 includes a bottom
outlet pipe 17 in fluid communication with a conduit 7 that is
coupled to a pump device 7a as shown in FIG. 19. The pump device 7a
is selectively operated so that the liquid refrigerant accumulated
in the bottom portion of the shell 110 recirculates back to the
distribution part 20 of the evaporator 110 via the conduit 6 and
the inlet pipe 11 (FIG. 1). The bottom outlet pipe 17 may be placed
at any longitudinal position of the shell 110.
[0086] Alternatively, the pump device 7a may be replaced by an
ejector device which operates on Bernoulli's principal to draw the
liquid refrigerant accumulated in the bottom portion of the shell
110 using the pressurized refrigerant from the condenser 3. Such an
ejector device combines the functions of an expansion device and a
pump.
[0087] Accordingly, with the evaporator 110 according to the second
embodiment, the liquid refrigerant that did not evaporate can be
efficiently recirculated and reused for heat transfer, thereby
reducing the amount of refrigerant charge.
[0088] In the second embodiment, the arrangements for a tube bundle
130 and the trough part 140 are not limited to the ones illustrated
in FIG. 19. It will be apparent to those skilled in the art from
this disclosure that various changes and modifications can be made
herein without departing from the scope of the invention. For
example, the arrangements of the tube bundle and the trough part
shown in FIGS. 12-15, 17 and 18 can also be used in the evaporator
110 according to the second embodiment.
Third Embodiment
[0089] Referring now to FIGS. 20 to 25, an evaporator 201 in
accordance with a third embodiment will now be explained. In view
of the similarity between the first, second and third embodiments,
the parts of the third embodiment that are identical to the parts
of the first or second embodiment will be given the same reference
numerals as the parts of the first or second embodiment. Moreover,
the descriptions of the parts of the third embodiment that are
identical to the parts of the first or second embodiment may be
omitted for the sake of brevity.
[0090] The evaporator 201 of the third embodiment is similar to the
evaporator 101 of the second embodiment in that the evaporator 201
is provided with the refrigerant recirculation system, which
recirculates the liquid refrigerant accumulated at the bottom
portion of a shell 210 via the bottom outlet pipe 17 and the
conduit 7. When the compressor 2 (FIG. 1) of the vapor compression
system utilizes lubrication oil, the oil tends to migrate from the
compressor 2 into the refrigeration circuit of the vapor
compression system. In other words, the refrigerant that enters the
evaporator 201 contains the compressor oil (refrigerant oil).
Therefore, when the refrigerant recirculation system is provided in
the evaporator 201, the oil is recirculated within the evaporator
201 along with the liquid refrigerant, which causes high
concentration of the oil in the liquid refrigerant in the
evaporator 201, thereby decreasing performance of the evaporator
201. Therefore, the evaporator 201 of the third embodiment is
configured and arranged to accumulate the oil using a trough part
240, and discharge the accumulated oil outside of the evaporator
201 toward the compressor 2.
[0091] More specifically, the evaporator 201 includes the trough
part 240 that is disposed below a part of the lowermost row of the
heat transfer tubes 31 in a tube bundle 230. The trough part 240 is
fluidly connected to a valve device 8a via a bypass conduit 8. The
valve device 8a is selectively operated when the oil accumulated in
the trough part 240 reaches a prescribed level to discharge the oil
from the trough part 240 to outside of the evaporator 201.
[0092] As mentioned above, when the refrigerant that enters the
evaporator 201 contains the compressor oil, the oil is recirculated
with the liquid refrigerant by the refrigerant recirculation
system. In the third embodiment, the trough part 240 is arranged
such that the liquid refrigerant accumulated in the trough part 240
does not overflow from the trough part 240. The accumulated liquid
refrigerant in the trough part 240 boils and/or evaporates as it
absorbs heat from the water flowing inside the heat transfer tubes
31 immersed in the accumulated liquid refrigerant, while the oil
remains in the trough part 240. Therefore, concentration of the oil
in the trough part 240 gradually increases as recirculation of the
liquid refrigerant in the evaporator 201 progresses. Once an amount
of the oil accumulated in the trough part 240 reaches a prescribed
level, the valve device 8a is operated and the oil is discharged
from the evaporator 201. Similarly to the first embodiment, the
overlapping distance between the trough part 240 of the third
embodiment and the heat transfer tube 31 disposed directly above
the trough part 240 is preferably set to be equal to or greater
than one-half (0.5), and more preferably equal to or greater than
three-quarters (0.75), of the height of the heat transfer tube 31
as viewed along the horizontal direction perpendicular to the
longitudinal center axis C.
[0093] In the third embodiment, a region of a tube bundle 230 where
the trough part 240 is disposed constitutes the accumulating region
A while the rest of the tube bundle 230 constitutes the falling
film region F.
[0094] Accordingly, with the evaporator 201 of the third
embodiment, the compressor oil that has been migrated from the
compressor 2 to the refrigeration circuit can be accumulated in the
trough part 240 and discharged from the evaporator 201, thereby
improving heat transfer efficiency in the evaporator 201.
[0095] In the third embodiment, the arrangements for the tube
bundle 230 and the trough part 240 are not limited to the ones
illustrated in FIG. 20. It will be apparent to those skilled in the
art from this disclosure that various changes and modifications can
be made herein without departing from the scope of the invention.
Several modified examples will be explained with reference to FIGS.
21 to 23.
[0096] FIG. 21 is a simplified transverse cross sectional view of
an evaporator 201A illustrating a first modified example for an
arrangement of a tube bundle 230A and a trough part 240A according
to the third embodiment. As shown in FIG. 21, the trough part 240A
may be placed at a center region below the lowermost row of the
heat transfer tubes 31, instead of the side region as shown in FIG.
20.
[0097] FIG. 22 is a simplified transverse cross sectional view of
an evaporator 201B illustrating a second modified example for an
arrangement of a tube bundle 230B and a trough part 240B according
to the third embodiment. The heat transfer tubes 31 of the tube
bundle 230B are arranged not in a staggered pattern, but in a
matrix as shown in FIG. 22.
[0098] FIG. 23 is a simplified transverse cross sectional view of
an evaporator 201C illustrating a third modified example for an
arrangement of a tube bundle 230C and a trough part 240C according
to the third embodiment. In this example, the heat transfer tubes
31 of the tube bundle 230C are arranged in a matrix. The trough
part 240C is disposed in the center region below the lowermost row
of the heat transfer tubes 31.
[0099] Moreover, the heat transfer tubes 31 of the tube bundle 230
according to the third embodiment may be arranged in a similar
manner as the heat transfer tubes 31 of the tube bundle 30F as
shown in FIG. 18. In other words, the heat transfer tubes 31 of the
tube bundle 230 of the third embodiment may be arranged so that a
vertical pitch between the heat transfer tubes 31 is larger in an
upper region of the tube bundle 230 than in a lower region of the
tube bundle 230, and a horizontal pitch between the heat transfer
tubes 31 is larger in an outer region of the tube bundle 230 than
in a center region of the tube bundle 230.
Fourth Embodiment
[0100] Referring now to FIGS. 24 and 25, an evaporator 301 in
accordance with a fourth embodiment will now be explained. In view
of the similarity between the first through fourth embodiments, the
parts of the fourth embodiment that are identical to the parts of
the first, second or third embodiment will be given the same
reference numerals as the parts of the first, second or third
embodiment. Moreover, the descriptions of the parts of the fourth
embodiment that are identical to the parts of the first, second or
third embodiment may be omitted for the sake of brevity.
[0101] The evaporator 301 of the fourth embodiment is basically the
same as the evaporator 1 of the first embodiment except that an
intermediate tray part 60 is provided in the falling film region F
between the heat transfer tubes 31 in the supply line group and the
heat transfer tubes 31 in the return line group. The intermediate
tray part 60 includes a plurality of discharge openings 60a through
which the liquid refrigerant is discharged downwardly.
[0102] As discussed above, the evaporator 301 incorporates a two
pass system in which the water first flows inside the heat transfer
tubes 31 in the supply line group, which is disposed in a lower
region of the tube bundle 30, and then is directed to flow inside
the heat transfer tubes 31 in the return line group, which is
disposed in an upper region of the tube bundle 30. Therefore, the
water flowing inside the heat transfer tubes 31 in the supply line
group near the inlet water chamber 13a has the highest temperature,
and thus, a greater amount of heat transfer is required. For
example, as shown in FIG. 25, the temperature of the water flowing
inside the heat transfer tubes 31 near the inlet water chamber 13a
is the highest. Therefore, a greater amount of heat transfer is
required in the heat transfer tubes 31 near the inlet water chamber
13a. Once this region of the heat transfer tubes 31 dries up due to
uneven distribution of the refrigerant from the distributing part
20, the evaporator 301 is forced to perform heat exchange by using
limited surface areas of the heat transfer tubes 31 that are not
dried up, and the evaporator 301 is held in equilibrium with the
pressure at the time. In such a case, in order to rewet the dried
up portions of the heat transfer tubes 31, more than the rated
amount (e.g., twice as much) of the refrigerant charge will be
required.
[0103] Therefore, in the fourth embodiment, the intermediate tray
part 60 is disposed at a location above the heat transfer tubes 31
which requires a greater amount of heat transfer. The liquid
refrigerant falling from above is once received by the intermediate
tray part 60, and redistributed evenly toward the heat transfer
tubes 31, which requires a greater amount of heat transfer.
Accordingly, these portions of the heat transfer tubes 31 are
readily prevented from drying up, ensuring good heat transfer
performance.
[0104] Although in the fourth embodiment the intermediate tray part
60 is provided only partially with respect to the longitudinal
direction of the tube bundle 330 as shown in FIG. 25, the
intermediate tray part 60 or a plurality of intermediate tray parts
60 may be provided to extend substantially the entire longitudinal
length of the tube bundle 330.
[0105] Similarly to the first embodiment, the arrangements for the
tube bundle 330 and the trough part 40 in the fourth embodiment are
not limited to the ones illustrated in FIG. 24. It will be apparent
to those skilled in the art from this disclosure that various
changes and modifications can be made herein without departing from
the scope of the invention. For example, the intermediate tray part
60 can be combined in any of the arrangements shown in FIGS. 12-15
and 17-23.
GENERAL INTERPRETATION OF TERMS
[0106] In understanding the scope of the present invention, the
term "comprising" and its derivatives, as used herein, are intended
to be open ended terms that specify the presence of the stated
features, elements, components, groups, integers, and/or steps, but
do not exclude the presence of other unstated features, elements,
components, groups, integers and/or steps. The foregoing also
applies to words having similar meanings such as the terms,
"including", "having" and their derivatives. Also, the terms
"part," "section," "portion," "member" or "element" when used in
the singular can have the dual meaning of a single part or a
plurality of parts. As used herein to describe the above
embodiments, the following directional terms "upper", "lower",
"above", "downward", "vertical", "horizontal", "below" and
"transverse" as well as any other similar directional terms refer
to those directions of an evaporator when a longitudinal center
axis thereof is oriented substantially horizontally as shown in
FIGS. 6 and 7. Accordingly, these terms, as utilized to describe
the present invention should be interpreted relative to an
evaporator as used in the normal operating position. Finally, terms
of degree such as "substantially", "about" and "approximately" as
used herein mean a reasonable amount of deviation of the modified
term such that the end result is not significantly changed.
[0107] While only selected embodiments have been chosen to
illustrate the present invention, it will be apparent to those
skilled in the art from this disclosure that various changes and
modifications can be made herein without departing from the scope
of the invention as defined in the appended claims. For example,
the size, shape, location or orientation of the various components
can be changed as needed and/or desired. Components that are shown
directly connected or contacting each other can have intermediate
structures disposed between them. The functions of one element can
be performed by two, and vice versa. The structures and functions
of one embodiment can be adopted in another embodiment. It is not
necessary for all advantages to be present in a particular
embodiment at the same time. Every feature which is unique from the
prior art, alone or in combination with other features, also should
be considered a separate description of further inventions by the
applicant, including the structural and/or functional concepts
embodied by such feature(s). Thus, the foregoing descriptions of
the embodiments according to the present invention are provided for
illustration only, and not for the purpose of limiting the
invention as defined by the appended claims and their
equivalents.
* * * * *