U.S. patent application number 10/618196 was filed with the patent office on 2004-02-26 for heat exchanger for cooling air.
Invention is credited to Honda, Tomoo, Makida, Kazuhisa, Nishijima, Haruyuki, Ueno, Toshio.
Application Number | 20040035562 10/618196 |
Document ID | / |
Family ID | 29783089 |
Filed Date | 2004-02-26 |
United States Patent
Application |
20040035562 |
Kind Code |
A1 |
Nishijima, Haruyuki ; et
al. |
February 26, 2004 |
Heat exchanger for cooling air
Abstract
In a heat exchanger for cooling air, a tube has a
streamlined-shaped cross-section so that air flows along an outer
surface of the tube without stagnating. Therefore, it is less
likely that moisture contained in the air will adhere on the outer
surface of the tube. Accordingly, the formation of frost is
restricted.
Inventors: |
Nishijima, Haruyuki;
(Nagoya-city, JP) ; Honda, Tomoo; (Obu-city,
JP) ; Makida, Kazuhisa; (Handa-city, JP) ;
Ueno, Toshio; (Chiryu-city, JP) |
Correspondence
Address: |
HARNESS, DICKEY & PIERCE, P.L.C.
P.O. BOX 828
BLOOMFIELD HILLS
MI
48303
US
|
Family ID: |
29783089 |
Appl. No.: |
10/618196 |
Filed: |
July 11, 2003 |
Current U.S.
Class: |
165/133 ;
165/177 |
Current CPC
Class: |
F28F 13/06 20130101;
F28D 1/0478 20130101; F28D 1/05383 20130101; F28F 2250/02 20130101;
F28D 1/05391 20130101; F28F 1/022 20130101; F28F 19/006
20130101 |
Class at
Publication: |
165/133 ;
165/177 |
International
Class: |
F28F 001/02 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 12, 2002 |
JP |
2002-204334 |
Jul 12, 2002 |
JP |
2002-204335 |
Mar 25, 2003 |
JP |
2003-082577 |
Claims
What is claimed is:
1. A heat exchanger for cooling air comprising tubes through fluid
flows, wherein the tubes are disposed such that outer surfaces of
the tubes are generally exposed to the air, wherein the tubes have
streamlined-shaped cross-sections so that air flows along the outer
surfaces of the tubes.
2. The heat exchanger according to claim 1, wherein the tubes are
arranged in row in a staggered configuration.
3. The heat exchanger according to claim 1, wherein each of the
tubes is formed with a plurality of passages through which the
fluid flows, wherein a most-downstream passage with respect to an
air flow direction has a cross-section of a flow area greater than
that of a most-upstream passage.
4. The heat exchanger according to claim 1, wherein the
streamlined-shaped cross-section is symmetric with respect to its
longitudinal centerline.
5. The heat exchanger according to claim 1, wherein the tubes are
coated with a defrosting agent that restricts adhesion of frost
particles.
6. The heat exchanger according to claim 1, wherein the tubes are
coated with a water repellent.
7. The heat exchanger according to claim 1, wherein the tubes are
corrugated in directions perpendicular to an air flow
direction.
8. A heat exchanger for cooling air comprising a flat tube through
which fluid flows, wherein the tube has an outer surface generally
exposed to the air, wherein the tube is arranged such that a
longitudinal centerline of its cross-section is parallel to an air
flow direction and is corrugated in a direction perpendicular to
the air flow direction.
9. The heat exchanger according to claim 8, wherein the tube has
substantially an elliptic-shaped cross-section.
10. The heat exchanger according to claim 8, wherein the tube has a
streamlined-shaped cross-section so that air flows along the outer
surface.
11. The heat exchanger according to claim 10, wherein the
streamlined-shaped cross-section is symmetric with respect to the
longitudinal centerline of the cross-section.
12. The heat exchanger according to claim 8, wherein a dimension of
the cross-section of the tube in a direction perpendicular to the
air flow direction is maximum at substantially an air midstream
position and reduces toward an air downstream position of the
tube.
13. The heat exchanger according to claim 8, wherein the tube is
formed with a plurality of passages through which fluid flows,
wherein a most-downstream passage with respect to the air flow
direction has a cross-section of a flow area greater than that of a
most-upstream passage.
14. The heat exchanger according to claim 8, further comprising
tanks connected at ends of the tube.
15. The heat exchanger according to claim 8, wherein an outer
surface of the tube has water repellency.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This application is based on Japanese Patent Applications
No. 2002-204334 filed on Jul. 12, 2002, No. 2002-204335 filed on
Jul. 12, 2002, and No. 2003-82577 filed on Mar. 25, 2003, the
disclosure of which is incorporated herein by reference.
FIELD OF THE INVENTION
[0002] The present invention relates to a heat exchanger for
cooling air. More particularly, the present invention relates to an
evaporator for a refrigerator and a freezer.
BACKGROUND OF THE INVENTION
[0003] According to an evaporator for a refrigerator disclosed in
JP-A-2002-115934, tubes having substantially elliptic-shaped
cross-sections are arranged such that longitudinal axes of the
cross-sections are parallel to an air flow direction. Outer fins
are not provided between the tubes and the outer surfaces of the
tubes are generally exposed to the air. With this configuration,
frost is generated intensively at air downstream portions of the
tubes and the formation of frost between tubes, which results in
blocking of air passages, is restricted. Accordingly, an air flow
resistance reduces and cooling capacity of the evaporator
improves.
SUMMARY OF THE INVENTION
[0004] It is an object of the present invention to provide a heat
exchanger for cooling air capable of improving efficiency of heat
exchange.
[0005] It is another object of the present invention to provide a
heat exchanger for cooling air capable of restricting the formation
of frost thereon.
[0006] According to an aspect of the present invention, a heat
exchanger for cooling air includes tubes through which fluid flows.
The tubes are disposed such that outer surfaces are generally
exposed to the air. The tubes have streamlined-shaped
cross-sections so that air flows along the outer surfaces of the
tubes.
[0007] Because air smoothly flows around the tubes without
stagnating, it is less likely that moisture, which result in frost,
will adhere on the outer surfaces of the tubes. Therefore, the
adhesion of frost particles and the growth of frost on the tubes
are restricted. Accordingly, an air flow resistance reduces and
efficiency of heat exchange improves.
[0008] According to another aspect of the present invention, a heat
exchanger includes a flat tube through which fluid flows. The flat
tube is arranged such that a longitudinal centerline of its
cross-section is parallel to an air flow direction and is
corrugated in a direction perpendicular to the air flow
direction.
[0009] The heat exchanger is not provided with outer fins.
Therefore, if moist air flows around the tube, moisture condenses
intensively at an air downstream position of the tube and grows
into frost. Because the frost grows in a direction parallel to the
air flow direction, the air flow is not obstructed. Accordingly, a
resistance of air flow passing around the tube reduces, so
efficiency of heat exchange improves.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] Other objects, features and advantages of the present
invention will become more apparent from the following detailed
description made with reference to the accompanying drawings, in
which like parts are designated by like reference numbers and in
which:
[0011] FIG. 1 is a schematic perspective view of a refrigerated
vehicle according to the first embodiment of the present
invention;
[0012] FIG. 2 is a schematic diagram of a vapor compression
refrigerant cycle system of the refrigerated vehicle according to
the first embodiment of the present invention;
[0013] FIG. 3 is a perspective view of a rear end of the
refrigerated vehicle according to the first embodiment of the
present invention;
[0014] FIG. 4 is a perspective view of an evaporator of the vapor
compression refrigerant cycle system according to the first
embodiment of the present invention;
[0015] FIG. 5 is a partial perspective view of a core portion of
the evaporator for explaining flows of air and refrigerant
according to the first embodiment of the present invention;
[0016] FIG. 6A is a cross-sectional view of a tube of the
evaporator according to the first embodiment of the present
invention;
[0017] FIG. 6B is an explanatory view of the tubes according to the
first embodiment of the present invention;
[0018] FIG. 6C is a partial enlarged view of an air downstream
portion of the tube shown in FIG. 6B for explaining an air stream
around the air downstream portion of the tube according to the
first embodiment of the present invention;
[0019] FIG. 7 is a partial cross-sectional view of the evaporator
for showing tube arrangement according to the first embodiment of
the present invention;
[0020] FIG. 8 is a time chart for showing operation timings of an
engine, doors and a defrosting valve according to the first
embodiment of the present invention;
[0021] FIGS. 9A and 9B are cross-sectional views of tubes of the
evaporator according to the second embodiment of the present
invention;
[0022] FIG. 10 is a cross-sectional view of a tube of the
evaporator according to the third embodiment of the present
invention;
[0023] FIG. 11 is a cross-sectional view of a tube of the
evaporator according to the fourth embodiment of the present
invention;
[0024] FIG. 12 is a psychrometric chart according to the fifth
embodiment of the present invention;
[0025] FIG. 13 is a partial perspective view of a tube of the
evaporator according to the sixth embodiment of the present
invention;
[0026] FIG. 14 is a partial cross-sectional view of the tubes
according to the sixth embodiment of the present invention;
[0027] FIG. 15A is a cross-sectional view of a tube of the
evaporator according to the seventh embodiment of the present
invention;
[0028] FIG. 15B is an explanatory view of the tube according to the
seventh embodiment of the present invention; and
[0029] FIG. 15C is a partial enlarged view of an air downstream
portion of the tube shown in FIG. 15B for explaining an air stream
around the air downstream portion of the tube according to the
seventh embodiment of the present invention.
DETAILED DESCRIPTION OF EMBODIMENT
[0030] Embodiments of the present invention will be described
hereinafter with reference to drawings.
[0031] A heat exchanger for cooling air of the first embodiment is
for example used for an evaporator 13 of a refrigerated vehicle 1,
which transports goods or freights such as frozen food while
maintaining them cold, as shown in FIG. 1.
[0032] The refrigerated vehicle 1 has a freezing container 2 for
storing the freights. The freezing container 2 has an opening 18,
and doors 3, 4 at its rear end. The freights are carried in and out
through the opening 18.
[0033] A vapor compression refrigerant cycle system 5 for cooling
air in the freezing container 2 is mounted at the front of the
refrigerated vehicle 1. As shown in FIG. 2, the system 5 includes a
compressor 6, a condenser 9, an electric fan 10, a receiver 11, a
pressure reducing device 12, and evaporator 13.
[0034] The compressor 6 is driven by an engine 8 through an
electromagnetic clutch 7. The condenser 9 cools high-temperature,
high-pressure refrigerant discharging from the compressor 1. The
fan 10 blows cooling air to the condenser 9. The receiver 11
separates the refrigerant discharging from the condenser 9 into gas
refrigerant and liquid refrigerant and discharges the liquid
refrigerant to the pressure reducing device 12. The surplus
refrigerant is stored in the receiver 11 as the liquid
refrigerant.
[0035] The pressure reducing device 12 decompresses the liquid
refrigerant. In the evaporator 13, the refrigerant from the
pressure reducing device 12 evaporates by absorbing heat from air
to be blown into the freezing container 2. The evaporator 13 will
be described later in detail.
[0036] In addition, an accumulator 14 is provided between a
refrigerant outlet of the evaporator 13 and a refrigerant inlet of
the compressor 6. The accumulator 14 separates the refrigerant
discharging from the evaporator 13 into gas refrigerant and liquid
refrigerant. The gas refrigerant is sucked in the compressor 6 and
the liquid refrigerant is stored in the accumulator 14.
[0037] A bypass 15 is disposed to introduce the high temperature
refrigerant (hot gas) from the compressor 6 to the evaporator 13
while bypassing the pressure reducing device 12. The bypass 15 is
provided with a defrosting valve 16. The defrosting valve 16 is an
electromagnetic valve. The defrosting valve 16 allows the hot gas
to flow through the bypass 15.
[0038] A blower unit 19 is provided at the bottom of the opening 18
outside the freezing container 2. The blower 19 forms an air
curtain for separating the inside of the freezing container 2 from
the outside when the doors 3, 4 are open. The blower unit 19
includes cross flow fans 20, 21 each horizontally placed at the
bottom of the opening 18. In the cross flow fans 20, 21, air flows
within cross-sections that are perpendicular to axes of multi-blade
cylindrical fans 20a, 21a (see JIS B0132 No. 1017).
[0039] Next, the evaporator 13 will be described in detail with
reference to FIGS. 4 to 6C. As shown in FIG. 4, the evaporator 13
includes a plurality of tubes 131 through which refrigerant flows
and tanks 133 connected at longitudinal ends of the tubes 131 to
communicate with the tubes 131. The tubes 131 constructs a core
portion for exchanging heat between the refrigerant and air.
[0040] It is noted that outer fins, which are generally joined to
outer surfaces of tubes, are not provided between tubes 131, so
that outer surfaces of the tubes 131 are generally exposed to the
air. As shown in FIG. 6A, the tubes 131 have streamlined-shaped
cross-sections for restricting air streams around the tubes 131
from separating from the tubes 131 at their air downstream portions
(rear sides). (See, e.g. Fluids engineering, University of Tokyo
Press). The streamlined shape is symmetric with respect to a
longitudinal centerline CL of the cross-section. Air upstream
portions (front sides) of the tubes 131 are gently curved.
Hereinafter, the terms "downstream" and "upstream" are used with
respect to a direction (A1) of air flowing through the evaporator
13.
[0041] In the embodiment, a teardrop shape (a wing shape) is
employed as the streamlined shape. A dimension (thickness) of the
tube 131 in a direction perpendicular to the centerline CL
increases at a maximum value at a substantially middle position of
the tube 131 with respect to the air flow direction A1 and reduces
toward the air downstream position.
[0042] Each of the tubes 131 is formed with a plurality of
refrigerant passages 132. The refrigerant passages 132 are parallel
and in line from the upstream portions to the downstream position
of the tube 131. In the embodiment, the tube 131 is formed by
extrusion and drawing of aluminum, for example. Thus, the
refrigerant passages 132 are formed at the same time as molding the
tube 131.
[0043] As shown in FIG. 5, the tubes 131 are arranged in rows in
directions perpendicular to the air flow direction Al. Further, as
shown in FIG. 7, the tubes 131 are arranged in a staggered
configuration. A first array pitch Tp1 of the tubes 131 of an
upstream row is greater than a second array pitch Tp2 of the tubes
131 of a downstream row. Here, the pitches Tp1, Tp2 are distances
between the centerlines CL of the tubes 131 in the directions
perpendicular to the air flow direction A1.
[0044] The tubes 131 in the same row are communicated with the same
tank 133. In view of broad perspective, the refrigerant flows from
the air upstream side to the air downstream side in the evaporator
13, as shown by arrows R1.
[0045] Next, an electronic control unit will be described. A
control unit 22 includes a computer such as a microcomputer. The
control unit 22 is programmed to control operation of the vapor
compression refrigerant cycle system 5 based on signals from the
following sensors and switches.
[0046] A temperature sensor 24 detects an inside temperature of the
freezing container 2. The inside temperature is manually set with a
temperature controller 25. For example, the inside temperature is
set within a range between -10 degrees Celsius and -20 degrees
Celsius.
[0047] A refrigerator switch 26 is manually operated. The
refrigerant switch 26 produces on and off signals of the vapor
compression refrigerant cycle system 5. An engine operation switch
27 produces signals in accordance with on and off states of the
engine 8. A door switch 28 is located on a periphery of the opening
18. The door switch 28 is turned on and off in accordance with
opening and closing of the doors 3, 4.
[0048] Further, the control unit 22 controls the electromagnetic
clutch 7, the fans 10, 17, the defrosting valve 16, the blower unit
19 and the like.
[0049] Next, refrigerating operation of the vehicle 1 will be
described with reference to FIG. 8. During the vehicle running, the
compressor 6 is driven by power from the engine 8 through the
electromagnetic clutch 7. The fans 10, 17 are operated. Also, the
vapor compression refrigerant cycle system 5 is on. With this, the
air cooled by the evaporator 13 is blown into the freezing
container 2 by the fan 17, thereby cooling the freights in the
freezing container 2. At this time, the defrosting valve 16 is
closed so that the refrigerant does not flow through the bypass
15.
[0050] When the engine 8 stops to carry in or out the freight, the
fan 17 of a cooling unit 130 (FIG. 1) is turned off. Then, when the
doors 3, 4 are opened, the door switch 28 is turned on so that the
cross flow fans 20, 21 start operation. The air curtain is formed
from the bottom to the top of the opening 18 to restrict entering
of outside air.
[0051] At this time, the defrosting valve 16 is opened. By the
pressure gap between the outlet of the compressor 6 and the
upstream portion of the evaporator 13, the hot gas flows into the
evaporator 13 through the bypass 15. Therefore, frost on the
evaporator 13 melts into water and is discharged outside. When the
doors 3, 4 are closed, the door switch 28 is turned off and the
defrosting valve 16 is closed.
[0052] Next, advantages of the embodiment will be described.
[0053] Since the tubes 131 have the streamlined-shaped
cross-sections, air smoothly flows along the outer surface of the
tubes 131 without stagnating, as shown in FIG. 6C. It restricts
moisture, which results in the formation of frost, from condensing
or adhering on the outer surfaces of the tubes 131. Thus, the
growth of frost on the tubes 131 and further adhesion of frost
particles thereon are limited. In the evaporator 13 of the
embodiment, an amount of frost is reduced at substantially one
fifth as compared with a prior evaporator.
[0054] Further, the formation of frost is restricted to the
downstream portion of the tubes 131, as shown in FIG. 6C. Because
the moisture does not adhere on the side surfaces of the tubes 131,
it is less likely that the air passages between the tubes 131 will
be obstructed by frost. Therefore, the resistance of air flow is
not increased by the frost. Accordingly, cooling capacity of the
evaporator 13 improves.
[0055] Because the tubes 131 are staggered, the tubes 131 of the
downstream row are not located in thermal boundary layers generated
by the tubes 131 of the air upstream row. Therefore, an efficiency
of hat exchange of the evaporator 13 improves.
[0056] In the second embodiment, a cross-section of the refrigerant
flow area of the most-downstream refrigerant passage 132 is larger
than that of the most-upstream refrigerant passage 132, as shown in
FIG. 9A.
[0057] Because the tubes 131 have the streamlined-shaped
cross-sections, the adhesion of moisture on the tubes 131 is
reduced. However, it is difficult to completely prevent the
formation of frost. Although it is a small amount, the frost is
formed at the downstream portions of the tubes 131.
[0058] Since the most-downstream refrigerant passage 132 has the
flow area larger than that of the upstream refrigerant passage 132,
a flow rate of the hot gas increases at the downstream portion of
the tubes 131. Therefore, even if the downstream portion of the
tube 131 is frosted, it is readily defrosted during the defrosting
mode. The refrigerant passages 132 can have substantially
rectangular-shaped cross-sections as shown in FIG. 9B.
[0059] In the third embodiment, the cross-sections of the
refrigerant flow areas are changed in accordance with an outer
dimension (thickness W) of the tube 131, as shown in FIG. 10. Also
in this embodiment, the evaporator 13 provides advantages similar
to the first embodiment.
[0060] In the fourth embodiment, the tubs 131 have
streamlined-shaped cross-sections that are asymmetric with respect
to the centerline CL, as shown in FIG. 11. Also in this embodiment,
the evaporator 13 provides advantages similar to the first
embodiment.
[0061] In the fifth embodiment, the tubes 131 are coated with a
defrosting agent for restricting the moisture and frost particles
from adhering on the outer surfaces of the tubes 131. For example,
the defrosting agent includes a super-repellency coating and a
material having water repellency, such as Teflon.
[0062] With reference to FIG. 12, for example, the temperature of
the freezing container 20 is -20 degrees Celsius (T1). When the
doors 3, 4 open, outside air (e.g. 35 degrees Celsius, 60% relative
humidity) enters the freezing container 2. The air is quickly
cooled lower than the freezing point, and the inside air is
supersaturated. Under the temperature T2, which is lower than the
freezing point, a small amount of vapor (M1) can exist as moisture
(water vapor) in the inside air, for example.
[0063] Therefore, moisture (M2) contained in the outside air is
supersaturated steam and is sublimated into sublimated particles
without liquefying. The sublimated particles adhere to the outer
surfaces of the tubes 131 and grow into frost. In the embodiment,
the tubes 131 are coated with the defrosting agent. Therefore, it
is less likely that the sublimated particles (frost particles) will
adhere on the tubes 131. Accordingly, the growth of frost on the
tubes 131 is restricted.
[0064] In the sixth embodiment, the evaporator 13 includes flat
tubes 231 and tanks 233 as shown in FIG. 13. The tanks 233 are
connected at the ends of the tubes 231. The tubes 231 are formed
with a plurality of refrigerant passages 232 and produced by
extrusion and drawing, similar to the first embodiment.
[0065] The tubes 231 are disposed such that the centerlines CL of
the cross-sections are parallel to the air flow direction A1.
Further, the tubes 231 are corrugated in directions perpendicular
to the air flow direction A1, as shown in FIGS. 13 and 14.
[0066] Straight portions 231b of the tubes 231 are connected
through turn portions 231a. The tubes 231 are arranged such that
the straight portions 231b are staggered, as shown in FIG. 14. An
array pitch Tp4 of the straight portions 231b of the downstream
tube 231 is smaller than an array pitch Tp3 of the straight
portions 231b of the air upstream tube 231, for example.
Alternatively, the pitch Tp3 and Tp4 can be equal.
[0067] Also in the embodiment, the tubes 231 have streamlined
cross-sections similar to the first to the fourth embodiment.
Accordingly, the tubes 231 provide advantages similar to those of
the first to the fourth embodiments.
[0068] In the seventh embodiment, the tube 231 has substantially an
elliptic-shaped cross-section. The straight portions 231b of the
tubes 231 includes substantially flat surfaces lying in parallel to
the air flow direction A1, as shown in FIGS. 15A and 15B. The
upstream sides and the downstream sides of the straight portions
231b, which connect the flat surfaces, are gently curved.
[0069] As shown in FIG. 15C, air stagnating area is formed at the
air downstream portion of the tube 231. The air stream around the
tube 231 separates from the tube 231 and whirls at the downstream
portion of the tube 231, as shown by arrows A2.
[0070] If moist air passes around the tube 231, moisture adheres on
the downstream portion of the tube 231 and grows into frost
thereon. Because the tube 231 is not provided with the outer fins,
the frost only grows at the downstream portion of the tube 231 in
the direction parallel to the air flow direction A1. It is less
likely that the frost generates on the straight portions 231b to
block the air passages therebetween. Therefore, the resistance of
air flow reduces, hence the cooling capacity of the evaporator 13
improves.
[0071] As a modification, the refrigerant passages 132, 232 can
have any cross-sectional shapes other than circular shape and
square shapes. The array pitches Tp1, Tp2, Tp3, Tp4 of the tubes
131 and the straight portions 231b can be changed. Also, the number
of rows of the tubes 131 is not limited.
[0072] The present invention can be employed to a refrigerator for
other purposes. For example, the present invention can be used for
a cold storage. Further, the present invention can be employed to a
heat exchanger that cools air with sensible heat. Also, the tubes
having the streamlined-shaped cross-sections can be used for
another heat exchanger that performs heat exchange between fluid
and air, other than the heat exchanger for cooling air.
[0073] The present invention should not be limited to the disclosed
embodiments, but may be implemented in other ways without departing
from the spirit of the invention.
* * * * *