U.S. patent application number 13/727803 was filed with the patent office on 2013-10-17 for heat exchanger.
The applicant listed for this patent is Katsumi HISANO, Takuya HONGO, Mitsuaki KATO, Tomoyuki SUZUKI, Tomonao TAKAMATSU. Invention is credited to Katsumi HISANO, Takuya HONGO, Mitsuaki KATO, Tomoyuki SUZUKI, Tomonao TAKAMATSU.
Application Number | 20130269918 13/727803 |
Document ID | / |
Family ID | 49324037 |
Filed Date | 2013-10-17 |
United States Patent
Application |
20130269918 |
Kind Code |
A1 |
HONGO; Takuya ; et
al. |
October 17, 2013 |
HEAT EXCHANGER
Abstract
According to an embodiment, a heat exchanger is provided with a
manifold, a heat exchange unit and a first porous body. The
manifold has an inlet for a medium and an outlet for the medium.
The heat exchange unit has a channel which communicates with the
outlet. The first channel has a cross section of a typical length
which is not more than a predetermined constant. The porous body is
provided between the inlet and the outlet, and contains a plurality
of pores with a mean diameter which is not more than the typical
length.
Inventors: |
HONGO; Takuya;
(Kanagawa-ken, JP) ; SUZUKI; Tomoyuki;
(Kanagawa-ken, JP) ; TAKAMATSU; Tomonao;
(Kanagawa-ken, JP) ; KATO; Mitsuaki;
(Kanagawa-ken, JP) ; HISANO; Katsumi; (Chiba-ken,
JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
HONGO; Takuya
SUZUKI; Tomoyuki
TAKAMATSU; Tomonao
KATO; Mitsuaki
HISANO; Katsumi |
Kanagawa-ken
Kanagawa-ken
Kanagawa-ken
Kanagawa-ken
Chiba-ken |
|
JP
JP
JP
JP
JP |
|
|
Family ID: |
49324037 |
Appl. No.: |
13/727803 |
Filed: |
December 27, 2012 |
Current U.S.
Class: |
165/173 |
Current CPC
Class: |
F28D 21/0001 20130101;
F28F 2265/00 20130101; F28F 13/003 20130101; F28F 2260/02 20130101;
F28F 7/02 20130101; F28F 9/00 20130101; F28F 19/00 20130101 |
Class at
Publication: |
165/173 |
International
Class: |
F28F 9/00 20060101
F28F009/00 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 12, 2012 |
JP |
2012-091230 |
Claims
1. A heat exchanger, comprising: a first manifold having a first
inlet and a first outlet for a first medium; a heat exchange unit
having a first channel which communicates with the first outlet,
the first channel having a cross section of a typical length
H.sub.1 which satisfies the following expression; and a first
porous body provided between the first inlet and the first outlet
and contains a plurality of pores having a mean diameter not more
than the typical length H.sub.1, where, in the following
expression, .sigma..sub.f is a surface tension of the first medium
at the first outlet, g is a gravitational acceleration, .rho..sub.1
is a liquid-phase density of the first medium at the first outlet,
and .rho..sub.2 is gas-phase density of the first medium at the
first outlet. H 1 .ltoreq. .sigma. 1 g ( .rho. 1 - .rho. 2 )
##EQU00004##
2. The exchanger according to claim 1, wherein the first porous
body is lyophilic.
3. The exchanger according to claim 1, further comprising a heat
receiving unit for receiving heat from a heat source, and a flow
tube for connecting the heat receiving unit and the first
inlet.
4. The exchanger according to claim 2, further comprising a heat
receiving unit for receiving heat from a heat source, and a flow
tube for connecting the heat receiving unit and the first
inlet.
5. The exchanger according to claim 1, further comprising a second
manifold and a second porous body, wherein the second manifold
includes a second inlet and a second outlet for a second medium,
the second porous body is provided between the second inlet and the
second outlet and contains a plurality of pores, the heat exchange
unit including a second channel which has a cross section of a
typical length H.sub.2 which satisfies the following expression,
the second channel communicating with the second outlet and being
provided in parallel with the first channel, and the plurality of
pores have a mean diameter not more than the typical length
H.sub.2, where, in the following expression, .sigma..sub.2 is a
surface tension of the second medium at the second outlet,
.rho..sub.3 is a liquid-phase density of the second medium at the
second outlet, and .rho..sub.4 is a gas-phase density of the second
medium at the second outlet. H 2 .ltoreq. .sigma. 2 g ( .rho. 3 -
.rho. 4 ) ##EQU00005##
6. The exchanger according to claim 5, wherein the second porous
body is lyophilic.
7. The exchanger according to claim 1, wherein the typical length
H.sub.1 of the cross section of the first channel is 20 .mu.m or
more.
8. The exchanger according to claim 5, wherein the typical length
H.sub.1 of the cross section of the first channel and the typical
length H.sub.2 of the cross section of the second channel are 20
.mu.m or more.
9. The exchanger according to claim 1, wherein the first medium is
water.
10. The exchanger according to claim 5, wherein the first medium
and the second medium are water.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application is based upon and claims the benefit of
priority from the prior Japanese Patent Application No.
2012-091230, filed on Apr. 12, 2012, the entire contents of which
are incorporated herein by reference.
FIELD
[0002] Embodiments described herein relate generally to a heat
exchanger.
BACKGROUND
[0003] In recent years, radiators are sought to be developed in
order to address an increase in heat generation density with higher
integration of semiconductor devices, or miniaturization of
electric devices such as a mobile phone. A momentum for recovering
energy efficiently even from a low-temperature heat source
radiating heat is enhanced from the view point of preventing global
warming. Such heat has been wasted as exhaust heat. Accordingly,
development of a heat exchanging technology using a microchannel
heat exchanger progresses. The microchannel heat exchanger employs
channels having a diameter of about tens of micrometers to 1 mm to
realize a small-sized and highly efficient heat exchanger.
[0004] However, in the microchannel heat exchanger, air bubbles can
not be removed from a heat-exchange medium thoroughly, even if
remaining air bubbles are removed from the medium as much as
possible by deaerating the medium. As a result, air bubbles may
enter into the channels with flow of the medium to clog up the
channels. The air bubble clogging reduces heat-exchange performance
of the heat exchanger.
BRIEF DESCRIPTION OF THE DRAWINGS
[0005] FIG. 1 is a view showing a configuration of a heat exchanger
in accordance with a first embodiment schematically.
[0006] FIG. 2 is a cross section showing an inside of the heat
exchanger of FIG. 1.
[0007] FIG. 3 is a sectional view taken along a X-X plane of the
heat exchanger of FIG. 1.
[0008] FIGS. 4A and 4B are views to explain a relation between a
microchannel and an air bubble in the heat exchanger in accordance
with the first embodiment.
[0009] FIGS. 5A and 5B are views to explain operation of the heat
exchanger in accordance with the first embodiment.
[0010] FIG. 6 is a characteristic view to explain an experimental
result of a performance of the heat exchanger in accordance with
the first embodiment.
DETAILED DESCRIPTION
[0011] A heat exchanger in accordance with an embodiment is
provided with a first manifold, a heat exchange unit, and a first
porous body. The first manifold has a first inlet for a first
medium, and a first outlet for the first medium. The heat exchange
unit has a first channel which communicates with the first outlet.
The first channel has a cross section of a typical length H.sub.1
which satisfies the following expression. The first porous body is
provided between the first inlet and the first outlet, and contains
a plurality of pores with a mean diameter which is not more than
the typical length H.sub.1. In the above expression, .sigma..sub.1
is a surface tension of the first medium at the first outlet, g is
a gravitational acceleration, .rho..sub.1 is a liquid-phase density
of the first medium at the first outlet, and .rho..sub.2 is a
gas-phase density of the first medium at the first outlet.
H 1 .ltoreq. .sigma. 1 g ( .rho. 1 - .rho. 2 ) ##EQU00001##
[0012] Hereinafter, further embodiments will be described with
reference to the drawings.
[0013] In the drawings, the same reference numerals denote the same
or similar portions respectively.
[0014] A first embodiment will be described below.
[0015] FIG. 1 is a view showing a configuration of a heat exchanger
in accordance with the first embodiment schematically. FIG. 2 is a
cross section taken in parallel to the plane of the paper, and
shows an inside of the heat exchanger of FIG. 1. FIG. 3 is a
sectional view taken along the X-X plane of the heat exchanger of
FIG. 1.
[0016] As shown in FIGS. 1 and 2, the heat exchanger of the
embodiment is provided with a heat exchange unit 10, a first
manifold 20, a second manifold 30, a heat receiving unit 40, flow
tubes 50 and 60, and porous bodies 70 and 80. The heat exchange
unit 10 exchanges heat between first and second mediums. The first
manifold 20 divides a flow of the first medium. The second manifold
30 divides a flow of the second medium. The heat receiving unit 40
receives heat from a heat source (not shown). The flow tube 50 is
connected to the heat receiving unit 40, and flows the first
medium. The flow tube 60 flows the second medium. As shown in FIG.
2, the porous body 70 is provided inside the first manifold 20 so
that the porous body 70 can block the flow of the first medium. The
porous body 80 is provided inside the second manifold 30 so that
the porous body 80 can block the flow of the second medium. The
embodiment employs water as the first and second mediums. The first
and second mediums are employed as a high-temperature medium and a
low-temperature medium, respectively.
[0017] The heat exchanger can be used for a hot water dispenser,
for example. Specifically, the heat receiving unit 40 is provided
near a heat source. The heat receiving unit 40 receives heat from
the heat source and provides the received heat to the first medium.
The heat exchange unit 10 exchanges heat between the first medium
and the second medium. As a result, the heat of the heat source is
transported from the first medium to the second medium. Further,
heat from the second medium is transported to a liquid in the hot
water dispenser, which can rise the temperature of the liquid. In
the embodiment, the first medium or the second medium is conveyed
by natural convection.
[0018] As shown in FIG. 3, the heat exchange unit 10 is a laminar
member having channels including first channels 11 and second
channels 12 with small diameters. The channels are referred to as
"microchannels" hereinafter. The microchannels penetrate the heat
exchange unit 10 in a thickness direction of the heat exchange unit
10. The first channels 11 and the second channels 12 are provided
to be in parallel with the thickness direction of the heat exchange
unit 10. In the following description, the typical length of the
cross sections of the microchannels is defined as being not more
than a Laplace constant of water (about 2.5 mm) under the
conditions of a room temperature and an atmospheric pressure.
[0019] For the heat exchange unit 10, high thermal conductive
materials such as aluminum, copper or stainless steel may be used.
As shown in FIG. 3, the microchannels of the heat exchange unit 10
are illustrated as having circular cross sections. The cross
sections of the microchannels may be ellipsoidal, semicircular,
rectangular or various form in addition to the circular form.
[0020] As shown in FIG. 3, the microchannels of the heat exchange
unit 10 are arranged in a lattice. In the embodiment, the
microchannels are arranged to have four columns in a x-axis
direction and four rows in a y-axis direction so that the number of
the microchannels is 16 totally. In the following description, the
microchannels are treated as a plurality of microchannel groups
which have four rows and one column respectively. The microchannel
groups which consist of the first channels 11 are defined as "A",
and the microchannel groups which consist of the second channels 12
are defined as "B."
[0021] As described below in detail, the heat exchange unit 10
exchanges heat between the first medium which passes through the
groups A, and the second medium which passes through the groups B.
Thus, the performance of the heat exchanger affects the flow of the
first medium or the second medium inside the respective
microchannels. For example, air bubbles may be produced during
circulation of the first medium or the second medium. The air
bubbles may enter into the respective microchannels for circulating
the respective mediums, which prevents the flow of the first medium
or the second medium in cases.
[0022] The influence of air bubble clogging in the microchannels is
considered to be suppressed by setting the mass flow rate of the
first medium or the second medium which flows in each microchannel
to a high rate of 100-200 kg/(m.sup.2s), for example. However, such
a high mass flow rate may increase a pressure loss between the
inlet and the outlet of each microchannel. Accordingly, the mass
flow rate is desirably as low as possible. For example, a mass flow
rate as high as 10 kg/(m.sup.2s) is desirable in a case of
transporting mediums by natural convection as the embodiment.
[0023] Further, the influence of air bubble clogging in each
microchannel may be eliminated by enlarging the diameter of each
microchannel. However, the number of microchannels per unit volume
of the heat exchange unit 10 needs to be reduced when the size of
the heat exchange unit 10 is maintained. As a result, a heat
transfer area decreases. Thus, the diameter of each microchannel is
desirably as small as possible in order to enhance heat conducting
performance.
[0024] In the embodiment, the typical length of each microchannel
that is the minimum length H of the cross section of each
microchannel in a direction of gravitational force is defined as
follows.
H 1 .ltoreq. .sigma. g ( .rho. f - .rho. g ) ( 1 ) ##EQU00002##
[0025] In the expression, a denotes a surface tension of a medium,
g denotes gravitational acceleration, .rho..sub.f denotes a
liquid-phase density of the medium, and .rho..sub.g denotes a
gas-phase density of the medium. In the embodiment, the typical
length H of the section of each microchannel is a diameter of each
microchannel. The right-hand side of the expression (1) represents
a Laplace constant. As the surface tension a, a surface tension at
the inlet of each microchannel is employed which is calculated in
advance based on designed use conditions such as temperature and
pressure for performing the heat exchanger. As the liquid-phase
density .rho..sub.r and the gas-phase density .sigma..sub.g, a
density at the inlet of each microchannel is employed.
[0026] A Laplace constant shows a scale under which the gravity
force acting on a medium and the surface tension of the medium
becomes equal to each other, generally. Thus, when a scale larger
than the Laplace constant is used, the gravity force acting on a
medium is larger than the surface tension of the medium. When a
scale smaller than the Laplace constant is used, the surface
tension of a medium is larger than the gravity force acting on the
medium.
[0027] As shown in FIG. 4A, in a case where the diameter of each
microchannel is larger than the Laplace constant, when an air
bubble 90 goes into each microchannel 11 or 12, the gravity force
acts on the medium more than the surface tension of the medium.
Thus, the bubble 90 is easy to be eccentrically-located in the
direction of the gravity force inside each microchannel. In
contrast, as shown in FIG. 4B, in a case where the diameter of each
microchannel 11 or 12 is less than the Laplace constant, when the
air bubble 91 goes into each microchannel 11 or 12, the surface
tension acts on the medium more than the gravity force acting on
the medium. Accordingly, the air bubble 91 is easy to be located to
prevent flow of the first medium or the second medium independently
on the direction of the gravity force rather than being
eccentrically-located in an opposite direction of the gravity
force.
[0028] As a lower limit of the typical length H shown in the above
expression, 20 .mu.m may be used. When the typical length H is less
than 20 .mu.m, each microchannel is difficult to be manufactured
and the pressure loss increases remarkably. The respective
microchannels may have the same diameter, or have different
diameters within a range of the above expression.
[0029] The heat exchange unit 10 may be manufactured by laminating
laminar members which have a plurality of through-holes with
microscopic diameters, or by laminating laminar members which have
many grooves with microscopic diameters. The laminar members may be
fixed to each other by diffusion bonding, brazing, etc. The heat
exchange unit 10 may be manufactured using a single member which
has through-holes. The through-holes or grooves may be made by
chemical processing such as etching, electroforming, optical
shaping or anode oxidation, or by mechanical processing such as
drilling, press working, electrospark machining or laser
machining.
[0030] As shown in FIG. 2, the first manifold 20 is a hollow member
which has a first inlet 21 and a first outlet 22 and allows the
first medium to flow through the member. The first manifold 20
divides the flow of the first medium which enters into a hollow
interior of the member, and discharges the first medium into the
heat exchange unit 10 via the first outlet 22.
[0031] The first manifold 20 has the first inlet 21, a chamber 23,
a buffer 24, and the first outlet 22 which are provided along a
flow direction of the first medium. The chamber 23 is filled with
the first medium. The buffer 24 divides the flow of the first
medium. The first inlet 21 communicates with the flow tube 50. The
first outlet 22 communicates with respective ends of the
microchannel groups A of the heat exchanger 10 shown in FIG. 3. In
addition, the other ends of the microchannel groups A communicate
with the flow tube 50.
[0032] The second manifold 30 is a hollow member which has a second
inlet 31 and a second outlet 32 and allows the second medium to
flow through the member. The second manifold 30 divides the flow of
the second medium which enters into a hollow interior of the
member, and discharges the second medium into the heat exchange
unit 10 via the second outlet 32.
[0033] The second manifold 30 has the second inlet 31, a chamber
33, a buffer 34 and the second outlet 32 which are provided along a
flow direction of the second medium. The chamber 33 is filled with
the second medium. The buffer 34 divides the flow of the second
medium. The second inlet 31 is connected to the flow tube 60. The
second outlet 32 communicates with respective ends of the
microchannel groups B of the heat exchanger 10. In addition, the
other ends of the microchannel groups B communicate with the flow
tube 60.
[0034] The first porous body 70 is a member containing a plurality
of pores. The first porous body 70 is provided inside the first
manifold 20 so as to perform blocking between the first inlet 21
and the first outlet 22. In more detail, the first porous body 70
is provided between the chamber 23 and the buffer 24.
[0035] As the first porous body 70, a member which is obtained by
hardening sponge or fiber bundles made of a material such as
polyvinyl alcohol with binder may be employed. Desirably, the first
porous body 70 is a lyophilic member for the purposes of allowing
the medium to go through the body 70 and preventing transit of air
bubbles. The "lyophilic" is defined as having a contact angle of
less than 90.degree. between the porous body and the medium.
[0036] As described above, in a case where the diameter H of the
first channels 11 of FIG. 3 is defined by the expression (1), the
heat transfer area per unit volume can be increased but the bubbles
may clog up the channels 11 when air bubbles having a diameter more
than H enters into the first channels 11. This may decrease the
flow rate of the medium passing through each microchannel.
[0037] In the embodiment, the mean diameter of the pores which are
contained in the first porous body 70 is set below the diameter H
of the first channels 11. The mean diameter is calculated from the
following expression (2) by using the distribution of the volume V
of the pores and the diameter D of the pores corresponding to the
volume V. The diameter D corresponding to the volume V is obtained
on the assumption that the pores are spherical. The volume V can be
measured by a mercury press-fit technique using a porosimeter.
Mean Diameter D _ = .intg. D V .intg. V ( 2 ) ##EQU00003##
[0038] When the mean diameter of the pores is set below the
diameter H of the first microchannels, air bubbles having diameters
larger than the diameter H can be removed using the first porous
body 70 so that air bubbles can be prevented from clogging up the
interiors of the first channels 11. The embodiment can achieve
increase in the heat transfer area by setting the diameter H of the
first channels 11 to satisfy the expression (1). In addition, the
embodiment can achieve ensuring the flow rate of the medium by
preventing air bubbles from clogging up the first channels 11. As a
result, even when the first and second mediums have a low flow
rate, the heat exchange performance is enhanced.
[0039] The second porous body 80 is a member containing a plurality
of pores. The second porous body 80 is provided inside the second
manifold 30 so as to perform blocking between the second inlet 31
and the second outlet 32. In more detail, the second porous body 80
is provided between the chamber 33 and the buffer 34.
[0040] As the second porous body 80, a member which is obtained by
hardening sponge or fiber bundles made of a material such as
polyvinyl alcohol with binder may be employed. Desirably, the
second porous body 80 is a lyophilic member for the purposes of
allowing the medium to go through the body 80 and preventing
transit of air bubbles.
[0041] In the embodiment, the mean diameter of the pores contained
in the second porous body 80 is set below the diameter H of the
second channels 12. The mean diameter is calculated from the
expression (2).
[0042] FIGS. 5A and 5B are views for explaining function of the
heat exchanger in accordance with the embodiment. FIG. 5A is a view
corresponding to FIG. 2, and FIG. 5B is a view corresponding to
FIG. 3.
[0043] In FIG. 5A, a flow C+D of the first medium goes into the
heat receiving unit 40 which is under receipt of heat from a heat
source, and the first medium receives the heat. The flow C+D of the
first medium goes through the flow tube 50, and further goes into
the chamber 23 of the first manifold 20 through the first inlet 21.
When the flow C+D of the first medium goes through the first porous
body 70, the first porous body 70 removes air bubbles having
diameters not less than the diameter H of the first channels 11,
from among air bubbles produced inside the flow tube 50 or the
chamber 23. The flow C+D of the first medium which goes through the
first porous body 70 is divided into a flow C of the first medium
and a flow D of the first medium. The respective flows C and D go
through the first outlets 22, as shown in FIG. 5B, and further go
into the microchannel groups A containing the first channels 11 of
the heat exchange unit 10.
[0044] On the other hand, a flow E+F of the second medium goes
through the flow tube 60 and further goes into the chamber 33 of
the second manifold 30 via the second inlet 31. When the flow E+F
of the second medium goes through the second porous body 80, the
second porous body 80 removes air bubbles having diameters not less
than the diameter H of the second channels 12, from among air
bubbles produced inside the flow tube 60 or the chamber 33. The
flow E+F of the second medium which goes through the second porous
body 80 is divided into a flow E of the second medium and a flow F
of the second medium. The respective flows E and F go through the
second outlets 32, and further go into the microchannel groups B
containing the second channels 12 of the heat exchange unit 10.
[0045] At this time, in the heat exchange unit 10, heat is
transferred, from the first medium passing through the microchannel
groups A, to the second medium passing through the microchannels B
by heat transfer.
[0046] The flows C and D of the first medium go out of the
microchannel groups A, and go back to the heat receiving unit 40
via the flow tube 50 for performing circulation. The flows E and F
of the second medium going out of the microchannel groups B
circulate through the flow tube 60. As a result, the heat of the
heat source is transferred from the first medium to the second
medium, which can warm a space other than the heat source.
[0047] FIG. 6 is a view showing an experimental results obtained by
using the heat exchanger in accordance with the first embodiment.
FIG. 6 shows a relation between mass flow rate and thermal
resistance. The experimental conditions are following. As the
microchannels, channels of 250 .mu.m in diameter were used. As the
porous bodies, hydrophilic porous bodes of polyvinyl alcohol were
used. The hydrophilic porous bodies contained pores with an mean
diameter of 130 .mu.m, and had a contact angle of 36.degree. to
water. As the first medium, water was used. The water indicated a
temperature of 60.degree. C., a liquid-phase density of 983
kg/m.sup.3, a gas-phase density of 0.13 kg/m.sup.3, and a surface
tension of 0.066 N/m. As the second medium, water was used. The
water indicated a temperature of 15.degree. C., a liquid-phase
density of 999 kg/m.sup.3, a gas-phase density of 0.014 kg/m.sup.3,
and a surface tension of 0.073 N/m.
[0048] As shown in FIG. 6, the heat exchanger having the porous
bodies 70 and 80 in accordance with the embodiment could present a
thermal resistance smaller than that of a heat exchanger without
porous bodies 70 and 80, though the mass flow rate was 10
kg/(m.sup.2s) which is much smaller than 100-200 kg/(m.sup.2s). The
thermal resistance of the embodiment was much close to a design
value.
[0049] The heat exchanger of the embodiment can prevent air bubble
clogging in the microchannels even at a low mass flow rate of 100
kg/(m.sup.2s) or less, for example. In a case where natural
convection is utilized for circulation of the mediums, the lower
the height of the heat source is, the lower the mass flow rate is
for efficient heat exchange. Thus, the heat exchanger can prevent
air bubble clogging in the microchannels even at a low mass flow
rate without being restricted due to the height of the heat source
i.e. the size of the heat exchanger etc. Further, when the mass
flow rate is low, increase in pressure loss can be prevented so
that it is possible to reduce burden on a pump in a case where the
pump is used to generate a flow of the mediums.
[0050] The heat exchanger in accordance with the embodiment can
ensure the performance of heat exchange using microchannels.
[0051] While certain embodiments have been described, these
embodiments have been presented by way of example only, and are not
intended to limit the scope of the inventions. Indeed, the novel
embodiments described herein may be embodied in a variety of other
forms; furthermore, various omissions, substitutions and changes in
the form of the embodiments described herein may be made without
departing from the spirit of the inventions. The accompanying
claims and their equivalents are intended to cover such forms or
modifications as would fall within the scope and spirit of the
inventions.
* * * * *