EP0334683A2

EP0334683A2 - Heat exchanger

Info

Publication number: EP0334683A2
Application number: EP89303044A
Authority: EP
Inventors: Yutaka Ishii
Original assignee: Sanden Corp
Current assignee: Sanden Corp
Priority date: 1988-03-25
Filing date: 1989-03-28
Publication date: 1989-09-27
Also published as: EP0334683A3; JPH01144659U

Abstract

A heat exchanger (310) is disposed within a duct (320) through which a first fluid flows with a velocity profile. The heat exchanger (310) includes a plurality of pipe members (311a) through which a second fluid flows and a plurality of fin members (312a,312d) fixedly disposed between the pipe members (311a). Those fin members (312a) through which the first fluid flows faster are made of a material of higher thermal conductivity.

Description

This invention relates to a heat exchanger, such as a heat exchanger for exchanging heat with air.
With reference to Figure 1 of the accompanying drawings, a heat exchanger 10 for exchanging heat with air, for example an evaporator for an automotive air conditioning system, is disposed within an enlarged sectional area portion 20a of a duct 20 in which a first fluid, for example air, flows in the direction of arrow 21. The heat exchanger 10 comprises a serpentine flat pipe 11 for the flow of a second fluid, for example a refrigerant, and fin members 12 are fixedly disposed between straight portions 11a of the flat pipe 11 as shown in Figure 2.
Figure 3 shows a velocity profile at a section A-B in Figure 1. According to Figure 3, the velocity of flow of the first fluid is gradually reduced towards the wall of the duct 20 from a central portion of the duct 20.
Furthermore, the first fluid flowing with an "inclined" velocity profile as mentioned above causes the heat transfer rate of the heat exchanger 10 to be smaller than if the first fluid flows with a "level" velocity profile as shown in Figure 4, in which a solid line Q and a dashed line P indicate a first fluid flow having an inclined velocity profile and a first fluid flow having a level velocity profile, respectively.
While a difference of the heat transfer rate of the heat exchanger 10 between lines P and Q can be compensated by enlarging the heat exchanger 10 or increasing the sectional area of the duct 20 outside the portion 20a, the space and cost of material of the duct 20 and heat exchanger 10 are increased.
To overcome the above-mentioned defects, Japanese Patent Application Publication No. 60-175992 discloses two types of heat exchanger which utilize a concept of a fluid resistance.
Figure 5 shows one type of heat exchanger 110. This comprises a serpentine flat pipe 111 for the flow of the second fluid, for example a refrigerant, and fin members 112 are fixedly disposed between straight portions 111a of the flat pipe 111. According to the inclined velocity profile of the first fluid flow, the spacing of the adjacent straight portions 111a is gradually reduced towards the centre to gradually increase fluid resistance of the first fluid flow, towards the centre from both sides of the heat exchanger 110. As a result, the velocity profile of the first fluid flow is leveled, so that the heat transfer rate of the heat exchanger 110 can be maintained as line P in Figure 4 without increasing the overall space and the cost of material of the duct and the heat exchanger.
Figure 6, shows another type of heat exchanger 210. This comprises a serpentine flat pipe 211 for the flow of the second fluid, for example a refrigerant, and fin members 212 fixedly disposed between straight portions 211a of the flat pipe 211. According to the inclined velocity profile of the first fluid flow, the spacing of the adjacent fin members 212 is gradually reduced towards the centre to gradually increase the fluid resistance of the first fluid flow, towards the centre from the sides of the heat exchanger 210. As a result, the velocity profile of the first fluid flow is leveled, so that the heat transfer rate of heat exchanger 210 can be maintained as line P in Figure 4 without increasing the overall space and the cost of material of the duct and the heat exchanger.
However, in the prior art, particularly in the prior art shown in Figure 5, the structure of the heat exchanger 110 is complicated owing to the flat pipe 111 being bent into various curvatures. On the other hand, in the prior art shown in Figure 6, the structure of the heat exchanger 210 is also complicated owing to the provision of fin members 212 with different spacing.
It is an object of this invention to provide a simply constructed heat exchanger which avoids the problem of reduced heat transfer rate even if the heat exchanger is disposed within a duct in which fluid flows with variable speed.
According to the invention, a heat exchanger which is arranged to be disposed within a duct through which, in use, a first fluid flows at velocities which vary across the duct, the heat exchanger including a plurality of pipe members through which in use, a second fluid flows, the pipe members being located in parallel with one another and linked to one other; and a plurality of fin members by which heat of the second fluid is dissipated fixedly disposed between the pipe members; is characterised in that the heat exchanger has higher and lower thermally conductive fin members in respective portions of the heat exchanger exposed, in use, to respectively higher and lower velocities of the first fluid flow.
In the accompanying drawings:-

Figure 1 is a schematic diagram of a duct having a heat exchanger in an englarged sectional area thereof;
Figure 2 is a perspective view of the heat exchanger shown in Figure 1;
Figure 3 is a graph showing velocity profile at a section A-B shown in Figure 1;
Figure 4 is a graph showing a relation between a flow rate of a first fluid and a heat transfer rate, a solid line showing first fluid flow having an inclined velocity profile and a dashed line showing first fluid flow having a level velocity profile;
Figure 5 is a perspective view of one prior heat exchanger;
Figure 6 is a perspective view of a second prior heat exchanger;
Figure 7 is a perspective view of a heat exchanger in accordance with one embodiment of the present invention;
Figure 8 is a fragmentary enlarged vertical longitudinal sectional view of a high thermal conductive fin member shown in Figure 7; and,
Figure 9 is a diagrammatical transverse sectional view of the exchanger shown in Figure 7 in an enlarged sectional area of a duct.

A heat exchanger disposed within a duct through which a first fluid flows is shown in Figures 7 and 9. With reference to Figure 7, the heat exchanger 310 comprises a serpentine flat pipe 311 of Al alloy, such as Japanese Industrial Standard Al070. The serpentine flat pipe 311 includes straight portions 311a which are located parallel to one other. An inlet pipe 313 is fixedly disposed at one end opening of the serpentine flat pipe 311. An outlet pipe 314 is fixedly disposed at another end opening of serpentine flat pipe 311. Between each outermost straight portion 311b and adjacent outer straight portion 311c of the flat pipe 311, conventional thermally conductive fin members 312d are fixedly disposed by brazing. Such conventional thermal conductive fin member 312d is formed of a brazing sheet (not shown) containing a core sheet (not shown) and Al-Si alloy clad material clad (not shown) onto both sides of the core sheet. The brazing sheet of conventional thermally conductive fin member 312d is 0.16mm in thickness and comprises the core sheet of 0.12mm thickness formed of Al alloy, for example AA3003 (Registered alloy of Aluminium Association U.S.A(AA)) and Al-Si alloy cladding material 0.02mm in thickness clad on both surfaces of the core sheet. Between the straight portions 311a other than the outermost straight portion 311b and next outer straight portion 311c, high thermally conductive fin members 312a as described in Japanese Patent Application No. 62-229716 are fixedly disposed by brazing. Such high thermally conductive fin members 312a are formed of a brazing sheet 312′a containing a core sheet 312b and Al-Si alloy cladding material 312c clad onto both sides of the core sheet 312b as shown in Figure 8. The brazing sheet 312′a is of 0.20mm thickness and comprises the core sheet 312b of 0.15mm thickness formed of Al alloy which consists essentially of Si 0.03-0.1 wt.%, Fe 0.05-0.3 wt.%, Zr 0.01-0.3 wt.%, In 0.001-0.009 wt.% and the balance Al, and Al-Si alloy cladding material 312c of 0.025 thickness clad on both surfaces of the core sheet 312b. The core sheet 312b of the high thermally conductive fin members 312a can alternatively be of the following Al alloys:

(1) Al alloy consisting essentially of Si 0.03-0.1 wt.%, Fe 0.05-0.3 wt.%, Zr 0.01-0.3 wt.%, In 0.001-0.009 wt.%, Zn 0.2-2.0 wt.%, and the balance Al as also described in Japanese Patent Application No. 62-229716;
(2) Al alloy consisting of Fe 0.2 wt.% or less, Si 0.1 wt.% or less, and the balance of Al and unavoidable impurities;
(3) Al alloy consisting Fe 0.2 wt.% or less, Si 0.1 wt.% or less, at least one of Zr 0.01-0.3 wt.% and Cr 0.01-0.3 wt.%, and the balance Al and unavoidable impurities;
(4) Al alloy consisting Fe 0.2 wt.% or less, at least one of Zn 0.2-2.0 wt.%, Sn 0.01-0.1 wt.% and In 0.01-0.1 wt.%, and the balance Al and unavoidable impurities;
(5) Al alloy consisting Fe 0.2 wt.% or less, Si 0.1 wt.% or less, at least one of Zr 0.01-0.3 wt.% and Cr 0.01-0.3 wt.%, at least one of Zn 0.2-2.0 wt.%, Sn 0.01-0.1 wt.%, and In 0.0-1-0.1 wt.%, and the balance Al and unavoidable impurities.

The above mentioned Al alloys (2)-(5) are disclosed in Japanese Patent Application Publication No. 60-187653 corresponding to U.S. Patent No. 4,749,627.
As shown in Figure 9, the above-described heat exchanger 310 is disposed within an enlarged sectional area portion 320a of a duct 320 in which a first fluid, for example air flows in the direction of arrow 21. Accordingly, with Figure 3 in mind additionally, in the portion with the high thermally conductive fin members 312a, the heat transfer rate is effectively increased owing to heat exchanging between a relatively high velocity air with the high thermally conductive fin members 312a. This manner of heat exchanging can sufficiently compensate the inefficient heat exchanging between relatively low velocity air with the conventional thermally conductive fin members 312d. As a result, the heat transfer rate of the whole heat exchanger can be maintained in the condition of, or even exceed, line P in Figure 4 with a simple construction.
Furthermore, the cost of material is saved by disposing costly high thermally conductive fin members only where they are needed in the heat exchanger. The spacing of the adjacent flat portions of the pipe 311 may be constant as may the spacing of the fin members 312a and 312d.

Claims

1. A heat exchanger (310) which is arranged to be disposed within a duct (32) through which, in use, a first fluid flows at velocities which vary across the duct, the heat exchanger including a plurality of pipe members (311a) through which in use, a second fluid flows, the pipe members being located in parallel with one another and linked to one other; and a plurality of fin members (312a,312d) by which heat of the second fluid is dissipated fixedly disposed between the pipe members; characterised in that the heat exchanger has higher and lower thermally conductive fin members (312a,312d) in respective portions of the heat exchanger exposed, in use, to respectively higher and lower velocities of the first fluid flow.

2. A heat exchanger according to claim 1, wherein the higher thermally conductive fin members (312a) are formed of a brazing sheet containing a core sheet (312b) and an Al-Si alloy cladding (312c) material clad onto both sides of the core sheet.

3. A heat exchanger according to claim 2, wherein the core sheet (312b) is formed of an Al alloy which consists essentially of Si 0.03-0.1 wt.%, Fe 0.05-0.3 wt.%, Zr 0.01-0.3 wt.%, In 0.001-0.009 wt.%, and the balance Al.

4. A heat exchanger according to claim 2, wherein the core sheet (312b) is formed of an Al alloy which consists essentially of Si 0.03-0.1 wt.%, Fe 0.05-0.3 wt.%, Zr 0.01-0.3 wt.%, In 0.001-0.009 wt.%, Zn 0.2-2.0 wt.%, and the balance Al.