EP0930480A2

EP0930480A2 - Heat exchanger

Info

Publication number: EP0930480A2
Application number: EP98310306A
Authority: EP
Inventors: Hideo Kawamura
Original assignee: Isuzu Ceramics Research Institute Co Ltd
Current assignee: Isuzu Ceramics Research Institute Co Ltd
Priority date: 1997-12-26
Filing date: 1998-12-16
Publication date: 1999-07-21
Also published as: JPH11190595A; EP0930480A3

Abstract

A heat exchanger is preferable to be applied to intercoolers, radiators and cooling means in semiconductor circuits and improved in heat exchanging efficiency by provision of gas paths that are formed with porous metal bodies large in heat-transfer surface.

The heat exchanger includes porous metal bodies(1,21) having intercommunicating porosity to provide gas-flow paths(4,24) for suction air(IA) and to make the heat-transfer surface larger, porous metal bodies(1,21) being made of metal such as aluminum or aluminum alloy high in thermal conductivity. The porous metal bodies(1,21) are pierced with tubular elements(2) in which cooling water flows through. The porous metal bodies(1,21) may be fabricated by preparing a mold of foamed urethane resin filled with salt cores, pouring a metal having a melting temperature lower than that of the salt cores in to the mold.

Description

The present invention relates to a heat exchanger for exchanging heat between gases flowing through a porous metal body of intercommunicating porosity and a heat exchanging material arranged in contact with the porous metal body, the porous metal body being made of any metal, such as aluminum, high in thermal conductivity.
Conventionally, the gasoline engines and diesel engines in general have the superchargers such as turbochargers. It is well known that compressing air by the supercharger in the engine causes temperature rise in the air owing to adiabatic compression. The temperature rise in a suction air in the engine decreases the volumetric efficiency and increases the temperature of air-fuel mixture, which results in increasing the tendency to knock. To cope with the phenomenon, the engines are in general provided with the intercoolers of either air- or water-cooling type. The intercooler of water-cooling type is under substantially no restriction on where it is installed because of no requirement of air flowing through the cooler, nevertheless has the necessity of radiators and pumps.
The engines have also ordinary radiators for heat exchanging with a hot coolant. It is usually desired that the radiator is resistant to pressure and vibration, compact in size and superior in cooling performance. The prior radiators are designed such that the cooling water circulating in the radiator core is heat exchanged with atmospheric airflow taken with the moving velocity of the vehicle or by the cooling fan. The radiator cores are usually composed of tubes for flowing cooling water therethrough, and radiation fins. In such radiators, the heat-transfer surface of the radiation fins is inevitably to be extended so that the radiator core becomes larger in size.
Further in prior semiconductor circuits, the heavy-duty thyristors or power transistors are generally used for the high-output inverter converting the large current to the sinusoidal waveform. The electronic parts such as thyristors, power transistors or the like in the prior semiconductor circuits are ordinary large in heat loss and very often subject to heat deterioration in electronic performance owing to heating in their actuation. To cope with this, various cooling apparatus have been developed for heat exchanging the semiconductor circuits to protect the circuits from heating generated in their operation. The inverter is to convert the direct to the alternating current, and to control the speed or the like by converting the voltage and frequency. For example, the inverter may convert the frequency in the range of from 10 to 600 cycles to thereby change the rotational frequency of the motor or rotating shaft.
Meanwhile, the intercooler or radiator for cooling the suction air for engines has involved a complex subject on construction that it should be large in efficiency of heat exchanging with gas or air to be cooled, nevertheless compact in size.
On the other hand, the semiconductor circuit mounted on a substrate is provided with cooling means, because that heat occurs in the power transistors on changing the frequency by the actuation of the inverter, causing the deterioration of performance of the semiconductor. The prior cooling means for the semiconductor circuits is usually of a structure with radiation fins, which requires a large-scaled fan and thus becomes larger in size, nevertheless poor in cooling efficiency. Consequently, it is very hard to employ the aluminum-made large-scaled fan for miniaturized devices such as controllers of semiconductor circuits or the like. It has been desired to develop cooling means for the semiconductor circuits, which is superior in cooling performance with compactness in size.
It is well known that aluminum or aluminum alloy is relatively higher in thermal conductivity among metallic substances. Moreover it is capable of producing a porous metal body of metallic substance high in thermal conductivity. Thermal conductivity of aluminum is 220W/m · K, Si₃N₄ is 20W/m · K and SiC is 90W/m · K. It will be understood that aluminum is higher in thermal conductivity in comparison with Si₃N₄ and SiC. Accordingly, it may be proposed to produce the radiator or intercooler with making use of aluminum high in thermal conductivity.
Considering thermal conductivities of substances, gases such as air is low in thermal conductivity and, therefore, it is necessary for uniform heat transmission to extend the area of heat-transfer surface in contact with the gases.
This inventor filed a co-pending patent application in Japan, Japanese Patent Laid-Open No. 299472/1998, concerning a heat exchanger having a porous ceramic member. As having been explained in the specification of the co-pending application, quantity Q of heat transmitted from one substance to another is defined by Q = K· Ag (TG - TS) · t
Moreover, over-all heat transmission coefficient K is given by K = 1 / (X1 + X2 + X3) in which X1 = (1/ αg) × (AS /Ag) X2 = (δ1 / λ1) × (AS /A1) X3 = (1/ αC) × (AS /AC) where K is the over-all heat transmission coefficient; A_S , the mean area of heat-transfer path; T_G , the temperature of hot gas; T_C , the temperature of cool medium and t is the heat-transfer interval: and further where α_g is the heat-transfer coefficient of gases; λ₁, the thermal conductivity of solids; α_C, the heat-transfer coefficient of liquids; A_S , A₁ and A_C, the area of contacting surface between heart-transfer substances; and δ₁ is the thickness of the wall.
As defined by the above formulae, as α_g is far too small, the over-all heat transmission coefficient K is the reciprocal of α_g and thus becomes large with the result of decreasing the quantity of heat transmitted from one substance to another. To cope with this, it should be required to lessen the influence of δ₁ on the over-all heat transmission coefficient K, that is, to make A_S and A_C large with respect to δ₁. It is thus preferred to make aluminum porous body larger in heat-transfer surface, which is in thermal communication with a heat-receiving side, whereby A_g counterbalances α_g and X₁ becomes large with the result of remarkable improvement in transfer of heat.
An aim of the present invention is, with reference to the above consideration, to provide a heat exchanger preferably applicable to intercoolers, radiators or cooling means for substrates having mounted transistors of semiconductor circuits.
Another aim of the present invention is to provide a heat exchanger for, especially, for heat transmission from gases such as air to another medium such as liquids or solids, in which a gas-flow paths are composed of porous bodies of solid substance such as aluminum or aluminum alloy high in thermal conductivity to thereby extend the contacting surface with the gases in the gas-flow paths so that the over-all heat transmission coefficient may become large with the result of improvement in heat exchanging efficiency.
A further aim of the present invention is to provide a heat exchanger comprising porous metal bodies of inter-communicating porosity providing gas-flow paths for the gases, the porous metal bodies being made of metal high in thermal conductivity, defining elements for covering around the porous metal bodies, the defining elements being made of metal identical with that of the porous metal bodies, and heat exchanging materials arranged in contact with the porous metal bodies and in heat exchanging relation with the gases flowing through the porous metal bodies.
Another aim of the present invention is to provide a heat exchanger in which porous metal bodies are made of aluminum or aluminum alloy, the porous metal bodies being fabricated by making use of a mold of foamed urethane resin filled with salt cores.
Just only melt-deposition of aluminum particles is insufficient to make aluminum a porous heat-transfer body that is uniform, continuous in metallography. It is important to provide metal-continuity without thermal interruption as well as porous structure involving an intercommunicating porosity therein. This subject may be solved by the provision of the mold filled with salt cores that have a melting point of 700°C higher than aluminum having a melting point of 600°C.
Most of prior heat exchanges used in diesel engines or the like are of finned metal structure in which the are of the heat-transfer surface in contact with gases, or gas-side heat-transfer surface, is at most about 4 times as large as that of the heat-transfer surface in contact with liquids, or liquid-side heat-transfer surface. Reaching 4 times causes the heat exchanger becomes too large in size.
Whereas the porous metal body developed for the heat exchanger of the present invention is capable of making the gas-side heat-transfer surface area extend in the range of from six to twenty times as large as the liquid-side heat-transfer surface.
A further aim of the present invention is to provide a heat exchanger in which the heat exchanging materials are of tubular elements extending through the porous metal bodies, and the ratio per area unit of gas-contacting surface in the porous metal bodies to heat-transfer surface on the liquid paths is determined in the range of from 20:1 to 10:1.
Another aim of the present invention is to provide a heat exchanger in which liquid flowing through the tubular elements of the heat exchanging materials is of cooling water or lubricating oil and also gas flowing through the gas-flow paths in the porous metal bodies is of suction air to be distributed to the cylinders of the engine, whereby the suction air may be cooled down by the liquid. The heat exchanger may be adapted to the intercooler in such a manner that the porous metal bodies and the tubular elements are arranged upstream the suction manifold.
Another aim of the present invention is to provide a heat exchanger adapted to a radiator in which a cooling air flows through the porous metal bodies and a water for cooling the engine flows through the tubular elements so as to be air cooled.
Another aim of the present invention is to provide a heat exchanger adapted to cooling means for semiconductor circuits, in which the heat exchanging materials are composed of metal bodies of metallic substance high in thermal conductivity having mounted thereon a substrate of insulating substance on which the semiconductor circuits are mounted, and the air flows through the gas-flow paths in the porous metal bodies to thereby cool down the substrate.
A further aim of the present invention is to provide cooling means for semiconductor circuits in which a dust filter for purifying the inflowing air is provided upstream with respect to the air paths in the porous metal bodies and a suction fan is arranged downstream with respect to the air paths.
A further aim of the present invention is to provide a heat exchanger for cooling the semiconductor circuits in which the heat-transfer surface area in contact with the gas flowing through the porous metal bodies is more or equal to six times as large as the contacting surface area of the substrate with the porous metal bodies.
In accordance with the heat exchanger of the present invention as described above, the gas-flow paths are constituted by the porous metal bodies having therein the intercommunicating porosity and the porous metal body itself is uniform, continuous in metallography to provide metal-continuity desirable to the heat- transmission body. The gas-side heat-transfer surface, or the contacting surface with the gases in the gas-flow paths may be made larger so that the over-all heat transmission coefficient may become large with the result of improvement in heat exchanging efficiency.
With the heat exchanger being arranged upstream the suction air passage of the engine, it may be made to work as the intercoolers or radiators. As an alternative, the suction air flowing through the porous metal bodies may be effectively cooed down with the cooling water that flows through the tubular elements arranged in the porous metal bodies. The substrate of the semiconductor may be effectively cooled with a cool wind flowing through the porous metal bodies which are arranged in thermal communication with the substrate.
In the intercooler having incorporated with the heat exchanger of the present invention, the suction air pressurized in the supercharger of the turbo-charger or the like is brought in contact with the aluminum-made porous metal bodies in radiant-heat transfer relationship. The emitted heat from the suction air is in turn transmitted from the porous metal bodies to the cooling water in the tubular elements. With the over-all heat transmission coefficient K being applied to the formula described above, the following relations may be given to X1, X2 and X3, for the suction air, aluminum-made porous metal body and cooling water, respectively.
Now on the supposition that the heat-transfer coefficient of liquid α_C is 1200 /K; the heat-transfer coefficientof gases α_g, 58/K; the thermal conductivity of aluminum-made porous body λ₁, 220W/m · K; and the thickness of the wall δ₁, 0.005m; X1=(1/ 58) (AS / Ag )=1.710 -2 (AS / Ag) X2=(0.005220)(AS /A1)=2.2710-5 (AS / A1) X3=(11200) (AS / AC )=0.8310 -3 (AS / AC)
If X1 and X2 are equal to each other, the resulting equation is given by 0.83×10-3(AS /AC)=1.7×10-2(AS × Ag) (Ag × AC )=20.5
This states that the area of heat-transfer surface in contact with suction air, or the air-side heat-transfer surface, should be more than or equal to about twenty times as large as that of the heat-transfer surface in contact with the cooling water, or the water-side heat-transfer surface.
Meanwhile, in order to provide the air-side heat-transfer surface of twenty times the water-side heat-transfer surface in the prior heat exchanger of finned-type, for example, having fins of 3mm in thickness, closely spaced apart with the interval of 2mm, it will be made abnormally large-scaled because the height of the fin should be determined a half as long as the span of the thickness of fin and the distance between the adjacent fins.
The gas-flow paths formed of porous metal bodies may, easily satisfy this requisition, or air-side heat-transfer surface of twenty times the water-side heat-transfer.
The heat exchanger of the present invention, constituted as described above, is capable of extending remarkably the gas-side heat-transfer surface with high efficiency in heat exchanging. Hence the heat exchanger may be made more compact in size depending on the extension of the heat transfer surface, in comparison with the prior finning heat exchanger.
The intercooler for the suction air in the engine with the turbo-charger, and the radiator for cooling the worm water with the atmosphere may be improved in heat exchanging efficiency and made compact in size by the use of the heat exchanger according to the present invention.
With the heat exchanger of the present invention being adapted to the cooling means for the semiconductor circuits having incorporated therein with the power transistors, the cooling means becomes better utilization of space and helps miniaturize the fan for generating the cool wind and the motor for driving the fan. Consequently, the semiconductor device with the cooling means according to this invention is greatly useful, for example, for the controllers of the generator in the cogeneration system or the controllers of the hybrid car having the motor.
Other aims and features of the present invention will be more apparent to those skilled in the art on consideration of the accompanying drawings and following specification wherein are disclosed preferred embodiments of the invention with the understanding that such variations, modifications and elimination of parts may be made therein as fall within the scope of the appended claims without departing from the spirit of the invention. An embodiment of the invention will now be described, by way of example only, with reference to the accompanying drawings in which:-
FIG. 1 is a schematic sectioned view showing a preferred embodiment of a heat exchanger according to the present invention;
FIG. 2 is a schematic cross-sectioned view along section line A-A of FIG. 1;
FIG. 3 is a schematic illustration explanatory of an intake manifold in which the heat exchanger shown in FIG. 1 is incorporated;
FIG. 4 is a schematic sectioned view showing a preferred embodiment of cooling means for a semiconductor circuit, which has incorporated with the heat exchanger shown in FIG. 1;
FIG. 5 is a schematic side view in elevation of the cooling means for the semiconductor circuit shown in FIG. 4; and
FIG. 6 is a graph of air resistance in a transistor substrate and porous metal member vs. multiples of a heat-transfer surface area per contact-surface area unit.
To begin with FIGS. 1 to 3, a preferred embodiment of a heat exchanger according to the present invention is described.
A heat exchanger of the present invention may be applied to, for example, an intercooler incorporated in an intake manifold 10. The intake manifold 10 is composed of a suction pipe 12 communicating with a supercharger in a turbo-charger or the like, and branched runners 11 integral with the suction pipe 12. As the manifold 10 is designed such that suction air in the pipe 12 is distributed to cylinders of the engine through the branched runners 11, the heat exchanger is adapted to the manifold 10 in combination with the upstream suction pipe 12.
The heat exchanger is incorporated in the suction pipe 12 and includes porous metal bodies of intercommunicating porosity providing gas-flow paths 4 for the suction air, the porous metal bodies being made of metal high in thermal conductivity. The heat exchanger further includes first tubular elements 3 covering around the porous metal bodies 1 so as to define the gas-flow paths and communicating at the opposing ends thereof with inlet pipes 5 and outlet pipes 6, the first tubular elements 3 being made of metal identical with that of the porous metal bodies 1, and heat exchanging materials arranged in contact with the porous metal bodies 1 and in heat exchange relation with the suction air flowing through the porous metal bodies 1.
The heat exchanging materials are of second tubular elements 2 extending through the porous metal bodies 1 to thereby define cooling liquid-flow paths 9, the second tubular elements being connected at opposing ends thereof with inlet conduits 7 and outlet conduits 8 via sealing members 13. In this embodiment of the heat exchanger, liquid flowing through the second tubular elements 2 of the heat exchanging materials is of cooling water W or lubricating oil and also gas flowing through the gas-flow paths in the porous metal bodies 1 is of suction airt IA to be distributed to the cylinders of the engine. It is to be understood that the suction air IA may be cooled down by means of the cooling water W.
It is preferred in the heat exchanger according to this invention to determine the ratio per area unit of gas-contacting surface in the porous metal bodies 1 to heat-transfer surface on the liquid paths 9 in the range of from 20:1 to 10:1.
Where the heat exchanger of the present invention is applied to the intercooler, the suction air IA pressurized in the supercharger of the turbo-charger or the like is brought into contact with the aluminum-made porous metal bodies 1 in radiant-heat transfer relationship. The emitted heat from the suction air IA is in turn transmitted from the porous metal bodies 1 to the cooling water W in the second tubular elements 2. With the over-all heat transmission coefficient K being applied to the formula described above, it will be understood that the area of the heat-transfer surface on the side of suction air IA should be more than or equal to twenty times as large as that on the side of the cooling water W. This requisition may be satisfied by the gas-flow paths for the suction air IA, which is formed of aluminum-made porous metal bodies 1.
In accordance with the embodiment described now, the porous metal bodies 1 are of aluminum or aluminum alloy and fabricated by the steps of, pouring molten aluminum in a mold of foamed urethane resin filled with salt cores with burning out of the urethane resin, and dissolving and flushing the salt cores our of an aluminum casting whereby the porous aluminum casting is made.
For application of the heat exchanger of the present invention to the radiators, the second tubular elements 2 are used instead of the prior radiator core tubes and the porous metal bodies are used for the radiation fins of the radiator core. As a result, the combination of the porous metal bodies with the tubular elements 2 according to the present invention may make the radiator core of the prior radiator compact remarkably in size with improvement in heat exchanging efficiency.
Next, with reference to FIGS. 4, 5 and 6, another embodiment of the present invention will be described.
The heat exchanger is illustrated in application to cooling means 20 for semiconductor circuits, which are designed so as to be adapted to control instruments. Power transistors 30 mounted on a substrate 25 of an insulating plate made of ceramics or the like develops heat owing to frequent switching operations. To cope with this, the cooling means 20 in the semiconductor circuit has incorporated with a porous metal body 21 of aluminum or aluminum alloy high in thermal conductivity, through which a cooling air flows thereby absorbing the heat from the porous metal body 21 itself. Thus, the porous metal body 21 may contribute to making the cooling means compact in size. The airflow in the porous metal body 21 may further cool down an aluminum frame 22 having mounted thereon the substrate 25 and thus cool electronic parts mounted on the substrate 25, for example, power transistors 30, thyristors 31, printed circuit elements 29 and the like, resulting in protection of the various electronic parts from thermal deterioration.
The cooling means 20 in the semiconductor circuit is mainly is composed of the aluminum frame 22 of high thermal conductivity having mounted thereon the substrate 25 of insulating substance such as ceramics, which is provided thereon with electronic parts apt to heat up due to the operation themselves, the porous metal body 21 mounted to the substrate 25 through the aluminum frame 22, a casing 23 covering the porous metal body 21, a fan 27 forcing a cooling air-flow in the porous metal body 21, and a motor 28 actuating the fan 27.
In the embodiment described now, a dust filter 26 for making the inflowing air dust-free is provided upstream with respect to the air paths 24 in the porous metal body 21 and the fan 27 driven by the motor 28 is arranged downstream with respect to the air paths 24. It is to be especially noted that the heat-transfer surface to be in contact with the air in the porous metal body is more or equal to six times as large as a contact-surface area unit of the substrate 25 with the porous metal body 21.
In order to realize a predetermined air resistance (mmHg) against the airflow as well as a required heat-transfer surface, it will be seen from FIG. 6 that the heat-transfer surface area per the contact-surface area unit is enough more or equal to six times. In connection with the porosity of the porous metal body 21, the finer the pore is, the larger is the area of surface contacting with air, resulting in improvement in heat exchanging efficiency.
Meanwhile, the porous metal body 21 is required to permit the air to flow with easy through the inter-communicating porosity. It is therefore desirable the porous metal body in which the porosity is finer, nevertheless the air may flow easily.
In the cooling means 20 in the semiconductor circuits, the substrate 25 is mounted on its one side 32 with the electronic parts and on its opposing side 33 with the aluminum frame 22. The porous metal body 21 is of aluminum or aluminum alloy high in thermal conductivity and has therein the intercommunicating porosity for forming the air paths 24. The casing 23 covers around the porous metal body 21 and defines an air inlet port 34 and outlet port 35, the inlet port 34 containing the dust filter 26 in the air cleaner, and the outlet port 35 containing the suction fan 27. The miniature motor 28 drives the suction fan 27 to thereby generate the airflow in the porous metal body 21 from the inlet port 34 towards the outlet port 35. The miniature motor 28 is preferably actuated so as to control the fan 27 in response to the operational conditions of the electronic parts.
In accordance with the cooling means 20 in the semiconductor circuit constructed as described above, the heat originating in the electronic parts such as transistors due to their operational conditions is in turn transmitted from the substrate 25 to the porous metal body 21 through the aluminum frame 22. Driving the miniature motor 28 rotates the fan 27 to suck the air from the outlet port 34 towards the porous metal body 21. The suction cool air flows in the porous metal body 21 through the dust filter 26 with absorbing the heat from the porous metal body 21, and flows out the outlet port 35 with emission of heat to the atmosphere. The porous metal body 21 in the present invention is remarkably large in the air-contact surface so that it is excellent in emission of heat. The volume of the airflow through the porous metal body 21 may be reduced whereby the motor 28 may be miniaturized, resulting in the space saving of the cooling means.
While the present invention has been described in its preferred embodiments, it is to be understood that the words which have been used are words of description rather than limitation and that changes within the purview of the appended claims may be made without departing from the true scope and spirit of the invention in its broader aspects.

Claims

A heat exchanger comprising porous metal bodies of intercommunicating porosity providing gas-flow paths for the gases, the porous metal bodies(1,21) being made of metal high in thermal conductivity, defining elements (3) for covering around the porous metal bodies(1,21), the defining elements(3) being made of metal identical with that of the porous metal bodies(1,21), and heat exchanging materials arranged in contact with the porous metal bodies(3) and in heat exchanging relation with the gases flowing through the porous metal bodies(1,21).
A heat exchanger according to claim 1, wherein the porous metal bodies are made of aluminum or aluminum alloy, the porous metal bodies(1,21) being fabricated by making use of a mold of foamed urethane resin filled with salt cores.
A heat exchanger according to claim 1, wherein the heat exchanging materials are of tubular elements(2) extending through the porous metal bodies(1,21), and the ratio per area unit of gas-contacting surface in the porous metal bodies(1,21) to heat-transfer surface on the liquid paths is determined in the range of from 20:1 to 10:1.
A heat exchanger according to claim 3, wherein liquid flowing through the tubular elements(2) of the heat exchanging materials is of any one of cooling water and lubricating oil and also gas flowing through the gas-flow paths in the porous metal bodies(1,21) is of suction air(IA) to be distributed to the cylinders of the engine, whereby the suction air(IA) may be cooled down by the liquid.
A heat exchanger according to claim 4, adapted to the intercooler in such a manner that the porous metal bodies(1,21) and the tubular elements(2) are arranged upstream the suction manifold(10).
A heat exchanger according to claim 3, adapted to a radiator in which a cooling air flows through the porous metal bodies(1,21) and a water(W) for cooling the engine flows through the tubular elements(2) so as to be air cooled.
A heat exchanger according to claim 1, adapted to cooling means(20) for semiconductor circuits, in which the heat exchanging materials are composed of metal bodies of metallic substance high in thermal conductivity having mounted thereon a substrate(25) of insulating substance on which the semiconductor circuits are mounted, and the air flows through the gas-flow paths in the porous metal bodies(1,21) to thereby cool down the substrate(25).
A heat exchanger according to claim 7, wherein a dust filter(26) for purifying the inflowing air is provided upstream with respect to the air paths in the porous metal bodies(1,21) and a suction fan(27) is arranged downstream with respect to the air paths.
A heat exchanger according to claim 7, wherein the heat-transfer surface area in contact with the gas flowing through the porous metal bodies(1,21) is more or equal to six times as large as the contacting surface area of the substrate(25) with the porous metal bodies(1, 21).
The use of a mold of foamed urethane resin filled with salt cores for the production of a porous metal body for a heat exchanger.