A method of manufacturing a heat exchanger

 

The invention relates to heat engineering and can be used in the manufacture of heat exchangers. A method of manufacturing a heat exchanger, comprising filling a porous metal space between the tubes for the flow of the cooled or heated fluid and the walls of the heat exchanger. Before filling between the tubes establish partitions and fall asleep granular material. The melting point of the granular material and the melting point of the material of the partitions is chosen above the melting temperature of the porous metal. After filling is heated granular material, pipes and walls to a temperature close to the melting temperature of the porous metal. Poured metal in the molten state, and after cooling, remove the granular material walls with obtaining a porous metal, alternating with continuous gaps. Inside the tubes and in the gaps additionally perform turbulizers elements. Gaps can be positioned at an angle to the direction of the blown air, and the porosity can be obtained by changing the volume. The technical result of the invention is to increase the mechanical strength and heat transfer capability used in the manufacture of heat exchangers for cooling and heating environments.

A known method of manufacturing heat exchangers for ovens, including the formation inside the channels for the movement of the media through what channel space in the housing is filled with molten metallurgical slags and simultaneously filled are blowing channels hot exhaust gases [1].

The disadvantages of this method are: - the presence of a large number of closed pores in the slag after cooling, which greatly reduces the heat output of the heat exchanger; the fragility of the porous material of the slag and its destruction vibratory loads; - there is no exact tasks required permeability and structure of the porous material.

A known method of studying the structure of the pore space of porous metal filling of the pores with the liquid substance. After hardening of the substance and removing the base material (dissolution, etching, etc.) remains solid sponge, accurately reproducing the pore space. The study of this sponge allows you to define the shape and size of pores, roughness of their surface and some other parameters of the pore space [2].

This method gives good results when the study and analysis of patterns of poronnik devices.

The closest technical solution, selected as a prototype, is the way in which produced automotive heat exchanger for cooling the oil in which the oil is pumped through tubes embedded in a layer of porous metal, through which pressure water flows to cool the oil to a predetermined temperature [3].

The disadvantages of this method are: - damage to the structure of the porous metal during pressing in the pipes, if it is produced after the sintering, since the driving tubes disrupted the structure of the first space not only in the field of securing tubes, but also in adjacent areas of the heat exchanger due to the transfer of mechanical stresses on the skeleton of porous metal; - by pressing the tubes before sintering of porous metal or by pressing the package with tubes of possible deformation of the tube during sintering or pressing of the package; - a large thermal resistance at the boundary between the tube wall and the porous metal during pressing of the tubes, which reduces heat transfer; - the low mechanical strength of such a heat exchanger.

The aim of the invention is: - increasing the mechanical strength and heat transfer SPO is Naya goal is achieved by the space between the tubes through which flows a cooling fluid, side walls and front and rear surfaces of the manufactured heat exchanger is filled with a porous metal, alternating with through gaps unfilled porous metal obtained from a compact molten metal, which according to the invention is made in the following sequence: between these tubes set partitions and the remainder of the said first space is filled with granular material, the melting point of which, as the melting point of the material of the walls, above the melting temperature of the desired porous metal, then heat the granular material, the partitions and the tube to a temperature close to the melting temperature of the compact metal fill the cavity between the grains of this metal in the molten state, and after cooling the granular material and the material of the partitions are removed by etching, dissolving, or otherwise.

Distinctive features of the proposed technical solutions are:
1. How they are placed in a porous metal tubes through which flows a cooled (heated) fluid, and perigourdine metal, retrieved from compact molten metal.

2. The sequence of manufacturing heat exchanger: install the tube and the partition between them and the rest of the said first space is filled with granular material, the melting point of which, as the melting point of the material of the walls, above the melting temperature of the desired porous metal, then heat the granular material, the partitions and the tube to a temperature close to the melting point of the metal of which must be made of porous metal, and then fill the cavity between the grains of this metal in the molten state and after cooling the granular material and the material walls removed (by etching, dissolution or otherwise).

The claimed technical solution distinctive signs are individually known in other fields of technology properties, and together with the characteristics of the prototype, exhibit properties that allow you to increase the mechanical strength and the heat transfer ability of the heat exchanger, to reduce the complexity of its manufacture, which indicates that the technical solutions according to the criterion of "substantial atualizacao the proposed method of manufacturing a heat exchanger.

In Fig. 2 depicts a schematic drawing illustrating an implementation of the method of manufacturing a heat exchanger with the turbulent elements within the above-mentioned tubes through which flows a cooled (heated) fluid.

In the schematic drawing (Fig. 1, 2) shows the elements, materials and accessories required for the implementation of the proposed method: thin-walled tube 1, installed in the mold 2 made of refractory metal or ceramic, the granular material 3, filling the mold 2 to the upper edge of the partition 4 mounted between the tubes 1, the sprue 5 of the mold 2, in the space 6 which is filled with molten compact metal flowing into the working space of the mold 2 through a narrow vertical slit hole 7. In addition, in the schematic drawing of Fig.2 shows turbulizers elements 8, for example, reducing the internal diameter (d) of the tubes 1 to (0,8-0,5)d by distance (3-5)d.

Below is a description of the options for implementing the proposed method of manufacturing heat exchangers.

The production version of the heat exchanger shown in Fig.1, is carried out as follows. At the bottom of the mold 2 to fill Oprea in granular material to the bottom of the mold, and fall asleep this material the mold 2 to the top edge. If several rows of tubes, then do the installation of partition walls 4, the granular backfill material 3 and the installation of the tubes 1 are sequentially row by row, falling granular material to the top edge of the mold 2. Then the mold 2 with the tube 1, the partitions 4 and granular material 3 is placed in a heating furnace and heated to a temperature close to the melting temperature of the compact metal of which must be made of porous metal. When the temperature of the mold 2, tube 1, the partitions 4 and granular material 3 becomes close to the melting temperature of the compact metal into the space 6 of the sprue 5 of the mold 2 is filled with molten compact metal through the vertical slot 7 enters the space of the mold 2, the filled tubes 1, the partitions 4 and granular material 3. The cavity between the grains of the granular material 3 is filled with molten metal to the upper edge of the mold 2, without closing the granular material 3 and partition 4. Allow to cool down the mold 2 and extract its contents, then the granular material 3 and the material of the partition walls 4 are removed by etching, dissolving, or otherwise, as well as OAS continuous metal film, then it is removed by milling before the dissolution or etching of the granular material and the material of the partitions. If necessary, in the bottom part of the mold 2 do channels to facilitate the filling of the spaces between the grains of the granular material 3. The resulting flows compact metal is also removed by milling before etching and dissolution.

In the case of the implementation shown in Fig.2, in addition to those described in the tubes 1 before placing in the mold 2 make turbulizers elements 8, for example mechanical knurling, reducing the internal diameter (d) of the tube (1) to (0,8-0,5)d intervals (3-5)d along its length.

The third embodiment of the inventive method of manufacturing a heat-exchange apparatus not shown in Fig.1 and 2, but it is obvious. So, if the mentioned partitions to shape that provides air flow turbulization, for example, to execute them in a wave of land or land with successive contractions and expansions in the direction of the air, the heat dissipation of this heat exchanger will naturally increase due to turbulence in the passing air flow.

The fourth embodiment of the inventive method of manufacturing a heat exchanger of apparatii at an angle to the side walls or the front and rear surfaces of the heat exchanger, the length of the channels, unfilled porous metal will increase. Therefore, will increase the time during which the blown air is in contact with the sections of porous metal heat exchanger that provides improved heat transfer heat exchanger.

Heat transfer in the heat exchange apparatus manufactured by the above method with the considered implementations can also be increased, if you vary the permeability of the porous metal in his volume, changing its removal from the tube 1 through which flows a cooled (heated) fluid, so that thermal resistance between the tubes 1 and the porous metal was minimal and at the same time it was possible for relatively free passage blown through the porous metal of the air.

Compared with the prototype [3] the proposed method allows to increase the mechanical strength and heat transfer capacity of heat exchangers, as well as reduce the complexity of their manufacture and cost.

This is confirmed by the following arguments.

High mechanical strength, vibration resistance and rigidity in heat exchange apparatus, manufactured on offer which, together with the tubes 1 single structure, similar to the structure of reinforced concrete structures, but in contrast, this structure is homogenous and it is permeable to air, as it has many winding channels and through the gaps, which is blown through the air.

Heat exchangers made by the proposed method have also increased heat transfer capability compared to similar heat exchangers, manufactured by known methods. It is provided as follows. First, the fact that thermal resistance between the porous metal and the walls of the tubes through which flows a cooled (heated) liquid becomes the minimum due to the practical disappearance of the border between the outer surface of the tubes and porous metal because education is actually a single crystal metal structure of these tubes and porous metal. Secondly, the fact that the length of the meandering channels in the porous metal, which is blown through the air, considerably greater than the thickness of the porous metal, as these channels are formed by voids in the metal have a different connection with each other and, therefore, the blown air does a tortuous path at the shoulder (or giving) more heat energy. Thirdly, the fact that blown through the porous metal heat exchanger air makes it turbulent motion, since the channels are composed of alternating cavities are narrow and extensions that create turbulence blown air and, thereby, contribute to the increasing heat. Fourthly, the fact that, by adjusting or setting the porosity of the porous metal and the thickness, the number and size of end-to-end gaps of the walls in the heat exchanger, it is possible to adjust or set the aerodynamic resistance of a porous metal heat exchanger as a whole blown air through it and obtain optimum mass flow rate of the blown air, which provides the highest heat output.

Simplicity of design and fabrication technology, heat exchanger manufactured according to the proposed method, no soldering and welding significantly reduces the complexity of its manufacture, and the use of relatively cheap and widely used metals and materials in the manufacture of these heat exchangers significantly reduces their cost. The starting materials for making the most simple taloutemme tubes, which flows cooled (heated) liquid aluminum ingots as a compact metal, made of porous metal salt as a granular material and a normal or quartz glass as a partition, and the solvent may be water, cold or warmed for salt and hydrofluoric acid for glass. These materials and metals suitable for the manufacture of the majority of heat exchangers used in vehicles and in stationary air conditioning equipment. It is clear that the cost of such heat exchangers are significantly lower than similar devices made according to the traditional technology. In principle partitions can be made from table salt in a compact form.

In those cases where the imposed more stringent requirements should be applied to other appropriate metals, materials and substances for dissolving or etching.

The possibility of increasing the heat transfer of a heat exchanger manufactured according to the proposed method, with varying porosity of the porous metal can be explained as follows.

thermal conductivity of a body of porous metal changing p is
whereandto- thermal conductivity of porous and compact metals, respectively; P is the porosity of the porous metal.

Formula (1) obtained for statistical mixtures and is valid only when the porosity to 0.66. For more porous bodies this expression cannot be used, because the calculated thermal conductivity values go to zero or become negative.

Hydraulic or aerodynamic resistance of porous metals (for passing through these media the less, the greater the porosity, i.e.


where k is the proportionality coefficient.

Therefore, to improve thermal conductivity and, accordingly, the heat transfer of a heat exchanger made of porous metal, it is necessary according to the formula (1) to reduce its porosity (P), and to improve heat dissipation during the passage of the cooling medium, for example air, it is necessary according to the formula (2) to reduce hydraulic or aerodynamic resistance, that is, to increase the porosity of the porous metal. These two conflicting requirements indicate that there is an optimum value of paristo the E. removal from the tube also contributes to the intensification of heat exchange.

Introduction through gaps formed remote partitions, alternating with sections of porous metal, allows to some extent to regulate the heat output of the heat exchanger: first, because of the possibility of regulating the aerodynamic resistance of the blown air, and secondly, due to the substantial increase in the surface blow-off sections of porous metal, determined by the number and cross-section through the gaps, and, thirdly, thanks to the heat pump, which is formed due to the temperature gradient between the surface temperature of the tubes and the temperature on the surface sections of the cooled porous metal and a relatively low thermal resistance of the skeleton of the porous metal. In a first approximation, the heat transfer (q) of this heat exchanger can be determined by approximate formula
q=qp(l+f), (3)
where qp- heat heat exchanger, made of porous metal without end-to-end gaps; f - coefficient depending on the ratio of the total area of the cross-cutting gaps and square heat exchanger by blown air and turbulizing processes in the channels formed by the remote partitions.

It should be noted that the partition can be mounted and parallel to the tubes, and also to form a section of the porous metal tubes and gaps unfilled porous metal, parallel to the tubes and perpendicular to them.

References
1. USSR author's certificate 1585627, CL F 23 L 15/04. - Bulletin of inventions 30, 1990

2. Belov S. C. Porous metals in mechanical engineering. - M.: publishing house "engineering", 1976, S. 50.

3. In the book "New in powder metallurgy". Translated from English-M.: Izd-vo "metallurgy", 1970, S. 168-179.


Claims

1. A method of manufacturing a heat exchanger, comprising filling a porous metal space between the tubes for the flow of the cooled or heated fluid and the walls of the heat exchanger, characterized in that before filling in the space between the tubes establish partitions and fall asleep granular material, the melting point of the granular material and the melting point of the material of the partitions is chosen above the melting temperature of the porous metal, then heat the granular material, pipes and partitions provide the standing cavity between the grains of the granular material, after cooling remove the granular material and the material walls with obtaining a porous metal, alternating with continuous gaps.

2. A method of manufacturing a heat exchanger under item 1, characterized in that inside the tubes for the flow of cooled or heated liquid execute or install turbulizers elements.

3. A method of manufacturing a heat exchanger under item 1, characterized in that the partitions perform such form that provides the turbulization of the air flow passing through the gaps formed by removing material of the walls.

4. A method of manufacturing a heat exchanger according to any one of paragraphs.1, 3, characterized in that the gaps are placed at an angle to the direction of the blown air.

5. A method of manufacturing a heat exchanger under item 1, characterized in that the filling of the space between the tubes for the flow of the cooled or heated fluid and the walls of the heat exchanger provide a porous metal porosity value, changing the volume.

 

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