METHOD FOR THE MANUFACTURE OF A HEAT EXCHANGER

Abstract: The invention relates to a method for the manufacture of a compact heat exchanger (1). To this end the hollow body (2) having at least two holes in the wall (3), in which two holes a heat conducting means (4) is provided, are immersed in a glass particle suspension and subsequently heated. The glass seals the gaps between the wall (3) and the heat conducting means (4). By providing holes which, in respect of the dimensions of the heat conducting means (4), are wide, and by filling the gaps with glass, there is no need to operate within close tolerances, so that the heat exchanger (1) can be manufactured at low cost. Preferably a heat conducting means (4) is inserted into two opposite wall parts of the heat exchanger (1). Licensing is possible.

Description: Method for the manufacture of a heat exchanger The present invention relates to a method for the manufacture of a heat exchanger, in particular a gas/gas heat exchanger, possessing a hollow body comprising a wall with an inlet opening and an outlet opening, wherein the wall is pro- vided with a hole, a surface-enlarging heat conducting means is inserted into the hole in such a manner that in the ready heat exchanger part of the heat conducting means is posi¬ tioned in the hollow body and another part of the heat con¬ ducting means remains outside the hollow body and wherein the surface-enlarging heat conducting means is attached to the wall using glass. Such a method is know from GB 1 521 683 (1974) . According to the method described therein for the manufacture of compact heat exchangers with a large heated surface per unit of volume, a heat conducting means is inserted into a hole in a wall part that is used to form a hollow body. There is a close fit between the rim of the hole and the heat con¬ ducting means. The close fit keeps the heat conducting means in place and its attachment is ensured by a glass lining. According to the description, two wall parts may be connected to each other by welding, resulting in a hollow body, whereby a seal is formed by melting the vitreous coating on the wall parts. When forming the hollow body, the individual wall parts are first provided with a glass coating before they are connected to each other, in order to allow ready access when applying the glass coating. The disadvantage of the method described is that, in order to ensure a tight fit between the rim of the hole and the heat conducting means, the working tolerances are very close. In other words, the dimensions of the holes and the dimensions of the heat conducting means must be maintained within very closely determined limits. For instance, making the holes by means of punching may result in deformation of the rim of the hole. Also, the formation of burrs may be bothersome. Working within close tolerances raises costs. Also, the close fit complicates the insertion of the heat conducting means. The object of the present invention is to improve the method according to the preamble and more specifically, to provide a method for the economical and simple manufacture of heat exchangers, in particular compact heat exchangers having a large heated surface per unit of volume, that can be operated at high temperature. To this end the invention provides a method as men¬ tioned in the preamble, characterized in that the wall of the hollow body is provided with at least two holes, that the surface-enlarging heat conducting means is provided in at least two holes, that the hollow body with its heat conduct¬ ing means is brought into contact with a suspension compris¬ ing glass particles and a means for keeping the glass particles in suspension, that said hollow body is then dried and is subsequently heated at a high, glass-melting tempera¬ ture, whereby gaps between the holes in the hollow body's wall and the heat conducting means are filled to form a seal, after which the hollow body thus provided with heat conduct¬ ing means and glass is cooled. During the manufacture of the heat exchanger accord¬ ing to the present method, the heat conducting means is kept in place by supporting the heat conducting means in at least two places. In this way there is no need for a close fit in order to be able to keep the heat conducting means in place. As working within close tolerances greatly increases costs, the method according to the invention makes it possible to manufacture heat exchangers considerably more economically. According to the invention, the great capacity of glass to fill gaps, which capacity is neither mentioned nor used in GB 1,521,683, is utilized to obtain a good seal between the inside of the hollow body and its surroundings. The preferred method for bringing the hollow body provided with the heat conducting means into contact with the suspension is by immersion. GB 537,733 (1940) describes a method in which a hollow body provided with a heat conducting means is immersed in a solder bath. Metal has a poor gap-fil¬ ling capacity, so that one has to work within close toler¬ ances. Moreover, large metal baths are very costly and in addition require much energy to liquefy the metal and main- taining it in the liquid state. A heat exchanger made with metal solder cannot be coated with glass and is not suitable for operation at high temperatures. Such a heat exchanger possesses, in contrast to a heat exchanger made according to the present invention, poor resistance to corrosive sub- stances. The use of glass for sealing is in itself prior art, albeit in another field. For instance DE-A-3400160 describes the use of glass granulate for attaching an electrode in a radiator. In the described method no use is made of a suspen- sion of glass particles. To provide a heat exchanger with an anti-corrosion glass coating by means of immersion in a suspension of glass particles is in itself prior art. However, it was never real¬ ized that by this means, economically and simply, by attach- ing the heat conducting means to the hollow body while sim¬ ultaneously applying an anti-corrosion glass coating, a heat exchanger may be manufactured, having heat conducting means protruding through the wall of the hollow body, which heat exchanger is suitable -for operation at high temperature. The invention will now be further elucidated with reference to the accompanying drawing in which Fig. 1 represents a partial top view of a heat exchanger manufactured by the method according to the inven¬ tion; Fig. 2 is a cross-section along line II-II in Fig. i; Fig. 3 is a partial cross-section of a heat exchanger manufactured by the method according to the inven¬ tion and equipped with a heat conducting means having partial heat conducting elements; and Fig. 4 is a cross-section along line IV-IV in Fig. 3. The heat exchanger 1 shown in Fig. 1 is comprised of a hollow body 2 having a wall 3, which wall 3 is provided with holes into which heat conducting means 4 are inserted. Both the wall 3 and the heat conducting means 4 are made of metal. In the embodiment shown, each heat conducting means 4 is inserted into two opposite wall parts of the hollow body 2. Due to the glass serving as sealing material between the wall 3 and the heat conducting means 4, a leak-tight seal is obtained. Such a heat exchanger 1 possesses good resistance to high temperatures and may, for instance, be placed after a steam boiler or gas turbine. If the heat exchanger 1 is manu¬ factured from unalloyed steel then the working range extends to about 600°C. The heat exchanger 1 according to the inven¬ tion may also be manufactured from other metals such as cop¬ per. It is even possible to manufacture the heat exchanger from different metals, a prerequisite being of course, that within the working range no stress occurs which could adversely affect the connection between the wall 3 and the heat conducting means 4. The heat exchanger 1, manufactured by the method according to the invention, is suitable for applications in a wide temperature range and is manufactured by providing holes in a metal plate to allow the introduction of heat conducting means 3. This may be realized by, for instance, punching. The method according to the invention does not require a close fit. A tolerance of 0.1 to 0.5 mm is suitable. Preferably the holes are 0.2 to 0.4 mm larger than the respective diameter of the heat conducting means 4. This loose fit facilitates easy insertion of the heat conducting means 4. Thus any poss¬ ible deformations that may have occurred while making the holes, will not hinder the insertion of the heat conducting means 4. The plate with the holes is then formed into the hollow body 2. In an advantageous embodiment the plate is formed into a rectangular hollow body 2, wherein the longi¬ tudinal edge, where the two plate rims touch after being formed into a rectangular hollow body, is sealed by means of a conventional welding operation. In a hollow body 2, formed in this manner, the two holes are provided in the two oppo¬ site sides of the wall 3 of the hollow body 2. The heat con¬ ducting means 4 is inserted into a hole in each of the two opposite sides, as shown in Fig. 2. It is not necessary that the sides run parallel to each other. After inserting one, or usually many heat conducting means 4 which are then distributed over the length of the heat exchanger, the hollow body 2 is immersed in a suspension comprising glass particles and a means for keeping the glass particles in suspension. Subsequently, the suspension is dried followed by heating at a high, glass-melting tempera- ture. For simple manufacture, the long sides of a heat con¬ ducting means 4 (or of a partial heat conducting means 5, which will be discussed below) are preferably in a more or less horizontal positioned during immersion. This is to ensure that the heat conducting means 4 is firmly mounted and to avoid it's being displaced or even falling out of the hol¬ low body 2. By coating the entire surface of the heat exchanger 1 with glass the heat exchanger is protected against corro- sion. By means of experiments, a person skilled in the art of glass coating will easily be able choose the type of glass suitable for the particular metal or alloy of which the hol¬ low body 2 and the heat conducting means 4 are made. Good results were obtained with a suspension prepared by grinding up 100 kg of a phosphorus silicon glass (Ferroglas 09014, Ferro, Rotterdam), 7 kg bentonite, 0.2 kg gum arabic, 10 kg quartz and 50 kg water. The glass is ground to an average weight particle size of 60 μ . 5% of the particles was smaller than 0.5 μm. Particles larger than 100 μm are, depen¬ ding on the size of the gap, not desirable. The weight aver¬ age particle size lies preferably between 55 and 65 μm. Apart from the above-mentioned phosphorus silicon glass it is also advantageous to use boron-containing glass for the manufacture of a heat exchanger 1. The suitable con¬ centration of glass particles in the suspension ranges from between 45 and 70% by weight/vol. and preferably between 55 and 65% by weight/vol. The preferred glass has a heat coeffi¬ cient of expansion substantially equal to or slightly less than that of the hollow body 2 and the surface-enlarging heat conducting means 4. This avoids the occurrence at certain temperatures of tensile stress between the glass and the metal of which the hollow body 2 and the heat conducting means 4 are made, which tensile stress might cause the glass to come loose from the metal or form cracks, so that the hollow body 2 would no longer be leak-tight. This would, dur¬ ing operation of the heat exchanger 1, result in leakage of the fluid. As glass possesses poor resistance to tensile stress but is resistant to pressure, it may be favourable that the heat coefficient of expansion of the glass is some- what less than that of the metal. By experimenting with dif¬ ferent glass compositions the person skilled in the art is able to select a glass type that suits the operational condi¬ tions of the heat exchanger 1. Likewise, by means of experiments, a suspension may be composed which is sufficiently stable for application in the present invention. The criterium is that so many glass particles are applied to the hollow body 2 provided with heat conducting means 4, and especially in the gaps between the wall 3 of the hollow body and the heat conducting means 4, that after heating the gaps are filled with glass to form a seal and if so desired, the entire surface of the heat exchanger 1 is coated with a layer of glass. The means that keeps the particles in suspension also contributes to their adherence to the heat conducting means 4 and the hollow body 2, during the stage succeeding immersion in the suspension and before the high, glass-melting temperature is reached. A suitable means (known from the literature) for keeping glass particles in suspension is clay. Known means such as gum ara- bic contribute to a good adherence of the glass particles and prevent the occurrence of cracks during drying. The high, glass-melting temperature is for instance 800-900°C, but clearly this will also depend on the type of glass used. A heat conducting means 4 runs through more than one hole, but this need not be limited to two holes in two oppo¬ site sides of the wall 3. A heat conducting means 4 may also be inserted into two or more holes in one side of the wall 3. According to an advantageous embodiment the heat conducting means 4 is formed by two or more partial heat conducting means 5a,b, each of which is inserted into a hole in the side of the wall 3 of the hollow body 2, and most preferably each is inserted into two holes in opposite sides of the wall 3. Thus, with one operation many partial heat conducting means 5 can be fitted, further simplifying the manufacture of the heat exchanger 1. Fig. 3 shows an example of such a suitable heat con¬ ducting means 4 which is provided with two partial heat con¬ ducting means 5a,b, and Fig. 4 shows this in cross-section. Such a heat conducting means 4 can be punched in one oper- ation, wherein it is both cut and bent. The great ability of glass to fill gaps, and the consequently less stringent tolerance requirements make it possible that heat conducting means 4, manufactured and formed in this manner, are still usable. By the method of the invention efficient heat exchangers can be manufactured possessing a large heated sur¬ face per unit of volume and heat conducting means 4 protrud¬ ing through the wall 3. Combining the sealing step with the step of anti-corrosion coating and of mounting the heat con¬ ducting means 4 into at least two holes, considerably simpli¬ fies manufacture. Because it is possible to allow a loose fit, deformation is a less critical factor and as a conse¬ quence the number of fins per unit of volume can be higher than with the known heat exchangers. The heat exchanger according to the invention is suitable for heat exchange between liquids, between gas and liquids and especially between gasses.

Claims: CLAIMS 1. A method for the manufacture of a heat exchanger, in particular a gas/gas heat exchanger comprising a hollow body comprising a wall with an inlet opening and an outlet opening, wherein the wall is provided with a hole, a surface- enlarging heat conducting means is inserted into the hole in such a manner that in the ready heat exchanger part of the heat conducting means is positioned in the hollow body and another part of the heat conducting means remains outside the hollow body and wherein the surface-enlarging heat conducting means is attached to the wall using glass, characterised in that the wall (3) of the hollow body (2) is provided with at least two holes, that the surface-enlarging heat conducting means (4) is provided in at least two holes, that the hollow body (2) with its heat conducting means (4) is brought into contact with a suspension comprising glass particles and a means for keeping the glass particles in suspension, that said hollow body is then dried and is subsequently heated at a high, glass-melting temperature, whereby gaps between the holes in the hollow body's (2) wall (3) and the heat con¬ ducting means (4) are filled to form a seal, after which the hollow body (2) thus provided with heat conducting means (4) and glass, is cooled. 2. A method according to claim l, characterized in that the hollow body (2) with its heat conducting means (4) is brought into contact with the suspension by immersion in the suspension. 3. A method according to claim 1 or 2, characterized in that the holes are made to be 0.2 mm to 0.4 mm larger than the respective diameter of the heat conducting means (4) . 4. A method according to one of the preceding claims, characterized in that glass is used with a heat coef- ficient of expansion substantially equal to that of the hol¬ low body (2) and the surface-enlarging heat conducting means (4). 5. A method according to one of the preceding claims, characterized in that glass is used having a heat coefficient of expansion which is smaller than that of the hollow body (2) and the surface-enlarging heat conducting means (4) . 6. A method according to one of the preceding claims, characterized in that glass particles are used pro- duced from phosphorus silicon glass or boron-containing glass. 7. A method according to one of the preceding claims, characterized in that the average size of the part¬ icles is 55 to 65 μm. 8. A method according to one of the preceding claims, characterized in that the concentration of glass par¬ ticles in the suspension ranges from between 55 and 65% by weight/vol. 9. A method according to one of the preceding claims, characterized in that the heat conducting means (4) is inserted into two opposite wall parts of the heat exchanger (1) . 10. A method according to one of the preceding claims, characterized in that a heat conducting means (4) is used provided with partial heat conducting means (5) , wherein each partial heat conducting means (5) is inserted into a hole of the hollow body's (2) wall (3).

Inventors: ROLLMANN PETER ULRICH, ROLLMANN, PETER, ULRICH
Applicants: KAT B V, ROLLMANN PETER ULRICH, KAT B.V., ROLLMANN, PETER, ULRICH
Application year: 1996
Main classification: F28F1
IPC codes: F28F1, F28F21