EP0994313A1 - Method for making a heat exchanger and heat exchanger made by this method - Google Patents

Abstract

Metal heat exchanger production, by investment casting using a lost plastic model, is new. A metal heat exchanger is produced by: (a) forming a heat exchanger model of plastic which evaporates at or below the metal melting temperature; (b) coating the model with a gas permeable supporting layer of heat resistant material; and (c) casting molten metal on the model to evaporate the plastic for replacement by the metal. An Independent claim is also included for a heat exchanger produced by the above process.

Description

The invention relates to a method for producing a Heat exchanger made of metal such as aluminum, copper, iron, Steel or brass, which includes heat exchangers: one room formed by a wall, which with a Inlet opening for supplying a first fluid into the room, and an outlet opening for discharging the first fluid the room is provided; essentially one helically extending around the space for a second fluid; and a number of protrusions from the Protrude wall into the room. In addition, the Invention obtained using the method Heat exchanger.

Such a heat exchanger is for example from the EP-A-0 794 393 is known. This publication describes one using a light metal casting technique manufactured heat exchanger with a closed, polygonal or curved inner wall that with at least a water channel, one located inside the inner wall extending combustion chamber for hot flue gases and at the Extending from the inside wall heat-transferring surface-enlarging elements, such as Cam or partition walls is provided. The water channel extends helically along the outside of the Inner wall and has adjacent turns.

The known heat exchanger is relatively compact. In addition, the known heat exchanger has a cheap one Efficiency due to the fact that the water channel is on is attached to the outside of the combustion chamber. This Arrangement namely leads to the fact that the temperature of the Approximately the heat exchanger on the outside Temperature of the water in the water channel corresponds while the hot flue gases are in the combustion chamber. So be the convection and radiation losses of the heat exchanger minimized.

The well-known heat exchanger is in a conventional Casting process using a casting core structure Cast sand, wax or plastic. Such In principle, casting processes create those for design of the heat exchanger desired freedom in the determination the relationship between the water side and Flue gas side surface for optimal heat transfer between the flue gases and the water.

A disadvantage of the known heat exchanger is that the Content of the water channel is relatively large, which results has that after the commissioning of the heat exchanger due to the high heat capacity of the water takes a relatively long time until the water in the water channel has the desired temperature. Most of all, this is undesirable if the water in the heat exchanger is part of a Water circuit for heating tap water is what is in a so-called combination boiler, which is designed to both Heat tap water as well as water for heating purposes, is common. The desired tap water heating only takes place instead of when the water flowing through the heat exchanger has reached the right temperature. The faster this happens, the higher the comfort for the user of the Be cauldron. Even if in the combi boiler Hot water storage tank to bridge the period between the time when hot tap water is needed arises, and the time when the desired degree of Heating of the tap water is reached, is used, is it desires the water flowing through the heat exchanger quickly at the right temperature. The faster because this happens, the smaller the can Be a hot water tank.

A first reason for the large content of the water channel in the well-known heat exchanger is that the water channel one must have a relatively large minimum cross-section to this Shape the channel using a traditional casting process to be able to. These minimum dimensions are not allowed be undercut because of the casting core in this case an insufficient one at least during the casting process Could provide support on the walls of the canal. Both in connection with and independently of The first reason mentioned is a second reason for the big one Content of the water channel that the water channel is almost extends over the entire outer surface of the combustion chamber, so that the water channel has a relatively large length.

The fact that a core part has a minimal Cross section is said to have the required stability ensure, as an additional disadvantageous effect, that the elements of the known heat exchanger that the enlarge heat transfer area, actually in one minimum determined by the casting process used mutual distance must be arranged.

Another disadvantage of the known heat exchanger is that this one, although light metal is used has relatively large mass since the different parts like e.g. the wall of the combustion chamber, the wall of the water channel and the elements that make up the heat transfer surface enlarge, are relatively thick. The reason for this thickness is the required minimum space between the parts of the Pouring core set in connection with inaccuracies in the Production of the casting core set, the assembly and its Use. The relatively large mass of the Heat exchanger implies that the heat capacity of the Heat exchanger is relatively large and that the material costs are relatively high. The adverse consequences of the big ones Heat capacity are related to the above Water channel has been explained.

The object of the invention is therefore to provide a method create a heat exchanger in such a way to establish the limitations of traditional Manufacturing process can be overcome and the cheap Properties of the known heat exchanger type further can be optimized.

This object is achieved in that the The process includes the following steps: a plastic becomes a copy of the heat exchanger manufactured, which plastic at least in the Melting temperature of the metal evaporates; the surfaces of the copy are covered with a gas permeable, supportive layer from one heat-resistant material coated; and Metal in liquid state on the copy within the gas permeable layer is poured around the plastic to evaporate and the space occupied by the plastic to fill with the metal.

To form the plastic heat exchanger copy, preferably made of polystyrene (EPS), can in itself known injection molding processes can be used with whose help is a copy of one or more parts can be manufactured. Manufacturing in parts becomes one choose if the geometry of the heat exchanger and so even the copy is complex. The one for molding the copy parts required form (s) can be relative in this case just run. The different parts of the Copy can easily be made with a suitable adhesive or by e.g. Welding the Plastic bonded together to form the copy become.

The plastic and any adhesive used should have an evaporation temperature that is lower than or at least as high as that Melting temperature of the metal from which the heat exchanger is made so that during the pouring of the liquid Metal on the copy of the space defined by the copy is gradually taken up by the metal during the Evaporate plastic and possibly the adhesive and through the gas permeable, supporting layer heat-resistant material escape.

In contrast to the prior art, in which a Casting core set as a starting point for defining the geometry of the heat exchanger is now used according to the invention Plastic copying this task is firstly one greater freedom of design possible in the other Construction elements such as soundproofing devices that contain one or more cavities as an integral Part of the heat exchanger can be provided. Further details of the heat exchanger, e.g. walls and projections, made with a smaller thickness be what the heat capacity of the heat exchanger significantly reduced and heat transfer improved. The cross section of the water channel can be reduced, so that the content of the channel and so the heat capacity of the Water decreases significantly, so that rapid heating of the water can take place.

Preferably in the method according to the invention coated the surfaces of the copy by first Surfaces of the copy with a gas permeable layer coated with a first heat-resistant material and then the gas-permeable layer with one layer from a supportive, porous second heat-resistant Material coated. The gas permeable layer from the first heat-resistant material, preferably one ceramic material, especially silicon dioxide, Alum, zircon, chromite and / or aluminosilicate, acts as a "skeleton" for the copy to preserve it Form before and during the casting process and also functions as a "partition" between the copy (and during the Casting process: the metal) and the layer of supportive, porous second heat-resistant Material, which is preferably a ceramic material, and especially consists of sand. The layer from the first heat-resistant material can be immersed by pour over or spray, and is preferably thin, e.g. 0.25 to 1.5 mm thick to make that Easily push the gas generated during the pouring process allow. The layer can also be thin because of the second heat-resistant material for the necessary support the layer of the first heat-resistant material, especially if there is liquid metal underneath. The layer is made of the second heat-resistant material usually thicker than the layer from the first heat resistant material and can be easily formed by it by first filling the cavities with the first heat-resistant material provided with sand fills copy and then the copy e.g. in a box with sand, so that the whole outside of the copy except the necessary pouring holes is sufficiently covered with sand. If compaction of the sand is necessary, it will shaken for a certain time. The sand will preferably no binder added. The sand can go on the casting process and the solidification of the metal be removed, taking the sand, if necessary, through shake can be removed from the cavities of the copy. The sand is hardly contaminated and can be used without problems reused or disposed of without special measures become. Incidentally, it is without in the context of this invention further possible means known to the sand add to the dimensional stability of the sand mass improve especially during the casting process, so that also on the application of the layer from the first heat-resistant material can be dispensed with can.

The object of the invention is in particular a Heat exchangers with a relatively low heat capacity, a relatively small water content, an excellent one Heat transfer, low weight and one to create low price. To meet one or Several of the above goals will be the heat exchanger prepared according to the previously described method.

Preferably, the heat exchanger according to the invention executed such that the heat exchanger has an integrated Contains outlet channel for the first fluid, the one Has inlet opening and an outlet opening, the Inlet opening of the inlet channel adjoins the outlet opening of the room. This way a connection can be made with the necessary seal between the room and the Exhaust duct can be saved, and a Combustion system, of which the heat exchanger is a part what makes it particularly compact.

Preferably are in the outlet channel close to it Inlet opening heat conduction elements to improve the Heat transfer from the first fluid to the heat exchanger appropriate. The channel extends for the second Fluid around the heat conduction elements Exhaust duct to the heat that in the exhaust duct first fluid is withdrawn, as effectively as possible to the second fluid to transmit.

It is preferably through the space and the outlet channel certain flow path for the first fluid U-shaped. It would be advantageous if the inlet was in the same Level as the outlet opening of the outlet duct would. This means that those belonging to the heat exchanger Components of a combustion system such as a burner, a flue gas outlet channel, etc. simple and as compact units can be mounted on the heat exchanger.

Advantageously, the inlet of the room and the Outlet of the outlet channel through a common flange educated. After pouring the heat exchanger needs in In this case, only one flange surface is reworked be what take place in a single processing step can. Any dimensional deviations of the casting have none or little influence on the connections on the mentioned Inlet and outlet opening. If on the flange too mounting components (in the case of a Incinerator: one burner and one Flue gas outlet) before assembly to a composite Components have been assembled, this can assembled component assembled in one operation become. Disassembly of a composite component leads to simplification of maintenance and cleaning of the heat exchanger.

The heat exchanger is preferably designed such that the cross-section of the room, transverse to the direction of flow of the first Considered fluids in the flow direction of the first Fluid decreases. In this way you can achieve that Flow velocity of the, in its flow direction cooling by heat transfer to the second fluid first fluid always remains high enough to be good To ensure heat transfer.

The turns of the channel are expedient positioned at a certain distance from each other. thanks this measure is the volume of fluid in the channel, usually water, small. The fluid can therefore be quick be warmed up.

The heat exchanger is preferably designed such that the protrusions on at least part of the wall of the room are missing, this part of the wall with itself, across to Considered the direction of flow of the first fluid in space, extending, protruding into the room is provided. To further improve heat transfer from the first The heat exchanger has fluid to the second fluid according to the invention one or more of the channel wall from projections protruding into the channel. Just like that Projections in the space for the first fluid can Projections in the canal in a variety of ways be trained (generally such that a Turbulence of the second fluid is generated or increased), for example as cones or ribs.

These bulges create turbulence in the flow of the first fluids and lead to an enlargement of the Heat exchanger surface in contact with the first fluid is coming. Both effects lead to an improvement in Heat transfer from the first fluid to the wall of the room. Parts of the are preferably located at the level of the curvatures Channel, so that also the heat transfer of the first Fluid to the second fluid is improved.

Figur 1

in perspektivischer Darstellung eine erste Ausführungsform einer Kopie des Wärmetauschers gemäß der Erfindung, in auseinander genommener Form

Figur 2

in perspektivischer Darstellung die Kopie aus Figur 1 in zusammengesetzter Form,

Figur 3

einen Teil der Kopie in Figur 1 in einer Seitenansicht gemäß dem Pfeil III in Figur 1,

Figur 4

in perspektivischer Darstellung eine zweite Ausführungsform der Kopie aus auseinander genommener Form eines Wärmetauschers gemäß der Erfindung und

Figur 5

in perspektivischer Darstellung die Kopie in Figur 4 in zusammengesetzer Form.

The invention is explained in more detail below with reference to the accompanying drawing. The drawing shows:

Figure 1

a perspective view of a first embodiment of a copy of the heat exchanger according to the invention, in disassembled form

Figure 2

1 is a perspective representation of the copy from FIG. 1 in assembled form,

Figure 3

part of the copy in Figure 1 in a side view according to the arrow III in Figure 1,

Figure 4

a perspective view of a second embodiment of the copy of the disassembled form of a heat exchanger according to the invention and

Figure 5

in perspective the copy in Figure 4 in assembled form.

In the different figures the same refer Reference number referring to the same parts or to parts with a similar function.

Figures 1 to 3 show a copy housing part 2, a Copy housing part 4, a copy housing part 6 and one Copy channel part 8. Include copy case parts 2 and 4 each side walls 10, 12 and 14, a bottom wall 16 and an inner wall 18. In the shown in Figure 2 assembled form of copy limit the side walls 10, part 12a of each of the side walls 12, part 16a of each of the bottom walls 16, and the inner walls 18 one Heat exchange room, its cross section from top to bottom considered decreases. The side walls 14, part 12b of each of the side walls 12, part 16b of each of the Bottom walls 16 and the inner walls define one Exhaust duct. The side walls 10, 12 and 14 and the Inner wall 18 of each copy housing part terminates at one common edge in the flange 20. The flanges 20 (Figure 2) in turn limit a large opening, inlet opening 22 of the heat exchange room, and a small opening, Called outlet opening 24 of the outlet duct. So is the inlet opening 22 in the same plane as that Outlet opening 24. In addition, the heat exchange space has a Outlet opening, which with the inlet opening of the Exhaust duct coincides and from the passage between the bottom walls 16 and the inner walls 18 is formed. With this design, the copy corresponds to one Heat exchanger from the room and the outlet duct certain flow path for the first fluid U-shaped.

On that side of each side wall 12 which is the other Copy housing part 4 faces is in the Heat exchange room a large number of pins 26 in one predetermined pattern attached. The pins 26 have in the Figures 1 and 3 a circular cross section; you can but also a different shape, such as one have an oval or rectangular cross-section. Can continue the pins 26 considered different over their length Have cross sections, for example larger at their foot ends than be at their free ends. The pins 26 can also by ripping or similar be replaced. Starting point for the Positioning and design of the tenons, ribs or similar is always that (in a copy corresponding to Heat exchanger) no fluid flowing past it straight distance from the inlet opening of the room to The outlet opening of the room must be able to travel because hence the heat transfer that goes over the tenons, the fins or similar takes place, demolition would be done.

In principle, even in the channel can be arbitrarily shaped Projections such as pin 27 or ribs to promote the Heat transfer that takes place in channel 28 be attached. The pins 27 or the like can to the Copy channel parts 6 or 8 (Figure 4) or to the Copy housing parts 2 or 4 (Figure 1) or both types of parts.

In the side walls 10 and 12 and in the inner walls 18 parts of a channel are formed, which parts together one helically around the heat exchange space extending channel 28 with a channel inlet 30 and a Form channel outlet 32. Mentioned parts of the channel can be found in the side walls 10 and the inner walls 18 also not shown in more detail, for example rib-shaped projections be provided. The channel parts in the side walls 10 and the inner walls 18 ensure that the wall of the this limited space is partially domed.

The copy housing parts 2 and 4 and the copy channel parts 6 and 8 are all designed so that they can with the help of a relatively simple shape made of a plastic material without the need to look at a certain angle Release direction of the mold to be used to move moldings must be able to be manufactured. If parts 2 to 8 are formed into a complete copy of the assembled to be manufactured heat exchanger, as in figure 2 is shown. For this, parts 2 to 8 are preferred glued together with a suitable adhesive. in the With regard to the pin 26 it should be noted here that this one can be of such a length and position that, according to the Assembling parts 2 and 4 a bridge between the form respective side walls 12 of parts 2 and 4. The Pin sets 26 of different parts 2 and 4 can also be positioned offset from one another and protrude between each other. Another possibility is, that the pin 26 of part 2 and the pin of part 4 probably cursed, but the ends of the cones are not touch each other. In the latter case, the cones of each part 2, 4 different lengths from each other must have to prevent (in one of the copies corresponding heat exchanger) part of the by the Heat exchanger flowing fluid in a direct way from the inflow opening can flow to the outlet opening.

After assembling the copy, it will be all over it Surface with a gas permeable layer made of a first heat-resistant material. Subsequently will copy all spaces with a second heat-resistant material is filled and the so obtained Copy also on the outside with the second heat-resistant material coated. If now one pouring liquid metal onto the copy evaporates it Material of the copy, the resulting gases through the layer of the first heat-resistant material and due to the porous second heat-resistant material escape. The metal solidifies within that first heat-resistant material certain shape, so that the desired heat exchanger is created. Then be the second and the first heat-resistant material removed, after which the cast heat exchanger for inclusion in and Use of an associated combustion system is done. When using the heat exchanger flows in first fluid like a hot flue gas from the inlet opening 22 to the outlet opening of the heat exchange space on the pin 26 over. The first fluid then flows through the Outlet channel and it leaves the heat exchanger through the Outlet opening 24.

At the same time, a second fluid flows in counterflow e.g. Water through channel 28 from inlet port 30 to its outlet opening 32, this second fluid from absorbs heat given off by the first fluid. At the Corrosion products and condensate arising from heat exchange can the heat exchanger via an outlet opening 34 (Figure 2) leave.

Figures 4 and 5 show an embodiment of the copy of a heat exchanger according to the invention, which in wide Areas similar to the copy of Figure 1 to 3 is formed. One differentiating point concerns the design of the protrusions 26a, which one have a rectangular cross-section. Next are the parts of the Channel 28, which extend on the side wall 10, completely on the side facing the heat exchange space the side wall 10 attached, resulting in a flat shape the outside of the copy leads. As can be seen from Figure 4, is the inner wall 18 partially duplicated to (in one the warmest part corresponding to the copy of the heat exchanger) of the heat exchange space, which is located directly at the inlet opening 22 connects as far as possible from a thermal point of view of the coldest part of the exhaust duct, the Outlet opening 24 immediately preceding to separate. Part of the Outlet duct contains, just like the heat exchange space, Projections 26b. The channel 28 extends helically around the heat exchange space and at the level of the projections 26b around the outlet duct.

Claims (17)

Method of manufacturing a metal heat exchanger, which comprises: a wall formed space provided with an inlet opening (22) for supplying a first fluid into the space and an outlet opening for discharging the first fluid from the space; a second fluid channel (28) extending substantially helically around the space; and a number of protrusions (26) protruding from the wall into the room, the method being characterized by the steps of: a) a copy of the heat exchanger is produced from a plastic, which plastic evaporates at least at the melting temperature of the metal; b) the surfaces of the copy are coated with a gas-permeable, supporting layer of a heat-resistant material; and c) metal in liquid state is poured onto the copy within the gas-permeable layer in order to evaporate the plastic and to fill the space occupied by the plastic with the metal. A method according to claim 1, characterized in that step b) comprises the steps that b1) the surfaces of the copy are coated with a gas-permeable layer of a first heat-resistant material; and b2) the gas-permeable layer is coated with a layer of a supporting, porous, second heat-resistant material. A method according to claim 1 or 2, characterized characterized that the plastic is polystyrene (EPS). A method according to claim 2 or 3, characterized characterized in that the first heat-resistant material contains ceramic material, in particular silicon oxide, Alum earth, zircon, chromite and / or aluminosilicate. Method according to one of claims 2 to 4, characterized characterized in that the second heat-resistant material contains ceramic material, especially sand. Heat exchanger manufactured according to the process one of claims 1 to 5. Heat exchanger according to claim 6, characterized in that this has an integrated outlet duct for the first Fluid includes which channel has an inlet opening and a Has outlet opening (24), the inlet opening of the Exhaust duct connects to the outlet opening of the room. Heat exchanger according to claim 7, characterized in that in the outlet channel near its inlet opening Heat conduction elements (26b) are attached. Heat exchanger according to claim 8, characterized in that the channel (28) for the second fluid in the amount of Heat conduction elements (26b) inter alia around the Exhaust duct extends. Heat exchanger according to one of claims 7 to 9, characterized in that the space and the Outlet channel determined flow path for the first fluid Is U-shaped. Heat exchanger according to one of claims 7 to 10, characterized in that the inlet opening (22) of the Space in the same plane as the outlet opening (24) of the Outlet duct is located. Heat exchanger according to claim 11, characterized characterized in that the inlet opening (22) of the room and the outlet opening (24) of the outlet channel from a single one common flange are formed. Heat exchanger according to one of claims 6 to 12, characterized in that the cross section of the room, transverse to the direction of flow of the fluid contained therein considered, decreases in the direction of flow of the first fluid. Heat exchanger according to one of claims 6 to 13, characterized in that the turns of the channel (28) are spaced from each other. Heat exchanger according to one of claims 6 to 14, characterized in that on at least part of the The projections are missing, the wall part with itself viewed transversely to the direction of flow of the first fluid in space extending arches protruding into the room is provided. Heat exchanger according to one of claims 14 and 15, characterized in that at the level of the bulges Parts of the channel are located. Heat exchanger according to one of claims 6 to 16, characterized in that one or more protrusions protrude from the canal wall into the canal.

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