Welded plate heat exchanger

Heat exchange – Flow passages for two confined fluids – Interdigitated plural first and plural second fluid passages

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Details

165167, 165DIG384, F28D 900

Patent

active

056388993

DESCRIPTION:

BRIEF SUMMARY
The present invention relates to a plate heat exchanger comprising a stack of thin heat transferring plates each of which has a central heat transferring portion provided with a pressed pattern of spacing protuberances and depressions and an edge portion extending along the edge of the heat transferring plate and surrounding said heat transferring portion, a first heat transferring plate, that is situated between two other heat transferring plates in the stack, being welded by its edge portion together with the edge portion of one of said two other heat transferring plates along an outer line and being welded together with the edge portion of the other one of said two other heat transferring plates along an inner line which is situated inside said outer line, and the edge portions of the heat transferring plates extending into contact with each other along said inner and outer lines.
A plate heat exchanger of this kind, known for instance by GB 580 368, may be manufactured by first welding together heat transferring plates in pairs along the respective said inner lines and, thereafter, welding together already united plate pairs along the respective said outer lines. A plate heat exchanger constructed in a different but alternative way is known by GB-A-2 126 703.
Conventional welding technique normally requires in connection with welding together of two plates that welding tools are put into contact with both of the plates. Modern welding technique, however, such as laser welding and electronic beam welding, makes it possible to weld together two superimposed plates by use of a welding tool only on one side of the two plates. An advantage of modern welding techniques also is that less heat has to be generated in the plates to be welded together.
By means of modern welding techniques it would thus be possible in connection with welding together of several heat transferring plates to stack the plates successively onto each other and successively weld them together by applying a welding tool only from one direction. Preferably, the first plate is placed on a horizontal support, whereafter the other plates one after one are superimposed and welded onto the underlying plate.
Possibly, modern welding technique will make it possible in the future also to weld together simultaneously several plates stacked on each other by use of welding tools only on one side of the plate stack.
However, in connection with attempts to manufacture welded plate heat exchangers of the initially defined kind by use of welding tools only on one side of the heat transferring plates to be welded together it has proved difficult to accomplish completely perfect welding joints between the plates, above all along the above mentioned outer lines. One reason for this is the difficulty of keeping, during a welding operation, the outermost edge portions of two adjacent heat transferring plates effectively pressed against each other, so that a good contact is obtained between the plates. Thus, it has not been sufficient for obtaining such a good contact, when one heat transferring plate has been superimposed onto another, to apply a compressing pressure in the area of the central heat transferring portions of the plates.
A complication in this connection is that the material in the heat transferring plates is expanded locally during the welding operation by the heat generated around the place of welding and that, as a consequence thereof, the edge portions of the plates lose contact with each other. As the point of welding is moved along the plate edge portions a gap--coming up in this way between the plates--has proved to grow, and the result of this has been that the material in the plate edge portions, instead of being united, has melted here and there and left through holes in the edge portions. (See the accompnaying drawing FIG. 6.)
For avoiding contact problems of this kind also the outermost edge portions of two plates to be welded together along their edge portions have to be kept very heavily together by means of a fixture of some suit

REFERENCES:
patent: 4723601 (1988-02-01), Ohara et al.
patent: 5125453 (1992-06-01), Bertrand et al.
patent: 5327958 (1994-07-01), Machata et al.

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