Heat exchange – Flow passages for two confined fluids – Interdigitated plural first and plural second fluid passages
Patent
1992-10-21
1994-03-08
Rivell, John
Heat exchange
Flow passages for two confined fluids
Interdigitated plural first and plural second fluid passages
165166, F28F 308
Patent
active
052919455
DESCRIPTION:
BRIEF SUMMARY
The present invention concerns a plate heat exchanger comprising a stack of plate elements, each of which has a central heat transferring portion and a surrounding edge portion, the heat transferring portions of the plate elements being permanently joined together at several spaced places and confining between themselves flow spaces for two heat exchange fluids, and the edge portions of the plate elements having parts extending around the plate elements, which parts are bent in the same direction in said stack and are permanently joined together by a connecting material, e.g. a brazing material, which at one time has been liquid.
A plate heat exchanger of this kind, shown for instance in GB-A 2 005 398, is produced in a way such that a large number of plate elements are stacked together with thin foils of some suitable brazing material in the plate interspaces, whereafter the finished stack is pressed together and put into a furnace. In the furnace the brazing material melts to liquid and the plate elements are brazed together. In the heat transferring portions the plate elements are brazed together at a lot of spaced points, where crossing corrugation ridges of adjacent plate elements abut against each other, and along the edge portions the plate elements are brazed together around the whole of their peripheries, so that the flow spaces between the plate elements are closed from connection with the surrounding atmosphere.
Brazed heat exchangers of the kind here described are very cheap to manufacture. Firstly, all the plate elements may be shaped alike, every second one being rotated 180.degree. in its own plane relative to the others.
Secondly, the plate elements may be easily stacked upon each other, since the edge portions bent in the same direction function as guiding means between adjacent plate elements. Even the stacking operation itself is facilitated because the plate elements after having been produced can be maintained with their edge portions oriented in the same direction.
It has long been desired that the so called double-wall technique should be used also in connection with brazed plate heat exchangers of the kind just described as in connection with other types of plate heat exchangers. The double-wall technique means that each plate element comprises two separate heat transferring plates which abut closely against each other but, in spite of this, admit a heat exchange fluid leaking out through a hole in one of the heat transferring plates to be conducted between the heat transferring plates to the edge portion of the plate element, where the leakage may be observed.
Plate heat exchangers using the double-wall technique are needed in connection with the transfer of heat from one fluid to another, when the fluids are of a kind requiring an extra security to be created for preventing one fluid from leaking into the flow ways of the other. The alternative to the double-wall technique in such cases is the use of two separate conventional plate heat exchangers, a third fluid of some suitable kind being used to receive heat in the one plate heat exchanger from said one fluid and to transmit the heat to said other fluid in the other plate heat exchanger. Plate heat exchanger systems of this kind comprising brazed plate heat exchangers are used for instance in connection with heating of tap water in houses by means of hot water from a remote heating plant.
In attempts to use the double-wall technique in connection with brazed heat exchangers of the initially described kind difficulties have arisen in connection with the brazing operation, however, since brazing material has found its way in between and, uncontrollably, brazed together the heat transferring plates in each separate plate element. Thereby, the possibility of observing leakage of a heat exchange fluid through one of the heat transferring plates in a plate element could not always be guaranteed.
The double-wall technique has, indeed, been used previously in connection with brazed plate heat exchangers of a different kind, which can be
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patent: 3438435 (1969-04-01), Wennerberg
patent: 4249597 (1981-02-01), Carey
patent: 4708199 (1987-11-01), Yogo et al.
patent: 4987955 (1991-01-01), Bergqvist et al.
patent: 5069276 (1991-12-01), Seidel
Blomgren Ralf
Engstrom Anders
Alfa-Laval Thermal AB
Leo L. R.
Rivell John
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