Heat exchange – Flow passages for two confined fluids – Interdigitated plural first and plural second fluid passages
Patent
1991-09-16
1992-12-29
Flanigan, Allen J.
Heat exchange
Flow passages for two confined fluids
Interdigitated plural first and plural second fluid passages
165167, 165147, F28F 302
Patent
active
051743701
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a plate heat exchanger, for the evaporation of a fluid, which comprises a plurality of heat transfer plate pairs. Each plate of the pair has a ridged and grooved corrugation pattern. Between adjacent plates are flow spaces, each having an inlet and an outlet. The ridges of each plate of each pair abut the ridges of the other plate in the pair D to form a plurality of supporting points. The flow spaces between alternate plates form passages for the fluid, and the remaining flow spaces form passages for a heating fluid.
In a known heat exchanger of this kind as described in DE-A1 3721132, the main part of the heat transfer portion of each entire surface. However, this design has proved to be ineffective in improving the heat transfer capacity of the plate heat exchanger.
An object of the present invention is to increase the efficiency of plate heat exchangers of the type described. This is accomplished by arranging the plurality of plate pairs so that at least alternate plates have a plurality of zones with different corrugation patterns, arranged sequentially in the direction of fluid flow, to provide flow resistance which gradually decreases in the direction of fluid and generated vapour flow.
When a fluid flows through the evaporation passage and gradually evaporates, a greater amount of volume is required for the produced vapour. However, it is difficult to provide for such increased volume in the plate interspace. Therefore, the exchanger must effectively accommodate a gradually increasing flow rate of the produced vapour.
Although the above-mentioned corrugation patterns of the heat transfer plates are intended to improve the efficiency of the plate heat exchanger, the patterns also cause a considerable flow resistance to the produced vapour. As a result, a significant pressure drop in the rapidly flowing vapour is created. Therefore, the absolute pressure in the section of the passage in which evaporation is to begin must be maintained rather high, i.e., the boiling point of the fluid must be maintained rather high.
One object of this invention is to keep the boiling point of the fluid as low as possible so that the heating fluid may be maintained at the lowest temperature possible. Simultaneously, another object is to employ heat transfer plates having corrugation patterns which maximize the efficiency of the heat exchanger.
In a plate heat exchanger according to the invention, a gradually decreasing flow resistance in the flow direction is obtained in the evaporating passages for the fluid and generated vapour. A very efficient heat transfer to the fluid is thereby achieved in the inlet portion of the flow spaces despite the relatively low flow rate of the fluid. At the same time, an excessive flow resistance for the produced vapour, i.e., excessive pressure drop of said vapour, is avoided in the outlet of the flow spaces. In practice this leads to the result that if a certain, previously-used, plate size is maintained, it is possible to reduce the total heat transfer surface and, thus, the number of plates in a plate heat exchanger, for solving a certain evaporating task. In other words, the invention, which applies to both falling film and climbing film evaporators, enables the design of a plate heat exchanger which provides optimal heat transfer at a given saturation pressure for the generated vapour.
It has been previously known in the art that the heat transfer between two heat transfer plates and a heat transfer fluid flowing through a passage between the two plates is influenced by the position of the ridges of a plate with respect to both the position of the ridges of the other plate in the pair as well as the direction of fluid flow. If the ridges of each plate in an abutting plate pair intersect at an obtuse angle relative to the flow direction of the fluid, both a greater fluid pressure drop as well as a more efficient heat transfer would be obtained than if the ridges intersected at an acute angle. In accordance with the invention, the design of the corru
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Alfa-Laval Thermal AB
Flanigan Allen J.
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