Heat exchange – Flow passages for two confined fluids – Interdigitated plural first and plural second fluid passages
Patent
1994-10-19
1996-04-23
Leo, Leonard R.
Heat exchange
Flow passages for two confined fluids
Interdigitated plural first and plural second fluid passages
159 286, 202236, F28F 310, B01D 122
Patent
active
055094716
DESCRIPTION:
BRIEF SUMMARY
The present invention refers to a plate heat exchanger for evaporation of a liquid, comprising a number of vertically orientated and against each other abutting thin heat transfer plates, provided with pressed corrugation pattern in the form of ridges and grooves, and between the heat transfer plates arranged gaskets or the like, which in each second plate interspace delimit a flow space for said liquid and in the remaining plate interspaces delimit flow spaces for a heating fluid, and in each of the flow spaces for the liquid there are several inlet openings horizontally distributed across the width of the heat transfer plates for supply of said liquid.
Through GB 1299481, GB 1412414, GB 1425176 and WO 91/06818 plate heat exchangers in the form of falling film evaporators are previously known, which in the flow space for the liquid show a number of openings for inflowing liquid, as for instance milk or saltwater to be desalted. In connection to these inlet openings between the heat transfer plates one or a small amount of relatively narrow rills of liquid appear. These narrow rills shall later be divided so that the flow or parts of the flow will be spread to an unbroken liquid film across the width of the heat transfer plates.
For certain applications a completely even distribution of the liquid film is tried to be obtained. In other cases a certain maldistribution with larger flow per unit of width on certain parts of the plate and lower on other parts may be optimum depending on downstream conditions. Such uneven flow distributions may on one hand be obtained by varying the relative flow of the different rills or by spreading the location of the rills unequally across the width so that rills lying closely together correspond to a larger flow per unit of width.
Along the heat transfer surface of a falling film evaporator the liquid flow is gradually evaporated and it will be difficult to maintain a completely covering liquid film. To avoid dry surface portions the right flow distribution must be achieved already in the upper part of the heat transfer plates. This flow need not be evenly distributed, but it should cover completely.
Thus, in connection with falling film evaporators usually all of the heat transfer surface should be covered by liquid film, to avoid that dry parts will appear on the heat transfer surface, which gives no or insignificant heat transfer. If the liquid to be evaporated also contains non-evaporative products, a contamination of the heat transfer plates may occur, especially in or at dry areas. In case of concentration of milk products strong hard-removable contamination may occur, so called fouling.
In connection with known falling film evaporators where the liquid flows in the upper part of the plate interspaces, in the shape of a number of narrow rills, a certain height of the heat transfer surface is required to fully distribute these rills across the width of the plates. Thus, dry areas arise between the rills. In such cases when the liquid has not become fully distributed across the width of the plates, before the main evaporation begins, undesired contamination and fouling can occur in these dry areas.
The object of the present invention is early to attain a fully covering distribution of the liquid across the width of the heat transfer plates in a plate heat exchanger of the described kind. An additional object is that said distribution shall be attained without an increasing flow resistance for the heating fluid in its flow space.
These objects are obtained by adjacent heat transfer plates having opposite located horizontally extended portions, which show a corrugation pattern having essentially less pressing depth than the remaining part of the corrugation pattern of the heat transfer plates, that the ridges in said portions of two adjacent heat transfer plates are crosswise arranged and that the corrugation patterns are so designed that the heat transfer plates in said portions via the crosswise arranged ridges, abut against each other in the flow space for said liquid
REFERENCES:
patent: 4162703 (1979-07-01), Bosaeus
patent: 4572766 (1986-02-01), Dimitriou
patent: 5174370 (1992-12-01), Hallgren
patent: 5203406 (1993-04-01), Blomgren et al.
patent: 5232557 (1993-08-01), Kontu et al.
Alfa Laval Thermal AB
Leo Leonard R.
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