Heat exchange – Flow passages for two confined fluids – Interdigitated plural first and plural second fluid passages
Reexamination Certificate
1999-10-13
2001-05-15
Flanigan, Allen (Department: 3743)
Heat exchange
Flow passages for two confined fluids
Interdigitated plural first and plural second fluid passages
C029S890039, C165S174000
Reexamination Certificate
active
06230794
ABSTRACT:
FIELD OF THE INVENTION
The present invention concerns a method of producing heat transfer plates, which are of the same size and have central heat transfer portions of the same shape. Each of the heat transfer plates has on respective sides of the heat transfer portion through holes, so called port holes, for through flow of at least one heat exchange fluid. Additionally each heat transfer plate has a passage portion which, when the heat transfer plate abuts against another heat transfer plate in a plate heat exchanger, is adapted to delimit a distribution passage for through flow of said heat exchange fluid. The passage portion extends from one of said port holes to an area in or near said heat transfer portion, which area has the same position in relation to the heat transfer portion in the different heat transfer plates. During production of the heat transfer plates separate operations are carried out for pressing the passage portions of the heat transfer plates and for punching the holes which shall form said port holes, respectively.
BACKGROUND OF THE INVENTION
In a plate heat exchanger heat transfer plates abut against each other in a way such that they form a plate package with heat transfer passages between the heat transfer plates. The port holes of the heat transfer plates form port channels through the plate package.
Plate heat exchangers are often used as evaporators in cooling systems. In such a plate heat exchanger most often at least one heat exchange fluid, which is constituted by a refrigerant, flows into one of the port channels in the form of a liquid-gas mixture. From the port channel the refrigerant is conducted through inlet or distribution passages, of the kind initially mentioned, into the heat transfer passages intended for the refrigerant. When flowing through the distribution passages the refrigerant is subjected to a substantial pressure drop, whereby as nearly even a distribution of the refrigerant between the different heat transfer passages as possible is achieved. In the heat transfer passages the refrigerant evaporates by absorbing heat from another heat exchange fluid flowing through adjacent heat transfer passages.
In the past only a few rather similar refrigerants have been used in most cooling systems. Plate heat exchangers for such cooling systems have been produced in several different sizes, but plate heat exchangers of the same size have normally been given a uniform design, irrespective of the refrigerant to be used in them. Thus, the distribution passages have had the same dimensions in all plate heat exchangers of a specific size, which has meant that the pressure drop to which a refrigerant has been subjected in the distribution passages has not necessarily been optimal for this particular refrigerant.
As a consequence of old environmentally dangerous refrigerants, having been forbidden and a large number of new more environmentally friendly refrigerants having been introduced, a need has arisen for adaptation of the pressure drop in the distribution passages individually for each plate heat exchanger with regard to the refrigerant to be used in it. The new refrigerants, in other words, show large individual differences between their evaporation pressures at a specific temperature.
SE 8702608-4 shows a plate heat exchanger formed with restrictions, which are adapted to reduce the pressure of a refrigerant, when it flows from a port channel into a number of heat transfer passages. The restrictions can be constituted by holes drilled in rings, which are arranged between the heat transfer plates around the port channel, or by holes drilled in a pipe, which is arranged in the port channel constituting the inlet channel for the refrigerant. According to a further embodiment the heat transfer plates may abut against each other two by two around the port holes forming the inlet channel for the refrigerant, except in limited areas where inlet passages have been left. The restrictions can be adapted to a certain refrigerant, a certain pressure drop and a certain temperature difference.
SUMMARY OF THE INVENTION
The object of the present invention is to produce, in a simple and cost effective way, heat transfer plates of the initially described kind, which are intended for plate heat exchangers of different kinds with respect to the pressure drop that is to be attained in their distribution passages.
This object can be achieved, by means of the initially mentioned method of producing heat transfer plates, by providing by said punching operation each one of separate or interconnected sheet metal pieces, which are to form the said heat transfer plates, with holes in a way such that the one port hole in a first sheet metal piece is of a different kind than the corresponding port hole in a second sheet metal piece, the respective port holes of the sheet metal pieces being shaped by the punching operation such that they result in finished heat transfer plates having differently sized passage portions.
By the invention heat transfer plates for plate heat exchangers, which are individually adapted for different refrigerants, can be produced at almost the same cost as heat transfer plates for plate heat exchangers, which are not individually adapted for different refrigerants. The invention contemplates that different punching tools are used for the punching of port holes of different kinds. However, the increase in cost for each heat transfer plate, as a consequence of this, will be marginal in connection with a large production series.
Either the punching operation for punching said port hole can be performed before the pressing operation for the shaping of the passage portions, or the two operations can be performed in the inverse order.
The port holes of different kinds can be shaped as circles but with different diameters; alternatively they can be given a shape differing from a circular shape. In these different ways the heat transfer plates can easily be provided with differently sized passage portions.
Normally the heat transfer portion of a heat transfer plate is provided with a pressing pattern of depressions and elevations by a pressing operation. It is convenient to shape the passage portion of the heat transfer plate in the same pressing operation.
In a preferred way of carrying out the method according to the invention the passage portion of each of the heat transfer plates is shaped so that it forms a groove. Thus, a distribution passage between two adjacent plates in a plate heat exchanger will be given the shape of a channel having a specific uniform through flow area. It is easy to calculate which length such a channel should have for obtaining of the desired pressure drop in a refrigerant flowing through the channel.
The passage portion can alternatively be provided with a pressing pattern of elevations and/or depressions.
The invention also concerns an assortment of heat transfer plates, which are of the same size and have central heat transfer portions of the same shape. Each of the heat transfer plates has through holes, so called port holes, on the respective sides of its heat transfer portion for through flow of at least one heat exchange fluid and one passage portion which, when the heat transfer plate abuts against another heat transfer plate in a plate heat exchanger, is adapted to delimit a distribution passage for through flow of the heat exchange fluid. The passage portion extends from one of the port holes to an area in or near the heat transfer portion, which area has the same position in relation to the heat transfer portion in each of the different heat transfer plates.
The heat transfer plates of the assortment are characterized in that their port holes at the respective passage portions are of different kinds and shaped such that the passage portions of the heat transfer plates have different sizes.
The phrase an assortment of heat transfer plates, when used here, should be understood to mean at least two different kinds of heat transfer plates. In a plate heat exchanger comprising heat transfer plates from the ass
Alfa Laval AB
Fish & Richardson P.C.
Flanigan Allen
LandOfFree
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