GB2066938A

GB2066938A - Plate heat exchanger

Info

Publication number: GB2066938A
Application number: GB8038573A
Authority: GB
Original assignee: Alfa Laval AB
Current assignee: Alfa Laval AB
Priority date: 1980-01-09
Filing date: 1980-12-02
Publication date: 1981-07-15
Also published as: FR2473694A1; SE8000160L; SE420020B; DE3046929A1; JPS56102696A

Abstract

In a heat exchanger comprising a plurality of plates (20) stacked to define between them passages (21-27) for two mutually heat exchanging fluids (A,B), and wherein at least one of the passages (e.g. an end passage 21 or 27 of the plate pack) is bounded on one side only thereof by a plate serving to exchange heat with fluid in an adjacent passage, the said one passage (or passages) is arranged to have a higher fluid flow resistance than the other passages in the plate pack conveying the same fluid as said one passage (or passages). Such higher flow resistance may be effected by providing in the walls of said one passage (or passages) a corrugation arrangement which has a higher fluid flow resistance than a corrugation arrangement provided in the walls of said other passages (e.g. Figures 4 and 5). <IMAGE>

Description

SPECIFICATION Plate heat exchanger The present invention relates to a heat exchanger comprising a plurality of plates stacked together to define between them sealed passages for two mutually heat exchanging fluids.

In conventional plate heat exchangers all the heat exchange passages, or at least all the passages for one and the same fluid, have identical flow conditions. This means that the flow and the pressure drop will be generally equal in these passages, including those passages which are enclosed on one side only by a plate which transfers heat, i.e. usually the outermost or end passages of the heat exchanger.

In comparison with the passages which are enclosed on both sides by heat exchanging plates, the flow and pressure drop in said outermost passages are the same whereas the heat exchanging area is only half as large. Consequently, the change of temperature in the fluid flowing through the outermost passages will be less than in the fluid flowing through the intermediate passages since the heat transfer to or from the outer passages is only about half of that of the other passages. This is disadvantageous, primarily because it results in different heat treatment of different portions of the fluid. This may in turn have a negative effect on the quality of a product treated in the plate heat exchanger.Secondly, all the heat exchanging surfaces in the heat exchanger are not utilized as efficiently as possible which is of economic importance, especially when expensive plate material is used. Thirdly, the temperature of the fluid in the passages situated adjacent to the outer passages is also affected. This effect decreases successively with increasing distance from the outer passages, i.e. usually from the ends of the plate stack.

The present invention aims to eliminate or reduce substantially the above drawbacks of hitherto used plate heat exchangers, and according to the invention there is provided a heat exchanger comprising a plurality of plates stacked together to define between them a series of sealed passages for two mutually heat exchanging fluids, at least one passage being confined on one side only by a plate which transfers heat from the fluid flowing in said passage to the other fluid flowing in an adjacent passage, and said at least one passage having a higher flow resistance than the other passages for the same fluid.

With a heat exchanger according to the invention it has been found possible to obtain generally equal change of temperature in all the passages for one and the same fluid, whereby the heat treatment of the fluid will be equal in all the passages. The quality of a product treated in the heat exchanger can thereby be improved, and at the same time all heat exchanging surfaces can be effectively utilized.

The invention will be described in more detail below with reference to the accompanying drawings, in which: Figures 1 and2 illustrate diagrammatical sections of conventional plate heat exchangers; Figure 3 shows a corresponding section of a heat exchanger according to the invention; and Figures 4 and 5 show exploded perspsective views in a diagrammatical form of two embodiments of the invention.

The convention heat exchanger shown in Figure 1 comprises seven plates 1-7 defining between them six heat exchange passages 9-14. A fluid A flows through three passages 10, 12, 14 and exchanges heat with a fluid B flowing through the other passages 9,11,13.

Of the three passages 10, 12, 14 for fluid A the two first mentioned are enclosed on both sides by heat exchanging plates 2,3 and 4, 5, respectively, which are exposed to fluid B while the passage 14 is enclosed by such a plate 6 on one side only. It should therefore be easily realized that the change of temperature in the fluid flowing through the passage 14 is considerably less than for that flowing in the passages 10 and 12, assuming the flows in all three passages are equal. The conditions for fluid B are similar in that the passages 11 and 13 are enclosed on both sides by heat exchanging plates exposed to fluid A while the passage 9 exchanges heat through the plate 2 only.

The conventional heat exchanger illustrated in Figure 2 corresponds to that in Figure 1 with the exception that it is provided with an additional plate 8, whereby an additional heat exchange passage 15 is formed for fluid B. In this case all the passages 10, 12, 2,1 4 for fluid A are enclosed by heat exchanging plates on both sides. Nevertheless, the change of temperature in these passages will not be equal.

Since the temperature in the outer passages 9 and 15 which exchange heat to one side only differs from that in passages 11 and 13 for the same fluid, the temperature in the adjacent passages 10 and 14 will also be influenced and will consequently differ from that prevailing in passage 12.

Figure 3 illustrates a heat exchanger according to the invention which comprises eight plates 20 enclosing between them seven passages 21-27. The outer passages 21 and 27 are shown narrower than the intermediate ones in order to indicate that the flow resistance is higher in the outer passages, whereby the flow therein will be about half of that in the intermediate passages. Due to the fact that the flow rates in the outer passages have thereby been adapted according to their heat exchanging surface areas, the change of temperature therein will be generally equal to that of the intermediate passages 21,25 for the same fluid B. In the passages 22, 24, 26 for the other fluid A the change of temperature will also be substantially equal. A product treated in this heat exchanger will thus be subjected to the same heat treatment in all the passages.

It is indicated in Figure 3 that the outer passages have been made narrower in order to reduce the flow therethrough. Other preferred means for achieving this effect are illustrated in Figures 4 and 5.

The heat exchanger illustrated diagrammatically in an exploded view in Figure 4 is assembled of two different kinds of plates 30 and 31, respectively, which are provided with corrugations in a so-called herring-bone pattern. The corrugations are indicated diagrammatically at 30a and 31a. As appears from the Figure, the corrugations 30a of the plates 30 form a wider angle with the iongitudinal axes of the plates than the corrugations 31a of the plates 31. It is presumed that the plates are equally spaced. As is well known by anyone skilled in the art, a wider angle provides for a higher flow resistance than a smaller angle.The two outer passages are on both sides enclosed by plates 30 having the wider angle corrugations, while the rest of the passages are enclosed on the one side by a plate 30 and on the other side by a plate 31 having the smaller angle corrugations. The flow resistance is thereby higher in the outer end passages than in the inner passages, and consequently, the flow rates are correspondingly smaller. Thus, in this way a desired reduction of the flow rate in the outer passages can be obtained, so that the change of temperature will be equal in all passages for the same fluid.

The plate combination illustrated in Figure 5 is assembled of plates 30 and 31 of the same kind as those in Figure 4. In this case, however, only two plates 30 having the wider angle corrugations are used and they are disposed at the opposite ends. All the intermediate plates 31 have the smaller angle corrugations. The two outer passages are thus enclosed on the one side by a plate 30 having the wider angle corrugations and on the other side by a plate 31 having the smaller angle corrugations.

These passages thereby present a higher flow resistance and a correspondingly smaller flow rate than the intermediate passages which are each enclosed by two plates 31 having the smaller angle corrugations.

The above described embodiments should be considered as examples only and it should be realized that even other embodiments are possible within the scope of the following claims.

Claims

1. A heat exchanger comprising a plurality of plates stacked together to define between them a series of sealed passages for two mutually heat exchanging fluids, at least one passage being confined on one side only by a plate which transfers heat from the fluid flowing in said passage to the other fluid flowing in an adjacent passage, and said at least one passage having a higher flow resistance than the other passages for the same fluid.

2. A heat exchanger according to claim 1, wherein the flow resistance of said at least one passage is such that the flow rate therethrough is about half that through the other passages for the same fluid.

3. A heat exchanger substantially as herein described with reference to Figures 3,4 and 5 of the accompanying drawings.