CA1078372A

CA1078372A - Plate heat exchanger

Info

Publication number: CA1078372A
Application number: CA289,749A
Authority: CA
Inventors: Kaj A. Rissler
Original assignee: De Laval Separator Co
Current assignee: De Laval Separator Co
Priority date: 1976-10-29
Filing date: 1977-10-28
Publication date: 1980-05-27
Also published as: FR2369529B1; JPS5355545A; DE2748224A1; GB1558575A; SE7612047L; SE402485B; IT1086913B; FR2369529A1

Abstract

PLATE HEAT EXCHANGER
ABSTRACT OF THE DISCLOSURE

A heat exchanger having a plurality of parallel plates and a chamber between each pair of adjacent plates for a first or a second heat exchange medium, at least one medium passing through its chambers without change of state from liquid to gas or vice versa. Inlet passages which are formed by aligned holes in the plates and are each of uniform cross-section throughout, distributes the media to their respective chambers; and likewise, outlet passages, which are formed by aligned holes in the plates and are each of uniform cross-sectional area throughout, remove the media. The cross-sectional area of the outlet passage of at least one medium is larger than its inlet passage area, thereby producing a pressure drop as the medium passes through its chambers. The outlet passages may be divided up into at least two channels, the sum of whose cross-sectional area is greater than the inlet area.

Description

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The present invention relates to a plate heat exchanger for heat exchange between media, of which at least one medium passes through the heat exchanger from an ~ -inlet passage to an outlet passage without changing its condition from liquid to gas or vice versa on passing.
More particularly, the invention relates to plate heat exchangers in which the passages are formed by holes in the plates that are aligned when the plates are assembled.
One problem of prior heat exchangers of this kind is that the said inlet and outlet passag~s present a relatively large flow resistance to the media exchanging heat.
It is an object of the present invention to reduce this flow resistance without change of size of the exchanger or of its plates and without substantial change in heat exchanging properties. It has surprisingly been discovered that this object can be fulfilled according to this invention by the plates of the heat exchanger being formed such that the area of the outlet passage for at least one medium is substantially larger than the inlet passage for the same medium. In other words, redistribution of the cross-sectional areas of the inlet and outlet passages whilst maintaining the total cross-sectional area of the two passages unchanged and the size of the heat exchange areas of the plates likewise unchanged, the pressure drop over the heat exchanger decreases by up to 25%, without the heat exchanging properties of the heat exchanger being substantially changed.
According to a preferred embodiment of the invention, the inlet passage and the outlet passage each have cross-sectional areas which are respectively ... . .. .. .. . .. . . .. .

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substantially constant along the lengths of the respective passages. By this means all the heat exchange plates may have inlet holes of the same size and outlet holes of the same size, which is an advantage in the manufacturing of the heat exchange plates.
According to one embodiment of the invention the outlet passage is divided up into at least two channels whereby it becomes possible to make the heat exchange plates with holes which are of the same size which is advantageous in the production of the plates.
In the prior art,U.S. patent 3,117,624 discloses a plate heat exchanger having a plurality of heat exchange plates with outlet holes which are larger than the inlet holes. However, this difference in size of the holes was due to the fact that the condition of the medium changed by vaporization from a liquid to a gas, between the heat exchange plates, the medium quite naturally requiring wider channels for the flow in gaseous state than in liquid state.
This patent did not perceive that a heat exchanger in which the condition of the medium did not change between liquid and gas could be improved without loss of capacity or increase in size or increase in cost.
In the drawing, Figure 1 shows a longitudinal sectional view through a plate heat exchanger of a known structure.
Figure 2 shows a ~ngitudinal sectional view taken along line II-II of Figure 3, through a heat exchanger according to one form of the invention.
Figure 3 is an elevation view of a heat exchange plate viewed along line III-III in Figure 2.
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: 1~783~2 Figure 4 is a graph showing how the pressure drop in the heat exchanger of this invention varies with the ratio between the cross-sectional areas of an outlet passage and an inlet passage.
Figure 5 is a diagrammatic exploded perspective view of another embodiment of the heat exchange plates ;
according to this invention.
Figure 6 is a view similar to Figure 5 of a further embodiment of heat exchange plates according to this invention with six holes.
Referring to the drawings, the invention illustrated in Figures 2 and 3 may be compared with a prior art con-~g~A7i~D
struction shown in Figure 1 wherein like parts are dex;i~ff~*
by like reference numerals.
The heat exchanger according to this invention comprises a plurality of parallel heat exchange plates 1 which are arranged between two end elements 2 and 3 which may be in the form of plates. The heat exchange plates 1 which may be of flat rectangular shape as shown in Figure 3, or of other suitable desired shape, are spaced apart by sealing and separating members 12 which may be of irregular shape as shown in Figure 3 or of other shape suitable to enable them to form the periphery of individual heat ; transfer passages or chambers.
In Figure 3 the heat exchange plate 1 which may be considered to be the one located at the left end of the assembly in Figure 1, is seen in front of the end-plate 2.
In front of the heat exchange plate is a spacing and sealing member 12.
Each heat exchange plate has four holes through it adjacent its corners which when assembled in alignment provide inlet passages and outlet passages for the heat ~C~7837Z
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transfer media. Two holes 8A at one side are of smaller diameter than the two holes lOA at the other side.
When the heat exchange plates 1 and separator members 12 are assembled as in Figure 2 they confine a plurality of first heat exchange chambers 4 and a number of second heat exchange chambers 5.
Through the chambers 4 a first medium flows, while a second medium flows through the chambers 5. Each heat exchange plate forms a common wall between adjacent heat exchange chambers whereby the heat transfer between the media in adjacent chambers 4 and 5 takes place through the common heat exchange plates.
The first medium is introduced into the heat exchanger through an inlet conduit 6 and a convergent 15 fitting 15. The fitting 15 is affixed to the end-plate 2 around an opening in the end-plate which opens into an inlet passage 7a by which the medium is distributed to the first heat-exchange chambers 4.
The inlet passage 7A is formed by the small inlet holes 8A in the top of the heat exchange plates and along its length is of substantially uniform cross sectional area.
When the first medium has passed through the chambers 4 it is collected in an outlet passage 9A which is formed by large outlet holes lOA through the bottom of the heat exchange plates. This passage is of substantially uniform cross-section along its length.
Between the second and third heat exchange plates, , .
reading from left to right in Figure 2 (and likewise between the 4th and 5th, 6th and 7th, et sequi) sealing means is provided around the passage 7A and the passage 9A, dimension-ed in each instance so that the cross sectional area of the passages 7A and 9A between the holes in one heat transfer . .
~ . . . ,- - . .. . ..

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plate and the next, is maintained uniform. This sealing means may be made integral with the separator member 12.
It allows distribution of the medium only to alternate chambers.
The second medium flows in an analogous way through an inlet conduit, an inlet passage, heat exchange chambers 5, an outlet passage and outlet conduit, of which only the chambers 5 are shown in Figure 2. In the case of the second medium, the inlet is at the bottom through small passages and the outlet at the top through large passages. The same form of separating means 12 can be used for providing the chambers 5, by inverting the separators end-over-end.
In the prior art of Figure 1, the inlet passage 7 and the ou~let passage 9 are of the same cross-sectional area; and because the medium was not intended to change its state but was intended to remain always in a liquid state, the flow resistance of the medium was relatively large.
In the present invention, as shown in Figures 2 and 3, the outlet passage 9A and each outlet hole lOA have a cross-sectional area that is substantially larger than the cross-sectional area of inlet passage 7A and each inlet hole 8A. At the same time the sum of cross-sectional areas of the inlet and outlet passages 7A and 9A is kept substan-tially unchanged. As a result of observing these para-meters, the pressure drop of the medium will decrease during its flow through the heat exchanger while the heat exchange area of the plates 1 is maintained the same as heretofore. In consequence, improved and more efficient operation of the heat exchanger is attained.
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Figure 4 is a graph where A2 is the cross-sectional area of the outlet passage 9A, and Al is the - cross-sectional area of the inlet passage 7A, and C is a constant. Figure 4 shows how the pressure drop,~ p, can ~07837Z
vary, when the ratio A2 is changed.
Al A

~p decreases by about 25% when 2 increases to about 1.8.

At A2 = 2.8 ~p has again increased to the same value as at A2 = 1. In other words, Fig. 4 shows that A2 should be larger than Al but less than 2.8~Al, in order to obtain a sig-nificant reduction in the pressure drop, the latter being reduced the greatest amount when A2 is about 1.8 Al.
Furthermore, in the graph of Figure 4 the condition Al ~ A2 = C applies, and the flow of the medium through the heat exchanger is not changed.
In prior art heat exchangers, for example, see Figure 1, a special convergent connecting pipe fitting 15 at the inlet to the exchanger and a special divergent connecting fitting at the outlet from the exchanger were often required. The purpose of the fittings 15 and 16 was to accomplish a smooth transition between inlet and outlet conduits 6 and 11, respectively. The conduits usually are dimensioned for a flow velocity of 2-4 m/s, while the connections of the heat exchanger usually are dimen-sioned for a higher flow velocity, namely 5-8 m/s. ~y the inven-tion the outlet passage of the heat exchanger is better adapted to the diameter of the outlet conduit; and in many cases a special connecting fitting between the conduit 11 and the heat exchanger can be avoided (see Figure 2).
The plates of the heat exchanger may have different ~orms.
In Figure 5 wherein equivalent parts have the same reference numerals as in Figures 2 and 3, the small inlet holes 8A and the large outlet holes lOA are located in diagonally opposite corners. The upper small holes 8A form the inlet pas-. - 6 -sage for the first medium and distribute the first medium to the heat exchange chambers 4 as shown by .~,'' :
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the broken lines and arrows 13. The lower large holes lOA , form the outlet passage for the first medium.
In equivalent manner the lower small holes 8A form the inlet passage for the second medium and distribute the second medium to the heat exchange chambers 5 as shown by the broken lines and arrows 14. The upper large holes lOA
form the outlet passage for the second medium.
The separating and sealing members 12 form the ; peripheries of the chambers 4 and 5 in the same way as before; and sealing meanis between the holes in adjacent plates to complete the inlet and outlet passages, respectively, is provided in equivalent fashion, as before.
In Figure 6 an embodiment is shown in which each plate has six holes, three adjacent the top edge and three adjacent the bottom edge. All the holes are of the same size but one hole at the top and one at the bottom are used as inlet holes and two at the bottom and two at the top are used as outlet holes. In the particular illustration of Figure 6 the middle hole at the top and the middle hole at the bottom are used as inlet holes. The separating and sealing members which define the chambers 4 for the first medium exclude the lower middle inlet hole and two upper outer outlet holes; and similarly the sealing members which define chambers 5 for the second medium exclude the upper middle inlet hole and two lower outer outlet holes.
By the Figure 6 arrangement there is one inlet passage or channel for each medium and two outlet passages or channels for each medium. Thus the cross-sectional area of the outlet is twice the size of the inlet area.
In all the arrangements illustrated, decreased pressure drops result for both the first and the second heat exchange mediums.

~ ~ 1078372 Without departing from the invention, the outlet area for the first media can be larger than the inlet area, whether one or more holes or channels are provided for the ; outlet, while the inlet area or holes for the second media ` 5 can be substantially larger than the outlet area or holes.
Such an arrangement would be employed if the second medium enters the heat exchanger in a gaseous state and then condenses and leaves the exchanger in a liquid state.
Many modifications of the invention will occur to those skilled in the art. Therefore, the invention is not limited to the specific embodiments illustrated and described.

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A Heat exchanger comprising a plurality of parallel heat exchange plates, means separating adjacent plates and form-ing a plurality of separate parallel chambers through which first and second heat exchange media flow, at least one of said media passing through the exchanger without changing its state from liquid to gas or vice versa, spaced holes in said plates aligned in the exchanger forming an inlet passage and an outlet passage for distribution to and removal from the chambers of the first medium and other spaced holes in said plates aligned in the exchanger forming an inlet passage and an outlet passage for distribution to and removal from the chambers of the second medium, the cross-sectional area of the outlet passage from the chambers of said at least one medium being substantially larger than the cross-sectional area of the inlet passage to the chamber of that medium, creating a pressure drop of that medium whereby resistance to flow of that medium through the exchanger is reduced without change of its physical state, the cross-sectional area A2 of the outlet passage from the chambers of said at least one medium being less than 2.8 times Al, where Al is the cross-sec-tional area of the inlet passage to the chambers of said at least one medium.

2. A heat exchanger as claimed in claim 1 wherein A2 is about 1.8 times Al.