The present invention relates to a plate heal exchanger.

More particularly the invention relates to a plate heal exchanger compπsing a front cover plate, a plurality of channel forming plates and a rear cover plate - all being of a basically symmetric shape relative an axis extending in the direction of the length of the exchanger, the said front cover plate being provided with fittings for connections to inlet and outlet ports for heat exchanging media, the said channel forming plates being pro\ ided w ith a pressed pattern.

A heat exchanger should have a large heat exchanging capacity relative to its cost of manufacture and its volume. The cost of manufacture will decrease with decreasing number of parts and with increasing heat exchange capacity per channel forming plate. I t is usualU desired that equal connection heights are obtained at the inlet and outlet ports for the heat exchanging media and - in case O-πng connections are used - that the sealing surl aces are located in a common plane at the end surface of the exchanger.

In certain applications, e g. in case one of the media is ol a delicate nature, it is a must that the heat exchanger does not e any blind channels or voids in which some of a heat exchanging medium could be trapped and not follow the rest of the How or in which the How veloc becomes \ ery low. A stop or a very small flow will cause a πsk of crevice corrosion or freezing

The present invention has lor its object to provide a plate heat exchanger which better meets these u ishes, and this is acording to the present invention obtained thereby that en the t ront er plate is provided w nh a pressed pattern, that the areas o[ said front co\ er plate around the inlet and outlet ports arc located in a common plane, and that the said er plate together u ith the adjacent channel l υπviing plate provides a distnbution channel crossing the direction betw een adjacent inlet and outlet ports and bordering areas around said ports in which plane parts of the said cover plate and the adjacent channel forming plate are contacting each other.

The inv ention w ill be descnbed belou in more detail reference being made tυ the draw ings in which

Figure 1 is an exploded \ icw showing the basic design of a two circuit plate heat exchanger,

Figure 2 is a section in the direction ol the arrows 11 — 11 through a known heat exchangci according to the pπnciple of Figure 1 ,

Figure 3 is a corresponding section through a another known plate heat exchanger, Figure 4 is a corresponding section through a plate heat exchanger according to the present invention.

Figure 5 is a plane view ol a channel lorming plate according to the present invention. Figure 6 is a section along the line VI-VI in Figure 5 at a greater scale,

Figure 7 is a section along the line VII-VII in Figure 5 - also at a greater scale, Figure 8 is a plane view of the front cover plate in the heat exchanger of Figure 4, Figure 9 is a section along the line 1X-IX in Figure 8 at a greater scale, Figure 10 is a section along the line X-X in Figure 8 at a greater scale, Figure 11 shows the flow between the front cover plate and an adjacent channel forming plate,

Figures 12, 13 and 14 show the rear cover plate,

Figure 15, 16 and 17 show an alternative design of the front cover plate, and Figure 18 is a section corresponding to Figure 4 through a heat exchanger hav ing the alternative design of the front cover plate shown in Figures 15- 17 and channel forming plates of know n design (Figures 2 or 3) and a rear cover plate according to Figures 12- 14

Figure 1 shows a number of mainly rectangularly shaped plates arranged after each other. The plates are of substantially length-symmetπc shape - i.e. almost symmetnc relative a plane vertically disposed relative the plate through a central line in the plate. The plate designated b\ 1 is a front cover plate and is f ollowed by a number of channel forming plates 2-7, w hile the last plate 8 is a rear cover plate. The channel plates 2-7 are of identical shape, but a f ollow ing channel plate has been turned 180° relative the antecedent one. All channel plates have a pressed pattern of arrow πdges 9 and, therefore, although the plates are stacked to contact each other, channels are lormed between them. The number of channel forming plates could be greater or less than the six show n in Figure 1.

Each plate has four holes designated by 10, 1 1, 12 and 13. The holes 10 form an inlet port lor a first heat exchanging medium and the holes 1 1 form an oulet port for the same first medium. The holes 12 form an inlet port for a second heat exchanging medium and the holes 13 lorm an outlet port lor said second medium. As w ill be understood f rom the follow ing explanations ith ref erence tυ Figure 2 a channel will be f ormed between the channel plates 2 and 3 af ter stacking and joining the plates e.g. by brazing. Only the second heat exchanging medium w ill be able to pass between said plates 2 and 3 in the downwards direction. Similar channels for said second heat exchanging medium will be formed betw een the channel forming plates 4-5 and 6-7 Likewise channels will be formed between the plates 3-4 and 5-6 through which only said first heat exchanging medium may pass upwardly. All channel forming plates are made of thin sheets of a material being conductive to heat - e.g. a metal.

The two heat exchanging media will pass counter-currenth through their respective sy tems of channels.

Figure 2 shows a section of Figure 1 in the direction of the arrows 11 —I I at a greater scale. In this known design the front er plate 1 has been directly brazed to the first channel plate 2 which -like the remaining channel f orming plates 3-7 - has a circumferentially extending, downwardly and slightly outwardly directed collar 14. When stacking the plates the collars 14 will engage each other and make it possible to forni a sealing connection by brazing. The front cover plate 1 has been provided with a brazed tubular fitting 15 at the inlet port 10 for the said

first heat exchanging medium and with a tubular fitting 16 at the outlet port 13 for said second heat exchanging medium. As it is desired that the two fittings 15 and 16 should ha\ e equal heights the areas of the cover plate 1 around the ports 10 and 13 should be located in the same plane. This is also a necessity in case the fittings should be replaced by O-πng connections direct to the cover plate I. Consequently no channel for a heat exchanging medium can be made between the cover plate 1 and parts of the channel forming plate 2. In order to seal against entrance of heat exchanging medium between the cover plate 1 and the channel plate 2 a spacer ring 17 has been provided and fastened between them by brazing. The draw back in this known design is that the front cover plate 1 has no channel forming function and that the spacer nng 17 is an extra element in the device. Also the rear cover plate 8 is not used as a wall in a channel for a heat exchanging medium.

Figure 3 shows how the front cover plate 1 previously has been formed so that the spacer ring can be omitted. As shown in Figure 3 this is obtained thereby that the areas of the cover plate 1 around the ports 10 and 13 have been located in different planes, and this makes the use of O-πng seals at the tube connections to the heat exchanger diff icult. Also the tube connections will be more complicated. The design according to Figure 3 does not either make it possible to use the co\er plate 1 as a wall limiting a channel for a heat exchanging medium

Figure 4 shows an embodiment according to the present invention. The front er plate 1 has the same arrow shaped pattern 9 of πdges and depressions as the channel plates 2-7 and also the same circumferential collar 14 for a sealing braze connection to the first channel forming plate 2. Around the inlet port 10 the first channel plate 2 has partial depressions 18 forming distribution channels between the cover plate 1 and the channel plate 2. These distnbution channel forming depressions 18 will be descnbed in more detail w ith rclerence to Figure 5 showing from abo\ e a channel forming plate according to the invenuon. Figure 4 shows also the rear cover plate 8 - e\ en this provided with a pressed pattern 9 and a collar 14

The channel plate show n in Figure 5 has the four previously discussed ports: the inlet ports 10 and 12 as well as the outlet ports 1 1 and 13. As will be seen when follow ing the section shown in Figure 6 along the line VI-VI in Figure 5 from the area around the port 10 in the direction against the port 13 you first meet the distnbution channel 18 as a short depression after which the same level is reached as that around the port 10. After a little mυre than hall the distance to the port 13 the level of the plate is lowered by approximately twice the depth ol the distribution channel 18. The difference between the levels of the plate areas around the two holes 10 and 13 coπesponds to the depth of the pressed arrow shaped pattern 9 as shown in Figure 7. The section VI-VI follows the top of a ridge from the distnbution channel 18 to the plane area 31 around the pon hole 13.

The channel forming plate 3 has the same appearance as the the channel plate 2, but it has been turned 180°, so that the distribution channels 18 in in the channel plate 3 will be located around the ports 12 and 13.

Figure 8 shows from above the front cover plate 1. From the section - Figure 9 - in the direcuon of the arrows IX-IX shown in Figure 8 it appears that the plate areas around all poπs 10-13 are located in a common plane. Also shown is the pressed arrow shaped pattern 9 and the collar 14.

The channel system in the plate heat exchanger between the front co\ er plate 1 and the adjacent channel forming plate 2 will be descπbed with reference to Figure 1 1 and also to Figure 4. The flow passing between the cover plate 1 and the channel plate 2 is a flow of the second heat exchanging medium and enters through port 12 and exits through port 13. The pattern ridges of the channel plate 2 and plate areas located at the same lev el have been designated by 20. The front cover plate 1 which should be placed on the top of the channel plate 2 should be turned 180° relative the position in Figure 8 in order to obtain opposite directions of the contacting arrow shaped pattems. Thus u ill be the plane area 30 at the top of Figure 8 which covers the area around the ports 10 and 13 in Figure 1 1. The area 20 in Figure 1 1 around the port 10 will completetly contact the cov er plate 1 (and be brazed to said plate). The distnbution channels 18 will drain the areas 31 (Figure 5) which otherwise would form blind channels containing stationary heat exchanging medium.

Figures 12, 13 and 14 show the rear cover plate. Figure 12 is a plane view , w hereas Figures 13 and 14 are sections along the lines XIII-XIII and XIV-XIV respectiv ely . The areas around the ports 10-13 are located in a common plane, and the areas 40, 41 at the shorter sides υl the plate are located in a lower plane as will be seen in Figure 13. The last mentioned areas together with the adjacent channel forming plate will form distribution channels hav ing the same draining function as the previously descπbed channels 18.

Figure 15 show s an alternative design ol the I ront cov er plate 1 Figures 16 and 17 aic sections along the lines XV1-X VI and XVII-XVII respectiv ely . Here elev ated parts 50 hav e been pressed between the ports at the shorter sides of the cov er plate. As shown in Figure 18 - which corresponds to Figure 4 - said elevated parts 50 w ill have the same draining function as the distribution channels 18 in the embodiment show n in Figure 4

Compared with the known designs shown in Figures 2 and 3 a saving corresponding to the cost of two channel forming plates (and in some cases even two spacer rings) as well as the cost for mounting and storage is obtained. However, said saving should be reduced by the greater cost of mateπal lor a cov er plate and the cost of forming the cover plates.

The rear cover plate 8 may be provided with holes for tube connections. However, in e.g. a two or three circuit heat exchanger system in which all tube connections are established at the f ront cover plate 1 such holes at the rear cov er plates should be blinded.