Plate heat exchanger

In a plate heat exchanger, in which the plates are provided with a turbulence generating pattern of grooves and ridges which also form supporting points for plates disposed adjacent to each other, the thermal treatment of a medium will be different in different parts of one and the same passage due to the different length of different flow paths within the passage. In order to equalize the differences of thermal treatment within one and the same passage and/or to provide mutually different treatment of the heat exchanging media, each passage is formed by plates corrugated in a pattern which is unsymmetrical with regard to the central plane of the plates, the ridges and grooves of plates disposed adjacent to each other extending in mutually different directions relative to the longitudinal axis of the plates.

The present invention relates to heat exchangers of the kind comprising a 
plurality of heat exchanging plates arranged adjacent to each other and 
forming between them sealed passages adapted for through-flow by two heat 
exchanging media. More precisely, the invention relates to a plate heat 
exchanger in which the heat exchanging surfaces of the plates are provided 
with creases or corrugations which on each side of the plates form a 
wave-like pattern of ridges and grooves. The primary object of the 
corrugations is to cause a heavy turbulence of the heat exchanging media. 
The plates are usually provided with marginal sealing gaskets and are 
clamped together in a supporting structure. However, the plates may 
instead be interconnected permanently, as by welding or soldering, in 
which case the sealings and supporting structure are omitted. 
By letting the corrugations of adjacent plates form an angle relative to 
each other, a large number of supporting points are also obtained in which 
the ridges of adjacent plates are in contact with each other. In prior 
heat exchangers of this kind, the corrugations extend at a fixed angle 
relative to the longitudinal axis of the plate, and the above-mentioned 
angle between corrugations of adjacent plates is obtained by turning every 
other plate 180.degree. in its own plane. Furthermore, the corrugations 
are made symmetrical with regard to the central plane of the plate, and in 
addition, the angle of the corrugation relative to the longitudinal axis 
of the plate is equally large on each side of the center line of the 
plate. 
Due to the symmetrical construction of the plates of the prior heat 
exchangers, equal thermal properties are obtained in all heat exchanging 
passages. This is the case even when two kinds of plates are used which 
are arranged alternately. Further, passages are provided which throughout 
their entire area present unchanged thermal properties. Thus, the 
so-called thermal length or heat transfer capability of an element of a 
passage is equal to the thermal length of another element having the same 
area and being located in another part of the passage. 
However, as is well known, since different flow paths within a passage are 
not equally long, the portion of a heat exchanging medium taking a longer 
flow path through the passage will be exposed to a different thermal 
treatment than the portion of the medium taking a shorter path through the 
same passage. Since it is desired to obtain equal thermal treatment of the 
medium irrespective of the flow path through the passage, the 
above-described state of things is unsatisfactory. 
In order to rectify this drawback, it is an object of the present invention 
to provide heat exchanging passages in which elements located in a longer 
flow path have less thermal length than equally large elements located in 
a shorter flow path. In this way a mutual equalization of the total 
thermal length of flow paths of different lengths can be provided, whereby 
the thermal treatment of the medium will be the same irrespective of the 
flow path between the inlet and outlet of the heat exchanging passage. 
It is a further object to provide a plate heat exchanger in which the 
passages for both heat exchanging media may have mutually differing 
thermal lengths. 
In the heat exchanger of the present invention, the above-mentioned objects 
are fulfilled and at the same time the above-described drawbacks of prior 
heat exchangers are eliminated. This is achieved by a plate heat exchanger 
of the above-mentioned kind which is generally characterized in that it 
comprises passages formed by plates each having a corrugation which is 
unsymmetrical in relation to the central plane of the plate, the 
corrugation grooves of both the plates forming a passage extending in 
mutually differing directions in such way that the angle formed between 
the grooves and the longitudinal axis of one plate is smaller than the 
corresponding angle of the other plate.

The invention will be described more in detail below with reference to the 
accompanying drawings, in which FIG. 1 is an exploded, diagrammatical 
perspective view of a series of conventional heat exchanging plates; FIGS. 
2-4 are diagrammatical plan views of different embodiments of heat 
exchanging plates according to the invention; and FIG. 5 is an exploded, 
fragmentary perspective view of a series of heat exchanging plates 
according to the invention. 
The conventional heat exchanging plates 1 shown in FIG. 1 are provided with 
corrugations 2 which are indicated diagrammatically and made in a 
so-called herringbone pattern. The corrugations form an angle "a" against 
the longitudinal axis 3 of the plates. This angle is the same on both 
sides of the center line, as indicated in FIG. 1. In order to obtain a 
mutual angle between the corrugations of adjacent plates, every second 
plate is turned 180.degree. in its own plane. In a heat exchanger 
assembled from such plates, each corrugation of which is completely 
symmetrical in all respects, the thermal properties of all heat exchanging 
passages are equal. The thermal properties are also equal on each side of 
the center line 3 of the plates. 
In FIG. 2, two plates 10 and 11 are shown which are made in accordance with 
the invention. The plates 10 and 11, which are arranged alternately in a 
heat exchanger, are of two kinds and differ in that the corrugations 12 
extend at different angles b and c, respectively, with relation to the 
longitudinal axis 13. The plates are provided in a conventional way with 
corner openings 14 and sealing gaskets 15. 
The plates 20 shown in FIG. 3 are identical, one of them being turned 
180.degree. in its own plane. The plates 20 are each provided with a 
corrugation 22 which on one side forms a first angle d in relation to the 
longitudinal axis 23 and on the other side forms a second angle e in 
relation to the same axis. 
The two plates 30 and 31 shown in FIG. 4 are provided with corrugation 
patterns 32 each presenting different angles on each side of the center 
line of the plate and also different angles relative to the corrugation of 
the other plate. The corrugation of the plate 30 thus extends at angles f 
and g, respectively, in relation to the longitudinal axis 33, and the 
corresponding angles of the plate 31 are designated h and i. 
In FIG. 5, three fragments 40, 41 and 42 of the heat exchanging portion of 
heat exchanging plates according to any of FIGS. 2-4 are shown. The 
cross-section of the plates is shown in FIG. 5, where it appears that the 
corrugation pattern is made unsymmetrical in such a way that the ridges on 
one side of the plate have sharp creases 44 and on the other side plane 
portions 45. As appears, all the plates face the same direction and thus 
have the sharp creases 44 facing forwards in the Figure, the sharp creases 
44 of one plate abutting the plane portions 45 of an adjacent plate. In 
the Figure, the corrugation grooves of adjacent plates extend at right 
angles to one another, but of course, other mutual angles are also 
applicable. 
Although the volume of the passages formed between plates 40-42 are 
essentially equal, their thermal properties may still vary due to the flow 
direction. This is because of the unsymmetrical corrugation pattern of the 
plates which more or less affects the flow of the media, due to their 
direction in relation to the grooves of the plates. For instance, if the 
flow direction in the passage between the plates 40 and 41 is parallel to 
the grooves of the plate 41, the medium will be subjected to a heavier 
flow resistance and turbulence than if the flow direction is parallel to 
the grooves of the plate 40. This state of things is essentially due to 
the fact that as to each passage between adjacent plates, the two portions 
of the passage located on each side of a plane through the points of 
contact of the plates have different volumes due to the unsymmetrical 
corrugation pattern. 
In FIG. 5, supposing that both the media flow in a direction at the same 
angle to the grooves of all the plates, i.e., 45.degree. , the thermal 
properties of all the passages will be equal. 
As appears from the above, it is possible to adapt the thermal properties 
of the heat exchanging passages as needed by providing the plates with an 
unsymmetrical corrugation pattern, such as the kind shown in FIG. 5, and 
by having the corrugation grooves extend at a suitable angle in relation 
to the general flow direction of the heat exchanging media. 
In this way, it is possible to obtain heat exchanging passages in which an 
element located in a shorter flow path has a greater thermal length than 
an element having the same area and located in a longer flow path through 
the same passage. 
In an embodiment according to FIG. 3 or 4, by choosing suitable angles d 
through i, it is possible to obtain a heat exchanger in which the passages 
on the side of the center line closest to the inlets and outlets has 
greater thermal length per unit of area than on the opposite side of the 
center line. In an embodiment according to FIG. 2 or 4, it is further 
possible to obtain a heat exchanger in which the thermal properties of the 
passages for both the heat exchanging media differ mutually. 
Further embodiments than those shown on the drawings are also possible 
within the scope of the invention. Thus, the unsymmetry of the corrugation 
pattern may be different on two adjacent plates. Furthermore, the grooves 
of the corrugation need not be broken along the center line of the plates, 
as is shown in the figures, but can be broken along several lines, for 
example.