Plate Heat Exchanger
A plate heat exchanger comprising separate flow paths for two flows of fluid said paths having different pressure drops at equal mass flows may according to the invention be designed economically by stacking pairs of two plates (4, 5) provided with pressed patterns, at least one of the plates (4) in a pair (4, 5) being provided with at least two different press depths (D1, D2), the smaller (D2) being at least 40% of the greater (D1).
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The present invention relates to a plate heat exchanger comprising at least two separate flow paths for primary and secondary fluids to exchange heat, the said two flow paths being substantially defined by permanently interconnected heat exchanger plates provided with a herring bone pattern of ridges and depressions and offering different pressure drops at equal mass flows of the two fluids.
Many heat exchangers of the above type are used for heating tap water by means of hot water also used for heating dwelling houses. The inlet temperature of the heating water may be e.g. 75° C., and the outlet temperature thereof may be about 60° C. The inlet temperature of the tap water may be about 10° C. and the outlet temperature thereof may be 55° C. This indicates that the mass flow of the heating water must be 2.5 times the mass flow of the tap water. Therefore, it is economical to make the cross section of the flow path for the heating water wider than that of the tap water. E.g. by making the tops of the herring bone pattern flat—and thus wider—while the bottoms are unaltered this may be obtained.
Although this making the heat exchanger “asymmetric” is an improvement it is still an object to further increase the efficiency of the exchanger—i.e. to increase the heat transmission between the heat exchanging fluids without increasing the weight of the plate heat exchanger.
The Japanese Patent Application No. 11173771 A published Jul. 2, 1999 discloses a plate heat exchanger having different pressure drops in the flow paths in case of equal mass flows.
This is done by increasing the pitch—i. e. the distance between the contacts of adjacent ridges in the herringbone pattern. This known device is adapted to exchange heat between water and a cooling fluid the water flowing through the flow path having the smaller pressure drop. By making small depressions in parts of plates forming the water channels it is obtained that freezing of water will not cause damage to the plate heat exchanger. However, the areas of contact between plates will thus be relatively great and lost for the heat exchange between the fluids. The small depressions in the channels guiding the water flow will cause corresponding very narrow flow channels in the flow path for the cooling fluid. The areas of contact between adjacent plates are not rigidly interconnected in order to increase the elasticity of the plate heat exchanger, but the mechanical strength of the exchanger will be rather poor making the exchanger unsuitable for high pressure fluids.
The Japanese Patent Application No. 11281283 A also discloses a heat exchanger in which the pressure drops of two heat exchanging fluids are different in case of equal mass flows. According to the embodiment in FIG. 5 of said disclosure the flow paths forming a herring bone pattern comprise channels having greater cross sectional flow area provided with two small secondary depressions in the channels of greater cross section. This involves that the flow path having a total relatively high pressure drop will consist of parts causing very different pressure drops. This is an uneconomical way of using the material in the exchanger for exchanging heat. Also—as the pitch will increase with increasing numbers of the secondary depressions—the mechanical strength of the exchanger will decrease due to the smaller numbers of contact points at which the plates could be rigidly connected.
The object of the present invention is to design an “asymmetric” plate heat exchanger in which the material of the plates is used in a more economic way and thus in which the efficiency is improved while maintaining a high mechanical strength of the exchanger
According to the present invention this is obtained thereby that the depressions in at least some pairs of plates defining the flow path having the lower pressure drop at least partly are alternatively of two different press depths measured from the plan defined by the tops of the ridges of the herring bone pattern of the heat exchanger plate, the smaller being located between two tops of the herring bone pattern and being at least 40% of the greater, and thereby that the tops of the ridges engaging the tops of a neighboring plate to define a flow channel having high pressure drop substantially contact each other along points defined by crossing lines.
The invention will be described in more detail with reference to the accompanying drawings in which:
By increasing the pitch P and making the tops 2 of the ridges flat the flow path of one of the fluids will obtain a greater cross section than the flow path of the other fluid.
However, as shown in
Another proposal for manufacturing an “asymmetric” plate heat exchanger has been described in the Japanese Patent Application No. 11281283 A. Here the contact areas between the plates of the exchanger has been established by replacing the plan contact areas by areas containing small depressions. This has been shown in
The herring bone patterns of the two plates 4 and 5 shown in
It has been found that the secondary press depth D2 should be at least 40 percent of the press depth D1—preferably about 50 percent thereof.
According to the embodiment of
It will be understood that a heat exchanger according to the present invention may comprise other combinations of pairs of plates than those described above. E.g. some pairs may be of the known type shown in
Claims
1. A plate heat exchanger comprising at least two separate flow paths for primary and secondary fluids to exchange heat, the said flow paths being substantial defined by permanently interconnected heat exchanger plates provided with a herring bone pattern of ridges and depressions and offering different pressure drops at equal mass flows of the two fluids, wherein the depressions in at least some pairs of plates defining the flow path having the lower pressure drop at least partly are alternatively of two different press depths (D1, D2) measure from the plan define by the tops of the ridges of the herring bone patter the heat exchanger plate, the smaller (D2) being located between two tops of the herring bone patter and being at least 40% of the greater (D1), and thereby that the tops of the ridges engaging the tops of a neighboring plate to define a flow channel having high pressure drop substantially contact each other along points defined by crossing lines.
Type: Application
Filed: Jul 7, 2005
Publication Date: Feb 7, 2008
Applicant: SWEP INTERNATIONAL AB (Landskrona)
Inventor: Peter Nilsson (Landskrona)
Application Number: 11/632,582
International Classification: F28D 9/00 (20060101);