Plates For Directing The Flow Of Fluids

Abstract

A plate for directing the flow of fluids which is shaped so as to provide contact points capable of spacing it from and supporting it against similar plates, is also provided with further contact points so that by suitable arrangement of the plates, the spacing therebetween can be varied. The basic contact points on the standard plate are provided by a herring-bone pattern of V-shaped hill and valley corrugations and, preferably, the further contact points are formed by stamping the plate so that portions of the hill structure of the corrugations are provided with reversed hill and valley formations, although they may be formed by studs or projections attached to the plate.

Description

This invention relates to plates for directing the flow of fluids, and, more particularly, to a new and improved plate which is capable of being oriented in either of two relationships with another similar plate so as to vary the cross-sectional area of the flow channels therebetween. In a preferred embodiment of the invention described below, the plates are employed in the environment of a plate heat exchanger.

Plate heat exchangers are widely used for the transfer of heat from one fluid to another, but are nevertheless subject to a number of compromises and disadvantages in practice. It has long been recognized that plate heat exchangers are useful because of their compactness and versatility of operation, but the tooling equipment required to manufacture plates is costly and therefore it is not generally economical to manufacture more than a relatively few different designs of plate. One of the major costs in producing a plate heat exchanger is the development of, and stamping equipment capitalization for, the particular plate design chosen. Manufacturing equipment is costly and manufacturers have found it generally uneconomical to manufacture more than one design of plate for a given size; for example, even for the larger manufacturers, more than three or four different sizes of plate are uncommon, if not unknown. Consequently, each type of plate made by a manufacturer is often used inefficiently for a wide range of different applications. It is obviously very desirable for a single form of plate to be used and for the desired flowpaths for the two fluids to be created by suitably arranging the plates in the exchanger. Because one main source of the cost of plate heat exchangers lies in the amount of metal used, which is often relatively expensive, the plates are generally thin, but the thinness of the plates makes them relatively weak and so necessitates their having a good self-supporting design. It is also desirable, if there are appreciable heat transfer surfaces and/or pressure drops to be provided for, for the plates to be self-supporting against fluid pressures. This requires, in practice, that the individual plates in a heat exchanger shall be in contact at spaced locations over their surfaces, so as to be self-supporting and/or to ensure that the flowpaths between them remain generally constant when the heat exchanger is in use. These requirements have precluded the adoption of advantageous variations in flowpath spacing and other geometry however.

A conventional heat exchanger plate is of rectangular form, having ports in each of the four corners of the rectangle and having its major portion embossed, such as in a rib formation. A common practice is to impress raised portions or a herring-bone or other pattern of "hill-and-valley" corrugations over the entire major area of each plate, with appropriate subsidiary hill-and-valley corrugations leading from and to each of the ports in the corners, a circumferential marginal region being provided for co-operating with a gasket or other sealing member to prevent leakage between dissimilar fluid flowpaths and/or fluid leakage to the exterior of the plate exchanger package, so as to seal the plate relative to the next ones in the heat exchanger. If a number of identical plates of such a form were to be arranged with their corrugations similarly directed, no sealing members being interposed, the plates would nest completely and there would be substantially no spaces between them. It is common practice, therefore, to form a plate heat exchanger by reversing each alternate plate, so that the impressed configuration is directed alternately in the respective plates in the heat exchanger, for example, in a "herring-bone" pattern. The necessary support of the plates is then given by virtue of the points of contact where the hill formations on one plate cross the hill formations of the adjacent plates. It will be appreciated that what is a hill formation on one side of a plate is a valley formation on the other. With an arrangement of this kind, it will be seen that the plate spacing equals the size of the hill-and-valley corrugations in the individual plates.

While it is possible to form a heat exchanger with a number of identical plates of this kind and to obtain reasonable operating results from it, it is almost universally true that the two fluids which are passed through a heat exchanger are different, either being different liquids or possibly the same fluid having different temperatures. In any practical case therefore, a compromise is necessarily adopted because the flowpath for one of the fluids is clearly not so ideally suited to the other fluid. For example, if one of the fluids has a higher viscosity than the other, it is evident that, given equal spacing between and arrangement of the plates in the respective flowpaths, the more viscous fluid will require to be fed at a higher pressure. A particular example of inefficient two-component, liquid-liquid heat exchange in a plate heat exchanger is the cooling of a viscous oil by water. It is self-evident that a plate spacing which is well suited to the viscosity, thermal conductivity, temperature and pressure of the oil is not well suited to the similar properties of the water. For pressure drop reasons alone, the characteristic flexibility of plate exchangers in adjusting the lengths of the flowpaths of one of the fluids, with respect to the other, is not generally sufficient. It is therefore highly desirable to provide for flowpath cross-sectional area and geometry differentiation in all heat transfer applications. It is also highly desirable to provide for flowpath differentiation in all heat transfer applications involving gas and liquid or vapor and liquid. If the plate spacing can be varied and consequently the cross-sectional flow area of the flowpaths, the pressure drop of that flowpath can be readily controlled. This allows an improved performance to be obtained, employing a narrow high-pressure-drop flowpath for liquids, together with a wider low-pressure-drop flowpath for vapor or gas.

According to the invention, a variable spacing between the respective plates of a plate heat exchanger is achieved, the plates otherwise being identical, by providing a secondary set of self-supporting contact points on at least some of the plates in the heat exchanger plate assembly, whereby respective pairs of plates can be assembled to have a flowpath spacing which is less than, equal to or greater than the spacing given by the primary set of self-supporting contact points of the set of plates. In addition to varying the plate spacing and therefore the cross-sectional area of the flowpath, it will be appreciated that, by proper selection of the embossed form of the primary set of plates and of the secondary set of self-supporting contact points, the actual geometry and therefore the thermal characteristics of the resulting flowpath may be advantageously modified, in a wide variety of ways.

The present invention offers for the first time a convenient and economical means of varying the mechanical and thermal characteristics of plate heat exchangers for some of the fluids in process substantially independently of the others. Working fluids are in general dissimilar in properties and so it follows that the heat exchanger flowpaths should be correspondingly different. Materials differing in density, viscosity, specific heat and thermal conductivity must, for efficient heat transfer, have different flowpath conditions.

It is well-known from conventional plate heat exchanger design that it is generally impractical to vary the plate spacing by using a number of different plate forms. Normally the duty is for two working fluids, so that one plate forms the flowpath boundary for both fluids. Each fluid flows in alternate passage-ways. Since economic considerations preclude the manufacture and use of a complicated spacer for varying the flowpath geometry and spacing and because of the general necessity for the plates to be of a self-supporting nature, for existing plate heat exchanger design, the flowpath for one fluid cannot be varied independently of the other. The flowpath for one fluid cannot be varied independently of the other, since each plate forms a boundary for the two flows. The use of a spacer to increase plate separation is uneconomical and impractical because of the necessity for the plates to be self-supporting.

In putting the invention into effect, one preferred way is to form the secondary supports by a simple stamping or fabricating operation. Their form and/or depth may be varied for finer adjustment in flowpath conditions. In this way, a single plate design may be simply and cheaply varied for a wide range of duties. The primary form of plate may be designed so that relative roughness, turbulence, hydraulic diameter and other factors may be increased or decreased by correct selection of the secondary support design and orientation.

Other ways in which the desired subsidiary set of contact points can be provided is for those plates which require modification to have secondary contact points in the form of studs, projections or other small abutment members attached or otherwise disposed at appropriately spaced locations on the plates. Another way in which the subsidiary spacing can be obtained is by the interposition between plates of a set of subsidiary contact points in the form of sets of contact members having the form for instance of a wire spider or other member to which stud or other contact members are attached. The individual wires in the spacer assembly so formed may desirably be shaped and arranged so as to follow the channels which are defined between the hill-and-valley formations of adjacent plates, so that the spacer members attached to the wires and not the wires themselves govern the modified spacing between the adjacent plates. In this embodiment, a plate heat exchanger can be simply manufactured by appropriately arranging a plurality of identical and unmodified plates and inserting spacer assemblies for instance between each alternate pair of plates, so as to appropriately enlarge, decrease or modify the flowpath spacing for one of the two fluids. It will be appreciated that, in all cases, the sealing member or gasket material used is varied in thickness to suit the varied plate spacings which are present in the assembled heat exchanger.

In order that the invention may be more readily understood, a preferred embodiment is described below by way of illustration in conjunction with the accompanying drawings. In the drawings:

FIG. 1 shows, in exploded perspective view, portions of the individual plates and gasket members of a heat exchanger according to one embodiment of the present invention;

FIG. 2 shows the assembled plates of the heat exchanger of FIG. 1;

FIG. 3 shows an end elevation of the plates of the heat exchanger of FIGS. 1 and 2.

Referring to the drawings, a number of the plates of a plate heat exchanger are shown at 10, 11, 12, 13, 14 and 15. Referring to the lowest plate 10, for simplicity, each plate in the exchanger is of elongated rectangular sheet and parts of the two longer sides only are shown for the plate 10. In the peripheral region of each plate, in this embodiment, a flat channel structure 16 is formed for the reception of a sealing gasket on either side. In this example, the main face area of the plate 10 within the rectangular gasket channel formation 16 is embossed with a herring-bone pattern of shallow V-shaped hill and valley corrugations 17. Each corrugation 17 consists of two oppositely-inclined surface portions 17a, 17b which form a straight line of intersection 17c, which forms a hill on one side of the plate and a valley on the other side of the plate. Circular or other apertures are provided in advantageous locations on the plate 10 (not shown) for use as the ports and the channel formations 17 are appropriately arranged adjacent the respective ports, so that the appropriate connections are provided in a convenient manner.

In the embodiment illustrated, the alternate plates 10, 12 and 14 have the basic structure which has just been described above in relation to plate 10 and it will be noted that the plates are arranged to have the herring-bone pattern facing alternately in one direction and the other, the plates 10 and 14 being identical in form and arrangement and the plate 12 having the same form but being reversed so that its herring-bone pattern faces the other way.

Each of the alternate plates 11, 13 and 15 is basically identical with the cooperating plate below it in both portions and dimensions, but each of these plates 11, 13 and 15 is provided with small reversed corrugation areas which constitute abutments disposed within the valleys of the corrugations. These abutments function as a secondary set of contact points. As shown for the plate 11, a secondary pressing is effected on the plate so that portions of the hill structures of the corrugations 17 are provided with integrally formed valley formations 18 which have their intersecting lines 18c between the opposed faces 18a and 18b directed at right angles to the hill and valley crest lines 17c of the main corrugations. The subsidiary corrugations as shown are partial, though they can be complete in that the relevant portions of the plate are completely reversed in hill-and-valley corrugated formation. The extent of this secondary shaping can be such that hills are formed which are higher than the primary hill structure.

The plates are arranged in pairs of two plates that are similarly oriented. As shown in FIG. 1, pairs are formed by plates 10 and 11, 12 and 13, and 4 and 15. Each pair of plates has an orientation opposite that of the adjoining pairs. As best shown in FIG. 3, the spacings provided between the plates 11 and 12 and between the plates 13 and 14 (which constitute parts of one of the flowpaths through the heat exchanger) can be regarded as conventional when they occupy a first cooperative relationship in that the spacing is governed by a primary set of contact areas where the hill ridge lines of intersection 17c of the plate cross and contact the hill ridge lines of intersection 17c of the adjacent plate. A standard thickness gasket 19 is provided between these plates, as shown best at FIG. 2. It can be seen from FIG. 1 in particular that the directions of the main corrugations 17 in the superposed portions of the plates 11 and 12 and 13 and 14 respectively are differently oriented so as to provide this standard spacing. The spacing which is produced between the plates 10 and 11, the plates 12 and 13 and the plates 14 and 15 respectively is less than this standard spacing, because the main ribs on the corrugations 17 in superposed areas similar and, therefore, internesting occurs to the extent permitted by the subsidiary corrugations 18 in the plates 11, 13 and 15. When the plates occupy this second possible cooperative relationship, the ridges 18c of the subsidiary corrugations contact with a secondary set of points spaced along the ridges 17c of the plates underlying the plates 11 and 15 respectively. In this embodiment the flow channels between the cooperating plates have a smaller cross-sectional area when they occupy this second internested relationship than when they occupy the first non-internested relationship. This is due to the dimensions of the abutments 18. It can be seen from the figures that a narrower gasket 20 is provided for these plates. The spaces between the plates 10, 11, 12, 13 and 14, 15 constitute successive portions of the other flowpath through the heat exchanger. By this simple modification of each alternate one of the plates in a stack of plates, with appropriate sizing of the gaskets a relatively large flowpath for one of the fluids is given and alternates with a relatively narrow flowpath for the other of the fluids, as can be readily seen in FIG. 3.

Claims

What we claim is:

1. A plurality of heat exchanger plates arranged in stacked relationship and defining a plurality of flow channels between the plates, each plate comprising a sheet of material the surface of which forms a pattern of hill and valley corrugations, each corrugation consisting of two oppositely inclined surface portions that intersect to form a crest line, at least every second plate including a series of surface deformations that form abutments disposed within the valleys of the corrugations, the plates being arranged in pairs of two plates that are similarly oriented so that the plates which form a pair are internested and the abutments are utilized as contact points, each pair of plates having an orientation opposite that of the adjacent pairs so that spaced locations along the crest lines are utilized as contact points between plates of different pairs to prevent internesting, whereby flow channels of at least two different crosssectional areas are provided.

2. The apparatus of claim 1 wherein each plate is rectangular in shape.

3. The apparatus of claim 1 wherein the corrugations of each plate are arranged in a herring-bone pattern.

4. The apparatus of claim 1 wherein said abutments are formed by reversed hill and valley corrugations pressed into the plates on which they are provided.

5. The apparatus of claim 1 wherein the corrugations are substantially V-shaped.