US 3430694 A
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Description (OCR text may contain errors)
March 4, 1969 o. CARDELL PLATE STRUCTURE FOR HEAT EXCHANGERS Filed Nov. 5, 1966 IN V EN TOR. 0.4 OF (1920:: L
ya fJ/ wu United States Patent 3 430 694 PLATE STRUCTURE TOE! HEAT EXCHANGERS Oiof (Jardell, Strandvagen 1, Sollentuna, Sweden Filed Nov. 3, 1966, Ser. No. 591,794 Claims priority, application Sweden, Nov. 9, 1965, 14,409/65; Jan. 24, 1966, 883/66; Sept. 26, 1966, 12,929/66 U.S. Cl. 165166 3 Claims Int. Cl. FZSE 3/10 ABSTRACT OF THE DISCLOSURE Plate structures for heat exchangers composed of parallel sheet metal members at small mutual distances to form shallow flow passages for the heat-exchanging media may be manufactured by interconnecting said members by electrical resistance welding of distance pieces between the members. The shape of the contact surfaces of the distance pieces and the sheet metal members and the mass of said pieces must not differ from certain relative values to avoid disadvantages in welding and during the subsequent use or" the heat exchanger. The radius of curvature of the contact surfaces of the distance pieces should be greater than half the distance between the sheet metal members, because otherwise the mass of the distance piece is too small to obtain a correct weld produced by electrical resistance welding. Suitable distance pieces are obtained by cutting wires having elliptic cross section. Also metallic tablets are usable.
This invention relates to plate structure for heat exchangers of the type comprising opposite plates of sheet metal which pairwise define passages for heat exchanging media and in which the sheet metal members are located relatively close to each other so that narrow passages are formed between the plates. Said members are usually assembled to provide for a heat exchanging medium to flow between every second pair of members and another heat exchanging medium to flow between the other pairs.
The object of this invention is to provide a heat exchanger of the type indicated which is able to resist comparatively high and varying pressures.
In accordance with the invention the plates or members are pairwise connected to each other by means of distance pieces having curved surfaces which are secured to the plates or members by resistance welding, the radius of curvature of said surfaces being equal to or greater than half the distance between the plates connected to each other by the distance pieces. Due to the above indicated form of the distance pieces and their connection with the opposite plates or members it is possible to connect said members to one another in a very effective manner so as to obtain a permanently durable structure. It has proved in practice that the shape of the distance pieces is highly important to effective welded joints at opposite plates of the heat exchanger, especially if the distance between the plates is small. It the distance pieces are not suitably shaped at the places to be welded together sparks will occur during the welding operation with molten metal spurting around from the weld area. Such molten metal adheres to the plates of the heat exchanger and is likely to cause corrosion and increased resistance to the flow of the heating medium. In this connection a further fea ture consists in that too small a mass of the distance piece may result in that the distance piece will more or less melt as the welding current is switched on. In that case it is of course not possible to obtain the desired distance between opposed plates of the heat exchanger. By way of example, if the distance between the plates is smaller than 1 to 2 mm., distance pieces in the form of balls cannot be used because their mass is too small to permit electric resistance welding. The radius of curvature of a spherical ball at the places of contact between the plates is constant and equal to half the distance between the plates. A distance piece having a curved contact surface cannot be used in case of small distances between the plates unless its mass is greater than that of a spherical ball, and for this reason the radius of curvature of such a distance piece must be greater than half the distance between the plates.
Distance pieces in the form of balls have the advantage that they can be easily applied to their positions and need not be directed as is the case with distance pieces in the form of studs or the like the end surfaces of which are connected to the plates.
Special advantages can be obtained if the distance pieces consist of pieces of wire arranged in rows between the plates and being of circular cross section in case of greater distances between the plates and of oval, such as elliptic cross section in case of smaller distances between the plates and disposed between the plates such that the minor axis of the ellipse is perpendicular to. the planes of the plates. Such distance pieces can have a suitable mass for obtaining a favourable thermal balance during the welding operation because the mass can be selected in a simple manner by suitable choice of the lengths of the pieces of wire. Thus, a small distance between the opposed plates and a corresponding small minor axis of the elliptic cross section of the wire can be compensated for in a simple manner by a correspondingly greater length of the piece of Wire. Exact dimensions of the distance pieces can be obtained if these pieces are made from calibrated wire which is obtainable with close tolerances and consequently with high dimensional accuracy.
The strength of the heat exchanger and its dimensional accuracy can further be favourably affected by suitable connection of the edges of the plates and by a suitable shape of the marginal portions connected to each other. Examples thereof are described hereinbelow with reference to the annexed drawings.
In the drawings, FIG. 1 is a fragmentary perspective view of plates comprised in a heat exchanger according to the invention. FIGS. 2, 3 and 4 illustrate a first embodiment of a distance piece as viewed from a side, from one end and from a side at right angles to FIG. 2, respectively. FIGS. 5 and 6 illustrate a lateral view and an end view, respectively, of a second embodiment of a distance piece. FIGS. 7 and 8 illustrate a lateral view and an end view, respectively, of a third embodiment. FIG. 9 illustrates a fourth embodiment of the distance piece. FIG. 10 is a ftagementary perspective tvie w of a marginal portion of a heat exchanger and FIG. 11 a similar fragmentary perspective view of a modification of the marginal portion. FIGS. 12 and 13 are further perspective fragmentary views of modified embodiments of the heat exchanger. FIG. 14 illustrates how the distance pieces can be welded to the plates.
Referring to the drawing, reference numerals 1,2,3 and 4 denote fragments of parallel opposed plates in a heat exchanger. The plates define narrow flat passages 5, 6, 7 for heat exchanging media. In the passages 5 and 7 a first fluid is assumed to flow in the direction indicated by the arrows 8 and in the passage 6 a second fluid flows in the direction of the arrows 9 which means that the heat exchanger exemplified is of the cross-current type. The heat exchanger may be of a different type, such as counter-current or concurrent type. The plates are pairwise kept together by means of distance pieces which also keep the plates at a desired distance from each other. Between the pair of plates 1, 2 there are disposed rows of distance pieces 10 which are spaced from each other in all directions and between the plates 3, 4 there are provided distance pieces 10'. In the passage 6 between the plates 2 and 3 there are no distance pieces. Alternatively each passage may contain distance pieces. The distance pieces consist of pieces of \wire which according to FIGS. 2 to 4 are elliptic and according to FIGS. 5 to 9 circular in cross section. In case of distance pieces of elliptic cross section the pieces are orientated in such a manner between the plates that the minor axis of the ellipse is perpendicular to the planes of the plates as shown in FIG. 1.
The above described shapes of the distance pieces are particularly advantageous from the point of view of welding. The pieces of wire are easily placed in the most suitable positions for resistance welding. Pieces elliptic cross section have the minor axis perpendicular to the plates resulting in a stable position. The same holds true of the tablet-like distance pieces shown in FIGS. 7, 8 and 13. They have an arcuate uniform surface in contact with the surface of the plate to which they are to be welded with the result that the risk of sparks and drops of molten metal spurting around is very small. Favourable thermal balance can be obtained during the resistance welding operation because the mass of the pieces of wire can be conveniently adapted by suitable selection of the diameter and/or length of the pieces. Since the mass of the distance pieces is most suitable from the point of view of welding the finished product will have a high dimensional accuracy. Further, the distance pieces can be secured in such positions that a uniformly rounded surface faces the direction of How (arrow 8 in FIG. 1) of the working medium in the passage between the plates which are connected to each other by the distance pieces, resulting in a low resistance to flow in the heat exchanger. This effect can be further improved if the distance pieces are separated such as cut off from the wire blank in such a manner that their ends are rounded as shown in FIGS. 2 and 4.
The distance pieces are attached by electric resistance welding and it is possible to start with strip-like metal sheets between which the distance pieces are placed in rows and all distance pieces in a row are welded simultaneously. As shown in FIG. 14, electrodes 1a, 2a are forced against the outsides of the plates 1, 2 opposite to the distance piece 10, and electric current is caused to flow from one electrode to the other via one plate, the distance piece 10 and the other plate. At the contact places between the distance piece and the plates the metal of these parts will melt to such an extent that a secure connection is obtained as is the case in customary electric resistance welding.
Distance pieces in the form of balls (FIGS. 9 and 14) are suitable in cases of great distances between the plates However, in case of small distance balls have too small masses so that there is the risk that the whole ball is likely to melt. In that case tablets according to FIGS. 7, 8 and 13 or pieces of wire of suitable lengths according to FIGS. 2 to 6 are preferred.
In the exemplified embodiments of distance pieces in the form of wires of circular or oval cross section the distance piece is in linear contact with the opposite plates prior to the welding operation. During the welding operation the metal melts along these contact lines which will be transformed into surfaces along which the weld joint is formed. Due to the advantageous shape of the distance pieces the strength of such a weld joint is very high. Preferably all distance pieces in one and the same cross row are welded simultaneously and the plates are held in spaced relation ahead of the welding place.
The plates are pairwise connected to each other not only by means of the distance pieces, but also directly at the sides of the heatexchanger. This connection may be effected in any suitable manner which may be known per se. Two embodiments which are especially advantageous from the point of view of welding are illustrated in FIGS. 10 and 11 which show the connections on one side of the heat exchanger. Similar connections may be provided on the opposite side of the heat exchanger. According to FIG. 10 the four plates 1, 2, 3, 4 are pairwise connected to each other by bending the marignal portions of the plates 1 and 2 toward each other and connecting the edges by a weld joint 11 and similarly connecting the bent marginal portions of the plates 3 and 4 by a weld joint 11. As a result the plates 1 and 2 form opposite sides in a flat hollow body. The same holds true of the plates 3 and 4. The hollow bodies are connected to each other by distance pieces 10, but the interior of the hollow bodies is clear of distance pieces. Additional distance pieces 10' may be provided for connecting the hollow bodies illustrated with further hollow bodies located above and below. The longitudinal direction of the distance pieces 10, 10' is perpendicular to the interconnected longitudinal edges of the hollow bodies, i.e. perpendicular to the weld joints 11, 11'. Consequently, the rounded sides of the distance pieces are facing the direction of flow indicated by the arrows 9.
FIG. 11 also shows four plates 21, 22, 23 and 24 which are pairwise connected to each other by means of distance pieces. The distance pieces 10 are disposed between the plates 21 and 22, and the distance pieces 10 are disposed between the plates 23 and 24. All of the plates have their marginal portions bent in the same direction and they are welded together such that the edge 25 of a plate is in contact with the convex side 26 of the adjacent plate. The result is a very stiff structure in which the weld joints on the sides of the heat exchanger are easy to effect. As distinguished from the welded joints at the contact places between the distance pieces and the opposite surfaces of the adjacent plates, the connection at the edges is suitably made by electrode welding with the use of filler metal prior to the welding operation.
Especially Wide hollow bodies can be obtained if two or more strips of plates 28, 29 have upwardly bent marginal portions 30, 31 which are welded together as shown in FIG. 12. The hollow space between the plates is provided with distance pieces 32 which are welded in the manner described above.
The invention is not limited to the embodiments illustrated. The distance pieces may be provided Within the flat hollow bodies Which form passages for one or more of the heat exchanging media, and/or on the outside of the hollow bodies. In the later case all of the plates will be connected by means of distance pieces.
What I claim is:
1. A heat exchanger having a plurality of pairs of spaced parallel imperforate thin metal plates of substantial area, every second of said pairs of plates having distance pieces of solid metal therebetween which interconnect the plates of said pair, said interconnected pair of plates forming side walls of a tube member of substantially rectangular cross section having open ends for the flow therethrough of a first fluid in indirect heat exchange with a second fluid on the outer sides of the plates of said pair so that said first and second fluids flow through alternate passages between said plates, the distance pieces being short pieces spaced from each other in all directions and being shaped to have a cross section in which confronting sides, which face the plates on both sides of the distance pieces, are curved outward with a radius of curvature which is greater than half the distance between the plates so that the plates are tangential to said sides where they abut against the distance pieces and so that at each such abutment abutting metal from the plate and the distance piece is fused together without addition of other metal.
2. Aheat exchanger as claimed in claim 1, in which said distance pieces are circular when viewed in a direction perpendicular to said plates.
3. A heat exchanger as claimed in claim 1, in which said distance pieces comprise short lengths of metal hav- 5 6 ing uniform cross-sectional configuration over a substan- 2,267,619 12/1941 Strom 165-166 X tial portion of their length. 2,601,973 7/1952 Jensen 165-166 3,211,219 10/1965 Rosenblad 165-166 References Cited 3,255,816 6/1966 Rosenblad 165166 UNITED STATES PATENTS 5 ROBERT A. OLEARY, Primary Examiner. 2,611,586 9/1952 Colhns 165166 3,280,906 10/1966 Rosenblad 5 1 X T. W. STREULE, Asszszarzt Exammer.
1,648,511 11/1927 Solomiac 165-166