ARRANGEMENT AT PLATE HEAT EXCHANGER

Abstract: A plate heat exchanger, which comprises a plurality of plates located to the side of each other and consisting each of two sheets facing toward each other, which sheets are formed with longitudinal valleys, which facing toward each other form passages between the sheets when the sheets abut each other. The object of the invention is to provide a plate heat exchanger with straight unobstructed passages in order to reduce the problem of clogging and to facilitate cleaning. Between adjacent passages there must be free flow so that washing can be carried out even when a single passage should have been clogged. A further advantage is that the sheets can be formed in press tools without risk of fracture indications to arise. The invention implies that the valleys (5) are formed with grooves (19) transverse to the longitudinal direction of the valley and extending continuously from one outermost located valley to the other outermost located valley.

Description: Arrangement at plate heat exchanger. This invention relates to an arrangement at a plate heat exchanger comprising a plurality of plates, which are arranged to the side of each other and consist each of two plates facing toward each other and formed with longitudinal valleys, which facing toward each other form passages between the plates when the plates abut one another. The object of the present, inven¬ tion is to produce a plate heat exchanger, the plates of which are made of thin sheet metal of 0,75-1,5 mm and can operate at unidirectional pressure of up to 25 bar at a temperature of 150 C. It shall be possible to joint the sheets with a minimum of welding and in such a manner, that repairs can be carried out without having to substantially dismantle the apparatus. A further object is to design the end boxes or end connecting pieces so, that the welded joint withstands without arrangement of extra reinforcements or tie-rods. The resulting plate heat exchanger shall be compact and include straight unobstructed passages, in order to reduce the problem of clogging and to facilitate cleaning. There shall be free flow between adjacent passages so that washing can be carried out even when a single passage has been clogged. It is also endeavored to design the passages.so as to yield a good flow pattern with respect to pressure drop and heat transfer. A further object of the in¬ vention is to achieve a structure, which permits forming of the plates in press tools without risk that indications of fracture may occur. For achieving the aforesaid objects, the invention has been given the characterizing features, which are defined in the attached claims and which substantially imply, that the valleys are formed with grooves, which extend perpendicularly to the longitudinal direction of the valley continuously from one outermost located valley to the other outermost located valley. The arrangement of the transverse grooves implies, in addi¬ tion to the aforesaid advantages and objects, that no spring- back occurs after the pressing of the plates. The pressing, therefore, can be carried out without edge holding, and no trimming of the edges after pressing is required. The opera¬ tions, thus, are fewer, and the material consumption is smal ler. Owing to the arrangement of the grooves, furthermore, t plates are provided with support points, so that between the support points free openings are formed, through which flow between two adjacent passages can take place. A further problem involved with plate heat exchangers of thin sheet metal is to establish the connection between the plates and the distribution connecting piece and collection connecting piece at each end. A special embodiment of the in vention solves this problem so, that good welded joints with out weakening edge displacements are obtained. The plate package can be held together in a way know per se, but a special embodiment thereof is comprised in the inv tion idea. The invention implies improvements from a flow aspect, a in this respect the grooves in the plates have a favourable impact both on the medium flowing within the passages of the plates and on the medium flowing outside and about the plate The intersecting and inclined grooves and ridges yield repea cross-sectional changes. The flow rate for the media thereby is constantly varied, and the grooves and ridges give impuls to directional changes of the flowing media, which contribut to a good heat transfer. As already mentioned, the invention facilitates the clea ing of the passages. At a plate heat exchanger with closed passage sides the exchanger must be opened for a mechanic cl ing of completely clogged passages. The present invention re ders possible a chemical cleaning in situ of the plate heat exchanger without dismantling and disassembling, because the are openings between the passages through which the cleaning agent can flush past the clogged place and thereby dissolve the clogging when the flushing is carried out for a sufficie ly long time. The invention is described in the following with referen to the accompanying drawings. The plate heat exchanger " prope is illustrated by way of one embodiment while five different embodiments of the plates are shown. JK 0 ^ -. W1 Fig. 1 is a perspective view, .partially in section, of a plate heat exchanger without enclosing casing, and of only the upper parts of the plates with associated connecting piece for ' connection to a distribution box or collection box. Fig. 2 is a section on a smaller scale in the longitudinal direction of the plates through the upper part of a plate heat exchanger according to Fig. 1 , Fig. 3 is a section along the line III-III in Fig. 2, F Fiigg.. 4 4 is a section along the line IV-IV in Fig. 2, Fig. 5 shows the cross-sectional shape of a sheet, Fig. 6 is a cross-section through Fig. 5 according to the line VI, Fig . 7 shows two plates, each assembled with the sheets accord- ing to the shape in Fig. 5, Fig . 8 shows two plates 'assembled by the sheet shape accord¬ ing to Fig. 5, but in reversed shape, Fig . 9 is a section along the line 'IX-IX in Fig. 8, Fig. 1 0 shows a different shape of sheets, F Fiigg.. 1 111 shows two plates lying adjacent one another assembled of the sheets according to the shape in Fig. 10, Fig. 12 shows a modification of plates assembled with the sheets according to Fig. 10, Fig. 13 shows a further modified embodiment of a sheet for the plates, and Fig. 14 shows two plates assembled of sheets according to the shape in Fig. -13. The plate heat exchanger according to Fig. 1 comprises six upright plates 1. Each plate is assembled of two sheets 2 and 3, which are placed against each other and welded one to the other along the longitudinal edges 4. Each sheet is formed with a number of valleys 5. At the mounting, the valleys in one- sheet are positioned directly in front of the valleys in the second sheet, so that the valleys connected in pairs form passages. In Fig. 1 four valleys for every sheet 2 and 3 are shown. The sheets are flattened at the ends in the edge areas 6 and 7, respectively, and the edge areas are folded outward along an arc-shaped line such a distance downward on the sheets, that TCTKtATy- the passages are upwardly open in Fig. 1, in spite of the flat¬ tening of the sheets. Owing to the flattening and outward fold¬ ing,* in arc-shape, each plate is provided at the end edge with a semi-arc shaped valley 8 with straight edges 9 and 10. The ends of the valleys 8 have semicircle-shape along the edges 11 and 12. When the plates are assembled to a plate package, the plates are jointed preferably by fusion welding along the edges 9 and 10. The two outermost edges in the plate package - in Fig. 1 the edge 9 - and an edge 13 can be jointed simply by welding with a side, for example 14 or a connecting piece. For connecting the two remaining sides to the connecting piece, the edges of the sides must be formed so, that they agree with the semicircle-shaped edges 11 of' the plates. It appears from Fig. 1 that the sides 15 and 16 have been given wave-shape at the lowe edge 17 and 18, respectively. The edges 11 and 17, thus, agree as to their shape, and welding along these two abutting edges can be carried out. The jointing will be described further in the following with reference to Figs 2 and 4. The valleys 5, as appears from Fig. 1, form unobstructed passages in the longitudinal direction of the sheets, i.e. in parallel with the welded edges of the plates. The passage walls have arc-shape and -are reinforced in the grooves 19 are impres¬ sed therein perpendicularly to the longitudinal extension of the valleys 5. The grooves extend from one longitudinal edge of the sheet transversely across the valleys to the other longi¬ tudinal edge of the sheet, but terminate in a soft flattening to the sheet plane for preventing the sheet from being wave- shaped along this edge. It is to be observed that the grooves are impressed both in the bottom of the valleys and in the top points, and at least to a depth corresponding to the sheet thickness. This implies that the sheets on the inside have ele¬ vated points in the places where ' the grooves intersect the transition from a valley to an adjacent one. These elevations form contact ' points for the sheets lying directly in front of each other. Between the support points, thus, openings are formed which provide flow connection between passages extending in parallel and to the side of each other. UKtA •At the embodiment shown in Fig. 1 a casing enclosing the plate package is omitted. It is understood, that one of the two heat exchanging media flows through the plates, for examp¬ le downward from above according to Fig. 1 and through the passages formed by the valleys 5. The passages have a straight, extension, but it is understood that the cross-section of the passages constantly varies due to the groove arrangement. The flow rate, therefore, changes constantly, and the medium meets projecting edges and protrusions, which also contributes to rate changes and turbulence formations. The heat transfer be¬ tween the inside of the sheet and the medium is hereby improved. The second one of the two media flows between the plates and, for example, from the left to the right according to the direction of arrow 20. The flow of the medium is determined by the casing (not shown), its shape and its outlet and inlet, respectively. As appears from Fig. 1, the outer surfaces of the plates also are irregular, which favours the heat exchange with the plate surface advantageously. As an example thereof can be mentioned that when a condensation film would develop on the outer surfaces of the plates, the liquid film will follow the inclined grooves and then be released from the plate side in droplets. This implies that a plate surface never completely can be covered by a condensate film. The formation of a 'conden¬ sate film deteriorates the heat transfer between the flowing medium and the plate sheets. It may further be pointed out that the sheets can be manu¬ factured by pressing, even in only one operational step. The valleys can be given different cross-sectional shapes, as.appears from Figs 5-14, as will be described in the following. The grooves are impressed with a certain inclination relative to the longitudinal axis of the valleys. Grooves extending fully perpendicularly to the longitudinal axis yield a poorer effect than grooves having a certain angle of inclination relative to said axes. Although the grooves are impressed into the sheets, it was found that a very thin material can be used without risk of fracture indications. The grooves reinforce the sheets or increase their capacity of receiving- unidirectional pressure * loads. The grooves, thus, are of importance with respect to the manufacture of the plates proper as well as to the strength of the plates and, in addition, the grooves have a favourable effect on the flow pattern for the media. Fig. 2 is partially a section along the line II-II and on a smaller scale of Fig. 1. The numeral 21 designates a passag in a plate. The cross-section, it is understood, comprises fi passages 21 instead of the four passages shown in Fig. 1. The numeral 22 designates the supporting points, which were menti ed earlier, and which are located between each sheet in the plates. The connecting piece or distribution box has the side walls 15 and 16 as in Fig. 1. Said walls, as can be seen, hav a greater material thickness than the sheets. Longitudinal joint edges between the sheets in the plates are designated b 23. In the same way as described with reference to Fig. 1, th lower edge 17 of the side 15 has wave-shape for connection to the wave-shaped edges 11 of the plates. This is apparent also from Fig. 4, which is a section along the line IV-IV in Fig. In order to facilitate the welding between the edge 17 and th edge 11, an annular area 24 is milled out in the side 15 near the edge 17 whereby a laterally projecting flange edge 25 is formed, see the left-hand portion of Fig. 2 and the left-hand portion of Fig. 4. The reference numerals refer to these part of the figures only for reason of better clearance. Said flan edge 25, which has the same wave-shape as the edge 17, and th as the edge 11,* provides a good fusion welding possibility be tween the two wave-shaped edges of the sides 15 and the plate In this connection may be mentioned, that the edges 11 and 17 have been given wave-shape, but that, of course, also another shape, for example a rectilinear one, can be used. The edge line 17 in such a case will be given a tooth-shaped appearanc and the edge line 11 a corresponding tooth-shaped one. To the sides 15 and 16 and opposed sides then a pipe connecting piec a distribution box or the like can be connected. Fig. 3 is a section along the line III-III in Fig. 2 and shows that support sheets 26 are inserted in parallel with th sides 15 and 16 within the connecting piece, in order to with stand high pressure. From Fig. 3 appears the shape of these support sheets which agrees with what has been described above concerning the attaching or jointing between the edges 17 and 11. In the above descriptive part the reference numerals 15 and 16 have designated sides in a connecting piece. The sides 15 and 16 may also be regarded as strips, and the same applies to the sides opposed thereto, and assembled and mounted they may be regarded constituting a transmission piece from the plate package to a distribution box. It is known from experience that just this area is one of the most difficult ones from a welding point of view and that it also is the area exposed to the most substantial stresses purely mechanically. From Figs 2-4 also a suitable structure of the casing en¬ closing the plate package is apparent. The casing, as can be ' seen, can be assembled of a first plane metal sheet 27 and a second plane metal sheet 28, between which a corrugated metal sheet 29 is located. Said corrugated sheet 29 preferably is designed so that wave crests and wave troughs are formed right- angled, as also is apparent from the figures. The three sheets may be spot-welded in such a manner, that some kind of honeycomb structure is obtained. In this way four sides of a casing* are formed, and the jointing of the casing can be carried out in any suitable way. The casing is held together against inside pressure either only by its own rigidity, or frame structures of beam material may enclose the casing, which also can be effected in a manner known per s ' e. A suitable structure in this respect is to be chosen in view of the inside pressure the casing is intended to withstand. In Figs 5-14 different shapes of sheets and of plates assembled thereof are shown. Fig. 5 shows the cross-sectional shape of a sheet disclosing the valleys 5. It is to be observed that the grooves do not appear here. From Fig. 5 is apparent that the cross-section of the valleys in principle have been given the shape of half a pear. In Fig. 6 a cross-section along the line VI in Fig. 5 is seen, and from this section both the valley 5 in its longitudinal extension and the grooves 19 are apparent. Fig. 7 shows two plates assembled of the sheets having valleys of the shape shown in Fig. 5. It is to be observed that the sheets 2 and 3 here are turned so that the passage shape is asymmetric. It appears from Fig. 7, that the plate shape a such two adjacent plates falls one into the other, and that a meandering path between two adjacent plates in the direction arrow 20 is obtained. See also Fig. 1. Fig. 8 shows two plates assembled of sheets having. the shape as shown in Fig. 5, where the sheets 2 and 3, however, have been turned so that a cross-sectional shape resembling a entire pear is obtained. Also in this case a meandering path . between two adjacent plates in the direction of arrow 20 is obtained. Fig. 9 is a cross-section according to line IV-IV i Fig. 8 from which the grooves 19 and the passages 5 are appa¬ rent. Fig. 10 shows another cross-sectional shape of a sheet. Fig. -11 shows two plates one adjacent the other and assembled of two sheets according to Fig. 10. Fig. 12 show ' s an alternat assemblage of the sheet shape shown in Fig. 10 and two plates adjacent each other. Fig. 13 shows still another embodiment of a sheet, and Fig. 14 shows two plates adjacent each other and assembled of two sheets having the shape as shown in Fig. 13. Although according to the aforesaid the valleys at a part cularly suitable embodiment have been given asymmetric cross- sectional shape relative to their symmetry line, it is to be understood that the cross-sectional shape can be entirely sym metric and, for example, have the shape of a portion of an .ar The cross-sectional shape of the grooves 19 appears, for exam le, from Figs 6 and 9, but this shape can be. varied within th scope of the invention idea and may be more or less meanderin at the bottom or pointed. The inclination angle to the longit dinal extension of the valleys can be varied within the scope of the invention idea and can be said to be, for example, be¬ tween 15° and 45°.

Claims: C L A I M S 1. A plate heat exchanger comprising a plurality of plates arranged to the side of each other, each plate consisting of two sheets facing toward each other and formed with longitudi¬ nal valleys, which facing toward each other form passages be¬ tween the sheets when the sheets abut each other, c h a r ¬ a c t e r i z e d i n that the valleys are formed with im¬ pressed grooves extending transversely to the longitudinal direction of the valley and continuously from one outermost located valley to the other outermost located valley. 2. A plate heat exchanger as defined in claim.1, c h a r ¬ a c t e r i z e d i n that the grooves extend at a certain acute angle to the longitudinal direction of the valleys. 3. A plate heat exchanger as defined in claim 1, c a r ¬ a c t e r i z e d i n that the impression depth of the grooves corresponds at least to the thickness of the sheets. 4. A plate heat exchanger as defined in claim 1, c h a r ¬ a c t e r i z e d i n that the grooves at the intersections with the defining lines between the valleys form a number of equally high located points, which form.support surfaces for sheets laid against each other. 5. A plate heat exchanger as defined in claim 1, c h a r ¬ a c t e r i z e d i n that the cross-sectional shape of the valleys is asymmetric relative to the central line of the valley. 6. A plate heat exchanger as defined in claim 5, c h a r ¬ a c t e r i z e d i n that the cross-sectional shape corre¬ sponds to the shape of half a pear. 7. A plate heat exchanger as defined in claim 1, c h a r ¬ a c t e r i z e d i n that the ends of the sheets where the valleys terminate are flattened and folded outward to the side where the valleys bulge, and such a distance that it corresponds at least to the height of the bulging, whereby the free edge can be placed against a likewise free edge of an adjacent sheet and welded together along the edges. 8. A plate heat exchanger as defined in claim 7, c h a r ¬ a c t e r i z e d i n that the outward folding has arc- shape, so that the longitudinal edges of two sheets forming a plate terminate at the passage ends of the plate in a semicircle shaped edge. 9. A plate heat exchanger as defined in claim 8, c h a r ¬ a c t e r i z e d i n that the semicircle-shaped edges form joint edges for the walls of a distribution connecting piece to the plates. 10. A plate heat exchanger as defined in claims 8 and 9, c h a r a c t e r i z e d i n that strips welded on the plates constitute a transition to the walls of the distribution connecting piece, which strips have a greater thickness than the plate walls. 11. A plate heat exchanger as defined in claim 10, c h a r a c t e r i z e d i n that the strips have recesses, the contour of which corresponds to the attaching edges of the strips and are located adjacent the same, so that a flange projecting from the plane of the strips is formed for welding together with said plate edges. 12. A plate heat exchanger as defined in claim 1, c h a r ¬ a c t e r i z e d i n that the casing about the plates con¬ sists of two spaced metal sheet layers, between which a corru¬ gated metal sheet is laid which preferably has wave crests and troughs of rectangular cross-section.

Inventors: BENGTSSON F
Applicants: BENGTSSON F, LOCKMANS ING BYRA AB, LOCKMANS INGENJOERSBYRA AB C J
Application year: 1979
Main classification: F28F3
IPC codes: F28D1, F28D9, F28F3, F28F9