GB2215451A - A cross-flow plate heat exchanger - Google Patents

Abstract

A cross-flow plate heat exchanger has a core K which is received in a casing G and which, to form crossing flow channels for the two heat-exchanging media, is embodied by discrete contiguous rectangular plates interconnected by first weld seams 9 to form plate pairs having flow channels for the heat-yielding medium, and contiguous plate pairs form, by the joining together of adjacent plates of two plate pairs by way of second weld seams, flow channels for the other heat-receiving medium, and the heat exchanger core thus formed is connected at its four connection edges, by way of third weld seams 14 extending perpendicularly to the said first and second weld seams and operative as build-up weld seams, to the casing G, semicircular expansion members D which have connecting bends disposed on both their long sides being provided between the build-up weld seams 14 and the heat exchanger casing or components rigidly secured thereto, the connecting bends being operative for resilient suspension of the exchanger core K in the casing G. <IMAGE>

Description

A CROSS-FLOW PLATE HEAT EXCHANGER The invention relates to a cross-flow plate heat exchanger according to the preamble of claim 1.

The function of heat exchangers is to transfer heat from a relatively hot medium to a relatively cool medium, often with the presence of substantial pressure differences between the two media. To achieve high heat exchange efficiencies, the heat exchanger core is required to be very dense - i.e., it is required to have a large heat-exchange area per unit of volume and a high heat transfer coefficient a; these requirements can be met, for example, by cores which are made of thin-walled shaped or profiled plates1 such cores also ensuring a relatively reduced structural weight and, if their flow channels are streamlined, providing high aerodynamic efficiency - i.e., an optimal relationship between the heat exchange performance achieved and unavoidable flow losses.

However, the performance advantages of cores made of welded-up thin-walled shaped plates are offset by strength problems since due to the mechanical construction multi-axis stress states arise because of the self-weight of the core, welding stresses, stresses due to pressure differences and temperature-differenceinduced expansion differences between the core and the casing parts, more particularly the side plates which, more particularly at high pressures, are relatively thick-walled. In particular, the considerable temperature and pressure differences between the two heat-exchanging media therefore lead to considerable heat expansions which manifest in the form of high local stresses preferably in the transition zones to the weld seams.Cores of this kind are of course devised from discrete plates welded together to form pairs of plates which are then welded together to form a stack by further weld seams at right-angles to the first weld seams. The edges of such a stack are then provided with corner weld seams to provide the necessary mechanical rigidity and means of connection for the casing. Also, vibrations of the material occur which are caused by pressure variations of the media, the vibrations being propagated in all directions and building up by reflections to produce high local stress peaks.These heat and mechanical loads must be received by the overall strength of the heat exchanger and lead in extreme cases to stress and vibration fractures, more particularly in the transition zones between the inherently resilient plates1 which are relatively thin to ensure a high heat transfer coefficient, and the relatively rigid and brittle weld seams and above all in the connection zones between the resilient core and the relatively torsionally resistant heat exchanger casing. A further complication is that the outer plates of the core, due to external cooling, experience temperature variations different from those experienced by the plates disposed further inwards.

A heat exchanger of this kind has been disclosed, for example, bv DE-PS 1 601 215 wherein the core combined from thin-walled plates is rigidly welded by way of non-resilient retaining means to the exchanger casing. Because of this rigid connection and of the high thermal and mechanical loads which occur in operation, the discrete plates tear off after a short period of operation and seam breaks occur. Consequently, the only plate heat exchangers introduced so far have cores made of shaped thin-walled plates; cf. e.g. GB-PS 1 357 282. These plates are stacked on stable webs and held together by two flexurally resistant end plates by way of clamping bolts, the discrete plates bearing on one another by way of their shaped parts to form flow channels.Also, resilient seals are introduced between the discrete plates to provide sealing tightness and to determine their separation from one another. Consequently, the stress states and vibrations previously referred to cannot occur in this case because of the "loose" construction.

It is the object of the invention to obviate the disadvantages described of all-welded plate heat exchangers by a novel form of suspension for the core in the exchanger casing, such suspension being adapted so to receive substantial expansion forces arising in operation because of the thermal loading and of mechanical stresses that the heat exchanger core remains free from stress cracks and seam breaks for prolonged periods of operation.

The invention solves this problem by the features of claim 1.

Other features of the invention are disclosed by the subclaims.

The core suspension according to the invention can resiliently intercept the locally different expansions caused by operating loads so that stress peaks initiated by local temperature differences in the core are reduced or precluded from the start.

Also, the collars according to the invention attenuate harmful vibrations and cause them to decay rapidly. The discrete exchanger plates, more particularly at the weld seams, therefore remain free from local cracking.

The longitudinal load-relieving grooves in the apex zone of the collars and in the connecting bends help to increase the resilience of the collars and their connecting bends on either side. The presence of such grooves makes it possible to optimize the resilience both of the collars and of the connecting bends by appropriate dimensioning of groove depth and, if necessary, by local variation.

An embodiment of the invention is shown fairly diagrammatically in the drawings wherein: Fig. 1 is a view of a heat exchanger in longitudinal section with its core shown in elevation; Fig. 2 is a perspective view showing part of the exchanger near an expanding collar, the front side wall having been omitted; Fig. 3 is a view also in perspective of a part of the exchanger core, and Fig. 4 is a partial view in elevation looking in the direction of an arrow M2 in Fig. 2.

As can be gathered from Fig. 1, a heat exchanger casing G is subdivided into two zones in the direction of flow, namely first a hood zone having a gap-side feed hood Ol for a first gaseous heat-exchanger medium, namely the heat-yielding medium M1, and a gap-side discharge hood G2 for collecting the medium M1 after the same has passed through the core K, and second a box-like zone having a tube-like inflow part 03.f or the second heat-exchanging medium, namely a heat-receiving medium M2, a discharge part G4 for the now heated medium M2 and a central casing part G5 which has casing walls 18 and a number of deflecting walls 6.

As can be seen in greater detail in Fig. 3, a heat exchanger core comprises a number of discrete thin-walled honeycomb-shaped plate elements or plates K1, K2, K3, K4, K5 etc.; in all cases two individual plates K2, K3 or K4 and K5, placed on one another in laterally inverted form are joined together on their opposite edge zones 7, 8 by first weld seams 9, which are roll seams, to form plate pairs P1 to Pn, the discrete plates each forming by way of their corresponding shapings a flow gap S for a heatyielding medium M1. Each plate pair P2, P3 is rigidly connected to the adjacent plate pair P4, P5 by opposite second seams 10, which are transverse seams and extend on the plate pair edges and perpendicularly to the first seams 9 - i.e., roll seams i.e., the seams 10 rigidly interconnect the adjacent plates K1, K2 and K3, K4 of any one pair by way of their opposite edge zones 11, 12; the plates K1 K2 and K3, K4 which are near one another bound by their corresponding shapings flow tubes 13 for a heatreceiving medium M2.

There therefore arises a plate group of a predetermined height in accordance with the required heat exchanger performance and the group is consolidated in the direction of stack height - i.e., perpendicularly to both the roll seams and transverse seams - by four corner build-up seams 14 at the corners of the group. The seams 14 are also effective to connect the exchanger core to the exchanger casing.

The core K is suspended in the casing G hereinbefore described by way of four metal components which, to provide a resilient mounting of the core K, are formed with semicircular or guttershaped expansion collars D each associated with a connecting bend BK on the core side and with a connecting bend BO on the casing side. The core-side bends BK are rigidly connected to the core K by way of an installation seam 14 perpendicular to the seams 9 and 10. The caslng-side bends BO are each rigidly connected to the feed hood G1 and discharge hood G2 by way of a weld seam 15 parallel to the seam 14 (see more particularly Figs. 2 and 4, each of which shows just one side wall 18).

By way of a weld seam 17 - the final transverse seam (see Fig. 4) - the collars D are sealingly and rigidly connected at their ends 16 by way of their bends BK, BG to casing side walls 18. The build-up seams 14 into which the seams 17 merge, the collars D and their connecting bends BK, BG hermetically separate the two media M1, M2 - i.e., the flow channels thereof - by subdivision into two pressure chambers, only one end being shown in each case. There is therefore no risk of the seams 17 rupturing since the temperature conditions in the outer zones of the heat exchanger both for the core K and also for the casing components are very similar because of the substantial heat capacity of the relatively thick side walls 18.The temperature differences here which occur in operation are not large enough for the seams 17 to be jeopardized by possible expansions. On the other hand, heat expansions in the central zone, more particularly where the heat-yielding medium M1 enters, are at a maximum and are taken up resiliently by way of the length of the collars D and of the bends BK, BG.

Both the crest zone of the collars D and the bends BK, BG are formed with load-relieving grooves 19 which indrease the resilience of the collar D and bends BK, BG. - The grooves 19, although not strictly necessary, give the designer an opportunity not only of providing an overall increase in the resilience of the collars D and bends BK, BG but also to vary resilience over their length, for example, more particularly by different depths or by the physical pattern of the grooves 19.

Consequently, each collar D forms an expansion element which is clamped on both sides and whose greatest expansion occurs in the centre in the zone enclosed by the side walls.

Claims (7)

CL Al MS

1. A cross-flow plate heat exchanger having a core which is received in a casing and which, to form crossing flow channels for the two heat-exchanging media, is embodied by discrete cdntiguous rectangular profiled plates interconnected by way of their opposite edge zones by first weld seams to form plate pairs having more particularly gap-like wavy flow channels for the first medium, and contiguous plate pairs form from pair to pair, by the joining together of adjacent plates by way of their other opposite edge zones by second weld seams, tubular flow channels for the second medium; and the heat exchanger core thus formed is connected in pressure-tight manner at its four outside edges, by way of third weld seams extending perpendicularly to the said first and second weld seams and operative as build-up weld seams, to the heat exchanger casing or components rigidly secured thereto, characteri6ed in that the heat exchanger core (K) is connected in pressure-tight manner to the casing (G) at least to some extent by way of resilient metal components (D).

2. A heat exchanger according to Claim 1, characterized in that the components (D) are disposed between the build-up seams (14) and the casing (G) or components rigidly secured thereto, and are in the form of expansion collars (D), the collars having on both their long sides connecting bends (BK, BG) disposed towards the components (G1, G2 respectively) secured to the casing, the end faces (16) of the bends being welded in pressure-tight manner to the casing side walls (18) and being resilient within a central zone included by the core edge zones.

3. A heat exchanger according to Claim 2, wherein the components (D) are disposed between a feed hood (G1) supplying the heat-yielding medium M1) to the exchanger core (K) and a discharge hood (G2) collecting the latter medium.

4. A heat exchanger according to Claim 2 or Claim 3 wherein said expansion collars (D) are of semicircular cross-section.

5. A heat exchanger according to .any one of Claims 2 - 4, characterized in that grooves (19) for relieving stress peaks extend lengthwise both in the crest of the collars (D) and also in both the connection bends (BK,BG).

6. A heat exchanger according to Claim 5, characterized in that the extent of resilience of both the collars (D) and the bends (BK,BG) on both sides thereof can be deteremined by different depths of the stress-relieving grooves (19) and by local variation of the depth dimensions thereof or by their physical pattern.

7. A heat exchanger substantially as hereinbefore described with reference to, and as illustrated in, the accompanying drawings.