US2064931A - Heat transfer - Google Patents

Description

A. LYSHOLM Dec; 22, 1936.

HEAT TRANSFER Filed Oct. 21, 1952 Patented Dec. 22, 1936 PATENT OFFICE HEAT TRANSFER Alf Lysholm, Stockholm, Sweden, assignor to Aktiebolaget Ljungstroms Angturbin, Stockholm, Sweden, a joint-stock company of Sweden ApplicationOctober 21, 1932, Serial No. 638,979

In Great Britain '7 Claims The presentinvention relates to heat transfer and has particular reference to heat transfer between two fluids. Still more particularly the I invention relates to heat transfer between two gaseous fluids such as air and combustion gases,

as effected for example in air prehaaters for power plants.

A primary object of the invention is to provide novel method and apparatus whereby heat lo transfer between fluids may be effected efflciently with respect'to rate of heat transfer while at the same time without producing high resistance to flow of the fluids, and consequent high pressure drop, because of highly turbulent flow.

- Other and more detailed objects of the invention and the manner in which the advantages to be derived from the invention may be realized will appear more fully in connection with the ensuing description forming a part of this specification.

In accordance with the present invention, I effect heat exchange between streams of fluid at diflerent temperature by causing such fluids to pass each other in separate channels, separated from each other by solid elements of platelike form, usually of metal, and constituting heat exchange elements through which heat is transferred from one stream of higher temperature to. an adjacent'stream of lower tempera.- 30 tureby conduction through the structure forming the walls separating the two adjacent passages.

This method of transfer is broadly old and heretofore heat transfer of this kind has been 35 eifected with numerous different forms and arrangements of construction of separating walls,

hereinafter referred to as plate structure. In fplate' structure of this kind two major rconsiderations must be taken into account. On 40 the one hand a hign rate of heat transfer per unit of plate area is desired. On the other hand resistance to flow of the fluids is desired. In some structures heretofore proposed,

high rates of heat transfer have been obtained by producing highly turbulent flow of the fluids but 'such highly turbulent flow necessarily results in high resistance to flow. In other structures where it has been attempted to avoid high resistance to .flow by employment of smooth plate structure this object has been obtained but only at the sacrifice of efficiency of heat transfer, because of the tendency of the gases of the fluids laning" in the passages so that heat to be transferred from the portions of the 55 gases in the central parts of the passages must December 21, 1931 be transmittedthrough substantial portions of the fluid itself before reaching the heat transfer provement in heat transfer efliciency as compared with smooth plate heat transfer structure, can be obtained without materially increasing the resistance to flow as compared with that resulting with smooth plate structure, by employing spaced heat transfer plates which provide relatively wide and shallow paths of substantially constant cross-sectional area from the inlet to the outlet ends of the passages for free and unobstructed flow of fluidin the direction of the length of the passages, such plates being obliquely corrugated with the plates forming the opposite side walls of each passage being corrugated in obliquely opposed relation.

Preferably the corrugations are relatively narrow and shallow as compared with the width of the passages and the; spacing of the plates is such that the majorportion of the fluid in each passage is free to flow in the unobstructed space between the plates while a minor portion there of is caused to flow obliquely in the iiblique channels provided by the corrugations. Also the corrugations preferably are arranged at an angle of 45 with respect to the length of the passages, this construction being particularly advantageous for certain forms of heat transfer structure as will hereinafter be pointed out.

In order to more fully illustrate the nature and application of the invention I have shown in the accompanying drawing a preferred form of structure embodying the invention, but it is to be understood that the invention is not limited in its application to the specific structure shown but may be applied to other specific forms.

In the accompanying drawing forming a part of this specification Fig. 1 is a broken transverse section through heat transfer a paratus embodying the 'invention, the section being takeri on line l--I of Fig. 2;

Fig. ,2 is a section taken on the line 2-2 of Fig. 1; and

Fig. 3 is a section taken on the line 3-3 of Fig. 1.

Referring now to the drawing, there is shown therein a recuperative cross-flow heat exchange apparatus adapted to be used as an air preheater. The heat-transferring elements consist of thin plates I which are corrugated at an angle of 45 with relation to the direction of the main flow Y structure in the passages and in the direction inof the gas and air as indicated by the diagonal solid lines 30 and the diagonal dotted lines 3| which show respectively the corrugations of adjacent plates I. At the upper and lower edges, 6 adjacent plates are bent against each other and welded together as indicated in Fig. 2. At the air inlet 32- and the air outlet 33 the plates are clamped between suitable holding members (not illustrated) by means of rivets 9 or the like to formpacks of convenient size. Angle irons l and I0 are advantageously fastened to the sides by welding to form' guides and supports for the element packs. The several 'packs the number of which will be dependent upon" the size of the preheater, are bolted together in any suitable manner so that the assembly of packs forms a battery extending over the entire width of the air preheater. At one side the sliding rail formed by one of the angle irons I0 is supported on angle iron l3 fixed in the outer casing ll, of the preheater, the angle iron l0 being supported by angle iron l3 which has a recess l acting as a guide. ,Thus expansion of the packs is afforded by sliding action.

The hot gases pass through the heat transfer dicated by the arrows I1 and the air to be preheated passes through the structure in the channels and in the direction. of the arrows l8 (see Figs. 2 and 3). The end walls of the channels for the hot gases are formed by rectangular metal pieces I 9' which are disposed between the plates as shown in Fig. 3 and annular spacing members 20 are positioned between each pair of plates forming an air channel. r

As will be observed from the arrows: in Figs. 2 and 3, the flow of air to be preheated is at right angles to the flow of the hot gases in the intervening channels and by corrugating the plates obliquely with the corrugations extending at 45 it is possible to secure passages of like nature for both air and gas by utilizing but one form of corrue'ated plate. This contributes materially to the economical construction of the apparatus.

From the drawing it will be evident that in each of the flow passages, such for example as the passages l1, shown in Fig. 2, there is provided a relatively wide and shallow path for free unobstructed flow of the gaseous fluid, which results in very little resistance to flow. At the same time the oblique channels at the side of the passage, formed by the corrugatons in the plates, cause lateral flow in opposed oblique directions at the sides of the channels as will be evident from a consideration of the arrangement of the corrugations as shown in Fig. 1, This lateral flow which is of relatively gentle nature sets up a secondary lateral flow of the fluid in the central and wholly unobstructed portion of the passage,

the plate structure itself any substantial obstruc tion to free flow.

Also it is to be noted that the arrangement does not involve sudden contraction or enlargement'of due to molecular friction between the fluid which the total cross-sectional area of thepassages in the direction of flow of the fluids, thus avoiding sudden pressure variations of the fluids within the passages which pressure variations are undesirable because of the increasein' flow resistance occasioned thereby.

While for purposes of illustration I have 'described the invention. and its application to a stationary recuperative heat exchanger, it is to be understood that heat exchange plate structure embodying the invention may readily be incorporated in other forms of heat exchanges of recuperative or regenerative type, and that changes and modifications in the specific structure illus-.

the length of the passages, the spaced portions of said plates being formed with corrugations disposed to provide a series of channels for uninterrupted flow of fluid obliquely with respect to the direction of length of the passages and the corru-' gations of adjacent plates being disposed in oppositely oblique directions, whereby to cause oblique flow in opposite directions of the portions of the fluid flowing adjacent to the side walls of the passage and to thereby cause the portion of the fluid in such passage having unobstructedflow in the direction of length of the passage to move sideways in one direction adjacent to one side wall thereof and to move sideways in the opposite direction adjacent to the opposite side wall thereof due to molecular friction with the obliquely flowing fluid. I

2. In heat transfer apparatus, a heat transfer plate structure comprising. plates having portions spaced to form side walls separating adjacent passages between the plates for flow of fluid in heat exchange relation in adjacent passages, the cross sections of said pas sages having a width many times the height thereof, said passages providing relatively wide and shallow paths for free and unobstructed flow of fluid in the'direction of the length of the passages, the spaced portion of said plates being formed with'corrugations disposed to provide a series of channels for uninterrupted flow of fluid obliquely with respect to the direction of length of the passages and the corrugations of adjacent plates being disposed in oppositely oblique directions, whereby to cause oblique, flow in opposite directions of the passage to move sideways in one direction adjacent to one side wall thereof and to move sideways in the opposite direction adjacent to the opposite side wall thereof due to molecular friction with the obliquely flowing fluid, the cross sectional area of the passages providing paths for free and unobstructed flow of the fluid constituting the major portion of the total cross sectional area for flow of fluid through the apparatus.

aoeegesi providing relatively wide and shallow paths of substantially constant cross sectional area from the inlet to the outlet ends of the passages for free and unobstructed flow of fluid in the direction of the length-of the passages, the spaced portions of said plates being formed with corrugations disposed to provide a series of channels for uninterrupted flow of fluid obliquely with 're-' spect to the direction of the length of the pasf sages and the corrugations of adjacent plates beingdisposed in oppositely oblique directions; whereby to cause oblique flow of the portions of the fluid flowing in the passages adjacent to the side walls thereof and to thereby cause the pertions of the fluid having unobstructed flow in the direction of the length of the passages to move sideways in one direction adjacent to one .side wall and to move sideways in the opposite direction adjacent to the opposite side wall of each passage due' to molecular friction with the obliquely flowing fluid while maintaining sub transfer between diiferent bodies of gaseous fluid flowing through adjacent passages and the walls of the passages through which the fluid flows, without substantially increasing the resistance to flow of the fluid as compared withv straight flow of fluid through-the passages, whichconsists of flowing in each passage a portion of the fluid through the passage in a free unobstructed path of flow and flowing obliquely with respect to the length of the passage, and oppositely with respect to each other, portions of the fluid at either side of the first mentioned portion and between the first mentioned portion and the respective side walls of the passage, whereby to produce lateral movement in opposite direction of the parts of the first mentioned portion of the fluid at the opposite sides of such portion due of the fluid in a free unobstructed path of flow and flowing obliquely with respect to the length of the passage, and oppositely with respect to each other, portions of the fluid aggregating a minorportion of the total amount of' fluid at either side of said major portion and between said major portion and the respective side walls of the passage, whereby to produce lateral movement in opposite direction of the parts of said major portion at the opposite sides thereof due to molecular friction between said major portion and the obliquely flowing minor portion.

6. In heat transfer apparatus, plate structure providing a plurality of side by side passages for flow of fluid in heat exchange relation between adjacent passages, said plate structure comprising a plurality of plates having portions spaced to provide the side walls of said passages, said plates having relatively narrow and shallow uniform corrugations, the corrugations of alternate plates being disposed obliquely in one direction with respect to the length of the passages and the corrugations of the remaining plates being disposed obliquely in opposite direction with respect to the length of the passages, and said plates being spaced so that the tops of the corrugations of the adjacent plates are appreciably removed from each other, whereby to provide passages forfree and unobstructed flow of fluid between adjacent plates.

'7. In recuperative heat transfer apparatus, a heat transfer plate structure comprising a plurality of spaced plates providing passages for flow of fluid between adjacent plates, means for supplying a first fluid to and withdrawing said first sists in flowing in each passage a major portion at right angles to the flow of fluid in the other series of passages, said plates being provided with shallow uniform corrugations of relatively small width as compared to the width of the passages and being spaced from each other to provide a relatively wide and shallowpath for free unobstructed flow of fluid through each of the passages, the corrugations of adjacent plates being disposed at substantially with respect to each other and the corrugations being disposed at substantially 45 with respect to the general directions of fluid flow through said passages.

ALF LYSH OLM,

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