US3196942A - Heat exchanger construction including tubular closure plates - Google Patents

Description

July 27, 1955 K. R. PREN-rlss 3,196,942

HEAT EXCHNGER CONSTRUCTION INCLUDING TUBULAR CLOSURE PLATES Filed July 5, 1963 lNvENToR KENNETH R- PREN-r l ss BYK'L RNEY United States Patent O 3,196,942 HEAT EXCl-KANGER CUNSTRUCTHQN )INCLUD- lNG 'EUBULAR QLSUR PLATES Kenneth Prentiss, `ifi/est Hartford, Conn., assigner to United Aircraft Corporation, East Hartford, Conn., a

corporation of Delaware liied .indy 5, i963, Ser. No. 292,892 l Claim. (Ci. 16S- 166) This invention relates `to heat exchangers and particularly to the construction of the core thereof.

Compact heat exchangers for high temperature service usually require the use of brazed stainless steel plate and tin type of heat exchanger cores. Normally, a high temperature iuid flowing through one set of heat exchanger passages is cooled by a low temperature huid flowing through adjacent alternate passages. Two sides of each passage are formed by rectangular bars or tubes brazed between the plates which form the remaining two sides of the passage. Extended heat transfer surface (tins) brazed to the plates are used to transfer heat to or from the plates from or to the fluid flowing within the passage. Usually the heat exchanger iiuids are in cross, countertlow arrangement with each other in order to provide near optimum thermal effectiveness. Fluid headers are attached to the heat exchanger core through core bands or extensions which are brazed or welded to the sides of the core.

The tiuid iiow arrangement and type of heat exchanger construction causes severe metal temperature differentials at the core fluid entrance and/ or exit areas with resultant thermal stresses. During heat exchanger start-up, shutdown or change in operating conditions, the thermal gradients and resultant stresses become more severe, particularly in stainless steel heat exchangers because of the low metal thermal conductivity. I have found that when the core is constructed in accordance with this invention the thermal stresses Within the plate and iin core will be reduced, the thermal stresses between the core and attached headers will be reduced, and a core structure which will readily accommodate a leak tight core-to-header weldment without the use of intermediate core bands or extensions will be realized.

In accordance with this invention the core of the heat exchanger is constructed to contain a plurality of rectangular tubes forming side walls. These tubes are hollow for defining liuid iiow passages and are notched a short distance from the tube end and bent to form a ninety degree mitre elbow at each end of the tube. The core is assembled by alternately stacking cold and hot fluid passages in such a manner that the mitred corners form a solid wall for attachment of fluid headers on each side of the corner. This construction provides a suitable surface for welding the fluid inlet and exit headers to the core. The flow of fluid through the rectangular channel will establish heat transfer between the tube and the iiuid, thus providing a mean metal ternperature which approaches that of the plate and tins adjacent to the tube. As is generally well understood in the art the rate of fluid flow through the core of the heat exchanger is determined by the pressure diiferential between the inlet and outlet of said core. It is also Well lrnown convective conductance is the function of the rate of iiuid flow. Since uid flow is a function of the cross sectional area of the tubes, the desired convective conductance in the tubes may be regulated by proper selection of the hydraulic radius of the tubes. Another method of obtaining desired heat transfer convective conductance in the tubes is by adding turbulence promoters to the tubes. With proper design, the thermal gradient from the uid headers into the core struc- CII ICC

ture can be minimized for the most severe temperature differential or time-temperature situation encountered.

lt is therefore an object of this invention to provide a plurality of stacked elongated hollow tubes, each of which are bent and rectangular in cross section, for defining leak tight cornered walls of a heat exchanger core for readily supporting headering.

It is a further object of this invention to provide a plurality of stacked hollow tube members arranged in indirect heat exchange relation wherein the hollow tubes form supporting surfaces for receiving headering and being arranged to provide fluid tlow passages arranged to assure a less severe step change in temperature that was heretofore realized in conventional plate and fin heat exchanger cores.

Other features and advantages will be apparent from the specification and claim and from the accompanying drawings which illustrate an embodiment of the invention.

FIG. l is an isometric showing of a heat exchanger.

FIG. 2 is an enlarged fragmentary sectional view showing the core of the heat exchanger.

FlG. 3 is an enlarged fragmentary cross-sectional view taken through the high temperature iiuid inlet section of FG. l; and

FIG. 4 is an enlarged fragmentary cross-sectional View 'taken through the low temperature uid exit section of FIG. l.

Referring now to FlG. l which generally shows a heat exchanger indicated by numeral 1t) having a core 12, low temperature iiuid inlet header 14 and low temperature tiuid exit header lo, high temperature inlet duid header l, high temperature fluid exit header 2@ and turning headers 22 and 24. Suitable piping are connected to each or" the headers for conducting iiuid into core l2 and discharging iiuid therefrom. In essence, this is a cross ow heat exchanger which passes ow through a series of passes formed by the core so that hot air passages alternate with cold air passages for obtaining indirect heat transfer.

Referring now to FIG. 2 which is a lshowing of the core 1Q; which comprises top plate 30 and bottom plate 32 and a series of stacked layers of ycorrugated tins `stacked therebetween defining Ithe flow passages for the h'ot and low temperature uid. As noted from this drawing, corrugated fin 34 extends through the core 12 and is ysandwiched between to-p plate 30 and intermediate plate 35 defining :therewith open ended channels. At the end of the itin is closure plate 39 which is a rectangular tubular member `extending the length of the core. It is to be understood that a similar clos-ure member is -on the opposite end of the core and .as will be appreciated from the description to follow, these closure members dene the side and end walls of t-he core. The next layer is composed of rutiied `tin which extends through the lcore transversely to the yadjacent layer of the corrugated tins. As noted, this ruffled fin 4t) -is sandwiched between the intermediate plates 36 and 13d and together therewith define an open ended channel for vaccommodating the passage yof hot air. The core is built up by alternatin g these llayers yas described. 1t will `be noted that such la construction is customary in the heat exchange tart and the details `are eliminated here for facilitating the description of this invention. Preferably the material selected for this `construction is stainless steel, but it is to be runderstood that `any other material may be employed without deviating from the `scope of this invention.

lAs noted Ifrom LFIG. 2, the rutiied tins are closed off by a series lof closure plates 39, 411, 42 and 44,. This invention is concerned with lthese closure plates as they form the essence of the construction of this type of core.

snoepen As noted from FIGS. 3 and 4, these closure 'plates areformed from elongated tubular members rectangular in cross section. 'l'lhe rectangular members may be assembled in the core prior to being bent `and when inserted in their proper position, they are bent substantially 90 forming the corners of the core. As is noted, ya V-slot is eut into this tubular member in any known manner eo that the end is Ireadily and easily bent as 4is shown in lFIGS. 2, l3 and 4. Also noted from these tigures, the tubes yare stacked adjacent to each other so that the overlay of the `bent portion which extends only a relatively short distance adjacent the end of the tn deiines a substantial rigid side corner having a dat surface for accommodating the headers. IIt therefore is a relatively simple procedure to weld the headers .in any suitable manner -to the surfaces as is shown by the drawings.

It will be appreciated that these closure members are hollow kfor accommodating the passage of iiuid therethrough. As can be seen from FG. 3, the high temperature fluid entering the inlet fheader 18 is conducted. through one yof the tubular members identied by numeral 50. Another portion of this tluid enters t-he passage area between the closure tube and the iins 52 While .the remaining portion enters the iin area of the passage. As illustrated in UFIG. 4, the low temperature Huid stream discharges from the passage 4in the rectangular closure tube :identified as numeral 60, While a portion 0f the sFluid discharges between `the closure tube and the tins `62 and the remaining portion leaves the tin area of the passage. The formed closure 4tube arrangement of this invention provides (l) solid leak tight corner walls for welding the lheaders to the core, (2) the llow of uids through the .tubes with the resultant heat transfer that precludes the severe step change in temperature between the header .and the core and `(3) the heat trans-fer rate It is Ito be understood that `the invention is not limited to the specic embodiment herein illustrated and described, but may be used in other ways without departing yfrom its spirit.

I claim:

A tcross-How heat exchanger comprising a plurality of corrugated tine elements, flat parallel spaced plates sand- Wicbing said corrugated tin elements `and dening there- With a series Iof separate parallel open ended channels terminating at opposite edges of the elements, the corrugations of the iin element in each channel being vat substantially 90 to the corrugations of the iiin element in the next .adjacent channel, means for spacing said tlat plates and for minimizing the temperature gradient .at the corners of the heat exchanger occasioned by the startingup or shutting-down of the heat exchanger, said means including a plurality of spaced parallel hollow tubes of rectangular cross section adjacent Ithe sides of said corrugated yfin elements and disposed substantially parallel with the corrugations, each tube having an end po-rtion on each end lying at substantially 90 to the corrugations extending a relatively short distance toward the in element and .adjacent the ends of the adjacent corrugated tin element, the ends of the tubes overlying a portion of a tube fin a next adjacent channel thereby defining a `continuous rigid corner `surface at eac-h end of each tube, headers mounted on said surfaces forming inlets and outlets for providing communication with the channels at opposite ends of the hn elements and said parallel hollow tubes, so that tluids passing through adjacent nell-ow tubes adjacent said corner surfaces are in indirect heat exchange relationship with each other for reducing the thermal gradient across said corner surface.

References Cited by the Examiner UNITED STATES PATENTS 2,566,310 9/51 Burns etal 165-167 3,071,187 l/63 Fairbanks 16S- 170 FOREIGN PATENTS 1,037,568 5/53 France.

686,431 1/53 Great Britain.

w ROBERT A. OLEARY, Primary Examiner. CHARLES SUKALO, Examiner.

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