US3006979A - Heat exchanger for thermoelectric apparatus - Google Patents

Description

D. G. RICH 3,006,979 HEAT EXCHANGER FOR THERMOELECTRIC APPARATUS Oct. 31, 1961 Filed April 9. 1959 FIG. I

FIG. 2

FIG. 3

INVENTOR. DONALD G. RICH mq Jg.

A 7' TORNE Y 3,006,979 `Patented Oct. 31, 1961 ice l Ware Filed Apr. 9, 1959, Ser. No. 805,220 4 Claims. (Cl. 13G-4) This invention relates to thermoelectric apparatus and in particular thermoelectric apparatus having heat exchange structure employed therewith.

Various constructions have been heretofore proposed for thermoelectric apparatus employing a fluid medium in heat exchange relation with the thermoelectric junctions therein to provide heating or cooling of the junctions or to transfer the heat or refrigeration produced by the junctions to a remote point. These prior proposals have suffered from the disadvantage that conventional heat exchange coils have been employed externally of the thermoelectric panels in the apparatus and have employed heat exchange coils of generally circular configuration or coils having external ns which, by reason of their construction and their location in the apparatus, have not provided entirely satisfactory heat transfer characteristics.

Heat exchange tubes having a circular cross section suffer the disadvantage that when in heat exchange relation with a ilat panel such as might be part of a thermoelectric apparatus only a narrow area approaching a thin line is in intimate contact with the panel. This narrow line of contact acts as a restriction to the free iiow of heat and cuts down on the eiciency of the heat exchange. Heat exchange tubes of non-circular cross section, such as those having ilattened sides, can provide a larger area of contact with the panel which improves heat transfer. However, tubes of such construction require thicker walls to withstand pressures encountered both from within and Without, than do tubes of circular cross section which are inherently stronger. The thicker walls required offer greater resistance to the flow of heat between the uid carried in the tube and the panel to which it is attached consequently offsetting, in some measure, the advantage obtained by making the tube non-circular. Further, ordinary tubes, even of non-circular cross section, have only a relatively small area of contact with the fluid passing through them and only the periphery of the uid stream is in eicient heat exchange relation with the panel to which the tube may be secured. Furthermore, heat exchange tubes attached to the exterior of a thermoelectric panel possess the disadvantage that they are separated from the thermoelectric junctions in the panel by the Walls of the panel which offer an undesirably high resistance to the transfer of heat between the thermoelectric junctions and the uid passing through the heat exchange tubes.

It is the principal object of this invention to provide a thermoelectric apparatus with heat exchange means associated therewith in such relation as to provide eli'icient heat transfer with the thermoelectric junctions of .the apparatus.

It is a further object of this invention to provide heat exchange tubes in a thermoelectric apparatus which may be of non-circular cross section and have thin walls and yet provide the desired strength as well as having a large area of contact with the liuid passing through the tubes.

It is a further object of this invention to provide a construction for a thermoelectric apparatus which avoids the disadvantages inherent in the use of heat exchange coils externally of the heat exchange panels of the apparatus.

It is a further object of this invention to provide a simple, inexpensive and eflicient heat exchange tube structure and location for passing a liuid in heat exchange relation with the thermoelectric elementsof a thermoelectric apparatus. These and other objects of my invention will ybecome apparent with reference to the following description.

These and other objects of this invention are achieved by providing heat exchange coils having a pair of flat parallel sides disposed within a thermoelectric panel between one of its outer walls and the thermoelectric junctions so as to provide the least resistance to the flow of heat between the junctions and the fluid passing through the heat exchange tubes. I achieve a substantial area of `contact between the iiuid flowing through the heat exchange tubes and the tubes themselves by the use of an internal iin which at the same time serves to reinforce the heat exchange tube enabling me to use thin walled tubes which further contribute to efficient heat transfer.

FIGURE 1 is a fragmentary cross sectional View through a thermoelectric panel;

FIGURE 2 is a fragmentary cross sectional view of a modified thermoelectric panel;

FIGURE 3 is a fragmentary cross sectional view of a thermoelectric panel showing a modified -heat exchange structure.

Referring particularly to Ythe drawings wherein like reference numerals vare used throughout to designate corresponding parts, FIGURE l shows a thermoelectric panel 22, comprising a first pressure plate 10 and a second -pressure plate 11. Disposed between the pressure plates are a plurality of thermoelectric elements 18 which are disposed generally parallel to one another. The thermoelectric elements 18 are connected in series fashion by a plurality `of first jumpers 16 on one end of elements 18 and a plurality of second jumpers 17 on the other end of elements 18, in alternating fashion with one P-type element and one N-type element contacting each jumper as shown in the drawing to form thermoelectric junctions. In order to accurately position the thermoelectric elements 18 in the thermoelectric panel they may convenientlybe disposd in a block of insulation 20 of a material such as polyurethane foam which serves to electrically and thermally insulate the thermoelectric elements 18 and to provide substantial resistance to shock which may be encountered by the panel assembly during insulation or use.

The jumpers 16 and 17 maybe madeof any suitable material such as copper or iron and electricallyv connect alternating pairs of thermoelectric elements 18 in series relation as will be understood by those skilled in the alt. The jumpers 16 and 17 may overhang the thermoelectric elements as shown to provide more heat transfer area without increasing the resistance of the circuit. One side of jumpers 16 is shown in contact with adjacent pairs of thermoelectric elements 18 and the other side of the jumpers is shown in contact with one face of a sheet of electrical insulating material 19 such as mica. The other face of electrical insulation 19 is shown in contact with one side of a plurality of first heat exchange members 12.

The heat exchange members 12 comprise a generally elongated tubular member having substantially liat parallel sides 31 and 32 disposed outwardly and inwardly, respectively, of panel assembly 22 and rounded end portions 33 and 34. Inside the tubular heat exchange members 12 is an internal iin 14 of generally sinusoidally corrugated sheet metal material. The corrugations of the sheet metal iin 14 contact the parallel sides of the heat exchange member at 15 and may be integrally secured thereto by any convenient means providing good heat transfer characteristics. For example, if the heat exchange tubes and ns are made of aluminum the con- 3 tacts 15 may be made by salt bath brazing or if the ns and tubes are stainless steel the contact 15 may be made by .furnace brazing. As will be appreciated the contacts 15 extend along lines generally 'axial of the tubular heat exchange member 12.V Internal fin 14 divides the in-Y terior'chamber of the heat exchange member into a plurality of axial ow paths 21 presenting a large area of metal in heat exchange relation withv a fluid medium adapted to be passed therethrough. If desired, the iin need not be Iaxially smooth and straight but may be corrugated or louvered valong its axial extent to improve its heat transfer characteristics. The width of therat parallel side 32 of the heat exchange members may be substantially co-extensive with the length of jumpers 16 thereby providing a large surface area adjacent jumpers 16 to enable maximum heat transfer between the thermo-V electric junctions formed by the Vjumpers and the fluid passing through heat exchange members 12. The otherV side 31 of the heat exchange members 12 is in contact with rst pressure plate 10.

Heat exchange members 12 may be formed by flattening a cylindrical tube of initially circular cross section to provide ilat sides 31 and 32 and rounded ends 33 and 34, thereafter inserting corrugated iin member 14 into the flattened tube and integrally securing the iin to at sides31 and 32 by brazing or soldering. However, :the

kheat exchange members maybe conveniently fabricated instead by positioning the internal iin 14 lengthwise on a piece of at metal stock, bending the stock around the iin to -form a closed tube which may be secured by seamY welding and thereafter brazing or soldering theun to Y secure a good metal to metal contact with sides 31 andA 32 for purposes of eicient heat transfer. The brazing can be omitted in some cases if suicient pressure Yis exerted on the heat exchange tubes by thel pressure plates and the pressures in the tube are not so -great as to deform the tube walls. Y

Heat exchange members 12 may be connected to a common header (not shown) at their ends or they may be connected -by means of return bends (not shown) to form a Ysingle serpentine coil. Appropriate supply and d.ischarge connections are provided to complete the heat exchange unit. In the event that return bends are employed they may have the same Vcross sectional configuration as shown for the heat exchange tubes 12 inYFIG- URE 1 including the internal iin for added strength.

However it is usually preferable to employ -a bend of generally circular cross section having transition portions at its ends adapted to beY secured to tubes 12. When a bend of circular cross section is employed, the internal iin may be omitted in the bend as it is not needed for strength.

As will be seen from the upper portion of FIGUR-E l, a second sheet of electrical insulation 25 may be positioned in facewise contact with second jumpers 17. A second pressure plate 11 may begdisposed against the insulation sheet 25 and the assembly may be completed by suitable means (not shown) to secure the pressure plates in position or to hold the assembly together. j

The embodimentV shown in VFIGURE 1-is particularly adapted to use in ay thermoelectric generator where second pressure plate 11 may be heated and the heat exchange members 12 provide cooling at the coldjunctiou side ofthe generator. 'Y

In FIGURE ZYthere'is, shown thermoelectric apparatus having a thermoelectric panel 23Y similar to thatrshown in FIGURE 1' except that a second set of heat exchange elements 1 3 have been interposed between the second presf sure' plate 114 and the layer-offelectfric insulationZS shown at the top portion of' FIGUREzZ- The operation ofthe embodiment shown VinFIGUVRE 2 is similar tol that shown in FIGURE 1 except that by thisconstr'uction both the hot 'and cold junctions of YVthermoelectric elements 18 are placed in heat exchange relation with respective adjacent heat exchange elements 12 and 13. The assembly;shownY through heat exchange tubes 13 adjacent to the cold junc-V tions formed by Yjumpers V17V is cooled and the cold brine solution may be pumped to a remote area to be cooled.`

FIGURE 3 shows'a modified embodiment of the heat exchange members shown in FIGURES l and 2. In the embodiment of FIGURE 3 the heat exchange members 36 are shown in a thermoelectric panel 24 and have generally ila-t parallel sides 28 and 29 similar to those shown at 31 and 32 of FIGURES l and 2. However, in this embodiment the heat exchange members are formed from a pair of sheets 3S and 36. The ends 37 and 38 ofthe heat exchange members Vare shown to be pinched together andV k having seams| 39 secured by any appropriate means such as brazing or welding. By pinched togetherV itV isrrnea'ntV thatshee- ts 35 and 36, which form the heat exchange mem- I 'bersghave'portions brought together and secured at seams 39 to fo-rm a plurality of tubular chambers similar to those with an unfusable matrix painted on one ofthe sheets.

Thereafter the sheets may be fused together and expanded away from one another in the unfused areas formed Yby the unfusable4 matrix forming tubular chambers .for the' reception ofv sinusoidally corrugatedy sheet metal 14 similar to that shown in FIGURES l and2. Alternatively the pinched construction describedV could be achieved by preforming sheets 35, 36 in the desired shape and welding them together at 39. Another alternative is to blow the tubular portions at 28, 29 from a single sheet of material having voids of appropriate size and yshape leaving portions at` 39 integrally attached. Each of these construcf tions' produces pinched shaped ends 37 and 38. As in the embodiments of FIGURES l and 2 then 14 forms a plurality of axial flow'paths 21 and aids in efficient heat transfer. The ends of the heat exchange members/.so formed may be either connected to common headers or may comprise a serpentine coil by means of return bends attached to ends of the members as explained for the preceding embodiment. Y

This construction enables the heat exchange members to be made simply and inexpensively to provide a maxi# mum heat transfer between the heat exchange members and the fluidvadapted to be passed'through the heat ex# change members.V It will be appreciated that the construction Yof the heat exchange coils of this embodiment may Y be employed inv conjunction with or in lieu of the heat ing Athrough the heat exchange tubes is ncontact not only v Vwith the tube walls but also with internal nrwhich provides a substantial area of heat exchangefsu'rface tothe fluid. The heat exchange tubes need not have appreciably thickened walls to Vcomp'ensate'forv the normally less rigid characteristics of a non-circular tube since the internal Y iin reinforcest'he tube asA a'whole'. At the same time, by

positioning the heat exchange tubes Ywithin the panelgassembly'of thethermoelectric apparatus instead of-externally thereofjand by reason of the large surface presented to theV thermoelectric junctions by theV attened lheat exchange tubes I achieveVV exceptionallyeiiicient heat trans- V Y fer.

' 'l While I have shown the preferred -forms 'of my inven- Q tion it willibe understood that my invention is not limited f thereto butfmay be otherwise embodiedV within the scope Y.

ofthe following claims.

I claim:

1.-.V In.a,thrtrnrleY trcapparatus, aeunitaryV thermoelec- Y tric panel assembly comprising a plurality of thermoelectric elements disposed in parallel spaced relation, a plurality of jumpers, pairs of said thermoelectric elements being joined at one end by contact with a face of the jumpers, a sheet of electrical insulation in facewise contact with the opposite face of the jumpers, a plurality of heat exchange members forming a fluid circuit for a heat exchange fluid, each of said heat exchange members having a pair of substantially flat spaced parallel relatively thin metal sides and a pair of ends forming a metal tube adapted to carry a heat exchange uid, one of said sides 0f each of said heat exchange members contacting and being in facewise engagement with a side of said sheet of electrical insulation on the side thereof opposite that in contact with said jumpers, a pressure plate contacting the other flat side of said heat exchange members, each said heat exchange member comprising a thin wall metal tube and having disposed therein a sinusoidally corrugated sheet metal partition forming an internal fin, the corrugations of said internal fin contacting both said flat sides of said heat exchange members internally thereof forming a heat conducting path to enhance heat transfer with a fluid medium passed through the interior of said member, said contact extending along a plurality of lines extending axially of said heat exchange members and forming a plurali-ty of axial flow paths within each said member adapted to pass a uid in heat exchange relation with said jumpers and said pressure plate, said sinusoidal sheet metal partition serving to reinforce said heat exchange members so that the heat exchange members comprise a rigid fluid passage and the sides thereof may be relatively thin walled to improve the heat transfer characteristics of said thermoelectric apparatus.

2. A thermoelectric apparatus as described in claim 1 including second jumpers at the other end of the thermoelectric elements, a second insulating sheet in facewise contact with said second jumper, a plurality of second heat exchange members in contact with the opposite face of said second insulating sheet from that in engagement with the said second jumpers, each of `said second heat exchange members comprising a thin wall, flat sided, metal tube, having a sinusoidally corrugated internal n contacting and reinforcing the sides of said tube to provide rigidity and to enhance heat transfer with a uid adapted to pass through the interior of said heat exchange member, and a second pressure plate engaging said heat exchange members to form a thermoelectric panel adapted for use in a thermoelectric refrigeration apparatus.

3. A thermoelectric apparatus as defined in claim l wherein said pair of ends of said heat exchange members are rounded to form a uid passage.

4. A thermoelectric apparatus as defined in claim 1 wherein said pair of ends of said heat exchange members are pinched together to form a uid passage.

References Cited in the le of this patent UNITED STATES PATENTS 1,848,655 Petrik Mar. 8, 1932 2,749,716 Lindenblad June 12, 1956 2,758,083 Hoek et al. Aug. 7, 1956 2,844,638 Lindenblad July 22, 1958 2,870,610 Lindenblad Jan. 27, 1959 2,886,618 Goldsmid May 12, 1959 2,949,014 Belton et al. Aug. 16, 1960

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