US2577359A - Apparatus for heat transfer between fluids - Google Patents

Description

Dec. 4, 1951 c. A. PHIPPS APPARATUS FOR HEAT TRANSFER BETWEEN FLUIDS 2 SHEETSSHEET 1 Filed NOV. 16, 1946 INVENTOR w Dec. 4, 195] c. A. PHIPPS 2,577,359

APPARATUS FOR HEAT TRANSFER BETWEEN FLUIDS Filed Nov. 1a, 1946 2 SHEETS-SHEET 2 JECT/O/VA-A M F/G. 6A 11 F/G 65 H6? (3 VENTOR/ EZM Patented Dec. 4, 1951 APPARATUS FOR- HEAT TRANSFER :BETWEEN FLUIDS Charles A. Phipps, Hartsdale, N. Y.; Frank Northern Magill, executor of said Charles A. Phipps, deceased, assignorv to Carolyn Magill Phipps,

Hartsdale, N. Y.

Application November is, 1946, Serial No; 710,255

I This invention relates to apparatus for passingheat through partition members separating two fluid streams, and more particularly for passing heat from one stream to another through heat exchange surfaces arranged in the general form of a convolute.

. object of this invention is to provideheat exchange apparatus in which a major portion of the total surface area enclosingthe two fluid streams is common to both streams, thusincreasing the exchange of heat between the streams.

Another object of this invention is to provide animproved. wiping effect of the heat exchange surfaces throughout the flow of both vfluids withinthe heat exchange apparatus, thus increasingthe rate of heat transfer per unit'of surface'area.

A further object of this invention is to provide a very efficient heat exchange apparatusin a relatively small space.

Still further objects are to provide an improved design of a heat exchanger element suitable for use with gases without the use of fins, and which provides economies. of manufacture not available in present heat exchange equipment.

The transfer of heat between separate fluids of substantially different densities, such. as between water and air, is ordinarily cared for by passing ,themore dense fluid through. metal tubes, and passing the less dense fluid in contactwith the external surface of the tubes, which may be greatly increased in effective surface area by the addition of ribs, fins ortthe like. However, this constructionais notwelladapted for use with two fluids of approximately equalrdensity, such as betweencool and warm air, for which efficient design requires that. each stream have approximately the same amount of effective surface in heat exchange relationship with the fluid. v

The use of ordinary round tubing, ducts. or the like without fins to obtain approximately equal surface area in contact with both-streams is uneconomical. This is due to the fact that, for agiven capacity of fluid flow within the tube, a round tube presents the least possible surface area in heat exchangecontact with the fluid and ordinarily flattened tubes do not greatly extend the area. It is, of course, desirable, to improve this condition by providing a maximum of such surface area in a very economical manner. The present invention accomplishes'. this desired result. In the usual heat exchange'apparatus, certain v volute.

surfaces are ordinarily conceded to be provided for other purposes than for the direct exchange of heat, and are not included .in the computations for heat exchange capacity. Such sur faces mayjnclude bafiles, the outer shell, and other miscellaneous surfaces. The present invention holds such non-transfer surfaces to a minimum, and comprises an arrangement whereby a very large part of the total surface area is in direct heat exchange relationship with both fluids. This produces a moreefiicient heat exchange unit with regard to initial cost, total space occupied, and heat transfer per unit of material used. V g

These advantages are obtained by a novel construction in which two longitudinalmembers of relatively thin heat conducting material of approximately equal width, such as sheetmetal, are positioned with two of theirprincipal surfaces parallel, forming a space between them suitable for continuing the flow of one of the fluids. In addition to this spacing, the two members are also-positioned so that, in a view showing. their longitudinal edges, they are in the general form of a-double-wound spiral or con- This positioning is such as to provide a second space between the turns ofthe spiral, which brings the other two principal surfaces into opposition, with the space between them suitable for-containing the flow of thesecond fluid.

The two spaces thus provided comprise the -walls of two separate passages from the-outer edge of the spiral to the vicinity of its center.

. This structure, in its several modifications described in the present application, is referred toas a convolute. I

To complete the closure of 'the passages, the two open ends formed by the longitudinal edges of the metal sheets may be capped by any suitable covering, such as a soldered closure. How.-

ever, this capping may be accomplished with greater speed and economy of manufacture by fastening an insulating board or other rigid member, faced with a resilient moisture-proof gasket or cement, such as a mastic or rubberlike material, over each of the two open ends. Such capping also includes the advantage of ready accessibility to the interior for cleaning. inspection of controls, etc. r

The two fluids maybe introducedflnto: and withdrawn from their respective-passages by suitable ducts at the outside and-center terminations of the convolute. The fiow'may be in either directionv in each passage='as'irequired.

ing air is precooled by heat transfer as'it, flowstoward the center of the convolute. At or near the center, a cooling means such as an evaporator coil of a refrigerating apparatus is provided to establish a temperature differential between the inward-flowing and outward-flowing portions of, the stream; then as the air flows outwardly through the other passage, it is reheated bythe same heat transfer" that is precooling another portion of the entering stream. 'Thetotalcooling effect :of the precooling and the refrigerating of the'entering air'is sufficient-to cause its tempera ture to fall below its dew pointand' to precipitate moisture; the air leaving the convolute is reheated during its outward travel so as tobe more readily usable thancold air; and the load on the refrigerating apparatus may be economically limited to that required to provide an adequate tempera- 'ture differential across the heat transfer surfaces,

and to remove the latent 'heatreleased by the condensation of moisture, at aconsiderably large saving of refrigerating equipment. I

' A generally similar arrangement'may be used to conserve heat in chemical or distillation processes. For example, a fluid may be'preheate'd by heat transfer as it flows inwardly toward a heating means located in the vicinity of the center of the convolute; and subsequently, it may give up part of its heat to other entering fluid. "In such applications, the convolute may, in efiect, be incorporated in the walls of a vessel;

In order to provide improved wiping action of both the inward-flowing and the outward-flowing streams, and to 'provide increased heat transfer surface at low cost, indentations may be pressed into the metal sheets in a manner to not unduly obstruct the flow of the fluid nor toform pockets of lowered velocity. Such indentations would preferably be arranged to deflect the fluid alternately in one direction and then the-other so as to increase the wiping 'action'of-the fluid against the heat transfer surfaces-on both sides of the passage. Such indentations are preferably in the form of a pattern of blisters designed to face alternately toward each surface ofthe sheet in which they are pressed, and to be staggered to avoid any substantially straight flow of fluidbetween two of these'sheets. A pattern'of such blisters may be impressed-in the metal sheets cheaply by passing the sheet between a pair of forming rolls, or by the use of suitable dies or the like. Although corrugations may be used, they are not as satisfactory as a pattern of blisters or similar protrusions; This is because corrugations require a greater length'of original stock. They also cause undue restriction of narrow passages in locations where the protruding ridges fall opposite to one another The valleys of'the corrugations -provide pockets of lowered fluid velocity, tending to reduce the rate of heat transfer.

The, improved heat transfer element'of this invention, provided with localized concave and 75 4 convex projecting curved surfaces which are each much smaller than the width of the element or sheet, and which project in alternate directions from the surf aces along both its length and width, can then be rolled even tightly on itself, in the form of a moo'th spiral or in any'irregula'r shaped convolute, without blocking of the air passages between the surfaces. Even when tightly wound on itself, the surfaces of adjacent turns can come in -contact at only a few scattered points. Generally in use it is preferred to separate the turns by a distance slightly greater than twice the height of the projections, so that they do not actually touch at any point in order to avoid direct transfer of heat by conduction from wall to wall.

."AH. alternative. modification of the present invention comprises the soldering of cooling or heating coils directly to the heat transfer surfaces in the vicinity of the center of the convolute, thereby increasing the heat absorbing or heat dissipating area of such coils, and providing an economical and eiiicient means-for introducing'a temperature difierential when a convolute is used for reverse flow of the same fiuid.- a v All of the foregoing description uses the general spiral formas the simplest variation of the present invention. However, the overall shape of the complete heat exchange unit may be varied to fit intoa particular available space For example, if a long and relatively thin space isavailable, the heat exchange unit may be modified toflt into-the space by introducing straight lengths of metal sheets, with the curvature at the-ends arranged to' provide the spiral effect of inward and outward passages. --Such an elongated unit may, in turn, be constructed with be'nds along its length to conform-with the shape of whatever space is found to beavailable. Thus, such overall shapes as a U-shaped-mnt, an L-shapedunit. etc. may be readily produced while-retainingthe basic improvement-ofthe present invention- The drawings presented herewith are illustrative of several modifications of the present invention. The same numerals represent similar elements throughout the several figures.

Figure 1 isa diagrammatic sketch in sectional plan of a' heat exchange unit in'the form of a convolute; 4 v

Figure 2 is a modification of 'Fi'gurel, inv which the convolute is elongated by the introduction of substantially-straight sections of heat exchange surface. x

- Figure .3.is a modification ofFigure 2 in which an elongated convolute iscurvedto. conform with a required external shape. 7

Figure .4 is a modification of Figure l in which the convolute-is incorporatedin the walls .of a vessel, with provision for additional heat transfer between-thevessel and an external heat supplying or receiving zone.

Figure 5 is another modificationof Figure 2 in which the central portion of the convolute has means for providing a temperature differential.

Figure GA-is a section on line. A- A of Fig-.-

v ure 63. his a diagrammatic'sketch in sectional plan of a typical patternof indentations inith'e walls of a convolute of any of the types illustrated'in Figures 1 to 5,, inclusive, to increase the'transfer of heat through the walls. Figure 6B is a'similar elevation view of Figure 6A taken fromlineBB.

Figure 7 is a section on line C--O:of Figureil.

It is a diagrammatic. sketch inv partial sectional '8 elevation of the convolute of Figure 8, in which the ends are closed by an arrangement of gaskets, substantially rigid members and bolts.

Figure 8 is a diagrammatic sketch in partial sectional plan of a device for drying air in ac-.

cordance with the present invention.

Referring to Figure 1, two heat exchange sur faces are represented by edges l and 2 viewedin" sectional plan. These surfaces areseparated by space 3, which is suitable for containing a fluid stream passing in eitherdirection between ends; and 6 of space 3. The two surfaces l and 2 are curved to form a convolute, thus also forming space 4, which is suitable for containing a second fluid stream passing in either direction between ends I and 8 of space 4. A suitable closure is provided over the edges, of the heat exchange sur faces, as described later, to prevent the escape ofv either fluid except at 5, 6,1 or 8. The two pas},

sages 3 and 4 may be connected at their inner ends 6 and 8 to separate fluid conduits 9 and-29,

as illustrated in Figure 1, or they may connect directly with each other, thus reversing the flow of fluid on itself through the convolute, as shown in Figures 2-,5 and 8.

Referring to Figure 1, assuming one fluid stream to enter at 5, and another at 8, the two fluids in this case move in counter-flow, emerging at 6, and 1, respectively. Throughout the major Similarly, the fluid stream enteringat 5 is in contact with heat exchange surfaces! and 2 throughout its travel. The arrangement is preferably such that the flow of heat to or from the surrounding air through that part of surface I forming the outer shell-is favorable by passing the warmer or the cooler fluid through space 3, as may be desired. Otherwise this outer shell may beinsulated. The remaining areas of heat exchange surfaces 1 and 2 are all in direct heat 1 exchange relationship with the. other fluid in space 41 This provides an arrangement with a veryhigh proportion of the total surface area in direct heat exchange relationship with both fluids, and the amount of such surface may be readily increased by adding turns without in: creasing the outer shell area ,in the same pro-. portion. This arrangement also gives a choice of parallel flow or counter flow, and a choice between'points of entrance and discharge of each fluidso as to take the maximum advantageof the available temperature differentials and to thus obtain the greatest flow of heat.

The arrangement is economical of metal because it is made by forming flat sheets, which are not only cheaper to produce than othertypes of surface, but also may be used in thinner gauges than are ordinarily available in the walls of tubes or the like. I In case a cylindrical overall shape is not suit able, the convolute may be modified in any 10f several ways to conform with the limitations of an available space.

' Forexample, Figure 2 illustrates an elongated heat transfer unit similar to that illustrated ,in Figure 1, except that the introduction of subs, stanti'ally non-curved heat transfer surfacesh'as, extended its length. This increases the heat transfer capacity of the unit. If itis 'desired'ito provide an elongated'unit of equivalent capac' y to that of a cylindrical unitper' Figure 1, t e width'of the heat transfer surfaces or the radii of curvature at the ends, "or both, may be reduced. This provides flexibility of design to meet the conditions of practical applications. In such designs it is desirable to provide an extension of one heat exchanger surface strip around the end of the other, as at I9, to provide for maximum utilization of the available surface for heat exchange.

A further advantage of an elongated unit as shown in Figure 5, is that cooling or heating coils [0 may be readily fastened to any of the non-curved heat transfer surfaces to provide a desired temperature differential, or where passages 5 and I do not connect at the center, to control the precooling or preheating effects as may be desired.

Figure 3 is illustrative of further modifications of the overall shape of the heat transfer unit. In this case, it is assumed that the available space for heat transfer equipment is in the shape of an' L and that a unit generally similar to that illustrated in Figure 2 is provided with curved elongated surfaces 'to meet this requirement. Such surfaces may, for example, be curved to provide an overall U shape, 8 shape, or. other desired shape of the heat exchange unit to meet the requirements of practical applications in restricted spaces, while retaining the characteristic high capacity of heat transfer provided in this general type of unit.

Figure 4 illustrates a modification of Figure 1 suitable for preheating or precooling a fluid stream as it approaches a vessel at the vicinityof the center of the convolute, by heat exchange from a fluid stream leaving the vessel. This is suitable for economically operating a continuous process requiring the heating of a fluid, which may include chemical processing, food processing, distilling, crystallization, and the like. Such operation -may be conducted in the space 38, which may be provided with suitable means for removing a solid, liquid or vapor phase from the fluid passed therethrough. This device is also applicable for the cooling and reheating cf-afluid in a continuous process, such as the cooling and reheating of air in a dehumidifying process. In such cases, a cooling means such as a refrigerating coil 40 is provided in heat exchange relationship with the fluid in the vessel. In all such constructions the convolute maybe built into, or may itself form the wall of the vessel.

The convolute of Figure 4 may be similarto that illustrated in Figures 1 or 2, with the inner terminations 6 and 8 opening into the walls of r the vessel. Suitable bailies l4 may be provided to assure that the fluid remains in the vessel for a sufliciently long period to complete the process in accordance with he needs of specific applica'- tions.'

' Figure 5 illustrates an elongated unit in which an arrangement is provided in the vicinity of the center of the convolute whereby the same fluid is redirected into the second passagerto provide for heat exchange between the entering and the leaving portions of the stream. This modification is suitable for application in those cases for which a vessel is not required but reversalof the fluid stream is necessary; or in cases Where the overall thickness of the elongated heat exchange unit in a reversed-flow application i a limiting factor. It is also of value where economy of manufacture is improved by the use of only two continuous members to provide the outer shell, the heat'exchangesurfaces, and the reversing means. This arrangement also provides a convenient and ecomam nominal mounting mean for -heating or coolin coils l0. which may beinjthe form of finned rad ator tubes or may be soldered to one orinore of the substantially straight heat exchange-surfaces in-the vicinity of the center of the convolute to provide the necessary temperature differential between the entering andtheleaving' fluids.

Figure 6A illustrates a section of the wall ofany of the foregoing heat exchangeaun-its, showing a seriesof blister-like convexj-H and concave 12indentations pressed into the heatexchange 811 faces- The purpose of" this arrangement-ism cause-greater turbulence. of the fluid. in its flow through the passages, thus increasing its wiping action on the walls. It also increases-the area of the heat exchange surface. Both ofthese factors improve. the heat transfercharacteristics of the unit.

Theblisters are preferably arranged in alstaggored pattern to insure thatall portions of the fluid stream'impinge on them. They are preferably alsoarranged to alternately protrude :from' opposite surfaces" of the wall, in both itslength and width, to further increase the air turbulence and to provide better spacing for the passage of the fluid.

The progressively increasing radius of curvature inherent in-theconvolute form makes itimpractical' to preserve a definite relationship be,- tween the spacing of protrusionsin opposing heat exchange surfaces. For this reason, it is preferredto restrict the maximum depth ofsuch protrusions to not greater thanone-half of the. normal spacing between the non-protruding portionsof the surfaces. If two protrusionsshould fall-in direct opposition, and make contact, such contactwill beat only one: point andwill'notma terially impede the flow of the fluid. With an arrangement generally similar to that illustrated. the openings between such protrusions will be sufficiently large to care for the necessary fluid flow, as the-concave portions of those protrusions facing in the opposite direction will tendto com,- pensate for any restrictions due to the convex portions in a given passage. The use of suitably shallow protrusions with rounded sides as. illus: trated assists in preventing the formation of pockets of relatively stagnant air, which would otherwise tend to reduce the rate of heat transfer.- Such protrusions, having spherical surfaces,-

preferably extend from the surface a distance of about'one-halfthe radius of the sphere.

This improved; heat exchanger surface iseasily prepared by passing a sheet of a suitable metal which canbe cold worked, such as copper or steel,

between closely fitting pressure rolls containing on their surfaces opposed concave and convex portions conforming to the desired blister pattern. The resulting sheet issues from the rolls with the blisters protruding from both surfaces. then be simply wound on itself to provide the heat exchanger elements illustrated in any of Figures 1 to 5, '7 and 8. The invention i not limited to the spherical form, of blisters illustrated, as such blisters may be relatively shallow concave and convex portions of any other shapes, elliptical, sinoidal, etc. While relatively smooth curves are preferred, the surfaces. may contain minor irregularities relative to the larger blisters.

Figure? illustrates an economical closure for the edges of the heat transfer surfaces. Al though I'netallic closures may be used, such as soldered joints or the like, the preferred closure consists of aresilient gasket '13, which maybe a sheetof resilient. material impervious tothe fluid It m y anu capable of withstandi g the temperatureconditions encountered. A sheet of neoprene: or

of one ofthe morefiexible vinylitescompositlons is suitable: material for" an ordinary asket 01! a this type.

Such gaskets may: be placed over bothends. of the heat exchangeunit; such ends-comprising, the planes. containing: the-"longitudinal edges of the heat exchange surfaces l5, and may; be held in place lay-substantially. rigid. members It asbacking: for the" flexible:- gaskets The: as sembly may beheld together bysuitable-m'echan ical fastening means Y such." as: clamps, bolts? or 'thelike 29; Therigid mem-b'ers Iii-used asback ing for the resilienttgasketsmay'be. composed of a suitable heatinsulating:material as may be required for 'specific applications.

Where a change ofpha'sei occurs; in condensation of moisturefromair-being cooled as it passes inwardly toward the center oftlieunit, it is often desirable toremove suchseparate phase from-the unit near its center in ordert'o' prevent itspassage' with the fluid through theoutgoing spiral passage; This may" be accomplishedby providing a suitable conduitor-"mechanic'al device, such asan A'rchiinedean screw, where the removal of a solid phase is desired connecting' with the interior of the unit For example in Figures 7 and S thet'ubes H are provided -to re- 30 move condensed water;

Figure 8 shows the application-of this inven tion in a device for drying air; A blower 18 supplies air throng-ha conduit-2U connectingwith entering duct-1 Located in the center of the convolute are heat absorption: tubes; or; ova"- orator's', 21 of 'arefrigeration unit comprising a compressor 22, condenser and heat dissipator 23'; refrigerant receiver 245 expansion valve 25; re'- frigera'nt supply iuct-2li and refrigerant return duct 21L I In operation the air supplied by the-blower l8 is cooled in' duct'd by indirect heatitransf'e r with the cooled air returning through duct 3 As the air 7 cools to below its dew point, moisture-forms on the heat exchanger walls, flows to the bottom of the duct, and is removed through the water drain tubes IT. The air is further cooled by contact with the cooling coils 2| whichmay be operated to cool theair, to 40 F., 32"" E. oran even lower temperature; These tubes 21' may have fins 28 (see Figure '7) or maybe mounted in a battery through a seriesof parallel connecting fins as is customary in airradiators and refrigerator condenser units. When operating at temperatures below. 32 F., some ice will form on such cooling tubes but by providing sufficient cooling surfaces and capacity, the air stream can be cooled to this; temperature or even lower, thereby reducing its'moisture content to an extremely low value. 'Where the unit is intended for intermittent operation, some defrosting-can, of course, occur between operating periods, or the cooling tubes may be warmed by bypassing the condenser 23 and expansion valve 25, thus recycling hot compressed refrigerant directly from the compressor 22 to the tubes 2|. The chilled and dried air is returned through the duct 3, is warmed. by the entering air in duct 4, and leaves the unit at. 5 through any suitabl con- 0 nection, dependent upon its intended use. Where warm dry air is desired,the air in duct 5 may be passed over auxiliary heating means, any desired portion'of the condenser 23 may be'located in this air stream. 75 It will be understood. that the.- compressionexpansion refrigerant cycle shown in Figure 8 is illustrative of only one method for supplying refrigeration in the tubes 2|, and that other methods of refrigeration may also be used.

This heat exchanger device, constructed as illustrated in Figure 8 with the heat transfer surfaces I and 2 constructed as illustrated in Figures 6A and 6B, has been found extremely efficient in drying air even with a temperature differential between the entering and exit air streams as low as two or three degrees F. In such operation the moisture content of the exit air has approached closely the theoretical moisture content based on the minimum temperature observed in the air stream at the center of the convolute.

I claim:

1. Heat exchange apparatus comprising two substantially parallel heat'transfer surface members spaced to provide afirst fluid passage between adjacent surfaces, and arranged in substantially the form of a double-wound convolute providing a second fluid passage between the reverse surfaces of said surface members in heat exchange relationship through said surface members with said first fluid passage the said heat transfer surface members comprising closely spaced adjacent concave and convex projections alternating both along the length and the width of said members to provide a continuously curved surface at each of said members.

2. Improved apparatus for heat transfer between two fluid streams comprising two relatively tween two fluid streams comprising two relatively long gas-impervious heat transfer strips of equal widtharranged in the general form of a double convolute with substantially parallel vertical surfaces and edges of both strips in the same two planes, closures in both planes for the said edges thereby providing two fluid channels, the inner ends of said channels connecting, means located in said channel near the center of said convolute for transfer of heat between a fluid passing therethrough and a second zone of heat transfer located exteriorly of said convolute, means connecting with the bottom of the central portion of said convolute for separately withdrawing from the fluid passages a new liquid phase formed during the passage of a fluid through the convolute and fluid inlet and exit conduits connecting with the outer ends of said passages.

4. Apparatus according to claim 3 in which said heat transfer surface members comprise closely spaced adjacent concave and convex projections alternating along both the length and the width of said members to provide a continuously curved surface of each of said members.

5. Apparatus according to claim 3 in which said heat transfer surface members comprise closely spaced adjacent concave and convex projections alternating along both the length and the width of said members, said projections extending not more than half the width of said passages to provide a continuously curved surface of each of said members.

6. Device for drying air comprising a pair of spaced metal strips wound in the form of a convolute about a substantially vertical axis providing an open air passage reversingon itself at the center, closure means on the two edges of the convolute, a heat transfer device having heat absorbing mean positioned in said air passage near the center of said convolute connecting with heat releasing means positioned exteriorly of said' said heat transfer surface members comprise spaced concave and convex projections alternating along both the length and the width of said members to provide a continuously curved surface of each of said members.

8. Apparatus according to claim 6 in which said heat transfer surface members comprise spaced concave and convex projections alternating along both the length and the width of said members, said projections extending not more than half the width of said passages to provide a continuously curved surface of each of said members.

9. A heat transfer element in strip form adapted to be wound on itself without contact of more than a small fraction of adjacent surfaces in any direction comprising a relatively long metal strip' continuously curved in alternately spaced adjacent concave and convex portions in both dimensions of the plane of said strip.

CHARLES A. PHIPPS.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 785,580 Shiels et al Mar. 21, 1905 1,576,410 Connery Mar. 9, 1926 1,956,133 Rosenblad Apr. 24, 1934 2,131,265 Bichowsky Sept. 27, 1938 2,236,976 Rosenblad Apr. 1, 1941 2,281,168 Paget Apr. 28, 1942 2,360,739 Strom Oct. 17,1944

FOREIGN PATENTS Number Country Date 9,815 Great Britain May 19, 1894

Images