US2692119A - Spirally wound refrigeration evaporator - Google Patents

Description

Oct. 19, 1954 s. H. MORSE SPIR`ALLY WOUND REFRIGERATION EVAPORATOR 3 Sheeucs-Sheet l Filed Feb. 26, 1952 mm Nwmwm oct. 19, 1954 s H, MOR-SE 2,692,119

SPIRALLY woUND REFRIGERATION EvAPoRAToR Filed Feb. 26, 1952 3 Sheets-Sheet 2 5km/ey. Morse,

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orneg Oct. 19, 1954 s. H. MORSE 2,692,119

-SPIRALLY WOUND REFRIGERATION EVAPORATOR Filed Feb. 26, 1952 5 Sheets-Sheet 3 :inventor Patented Oct. 19, 1954 SPIRALLY WOUND REFRIGERATION EVAPORATOR Stanley H. Morse, Manitou Beach, Mich., assigner to Addison Products Company, Addison, Mich.

Application February 26, 1952, Serial No. 273,409

Claims.

This invention relates to a heat exchange coil especially suited for use as a refrigeration evaporator, and it is particularly concerned with a spirally wound tubing formed with extended secondary heat transfer surface, and wherein the convolutions of the coil are xedly spaced and bound with respect to each other.

It has heretofore been proposed to form a refrigeration coil by winding a length of tubing into spiral form, and it has also been proposed to utilize extruded aluminum tubing for such coil, wherein the tubing is formed with longitudinal fins to increase the heat transfer capacity. Such proposals have not, however, heretofore met with general favor in the refrigeration industry, as it has been considered that the heat transfer capacity and eiiciency were relatively low, and that the manufacture of such coils involved undue expense.

I have discovered, however, that a highly efflcient heat transfer unit of the type described may be made by means of novel improvements in the structure thereof, providing a compact and durable coil, and one which may be made economically and without expensive equipment. My improved coil, a satisfactory mode of fabrication, and a typical application thereof to refrigeration service, will be described with reference to the accompanying drawings, wherein:

Fig. 1 is a plan of a length of tubing stock from which the coil is made, prior to any of the forming operations;

Fig. 2 is a view similar to Fig. 1, showing some of the initial steps of manufacture;

Fig. 3 is a view on an enlarged scale, showing further fabricating steps;

Fig. 4 is a fragmentary side elevation, on a reduced scale, of the right hand end of the tubing shown in Fig. 3;

Fig. 5 is an enlarged section on the line 5 5 of Fig. 4;

Fig. 6 is a side elevation, showing the formed tubing at the beginning of the winding operation;

Fig. 7 is a side elevation of the completely wound coil;

Fig. 8 is an enlarged side elevation of a com-- pletely wound and finished coil;

Fig. 9 is a fragmentary radial section, on an enlarged scale, of the coil shown in Fig. 8;

Fig. 10 is a fragmentary view of an outer end of the coil shown in Fig. 8; and

Fig. 11 is a view, partly in elevation and partly in section, showing the improved coil as utilized as an evaporator in a self-contained refrigeration machine. Y

Referring first to Figs. 1 to 7, there is shown in Fig. 1 a suitable straight length of tubing 20, which advantageously is composed of aluminum which has been extruded by known processes, and which comprises an axial tubular portion 2| of flat or slightly oval cross section, and two integral fins 22 disposed longitudinally of the tube 2l and along the narrow dimension thereof. The ns 22 are initially notched or slotted at the ends of the tubing, as indicated by the referencev numerals 23 and 24, and limited portions of the fins are also cut away to provide relatively free tabs, as indicated by the numerals 25 and 26, and tube end portions 21 and 28. Holes 29 and 3| are also punched in the tabs 25 and 26.

Portions of the fins 22 are also removed substantially midway of the free ends 21 and 28, as indicated by the reference numerals 32 and 33, and holes 34 and 35 are punched in the fins adjacent their central ends. It will be noted that the cut-away portions of the fins 22vare of un-v equal length. It may here also be noted that the complete coil, as specifically to be described, is a double coil, that is, one wherein there are two superimposed spiral sections interconnected by the integral portion of tubing 36. It will be apparent that in making a single coil, the severance of iin stock at the central portion of the tube length need not be undertaken. The length of tubing 20 is then passed through spaced pairs of knurling rollers, or is treated by equivalent means, to roughen the surfaces and to form small indentations or ripples over the surfaces of the fins 22, as indicated by the reference numeral 31.

The fins 22 are then corrugated or formed into recurrent wavy portions, to displace the metal as shown in Figs. 3, 4, and 5. This operation, which may readily be effected by spaced pairs of suitably contoured roller dies, draws or stretches the metal outwardly from the junction of the fins 22 with the tube 2| to the margins of the ns, thereby progressively reducing its thickness and increasing its length. Concurrently, the iin stock is forced upwardly and downwardly, with respect to the tube 2|, to provide crest portions 38, 39, projecting above and below the longitudinal axis of the tube, and thus deform the fins from their original plane configuration into substantially sinusoidal shape.

It will be noted, from Figs. 3 and 5 (as well as from the enlarged view of Fig. 9) that the amplitude or Vertical displacement of the n stock increases from nothing at the junction of the ns with the tube 2l to a maximum at the margins. It will further be noted that the crests 38, 39 of the iin 22 on one side are offset from or staggered with respect to the crests of the n 22 on the opposite. side of the tube 2|, or, stated otherwise, the sinusoidal waves are substantially 180 out of phase. The outwardly increasing amplitude of the wavy hns is such that approximately fty to sixty per cent of the displaced metal is above or below parallel lines drawn through the outside minor axis of the tube 2 I.

A further and important feature of the corrugated fins is the formation of reentrant flutes or saddles 49, .'lI, at the apices of the crests 33, 39. These saddles, as shown in Fig. 5, are semicircular in section, having a maximum radius directly at theV crests whichV diminishes axially because of the undulatory nature of the fins. The saddles are located adiacent the margins of the fins, and, for best results, their maximum, depth r radius is such that a line drawn through their bases, parallel to the outer surface ofthe tube 2l, will be slightly spaced from the tube, rather than intersect it. v

Infabricatingv a double coil, the central tube section 36.. is placed against a suitable bending tool, and is bent VinY its own plane, hairpin fashion, to form a return bend 42. This will bring thev right and left hand portions of the tubing 2i)V into parallelism, to provide two runs 43, 44, as shown in Fig. 3, and with the adjacent ns 2,2 of such runs either in light contact, or slightly spaced, depending upon the extent of bending; The focal Ypoint of bending the tube section 3 6V is subject to some variation. As shown in Fig. 3, it has been so displaced from a center that the crests 38, 39 of the run e?, are slightly staggered or out of phase with the crests of the run 44. By bending on Vcenten it will now be apparent that the crests of one run may be aligned with the crests of the other run, either on. the adjacent or remote fins 22.

TheV return bend 42 is next bent again, downwardly/with respect of the plane of the tubing Y fins 22 are only occasionally and randomlyv retain them against axial displacement. lThe spiral does not start from its geometric center, but some radial distance therefrom, as the views clearly show. This forms a hollow core which, in some instances, may be employed to house a small motor, or, in other instances, may be blocked with a solid disc, or, in others, be permitted to remain as it is. The coil essentially satisfies the equation of the Archimedean spiral, inasmuch as the radius at any point is directly arithmetically proportional to the arc swept out to reach such point.

As noted at the outset, Figs, 8,9; and l0 illustrate the completed double coil on an enlarged scale. After the coil has been completely wound, self tapping screws 5i may be driven through the. holes 29 and 3l into the underlying fin stock, and the ends of the wires 9 may be bent around them, thereby to secure the assemblyfrom any tendency to unwind itself. It will be seen that the crests of the convolutions of the aligned, due to the fact that the radius of the 20 toz form a curvilinear bend d5, as shown in Figs-6 and V7. isa double return bend` or hook, which may be utilized for some service applications, but such bend may also be of less extent, and no more than that required to conform it to the curvature of the spiral coil being fabricated.

TheY free ends 2'! and 28 of th tube 2l are Worked into circular section, to form sockets and 47. adapted to receive pieces 4S of aluminum tubing, by means of which the coil may be brazed to copper tubing customarily utilized in refrigeration circuits. Wires 49, preferably of greater. diameter than that of the saddles i0 and di, are next laid along the fins l22, and their ends are hooked into the holes 3d and S5 which are adjacent the return bend d2. The tubing portions 43 and 44 are then simultaneously wound on themselves to form a spiral coil, whereinA the wires 49 seat in the circumferentially aligned saddles, thereby to maintain a uniform spacing of the successive convolutions, and to The bend as herein illustrated coil progressively increases from convolution to convolution. t is also to be noted that, with spacing wires G9 of constant diameter, the. spacing between the successive convolutions is `constant, and thus the air flow or resistance to flow through the core is substantially uniform over its entire surface. ln addition to establishing such uniformity, the wires divide the air stream into paths directed toward the surfaces of the tubes 2l, and over the surfaces of the fins 22, thus assuringy maximum contact and therefore good heat transfer. Inasmuch as theA wires e9, when connected at their ends to the fins, lock the convolutions together against displacement in any direction, there is no need for special clamps or xtures to make the coil ready for mounting in a refrigeration machine.

The wires t9 may be of such diameter asis desired to provide the desired spacing of the convolutions. As shown in Fig. 8, for example,

they have the same radius as that of the saddles ll and 4|, so that the crests 38 and 39 would contact, if they were aligned. It may here be noted that Fig. 8 is a conventionalized radial section, in which such alignment is suggested, but this is due to the dimculty in showing misalignments of, the crests in a two-dimensional pen and ink sectional view. It will also be ap'- parent from Figs. 8 and 9 that the air paths from face to face of the coil are not normal to such faces, but follow courses which are inclined both upwardly and downwardly and laterallyV with respect to such faces.

The described double spiral coil is designated in Fig. 1l generally by the reference numeral Yf5.9, wherein it` is shown asan evaporator for a selfcontained or package type refrigeration system, particularly adapted for the cooling of large quantities of air on a non-frost cycle. As unit, machines of this general nature are well known, it is deemed unnecessary to illustrate in detail the customary refrigerant circuit and electrical connections. Briey described, the `unit Vcomprisesa bulkheadi of square or circular section, adapted to be inserted in an opening in a wall or floor of the cabinet or room to be cooled. On one side of the bulkheadV are depending supports 92. connectedl to flanges 93 welded to a hermetic compressor de.' A centrally:

apertured plate 65 isA secured tc the lower face of the bulkhead 6l, and an annular condenser 66 formed of finned tubing is secured to the plate 65 by bolts 61.

A motor 63 is also mounted on the plate 65 by means of a bracket 69, and the lower end of its-double ended shaft carries a fan 1| adapted to revolve in a shroud 12 mounted on the supports 62. It will be obvious that upon operation of the motor, the fan 1| will circulate air over the compressor and condenser, thereby cooling the high side of the system. So much of the machine is, of course, intended to be disposed outside of the space to be cooled, and leakage of heat from the high side into the conditioned space .is precluded by theinsulated bulkhead 6I and'a sealing gasket 13disposed around its perlineter.

The upper surface of the bulkhead 6| is dished to receive a similarly contoured centrally apertured metal plate 14, over which is disposed a mounting plate 15. Brackets 16 connected to the plate support a cylindrical housing 11 which encircles the evaporator coil 60. The lower end of the housing 11 is partially closed by a centrally apertured shroud ring 18, within which revolves a fan 19 secured to the shaft of the motor $8 which projects through the bulkhead 6|. A wire screen 8l extends across the housing 11 below the evaporator 60 and above the shroud 18, and a circular disc 82 is positioned in the upper open end or core of the evaporator coil to insure that substantially all of the air circulated thereover will pass between the convolutions thereof.

In operation, the fan 19 induces a flow of air through the open top of the housing 11, through the convolutions of the coil 60 in Contact with its knurled and corrugated ns 22, through the shroud 18 and outwardly over the dished plate 14. Moisture condensing on the coil 60 drains through the screen 8| and onto the plate 14, for disposal through a tube 83 in any desired manner. The cycling of the compressor 64 may be controlled by a customary thermostatic switch, whose power element bulb 84 is positioned in the dished plate 14, thereby making the operation primarily responsive to emergent air temperature. The tubing ends i6 and 4l' of the coil E0 are connected to the supply line from the condenser 65 and to the compressor suction line in the usual manner.

While, as noted above, the present machine is intended to operate on a non-frost cycle, and with a surface temperature of the coil 60 above freezing, conditions are frequently encountered when some frost will form on the coil. To effect its removal in a substantially automatic manner, a second thermostatic control switch is provided in the relay box S5, and its power element 86 is disposed between adjacent convolutions of the coil 60 in contact with their surfaces. This switch is adjusted to open the compressor motor circuit if the surface temperature of the coil 60 drops to a point where frost is formed, and thus override the action of the bulb 84. The ice may then melt, and any loose pieces of ice are retained on the screen 8| until they melt, and are accordingly prevented from dropping onto the blades of the fan 19.

It will be seen that the described spiral coil evaporator 63 lends itself effectively to refrigeration applications where a highly compact and eiiicient system is desired. Inasmuch as the capacity of a refrigeration machine depends, among other things, upon the length of the evaporator tubing and the extent of secondary sur- 6. face, the present evaporator provides a coil having both adequate length and iin area to provide for high capacity in a, unit of limited volume. Extended secondary surface is provided in the present coil by corrugating the fins 22, and further secondary surface is provided by the wires 49, which perform the several functions of mec chanically bonding the convolutions of the coil,

preventing axial displacements, adding strength and preventing noisy vibrations of the convolu tions by the motion of the air stream, dividing the air into paths directed against the ns and tube 2l, and also accepting heat from the ns for delivery directly to the air. 'f vIt may be additionally noted that inasmuc as the coil is relatively rigid when wound, no special spacing or retaining means are required to hold the convolutions in their desired relationship. The knurling or roughening of the surfaces of the fins 22 enhances the heat transfer capacity, and also reduces the surface tension effect between condensing moisture and the fins and tube, thereby enabling the coil to drain rapidly and remove films of moisture which otherwise would impede heat transfer.

It is therefore believed to be clear that the present invention provides a highly efficient heat exchange coil, which, when employed either as a single or multiple coil, supplies adequate tube length and secondary surface for the capacities of the other elements of the refrigeration machine. While the invention has been described with reference to a preferred embodiment, a method for its manufacture, and a typical application, it is to be understood that the scope of the invention is to be deemed commensurate with that of the following claims.

I claim:

l. A heat exchange coil comprising a continuous length of tubing formed with integral ns extending lengthwise along diametrically opposed portions thereof, said fins being corrugated outwardly from the tubing to their margins into substantially sinusoidal formations of increasing amplitude, reentrant saddles formed in the crests of the corrugations, said saddles being located adjacent the margins of the fins and being aligned lengthwise thereof, wires positioned in said saddles and anchored to the ends of the fins, said tubing, ins, and wires being wound spirally into a coil having a plurality of. convolutions, said wires engaging the saddles of the fins of adjacent convolutions and spacing and retaining said convolutions from displacement.

2. A spiral heat exchange coil asset forth in claim 1, wherein the crests of the convolutions of the opposed fins are staggered with respect to each other lengthwise of the tubing.

3. A spiral heat exchange coil as set forth in claimA 1, wherein the surfaces of the lns are formed with small indentations to provide roughened surfaces on said fins.

4. A spiral evaporator coil as set forth in claim 1, wherein the continuous length of tubing is formed with a return bend substantially midway between its ends, thereby to form a double coil having sections disposed alongside of each other.

5. A spiral heat exchange coil comprising a continuous length of relatively iiat tubing formed on opposite sides thereof with integral fins extending longitudinally and along its narrow dimension, said fins being corrugated into an undulatory contour along their margins progressively diminishing to their junctions with the tubing, the crests of said corrugations being disposedabove theat surfacesof the tubing along their margins and beingI staggered with respectv toeach other on opposite sides of the tubing, transversely arcuate reentrant saddles formed in the crests and being aligned lengthwise of the iins, said tubing and ns being Wound into a spiral, having its innermostv convolution spaced from the geometric center of the coil, said fins having spacing wires of uniform diameter in said saddles of each iin to maintain the convolutions in fixed position relative to each other and to provide unit air passageways between the convolutions axially of the coil ofv substantially constant size, said Wires having a diameter at least as great as that of the saddles, means for an- 15 horing the. ends or thewires'to the Y11 s,saigi ns being lightly knurled to provide. ronghened surfaces on said ns. Y

References Cited in the filev ofV this patent* UNITED STATES PA'lIEN'lSv` Number Name Y Date`l 1,822,068 Summers T.-. W Sept. 8, 1931 10 2,241,186 Coons i May 6., 13,41 2,347,957 McCullough V V- .T May 194,4L

FOREIGN PATENTS Number Country Date 239,413 Germany `.i -.v-.-, Apr. 15.191,9

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