Refrigerator

Abstract: A refrigerator (10) has a compartment (14) to be refrigerated and a refrigerant evaporator (18) normally operable at frost producing temperatures to refrigerate the compartment (14). The evaporator (18) includes an elongated tube (36) to receive refrigerant with an elongated spine fin ribbon (40) wrapped in an open spiral about and in intimate heat exchange contact with the tube (36). The ribbon (40) includes an elongated base (42) with a continuous series of fingers (44) projecting outwardly of the tube along each edge of the base (49). The space (55) between adjacent passes of ribbon (40) is greater than the width (52) of the base (42).

Description: BACKGROUND OF THE INVENTION For many years spine fin tubing has been used in heat exchange structures for air conditioners. In such heat exchangers the spine fin ribbon is wrapped about the evaporator tubing in a very tight knit fashion; that is, the spine fin ribbon is wound so that adjacent passes of ribbon are in contact and the fingers or spines are very closely spaced. With such a construction the spines or fingers provide a very large total surface area for heat transfer. At the same time the spines or fingers are so closely spaced that the overall structure acts much like a cylinder during manufacture. One attribute of that construction is that the spines are mutually supportive and resist being depressed or folded over when the tube is handled. One reason that air conditioner heat exchangers can use spine fin tubing with closely packed, very thin spines is that during normal operation they are not subjected to a build up of frost (frozen condensation). Despite the successful use of spine fin tubing in air conditioners for many years, such heat exchange structures have not been used in refrigerator evaporators. It has been the belief of many experienced practitioners that spine fin materials are not suitable for use in refrigerator evaporators. One basis for the belief was that the frost build up in a refrigerator evaporator quickly would render the spine fin ineffective as a heat transfer structure. In addition it was believed that the spine fin structure, as used in air conditioners, was too delicate to withstand the handling involved in manufacturing and installing refrigerator evaporators. On the other hand it was believed that, if the size of the spines were increased sufficiently to withstand the rigors of manufacturing, then the evaporator would not have sufficient heat exchange capacity to be effective with the stringent size limitations normally imposed upon such evaporators. Some proposals have been made for using fins in evaporators for refrigerators such as FR-A-1060659 and US-A-4527624 but these have either used radial fins or a relatively complicated tube structure. Accordingly, this invention seeks to provide an improved refrigerator with an evaporator incorporating a spine fin heat exchange structure. SUMMARY OF THE INVENTION According to the invention, there is provided a refrigerator having a compartment to be refrigerated and a refrigerant evaporator normally operable at frost collecting temperatures to refrigerate said compartment; said evaporator including an elongated tube to receive refrigerant and an elongated spine fin ribbon wrapped about said tube in an open spiral configuration; said ribbon including an elongated base strip in intimate heat transfer contact with said tube and a substantially continuous series of fingers projecting outwardly of said tube along the lateral edges of said base strip characterized in that the pitch of the spiral wrap of said ribbon is such that the distance between adjacent turns of the ribbon is greater than the width of the base strip to enhance the ability of the evaporator to effectively transfer heat from the air to the refrigerant as frost builds up around the tubing. BRIEF DESCRIPTION OF THE DRAWINGS The invention will now be described in greater detail, by way of example, with reference to the drawings in which: FIG 1 is a fragmentary cross-sectional side elevation view of a refrigerator incorporating one embodiment of the present invention; FIG 2 is a cross-sectional view taken laterally of the tubing of FIG 1; FIG 3 is a fragmentary cross-sectional view taken longitudinally of the tube of FIG 1; and FIG 4 is a fragmentary perspective view of the tube of FIG 1, partly broken away. DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to Fig. 1, a refrigerator 10 includes an outer cabinet 12 containing a freezer compartment 14 and fresh food compartment 16. The freezer compartment 14 is maintained at sub-freezing temperatures and the fresh food compartment 16 at above freezing-food preserving temperatures by circulating air through these compartments and over an evaporator 18 positioned in a vertically disposed evaporator chamber 20 positioned behind the freezer compartment 14 and separated from it by wall structure 22. More specifically, a fan 24 positioned in the upper portion of the evaporator chamber or compartment 20 discharges air through openings 26 in the wall 22 into the freezer compartment 14 and through a passage, partially shown at 28, to the fresh food compartment 16. The fan also draws air from within the freezer compartment 14 and fresh food compartment 16 back into the evaporator compartment 20 and over the evaporator. The return air from the freezer compartment flows through a passage partially shown at 30 while the air returned from the fresh food compartment flows through passage 32. The freezer compartment 14 is maintained below freezing while the fresh food compartment 16 is maintained above freezing by an appropriate division of air being discharged from the evaporator compartment 20, with the majority of the air going to the freezer compartment 14 and a smaller portion of the air going to the fresh food compartment 16. In order to maintain the freezer compartment 14 at sub-freezing temperatures, it is necessary that the evaporator 18 operate at below freezing temperatures, with the result that moisture contained in the air flowing through the evaporator chamber 20 collects on the outer surfaces of the evaporator in the form of frost. Periodically this accumulated frost is removed from the evaporator surfaces by energizing a heater 34 positioned in radiant and convection heating relationship with the evaporator surfaces. Refrigerator evaporators transfer heat from the air passing over the outside of the evaporator surface to the refrigerant flowing through the inside of the evaporator so as to cool the air. A typical refrigerator evaporator consists essentially of an elongated tube carrying refrigerant which is bent or formed into a serpentine configuration in order to fit in a more confined space and, thus, take up less room in the refrigerated compartments of a refrigerator. In order to enhance the heat transfer characteristic of the evaporator it is well known to provide some kind of fins extending outwardly from the tube to increase the surface area for transfer. With refrigerator evaporators, particularly those which provide cooling for freezing compartments, it is necessary for the evaporator structure to provide effective heat transfer even though a considerable body of frost has built up around the evaporator tubing. To this end, the greater the space provided between adjacent fins or adjacent rows of fins the longer effective air flow past the evaporator will take place. On the other hand, larger fin spacings reduce the number of fins and the total available heat transfer surface area. In the evaporator 18, a tube 36 is formed and disposed in a fashion well known in the art. That is, the tube 36 is bent in the form of serpentine to provide a plurality of horizontal conduit passes disposed in a vertical spaced arrangement connected by return bends. The overall layout of the evaporator 18 is a generally rectangular construction with the various passes of the tube 36 supported in spaced relationship on opposed frame members, one of which is shown at 38, at opposite sides of the evaporator 18. The frame members 38 mount the evaporator 18 in a generally vertical position within the evaporator chamber compartment 20 but slightly angled with respect to the vertical to more fully expose the horizontal passes of the tube 36 to the return air flowing upwardly through the evaporator compartment 20. The radiant heater 34 is periodically energized to warm the evaporator surfaces to defrosting temperatures. This heater conveniently may be of the type disclosed in co-pending application (90-HR-17667), assigned to General Electric Company, assignee of the present invention. As best seen in Figs. 2, 3 and 4, the evaporator 18 includes an elongated spine fin ribbon 40 wound or wrapped about the outer surface of tube 36 in an open spiral configuration. That is, each pass (one circumferential circuit around the tube) of the ribbon 40 is spaced apart from the longitudinally adjacent passes of the ribbon. More specifically, the ribbon includes a base 42 and a plurality of spines or fingers 44. The fingers 44 are arranged in rows 46 and 48 along the lateral edges of the base 42. Each of the rows 46 and 48 is formed of a substantially continuous series of fingers 44. That is the fingers are formed adjacent to each other without significant spacings between them where they join the base 42. When wrapped around the tube 36, as shown in Figs. 2-4, the fingers extend outwardly from the outer surface of the tube 36 adjacent the lateral edges of the ribbon base 42 and, preferably, they are disposed generally perpendicular to the outer surface tube 36. The pitch of the ribbon wrap, that is the number of windings of ribbon per longitudinal unit length of the tube is such that the adjacent passes are spaced apart, as indicated at 55. Preferably, the spaces 55 between adjacent passes and the width of the ribbon base 42 or distance between the rows of fingers 46 and 48, as indicated at 52 are asymmetric, i.e. the distance 55 between adjacent turns of the ribbon 40 is greater than the width of the base strip 42. This asymmetric spacing of the rows of fingers enhances the ability of the spine fin evaporator to continue to effectively transfer heat from the air to the refrigerant as frost builds up around the tubing 36. In household refrigerator evaporators subject to frost build-up, spacing between 0.762 mm (.030 inch) and 13.97 mm (.550 inch) is preferred. In a preferred embodiment of the present invention, the spines or fingers 44 are sized to optimize the effective available heat transfer surface while providing sufficient strength for the essentially free-standing fingers that the manufacturing process does not materially depress or bend over so many fingers as to adversely affect the subsequent operation of the evaporator. In a particular embodiment, in which the evaporator tube has an outer diameter of 9.525 mm (0.375 inch), the fingers were 8.89 mm (0.350 inch) long (that is in the dimension perpendicular to the tube 36), 0.838 mm (0.033 inch) wide (that is in the direction generally circumferential of the tube 36) and 0.229 mm (0.009 inch) thick (that is in the direction longitudinally of the tube 36). In a preferred embodiment of the present invention, both the evaporator tube and spine fin structure were made from aluminum; however, other materials may be used. In household refrigerator evaporators subject to frost build-up, fins or fingers between about 1.27 mm (.050 inch) and 101.6 mm (4.00 inches) long; between about 2.54 mm (.010 inch) and 5.08 mm (.200 inches) wide and between about 0.2032 mm (.008 inch) and 0.762 mm (.030 inch) thick are preferred.

Claims: A refrigerator (10) having a compartment (14,16) to be refrigerated and a refrigerant evaporator (18) normally operable at frost collecting temperatures to refrigerate said compartment (14,16); said evaporator including an elongated tube (36) to receive refrigerant and an elongated spine fin ribbon (40) wrapped about said tube in an open spiral configuration; said ribbon including an elongated base strip (42) in intimate heat transfer contact with said tube and a substantially continuous series of fingers (44) projecting outwardly of said tube along the lateral edges of said base strip (42) characterized in that the pitch of the spiral wrap of said ribbon (40) is such that the distance (55) between adjacent turns of the ribbon is greater than the width of the base strip (42) to enhance the ability of the evaporator to effectively transfer heat from the air to the refrigerant as frost builds up around the tubing. A refrigerator as set forth in claim 1 wherein said fingers are between 1.27mm (.050 inch) and 101.6mm (4.00 inches) long, between 2.54mm (.010 inch) and 5.08mm (.200 inch) wide and between 0.2032mm (.008 inch) and 0.762mm (.030 inch) thick. A refrigerator as set forth in claim 1 or 2 wherein the distance longitudinally of said tube between adjacent passes of ribbon is between about 0.762mm (.030 inch) and 13.97mm (.550 inch).

Inventors: BEERS DAVID GARDNER, BEERS, DAVID GARDNER
Applicants: GEN ELECTRIC, GENERAL ELECTRIC COMPANY
Application year: 1991
Main classification: F25B39
IPC codes: F28F1, F25B39, F25D19, F25D17