GB511000A - Improvements in or relating to heat transfer - Google Patents

Abstract

511,000. Refrigerating; heating systems. ELECTROLUX, Ltd. Sept. 29, 1938, No. 28362. Convention date, Sept. 30, 1937. [Classes 29 and 64 (ii)] The evaporator or cooling body 13, Fig. 1, of a refrigerating cabinet 10 is heated at intervals, to defrost it or to modify the temperature of the storage space, by a closed cycle condensing heat transfer system comprising an evaporator element 22 in the storage space and another evaporator element 26 adjacent the heated generator 17 of a refrigerating apparatus at the back of the cabinet, the evaporator elements being connected with a common condenser element 20 in the form of a coil attached to the cooling body 13. The coil 20 is connected to a conduit 19 from which a small-bore inverted U-tube 28 and a wider bore tube 23 lead to a reservoir 24 supplying the warmer evaporator element 26. During ordinary cooling periods the heat transfer medium, ethyl alcohol or glycerine, evaporates slowly from the cabinet element 22, which is warmer than the condenser element 20, and condensate gradually accumulates at the bottom of conduit 19 and small bore tube 28 and eventually syphons through this latter tube into the reservoir 24 and evaporator 26. The tube 28 is formed into a coil 29 within the reservoir 24 to delay the liquid flow, while the tube 23 acts as a vent pipe. As soon as liquid enters evaporator 26 it evaporates and defrosting begins, the liquid flow continuing through the small bore tube 28 by reason of equalization of vapour pressure at its ends through the vent tube 23. The vapour passes through conduit 23 and again condenses in coil 20, the condensate being pressed up to the top of the coil and delivered through conduit 21 to the evaporator element 22, now at lower pressure. Melted frost is collected in a pan 31 and led through a pipe 32 to an evaporating tray 33 heated by the flue 18 of the refrigerating generator 17. The cabinet evaporator element 22 may be disposed or screened so that a long period of evaporation, say twenty-four hours, is required before the syphon 28 is primed, while the evaporation in the other element 26 and defrosting may be effected in a few minutes. In order to control these relative periods the syphon tube 28 may be formed as a double helix 40, Fig. 2, of flexible metal, which may be altered in height to vary the position of the overflow point 60 by a regulating screw 44. A reservoir 46 may be provided in the conduit 19. In another arrangement an inclined flexible U-tube may be employed for the syphon, adjusted in inclination by a thermostat. Alternatively the conduit 19 man be connected through a depending pipe with the evaporator element 26, a valve in this pipe being controlled by a thermostat. The system maybe adapted for alterations of such frequency as to modify the cooling effect in the cabinet of the cooling body 13. The secondary cabinet evaporator element may be adapted to serve as the space cooling element 71, Fig. 5, the primary cooling body 13 then serving only for ice production, and the thermostatic control of the syphon may be varied or disabled for rapid ice-making. In this arrangement a conduit 73 connects the conduit 19 with a bellows chamber 74 having an outlet 76 into a chamber 82 connected by a pipe 86 with the evaporator element 71. The bellows chamber 78 of a cabinet thermostat 81 is mounted over the first bellows and the two bellows are adjustable by a screw 84 to vary the outlet 76 relatively to the fixed overflow point 72 of the syphon tube 28. In order to ensure manual restoration of thermostatic control after disablement the cap 79, Fig. 6, of the thermostatic bellows may be connected by a lever 90 to a spring catch 92 engaging the lip 93 of an icemaking tray, so that removal of the tray necessitates release of the catch and lever.