| 摘要 |
998,719. Refrigerating. DUNHOM-BUSH Ltd. Nov. 14, 1961 [Nov. 14, 1960], No. 40696/61. Heading F4H. In a compressor-type refrigeration system, the evaporator is defrosted by passing hot refrigerant from the compressor through a defrosting circuit which includes a heat exchanger in which the compressed refrigerant heats refrigerant returning to the compressor to evaporate any liquid refrigerant, and is reduced in temperature before entering the evaporator. As shown, Fig. 1, the refrigeration system comprises a compressor 2, condenser 4, receiver 6, heat exchanger 10, and evaporator 14. The defrost circuit comprises a hot gas by-pass line 32 leading from the compressor output line 3, through a strainer 34 and a solenoid valve 36, to a header 33 of the heat exchanger 22. A line 38 from the heat exchanger leads to the evaporator, the line passing under a condensate drain line 30 and having a loop or branch 43 under a drip tray 28. The hot refrigerant passes through an internal tube 40 in the evaporator to an outlet regulating valve 42, and a line 44 opening into the main refrigerant suction line 20. The evaporator consists of a number of tube assemblies, Fig. 3, joined in series and mounted in an external fin assembly 54, each tube assembly comprising a fin arrangement 56 in the annular passage between an inner tube 50 and an outer tube 52. The annular passages 58 carry liquid refrigerant during normal operation, and the inner tubes 50 carry warm refrigerant during defrosting. Return refrigerant from the evaporator passes from line 20 into the body of the heat exchanger 22 and leaves through line 24, any liquid refrigerant being trapped to the right of a baffle in the heat exchanger with its top edge above the heat exchanger centre line. This liquid is evaporated during defrosting by the hot refrigerant in the tubes 72 extending between headers 33, 37. A small slot at the base of the baffle allows oil to return to the compressor. To initiate a defrosting operation, a solenoid valve 46 at the evaporator inlet is closed by a time clock. The compressor 2 continues to operate until all liquid refrigerant has been evaporated from the evaporator. A fan 16 for the evaporator is then stopped by a thermal switch (not shown), and the valve 36 is opened. Hot gas pressure in the defrost circuit rises under control of the valve 42 and the compressor restarts. Defrosting of the evaporator then proceeds, with substantial condensation of refrigerant in line 38 and evaporator inner tube 40. The defrosting operation is terminated by the evaporator thermal switch which closes valve 36, opens valve 46, and after an interval restarts evaporator fan 16. U.S.A. Specifications 2,611,585 and 2,611,587 are referred to. |
