UN SISTEMA DE REFRIGERACION.

摘要

1,226,452. Automatic temperature control. CONTROLS CO. OF AMERICA. July 22, 1968 [Aug. 11, 1967], No.34804/68. Heading G3R. A refrigeration system comprises an expansion valve 16 operable to control refrigerant flow from a condenser 12 to an evaporator 14, a valve actuator 36, 40 responsive to an electrical signal to control the flow in dependence on the temperature of a thermistor 50 exposed to respond to either or both the temperature and physical state of the refrigerant. Valve actuator comprises a bi-metal plate carried on the end of needle valve 26, heated by a winding 36 and urged by spring 40 into contact with a metal ring 46. Thermistor 50 is suspended by its leads 52, 60 to contact the refrigerant and the leads 52, 60 pass into a thermally and electrically insulating terminal assembly 56. Thermistor 50 is connected in series with batteries 66, a manual or bi-metallic switch 68 which also controls the compressor 10, a variable resistor 86 to set the overall flow of refrigerant, and heater winding 36. A switch 88 shunting resistor 86 permits operation at a higher level. A high value resistance 82 in parallel with thermistor 82 increases its sensitivity. Thermistor 50 has a negative temperature co-efficient so that current through it rapidly increases on closing switch 68 thereby causing bi-metal winding 36 to heat bi-metal plate 38 and open the normally closed expansion valve 16. When excess refrigerant is passed through the evaporator 14 the thermistor 50 responds immediately to the change to liquid state, its resistance increases and the valve 16 tends to reclose. A normally open switch 84 controlled by a temperature sensitive element 85 exposed to evaporator 14 shunts thermistor 50 whenever there is the danger of evaporator freeze up. In Fig. 2 (not shown) two thermistors are strapped to the inlet and outlet ends of the evaporator so that their self heating effects are reduced. Increase in outlet temperature of the evaporator is detected by the outlet thermistor which causes valve 16 to open. Increase in inlet temperature is sensed by the inlet thermistor which causes an increase current flow in a circuit in parallel with the valve actuator thereby tending to close valve 16. The inlet and outlet thermistor therefore tend to maintain the temperature differential across the evaporator constant. A switch permits just the inlet thermistor to control valve 16 to maintain the evaporator temperatures and pressures constant.