Patent ID: 7506518

Claim:
A refrigeration device comprising: a main refrigerant circuit including a compressor that compresses gas refrigerant from a first pressure to a higher second pressure, a first heat exchanger configured to dissipate heat from the refrigerant gas at the second pressure, a receiver that stores liquid refrigerant condensed by the first heat exchanger, and a second heat exchanger configured to allow the refrigerant gas to absorb heat at the first pressure; and a liquid level detection circuit configured and arranged to detect if a liquid refrigerant level in the receiver is at a predetermined position, the liquid level detection circuit being configure to: extract a portion of refrigerant from the receiver at a predetermined level within the receiver, reduce the pressure of the portion of the refrigerant extracted from the receiver, heat the portion of the refrigerant after reducing the pressure of the portion of the refrigerant, measure the temperature of the portion of the refrigerant after heating the portion of the refrigerant, and return the portion of the refrigerant to an intake side of the compressor after measuring the temperature of the portion of the refrigerant, a refrigeration cycle operation at the second pressure of the refrigerant flowing into the receiver with the enthalpy of the refrigerant such that a slope or inclination of a vapor line of a pressure-enthalpy graph at the second pressure is negatively sloped or inclined downward toward a higher enthalpy and lower pressure portion of the graph.