The behaviour of water in the refrigerating cycle of automotive air conditioners that use R134a (a hydrofluorocarbon [HFC]) was experimentally investigated in detail. First, the saturated water content in the gas phase of R134a was determined. Second, the water content at both the inlet and outlet of the expansion valve and in the evaporator was measured in detail. These results showed that when the water content at the inlet of the valve was more than 500 ppm, water condensation (hereinafter called free water) occurred in the gas phase during evaporation, although no free water occurred in either the gas or liquid phase at the outlet of the valve. These data were measured under the following conditions - high pressure, 230 psi (1.6 MPa) - low pressure, 43.5 psi (0.3 MPa) - flow rate of refrigerant, 3.7 lbm (100kg/h) - flow rate of oil, 0.1 lbm (3kg/h). A polyalkylene glycol lubricant with water solubility of 1.1% at 25 deg C was used. Based on these results a new refrigerant drying technology was developed. With this method, free water could be generated again by cooling part of the superheated gaseous refrigerant coming out of the evaporator. This water could then be filtered and discharged into the atmosphere by employing a water-selective permeation membrane.

KEYWORDS: motor cars, air conditioning, unit air conditioners, refrigerants, R134a, drying, behaviour, water, measuring, refrigeration.