AN ULTRASONIC DEVICE FOR MEASURING THE OIL CONCENTRATION IN FLOWING LIQUID REFRIGERANT

Liquid refrigerant/oil concentrations in a flowing system were monitor ed using speed of sound and temperature measurements. Data were taken for dichlorodifluoromethane (R12) with 3GS and 5GS oils and tetrafluor oethane (R134a) with an ester-based oil with concentrations ranging fr om 0.0 to 10.64 and 0.0 to 9.11 mass%, respectively. Temperatures for the tests ranged from -22-degrees-C to 40-degrees-C. Analysis of the d ata showed that the predicted oil concentration depends linearly on bo th acoustic velocity and temperature. The technique was very reliable, with uncertainties of less than 0.23 wt% for the R12 mixtures and 0.2 6 wt% for the R134a mixtures at typical system concentrations. A sligh t dependence of acoustic velocity on pressure was found.