Flow of oil-refrigerant 12 solutions through horizontal capillary tubes and application as an oil return device for refrigerant compressores

The flow of oil-Refrigerant 12 (Dichlorodifluoromethane) solutions through horizontal capillary tubes was studied. The effect of different concentrations of solution on the mass flow through tubes of different bores and lengths was the primary concern. This is a now field of investigation; no previous work had been published on measurement of mass flows of such solutions. Although the capillary tube had been extensively used as an expansion device in refrigeration systems, specially in the smaller, and the hermetically sealed units, all investigations have been limited to the flow of R 12 only. New experimental techniques had to be developed to measure the mass flow of oil-R12 solutions, as none of the methods used by previous investigators on R 12 flow only, was suitable. Interest in the flow of Oil - R 12 solutions arose from the lack of published data which might be applied to the design of the capillary tube as an oil return from the oil separator to the compressor crank case. This would provide a simple substitute for the usual, expensive and complicated float valve mechanism. By arranging the tubes as a bypass in a main refrigeration circuit, complete control of the conditions was possible without having to establish a steady state in the main circuit. This improved accuracy, reduced the time required, so enabling a comprehensive series of tests to be conducted. The pressure and temperature distribution along the tube were also observed. The analysis of the problem was hindered by the lack of adequate basic data on the properties of Oil, O2 solutions at the relevant conditions. However, the mass flow of solutions has been compared with the actual and theoretical individual flows of it 12 vapour and oil. The investigation provided the necessary data and showed that the capillary tube could be a simple and inexpensive substitute for the usual oil return device. Such a tube could now be designed to deal with compressor operating conditions where the maximum oil pumped over is known. At compressor conditions with smaller oil flows some loss of refrigerating capacity mould be inevitable due to intermittent R 12 vapour leakage. It is shown that this loss is not large and that steps can be taken to reduce it