DE-2532 (RP 109) -- Pressure Loss and Liquid Transport of Oil-Refrigerant Mixtures in Suction and Discharge Lines PDF

In an air-conditioning or refrigeration system, a small percentage of the lubrication oil migrates out of the crankcase and into the working fluid. Two main concerns associated with this phenomenon are (i) what is the effect of this oil on the pressure drop in the system and (ii) under what conditions is the oil transported back to the compressor? Both questions have a direct relationship to the sizing of components and the efficiency of the unit. In relation to the second question, a deficiency of oil in the crankcase will eventually cause the system to shut down because of lack of lubrication.

In two previous papers, experiments were described and correlations developed for the effect of oil on pressure drop and the necessary conditions for oil transpor in suction and discharge lines (1,2). It is the purpose of this discussion to. report the recasting of these correlations in a form which is more directly applicable to the industry. Computations are also included for the first time for R-502 and R-500. Although the original experimental studies were conducted only with R-12 and R-22, the nature of the correlation suggest that extension can be made to other refrigerants.

A brief synopsis will be given of the appropriate relationships along with an explanation of the tabulated results. For further details of the experimentsand the bases for these correlations, refer to Ref. 1 through 3.