In certain types of application of refrigeration systems, partIcular advantages arise in the use of a so-called "liquid recirculation system." The refrigerant evaporator is fed an oversupply of liquid refrigerant, i.e., more than the amount necessary to produce the required refrigerating effect through evaporation. Liquid overfeed ratios of up to 5:1 are commonly used. In the design of such systems, there arises the problem of sizing the piping, which carries the two-phase gas-liquid mixture.

Over the past 25 years there have been extensive investigations of the flow dynamics, heat, and mass transfer processes associated with two-phase fluids. During the period from 1962 to 1966 Gouse compiled a listing of over 5000 references on two-phase flow processes. He estimated an expenditure of $22,500,000 on the research leading to those publications. The rate of publications in the past seven years have now probably doubled that figure.

Dukler and co-workers, under the sponsorship of the American Gas Association and American Petroleum Institute, collected and compared two-phase pressure drop measurements from some 100 sources. Over 8600 data points were included in their study. A critical comparison of proposed pressure drop correlations using this data was made by Dukler, Wicks, and Cleveland in 1964.

It was the purpose of this investigation first, to examine the existing two-phase literature, with emphasis on updating the information on pressure drop since 1965. Secondly, it was intended to identify quantitatively the most promising methods of pressure drop calculation for use in pipe sizing of refrigerant recirculation suction lines.

Finally, it was proposed to prepare pipe design tables for use over the range of conditions encountered in refrigerant recirculation systems using R12, R22, R502, and R7l7 (ammonia).