In an air-conditioning or refrigeration system, a small amount of oil migrates from the compressor and into the refrigerant. Thus the working fluid is not only a refrigerant but a refrigerant and oil mixture. The effects of oil on basic mechanisms such as pressure drop and heat transfer are not well understood. More importantly, a very serious problem exists if the oil does not return to the compressor. With regards to the latter, some information is available on minimum tonnage required to transport oil in suction and hot gas risers(l). However, this data is thought to have insufficient experimental verification, and it is the purpose of the paper to report more definitive results on oil transport.

The experimental facility required to carry out this objective will be discussed first, followed by an explanation of empirical relationships and the correlated results. The data is also cast in engineering terms that will be useful to the practicing engineer.