Pressure Drop During Two-Phase Flow of Refrigerants in Horizontal Smooth Tubes

摘要

A single tube evaporator test facility capable of measuring pressure drop and heat transfercoefficients inside horizontal tubes has been designed and developed at the Air Conditioning andRefrigeration Center at the Univ~ity of illinois. Baseline testing with R-12 and testing with R-134a, an ozone-safe refrigerant, have been completed. Tests were conducted using purerefrigerants and refrigerant-oil mixtures. For the refrigerant-oil testing, PAG and Ester oils wereadded to R-134a and mineral oils were added to R-12 with the oil concentration varying from 0to 5% by weight. The observed flow regimes were predominantly annular. A new correlationfor two-phase frictional pressure drop inside smooth tubes was developed for pure refrigerantsusing the Lockhart-Martinelli parameter "Xtt" and Eroude number "EI'J.". The two dimensionlessparameters predicted the-data well within the range of parameters considered in this study. Inaddition, a functional dependence between the ratio of the pressure drops with and without oiland the oil concentration "0)" was developed.