Heat transfer to oil-refrigerant mixtures evaporating in tubes

The main objective was to determine the quantitative effect of oil on flow and surface heat transfer characteristics of a refrigerant evaporator during two phase forced convection. This was achieved by measurements on a test evaporator which permitted the evaluation of local heat transfer coefficients and pressure gradients. The dependence of heat transfer coefficient on mass velocity, vapor mass fraction, and heat flux was studied with varying amounts of oil. Three 10 foot lengths of 3/8 inch O.D. stainless tubing separated by short glass tubes form the test evaporator which was heated electrically to produce a uniform heat flux. Local wall temperatures were measured by 93 thermocouples along the top, side and bottom of the heated tube sections.