AN EXPERIMENTAL-STUDY OF SUBCOOLED FILM BOILING OF REFRIGERANTS IN VERTICAL UP-FLOW

Subcooled film boiling has been investigated experimentally for vertic al up-flow in a directly heated tube using the refrigerants R-12, R-22 and R-134a as test fluids. The data cover a mass flux range of 530-30 00 kgm(-2) s(-1), an inlet subcooling range of 8-28 degrees C and a pr essure range of 0.83-1.6 MPa (corresponding to an approximate water pr essure range of 5-7 MPa, based on an equal liquid-to-vapour density ra tio). To the authors' knowledge, these are the first flow film boiling data obtained for R-134a and R-22. The results show strong effects of mass flux, inlet subcooling and pressure on the heat transfer coeffic ient. Also, the data exhibit complex trends of the heat transfer coeff icient as a function of thermodynamic equilibrium quality. Because of the wide range of conditions covered in this study, a systematic exami nation of the effect of flow parameters and fluid properties on the he at transfer coefficient was performed, and this has provided a unique insight into the heat transfer mechanisms. Copyright (C) 1996 Elsevier Science Ltd.