TWO-PHASE FLOW OF R245FA IN A 1 MM CORRUGATION DEPTH PLATE HEAT EXCHANGER - PART II: FLOW BOILING HEAT TRANSFER

This article is the second in a two-part study on two-phase flow of R245fa in a new promising and more compact plate heat exchanger (PHE). Two-phase adiabatic frictional pressure drops were detailed in Part I, while the flow boiling heat transfer coefficients were obtained and the results presented here in Part 11. Upward flow boiling heat transfer was investigated locally within the PHE prototype using an 1R camera to measure the local PHE wall temperatures with high resolution. A new experimental approach for PHEs was introduced in order to reduce the data and obtain the local pixelby-pixel flow boiling heat transfer coefficients throughout the PHE. The influences of heat flux, mass flux, saturation temperature, vapor quality, and inlet condition on flow boiling heat transfer coefficients were obtainable. During the tests, the vapor qualities changed from 0 to 0.78 for mass fluxes from 7.5 to 40 kg m(-2) s(-1), heat fluxes from 250 to 3700 W m(-2), and saturation temperatures from 19 degrees C to 35 degrees C. In addition, comparative flow boiling experiments were carried out with a small subcooling and then repeated with liquid-vapor (x(in) approximate to 0.1-0.2) flow at the PHE inlet. Several of the most widely used prediction methods in the PHE literature were evaluated with respect to the current mean and quasi-local (obtained in six windows) experimental databases. The prediction methods mostly showed a better agreement with the mean flow boiling heat transfer coefficients rather than the local database.