Micro-channel flow boiling heat transfer of R-134a, R-236fa, and R-245fa

The rapid development of micro-thermal technologies has conveyed an increasing interest on convective boiling in micro-channels. Although there is general agreement that these systems may be able to dissipate potentially very high heat fluxes per unit volume, their heat transfer characteristics are still unclear and require investigation. The present study illustrates heat transfer data for flow boiling in a single micro-channel, for two channel diameters, namely, 510 and 790 mu m, three fluids, namely, R-134a, R-236fa and R-245fa, mass velocities from 300 to 2,000 kg/m(2) s, and heat fluxes up to 200 kW/m(2). Stable flow boiling heat transfer data are analyzed through a parametric investigation, and are also confronted with measurements in the presence of two-phase oscillatory instabilities, which were found to significantly change the trends with respect to vapor quality.