Nucleate and film boiling heat transfer in R11: The effects of enhanced surfaces and inclination

A study of pool boiling heat transfer in Rll is reported as functions of surface characterization and inclination. Two specially prepared metal sprayed surfaces and flat copper and steel surfaces were subjected to heat fluxes to 180 kW/m/sup 2/ with surface orientations varying from horizontally facing downward (1800), to vertical (900), to horizontally facing upward (00). The resulting nucleate boiling curves display considerable boiling hysteresis with the hysteresis temperature difference decreasing with increase in angle of inclination. Minimum film boiling heat fluxes and temperature differences generally decrease with increase in angle of orientation. At 00 as surface roughness and porosity are increased the minimum film boiling heat flux and temperature differences increase. For 1800 the minimum heat flux is only slightly affected by surface characteristics whereas the surface superheat is moderately influenced as compared to 00. The results obtained are compared with values determined from existing theoretical and experimental work