Experimental evaluation of spray cooling of R-134a on plain and enhanced surfaces

An experimental assessment of the heat transfer coefficient in spray cooling of plain and enhanced upward-facing surfaces is presented. All surfaces of the heater were thermally insulated apart from the top end, onto which pieces with different surface geometries were attached. Average surface temperatures were obtained from four small thermocouples. Three copper surface geometries were evaluated: a plain surface (reference), a 10-pore-per-inch metal foam (90% porosity), and a surface with six 3-mm high 2-mm wide radial grooves. The surface areas of the latter surfaces were 5.1 and 2.2 times larger than that of the plain surface. Boiling curves are presented for increasing heat flux. A base area heat transfer coefficient enhancement factor of 1.35 is obtained for the copper-foam surface, for a coolant flow rate of 3 kg h−1 (8.333 × 10−4 kg s−1). The type of surface geometry is not seen to affect significantly the critical heat flux.

► Comparison of boiling curves for spray cooling on plain and enhanced surfaces.
► Enhanced surfaces are a 10-pore-per-inch copper foam (90% porosity) and a grooved copper surface.
► Heat transfer coefficient enhancement factor of 1.35 was obtained for the copper foam surface.
► Surface type did not influence significantly the critical heat flux.