Flow boiling of nanofluids of water and Al2O3 inside a 1.1 mm round channel

摘要: This study presents new heat transfer coefficient (HTC) data obtained during saturated flow boiling of solutions of alumina nanoparticles and DI-water. The main objective of the paper is evaluating the effect of nanoparticles concentration on the HTC. The experiments were performed for a stainless steel tube (AISI-304), 200 mm long and with an internal diameter of 1.1 mm. Results were obtained for mass velocities of 200, 400 and 600 kg/m²s, heat fluxes up to 400 kW/m², nanoparticles with diameter of 20-30 nm and volumetric concentrations of 0.1, 0.01 and 0.001%. The data shown that the flow boiling heat transfer coefficient decreases with the addition of alumina nanoparticles to DI-water for volumetric concentrations of 0.01 and 0.1%. No penalty on the heat transfer coefficient was observed for the volumetric concentration of 0.001%. The lowest heat transfer coefficient for flow boiling was observed for the experiments with DI-water after performing the tests with nanofluids. The boiling process promoted the deposition of a layer of nanoparticles on the test section surface that results an additional thermal resistance. For single-phase flow, the heat transfer coefficient increased about 30% for a volumetric concentration of 0.1% relative to pure DI-water. This behavior seems related to the increase of the thermal conductivity with the nanoparticle addition. After the test section being submitted to flow boiling experiments with nanofluids, thermal instability effects during flow boiling were reduced independently of the nanoparticles concentration.