Experimental study of the heat transfer coefficient at boiling of the nano-refrigerant of R141b/TiO2 nanoparticles on the surfaces with different wettability

The adding of the nanoparticles into the refrigerants is one of the promising and low-expensive ways to intensify the boiling processes in the evaporators of the refrigerators. The experimental studies in this area available currently are not numerous and contradictory. Therefore, the study of the effect of nanoparticles additives on the boiling process of the model refrigerant is currently important. The results of an experimental study of the influence of the additives of the TiO2 nanoparticles (0.1% by weight) and the surfactant Span80 (0.1% by weight) in the refrigerant R141b on the pool boiling heat transfer coefficient are presented in the paper. The heat flux values were varied during the experiment from 5 to 60 kW∙m-2. The pressure values in the experimental setup were maintained at 0.2, 0.3 and 0.4 MPa. The experimental investigation of the boiling the objects of study were carried out on two heaters surfaces with different wettability by the refrigerant R141b: the stainless steel surface and the similar surface, covered with a thin layer of Teflon. It was shown the superheating of the surface covered with Teflon during the boiling of the objects of the study was significantly higher in comparison with theirs boiling on the stainless steel surface. Consequently the lower values of heat transfer coefficient at boiling on Teflon surface have been observed. It was concluded the reduction of the roughness of the surface coated the Teflon layer in comparison with this characteristic for the stainless steel surface, not the change in the surfaces wettability, was the main cause of the decrease in the heat transfer coefficient. The enhancement of the heat transfer coefficient at low heat fluxes and low values of pressure during the boiling of the solution the surfactant Span-80 in the R141b and of the nanofluid of R141b/TiO2 nanoparticles/surfactant Span-80 in comparison with the heat transfer coefficient of the pure refrigerant R141b has been observed. It should be noted the heat transfer enhancement with adding the nanoparticles and surfactant was observed at the operating parameters typical for the evaporators of refrigeration systems.