Research On Pool Boiling Heat Transfer Of TiO₂/HFC245fa Nanorefrigerant

Pool boiling heat transfer experiment was performed, for theenvironmental friendly refrigerant HFC245fa and its nano refrigerant withTiO₂nanoparticles on a horizontal heating tube of outer diameter22.4mm.The boiling heat transfer of R11and TiO₂/R11were compared. Contact angleof HFC245fa at the copper surface was measured. Employing the models ofeffective thermal conductivity and active nucleation cavities distribution on aheating surface, pool boiling heat transfer of nanorefrigerant is analyzed.Finally, the compatibility of the Rohsenow pool boiling model is investigatedwhen applied to nanorefrigerant.The experimental results showed that nanoparticles have significantinfluence on the upper and bottom surface of the heating tube. For the bottomsurface, the addition of nanoparticles basicly enhanced the pool boiling heattransfer. On the contrary, for the upper surface, nano refrigerants withconcentrations excpet0.02g/L basicly deteriorate pool boiling heat transfercompared with pure refrigerants. From the average boiling heat transfer of theheating pipe surface, out of the tested concentrations,0.02g/L nanorefrigerantcaused most efficient enhancement. For instance, under the heat flux densityis25kW/m2, boiling heat transfer coefficient of0.02g/L nanorefrigerantreaches about9.6%and16.8%when the saturation temperature is25℃and30℃.Compared with the R11and TiO₂/R11, at a lower saturation pressure（ps=0.15MPa）, HFC245fa and TiO₂/HFC245fa has a no-worse boiling heattransfer performance; at the higher saturation pressure （ps=0.17MPa）, theboiling heat transfer of HFC245fa and TiO₂/HFC245fa becomes relativelystrong from relatively weak as the concentration increased. R11nanorefrigerant with concentration of0.01g/L, has the most enhancement ofboiling heat transfer.The addition of nanoparticles can increase the effective thermal conductivity of nanorefrigerant as the concentration of nanoparticles orsaturation temperature increasing. Nanoparticles can also increase thecavitation density, and thus enhance the boiling heat transfer. Rohsenowmodel is compatible with pool boiling heat transfer of nanorefrigerant.