Study On Thin-film Evaporation Heat Transfer Characteristics Of Nanofluids

The heat transfer efficiency of thin film evaporation is much higher than forced convection heat transfer.And nanofluids is a new type of heat transfer medium with excellent performance in the field of micro-scale heat transfer.Therefore,studying the thin film evaporation heat transfer characteristics of nanofluids is of great significance for the further application of nanofluids in the field of micro-scale heat transfer.Based on the kinetic theory and the augmented Young-Laplace equation,a mathematical model for the nanofluids thin film evaporation was established.Taking Fe3O4-water nanofluids as the working fluid.The effects of volume concentration,adjustment coefficient,nanoparticle deposition and magnetic field on the thin film evaporation and heat transfer of nanofluids were studied.In the condition of the process of nanofluids thin film evaporation,the nanoparticles assumed not deposited,the evaporation only change the concentration of nanofluids.Based on the augmented Young-Laplace equation and dynamics theory,a mathematical model was established.The changes of parameters such as thin film thickness,vapor-liquid interface temperature,heat flux,average velocity,curvature,mass flow rate and volume concentration were analyzed during the thin film evaporation heat transfer of nanofluids of different concentrations.And the effects of surface tension on the evaporation heat transfer of thin film evaporation were discussed.The parameters of thin film thickness,vapor-liquid interface temperature and heat flux of nanofluids with different concentrations in the process of thin film evaporation heat transfer change obviously.In the condition of that the concentration of nanofluids is constant,evaporation only lead to the deposition of nanoparticles.A mathematical model was established to analyze the discrete deposition of nanoparticles and the agglomerated deposition of nanoparticles.The effects of nanoparticle deposition on thin film thickness,vapor-liquid interface temperature,heat flux,average flow rate and mass flow were discussed.The results show that whether it is discrete deposition or agglomeration deposition,the deposition of nanoparticles enhance the thin film evaporation heat transfer.In the condition that the magnetic field gradient is uniform,the magnetic nanoparticles are in the state of saturation magnetization,and the influence of the magnetic field on the particle deposition is not considered.A mathematical model was established to analyze the evaporative heat transfer characteristics of nanofluids thin films under different magnetic field gradients.The effects of magnetic fields on vapor-liquid interface temperature,thin film thickness,heat flux and average residence were discussed.The heat transfer of ferrofluids thin film evaporation heat transfer also get larger with the magnetic field gradient.