Preparation And Thermal Properties Of The Nanofluids With Titanium Dioxide Particles Of Different Morphologie

Compared with the traditional heat transfer medium,nanofluids as a new heat transfer medium have higher thermal conductivity,they can greatly improve the heat transfer efficiency,and can meet the higher heat transfer requirements,which has great influence on the achieving of energy saving.Nanofluids have broad application prospects and have become a hotspot in many fields at home and abroad.In this paper,the preparation of TiO₂-water nanofluids with different morphology was studied,and the thermal properties of nanofluids such as thermal conductivity,viscosity and wettability were analyzed also.The main work is as follows:1.Three kinds of TiO₂-water nanofluids were prepared in the form of rod?rutile,200 nm,?30nm?,rhombus?anatase,105nm×15nm?and flaky?anatase,110nm×12nm?by hydrothermal method,and the effects of reactant concentration,reaction time and reaction temperature on the morphology and crystal form of rod TiO₂ nanoparticles were investigated.The results show that the reaction conditions of low concentration,long time and high temperature are favorable for the growth of rod particles and the degree of crystallization.2.The thermal conductivity of three kinds of TiO₂-water nanofluids was studied,and the effects of temperature,mass fraction,particle morphology and crystal form on the thermal conductivity of TiO₂-water nanofluids were explored,then the experimental values were compared with the calculated values of empirical model to study the thermal conductivity of nanofluids further.It is found that the thermal conductivity of nanofluids increases with the increase of temperature and mass fraction.Compared with the base liquid,the thermal conductivity increases by 49.10% mostly.The thermal conductivity of the anatase nanofluids is 3.28%⁴.47% larger than that of the rutile nanofluids,the thermal conductivity of flake nanofluids is 2.39% higher than that of rhombus nanofluids.Moreover,the results is consistent with calculated values of Sharma model,the error range is 2.15%⁵.13%,which indicates that the thermal conductivity of nanofluids can be predicted by Sharma model.3.The effects of temperature,mass fraction,particle morphology and crystal form on the viscosity of TiO₂-water nanofluids were investigated,and the experimental values were compared with the calculated values of empirical model to study the viscosity of nanofluids further.The results show that the viscosity of the nanofluids increases with the increase of the mass fraction,decreases with the increase of the temperature,the viscosity increases by 19.73% compared with the base liquid.The viscosity of anatase nanofluids is 2.5% higher than that of the rutile nanofluids,and the viscosity of flaky nanofluids is slightly larger than that of rhombus nanofluids.It is also found that the Bobbo model can accurately calculate the viscosity value of nanofluids with high mass fraction,and the minimum error is only 0.19%.4.The effects of temperature,mass fraction,particle morphology and crystal form on the wettability of TiO₂-water nanofluids were studied.The results show that:?1?The surface tension of nanofluids decreases with the increase of temperature and mass fraction,and the surface tension is 16.95% lower than that of base liquid.The surface tension of anatase nanofluids is 0.125⁰.917mN/m higher than that of rutile nanofluids.?2?Similar to the properties of surface tension,the contact angle of nanofluids decreases with the increase of temperature and mass fraction.Compared with the base liquid,the contact angle of nanofluids decreases by 21.98% 25%,the contact angle of anatase nanofluids is 0.5° greater than that of rutile nanofluids.The morphology has no obvious effect on the wettability of TiO₂-water nanofluids.