三元混合纳米流体稳定性及热性能

Stability and thermal performance of ternary hybrid nanofluids

采用两步法制备体积分数为0.005%~1%的Al_(2)O_(3)-TiO_(2)-Cu/水三元混合纳米流体,粒子体积比为40∶40∶20。为了提高其稳定性,添加少量的PVP(0.005%)表面活性剂,并用XRD、TEM、紫外分光光度计和沉淀观察法共同表征纳米流体的稳定特性。测量温度为20~60℃的黏度和热导率,并与相对应的单一纳米流体作对比。试验结果表明,三元混合纳米流体由于各种粒子的粒径和表面能不同,小粒径的Al2O3颗粒填充在大粒径TiO_(2)和Cu颗粒形成的间隙里,可形成致密的固液界面层。三元混合纳米流体由于粒子的特殊排布,使其热导率明显高于相同体积分数下对应的单一纳米流体,黏度却无明显增大。当体积分数和温度分别为1%和60℃时,与Al_(2)O_(3)/水纳米流体对比,其热导率增大了5.5%,黏度下降了2.6%。热导率随温度和浓度的升高而升高;而黏度随浓度的升高而升高,随温度的升高而下降,这与单一纳米流体的性质一致。最后,基于试验数据,对热导率和黏度分别进行与温度的拟合,R^(2)分别为0.9835和0.9820,能较精确地预测Al_(2)O_(3)-TiO_(2)-Cu/水三元混合纳米流体的热导率和黏度。

A two-step method was used to prepare Al_(2)O_(3)-TiO_(2)-Cu/water of ternary hybrid nanofluids at volume fraction from 0.005% to 1.0%,and the mixture ratio of nanoparticles was fixed at 40∶40∶20.In order to improve stability,a small amount of PVP surfactant was added.Moreover,the stability of nanofluids was characterized by XRD,TEM,UV-vis and sedimentation methods.The viscosity and thermal conductivity were measured at the temperature varying from 20℃ to 60℃,and the results were compared with the corresponding single nanofluids.Experimental results showed that due to the differences between nanoparticle size and surface energy,the space between large size of TiO_(2) and Cu nanoparticles was filled with small size of Al_(2)O_(3) nanoparticles.This special arrangement can form a dense solid-liquid interface layer,which makes higher thermal conductivity and relatively low viscosity compared to the corresponding single nanofluids.Compared with Al_(2)O_(3)/water nanofluids,the thermal conductivity increased by 5.5% while viscosity decreased by 2.6% at volume fraction of 1% and temperature of 60℃.Then,the thermal conductivity increased with enhancing volume fraction and temperature,while the viscosity decreased with an increase in the temperature and increased with increasing volume fraction.A good agreement was achieved with the properties of single nanofluids.Finally,correlations of the thermal conductivity and viscosity were fit by experimental data.The values of R^(2) were 0.9835 and 0.982,respectively,which shows a good agreement with predicted data.