Abstract: The influences of temperature，chemical dispersant，and volume fraction of nanoparticles on the shear viscosity of the nanoparticle-fluid mixture were experimentally investigated.The nanofluids including different types of nanoparticles were prepared by a two-steps method.The results showed that the shear viscosity of the mixture decreased with increasing temperature below a threshold of 60℃. Interestingly，the viscosity of Cu-water and Al₂O₃-water nanofluids increased with increasing temperature above 60℃.The Brownian motion was enhanced as temperature increased，and the moving of the nanoparticles covering surfactants would increase the viscosity.The viscosity hysteresis between the heating and cooling processes could be observed obviously.The shear viscosity of CuO-water nanofluid in this experiment was in good agreement with fluid dynamics continuum theory for the fluids without dispersant.After the dispersant was added in CuO-water nanofluid，the experimental value of shear viscosity was larger than the theoretical data.And the varying trend of viscosity was consistent with that of the dispersant.The use of surfactant had an important role in the calculation of viscosity.The viscosity of nanofluids increased with increasing particle volume fraction，but the viscosity increments for the nanofluids with the same particle volume fraction were not the same.So density，surface electrical and diameter of the nanoparticles should be considered when calculating the viscosity of nanofluids.

Key words: nanofluids, temperature, dispersant, volume fraction, viscosity

关键词: 纳米流体, 温度, 分散剂, 体积分数, 黏度