低浓度水基多壁碳纳米管纳米流体的流变特性

Rheological Characteristics of Low Concentrated MWCNT/Water Nanofluids

对纳米流体流变特性的研究有助于深入理解纳米流体的能量输运机理。本工作利用高级旋转流变仪,研究了MWCNT(Multi-walled carbon nanotube)纳米粒子体积分数为0.0047%、0.0238%、0.047%、0.0714%、0.095%的自来水基(tap)和蒸馏水基(DI)多壁碳纳米管(MWCNT)纳米流体在278~353 K温度范围内的粘度、触变性、粘度滞后的流变特性。结果表明:纳米流体粘度均高于基液水的粘度,其随纳米粒子体积分数的增大和温度的降低而增大;纳米流体相对粘度不受温度影响;MWCNT/水纳米流体从牛顿型流体转变为剪切稀化非牛顿流体的临界浓度为0.047%,其流动特性可用幂律模型来描述;当温度低于335 K时,MWCNT/水的流变特性不受基液性质的影响且无触变性;MWCNT/tap纳米流体出现高温引起的粘度滞后现象;基于实验数据,取得一个更准确的预测MWCNT/水纳米流体粘度的方程,为相关流动与热质传递模拟提供参考。

The investigation of the rheological properties of nanofluids helps to understand the energy transport mechanism of nanofluids.The rheological properties such as viscosity,thixotropy,and viscosity hysteresis phenomenon of MWCNT/tap and MWCNT/distilled(DI)water nanofluids are experimentally studied at five different low volume fractions(0.0047%,0.0238%,0.047%,0.0714%,0.095%)by using an advanced rheometer.The results show that the viscosity of nanofluids is higher than that of the base liquid,which increases with the solid volume fraction increasing and temperature decreasing;however,the relative viscosity is independent of temperature.Furthermore,it is found that the concentration of 0.047%is regarded as a critical point suggesting the transition from Newtonian fluid to shear thinning non-Newtonian fluid and the flow characteristics could be described very well by the power-law model.The rheological properties of MWCNT/water are not affected by the properties of the base liquid and there is no thixotropic behavior when the temperature is lower than 335 K.Besides,temperature sweep tests demonstrate that the viscosity hysteresis phenomenon caused by high temperature is observed in the case of MWCNT/tap nanofluid.Finally,based on the experimental data,a new and accurate correlation is proposed to predict the relative viscosity of MWCNT/water which can provide a reference for the work associated with the fluid flow simulation of nanofluids.