Al_2O_3-水纳米流体在微圆管内的流动特性

Flow behavior of Al_2O_3-water nanofluids in micro circular tubes

测定了不同体积分数下A l2O3-水纳米流体在内径0.193 mm和0.508 mm 2种玻璃微圆管内的流动阻力特性。结果表明:纳米流体流动从层流向湍流转变的临界雷诺数Rec发生在2 100附近;对0.508 mm微圆管,纳米流体由层流向湍流的转变与去离子水基本一致,对0.193 mm微圆管纳米流体流型转变较去离子水略有提前。在雷诺数小于1 500—1 700的层流范围,纳米流体和水的摩擦因子都与经典理论预测值吻合良好,同Hagen-Poiseu ille公式偏差小于7.5%,雷诺数大于此范围后前者的摩擦因子比后者和理论值有所偏高;而在过渡区和湍流范围,纳米流体的摩擦因子比水有较大提高,且随体积分数增加摩擦因子增加的趋势更为明显。

The flow behavior of Al2O3-water nanofluids in micro glass circular tubes with internal diameters of 0. 193 mm and 0. 508 mm was measured at different volume fraction. The results show that the critical Reynolds numbers Re of nanofluids in micro tubes at which the transition from laminar flow to turbulent flow occurred are both around 2100. For the 0.508 mm tube, the transition from laminar to turbulent is consistent with that of deionized water; for the 0. 193 mm tube, the transition of nanofluid flow behavior is little earlier than that of deionized water. In most of the laminar flow range where Re 〈 1 500-1 700, the friction factors of both nanofluids and deionized water agree well with the typical predicted value, with the deviation from the Hagen-Poiseuille predictions less than 7.5%. For Re higher than the aforesaid range, the friction factors of the nanofluids are somewhat higher than that of deionized water and the Hagen-Poiseuille predictions. In the region of transition and turbulent flow, the friction factors of nanofluids increase greatly compared with that of water. As the particle volume fraction increases, the difference becomes more obvious.