Rathnakumar P, Mayilsamy K, Suresh S, Murugesan P
J Nanosci Nanotechnol. 2014 Mar;14(3):2400-7. doi: 10.1166/jnn.2014.8505.
This paper presents an experimental investigation on the convective heat transfer and friction factor characteristics of CNT/water nanofluid through a circular tube fitted with helical screw tape inserts with constant heat flux under laminar flow condition. Nanofluids of 0.1% and 0.2% volume fractions are prepared by two step method. Thermo-physical properties like thermal conductivity and viscosity are measured by using KD2 thermal property analyzer and Brooke field cone and plate viscometer respectively. From the measurements, it is found that the viscosity increase is substantially higher than the increase in the thermal conductivity. The helical screw tape insets with twist ratios Y = 3, 2.44 and 1.78 are used to study the convective heat transfer and friction factor characteristics under laminar flow in the Reynolds number range of 520-2500. It is observed that, in a plain tube, maximum enhancement in Nusselt number for 0.1% and 0.2% volume fractions of nanofluids compared to pure water is 15% and 32% respectively. With the use of inserts, maximum enhancement in Nusselt number corresponding to twist ratios of 1.78, 2.44 and 3 are obtained as 8%, 16% and 4.6% for 0.1% volume fraction of nanofluid and 5%, 4% and 12% for 0.2% volume fraction of nanofluid when compared with water in plain tube. Thermal performance factor evaluation revealed that the values at all Reynolds number for all twist ratios and both concentration of CNT nanofluid are greater than unity which indicates that helical screw tape inserts with twist ratios considered are feasible in terms of energy saving in laminar flow.
本文介绍了在层流条件下，通过装有螺旋螺旋带插入物的圆管，对恒定热流的碳纳米管/水纳米流体的对流换热和摩擦系数特性进行的实验研究。采用两步法制备了体积分数为0.1%和0.2%的纳米流体。分别使用KD2热物性分析仪和布鲁克菲尔德锥板粘度计测量了热导率和粘度等热物性。通过测量发现，粘度的增加远高于热导率的增加。使用扭转比Y = 3、2.44和1.78的螺旋螺旋带插入物，研究了雷诺数范围为520 - 2500的层流条件下的对流换热和摩擦系数特性。观察到，在光管中，与纯水相比，体积分数为0.1%和0.2%的纳米流体的努塞尔数最大增强分别为15%和32%。使用插入物时，与光管中的水相比，对于体积分数为0.1%的纳米流体，对应扭转比1.78、2.44和3的努塞尔数最大增强分别为8%、16%和4.6%；对于体积分数为0.2%的纳米流体，分别为5%、4%和12%。热性能因子评估表明，所有扭转比和两种碳纳米管纳米流体浓度在所有雷诺数下的值均大于1，这表明所考虑的扭转比的螺旋螺旋带插入物在层流节能方面是可行的。
