Control of Heat and Momentum Transport Process by a Reversible Transform Micelle of Polymer

众所周知，非牛顿流体中的Thorns效应是减阻的主要原因。最近，据报道，添加少量的表面活性剂也提供了相同的减阻效果。减阻流动的特点是可以长距离输送热介质，能量损失小。对于减阻流动的机理，特别是对于实际应用中出现的湍流情况，还没有深入的研究。本文对具有可逆相变的聚合物胶束结构的行为进行了实验研究，并发展了表面活性剂对热流体现象的控制技术，对表面活性剂/水稀溶液在二维通道中的传热特性进行了实验研究。还测量了热边界层的温度分布。结果表明，减阻热边界层在近壁处存在高扩散层，且随着壁面热流密度的增大，边界层内温度波动的时间尺度变小。为了提高传热系数，采用网塞施加高剪切力破坏表面活性剂溶液中的胶束结构，使其产生湍流。网格塞表明，高传热区具有与水流相同的湍流强度。该网有助于产生高的壁剪切应力，从而破坏棒状胶束以引入湍流。结果表明，由于网塞仅产生局部高剪切应力，网塞下游的速度湍流强度逐渐降低，与减阻流相同。该技术可用于减阻流中的有效传热强化。

It is well known that Thorns effect in non-Newtonian fluid causes the drag reduction. Recently it has been reported that an addition of small amounts of surfactants also provided the same effect on the drag reduction. The characteristics of drag reduction flow can transport the long distance thermal medium with low energy loss. The mechanism of drag reduction flow has been stilt unexplored, especially for the turbulent flow condition that appears in a practical application. In the present study, experimental study has been performed on the behavior of micelle structure with reversible transform of polymer, and a controlling technique for thermo-fluid phenomena has also developed by using surfactant.Heat transfer characteristics of a dilute surfactant/water solution in a two dimensional channel has been experimentally investigated. Temperature profile measurements in the thermal boundary layer were also made. It was found that high diffusivity layer exists near the wall in the drag reducing thermal boundary layer and that the time scale of temperature fluctuation in the layer becomes smaller as increased of wall heat flux. In order to increase the heat transfer coefficients, the mesh plug was used to exert high shear stress to destroy micelle structure in the surfactant solution so that turbulence could be produced. The mesh plug indicated that the high heat transfer region had the same turbulent intensity as that of water flow. The mesh helped to create high wall shear stress and therefore to destroy the rod-like micelles for introducing turbulent. It was found that the turbulent intensities of the velocity gradually decreased to the same as those of drag reduction flow downstream form the mesh because the mesh plug only produced a local high shear stress. This technique can be applied for effective heat transfer augmentation in a drag reduction flow.