Studies on mechanism of outbreak and disappear of drag reduction by temperature change

为了寻找一种可行的控制加入少量表面活性剂减阻爆发和消失的方法，对加入少量表面活性剂的水流湍流摩阻减阻进行了三个参数的控制：1.添加表面活性剂的浓度，2.溶液的温度，3.溶液的速度。然而，在换热器的实际应用中，表面活性剂的浓度和操作中溶液的流速是很难改变的。通过局部加热和冷却来改变风道壁面温度是唯一可能的，当壁面附近的溶液温度超过或低于临界值时，才能观察到减阻现象的发生和消失。这些临界值取决于附加表面活性剂的浓度和溶液的速度。此外，临界温度的位置距离…约0.1 mm壁面越多，在这个范围内，温度几乎是恒定的，温度从爆发到减阻现象消失的程度取决于添加表面活性剂的浓度、溶液的温度和溶液的剪切速度。减阻现象从爆发到消失的过程随温度的变化并不剧烈，且存在滞后现象，特别是当表面活性剂的浓度大于1000ppm时，粘度随温度的变化而变化。在这种情况下，阻力的减小和雷诺数的变化是同时发生的。但是，我们还需要更深入的调查和数据。本实验明确了在闭合环流流道中加入少量表面活性剂来控制水流湍流摩阻减阻的可能性，所使用的阳离子表面活性剂为十六烷基三甲基氯化铵(CTAC)，其中加入了与反离子相同重量的水杨酸钠。较少

The purpose is to find the practicable control method of the outbreak and disappear of drag reduction by the addition of small amount of surfactant.Control of the reduction in turbulent friction drag of water flow by the addition of small amount of surfactant has been done by three parameter, 1. the concentration of additional surfactant, 2. temperature of the solution, and 3. velocity of the solution. In practical applications to heat exchanger, however, it is difficult to change the concentration of surfactant and velocity of the solution in operation. Change of temperature of duct wall by heating and cooling locally has the only possibility.The outbreak and disappear of drag reduction phenomenon are observed on the condition that temperature of the solution near the wall go over or go down the critical value. These critical values depend on the concentration of additional surfactant and velocity of the solution. Furthermore, the place of critical temperature is about 0.1mm from the … More wall and within this range, temperature is almost constant.The extent of temperature from the outbreak to the disappear of drag reduction phenomenon depend on the concentration of additional surfactant, temperature of the solution, and shear velocity of the solution. The change process from the outbreak to disappear of drag reduction phenomenon due to temperature is not sharp and the hysteresis was observed.Specially, in the case of concentration of additional surfactant over about 1000ppm, change of viscosity depend on temperature. In this case, reduce of drag and change of Reynolds number occur at the same time. But, we need an in-depth survey and data.Possibility of control of the reduction in turbulent friction drag of water flow by the addition of small amount of surfactant made clear in this experiment using a closed loop flow channel and the cationic surfactant used was cetyltrimethyl ammonium chloride(CTAC),which was added with the same weight of sodium salicylate as the counter ion. Less