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

目的是寻找一种可行的控制添加少量表面活性剂减阻的爆发和消失的方法。通过三个参数来控制加入少量表面活性剂对水流湍流摩擦阻力的减小。附加表面活性剂的浓度，2。溶液温度，3。溶液的速度。在换热器的实际应用中，表面活性剂的浓度和溶液的流速很难改变。通过局部加热和冷却来改变管壁温度是唯一的可能。在接近壁面的溶液温度超过或降低临界值时，观察到减阻现象的爆发和消失。这些临界值取决于附加表面活性剂的浓度和溶液的流速。临界温度发生在距壁约0.1mm处，在此范围内温度基本不变。从减阻现象发生到消失的温度范围取决于外加表面活性剂的浓度、溶液温度和溶液的剪切速度。温度引起的减阻现象从爆发到消失的变化过程并不剧烈，存在滞后性。特别地，在添加表面活性剂的浓度超过1000ppm左右的情况下，粘度的变化取决于温度。在这种情况下，阻力的减小和雷诺数的变化同时发生。但是，我们需要深入的调查和数据。本实验采用闭环流动通道，通过添加少量表面活性剂控制水流湍流摩擦阻力降低的可能性，实验中使用的阳离子表面活性剂为十六烷基三甲基氯化铵（CTAC），加入等量的水杨酸钠作为反离子。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