Study on Transition Suppressions in Pipe Flow and Radial Liquid-Film Flow by Surfactant Additives

实验研究了表面活性剂添加剂对管道流和径向液膜流层流-湍流过渡的影响。采用十二烷基苯磺酸钠作为表面活性剂。溶液的浓度从5到100 wppm不等。管道流动实验采用内径为2.5mm的不锈钢管、铜管、玻璃管和聚四氟乙烯管作为试验管道。在雷诺数逐渐增大和逐渐减小的条件下，得到了临界雷诺数。这些临界雷诺数随着表面活性剂浓度的增加而单调增加，直到在浓度为20wppm时，这些值比自来水高10%左右，然后随着浓度的进一步增加而下降。在径向液膜流动实验中，水通过圆形黄铜喷嘴顶部与玻璃板下表面之间的间隙排出，形成沿玻璃板径向流动的薄液膜。喷嘴内径15mm，间隙距离1mm。实验结果表明，当浓度低于6 wppm时，过渡半径迅速增大，之后不随浓度的进一步增大而变化。此外，大量关于6 - 76 wppm不同浓度下溶液临界雷诺数的数据表明，溶液的临界雷诺数约为溶剂的1.08倍。因此，少量表面活性剂的添加量虽然只有5% ~ 8%，但明显抑制了相变。

The effects of surfactant additives on the laminar-turbulent transitions of a pipe flow and a radial liquid film flow were studied experimentally. Dodecyl-benzensulfonicacid sodium was used as the surfactant. The concentration of solution was varied from 5 to 100 wppm.For the pipe flow experiment, stainless steel-, copper-, glass- and Teflon-tubes, which have a inner diameter of 2.5mm, were used as the test pipe. The critical Reynolds numbers were obtained under conditions of both gradual increasing and decreasing Reynolds number. These critical Reynolds numbers monotonously increased with surfactant concentration until these values came to be about ten percent higher than that of tap water at a concentration of 20 wppm, and then decreased with further increasing concentration.For the radial liquid film flow experiment, the flow was generated by a water discharge through a gap between the top of a circular brass nozzle and the lower surface of a glass plate, flowing radially in a thin liquid film along the plate. The inner diameter of the nozzle was 15mm and the distance of the gap 1mm. Experimental results showed that the transition radius increases quickly with the concentration bellow 6 wppm, after then does not change with the further increasing concentration. Furthermore, a lot of data on the critical Reynolds number of solution under various concentrations ranging from 6 wppm to 76 wppm indicated about 1.08 times as great as that of the solvent. Consequently, a small amount of additives of surfactant suppresses evidently the transition although its amount is only 5 to 8 percents.