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流和径向液膜流层流-湍流转变的影响。以十二烷基苯磺酸钠为表面活性剂。实验采用内径为2.5 mm的不锈钢、铜管、玻璃管和聚四氟乙烯管材进行管流实验。得到了在雷诺数逐渐增大和减小两种情况下的临界雷诺数。这些临界雷诺数随着表面活性剂浓度的增加而单调增加，直到浓度为20wppm时比自来水的临界雷诺数高出约10%，然后随着浓度的进一步增加而减小。在径向液膜流动实验中，径向液膜流动是通过圆形黄铜喷嘴顶部与玻璃板下表面之间的缝隙排放水产生的，沿板沿薄液膜径向流动。喷嘴内径15 mm，间隙距离1 mm。实验结果表明，当浓度低于6wppm时，跃迁半径随浓度的增加而迅速增大，之后随浓度的进一步增加而变化不大。此外，从6wppm到76wppm不同浓度范围内溶液的临界雷诺数的大量数据表明，溶液的临界雷诺数约为溶剂的1.08倍。因此，少量的表面活性剂添加剂虽然只有5%~8%，但对该转变有明显的抑制作用。

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.