Liquid Films in the Viscous Flow Region
Liquid Films in the Viscous Flow Region
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粘性流动区域中的液膜
DOI：
10.1021/ie50379a015
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发表时间：
1941
影响因子：
--
通讯作者：
C. Miller
中科院分区：
文献类型：
--
作者：
S. Friedman;C. Miller
在包括吸收、萃取、传热、增湿和蒸馏在内的扩散过程的一般领域中，薄液膜的流动经常受到干扰。冷凝器和换热器中的膜状冷凝以及填料塔或湿壁塔中的单相流动都涉及到薄液膜的形成和流动。在气膜控制的吸收情况下，当给定恒定的接触面积时，液体的流动特性不会明显成为影响操作效率的因素。然而，在处理膜状冷凝或扩散过程时，液膜和气膜或液膜单独控制时，膜状液体的流动特性对操作效率有一定的影响。膜厚度、界面速度和膜液体的平均速度计算得越精确，质量传递或热传递数据的分析就越精确。流体流动的两种一般类型是众所周知的，即流线或粘性流动和湍流。如果所有涉及的变量都能计算出来，粘性流的情况就可以从数学的观点严格地加以分析。另一方面，湍流已被证明是一种如此复杂的机制，以至于所有的相关性都是基于实验数据。对于流体在圆管中的流动，已有充分的证据证明粘性流动方程背后的数学理论，并对湍流数据的关联进行了大量的研究。虽然对液膜流动已经作了一些研究（§ 8，S，5），而且在湍流区和湍流区之前的过渡区也有相当多的数据，但在粘性范围内，特别是低粘性液体的数据却很少。现有的数据只表明，在雷诺数为1500的区域内，从流线流到紊流的转变发生了，并粗略地证明了支配这种流动的数学定律的正确性。然而，还没有尝试直接测量液-气界面处的速度。由于湿壁塔、填料塔和冷凝器中的粘性液膜经常被破坏，因此，人们认为最好对这一区域进行更彻底的研究，并证明数学处理是否严格适用于这一区域。
IN THE general field of diffusional processes, including ab-sorption, extraction, heat transfer, humidification, and distillation, the flow of thin liquid films is often encoun-tered. Filmwise condensation in condensers and in heat ex-changers and the flow of one phase in packed or wetted-wall columns involve theformation and flow of thin liquid films. In the case of absorption where the gas film is controlling, the flow characteristics of the liquid, when given a constant area of contact, do notappreciably enter into the factors influencing the efficiency of operation. However, in the treat-ment of filmwise condensation or in diffusional processes, where both liquid and gas films or the liquid film alone is con-trolling, the flow characteristics of the film liquid have a definite bearing upon the efficiency of the operation. The more exactly the film thickness, interfacial velocity, and average velocity of thefilm liquid can be evaluated, the more precisely the mass transfer or heat transfer data can be analyzed.Two general types of fluid flow are well known—namely, streamline or viscous flow and turbulent flow. The case of viscous flow may be analyzed rigorouslyfrom a mathematical standpoint, if all of the variables involved can be evaluated. Turbulent flow, on the other hand, has proved to be such a complex mechanism that all correlations have been based on experimental data. In the case of flow of fluids through circular pipes, sufficient evidence exists to prove the mathematical theory behind the viscous flow equations, and much investigation has been carried out in the correlation oftur-bulent flow data. Although some work has been reported on the flow of liquid films (¡ 8, S, 5), and considerable data are available in the turbulent region of flow and the transition region just preceding it, the data in the viscous range, par-ticularly of low-viscosity liquids, are sparse. The data available indicate only that the transition from streamline to turbulent flow occurs in the region of Reynolds number 1500 and prove roughly the validity of the mathematical laws governing thistype of flow. No attempt has been made, however, to measure directly the velocity at the liquid-gas interface. Since films in viscous flow are often encoun-tered in wetted-wall towers, packed towers, and condensers, it was thought advisable to investigate this region more thoroughly and to prove whether mathematical treatment was strictly applicable in this region.