The Investigation Of The Characteristic Parameters For Slug Flow In Vertical Pipe By Electrochemical Technique

By electrochemical method, characteristic parameters are investigated within the range of slug flow in vertical pipe. Emphases are placed on the study of the length distribution of elongated bubble and liquid slug with different diameter pipes in which slug flow can form when gas phase is introduced into CMC solutions whose concentrations are adjusted. Moreover, mass transfer coefficient (M.T.C.) together with the length distribution at different locations of the pipe, can be obtained in vertical pipe where slug flow is expected in the medium composed of gas and water.The introduction of small amount of gas can account for the greater enhancement with respect to single phase flow. While keeping gas superficial velocity constant, M.T.C increases as liquid superficial velocity. It is noticeable that the increase and the fluctuation of M.T.C experience two different phases. The first phase is characterized with the amplitude of the increase and fluctuation of M.T.C being at high level, but the amplitude of the increase and fluctuation becomes inapparent for the second phase. These phenomena can be explained clearly if the length of wake region is taken into account. The increase of gas or liquid superficial velocity has little contribution to the enhancement of M.T.C. According to the study of Compos, despite of the increase of Taylor bubble with the increase of gas superficial velocity, the value of M.T.C does not increase due to the fact that the length of wake region, along with the shear rate in the film around the bubble, does not change distinctively.The length distribution of liquid slug liquid slug can be depicted by log-normal distribution at three locations of the pipe such as 25D, 55D, 100D. As the measurement locations move upward, the gradual increase of the average length along with standard deviation shows that the coalescence between two consecutive bubbles occurs within the whole scope of measurement, so slug flow is under the condition of development.The length distributions of Taylor bubble and liquid slug are investigated in the system of CMC solution and gas with the changes of solution concentration, pipe diameters and gas or liquid superficial velocity. The length distributions of Taylor bubble and liquid slug are in accordance with normal distribution at the variety of concentration. With the exception of the concentration of 0.3wt%, the length of Taylor bubble increases as the solution concentration, and the length of liquid slug decreases as the solution concentration increases. The length ofelongated bubble decreases as liquid velocity increases, but the length of slug is immune to the change of liquid velocity. The effect of gas velocity on slug length distribution is more distinctive at high concentration of solution than at low. The length of Taylor bubble is always increases with increase of gas superficial velocity. The length distribution of Taylor bubble is susceptible to pipe diameter, but the length distribution of slug is not. The changes of Taylor bubble length can be explained according to the alterations of Re. and the length of wake region and development section.