Radiotracers in Gas-Liquid Transportation Problems-A Field Case

Abstract

Presented here are the results of a field program to develop and Presented here are the results of a field program to develop and evaluate radiotracer techniques for simultaneously measuring linear velocities of the individual phases of a multiphase stream. The flow properties monitored were used to compare experimental two-phase pressure drops with values predicted by techniques currently used pressure drops with values predicted by techniques currently used in design work. Introduction Numerous studies have been published on the transportation of gas-liquid mixtures through pipelines. However, the range of applicability pipelines. However, the range of applicability of most of the methods suggested for describing two-phase flow is generally limited to the conditions under which the investigations were performed. This shortcoming can be attributed performed. This shortcoming can be attributed either to improper design and instrumentation of the experiments or to departure of the analytic models, upon which the correlations are based, from the physical model or both. Therefore, further research in two-phase flow is needed to obtain more meaningful data for the solution of gas-liquid transportation problems. A prerequisite to understanding two-phase flow in a pipe is an adequate knowledge of the interrelationship between the velocities of the individual phases, individual densities, the gas volume fraction and the gas weight fraction. It is very difficult, however, to measure the relative velocities of the individual phases. In addition, the method most commonly used in the past to obtain the vapor volume fraction was very unsatisfactory. It constituted isolating a portion of the pipe by means of quick-closing valves, and subsequently measuring the actual quantity of liquid present. The volume fraction of vapor obtained in this manner was an average value over the length of the test section, so the effect of geometrical changes on density of the two-phase mixture could not be accurately determined. These are serious shortcomings of previous investigations of two-phase flow. In recent years a technique that has become more common for measuring fluid flow involves the use of radioactivity. This technique now offers easy and accurate means of measuring the linear velocity of each individual phase (radioactive tracer survey), and both the density and void fraction (gamma-ray attenuation). The method reported here to determine linear phase velocities is the Isotope Velocity method; a slug of radioactive material is injected rapidly into the flowing stream, and the transit time of the radionuclide between positions of known detector separation is measured. The accuracy of such a flow measurement depends upon the strength of the gamma rays emitted by the chosen isotope, accurate knowledge of the internal dimensions of the pipe, detector sensitivity and velocity profile. JPT P. 939