Two-phase, gas-liquid concurrent flow : an investigation of holdup, pressure drop and flow pattern in a pipe at various inclinations

Abstract

The cocurrent flow of two phases, gas and liquid is investigated analytically and experimentally. The investigation is concentrated on the problems of the holdups of two phases, the pressure drop due to wall friction and the characterization of flow patterns with particular ·emphasis on the effects of phase flow rates and pipe inclination. The results are as follows: Analytical It is clear that a point in the flow field of two phases can only be occupied by one phase at a time. Therefore, the important variable which is the local velocity cannot be generally defined for either phases. Consequently, it is more logical to treat the flow as a single fluid with properties dependent on the structure of the flow field and the properties of its constituents, namely gas and liquid. From this consideration a general holdup equation is derived using the field concepts and the concepts of fluctuating flow. The holdup equation can be reduced to simpler form when applied to practical situations. Its simplified form involves two constants which can be determined experimentally. A similar analysis results in an expression relating the pressure drop due to shear with other local quantities. This expression, however, cannot be solved in terms of measurable quantities since distribution profiles of the local quantities involved are unknown. A method called "dimensional analysis from differential equations" is employed, the analysis results in three dimensionless numbers which can be used for the purpose of data presentation. Flow pattern characterization is discussed and the conditions at the transitions between flow regimes are analysed. These conditions are found to depend on the values of a number of variables among which two variables are chosen as suitable for the presentation of flow regime maps. Experimental Experiments are performed with air and water flowing in a 4.55 cm ID clear plastic pipe. The pipe is set at 11 different inclinations: -90.00, -67.75, ~44.75, -20.00, -6.17, 0, 2.75, 20.75, 45.00, 70.00 and 90.00 degrees from horizontal. A total number of 1927 data points are obtained to test the validity of the theoretical expressions. It is found that the linearity of the holdup equation holds and the constants involved in it are the functions of water volumetric flow rate and pipe inclination. An empirical correlation for the prediction of the frictional pressure drop is attempted and the theoretical analysis concerning this quantity is tested against experimental data. The test shows that the analysis applies only in the region of high gas to liquid volume ratios. When fl ow pattern is of concern, the use of the two variables, chosen ·from the analyses of the conditions at the transitions between flow regimes, shows successful presentation of the flow regime maps. The .data points of the same flow patterns appear to gather in groups covering areas of certain sizes and having certain boundaries. Eleven flow regime maps are constructed and the effects of pipe inclination are clearly shown up in these maps.