An experimental investigation of two-phase (air-water) flow regimes in a horizontal tube at near atmospheric conditions

A series of air-water two-phase flow experiments was performed in a 25.4-mm horizontal tube at near atmospheric conditions. Measurements of the frictional pressure gradients, local void fractions, and gas-liquid interfacial area were taken. A twin-needle optical probe was used to measure the local void fractions at an axial location (l/d) of about 410. Simultaneous videotapes of the horizontal- and vertical-planes of the test section were also acquired.; Based on detailed analysis of the videotaped information of the flow, and using a methodology developed specifically for this study, the observed flow patterns were classified into stratified wavy, plug, slug, and annular flow regimes. The physical mechanisms that govern the transition between these regimes were identified and discussed.; Preliminary analysis of the videotaped horizontal- and vertical-planes of the flow showed that the data could be used to provide accurate measurements of the concentration of the air-water interfaces in stratified wavy and plug flow regimes. The recorded signals of the optical probes could also be used to obtain information on other parameters, such as frequency of liquid slugs, length, and passing frequency of air bubbles.; Models and correlations used to predict the friction losses and the average void fractions were reviewed and categorized into either (i) generalized models, which do not require prior knowledge of the flow regime, or (ii) regime-specific models, which were developed based on the particular characteristics of the flow regimes. The adequacy of these models to predict the friction losses and the average void fractions in each of the observed flow regimes was evaluated and discussed.; Based on the observed disposition of the phases in each flow regime, simplified two-fluid models were developed to predict the frictional pressure gradients. Results of these models clearly showed that the interactions between the phases at the interface have considerable effects on the velocity profiles within the phases such that, in general, the conventional definitions of the friction factors are invalidated.; The contributions of this experimental investigation include the following: (i) a flow regime map; (ii) validated drift-flux models; (iii) review and assessment of adequacy of models; (iv) experimental data that could be used to provide accurate measurements of the concentration of the gas-liquid interfaces, and important characteristics of the slug and plug flow regimes. (Abstract shortened by UMI.)...