Mechanistic modeling of flow and heat transfer in turbulent-laminar/turbulent gas-liquid stratified flow

Two-phase gas-liquid stratified flow is characterized by a structure in which the gas and liquid phases are separated from each other by a continuous interface. Adequately understanding its flow mechanism and heat transfer is important for analyzing two-phase stratified flow. This paper develops a mechanistic model of flow and heat transfer in turbulent-laminar/turbulent two-phase stratified flow in horizontal and slightly inclined pipes. First, a hydrodynamic model of two-phase stratified flow is developed by using the concept of two-fluid model. Second, a mechanistic model of heat transfer is derived based on the hydrodynamic model. The overall heat transfer coefficient is integrated by using the coefficients of local heat transfer of the liquid film and the gas core. Third, the effect of such flow geometries and parameters as the superficial Reynolds numbers for liquid and superficial gas, void fraction, pressure drop, and inclination angle of the pipe on heat transfer in two-phase stratified flow is comprehensively investigated. Finally, the relationships between the two-phase heat transfer multiplier and the overall void fraction and pressure drop multipliers are quantified. A simple correlation of the heat transfer multiplier for two-phase stratified flow is developed by using the void fraction as the input parameter serving as a quick but rough prediction of the heat transfer multiplier in two-phase stratified flow.