Mechanistic modeling of flow and heat transfer in vertical upward two-phase slug flows

Two-phase slug flow exhibits intrinsically stochastic and statistically periodic flow behaviors. Understanding the mechanisms of flow and heat transfer of upward two-phase slug flow is important. This paper develops a mechanistic model of flow and heat transfer for upward two-phase slug flow in vertical pipes. First, a hydrodynamic model of two-phase slug flow in regular-sized channels is developed based on the hypothesis of the slug unit cell. Each slug unit cell is hypothesized to be composed of a liquid slug and a Taylor bubble region. Second, a mechanistic heat transfer model is derived based on the hydrodynamic model. The overall heat transfer coefficient is integrated by using the local heat transfer coefficients of liquid slug and the Taylor bubble region. Third, the proposed mechanistic model is validated by the experimental void fraction, pressure drop, and two-phase heat transfer coefficient from different sources. Finally, the effect of flow geometry and parameters-such as superficial gas and liquid velocities, void fraction, slug frequency, pressure drop, and the ratio of slug length to unit cell length-on heat transfer in two-phase slug flow is comprehensively investigated. The enhancement in heat transfer in two-phase slug flow compared with that of single-phase flow can be attributed to an increase in the turbulence of the liquid due to the injection of air and a reduction in the thermal boundary layer owing to the frequent alternation between liquid slug and the Taylor bubble.

Automated summary

This paper develops a mechanistic model to study the flow and heat transfer of upward two-phase slug flow in vertical pipes. The effect of flow geometry and parameters on heat transfer in two-phase slug flow is comprehensively investigated.