Flow transitions during laminar stratified two-phase flow in mini channels.

Stratified flows are commonly observed two-phase flow regime in nuclear and chemical reactors. In the present work, stratified and wavy-stratified flows occurring in circular tubes of size 1.8–4.5 mm are studied experimentally and numerically. Free surface numerical modeling based on volume of fluids approach is used to study the changes occurring in stratified flow pattern, and the model is validated with adiabatic experimental results. The transition boundaries of smooth to wavy patterns are presented in the form of a map. The liquid film height distribution in spatial and time domain is also presented. The effect of constant heat flux on the flow patterns and liquid film thickness is detailed. It is found that, above a certain heat flux (33,000 W/m²), wavy appearance becomes predominant. A correlation is developed to determine the maximum and average liquid film thickness for various heat loads. [ABSTRACT FROM AUTHOR]