Heat transfer characteristics and field synergy analysis of gas–liquid two-phase flow in micro-channels

To meet the extreme cooling requirements in many high-tech fields, it is essential and meaningful to reveal the dominant factors of heat transfer performance of gas–liquid two-phase flow in micro-channel. In the present work, the flow and heat transfer characteristics of bubbly, slug and annular flow in circular micro-channel are numerically studied with the VOF model. Moreover, the field synergy principle is introduced to reveal the dominant mechanisms of heat transfer improvement under various flow patterns. As a result, the evolutions of local Nusselt number, volume fraction and near-wall average field synergy angle along the flow direction under various flow patterns are obtained. Moreover, the effects of gas and liquid flow rates are discussed on the average Nusselt numbers and average field synergy angle. The numerical results indicate that the heat transfer performance of gas–liquid two-phase flow is better than single-phase flow, and the slug flow owns the best heat transfer performance. It should be noted that the heat transfer enhancement of bubbly and slug flow is attributed to the decrease in field synergy angle in the boundary layer. By contrast, the liquid phase velocity near the wall plays a dominant role in heat transfer enhancement of annular flow. Furthermore, the heat transfer performance of gas–liquid two-phase flow is strongly influenced by the gas flow rate, and Reg= 24.5 is the optimal value to enhance heat transfer performance for the condition of Rel= 445. The results are expected to provide theoretical guidance for the design and optimization of the micro-channel heat exchangers.