Heat transfer enhancement of droplet two-phase flow in cylindrical microchannel

Abstract

The heat transfer enhancement of droplet two-phase flow in cylindrical microchannel is numerically studied by VOF method. The average vorticity magnitude inside droplet is extracted to quantitatively represent the circulation strength. Numerical results show that the local Nu at the position of droplet is about doubled while the average Nu in the entrance and the fully developed regions increase by more than 40% and 50%, respectively. However, the total pressure drop only increases by less than 15%. In particular, the average Nu increases firstly and then decreases rather than monotonically increases with the increasing of droplet diameter or flow rate. The effects of surface tension, viscosities of both dispersed and continuous phases, especially velocity slip of continuous phase, which be rarely concerned, are systematically investigated. By increasing the slip length, the heat transfer in both single-phase and droplet two-phase flow increases, however, the Nu promotion decreases. An empirical criteria is proposed to describe the effect of droplet size and volume fraction ratio on the heat transfer of droplet two-phase flow.