Modulated wall motion approach for augmenting slug flow heat transfer between two micro-parallel plates

Abstract

Liquid–liquid slug flow heat transfer in microchannels has been an interesting topic of research to many researchers. However, the heat transfer studies available in the existing literature deal with stationary walls of the microchannels. In the present work, a modulated motion is prescribed to the walls of the channel in the transverse direction during oil–water slug flow between micro-parallel plates. The influence of frequency and amplification factor of the modulated wall motion as well as capillary number on the droplet shape, film thickness, pressure drop, and heat transfer rate under uniform wall heat flux conditions is investigated computationally. The heat transfer results for the modulated wall motion case show a significant improvement over liquid-only flow and slug flow without any wall motion. Besides, the effect of slug length on the heat transfer has also been discussed for both modulated and unmodulated wall motions of the channel. A mean absolute deviation of 2%–75% in the pressure drop obtained from the numerical studies and existing semi-empirical models for stationary walls for the studied Capillary numbers is observed. This suggests that a better formulation is required for the pressure drop model. In addition, although Nusselt numbers are found to be in reasonable agreement with the existing model for stationary walls, requirement for the formulation of a generalized model considering the effect of wall oscillations is also suggested. This study proposes a new perspective for heat dissipation in micro-scale channels and promotes flow and heat transfer studies, which could bring benefits to relevant applications.