Entropy generation of droplet motion with surface tension hysteresis in a closed microchannel

Abstract

A transient heat transfer and entropy analysis is conducted to investigate the processes of thermocapillary droplet motion in closed microchannels. Both theoretical predictions and experimental data are presented for time-dependent temperature changes during the droplet acceleration. This paper develops a predictive model of the entropy production due to thermal and fluid irreversibilities in the microchannel. Thermocapillary, pressure and friction forces are modelled within the droplet, as well as surface tension hysteresis during start-up of the droplet motion. The spatial temperature change in the axial direction is measured experimentally, as well as the displacement of the droplet over time. The variation of the entropy generation number is reported for open and closed channels. Close agreement is obtained between the predicted and experimental data. The results show that water droplets have lower thermal and fluid irreversibilities than toluene and mineral oil.