Transient response of thermocapillary pumping of a droplet in a micro heat engine

Abstract

A new analytical model is developed to predict the transient velocity and voltage gnerated due to thermocapillary pumping in a micro heat engine (MHE). Modeling, fabrication, and experimental studies of the MHE are presented in this paper. The fabrication technique uses lead zirconate titanate (PZT) as a substrate for the MHE. Analytical and experimental results are reported for Ti-W microheaters that transfer heat to the thermocapillary motion. The effect of surface roughness on thermocapillary motion of the droplet in the MHE is examined. The results show that a higher bulk droplet velocity reduces the effect of surface roughness on the displacement of the droplet. The analytical model of the efficiency of the system considers the electromechanical coupling factor and frictional irreversibilities to yield about 1.6% efficiency with a maximum voltage of 1.25mV for the range of displacement considered in this study. Nomenclature A cross sectional area (m 2 ) b width of membrane (m) cp specific heat (J/kgK) Dij electrical polarization (C/m 2 ) dij piezoelectric coefficient (C/N)