Effects of superheat and temperature-dependent thermophysical properties on evaporating thin liquid films in microchannels

A model based on the augmented Young-Laplace equation and the Clausius-Clapeyron equation was developed to describe the extended evaporating meniscus in a microchannel. The effects of the adsorbed film thickness, channel height and temperature-dependent thermophysical properties of the fluid are included in the model at wall superheats up to 50 K. The liquid flow is coupled with the vapor flow to obtain the mass transport across the liquid-vapor interface. The results show that the constant thermophysical property model greatly overestimates the liquid pressure difference and the total thin film heat transfer rate at higher superheats compared with the variable thermophysical property model. The adsorbed film thickness, which is controlled by the disjoining pressure limit, reaches a minimum near about 20 K superheat for water. The maximum film curvature and liquid pressure difference then decrease at superheats larger than 20 K. The effects of the capillary pressure limit produced by the channel height can be reduced by increasing the superheat.