A new approach to thin film evaporation modeling

Two-dimensional computational modeling of thin film evaporation

Performance of finned tubes used in low-pressure capillary-assisted evaporator of adsorption cooling system

Thin film evaporation modeling is commonly used to simulate transport phenomena in two phase capillary cooling devices and microchannels. However, one of the difficulties faced in the application of such models is the absence of consensus in the implementation of boundary conditions. In the present work, different methods available in the literature are analyzed for their capability to model the physics of the problem. Both their strengths and shortcomings are highlighted. Hence, a novel method for estimation of the film thickness at the onset of evaporation is presented. It is tested for a wide range of superheats and is found to give physically realistic results. A new thin film evaporation model is also presented, consisting of the velocity slip boundary condition at the wall and a disjoining pressure consisting of both retarded and nonretarded terms. It is found that the heat flux decreases monotonically throughout the thin film region.

New insights on modeling of evaporation phenomena in thin films

An improved comprehensive semi-analytical model is devised and postulated to unveil the underlying physics of thin-film evaporating dynamics in a microfluidic channel using Al2O3 water nanofluid as working liquid with/without porous coating layer of nanoparticles. The model uses the mass transport equation based on the kinetic theory and the Young–Laplace equation for pressure differential and incorporates the slip boundary condition on the wall of the channel. It reveals that the wall slip is a crucial parameter that increases the cumulative heat transfer with decreased thickness of the thin-film evaporating meniscus. Furthermore, mainly three volume fractions 0.5%, 1%, and 2% has been considered in the present work and it is observed that nanofluid plays an important role in the increment of heat flux which is about 31% with the volume fraction of 2% and 25 nm diameter particles when only enhanced thermophysical properties are considered without slip. However, it exaggerates the results by 29% when porous coating layer of nanoparticles is neglected. It is also noticed that a porous coating layer deposited by the nanoparticles can even reduce the heat transfer phenomenon. Moreover, for a given combination of nanoparticle diameter and volume fraction, increase in the thermal resistance may reach up to an extent that even increased thermal conductivity cannot counteract it and hence, the heat transfer obtained using nanofluid can be worse than the heat transfer obtained using the base liquid water alone.

Wen Zeng

Papers

Comparison of different analytical models for heat and mass transfer characteristics of an evaporating meniscus in a micro-channel☆