Determination of the quench velocity and rewetting temperature of hot surfaces: Formulation of a nonisothermal microscale hydrodynamic model

Microscale thermoviscosity and evaporation at the three-phase contact zone

A microscale model of wetting at the three-phase contact zone that incorporates the thermoviscosity effect under nonisothermal and evaporation conditions is presented. The thermoviscosity effect is shown to change the content of both governing equations and boundary conditions. The differential equation of the liquid-vapor interface profile is expressed in terms of previously defined dimensionless groups and the new thermoviscosity change factor D(s). The temperature-dependent viscosity eta(T), and capillary number C(*) are defined as a product of eta and C and of 1-D(s)Theta(I), respectively. Model outputs show that increase of D(s) decreases the wave length and amplitude of the solution profile as well as the film thickness and slope. In the tested cases of water, nitrogen, and helium, increase of D(s) extends the physically feasible range of contact angle and wall temperature versus fluid velocity. Under rewetting conditions, the effect of increased D(s) is to shift the allowable range of wall temperatures toward smaller values, concurrent with increasing the feasible values of corresponding quench velocities. The capacity of the dimensionless groups, C, Ctheta(2)/F, N, and A, to change the liquid-vapor interface profile is diminished by D(s), the capillary number C and the Hamaker constant being most and least sensitive in this respect.