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Transient Cooling of a Hot Surface by Droplets Evaporation. Final Report. September 1992-August 1993.


pdf icon Transient Cooling of a Hot Surface by Droplets Evaporation. Final Report. September 1992-August 1993. (5083 K)
White, G.; Tinker, S. C.; diMarzo, M.

NIST GCR 94-662; 177 p. November 1994.

Sponsor:

National Institute of Standards and Technology, Gaithersburg, MD

Available from:

National Technical Information Service
Order number: PB95-143194

Keywords:

computer programs; droplets; evaporation; fire research; steady state; water; thermal conductivity

Abstract:

A computer code is developed and tested which simulates the transient evaporation of a single liquid droplet from the surface of a semi-infinite solid subject to radiant heat input from above. For relatively low temperature incident radiation, it is shown that the direct absorption of radiant energy by the droplet can be treated as purely boundary conditions, while a model for higher temperature incident radiation would require the addition of constant heat source terms. The heat equation is numerically coupled between the liquid and solid domains by using a predictor-corrector scheme. Three one-dimensional solution schemes are used within the droplet: a start-up semi-infinite medium solution, a tridiagonal Crank-Nicholson transient solution, and a steady-state solution. The solid surface temperatures at each time step are calculated through careful numerical integration of an axisymmetric Green's functions solution equation with the forcing function given by the past lower droplet surface and solid-vapor boundary heat fluxes. The time step is increased after a sensitive initial period to allow for reasonable run times. Two geometry models are included which give the droplet height as a function of current droplet volume and initial wetted radius; the second allows inclusion of the effects of initial contact angle and receding angle. Using water as the liquid and Macor, a low-thermal conductivity material, as the solid, the program output was compared to the experimental results in this line of research. They correlate well to the experiments in which the critical geometric shape factor and evaporation time were most easily measured.