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

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.
*