(Dr. William Black, advisor)

"Measurements of the Evaporation Rates of Heated Liquid Droplets"

Abstract

Very high heat transfer rates can occur from the evaporation of small diameter droplets that form a thin liquid layer over a surface.  In order to better understand the cooling rates that can be achieved with this method, the evaporation process of liquid droplets on horizontal heated surfaces was observed.  Water and n-heptane droplets were gently placed on aluminum and copper surfaces that were maintained at temperatures below the saturation temperature of the liquid.  The evaporation process occurred at one atmosphere pressure.  Changes in the shape of water droplets that were approximately 1 mm in diameter and of n-heptane droplets that were approximately 5 mm in diameter were videotaped throughout the entire evaporation process.  Transient variations of the diameter and height were measured for each droplet.  The droplets were shown to be in the shape of spherical caps throughout the evaporation process.  From the measured quantities, contact angle, volume, evaporation rate, and predicted heat flux values were calculated.  The test parameter that had the greatest influence on the shape and the evaporation rates was the surface temperature.  The experimental data obtained in this investigation will provide the means to validate mechanistic models for droplet cooling heat transfer.