Vaporization of moving water droplets in air at high temperatures

Author

Su-Ming Chan

Date of Award

3-1986

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Chemical Engineering

Major Professor

George C. Frazier

Committee Members

J. W. Hodgson, H. W. Hsu, J. J. Perona, J. S. Watson

Abstract

The vaporization rate of small droplets may control processes as diverse as the combustion of liquid fuels, spray-drying, and humidification operations. However, there are very few experimental data in the literature for the vaporization of small, freely moving droplets in the ambient temperature range above a few hundred degrees centigrade. This investigation was therefore undertaken to obtain vaporization data on water droplets in the temperature range of 500°C-850°C. These data are used to evaluate certain vaporization models that previously have been tested primarily in the moderately low temperature range with data obtained principally from vaporization experiments on suspended droplets. A subsidiary objective was to determine whether or not dissolved gases affect the vaporization rate.

A uniformly sized water droplet stream was directed through an elevated temperature air stream, and droplet size was evaluated photographically. The droplets are about 260 μm to 300 μm in diameter, spaced within two to three diameters of one another. Reynolds numbers range from 7 to 17.

Experimentally determined vaporization rates are compared with results computed according to the modified Froessling model and the Large Flux model, each with different coefficient on the ventilation factors. Although data scatter precludes an unambiguous choice of vaporization model and ventilation factor, the Large Flux model containing the ventilation factor correlation of Rowe, Claxton and Lewis gives the best agreement with the experimental results, the mean error in this case being only 0.6%. The extent of the agreement between the data and the model predictions suggests that droplet-droplet interaction effects are not important, even with the relatively close droplet spacings of these experiments. This result may be a consequence of the droplet train-air stream, cross-flow arrangement.

Recommended Citation

Chan, Su-Ming, "Vaporization of moving water droplets in air at high temperatures. " PhD diss., University of Tennessee, 1986.
https://trace.tennessee.edu/utk_graddiss/12221