Turbulent convective heat and mass transfer from accelerating particles



The rate of evaporation of acetone from single particles accelerating freely in a downward concurrent turbulent air stream was studied over a range of air velocities from 40 to 70 ft./sec. and at a constant air temperature of 410°F. The particles consisted of celite in the shape of spheres, cubes, disks and cylinders, varying in size from 0.15 to 0.40 in. Accurate particle velocity data were obtained with a new radioactive tracer technique, and high-speed photography at two positions along the column permitted measurement of the rate of rotation and showed that the particles rotated in a random manner.

Adequate prediction of the observed heat and mass transfer data could be obtained from the integration of a rate eequation previously reported for stationary particles. The concept of a new characteristic dimension, developed for the latter case, was found to be applicable to randomly rotating shapes and to account satisfactorily for the behaviour of nonspherical particles.