Mass Transfer of Rough Hailstone Models in Flows of Various Turbulence Levels

Abstract

The convective mass transfer of smooth and rough sphere test particles over a range of Reynolds numbers between 3 ? 103and 105 was studied by means of an electrochemical method at a Schmidt number of 2170. The experiments were carried out in a liquid tunnel where the electrolyte is forced past the stationary test particles at variable flow rates. Three distinctly different levels of turbulence intensity of the flow allowed an evaluation of the turbulence effect on the transfer rates. An extrapolation of the results to the heat and mass transfer coefficients of hailstone models in the atmosphere shows that surface roughness may account for increases in the transfer rates of up to a factor of 2. For relatively large roughness elements (cluster Particles) the increase in the convective transfer coefficients at equal Reynolds numbers (based on equal volume diameters) is approximated by the increase in surface area. Atmospheric turbulence is not expected to change these transfer coefficients significantly since the intensity of fluctuations with suitable time and space scales is expected to be rather small.