Experiments on the Load Convective Mass Transfer of Smooth and Rough Hailstone Models

Abstract

The local convective mass transfer (i.e., the mass transfer as a function of polar angle) of smooth and rough particles has been investigated with an electrochemiluminescence technique at a Schmidt number Sc ≈ 103 for Reynolds numbers 3 ? 103 < Re < 105. Comparative qualitative wind tunnel observations were made of the evaporation of naphthalene-coated rough spheres with Sc = 2.4 and, wherever possible, the findings were compared with existing heat transfer measurements in order to minimize their dependence on the molecular properties of the fluid. Although some uncertainty still exists, it is possible to present estimates of the qualitative and quantitative effect of surface roughness on the local convective heat and mass transfer of hailstones, and especially to show the large increase in local transfer at polar angles around 90° for Re > 104, which may help to explain the growth of big hailstones.