FORCED-CONVECTION HEAT AND MASS TRANSFER FROM COMPLEX SURFACES

Heal and mass transfer rates from complex surfaces to a turbulent channel flow were measured using an infrared imaging system and the naphthalene sublimation technique, respectively. The surfaces are composed of spherical particles embedded either in a layer of thermally conducting, nonevaporating liquid or in an isothermal layer of subliming naphthalene. The experimental results indicate that, in general, the surface heat and mass transfer coefficients vary as the surface roughness increases, whereas the surface heal transfer coefficient changes as the solid-to-liquid thermal conductivity ratio is varied. Mass transfer rates exhibit less sensitivity to variations in the naphthalene height for surfaces composed of smaller particles, and heat transfer rates from surfaces of smaller particles remain fairly constant as the liquid level and thermal conductivity ratios are varied. The results are discussed relative to drying of partially welled surfaces with surface complexity induced by the presence of droplets upon an impermeable substrate or a receding moisture front in a bed of granular material.