Prediction of mass transfer from spheres and cylinders in forced convection

Abstract

An expression is obtained relating mass transfer, due to forced convection, to hydrodynamic conditions over the entire surface of a sphere. In the case of the forward stagnation point no experimental data are required for the hydrodynamic conditions. The relationship may also be applied to circular cylinders in cross flow. Up to the point of separation of forward flow an established method, employing pressure distribution data, is suggested for the estimation of hydrodynamic conditions, whilst a method is developed for estimating the conditions over the area confined by the wake. By simple analogy predictions may be made for heat transfer which are in good agreement with experimental data. In the case of the forward stagnation point of a sphere (or circular cylinder in cross flow) the normal dimensionless forced convection transfer groups are shown to be independent of Reynolds number but the groups for the over-all or partial surfaces are shown to be dependent on Reynolds number, contrary to much popular opinion. No form of this dependency is suggested on account of its complexity but the observation explains the reason for various investigators obtaining different constants, for different ranges of Reynolds number, in the usual dimensionless expressions.