A. INTRODUCTION

Whether in terms of α, β, or g_φ, a major part of the analyst’s concern is with ascribing numerical values to the interaction coefficients. These depend on the properties of the fluid, on the velocity of flow over the surface, on the shape and size of the interface, and on other factors. What is derived is a formula, or set of formulas, of the kind

\[\label{eq123_1} \alpha =\alpha \mbox{fn}(\lambda, L, c_{p}, p, \rho, \eta, \Delta T,\ldots) \tag{1}\]

where α fn(...) represents “α as a function of...”, and the quantities in the bracket represent all those expected to influence the value of α, namely, the thermal conductivity, a linear dimension, the specific heat, the density, the velocity, the viscosity, the temperature difference, and so on.

Such formulas exist, although not yet in sufficient measure, and they are usually expressed, for compactness and for maximum generality, in terms of dimensionless quantities such as the Stanton or Reynolds numbers. Therefore, in order to facilitate the presentation of the formulas, the next few sections are devoted to introducing and discussing the more important of these quantities.