Hot-gas defrosting is a complex process involving spatial and time variations as well as many indeterminate factors. In order to model the process, it has been idealised by subdividing it into four stages depending on the outside surface condition, preheating, melting, vaporising, and dry heating. Each element of a coil may pass through three or four stages. An algorithm for the solution of the equations of the idealised process has been developed. In addition to coil geometry and initial conditions, several heat and mass transfer parameters (maximum surface water, free-convection air film conductance, air/water film conductance, and surface water vaporisation coefficient and exponent) require specification in order to solve for defrosting characteristics. Values of these heat and mass transfer parameters are not readily available from the literature and were determined experimentally. The evaluation of these parameters and the validation of the model are discussed in a companion paper. The scope of this paper is limited to a discussion of the physical and mathematical nature of the model.

KEYWORDS: calculating, hot, gas, deicing, evaporators, heat flow, algorithms