A model of evaporative cooling in a wetted hide

Abstract

A theoretical model is presented for the simultaneous transfer of heat and mass in a wet fur that occurs when an animal is cooled by blowing air over its wetted coat. This method for reducing severe heat stress in cows is referred to as forced evaporative cooling. Previously published models for latent heat loss from the body surface of mammals assume that the skin surface is the only site where evaporation occurs, while the rest of the coat remains dry. This assumption is only appropriate for a model to describe sweating, but is not suited to cope with the prevailing conditions during forced evaporative cooling. By allowing for evaporation throughout the entire depth of the coat, the present model enables the evaluation of integrated parameters that characterize the cooling capacity of a wet hide, such as “evaporative effectiveness” or “effective wettedness”. The application of these parameters is demonstrated with experimental data obtained using an excised fur of a dairy cow. Simulation runs showed that these parameters depend on ambient thermal parameters (temperature, humidity and air velocity) and on intrinsic local properties such as water content and distribution within the hide. The results of this study contribute to the development of a rational design of a forced evaporative cooling strategy.