HEAT TRANSFER PROPERTIES OF DRY AND WET FURS OF DAIRY COWS

Abstract

ABSTRACT Heat and mass transfer properties of an Israeli-Holstein dairy cow fur were examined. The skin was stretched over a heat flux assembly, inserted into a wind tunnel, and heat and mass transfer were examined at different air velocities with fur either dry or wet. The dry coat was divided into two layers the fur and the boundary layer. The thermal resistance of the fur itself hardly changed with air velocity. The resistance to heat transfer of the coat boundary layer was found to be proportional to the square root of air velocity, similar to a flat plate. However, at low air velocity, the resistance of the coat boundary layer was found to be somewhat lower than that of a plate, while at high air velocities, it was higher than that of a plate. For the wet fur, the efficiency of forced evaporative cooling was determined by a single parameter of wettedness, which equaled unity for a saturated fur and decreased as the coat got drier. TTiis parameter is specific for a given coat and is directly related to the water content within the fur. Experiments were performed to measure the relationship between the wettedness and the amount of water sprinkled over the fur. The maximum water content of a coat wet by means of a commercially available sprinkler was some 230 g/m2 which corresponded to wettedness of 0.6. The results of this investigation may be used to design the most cost effective procedure of forced evaporative cooling for the relief of heat stress in cattle