Development and evaluation of an evaporation model for predicting sprinkler interval time

Abstract.

Heat stress in swine causes decreased productivity and economic losses; hence, heat stress mitigation techniques must be developed to be economically and resource efficient. Current cooling strategies for livestock facilities, such as evaporative coolers or sprinklers, are governed by the Water Vapor Pressure (WVP) concentration gradient between the air (a function of dry-bulb temperature; t_db, Relative Humidity; RH, and atmospheric pressure) and the saturated WVP at the wet surface. Traditional sprinkler control systems operate at fixed ‘off‘ intervals (i.e., drying) regardless if the thermal environment (TE) has the capacity or not to evaporate the dispersed water. Therefore, the objectives were to develop and simulate a novel Variable Interval Sprinkler Control System (VISCoS) that dynamically changes the ‘off‘ interval based on t_db, RH, and airspeed feedback. A theoretical simplified pig evaporation model estimated water evaporation rate as a function of the TE, pig surface area and skin temperature, and mass of water applied. To evaluate the model in controlled conditions, a cylinder (assumed geometry of a pig) was placed inside an insulated enclosure where different combinations of t_db, RH, and airspeed could be simulated across the cylinder. The inside surface of the cylinder was heated and controlled to replicate the skin temperature of an animal, while the outer surface was wrapped in a thin chamois. Water was applied to the cylinder via a sprinkler where approximately 40% of the top portion of the cylinder was wetted. Comparison of modeled with measured evaporation time showed reasonable agreement with a root-mean-square error of 7.9 min for evaporation times ranging from 5 to 25 min.