Evaporative cooling due to a sparse spray

Abstract

The cooling effect of a sparse spray impinging on a semi-infinite solid is investigated. Experiments are conducted by monitoring (via infrared thermography) the surface of the solid heated by radiation and cooled by sprays of uniform size droplets until steady-state conditions are reached. The surface temperature field in the proximity of a single droplet is modeled with a closed-form solution based on the hypothesis of constant and uniform heat flux at the solid-liquid interface. In the far field, an instantaneous point-sink solution is adequate to represent a single droplet cooling effect. These closed form solutions are used to fit the results of a coupled model previously developed, which solves the liquid and solid temperature fields for the evaporative transient. Inputs from this model are necessary for the formulation of both the closed-form solutions. The spray model formulation is based on the superposition of the cooling effect of all the droplets deposited on the surface. The transient surface temperature distributions and the average surface temperature are compared for the data and computations. The results are in good agreement for similar random droplet distributions of the order of 1 g/m2/s with initial solid surface temperatures ranging between 130 and 160°C.