Investigation of the Cooling of Hot Walls by Liquid Water Sprays

An experimental study was conducted for the heat transfer from hot walls to liquid water sprays. Four full cone, swirl spray nozzles were used at different upstream pressures, giving mass fluxes impinging on the wall, G, from 8 to 80 kg m(-2) s(-1), mean droplet velocities, U, from 13 to 28 m s(-1) and mean droplet diameters, D, from 0.4 to 2.2 mm. A target consisting of two slabs of beryllium-copper alloy, each 4 x 5 cm in size and 1.1 mm thick, was electrically heated to about 300 degrees C and then rapidly and symmetrically cooled by water sprays issuing from two identical nozzles. The midplane temperature was measured by a fast response, thin-foil thermocouple and the experimental data were regularized by Gaussian filtering, The inverse heat conduction problem was then solved by an approximation of the exact Stefan solution to yield the wall temperature T-w and the heat flux q(w) transferred to the spray at temperature T-f. As a result, cooling curves expressing the heat flux q(w) as a function of T-w - T-f were obtained. The single-phase heal transfer coefficient h and the maximum heat flux q(c) were found to depend upon the mass flux G and the droplet velocity U, while the droplet size D had a negligible independent influence. Simple correlations for h and q(c) were proposed.