Spray water cooling heat transfer at high temperatures and liquid mass fluxes

Spray water cooling is an important technology used in industry for the cooling of materials from temperatures up to 1800 K. The heat transfer coefficient in the so-called steady film boiling regime is known to be a function of the water impact density. Below a specific surface temperature T-L. the heat transfer coefficient shows a strong dependence oil temperature (Leidenfrost effect). These findings are the results of complex self-organizing two-phase boiling heat transfer phenomena. The heat transfer coefficient was measured by an automated cooling test stand (instationary method) under clean (non-oxidizing) surface conditions. Compared to the common thought, all additional temperature dependency in the high temperature regime was found. The heat transfer from the material to the outflowing spray water is explained by it simple model of the two-phase flow region. From the experimental data, all analytic correlation for the dependence of the heat transfer coefficient 7 as all analytic function of water impact density V-s and temperature Delta T is provided. For water temperatures around 291 K, surface temperatures between 473 and 1373 K, i.e. Delta T > 180 K and water impact densities between V-s = 3 and 30 kg/(m(2) s) the heat transfer coefficient alpha was measured. The spray was produced with full cone nozzles (nu(d) approximate to 13-15 m/s, d(d) approximate to 300-400 mu m). (C) 2008 Elsevier Ltd. All rights reserved.