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 TL, the heat transfer coefficient shows a strong dependence on 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, an additional temperature dependency in the high temperature regime was found. The heat transfer from the material to the outflowing spray water is explained by a simple model of the two-phase flow region. From the experimental data, an analytic correlation for the dependence of the heat transfer coefficient α as an analytic function of water impact density VS and temperature ΔT is provided. For water temperatures around 291 K, surface temperatures between 473 and 1373 K, i.e. ΔT > 180 K and water impact densities between VS = 3 and 30 kg/(m2 s) the heat transfer coefficient α was measured. The spray was produced with full cone nozzles (vd ≈ 13–15 m/s, dd ≈ 300–400 μm).