The surface roughness plays an important role during spray cooling of hot surfaces in a presence of the boiling. Bubbles are formed in small cavities on the surface during nucleate pool boiling. Enhanced surface roughness causes that more bubbles are formed and it causes increased cooling intensity. The surface with increased roughness has also bigger surface area, which allows higher heat flow between surface and surrounding water. The influence of the surface roughness during pool boiling was investigated by many authors. The increased surface roughness causes shift of the Leidenfrost temperature to higher temperatures and increases critical heat flux during pool boiling. The influence of the surface roughness during spray cooling of hot surfaces was not still sufficiently investigated and it is not known if the effect of the surface roughness is similar like in a case of the pool boiling. Experiments for describing the effect of the surface roughness on the cooling intensity were conducted with water nozzle with flat jet. Test samples were heated in a protective atmosphere at a temperature 730 ºC and then cooled to the room temperature. Test samples were made of the austenitic stainless steel to minimize the forming of the scales on the surface. Results shoving influence of the surface roughness on the critical heat flux and on the Leidenfrost temperature are presented.Keywords: surface roughness, spray cooling, Leidenfrost temperature, critical heat flux, heat transfer coefficient
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