Critical heat flux and Leidenfrost temperature on hemispherical stainless steel surface

Abstract

In this experimental work, an investigation on the droplet evaporation lifetime using hemispherical stainless steel was carried out. The main objective of this experimental work is to obtain the critical heat flux (CHF) and Leidenfrost temperature, TL. The novelty of this study is the use of a hemispherical surface to evaporate the droplets. This hemispherical surface was constructed using Electrical Discharge Machining (EDM) which provided a nearly perfect and smooth hemispherical stainless steel surface. Ethanol was selected as the test liquid and the droplet size was approximately 3.628 mm in diameter. The droplet temperature was approximately 29.9 °C corresponding to liquid subcooling ΔTsub = 48.1 K. The droplet impact height was set to be around 65.0 mm corresponding to impact velocity of 1.129 m/s. The temperature range from a low temperature of Tw = 70 °C to a high temperature of Tw = 230 °C. As a result, the CHF point and Leidenfrost temperature was obtained at the surface temperatures of Tw = 120.1 °C and 193.6 °C respectively. The boiling curve obtained also showed a smooth exponential curve which was found to be similar to other literature. Keywords: Evaporation lifetime, EDM, Critical heat flux, Leidenfrost temperature, Hemispherical surface, Droplet impact