Executive Summary : | Boiling heat transfer is a challenging area to fulfil the requirements of various industrial sectors such as thermal and nuclear power plants, refrigeration and air conditioning units, electronics and battery cooling etc. The study of bubble dynamics during boiling of liquids over a heated surface is a complex process due to non-linear growth of bubbles. It is a well-known fact that the amount of heat removed during the boiling process is basically due to the formation of vapour bubbles on the heating surface. Hence, the boiling heat transfer coefficient is influenced by bubble departure diameter, bubble departure frequency, active nucleation site density, bubble growth and waiting period. To increase the boiling heat transfer, numerous methods have been explored in the past by fluid modification and surface treatment. The fluid modification approach uses additives or nano-particles have several issues in wide applicability as it puts constraints on fluid selection and operating conditions of the boiling system. The surface treatment approach includes enhancement of surface wettability, surface morphological alteration with porous coatings, artificial fins and nano/microstructures. Several studies analyzed the enhancement of the boiling heat transfer for hydrophilic and hydrophobic surfaces for pool boiling of distilled water. However, a robust mechanistic prediction of nucleate boiling heat transfer is still not available for a wide range of boiling conditions, including the enhanced surface geometries created by non conventional machining processes like Electrical Discharge Machining (EDM). |