Pool boiling heat transfer and bubble dynamics of modified copper micro-structured surfaces

In this work, hydrophobic copper micro-structured (HCM) surfaces are prepared to improve boiling heat transfer. A combination of chemical etching and heat treatment processes is employed to make the bare copper surface hydrophobic in nature. With the modification of wettability, a different micro-structured feature is developed on the surface. The static contact angle of the prepared hydrophobic surface is varied in between 114° to 140°. A saturated pool boiling experiment is conducted at atmospheric pressure by taking distilled water as the boiling fluid. The maximum heat transfer coefficient is 119.7 kW/m2K for the HCM surface with a contact angle of 140°. Due to its hydrophobic nature, the critical heat flux (CHF) of the HCM surfaces is a little smaller than the bare copper surface. Bubble dynamics are also observed during boiling. The surface roughness of the HCM surfaces is enhanced, which increases the active nucleation site of the HCM surfaces. The bubble departure diameter of the HCM surfaces is smaller than the bare copper surface, with a maximum reduction of 45% for the HCM-3 surface. It is also found that the micro-porous surface prepared by a combination of two conventional processes increases the heat transfer substantially.