Pool boiling on the aluminum alloy, copper and WC-coated copper with micro-finned textures and developed multimodal roughness formed by nanosecond laser radiation

Abstract

Boiling remains one of the most effective processes allowing heat to be removed from heat-loaded surfaces of technological equipment. Due to the development of technologies for metal surface treatment with laser radiation to form specified near-surface properties, including the type, texture configuration and wetting properties, the task of substantiating the use of heat transfer surfaces modified by laser radiation to intensify the boiling process has become relevant. The pool boiling characteristics in distilled degassed water (before the boiling crisis onset) were compared experimentally on the surfaces of samples made of aluminum alloy, copper, and WC-coated copper. Experimental samples were treated by two different methods, including widely used polishing with abrasive materials and laser radiation. Nanosecond laser treatment was used to make micro-finned and anisotropic (developed hierarchical roughness) textures. Textured samples were then hydrophobized. As part of the experiments on pool boiling, the characteristics of the forming bubbles were recorded on the prepared surfaces, heat transfer coefficients, and critical heat flux values were determined. Experimental results were compared with predicted characteristics using well-known models. The evolution of the functional properties of laser-textured metal surfaces after prolonged exposure to heat flux, which is typical of the operating modes of modern heat-loaded equipment, was assessed.