Novel and Efficient Superhydrophilic Surface for Improved Critical Heat Flux in Heat Pipe Applications

This paper presents an experimental investigation of a new combination of alkali solution for generating superhydrophilic copper surfaces and its characterization based on spreading parameters. We employ the versatile alkali solution-based oxidation technique, where different aqueous solutions (KOH, K2S2O8, (NH4)2S2O8, and NaOH) are used to induce the growth of copper oxide (CuO) microstructure on the copper surface. CuO microstructure growth is controlled by varying parameters such as immersion time, temperature, and heat treatment in the traditional sol–gel method. The effect of three different chemical combinations on the spreading area is investigated. Also, the critical heat flux (CHF) calculated from the spreading parameters and droplet evaporation technique is discussed. Different techniques like X-ray diffraction (XRD), contact angle measurement (θ), and scanning electron microscopy (SEM) are utilized to study the crystal structure, surface chemical composition, wettability, and morphologies of microstructure on copper substrate. The chemical combinations used in this study changed the wettability of the pristine copper (90.3°) to superhydrophilicity (~0°), which significantly affects the spreading parameter and hence the critical heat flux (CHF). The CHF increases by ~200% compared to the bare copper surface. Our work provides a novel chemical combination to obtain the superhydrophilic (SHP) copper oxide surface with high CHF which can be produced on a mass scale in the industry.