Effect of boiling-induced aging on pool boiling heat transfer performance of untreated and laser-textured copper surfaces

Abstract

Despite its importance for practical applications, investigation of aging of enhanced boiling heat transfer surfaces, which occurs during exposure to the boiling process, is often neglected. This study explores the boiling-induced aging behavior of an untreated and a laser-textured copper boiling surface during an eight-day testing period under pool boiling conditions using saturated water at atmospheric pressure. During the test, approx. 40–50 h of intermittent boiling operation were simulated. Boiling curve measurements are used to quantify boiling performance and measurements during steady state operation periods are used to analyze the heat transfer coefficient variations. SEM imaging, contact angle measurements and Raman spectroscopy are used to analyze the surface morphology, chemistry and wettability before and after exposure to hot water and boiling. The results show that no universal prediction of aging effects is possible. A distinct two-stage aging behavior resulting in increased performance was observed on the reference surface, while the boiling performance of the laser-textured surface changed very little during the test. The results also indicate that functionalized surfaces, which might primarily rely on surface microtopography for boiling enhancement, are presumably less prone to boiling behavior changes resulting from oxidation since slight changes in surface wettability will only have a minor effect on the overall boiling performance. Furthermore, evaluation of long-term performance of enhanced surfaces is necessary since their aging behavior differs from untreated surfaces.