Spray Cooling on Enhanced Surfaces: A Review of the Progress and Mechanisms

The rapid development of high-power electronic, energy, and propulsion systems has led us to the point where the performances of these systems are limited by their cooling capacities. Current electronics can generate heat fluxes up to 10–100 W/cm2, and heat flux over 1000 W/cm2 needs to be dissipated with a minimum coolant flow rate in next-generation power electronics. The multiple efficient heat transfer mechanisms have made spray cooling a high heat flux, uniform and efficient cooling technique proven effective in various applications. However, the cooling capacity and efficiency of spray cooling need to be further improved to meet the demands of next-generation ultrahigh-power applications. Engineering of surface properties and structures, which is enabled by state-of-the-art manufacturing techniques, can fundamentally affect the liquid–wall interactions in spray cooling, thus becoming the most promising way to enhance spray cooling. However, the mechanisms of surface-enhanced spray cooling are diverse and ambiguous, causing a lack of clear guiding principles for engineered surface design. Here, the progress in surface engineering-enhanced spray cooling is reviewed for surface structures of millimeter, micrometer, and nanometer scales and hierarchical structured surfaces, and the performances from the reviewed literature are evaluated and compared. The reviewed data show that spray cooling can achieve a critical heat flux (CHF) above 945.7 W/cm2 and a heat transfer coefficient (HTC) up to 57 W/cm2K on structured surfaces without the assistance of secondary gas flow and a CHF and an HTC up to 1250.1 W/cm2 and 250 W/cm2K, respectively, on a smooth surface with the assistance of secondary gas flow. A CHF enhancement up to 110% was achieved on a hybrid micro- and nanostructured surface. A clear map of enhancement mechanisms related to the scales of surface structures is proposed, which can help the design of engineered surfaces in spray cooling. Some future concerns are proposed as well. This work helps the understanding and design of engineered surfaces in spray cooling and provides insights for interdisciplinary applications of heat transfer and advanced engineering materials.