image: (a) Schematic of spray cooling on 3D-ordered hierarchical micro/nano-structured surface. (b) Top-view SEM image of the structured surface. (c) Partial enlargement SEM image of the sidewall surface. Spray cooling experimental set-up. Record-breaking heat transfer performance.
Credit: ©Science China Press
The generation or manipulation of heat accounts for approximately 90% of the energy used worldwide. Especially in cutting-edge applications such as Artificial Intelligence (AI), electric vehicles, data centers, and aerospace systems, the generation of large amounts of waste heat results in undesirable device temperature rise. To prevent these electronic devices from failure due to overheating at high heat fluxes, advanced thermal management methods with both high heat transfer coefficient (HTC) and critical heat flux (CHF) are required.
Among various cooling technologies, spray cooling, as an active cooling method with a low degree of superheat, is a promising solution for the thermal management of such high heat flux systems. It atomizes liquid into micro-droplets that spray on the surface and form a liquid film. Spray cooling generally involves three heat transfer mechanisms: forced convection, liquid film evaporation, and nucleate boiling.
To further enhance the heat transfer performance of spray cooling, researchers have adopted many methods. For example, single-phase convection is strengthened by increasing the spray flow rate to raise the CHF of spray cooling, but this often leads to a lower HTC. Using micro/nano-structured surfaces, boiling heat transfer can be intensified to increase HTC. However, the vapor bubbles generated by intense boiling in the micro/nano-structured surfaces tend to accumulate and form a vapor blanket, which makes it challenging to significantly improve the CHF for spray cooling.
In response to this challenge, professor Ronggui Yang from Peking University led a research team from Huazhong University of Science and Technology to combine the high-precision 3D printing of resin with template-assisted electrodeposition to prepare a 3D-ordered hierarchical micro/nano-structured surface. The hierarchical micro/nano-structured surface coordinates the transport of spray droplets, capillary liquid films, and boiling bubbles to enhance liquid film boiling and capillary evaporation, resulting in high heat flux and high HTC. Ultimately, record-breaking spray cooling heat transfer performance is achieved, with a maximum heat flux of 1273 W/cm² and an HTC of 443.7 kW/(m² K).
The novel structured surface with spray cooling is expected to be applied in the thermal management of high heat flux electronics such as high-power chips, laser weapons, aircraft rectifiers, and automotive power electronics. This enhancement scheme can be extended to practical scenarios with multiple heat sources or large-scale cooling demands by adopting multiple nozzle arrays.
Journal
Science Bulletin