Microfluidic-Based Sustainable Synthesis of SiO ₂ Nanofluids from Coal Gasification Fine Slag for Advanced Thermal Management

The resource recovery and high-value utilization of coal gasification slag (CGS) are vital to promoting green and sustainable advancement in the coal chemical industry. However, synthesizing advanced functional materials with stable performance and high economic value from CGS remains a significant challenge. This research presents an approach to utilize coal gasification fine slag (CGFS) as an economical silicon source for the continuous production of SiO₂ nanofluids in a spiral microreactor. The excellent mixing efficiency in the developed 3D-printed spiral microreactor is verified through numerical simulation and fluorescence visualization experiments. Following activation and desilication treatment of CGFS, the microreactor enables the continuous production of SiO₂ nanofluids, which exhibit homogeneous particle dimensions and outstanding colloidal stability. The flow boiling heat transfer performance of the fabricated nanofluids in high-power chip cooling applications is systematically evaluated. The results reveal that the 0.01 wt % SiO₂ nanofluids exhibit the best heat transfer enhancement, achieving a maximum increase of 49.52% in critical heat flux (CHF) and a 34.00% improvement in maximum heat transfer coefficient (HTC) compared to deionized water as the basic fluid. Through bubble visualization combined with deposition surface characteristic analysis, it is found that nanofluids effectively reduce the bubble size and shorten the bubble lifetime by increasing surface nucleation sites, improving wall wettability, and delaying bubble coalescence, thereby enhancing the boiling heat transfer process. This study not only establishes a novel pathway for the high-value utilization of CGFS but also offers theoretical insights and a technical foundation for developing cost-effective, high-performance cooling fluids.