Pool boiling heat transfer enhancement characteristics on multi-directional dynamic micro/nano coupled shape memory alloy surfaces

The excellent shape memory effect of shape memory alloys (SMAs) enables the adaptive optimization of boiling heat transfer performance to meet the operational requirements of different heat transfer stages. Nevertheless, previous studies have largely been limited to single-scale deformable structures; because of their fixed geometric configurations, optimal performance has been difficult to maintain across the full range of operating conditions. Based on the self-assembly technology of graphene oxide (GO) nanofluids during boiling, this study systematically investigates the effects of self-assembled nanostructured surfaces on pool boiling heat transfer performance at different deposition heat flux. Furthermore, the optimal nanostructured surface (NS-25W) is integrated with a multi-directional dynamic microstructured surface (MDS) with thermoresponsive properties to construct a novel multi-directional dynamic-nanostructured coupled surface (MDS-NS). By combining pool boiling experiments with visualization observations, the cross-scale synergistic enhancement mechanism of the coupled surface is revealed, and the boiling characteristics of each surface are systematically evaluated. The results demonstrate that the NS-25W surface exhibits a uniform structure and abundant nucleation sites, and its maximum heat transfer coefficient (HTC) and critical heat flux (CHF) are 35.7% and 43.8% higher, respectively, than those of a plain surface. Owing to the dual-enhancement mechanism, the MDS-NS surface overcomes the performance limitations of single-structure surfaces and achieves optimized boiling heat transfer performance, with a CHF of 32.6 W/cm 2 and an HTC of 1.01 W/(cm 2 ·K), corresponding to increases of 105% and 140%, respectively, compared with plain surfaces.