A passive self-adaptive heat exchanger that autonomously switches between cooling and insulation

Abstract Precise and dynamic thermal management is crucial for maintaining the performance and reliability of modern high-power-density electronics and energy systems. However, achieving this without external energy remains a significant challenge. Herein, we report a fully passive smart heat exchanger integrating nickel-titanium (NiTi) shape memory alloy (SMA) fins with an ultra-low thermal conductivity aerogel layer. Driven by the intrinsic phase transition of the SMA within a critical window of 10 °C–40 °C, the device functions as an autonomous ‘aerodynamic valve’ with a rapid response time of approximately 60 s. Experimental and numerical characterizations demonstrate that in the high-temperature cooling mode (>40 °C), the fins deploy to an upright state, achieving a Nusselt number of up to 270, comparable to static copper heat sinks. Conversely, in the low-temperature insulation mode (