Collaborative Research: Capillary-Controlled Thermal Diode using Heterogeneous Nanostructures

A thermal diode is a device that enables heat to flow in one direction more effectively than in the opposite direction, analogous to an electrical diode. An efficient, fast, and robust thermal diode is needed to substantially increase the efficiency of advanced thermal management, energy harvesting, and to develop novel applications such as thermal logic gate. This project studies a new class of thermal diodes by tailoring condensation/evaporation heat transport mechanisms through heterogeneous nanostructures under different temperature gradients. The working mechanisms will be studied using a combination of multiphysics-multiscale simulation approaches and experiments. The project aims to involve students from underrepresented groups in science and engineering. Outreach activities will be conducted for K-12 students and the public via summer camps to encourage their involvement in engineering and science. The rectification or thermal-switching ratio of current thermal diodes are much lower than that required in many applications. To address this challenge, a novel thermal diode that is based on the concept of capillary filling and emptying is proposed. The objectives of this project are to examine two hypotheses (1) the capillary filling/emptying in structural- and material-wise heterogeneous nanostructures (< 1,000 nm) enables control of the effective thermal conductivity using water as a working fluid at ambient conditions; (2) the capillary-controlled effective thermal conductivity changes under fast, cyclic switching of the temperature gradients (thermal diode cycle time, tcyc < 0.05 s) to realize highly-efficient (rectification ratio, R > 100) nanoscale thermal diode without significant hysteresis at ambient conditions.This collaborative multidisciplinary research will involve high-quality students for STEM education, with particular emphasis on underrepresented and K-12 students. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.