A close-cycle self-driving thermal energy harvester using liquid metal as energy carrier fluid has been proposed. The driving force that pushes the liquid metal against flow resistance and gravity is provided by a resistively heated volatile fluid based on thermo-pneumatic principle. The tested harvester prototype demonstrated its capability to extract thermal energy between small temperature gradient, at a scale of 10 °C. During a 5-h operation, it further demonstrated robust liquid metal recirculating performance at a time-average volume flow rate of 14 ml/min with a 12.25 W heating load. The prototype also managed to self-adjust to variable working conditions which indicated the reliability of this method. Advantages of this method include simple-structural design, rigid-motion free operation, and low-temperature actuation. These advantages make it uniquely suited for solar energy and low-grade heat harvesting, high heat flux electronics cooling, as well as autonomous machines actuating.

Appl. Phys. Lett. 108, 023903 (2016) 

(a) Experimental set-ups of the tested harvester prototype showing its working process with 6.25?W heating power. (Multimedia view) [URL: http://dx.doi.org/10.1063/1.4939829.1] (b) Liquid metal and isopentane distribution in the heat source chamber during operation. (c) Liquid metal and isopentane layered in the heat source chamber 1?h after heat charge is terminated.