Thermal pulse energy harvesting

•A thermal pulse operating mode can increase the maximum power of many thermal energy harvesting systems.•Two modes of pulsed heat transfer were modeled and compared to proof-of-concept experiments.•At a 1:2 heat engine–heat sink thermal resistance ratio, the enhancement exceeds 60% in power and 15% in efficiency.

This paper presents a new method to enhance thermal energy harvesting with pulsed heat transfer. By creating a phase shift between the hot and cold sides of an energy harvester, periodically pulsed heat flow can allow an available temperature gradient to be concentrated over a heat engine during each thermal pulse, rather than divided between the heat engine and a heat sink. This effect allows the energy harvester to work at maximum power and efficiency despite an otherwise unfavorable heat engine–heat sink thermal resistance ratio. In this paper, the analysis of a generalized energy harvester model and experiments with a mechanical thermal switch demonstrate how the pulse mode can improve the efficiency of a system with equal engine and heat sink thermal resistances by over 80%, although at reduced total power. At a 1:2 engine–sink resistance ratio, the improvement can simultaneously exceed 60% in power and 15% in efficiency. The thermal pulse strategy promises to enhance the efficiency and power density of a variety of systems that convert thermal energy, from waste heat harvesters to the radioisotope power systems on many spacecraft.