Detailed study of a micro heat engine for thermal energy harvesting

This paper presents a micro heat engine fabricated in silicon micro technology. Its operation principle is based on a cavity filled with a liquid-gas phase-change working fluid that performs a self-controlled reciprocating motion between a heat source and a heat sink. A bistable buckling membrane generates the respective upward and downward driving forces upon expansion and contraction of the working fluid. For prediction of the engine performance a hybrid model is developed. This model predicts an operation frequency of 0.72 Hz and a mechanical output power of 1.29 mu W at a temperature difference of 37 K. Loss mechanisms are theoretically explored and ways to enhance the overall engine efficiency are discussed. To verify this model, a functional demonstrator is fabricated. In the experiments, an operation frequency of 0.71 Hz is found at a temperature difference of 37 K.