A comprehensive review of micro-scale expanders for carbon dioxide related power and refrigeration cycles

• Developments of micro-scale expanders in carbon dioxide cycles are summarized. Comparison between turbines and volumetric analysed. Relations flow rate, pressure ratio rotational speed highlighted. Challenges future development directions for outlined. In recent decades, the cycles, including supercritical cycle, transcritical Rankine cycle refrigeration have been proven effective due to high efficiency compact structure, received increasing interests. The performance expander power particularly applications, is one essential components that determine still remains a significant challenge. This paper presents critical overview (<200 kW) cycles. Five types expanders, axial radial (dynamic expanders), scroll, piston vane (volumetric evaluated from experimental numerical aspects. Expansion mechanisms, speed, isentropic efficiency, mass rate considered. review suggests stand certain advantages more suitable potentially less leakage. For all internal external leakages remain vital challenge greatly reduce their which urgently needs be addressed.