Unsteady flow in the suction process of a scroll expander for an ORC waste heat recovery system

The scroll expander has played a vital role in the organic Rankine cycle for small scale waste heat recovery systems. The flow losses in the suction process of the scroll expander have great effects on the expander efficiency. In this paper, a three-dimensional transient computational fluid dynamic (CFD) numerical investigation based on dynamic mesh technology was performed to study the unsteady flow in the suction process of a scroll expander working with R123. For a given geometrical structure of the scroll expander, transient performances of the scroll expander were obtained, including mass flow rate, gas driving moment, and pressure in the working chambers. As key factors affecting transient performances of the scroll expander, unsteady flow behaviours in the suction port and suction chamber were investigated. The flow mechanisms of the vortexes existing in the suction and expansion chambers were revealed. A deep understanding of the suction process of a scroll expander provides an essential guidance for the optimal design of the suction port and the scroll top profile.