Modeling and evaluation of scroll expanders for a liquid-flooded Ericsson power cycle

Previous studies have shown potential for a Liquid Flooded Ericsson power cycle as a high efficiency and low cost alternative for concentrating solar power plants, but more research is needed to obtain high efficiency components necessary for achieving high cycle efficiencies. This study investigated a prototype scroll expander designed for liquid flooding and high temperature working conditions. Experimentation was carried out on the prototype expander using Nitrogen and Duratherm LT (flooding liquid) as the working fluids. Analysis of the test results showed poor performance over the tested working conditions. From irreversibility analysis conducted to identify different losses in the expander, it was found that the pressure drop, heat transfer and frictional losses were the major contributors to the poor performance, followed by leakage and over/under expansion losses. Certain geometrical features in the expander’s scroll profile such as the extra scroll provided at the suction for delayed porting might have contributed to the losses. However, a detailed analysis using deterministic model is required to study and determine the exact causes of the losses. In addition to the expander analysis, thermodynamic modelling of the Liquid Flooded Ericsson power cycle integrated with expander and compressor models was conducted. Optimum cycle working conditions were determined through a parametric study of different input variables. Cycle model simulation results showed poor performance due to the poor expander efficiency. A parametric study of the semi-empirical expander model input parameters was also carried out to analyze and determine the values of the constant input parameters for which internal losses are low and thus the component isentropic efficiencies are higher. Cycle performance was again evaluated using modified component model parameters, which showed considerable improvement in the cycle performance. The work done in this study provides a better understanding of flooded expansion at higher temperatures and allows a more realistic performance evaluation of LFEC. The Liquid Flooded Ericsson power cycle holds good potential as a cost effective alternative for concentrating solar power plants, but continued effort is required in the direction of developing high efficiency rotating components through testing and design improvements