Novel Off-Design Operation Maps Showing Functionality Limitations of Organic Rankine Cycle Validated by Experiments

Abstract

In this study, we developed a new methodology to analyze the off-design performance of the organic Rankine cycle. The methodology enabled us to predict the performance based on four-dimensional decision variables and a set of constraints. A corresponding formulation and algorithm with general applicability were constructed. The reliability and feasibility of this methodology were validated by a test rig of the cycle with R245fa as the working fluid and three experimental schemes. Under specific working conditions, the theoretical results illustrated the operation maps, functionality limitations, and their variation laws, considering the interactive characteristics among the variables. The functionality limitations predicted a maximum thermal efficiency of 9.42%, corresponding to a net power output of 697.1 W, whereas the maximum net power output was 2251.5 W, corresponding to a thermal efficiency of 8.04%. The experimental results indicated that when the R245fa mass flow rate was 0.120 kg/s, the experimental efficiency and power output were 6.94% and 1873.4 W, respectively; when the R245fa mass flow rate was 0.049 kg/s, they were 3.54% and 274.1 W, respectively. These findings were in good agreement with the theoretical results, with relative errors below 7.64%. This work is expected to be applied in future dynamic control systems to update the setting points and manipulated variables in real time.