Optimum design of limaçon gas expanders based on thermodynamic performance

Positive displacement expanders are acquiring popularity due to the current push to harvest energy from low-grade heat resources which have been previously overlooked. The limaçon technology does offer a simple and reliable design with a considerable potential for small-size (≤4 kW) power plants. This paper presents a thermodynamic model for the limaçon design and goes on to utilise this model in an optimisation procedure adopted to calculate the expanders geometric parameters for specific power and operating constraints. The numerical method employed to solve the thermodynamic model is presented for the benefit of the reader. Two design case studies, for expanders with and without an inlet control valve, are offered at the end of the paper to prove the validity of the presented concepts and their suitability for the analysis.