Modelling and design of a two-phase reciprocating expander for integration in a trilateral flash cycle

Two-phase expansion devices are used in a multitude of cycles and allow for an increase of the overall system efficiency. It has been shown that the trilateral flash cycle can improve the power output from the recovery of low temperature residual heat compared to the classic subcritical Organic Rankine cycle. Theoretical studies predict an improvement of at least 15%. The expanders that are mainly investigated for the purpose of two-phase expansion are the Lysholm and the reciprocating expanders. From these two, the reciprocating expander has been researched the least as it is not as easy to model. It has been shown that to model the reciprocating expander, there is a need to describe the non-equilibrium state of the phases during the expansion process. This study aims to fill the knowledge gap that exists for two-phase reciprocating expanders, by constructing a predictive model to describe the expansion process and the non-equilibrium phenomena occurring. The constructed model makes use of the homogeneous relaxation model to describe the thermal non-equilibrium between the phases. The working fluid used in initial modelling is cyclopentane. The resulting model will be used to formulate design guidelines for the construction of a two-phase reciprocating expander. This prototype will be used to gain experimental data, with which the theoretically predicted efficiency improvement can be validated.     «

Two-phase expansion devices are used in a multitude of cycles and allow for an increase of the overall system efficiency. It has been shown that the trilateral flash cycle can improve the power output from the recovery of low temperature residual heat compared to the classic subcritical Organic Rankine cycle. Theoretical studies predict an improvement of at least 15%. The expanders that are mainly investigated for the purpose of two-phase expansion are the Lysholm and the reciprocating expanders...     »