Piston-cylinder work producing expansion device in a transcritical carbon dioxide cycle. Part II: theoretical model

A simulation model for a piston-cylinder type expansion device in which the linear motion of the piston is converted to the rotational motion of a crank via a connecting rod was developed for its use in a transcritical CO2 cycle. The model is based on lubrication theory with an assumption that the piston ring is a slippery bearing. This model has been used to verify the proper operation of the device in a prototype application and to identify the loss mechanisms of the device in the design stage. In addition, an analysis of the device has been conducted using this theoretical model for the device as installed in a prototype cycle as reported in a companion part I paper.