Comprehensive optimization of a novel thermo-hydraulic machine for mechanical power generation

This paper is dedicated to the multi-aspect optimization of a novel thermo-hydraulic machine with liquid piston operating according to organic Rankine cycle, designed for mechanical power generation from low temperature reservoirs. This involves the implementation of thermodynamic and hydraulic analyses. Several issues have been identified in thermo-hydraulic machines built to date, particularly the limitation imposed by the location of the expansion phase under the equilibrium dome, which constrains maximum output work. This issue is addressed through the application of steam su-perheating followed by the organic Rankine cycle. The thermodynamic analysis showed that the R1233zd is the most suitable working fluid for the suggested novel machine within the temperature range of 65−130°C. The selection of the best working fluid was followed by the dimensioning of the hydraulic part of the machine under optimal operating condi-tions. A new parameter was introduced to link the gas and hydraulic sides of the machine. It is about the time scale of the cycle which influences significantly the mechanical output power. Furthermore, mathematical modelling of the hydraulic part of the machine concludes that high mechanical power output can only be achieved only in modes of operation with high thermal efficiencies. Conversely, operational modes with high second law efficiencies fail to deliver high mechanical power levels. These two conclusions can be regarded as equivalent to the various postulates of the second law of thermo-dynamics.