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In this study, thermal models for subcritical and supercritical geothermal powered organic Rankine cycles are developed to compare the performance of these cycle configurations. Both of these models consist of a detailed model for the shell and tube heat exchanger integrating the geothermal and organic Rankine cycles sides and basic thermodynamic models for the rest of the components of the cycle. In the modeling of the heat exchanger, this component was divided into several zones and the outlet conditions of each zone were found applying logarithmic mean temperature difference method. Different Nusselt correlations according to the relevant phase (single, two-phase, and supercritical) were also included in this model. Using the system-level model, the effect of the source temperature on the performances of the heat exchanger and the organic Rankine cycle was assessed. These performance parameters are heat transfer surface area and pressure drop of tube side fluid for the heat exchanger, and electrical and exergetic efficiencies of the integrated organic Rankine cycles system. It was found that 44.12% more net power is generated when the supercritical organic Rankine cycle is used compared to subcritical organic Rankine cycle. [ABSTRACT FROM AUTHOR]

In this study, the thermodynamic performance of an integrated geothermal powered supercritical regenerative organic Rankine cycle (ORC) and parabolic trough solar collectors (PTSC) is assessed. A thermal model based on the principles of thermodynamics (mass, energy, and exergy balances) and heat transfer is first developed for the components of this integrated system. This model gives the performance assessment parameters of the system such as the electrical and exergetic efficiencies, total exergy destruction and loss, productivity lack, fuel depletion ratio, and improvement potential rate. To validate this model, the data of an existing geothermal power plant based on a supercritical ORC and literature data for the PTSC are used. After validation, parametric studies are conducted to assess the effect of some of the important design and operating parameters on the performance of the system. As a result of these studies, it is found that the integration of ORC and PTSC systems increases the net power output but decreases the electrical and exergetic efficiencies of the integrated system. It is also shown that R134a is the most suitable working fluid type for this system; and the PTSCs and air cooled condenser are the main sources of the exergy destructions. [ABSTRACT FROM AUTHOR]