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Generalized pinch point design method of subcritical-supercritical organic Rankine cycle for maximum heat recovery

Sarkar, Jahar
Energy 2018 v.143 pp. 141-150
ammonia, heat recovery, mass flow, pentane
Novel methodology for pinch point design and optimization of subcritical and supercritical organic Rankine cycles is proposed for maximum heat recovery. The proposed method is able to predict pinch point locations in both evaporator and condenser simultaneously. As a main advantage, both evaporator and condenser pressures can be optimized simultaneously by optimizing only working fluid mass flow rate to get maximum net work output or heat recovery efficiency for given heating fluid and cooling fluid inlet conditions using selected working fluids. Working fluids have been selected based on thermodynamic and environmental criteria and compared based on various performance parameters (net work output, thermal efficiency, heat recovery efficiency, irreversibility, exergetic efficiency, turbine size parameter and heat transfer requirement). The present method seems to be better than previous pinch point design methods as it optimize the cycle by considering both source and sink. At optimum operation, ammonia is best in terms of lower mass flow rate requirement, higher exergetic efficiency, lower turbine staging and turbine size, whereas, isopentane is best in terms of higher power output and heat recovery efficiency. Novel contour plots are presented as well to select optimum ORC design parameters for available heat source and sink.