While solar thermal power plants are increasingly gaining attention and have demonstrated their applications, extending electricity generation after the sunset using phase change material (PCM) still remains a grand challenge. Most of the organic PCMs are known to possess high energy density per unit volume, but low thermal conductivity, that necessitates the use of thermal conductivity enhancers (TCEs) to augment heat transfer within PCM. In this paper, thermal performance and optimization of shell and tube heat exchanger-based latent heat thermal energy storage system (LHTES) using fins as TCE for medium temperature (<300 °C) organic Rankine cycle (ORC)-based solar thermal plant are presented. A commercial grade organic PCM, A164 with melting temperature of 168.7 °C is filled in the shell side and heat transfer fluid (HTF), Hytherm 600 flows through the tubes. A three-dimensional numerical model using enthalpy technique is developed to study the solidification of PCM, with and without fin. Further, the effect of geometrical parameters of fin, such as fin thickness, fin height, and number of fin on the thermal performance of LHTES, is studied. It is found that fin thickness and number of fin play significant role on the solidification process of PCM. Finally, the optimum design of the fin geometry is determined by maximizing the combined objective of HTF outlet temperature and solid fraction of PCM at the end of the discharging period. The latent heat thermal storage system with 24 fins, each of 1 mm thickness and 7 mm height, is found to be the optimum design for the given set of operating parameters.
In today's scenario ensuring sustainability of energy system particularly in the field of power generation is a major concern, and in this regard exergy analysis is widely accepted tool. For this purpose, first a comprehensive performance is carried out between two gas turbine plants i.e. GT2 (case I) and GT1 (case II) using various exergy performance parameters. Further a comprehensive performance evaluation is carried out between three cases; GT2 (case I), GT1 (case II) and CCPP (case III) using different sustainability indicators such as exergy efficiency, waste exergy ratio, exergy destruction factor and recoverable exergy ratio. Results demonstrate that exergetic sustainability index of combined cycle power plant (CCPP) is 0.45 when compared with GT2 (0.29) and GT1 (0.28). The increased sustainability index is because of the incorporation of a bottoming cycle, which ultimately decreases waste exergy ratio and leads to an increase in exergy efficiency and sustainability index of CCPP.
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