Sharif Digital Repository

This paper presents a theoretical framework for the energy and exergy evaluation of a basic as well as three modified Organic Rankine Cycles (ORCs). The modified ORCs considered incorporating turbine bleeding, regeneration and both of them. The results demonstrate that evaporator has major contribution in the exergy destruction which is improved by increase in its pressure. The results confirm that the integrated ORC with turbine bleeding and regeneration has the highest thermal and exergy efficiencies (22.8% and 35.5%) and the lowest exergy loss (42.2 kW) due to decrease in cold utility demand and high power generation  

The increment of using fossil fuels has caused many perilous environmental problems such as acid precipitation, global climate change and air pollution. More than 50% of the energy that is used in the world is wasted as heat. Recovering the wasted heat could increase the system efficiency and lead to lower fuel consumption and CO2 production. Organic Rankine cycle (ORC) which is a reliable technology to efficiently convert low and medium temperature heat sources into electricity, has been known as a promising solution to recover the waste heat. There are numerous studies about ORC technology in a wide range of application and condition. The main objective of this paper is to presents a... 

From a thermal point of view, zeotropic mixtures are likely to be more efficient than azeotropic fluids in low-temperature power cycles for reduction in exergy destruction occurring during heat absorption/rejection processes due to their suitable boiling characteristics. In this study, comprehensive energetic and exergetic analyses are mathematically performed for an organic Rankine cycle (ORC) system employing a potential binary zeotropic working fluid, namely R717/water. For this purpose, initially mass, energy, and exergy balance equations are derived. With regard to the similarity in molar mass of R717 (17.03 g mol−1) and water (18.01 g mol−1), there is no need to alter the size of the... 

This study presents a novel set-up for desiccant-based cooling and dehumidification systems. In this cycle, a solid desiccant and conventional combined cooling and power (CCP) systems, based on the ejector refrigeration cycle (ERC) and the organic Rankine cycle (ORC), are integrated to provide dehumidification and cooling, simultaneously. The ERC is integrated with the ORC for devising a self-powered design which has not been done until now. The proposed integrated system is useful for replacing the peak electricity demand with the heat demand, decreasing the pressure on the power grid in humid areas. Dynamic hourly simulation of the proposed system as well as a conventional system were... 

From a thermal point of view, zeotropic mixtures are likely to be more efficient than azeotropic fluids in low-temperature power cycles for reduction in exergy destruction occurring during heat absorption/rejection processes due to their suitable boiling characteristics. In this study, comprehensive energetic and exergetic analyses are mathematically performed for an organic Rankine cycle (ORC) system employing a potential binary zeotropic working fluid, namely R717/water. For this purpose, initially mass, energy, and exergy balance equations are derived. With regard to the similarity in molar mass of R717 (17.03 g mol −1 ) and water (18.01 g mol −1 ), there is no need to alter the size of... 

Wind turbine size has increased to megawatt capacity, and the related technologies and facilities have improved, including the cooling systems. Currently, all of the heat generated by wind turbine components is wasted to the environment. This study presents a conceptual design of a novel method for waste heat recovery of a wind turbine using an organic Rankine cycle (ORC). An organic Rankine cycle is implemented to the wind turbine as a part of the cooling system. The proposed system is thermodynamically modeled to evaluate the amount of recovered energy. Seven working fluids are chosen and investigated in the simulations to estimate the working fluid effect. The results revealed that the... 

The combination of concentrating photovoltaic (CPV) and organic Rankine cycle (ORC) systems not only leads to a reduction of photovoltaic (PV) operating temperature, but also leads to an additional electric power production. Increase in the temperature of the PV decreases its operating efficiency, while increases the ORC efficiency. Therefore, there is an optimum temperature in which the total electricity produced by the combined system will be maximum. In this study, a modified CPV/ORC system is simulated and the optimum operating temperature of the PV panel is determined for different PV efficiencies. The most striking result is that increase in the PV nominal efficiency will result in the... 

Exploration of the ejector refrigeration cycle (ERC) in the combination with well-known power cycles to produce cooling output as well as power output is highlighted in recent decades. Since organic Rankine cycle (ORC) is practically usable than other power cycles, a combination of the ORC/ERC in a novel form is presented. Power and refrigeration sub-cycles are combined by a common condenser in separate loops to form dual-loop power/refrigeration cycle. The exhaust of the turbine is mixed with the outlet flow of the ejector, and then the mixed flow is fed into the condenser. Thermodynamic and thermoeconomic analysis of the proposed cycle are carried out with different working fluids (i.e.,... 

Performance of a small-scale trigeneration system driven by low-temperature geothermal sources for producing fresh water, heating (hot water) and electricity is investigated from thermodynamic and economic standpoints. This system, utilizing a single stage absorption heat transformer leads to an increase in heat source temperature to be used in single stage evaporation desalination process and also providing water heating. Furthermore, an organic Rankine cycle is used for electric power generation. The developed model is validated with available data and effects of decision variables namely geothermal source, absorber and condenser temperatures on energy and exergy efficiencies of the... 

This paper deals with reconstruction of conventional combined cooling and power (CCCP) cycle for producing simultaneous power and cooling outputs for triple applications of freezing, refrigeration and air-conditioning. The proposed systems are integrated from organic Rankine cycles (ORCs) and an ejector refrigeration cycle (ERC). Single- and multi-objective optimisations of the proposed systems are conducted from energy, exergy and exergoeconomic viewpoints, using genetic algorithm (GA). The results of optimisation revealed that the thermal efficiency of the basic triple-evaporator CCP (B-TECCP) and regenerative TECCP (R-TECCP) systems can be improved by 7.48% and 6.23%, respectively,... 

In this paper, exergy analysis of a steam power plant located in southern Iran named Zarand power plant has been studied. In order to optimize the performance of the Rankine cycle and achieve higher exergy efficiency, several parameters have been considered as decision variables. Knowing that there is the ability to change some of the parameters in the specific range in the process of electricity production in power plant, temperature and output pressure of the boiler and output pressure of four steps of extraction turbine have been selected as six decision variables. Also, exergy efficiency has been considered as the objective function. For this purpose, the exergy efficiency of the system... 

Organic Rankine Cycles (ORCs) are promising approaches for generating power from medium or low temperature heat sources. In this regard, ORCs can be used to indirectly produce power from solar energy. Due to intermittent nature of solar energy, storage unit should be coupled with solar ORCs to improve the output power and operating hours. In this article, studies on solar ORCs integrated with various types of storage units were reviewed; the main findings of such studies were extracted and provided. Based on the findings, several factors such as the temperature and pressure at the inlet of the turbine, as well as the operating condition affect the performance of solar ORCs with thermal... 

Transcritical-CO2, supercritical-CO2, and organic Rankine cycles are numerically investigated and compared in simple Rankine, Rankine with internal heat exchanger, and regenerative Rankine configurations to assess their thermodynamic and thermoeconomic performance indicators. Subsequently, the systems are optimized using a multi-objective optimization method. Pareto optimal solutions are provided to present the trade-off between thermodynamic and thermoeconomic indicators. In addition, scatter plots of decision variables are presented to ascertain the optimal operating range of input variables. The results show that transcritical-CO2 systems can generate the highest power. The levelized cost... 

Bi-evaporator electricity/cooling cogeneration systems can be a favorable addition to the integrated power plants since the generated cooling load should be addressed for different demands. More consequentially, taking advantage of such an integral set-up operated with highly reliable heat source such as biogas can be appreciable for nowadays industries. Regarding this demand, an innovative bi-evaporator electricity/cooling cogeneration system is introduced at first. Next, the suggested system is integrated with a gas turbine cycle fueled by biogas. In the subsequent part, the plausibility of the introduced integrated power plant is examined from first and second laws of thermodynamics (as... 

Solar pond is a type of solar collector that stores solar energy in the form of heat. The solar pond can be used as a low-temperature heat source for electricity generation. In this paper, to find the most suitable power cycle for power generation from the solar pond, the performance of the Organic Rankine Cycle (ORC), Trilateral Flash Cycle (TFC) and their modified forms with an open feed liquid heater and an internal heat exchanger for different working fluids was investigated. Water was considered as the heat transfer fluid which transfers the stored heat from the solar pond to the working fluid of the cycle. The results indicate that in all cases, the energy and exergy efficiency of the... 

The combination of concentrating photovoltaic (CPV) and organic Rankine cycle (ORC) systems not only leads to a reduction of photovoltaic (PV) operating temperature, but also leads to an additional electric power production. Increase in the temperature of the PV decreases its operating efficiency, while increases the ORC efficiency. Therefore, there is an optimum temperature in which the total electricity produced by the combined system will be maximum. In this study, a modified CPV/ORC system is simulated and the optimum operating temperature of the PV panel is determined for different PV efficiencies. The most striking result is that increase in the PV nominal efficiency will result in the... 

This research work presents a novel integrated structure for the cogeneration of electricity and renewable syngas. The base structure of the process is developed by solid oxide cells in which electricity is generated by the natural gas-fueled fuel cell unit, and renewable syngas is produced by the electrolyzer cell unit. Direct integration between fuel cell and electrolyzer cell units is established for optimal use of fuel cell off-gases. To improve system's sustainability, a solar power cycle, including solar collectors coupled with an organic Rankine cycle (ORC), is designed to provide renewable electricity for steam and CO2 co-electrolysis operation. 1D mathematical approaches are...