This paper presents a review of the organic Rankine cycle and supercritical Rankine cycle for the conversion of low-grade heat into electrical power, as well as selection criteria of potential ...working fluids, screening of 35 working fluids for the two cycles and analyses of the influence of fluid properties on cycle performance. The thermodynamic and physical properties, stability, environmental impacts, safety and compatibility, and availability and cost are among the important considerations when selecting a working fluid. The paper discusses the types of working fluids, influence of latent heat, density and specific heat, and the effectiveness of superheating. A discussion of the 35 screened working fluids is also presented.
•Studies on ORC for waste heat recovery during the last four years are reviewed.•Reviews are on cycle configuration, working fluids, and operating condition.•Mostly studied heat sources have been ...internal combustion engines and gas turbines.•Statistics on fluids and configurations are reported for mostly studied sources.
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 review of studies both theoretical and experimental on ORC usage for waste heat recovery and investigation on the effect of cycle configuration, working fluid selection and operating condition on the system performance, that have been developed during the last fouryears. Finally, the related statistics are reported and compared regarding the configuration and the employed working fluid with type of the heat source.
One of the essential steps to design energy conversion-based systems is choosing an efficient working fluid under the design goals to access stable products with high efficiency and overcome ...environmental issues. In this regard, the current paper is motivated to devise and evaluate a novel geothermal-driven multigeneration system under the effect of various working fluids. The proposed system consists of a flash-binary geothermal power plant, an organic flash cycle (OFC), a power/cooling subsystem (an organic Rankine cycle (ORC) and a thermoelectric generator incorporated with a compression refrigeration cycle), and freshwater and hydrogen production units utilizing a humidification-dehumidification desalination unit and a low-temperature electrolyzer. Considering the design potential of the OFC and ORC, four different environmentally-friendly working fluids, i.e., R123 and R600 in the OFC and R1234yf and R1234ze(e) in the ORC are selected and classified in four groups to introduce the best one, under the energy, exergy, and economic (3E analysis) approaches. Also, the whole system is optimized through a genetic algorithm, respecting the optimal solution for the energy efficiency and unit exergy cost of the products. According to the results, R123/R1234ze(e) shows the highest cooling, hydrogen, freshwater production rates, and energy efficiency. Likewise, the maximum power generation and exergy efficiency belong to R600/R1234ze(e). Moreover, R600/R1234yf has the lowest unit exergy cost of products.
•Design of a new geothermal system to produce power, cooling, hydrogen, and freshwater.•Integration on organic flash and organic Rankine cycles for multi-heat recovery.•Classifications of four different environmentally-friendly organic working fluids.•Comparison of thermodynamic and economic performances of selected classifications.•R123/R1234ze(e) acts its best among selected classifications.
Geothermal energy is a renewable energy source that can be found in abundance on our planet. Only a small fraction of it is currently converted to electrical power, though in recent years installed ...geothermal capacity has increased considerably all over the world. This review focuses on Enhanced Geothermal Systems (EGS), which represent a path for turning the enormous resources provided by geothermal energy into electricity for human consumption efficiently and on a large scale. The paper presents a general overview of this ever-expanding technology from its origins to the current state of the art. The Geodynamics plant in Habanero (Australia), which started up on 2 May 2013, is the first privately-run commercial EGS plant to produce electricity on a large scale. Thanks to the technological development of EGS in recent years, the future looks bright for such plants in the decades to come.
Internal combustion (IC) engines are the major source of motive power in the world, a fact that is expected to continue well into this century. To increase the total efficiency and reduce CO
2 ...emissions, recently exhaust heat recovery (EHR) based on thermoelectric (TE) and thermal fluid systems have been explored widely and a number of new technologies have been developed in the past decade. In this paper, relevant researches are reviewed for providing an insight into possible system designs, thermodynamic principles to achieve high efficiency, and selection of working fluids to maintain necessary system performance. From a number of researches, it has been found the Rankine cycle (RC) has been the most favourite basic working cycle for thermodynamic EHR systems. Based on the cycle, various different system configurations have been investigated. Accepting a certain design and manufacture cost, a system based on heavy duty vehicle application can increase the total powertrain efficiency by up to 30% (based on NEDC driving condition). To achieve the highest possible system efficiency, design of systemic structure and selections for both the expander and the working fluid (medium) are critical.
This paper presents a review of the research on closed thermodynamic cycles of ocean thermal energy conversion (OTEC) system, including a description of thermodynamic cycles with either pure or ...mixture working fluids, and describes the effects of various working fluids on cycle efficiency. For cycles with pure working fluids, the efficiency changes due to change in the evaporation and condensation temperature caused by heat resource differences. For cycles with mixture working fluids, the efficiency may be improved by a number of techniques, such as heat recovery of ammonia-depleted solution and the intermediate extraction regeneration. Furthermore, the effect of the ejector on performance of the cycle is also reviewed. Finally, the techniques used to improve efficiency are discussed and summarized. In general, the thermodynamic efficiency can be improved by adopting suitable working fluids and measures which could increase the utilization rate of ocean thermal energy. The related methods need to be compared and analyzed under the same working conditions to determine which is the most effective.
•In this manuscript, a review on the historical development of closed thermodynamic cycles of ocean thermal energy conversion system is presented.•Various techniques applied in the system for efficiency improvement are summarized.•A number of working fluid types and their influences on thermodynamic cycle performance are reviewed.•The limitation of current research and future research directions are pointed out.
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•Detailed assessment of Organic Rankine Cycles is presented.•Mixture working fluids achieves higher thermodynamic efficiency.•Biomass and solar energy are still rarely adopted as ...ORC’s heat resources.•USA and Europe have major share in ORC systems.•Studies for reducing the levelized cost of electricity is needed to be carried out.
This paper presents state-of-the-art review on organic Rankine cycle (ORC) by assessing the working fluids, thermal resources, cooling utilities, and commercial status with future aspects. It is found that the mixture working fluids achieve higher thermodynamic efficiency. However, the difficulty in obtaining the optimum composition and components limits their applications. The thermal resources with different temperature ranges and cooling utilities are then assessed to investigate their effects on the thermodynamic performance of ORC. The low-temperature ORC utilizing waste heat and geothermal heat is dominant, while biomass and solar energy are still rarely adopted as ORC’s heat resources. From the commercial perspective, the USA and Europe are the leaders in conversion of low-grade waste heat into useful power using ORC. Furthermore, the main challenges of ORC are: (a) selection of appropriate working fluid with suitable expander, and (b) reducing the specific cost of the small-scale ORC system to compete with the renewable energy. Finally, several future research directions are identified such as: (1) overall performance of the ORC system including its thermodynamic efficiency, stability and safety needs to be investigated with experimental studies; (2) a general methodology should be developed for the selection of working fluids; (3) studies for reducing the net present cost and levelized cost of electricity with techno-economic optimization are needed to be carried out. This study benchmarks the recent progress on ORC technology and presents an insight into the scientific problems that need to be explored to nexus low-grade heat to power in the future.
•The CO2-based mixture working fluids are used for the dry-cooling solar thermal power generation system.•The comprehensive thermodynamic and heat transfer analyses under typical design and operating ...conditions are investigated.•Mixture working fluids show excellent performance at higher rejection temperatures, especially CO2-H2S.•The CO2-propane has the highest heat transfer coefficient and relatively low pressure loss in the recuperator.
Supercritical carbon dioxide Brayton cycle, distinguished by high thermal efficiency and compact structure, has great potential for application in solar thermal power generation systems. However, it faces the problem that the cycle thermal efficiency reduces with increasing ambient temperature in hot and water-deficient areas, where dry cooling is a necessary choice for power generation systems. In this paper, five CO2-based mixture working fluids, including CO2-cyclohexane, CO2-butane, CO2-isobutane, CO2-propane and CO2-H2S, are investigated in a 50 MW recompression Brayton cycles. Their impact on the cycle performance under typical operating conditions, such as main compressor inlet temperature, split ratio, turbine inlet temperature and maximum cycle pressure, are evaluated by energy and exergy analysis. The heat transfer and pressure drop in the recuperator are also discussed. The results show that the Brayton cycles using mixture working fluids have obvious performance advantages compared with sCO2 Brayton cycle under higher ambient temperature. According to the thermodynamic performance of working fluids in the cycle, CO2-H2S is the best choice. However, the CO2-propane has the highest heat transfer coefficient and relatively low pressure loss in the recuperator. This research can be used as a guide to the selection of mixture working fluids for dry-cooling supercritical Brayton cycle.
•Economic-environmental-sustainable analysis was performed for subcritical ORC system.•A double-layer optimization design framework is proposed for fluid selection in ORC.•Multi-objective ...optimization results of ORC system were studied and compared.•Optimal fluid selection scheme was obtained based on different geothermal temperatures.
Global issues such as the energy crisis and environmental pollution impulse the development of waste heat recovery technologies. Organic Rankine cycle (ORC) systems are a promising solution to utilize renewable energies and recover waste heat. However, the different heat source temperatures often force the ORC to use different working fluids. Matching the heat source temperatures with suitable fluids is important to enhance the system performance and promote the marketability of this technology. In this work, a double-layer multi-objective optimization framework is proposed for subcritical ORC systems applied in the geothermal field. Four kinds of objective functions are selected in the optimization model, including net power output, total product unit cost, greenhouse gas emissions, and ecological life cycle cost to characterize system thermodynamic, exergoeconomic, environmental, and sustainable performances, respectively. The feature of the established model allows simultaneous system comprehensive design and fluid screening under specific geothermal temperatures. Results showed that the impacts of decision variables, including evaporation pressure and condensation temperature, on system performances were different under the different performance indicators. According to the balanced weighting factor case study, it is found that R134a had excellent thermodynamic and sustainable performances while R600a performed better from economic and environmental aspects at 393.15 K geothermal temperature. In addition, it was observed that the obtained optimal point shifted regularly on the Pareto curve with the change of geothermal temperature and weighting factor. Finally, under different weighting factor schemes, the optimal plans of fluid selection were obtained at certain geothermal temperatures. HCs fluids showed superior overall performance in the double-layer optimization framework considering ecological impacts, while R152a exhibited excellent comprehensive performance among the selected safe fluids under the premise of strict consideration of system security.
•Seven working fluids are examined energetically and exergetically in a commercial PTC.•Water, Therminol VP-1, Molten salt, Sodium liquid, Air, CO2 and Helium are examined.•Every working fluid is ...examined in the proper temperature range from 300K to 1300K.•The global maximum exergetic efficiency achieved for Sodium liquid at 800K (47.48%).•CO2 and helium are the most suitable working fluids for extremely high temperatures.
Solar energy is a promising energy source for covering a great variety of applications from low up to high temperature levels. In this study, the most mature concentrating technology, a commercial parabolic trough collector (Eurotrough ET-150), is investigated energetically and exergetically for a great temperature range from 300K to 1300K. Pressurized water, Therminol VP-1, nitrate molten salt, sodium liquid, air, carbon dioxide and helium are the examined working fluids; each one to be studied in the proper temperature range. In the first part of this study, the optimum mass flow rate is determined to every working fluid separately. After this point, the exergetic and the energetic performance of the collector operating with all these working fluids is examined. The final results prove that the liquid sodium leads to the global exergetic maximum efficiency (47.48%) for inlet temperature equal to 800K, while the maximum exergetic performance of helium, carbon dioxide and air to be 42.21%, 42.06% and 40.12% respectively. Moreover, pressurized water is the best working medium for temperature levels up to 550K, while carbon dioxide and helium are the only solutions for temperatures greater than 1100K. The thermal analysis is performed with the EES tool.
