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Highlights • Effects of composition ratios and pressure drops of R245fa/R236fa mixtures are investigated. • The ORC system with R245fa/R236fa mixture has higher performances than that with R236fa or R245fa. • As pressure drop rises, the proportion of R236fa in mixture increases for optimal performances. • Exergy and exergo-economic analyses of the system are performed. Abstract The aim of this study is to investigate the effects of composition ratios of working fluids and pressure drops in heat exchangers on the performance of an organic Rankine cycle (ORC) system employing R245fa/R236fa for waste heat recovery (WHR). Thermodynamic analysis, heat transfer calculation, and the cost-evaluation of apparatus and maintenance of the ORC system are applied to assess the levelized energy cost for the economic performance. Moreover, exergoeconomic factors of the components in the ORC system are calculated. The results indicate that the ORC system cycled with R245fa/R236fa mixture has higher thermodynamic and economic performances than ORC system with either pure-component of R236fa or pure-component of R245fa. At optimal mixture ratio, R245fa/R236fa has higher net power output than R245fa by 7.07% and lower levelized energy cost than R236fa by 3.07%. Both the saturated temperature of liquid working fluid and the proportion of R236fa in R245fa/R236fa mixture increase as pressure drops in the heat exchangers of the ORC system increase. As pressure drop ratio equals to 0.16, R245fa/R236fa with optimal composition ratio is thermodynamically superior to R236fa and R245fa by 2.16% and 9.07%, respectively. Similarly, at the optimal composition ratio, R245fa/R236fa mixture also performs better than R236fa by 2.37% or R245fa by 1.5% in economic analysis. As for exergoeconomic factors, relatively high values for the pump and expander and moderate values for the heat exchanger devices are obtained in the system. On the whole, the values of exergoeconomic factor increase with composition ratio of R245fa/R236fa mixture. Compared with R245fa and R245fa/R236fa mixtures, R236fa has the highest value of exergoeconomic factor for each component of the ORC system. Finally, the correlations of the optimal thermodynamic and economic performances of the ORC system with R245fa/R236fa are proposed for WHR. [ABSTRACT FROM AUTHOR]

The aim of this study is to investigate the payback period and the payback-period reduction of the organic Rankine cycle (ORC) with mixtures for waste heat recovery from the exhaust gas of a large marine diesel engine. Working fluids with zero-ozone-depletion potential, such as R236fa, R245fa, R600, R1234ze, and their mixtures, are selected to analyze the economic and thermodynamic performances in the conversion cycle. The optimal mass fractions of the mixed working fluids R236fa/R245fa, R236fa/R1234ze, and R600/R1234ze for the lowest payback period with the corresponding optimal expander inlet temperature and condenser outlet temperature of the ORC have been obtained. R600/R1234ze possesses the best performance in terms of payback period. Under optimal conditions, the payback period of the ORC with R600/R1234ze is the lowest and is shorter than that with R236fa, R245fa, R600, R1234ze, R236fa/R245fa, and R236fa/R1234ze by 7.55%, 6.47%, 9%, 9.17%, 0.9%, and 2.88%, respectively. To evaluate the economic potential of mixed working fluids using different types of expander such as turbine, scroll, and screw expanders properly, the relationships between the isentropic efficiencies of the expander and their corresponding optimal expander inlet temperature and optimal mass fraction are obtained. Optimal correlations are proposed to conveniently predict the optimal mass fractions of the mixtures R236fa/R245fa, R236fa/R1234ze, and R600/R1234ze in the ORC and to assess the reduction of their payback periods for the waste heat recovery of a large marine diesel engine. The results highlight the significant potential of the mixtures used in the ORC for performance improvement and demonstrate the importance of mixture assessment for reducing the payback period in further work. [ABSTRACT FROM AUTHOR]

[Display omitted] • Performance analysis of controllable-blade vertical axis turbine is conducted. • Numerical and experimental studies of the proposed turbine are made. • A cam plate is used to control the six blades of the vertical axis turbine. • The performance of CBVAT is 143% and 103% higher than that of the FBVAT and ST. Phasing out high-carbon-emission fossil fuels and using renewable energy have become a global consensus for mitigating climate change. For the application of renewable energy, this study proposes a high-efficiency controllable-blade vertical axis turbine, which has six blades and a cam plate, for ocean current power generation. A novel design for the turbine using cam to control the opening and closing of blades to enhance the performance of vertical axis turbines. The design feature of the drag-type blade is to be active or open quickly in downstream. The effective area of the blade under thrust is increased to enhance the performance. On the other hand, the blade is designed to be inactive or close quickly in upstream and the drag of blade in upstream can be reduced. A commercial software, ANSYS FLUENT is used to simulate the performance of the vertical turbine. The streamline, velocity, and pressure around the turbines are then obtained. The power coefficients and torques are evaluated at various angular velocities and tip speed ratios and are validated by experimental results. The maximum power coefficient of the proposed turbine occurs at an angular velocity ratio of 4 with quick opening of blades and is higher than that of 3, 5, or 6 by 3.4 %, 2.7 %, or 7.4 %, respectively. In addition, performance comparisons among controllable-blade vertical axis turbine, fixed-blade vertical axis turbine, and Savonius turbine are made. The results show that the maximum power coefficient of the presented controllable-blade vertical axis turbine is 143 % and 103 % higher than that of the fixed-blade vertical axis turbine and Savonius turbine at V = 1 m/s, respectively. [ABSTRACT FROM AUTHOR]

The aim of this study is to investigate the economic performance improvement of a transcritical Rankine cycle system employing carbon dioxide mixtures for waste heat recovery. Five lower global-warming-potential working fluids, namely difluoromethane, fluoroethane, propane, tetrafluoroethane, and tetrafluoropropene, are selected to blend with carbon dioxide. In addition to thermodynamic analysis, the apparatus and maintenance costs of the waste heat recovery system are considered to evaluate the levelized energy cost for the economic performance study. The results indicate that the system cycled with carbon dioxide/fluoroethane exhibits the most effective economic performance, and is superior to that cycled with carbon dioxide/difluoromethane, carbon dioxide/tetrafluoropropene, carbon dioxide/tetrafluoroethane, carbon dioxide/propane, and pure carbon dioxide by 0.7, 13.89, 15.27, 20.88, and 21.52%, respectively. In the transcritical Rankine cycle operated with the carbon dioxide mixtures, not only are energy costs reduced, but the high pressure and temperature are also decreased. Furthermore, the optimal expander inlet pressures for the transcritical Rankine cycle with a minimal levelized energy cost are always smaller than those with maximal thermal efficiencies. Finally, economic performance correlations are proposed for the waste heat recovery system, utilizing various waste heat source temperatures. [ABSTRACT FROM AUTHOR]

The aim of this study is to investigate the economic performance of a novel compact waste heat recovering system for the marine diesel engine. The transcritical Rankine cycle is employed to convert the waste heat resources to useful work with R1234yf. To evaluate the utilizing efficiency and economic performance of waste heat resources, which are exhaust gas, cylinder cooling water and scavenge air cooling water, three operating models of the system are investigated and compared. The levelized energy cost, which represents the total cost per kilo-watt power, is employed to evaluate the economic performance of the system. The economic optimization and its corresponding optimal parameters of each operating model in the compact waste heat recovering system are obtained theoretically. The results show that the minimal levelized energy cost of the proposed system operated in Model I is the lowest of the three models, and then are Model II and Model III, which are 2.96% and 9.36% lower for, respectively. Similarly, the CO 2 emission reduction is the highest for Model I of the three models, and 21.6% and 30.1% lower are obtained for Model II and Model III, respectively. The compact waste heat recovering system operated in Model I has superiority on the payback periods and heavy diesel oil saving over the others. Finally, the correlations using specific work of working fluid and condensation temperature as parameters are proposed to assess the optimal conditions in economic performance analysis of the system. [ABSTRACT FROM AUTHOR]

The aim of this study is to investigate the economic optimization of a TRC system for the application of geothermal energy. An economic parameter of net power output index, which is the ratio of net power output to the total cost, is applied to optimize the TRC system using CO 2 , R41 and R125 as working fluids. The maximum net power output index and the corresponding optimal operating pressures are obtained and evaluated for the TRC system. Furthermore, the analyses of the corresponding averaged temperature differences in the heat exchangers on the optimal economic performances of the TRC system are carried out. The effects of geothermal temperatures on the thermodynamic and economic optimizations are also revealed. In both optimal economic and thermodynamic evaluations, R125 performs the most satisfactorily, followed by R41 and CO 2 in the TRC system. In addition, the TRC system operated with CO 2 has the largest averaged temperature difference in the heat exchangers and thus has potential in future application for lower-temperature heat resources. The highest working pressures obtained from economic optimization are always lower than those from thermodynamic optimization for CO 2 , R41, and R125 in the TRC system. [ABSTRACT FROM AUTHOR]

In this study, six working fluids with zero ozone depletion potential and low global warming potential are used in an organic Rankine cycle (ORC) system to recover waste heat from cylinder jacket water of large marine diesel engines. Thermodynamic analysis and a finite-temperature-difference heat-transfer method are developed to evaluate the thermal efficiency, total heat-exchanger area, objective parameter, and exergy destruction of the ORC system. The optimal evaporation and condensation temperatures for achieving the maximal objective parameter, the ratio of net power output to the total heat-transfer area of heat exchangers, of an ORC system are investigated. The results show that, among the working fluids, R600a performs the best in the optimal objective parameter evaluation followed by R1234ze, R1234yf, R245fa, R245ca, and R1233zd at evaporation temperatures ranging from 58 °C to 68 °C and condensation temperatures ranging from 35 °C to 45 °C. The optimal operating temperatures and corresponding thermal efficiency and exergy destruction are proposed. Furthermore, the influences of inlet temperatures on cylinder jacket water and cooling water in the ORC are presented for recovering waste heat. The results of this work were verified with theoretical solutions and experimental results in the literature and it was revealed that they were consistent with them. [ABSTRACT FROM AUTHOR]

Abstract: A numerical study of forced convection in a horizontal parallel-plate channel with a transverse fin located at lower channel wall is investigated. Through the use of a stream function vorticity transformation, solution of the transformed governing equations for the system is obtained using the control-volume method with non-uniform grid. The effects of the Reynolds number, thermal conductivity ratio of fin to fluid and fin profile area on heat transfer rate of the fin are presented. The results indicate that the optimum aspect ratio of a fin corresponding to the fin with maximum heat transfer rate increases with increasing Re but decreases with K for a fixed fin profile area. In addition, the optimum aspect ratio of a fin obtained from this study for smaller fin profile area and Re tends to approach that of analytical solution assuming constant heat-transfer coefficient. Finally, good agreements are found between the numerical predictions of this study and other experimental data. [Copyright &y& Elsevier]