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[en] Highlights: • An irreversible solar-driven heat engine is optimized. • Developed multi objective evolutionary approaches is used. • Power output, ecological function and thermal efficiency are optimized. - Abstract: The present paper illustrates a new thermo-economic performance analysis of an irreversible solar-driven heat engine. Moreover, aforementioned irreversible solar-driven heat engine is optimized by employing thermo-economic functions. With the help of the first and second laws of thermodynamics, an equivalent system is initially specified. To assess this goal, three objective functions that the normalized objective function associated to the power output (F_P) and Normalized ecological function (F_E) and thermal efficiency (η_t_h) are involved in optimization process simultaneously. Three objective functions are maximized at the same time. A multi objective evolutionary approaches (MOEAs) on the basis of NSGA-II method is employed in this work
[en] This communication introduces the basic concepts for techno-economic feasibility assessment of various solar thermal systems in a dynamic and market oriented economic environment. An analytical expression for calculating the payback period is derived by assuming a non-linear increase in maintenance cost and incorporating subsidy and salvage values. Further, a method is evolved to ascertain the lifetime of the system for an optimal return on investment mode, incorporating capital inflation during the lifetime and a non-linear increase in maintenance cost. The results for the payback period have been used, along with the lifetime, to optimize the cost of the system. (author)
[en] Highlights: • A novel solar driven multi-stage bubble column humidifier is developed and tested. • Single stage, two stage, and three stage configuration were tested. • Average day round absolute humidity is increased by 9% for 2 stage configuration. • Average day round absolute humidity is increased by 23% for 3 stage configuration. • Air absolute humidity increases up to 26% with the integration of Fresnel lens. - Abstract: In this study, a novel solar heated multi-stage bubble column humidifier is designed and tested. The overall objective of this work is to investigate the main operating parameters of the new humidifier. The study addresses the significance of the perforated plate geometric features, optimum balance of air superficial velocity and water column height, and the influence of inlet water temperature and inlet air relative humidity on the performance of the humidifier. The day round performance of the humidifier is investigated in single stage, two stage, and three stage configuration, in which each configuration was tested with and without the integration of the Fresnel lens. Findings show that the average day round absolute humidity, without Fresnel lens, increased up to 9% for the two stage configuration and 23% for the three stage configuration as compared to the single stage configuration of the humidifier. The integration of the Fresnel lens further increased the absolute humidity up to 25% as compared to the results obtained without the integration of the Fresnel lens under the same prevailing conditions, which is significant. Moreover, the current humidifier shows a higher humidification efficiency in the climatic conditions that have a lower inlet air relative humidity. Furthermore, the finding demonstrates that the newly developed multi-stage bubble column humidifier has better performance as compared to the conventional single stage bubble column humidifier. The findings from this study are of pivotal importance to understand the optimum operating conditions of the humidifier for its possible integration with the dehumidifier. Consequently, an improved humidification-dehumidification desalination system attained.
[en] A solar thermal cell is composed of the chemical reaction of 2-propanol/acetone/hydrogen and a fuel cell. We have examined the influence of the internal structure and the temperature in the solar thermal cell on the output of the cell. As the main results, (1) with increasing the temperature of the positive electrode, the short circuit current of the cell has increased, (2) with decreasing the thickness of the electrode space, the output of the cell has increased and (3) under the condition that the electrodes are kept in good contact with the polymer electrolyte, the performance of the cell increases and the short circuit current reaches 80 mA
[en] Highlights: • The dynamic model of photovoltaic–thermal collector with phase change material was developed. • The performances of photovoltaic–thermal collector are performed comparative analyses. • The performances of photovoltaic–thermal collector with phase change material were evaluated. • Upper phase change material mode can improve performances of photovoltaic–thermal collector. - Abstract: The operating conditions (especially temperature) of photovoltaic–thermal solar collectors have significant influence on dynamic performance of the hybrid photovoltaic–thermal solar collectors. Only a small percentage of incoming solar radiation can be converted into electricity, and the rest is converted into heat. This heat leads to a decrease in efficiency of the photovoltaic module. In order to improve the performance of the hybrid photovoltaic–thermal solar collector, we performed comparative analyses on a hybrid photovoltaic–thermal solar collector integrated with phase change material. Electrical and thermal parameters like solar cell temperature, outlet temperature of air, electrical power, thermal power, electrical efficiency, thermal efficiency and overall efficiency are simulated and analyzed to evaluate the dynamic performance of the hybrid photovoltaic–thermal collector. It is found that the position of phase change material layer in the photovoltaic–thermal collector has a significant effect on the performance of the photovoltaic–thermal collector. The results indicate that upper phase change material mode in the photovoltaic–thermal collector can significantly improve the thermal and electrical performance of photovoltaic–thermal collector. It is found that overall efficiency of photovoltaic–thermal collector in ‘upper phase change material’ mode is 10.7% higher than that in ‘no phase change material’ mode. Further, for a photovoltaic–thermal collector with upper phase change material, it is verified that 3 cm-thick phase change material layer is excellent both in electrical and thermal performance.
[en] Highlights: • An absorption power cycle is proposed for ocean thermal energy conversion (OTEC). • The performance of this cycle is valued by theoretical analysis. • This proposed cycle can be driven with a lower temperature difference. • This cycle provides a potential of broadening the scope of the OTEC application. - Abstract: An absorption power cycle with two ejectors is proposed for ocean thermal energy conversion. The ammonia–water is used as the working fluid. The ejectors are driven by vapor and solution from the sub-generator. Based on the first and second law, the mathematical model for this cycle is developed and theoretical analysis is conducted to evaluate the effects of thermodynamic parameters on the performance of this cycle. Results show that the absorption temperature is increased by 2.0–6.5 °C by employing the two-stage ejector sub-cycle, which indicates that this proposed cycle can be driven with a lower temperature difference. Further, the thermal efficiency, net thermal efficiency and exergy efficiency of this cycle can reach to 4.17%, 3.10% and 39.92% respectively. Besides, the generation pressure, the heating source temperature, the solution concentration, and the expansion ratio, as well as the entrainment ratio of the first stage ejector have significant effects on the absorption temperature, the thermal efficiency, the exergy efficiency and the exergy loss of this cycle. In addition, 49.80% of exergy loss in this proposed cycle occurs in the generators and reheater, followed by the ejectors of 36.12%
[en] Highlights: • A model coupling solar radiation transport and internal heat transfer is developed. • Two other treatment approaches for the concentrated solar radiation are compared. • Porous parameters significantly affect the distribution of absorbed solar radiation. • The TBC approach overestimates the solid temperature with a deviation up to 76.4%. • The CIR approach provides acceptable temperature field with deviation less than 3.4%. - Abstract: Volumetric receivers have become a promising technology for the solar thermal conversion. The absorption of concentrated solar radiation and the heat transfer to the working fluid are the two dominant processes. To effectively investigate the thermal performance of receiver, a numerical model coupling the solar radiation transport and the internal heat transfer is presented. Solar radiation transport from the dish concentrator to the interior of receiver is simulated with the Monte Carlo ray tracing method. Combining the distribution of absorbed solar energy in the receiver, the local thermal non-equilibrium model with P1 approximation is used to solve the internal heat transfer. Two other treatment approaches for the concentrated solar radiation are compared. One considers the solar radiation on the front surface of receiver as thermal boundary condition (TBC) and the other as a collimated incident radiation (CIR) beam. The results show that the porosity and mean cell size have a great effect on the distribution of absorbed solar radiation. Compared with the coupling approach, the TBC approach overestimates the solid temperature near the front surface with a deviation up to 76.4%, while the CIR approach provides acceptable temperature field with a deviation less than 3.4%. In addition, the fluid and solid temperatures both decrease as the slope error of concentrator increases.
[en] Highlights: • Boiler and oil/water heat exchanger are not considered as “black boxes”. • The off-design performance is compared using two calculation methods. • Main parameters of oil/water heat exchanger are optimized. • Total replacement of the third-stage extraction steam is more preferable. - Abstract: Using parabolic trough technology to collect solar thermal energy and preheat feedwater, is one of the most practical integration between solar and coal-fired power generation system. This study designs and compares two thermodynamic calculation methods related to solar aided power generation (SAPG) system. Method I simplifies oil/water heat exchanger and boiler as “black boxes”, while Method II is a new calculation method in which the heat transfer processes in the boiler and oil/water heat exchanger are considered. The results show that if the extraction steam to be replaced is located before the inlet side of reheated steam, using Method I would bring much calculation error in the main parameters of solar aided power generation (SAPG) system. Therefore, the calculation of thermal-to-electricity efficiency, solar-to-electricity efficiency (SEE) and solar power generation would be incorrect. Besides, Method I could not optimize the oil/water heat exchanger. As an improvement, the results derived by Method II demonstrated that totally replacing the extraction steam in the third stage is preferable to doing so in the first or the second stage. Such integration mode would not result in temperature fluctuations of the main steam or reheated steam without affecting the safety of boiler’s operation. In addition, the design SEE for this integration mode is the highest at 28.114%, whereas the other two modes are 18.188% and 20.575%, respectively. Furthermore, such integration mode requires lowest initial investment in the solar field and oil/water heat exchanger.
[en] Highlights: • Supercritical CO2 flow is proposed for natural circulation solar water heater system. • Experimental system established and consists of supercritical fluid high pressure side and water side. • Stable supercritical CO2 natural convective flow is well induced and water heating process achieved. • Seasonal solar collector system efficiency above 60% achieved and optimization discussed. - Abstract: Solar collector has become a hot topic both in scientific research and engineering applications. Among the various applications, the hot water supply demand accounts for a large part of social energy consumption and has become one promising field. The present study deals with a novel solar thermal conversion and water heater system achieved by supercritical CO2 natural circulation. Experimental systems are established and tested in Zhejiang Province (around N 30.0°, E 120.6°) of southeast China. The current system is designed to operate in the supercritical region, thus the system can be compactly made and achieve smooth high rate natural convective flow. During the tests, supercritical CO2 pipe flow with Reynolds number higher than 6700 is found. The CO2 fluid temperature in the heat exchanger can be as high as 80 °C and a stable supply of hot water above 45 °C is achieved. In the seasonal tests, relative high collector efficiency generally above 60.0% is obtained. Thermal and performance analysis is carried out with the experiment data. Comparisons between the present system and previous solar water heaters are also made in this paper
[en] Highlights: • Detailed algorithm to solve high temperature Kalina cycle in part load. • A central receiver concentrating solar power plant with direct vapour generation considered as case study. • Part-load performance curves and fitted equations presented. - Abstract: The Kalina cycle has recently seen increased interest as an alternative to the conventional steam Rankine cycle. The cycle has been studied for use with both low and high temperature applications such as geothermal power plants, ocean thermal energy conversion, waste heat recovery, gas turbine bottoming cycle, and solar power plants. The high temperature cycle layouts are inherently more complex than the low temperature layouts due to the presence of a distillation-condensation subsystem, three pressure levels, and several heat exchangers. This paper presents a detailed approach to solve the Kalina cycle in part-load operating conditions for high temperature (a turbine inlet temperature of 500 °C) and high pressure (100 bar) applications. A central receiver concentrating solar power plant with direct vapour generation is considered as a case study where the part-load conditions are simulated by changing the solar heat input to the receiver. Compared with the steam Rankine cycle, the Kalina cycle has an additional degree of freedom in terms of the ammonia mass fraction which can be varied in order to maximize the part-load efficiency of the cycle. The results include the part-load curves for various turbine inlet ammonia mass fractions and the fitted equations for these curves.