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Copyright of Journal of Engineering for Thermal Energy & Power / Reneng Dongli Gongcheng is the property of Journal of Engineering for Thermal Energy & Power and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

This article analyzes the validation trends of higher education based on effectiveness and efficiency indicators. The UNESCO definitions and the Cuban model established by the Ministry of Higher Education are taken as references, to encourage critical readings and qualitative assessments that allow problematizing the use of efficiencies as indicators or criteria for measuring career performance. [ABSTRACT FROM AUTHOR]

In an effort to make pumped hydropower storage (PHS) technology feasible for regions with a flat topography, recent research shows promising results using a contra-rotating reversible pump-turbine at low-head. In this study, the impact of dual variable speed and inlet valve control is analyzed to evaluate the effect of these three degrees of freedom (DOFs) on the system efficiency and operating range. To this end, analytical models are described to assess pump-turbine performance, conduit losses and electromechanical losses. Methodologically, optimal efficiency maps are computed for every combination of the three DOFs to evaluate individual and combined effects on the overall efficiency. Furthermore, three energy storage cycles are analyzed to further study the performance in realistic use-cases. Key conclusions include an increase in round-trip efficiency by combining variable speed ratio and inlet valve control of 5.6% and 2.0% compared with only variable speed ratio control and variable inlet valve control, respectively. Furthermore, it is shown that using only 1 DOF significantly limits the operating range, with the addition of a variable inlet valve granting a higher impact than a variable speed ratio. Combining inlet valve and speed ratio control leads not only to the highest efficiency, but also the largest operating range, with a maximum round-trip efficiency of 67.5% and an energy storage capacity of 58.6 Wh/m2. The results confirm that exploiting both dual variable speed operation and inlet valve control yields the maximum efficiency and operating range, and is thus the preferred topology for contra-rotating reversible pump-turbines in low-head operation.

The supercritical carbon dioxide (S-CO2) Brayton cycle is an efficient energy conversion system. It has the advantages of simple and compact, low noise and high efficiency. Therefore, it has attracted much attention from academia and industry in recent years. However, the current S-CO2 Brayton cycle study usually considers the application scenarios with ambient temperature 20 ℃, and the minimum cyclic temperature is 32 ℃. The adaptive analysis and optimization of low temperature cold source scenarios such as deep sea and polar regions are not optimized. CO2-SF6 mixture has lower critical parameters than pure CO2, so that it is expected to further reduce the compression power, improve the turbine pressure ratio, and thus improve the cycle efficiency with low ambient temperature. In this paper, the PR equation and van der Waals mixing rules were used to calculate the CO2-SF6 mixture thermal properties with the Nishiumi interaction coefficient model. The thermal properties calculated are in good agreement with the experiment data in literature. Based on the calculated thermal properties, a simple recuperation cycle was analyzed with a maximum pressure of 12 MPa, a minimum cyclic temperature of 15-55 ℃, and a minimum pressure slightly higher than the critical pressure. The results show that replacing the pure CO2 with a CO2-SF6 mixture can effectively improve the turbine pressure ratio, thereby improving the cycle efficiency, and reducing the critical temperature and the optimal compressor inlet temperature. And the use of CO2-SF6 mixture can effectively decrease cycle efficiency degradation when the compressor inlet temperature is lower than the quasicritical temperature, thereby improving the stability of the cycle under the low temperature cold source. The preliminary analysis results show that the use of CO2-SF6 mixed working fluid instead of pure CO2 working fluid can effectively improve the performance of the cycle in the low temperature environment, which also indicates that the mixed working fluid scheme is one of the effective solutions to expand the applicable temperature range of the S-CO2 Brayton cycle.

Copyright of Atomic Energy Science & Technology is the property of Editorial Board of Atomic Energy Science & Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Climate change has caused the inefficient operation of a significant number of old weirs to pass large discharges. Therefore, this study aims to increase the discharge capacity of the labyrinth weir. A new approach was proposed by modifying a labyrinth weir structure. The data was obtained from the quarter-round crest and different sidewall angles ranging from 8 to 35°. A conventional labyrinth weir was used for comparison. The results showed that the percentage of the notches area to sidewalls area of the weir (An/Aw) does not exceed 8%. Also, the percentage of the notches' length to total crest length (ΔL/Lc) does not exceed 32%. Also, the percentage of the notch depth to the sidewall depth (ΔP/P) does not exceed 30%. The other parameters are kept constant. These dimensionless terms provided a maximum compound coefficient of discharge of 0.74. Also, the compound discharge coefficient initially increased at low water head ratios and decreased at higher values of water head ratios. The regression empirical equations were generated. The maximum increase in efficiency was 10% for a sidewall angle of 6° when compared to conventional labyrinth weirs. The maximum improvement of the compound coefficient of discharge was 18.8% for a sidewall angle of 8°. HIGHLIGHTS A new approach to the labyrinth weir was proposed and named compound labyrinth weir to improve the discharge capacity of the labyrinth weir.; Derivation of hydraulic equation for compound labyrinth weir has been done.; Establishing the set of curves showing the relationship between the compound coefficient of discharge Cdc against total head over the entire compound labyrinth weir H′t/P′ with a range of sidewall angles.; Empirical equations for compound labyrinth weir and compound linear weir were created.; Using the compound labyrinth weir efficiency (έ) as a new tool to provide a guide in choosing a suitable design of the sidewall angle (α).;

In endoreversible cycles, irreversibility is considered only between the systems and their surroundings. In this paper, the modelling of heat interaction with a solar regenerative Brayton cycle is studied with regard to various fidelities based on the first and second laws of thermodynamics. The effect of linearity and nonlinearity related to both convective and radiative heat interactions with the hot and cold reservoirs as well as radiation losses of the solar Brayton cycle have been studied, which is complementary to similar attempts for Carnot cycle. Total efficiencies are compared between various implemented models. The effect of temperature of six critical sections of the whole engine on the collector efficiency, cycle thermal efficiency and the system total efficiency has been studied. Besides, a comparison is done for a real example to show the importance of considering the nonlinearities for calculating thermal efficiency of a closed-loop Brayton cycle at different hot source temperatures, as well. These would help a more efficient analysis of the emerging power cycles that can accelerate progress toward low-carbon power production. [ABSTRACT FROM AUTHOR]

High temperature gas cooled reactor combined with closed cycle magnetohydrodynamic power generation (CCMHD) is a promising technology for space applications. It can meet the requirements in space tasks for high power and high efficiency. The system mainly contains the nuclear reactor, the MHD generator, the regenerator, the compressors and the radiator. Helium is adopted as both the coolant and the power generation medium for its good ionization properties and chemical inertness. A set of 100 MWth space magnetohydrodynamic nuclear power system circulation scheme was proposed in other literatures. In this paper, thermodynamic models and mass models of this system were established dependently, and efficiency analysis along with specific mass analysis was conducted afterwards on the basis of verifying the accuracy of the program. Specifically, the developed analysis program was used, by means of selecting the same design parameters of the system cycle scheme for thermodynamic calculation and specific mass calculation, to compare with the literature results. Besides, the effects of the radiator temperature, the reactor outlet temperature, the number of compressors and the regenerator efficiency were also discussed for the use of parametric optimization. The research shows that increasing the temperature of the reactor outlet, decreasing the minimum cycle temperature, and increasing the number of compressor stages are all beneficial to improve the maximum cycle efficiency, and also increase the corresponding optimal enthalpy extraction rate and optimal pressure ratio. Moreover, increasing the regenerator efficiency is beneficial to improve the maximum cycle efficiency. However, it also reduces the corresponding optimal enthalpy extraction rate and optimal pressure ratio at the same time. After comprehensively considering many factors such as cycle efficiency, system specific mass, radiator area, system complexity, existing manufacturing capacity and technical level, a set of design parameters suitable for 1 MWth thermal power were finally given. The reactor outlet temperature was chosen as 1 800 K, the minimum cycle temperature was chosen to be 300 K, the number of compressor stages was selected as 3 for the system design parameter, and 0.93 was chosen to be the regenerator efficiency. The results show that the cycle efficiency of the system is 46.15%, along with a total mass of 4 375 kg. Besides, the specific mass is 9.48 kg/kWe, and the radiator area is 1 302.7 m2, which shows great competitiveness in future space applications. Finally, this research also provides system-level optimization parameters for the subsequent thermal design of the reactor.

[Introduction] The demand for energy storage of new power systems (dominated by renewable energy) is increasing. Liquid air energy storage is a new method of physical energy storage with large capacity for long time storage, which has a broad application prospect. the purpose is to explore the thermodynamic principle of liquid air energy storage system and the influence of key parameters on energy storage efficiency. [Method] The thermodynamic models of three basic cycles of liquid air energy storage system: separated cycle, cooling capacity recovery cycle and cooling capacity and heat recovery cycle were established. The influence of key parameters such as cold energy recovery, heat recovery, high pressure and discharge pressure on liquid yield and cycle efficiency was analyzed. [Result] The results show that there is a positive correlation between liquid yield and cycle efficiency. The liquid yield and cycle efficiency of the separated cycle are extremely low. The cooling capacity recovery cycle, using the cooling capacity during temperature rise, significantly improves the liquid yield and cycle efficiency. The cooling capacity and heat recovery cycle further improve the liquid yield and recycling efficiency for the use of heat of compression. The liquid yield and cycle efficiency increase with the increase of cooling capacity recovery, increase with the increase of high pressure, and decrease with the increase of discharge pressure. [Conclusion] Cooling capacity and heat recovery cycle is the optimal scheme of liquid air energy storage. Efficient cooling capacity storage plays an important role in improving cycle efficiency. The utilization of industrial waste heat in the process of liquid-air reheating is helpful to further improve cycle efficiency.

The Sub-megawatt-scale supercritical CO 2 Brayton cycles (SCBCs) have shown great potential in renewable energy and mobile power systems, but the response of technical performances to fluctuating operating load has not yet been completely known even for those basic cycle layouts. For this purpose, the present work investigated the performance characteristics of the global operating loads for the 0.1 and 1 MWe-scale recuperated SCBS systems. A thermodynamic model was proposed and demonstrated to be feasible to predict the cycle performance with 0.19%–9.59% relative error. Using the control-of-variables strategy, the response of cycle efficiency and net power were comprehensively examined to the 90%–110% reference load (namely ±10% fluctuations) of operating parameters, including the compressor inlet pressure, compressor inlet temperature, turbine inlet pressure, turbine inlet temperature, and mass flow rate. It was found that although the cycle performances depend upon the facility scale, the appropriate parameter matching can effectively improve the cycle efficiency and net power by 31.97% and 76.42% for the 0.1 MWe-scale cycle, and by 13.89% and 26.69% for the1 MWe-scale cycle respectively at a given the mass flow rate of CO 2. The results provide a positive reference for the performance assessment and operation optimization of the small-scale recuperated SCBC systems. [Display omitted] [ABSTRACT FROM AUTHOR]

The current research aims to valorize Moroccan agricultural waste by using it as a combustible fuel. The physicochemical properties of argan cake were determined and the results were compared with other studies of argain nut shell and olive cake. A comparison of argain nuts shell, argain cake, and olive cake was carried out in order to determine the best combustible in terms of energy, emissions and thermal efficiency cycle. The CFD modeling of their combustion was presented using Ansys fluent software, The Reynolds averaged Navier-Stokes (RANS) method is the foundation of the numerical approach, which models the turbulent flow using realizable.k-ε, A non-premixed combustion model is used for the gas phase, and a Lagrangian approach is chosen for the discrete second phase, there was a good agreement between the numerical and experimental data, as well as Wolfram Mathematica 13.1 is used to predict the mechanical work generated by the Stirling engine, and the result encourages the use of studied biomasses as combustible in order to generate heat and power.

Copyright of Atomic Energy Science & Technology is the property of Editorial Board of Atomic Energy Science & Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Journal of Engineering for Thermal Energy & Power / Reneng Dongli Gongcheng is the property of Journal of Engineering for Thermal Energy & Power and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

• RDC passage area has a significant impact on operating range of rotating detonation gas turbine. • The increase of RDC passage area makes the operating range of gas turbine move to the higher power. • Equivalence ratio of RDC replaces turbine efficiency as the greatest influence factor on cycle efficiency increment with different combustor passage areas. • Qualitative analysis based on sensitivity analysis of component parameters is further optimized to announced the comprehensive reason for change of cycle efficiency increment. Application of rotating detonation combustion can significantly enhance gas turbine performance, but the limited flow capacity caused by normally aspirated characteristic of rotating detonation combustor (RDC) severely constrains the operating range of gas turbine. In this paper, the detailed investigation was carried out for the influence of RDC passage area on cycle characteristic parameters for a 25MW single shaft gas turbine. The results demonstrated that changes of RDC passage area had a significant impact on operating range of rotating detonation gas turbine. As RDC passage area increased, operating range of gas turbine moved to the higher power, with the slight increases for cycle efficiency, cycle efficiency increment and net power increment compared to traditional gas turbine at identical net power. For the process when RDC passage area decreased from 0.0272 m2 to 0.0240 m2, the lower working limit of rotating detonation gas turbine decreased to 53.3 % of rated power, in which equivalence ratio of RDC replaced turbine efficiency as the greatest influence factor on cycle efficiency increment. [ABSTRACT FROM AUTHOR]

Carbon-free and sustainable energy storage solutions are required to mitigate climate change. One possible solution, especially for stationary applications, could be the storage of energy in metal fuels. Energy can be stored through reduction of the oxide with green hydrogen and be released by combustion. In this work a feasibility study for iron as possible metal fuel considering the complete energy cycle is conducted. On the basis of equilibrium calculations it could be shown that the power-to-power efficiency of the iron/iron oxide cycle is 27%. As technology development requires a more detailed description of both the reduction and the oxidation, a first outlook is given on the kinetic analysis of the reduction of iron oxides with hydrogen. Thermogravimetric experiments using Fe2O3, Fe3O4 and FeO indicate a three-step process for the reduction. The maximum reduction rate can be achieved with a hydrogen content of 25 %. Based on the experimental results a reaction mechanism and accompanied kinetic data were developed for description of Fe2O3 reduction with H2 under varying experimental conditions.

The global trend toward automatization and miniaturization of smart devices has triggered the development of reliable off‐grid power sources with low economic and environmental impact. Such autonomy can be provided when a photovoltaic cell is integrated with an electrochemical double‐layer capacitor in one monolithic power pack. This work demonstrates a reliable and straightforward approach to monolithically integrate high‐performance organic solar cells with mesoporous nitrogen‐doped carbon nanosphere‐based supercapacitors in a single device with a three‐electrode configuration. To assess the efficiency of the device, a novel approach is presented that relies on the direct monitoring of both integrating parts during illuminated and dark phases and accounts for possible losses. The evaluation with the standard literature approach shows an outstanding performance of the integrated photosupercapacitor with a peak photoelectrochemical energy conversion efficiency of 17%. However, this type of efficiency does not properly represent the real overall efficiency of the device. Based on the newly developed efficiency calculation, a more modest overall cycle efficiency of 2% is obtained, which represents the overall performance of the integrated device in a better way. This versatile evaluation approach is applicable for all kinds of integrated multifunctional photoconversion–storage systems. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Engineering for Thermal Energy & Power / Reneng Dongli Gongcheng is the property of Journal of Engineering for Thermal Energy & Power and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The paper discusses technological solutions in the field of production and use of hydrogen fuel, the combustion of which, in a steam-oxygen environment, can significantly increase the initial parameters of the steam turbine cycle and, thus, increase the thermal efficiency of traditional steam turbine thermal power plants. A study of technologies for the industrial production of hydrogen has been carried out. An analysis of the technical and economic features of hydrogen production technologies for use in the electric power industry showed that the most promising method is electrolysis, which makes it possible to obtain inexpensive hydrogen during hours of low demand for electricity or cogeneration of heat and electricity when electricity is a by-product. It is shown that in order to increase the power and efficiency of steam turbine TPPs, it is important to use external steam superheating from an external source of thermal energy, thus providing intermediate overheating of the working fluid by connecting an additional cycle with a higher equivalent initial temperature to the main steam turbine cycle. We have established that if we use hydrogen as a thermal energy source, the absolute efficiency of the steam turbine cycle can be increased up to 54%, taking into account the regenerative heating of feed water. In this case, at an overheating temperature equal to tnn = 760 °C, the absolute efficiency of the cycle is virtually equal to that of a CCGT unit operating at the initial gas temperature t0 = 1350 °C. At the same time, while maintaining the boiler performance, the rated capacity of the steam turbine power unit is increased by 12%. In addition, the study pays attention to the problem of increasing the power consumption of TPPs for the auxiliaries, as required to compress hydrogen and oxygen up to a pressure higher than that in the steam pipeline where the combustion chamber is installed. Our calculations have allowed us to conclude that, for the case of installing the combustion chamber in live steam, the share of additional power spent for auxiliaries should be 7%, whereas the main share of power is consumed for compressing hydrogen—94%. Despite the identified shortcomings, an economic analysis of the process of hydrogen production at TPP by electrolysis and its further use for intermediate overheating in steam turbines in order to increase their efficiency showed the effectiveness of this solution. [ABSTRACT FROM AUTHOR]

Analysis of internal combustion (IC) engine measurements for thermal efficiency improvement is a complex endeavor involving a number of competing interrelated factors. To simplify the process, a novel chart and its utilization are introduced. The proposed chart divides a potential indicated thermal efficiency improvement into the contribution factors of cooling system losses and cycle efficiency. Cycle efficiency is an ideal target or goal; how much in-cylinder net heat energy, less cooling losses and unburnt fuel losses from the lower heating value of injected fuel, can be effectively transformed into indicated work? This paper explains the definition and practical usage of this chart. Furthermore, several experimental case studies involving advanced engine technologies using the chart are illustrated to identify improvement pathways and their potential effects on thermal efficiency. [ABSTRACT FROM AUTHOR]

In order to improve the energy utilization efficiency and driving range of electric vehicle, an electromechanical flywheel hybrid system based on planetary gear power split is proposed in this study. First, based on the working principle of planetary gear, the performance of the system under six topologies was analyzed. The optimal design schemehe was confirmed. Specially, the speed regulating motor and the flywheel connect with sun gear and ring gear respectively, the power output from carrier. Then, to meet the design requirement of the vehicle, the parameters of electromechanical flywheel hybrid device, the drive motor and the transmission were optimized. Finally, a vehicle dynamic simulation model was constructed to analyze the dynamic and economic performances of the vehicle under different conditions. Results show that, compared with the original vehicle driven by a single motor, the new hybrid system designed is able to improve the vehicle economy effectively while maintaining the power performance. Under J1015, NEDC and HWFET cycles, the average operating efficiencies of the power system are increased by 8.2%, 5.6% and 4.3%. [ABSTRACT FROM AUTHOR]

Supercritical CO2 cycle has a high cold end temperature. Optimizing the cold end temperature plays an important role in improving the cycle efficiency. In order to obtain the best annual average efficiency, it is necessary to introduce artificial refrigeration to make the supercritical CO2 cycle run at a more optimized cold end temperature. For the supercritical CO2 recompression cycle with parameters of 550℃/20MPa, the annual average cycle efficiency under different cold end temperature of 5 to 35℃, with the combination of natural cooling and artificial refrigeration was analyzed by thermodynamic method, and the feasibility and economic analysis of the cold end temperature optimization method were studied as well. The annual average efficiency of the unit can be improved by choosing the optimal cold end temperature and combining natural cooling with artificial refrigeration. For northern China, the cold end temperature optimization method has better feasibility. The artificial refrigeration increases the investment of unit equipment, but the improvement of operation efficiency brings more power generation revenue and moreover increases the net income of the unit during its life cycle.

As the high-temperature latent heat storage (LHS) market continues to expand, ensuring its safe and stable operation is paramount for facilitating its rapid development. In specific operational scenarios and instances of failures, large-scale integrated LHS systems may operate with either single or partial sets of heat exchange tubes. However, a notable research gap exists in the comprehensive exploration of the impact of partial operational conditions on the thermal performance of LHS systems. Consequently, this study conducted experiments involving both- and single-sided charging and discharging using a cylindrical high-temperature LHS system equipped with two sets of heat exchange tubes. To comprehend the ramifications of single-sided operation on temperature distribution across both active and inactive sides, as well as its influence on charging/discharging power and accumulated stored/released energy on the active side. The analysis of phase change material (PCM) temperature distribution revealed that single-sided charging significantly influenced the inactive side, while single-sided discharging exhibited a comparatively minor impact on the inactive side. As PCM melted during charging, temperature disparities diminished due to natural convection, while non-uniform temperature persisted in unmelted PCM. Examination of the PCM liquidus indicated that the metal heat exchange tube enhanced heat transfer on the inactive side, resulting in substantial PCM melting during charging. However, the heat transfer effect of metal heat exchange tubes during discharging was insignificant, leading to a considerable amount of liquid PCM on the inactive side after discharging. The total heat storage for both-sided charging was 1002.71 MJ, whereas, for single-sided charging using two tubes, it was 1074.42 MJ and 1000.60 MJ, respectively. Correspondingly, during discharging, the average powers were 682.74 MJ, 543.62 MJ, and 538.11 MJ, respectively. The cycle efficiency for the both-sided operation was 68.09 %, while those for single-sided operations of two tubes were 50.6 % and 53.78 %, respectively. The reduced cycle efficiencies of single-sided operations were attributed to prolonged charging and discharging durations and the presence of more liquid PCM on the inactive side after discharging. • Explores the impact of partial operation on LHS systems' thermal performance. • Metal tubes enhance heat transfer on the inactive side during charging. • Cycle duration for single-sided was 21.57 h, slower than both-sided of 7.83 h. • Cycle efficiency for single-sided was 50.6 %/53.78 %, below both-sided of 68.09 %. • Emphasize importance of system design and optimization in single-sided operations. [ABSTRACT FROM AUTHOR]

Superior performance and compactness of supercritical CO2 power cycles are encouraging researchers to explore them for waste heat recovery (WHR) applications. This paper presents a comprehensive thermodynamic analysis of a dual recuperated dual expansion cycle utilizing industrial waste heat. The proposed cycle incorporates two recuperators and two turbines with a single compressor. The influence of operating parameters concerning cycle performance in the context of a WHR cycle is discussed. The low side, high side pressures, and the split ratio between the high-temperature and low-temperature turbines are optimized for maximum power rather than thermodynamic cycle efficiency. The cycle performance is evaluated with air as the primary heat transfer fluid in the waste heat recovery heat exchanger operating at a maximum source temperature of 500 °C. The sink temperature is assumed to be 40 °C to enable operation in tropical conditions like India. The paper also compares the performance of the proposed WHR cycle with the baseline single recuperated sCO2 cycle operating under similar conditions. The analysis shows that the proposed cycle is able to extract 60% more heat and produce 37% more power than the single recuperated sCO2 cycle. The maximum heat recovery factor for the analyzed WHR cycle is 17.4%, compared to 12.7% for the single recuperated sCO2 cycle. [ABSTRACT FROM AUTHOR]

The paper discusses technological solutions in the field of production and use of hydrogen fuel, the combustion of which, in a steam-oxygen environment, can significantly increase the initial parameters of the steam turbine cycle and, thus, increase the thermal efficiency of traditional steam turbine thermal power plants. A study of technologies for the industrial production of hydrogen has been carried out. An analysis of the technical and economic features of hydrogen production technologies for use in the electric power industry showed that the most promising method is electrolysis, which makes it possible to obtain inexpensive hydrogen during hours of low demand for electricity or cogeneration of heat and electricity when electricity is a by-product. It is shown that in order to increase the power and efficiency of steam turbine TPPs, it is important to use external steam superheating from an external source of thermal energy, thus providing intermediate overheating of the working fluid by connecting an additional cycle with a higher equivalent initial temperature to the main steam turbine cycle. We have established that if we use hydrogen as a thermal energy source, the absolute efficiency of the steam turbine cycle can be increased up to 54%, taking into account the regenerative heating of feed water. In this case, at an overheating temperature equal to tnn = 760 °C, the absolute efficiency of the cycle is virtually equal to that of a CCGT unit operating at the initial gas temperature t0 = 1350 °C. At the same time, while maintaining the boiler performance, the rated capacity of the steam turbine power unit is increased by 12%. In addition, the study pays attention to the problem of increasing the power consumption of TPPs for the auxiliaries, as required to compress hydrogen and oxygen up to a pressure higher than that in the steam pipeline where the combustion chamber is installed. Our calculations have allowed us to conclude that, for the case of installing the combustion chamber in live steam, the share of additional power spent for auxiliaries should be 7%, whereas the main share of power is consumed for compressing hydrogen—94%. Despite the identified shortcomings, an economic analysis of the process of hydrogen production at TPP by electrolysis and its further use for intermediate overheating in steam turbines in order to increase their efficiency showed the effectiveness of this solution.

Proton exchange membrane fuel cell (PEMFC) has become a promising alternative power source due to its quiet operation, low emission, and high theoretical energy conversion efficiency. However, a relatively large fraction of the energy (around 40 ~ 50%) is dissipated into the ambient environment by the cooling system, leading to a waste of thermal energy. The present study aims to improve the practical PEMFC performance by harvesting the thermal energy from the cooling system utilizing an organic Rankine cycle (ORC) system. The R134a and R245fa are selected as the working liquids for ORC to harvest energy from the PEMFC. A combined PEMFC and ORC model is established based on the first and second law thermodynamic analysis. It is found that the cycle efficiency (ηorc) of R134a (about 11.33%) is higher than that of R245fa (about 9.16%). The combined system efficiency (ηsys) for R134a can be increased by approximately 5.84%, compared with that of the fuel cell stack alone. For R134a, the effect of changes in the operating temperature and current density of the PEMFC stack on its cycle efficiency (ηorc) is investigated. The results indicate that as the working temperature of the PEMFC stack increases, both the ORC and combined system efficiencies (ηorc and ηsys) increase, while with the increase of the current density of the PEMFC, the ORC cycle efficiency (ηorc) remains almost constant, and the combined system efficiency (ηsys) decreases. The exergy efficiency is found to have the same variation trends with the energy efficiency. [ABSTRACT FROM AUTHOR]

Steam power plants have a considerable potential to meet the growing energy demand, but its dependence on conventional fossil fuels has hampered its viability. One of the ways to minimize fuel consumption and upgrade the performance of a Rankine cycle is by incorporating closed feedwater heaters(FWHs). The datasets contained in this paper are thermodynamic performance analysis carried out on reheat – regenerative steam power plant with FWHs using CyclePad V2.0 software. The thermodynamic performance indices assessed are thermal efficiency, network output, heat rate, fuel consumption, boiler efficiency and specific steam consumption. Result obtained show that an increase in the number of FWHs decreases the fuel consumption, heat rate, heat rejected in condenser and heat input to the cycle. This effect invariably can lead to a reduction in operating cost and environmental impacts.

Considering the pressure gain characteristic of continuously rotating detonation (CRD) combustion, a rotating detonation gas turbine cycle was established using methane as fuel. The variation of pressure gain characteristic and its influence on cycle performance at different compressor pressure ratios and air distribution proportions were investigated combined with a series of two-dimensional numerical simulations. The results were demonstrated that compared with the conventional approximate iso-pressure combustion, rotating detonation combustion could significantly improve the thermodynamic performance of gas turbine in various conditions. Due to the difference of entropy generation between rotating detonation and iso-pressure combustion, the pressure gain characteristic of the CRD combustor was provided a higher cycle efficiency. The efficiency gain was higher at lower compressor pressure ratio and air proportion entering CRD combustor. In the calculated cases, the pressurization ratio of the CRD combustor was higher than 1.37, cycle efficiencies of rotating detonation gas turbine were reached 0.395, cycle efficiency increasing rates were more than 22.5%, and power generation enhancements were greater than 1500 kW.

This manuscript presents a new combination based on a thermodynamic conversion, the idea is to combine the Organic Rankine Cycle (ORC) with the Vapor Compression Cycle (VCC). The novelty of the system appears essentially in: the development of new ORC–VCC combination architecture, the lowering of the ORC cycle temperature, the possibility of cold production by the ORC cycle upstream of the pumping phase, preheating of ORC cycle using VCC cycle fluid and new configurations based on the integration of heat recovery systems to improve overall system performance. In addition, each installation mode has several configurations depending on the recovery points that will be integrated later, besides its adaptation to any energy source, where we can use biomass, solar and heat rejects of industry at low temperatures (80‒160°C). This system can produce a cold with negative and positive temperatures. Although, thanks to its architecture, it is also characterized by many combination of selection fluid for the ORC and VCC cycles it is not necessarily to have the same working fluid as the classic systems. The main purpose of this study is to analyze the performance of a new system which combines Rankine-vapor compression cycle for the cogeneration of electricity and refrigeration. Coefficient of performance (COP) will be compared with other cooling systems and power system, such as the system turbo compressor Rankine. The fluids we used in the work are ammonia for the ORC and R600a for the VCC. [ABSTRACT FROM AUTHOR]

Owing to the wide applications of ammonia in hydrogen field and high energy consumption of the Haber-Bosch process, developing economic and environmentally benign ammonia synthesis process has attracted great interests. This work focuses on the moderately high two-step solar water-splitting of VN to produce ammonia, thus avoiding the reliance of fossil-fuel based heating source and pure hydrogen. Based on the equilibrium composition analysis, we find that V 2 O 3 , CH 4 and N 2 with mole ratio of 1:3:1.5 at T H = 1050 °C is enough for complete methane reforming and sufficient nitrogen fixation of V 2 O 3. As for the water-splitting of VN, the production of NH 3 is only possible at T L ≤ 400 °C, and inputting excessive water vapors is found to exert little effect on ammonia production at H 2 O:AlN>3:2. At the temperature range of full conversion between V 2 O 3 and VN, the cycle efficiency, η cycle , and solar-to-fuel efficiency, η solar-to-fuel, under different operating temperatures are compared, in which the highest η cycle and η solar-to-fuel are 31.9% and 35.3% respectively. Moreover, efficiencies could be increased up to more than 37% with consideration of heat recuperation, demonstrating the great solar energy storage and fuel production potential of the proposed system. • A solar thermochemical cycle based on V 2 O 3 /VN is proposed for ammonia production. • Both cycle and solar-to-fuel efficiencies are calculated and compared. • The operating temperature below 1250°C ensures high selectivity of syngas. • Heat recuperation and material recovery are underscored. [ABSTRACT FROM AUTHOR]

Due to its unique properties, helium has wide application in different industries and scientific fields, which has turned it into a strategic material. Helium liquefaction plants include wide temperature range from 300 k to 4.2 k, so these plants have high energy consumption. A lot of studies have done to optimize the operation of these cycles. In this research, an exergy analysis is performed for a liquid helium production plant. The optimal performance of 3 and 4 stage cycles is extracted using parametric study and the results are compared with those of Collins dual-expander cycle. The results show that by increasing the number of cooling stages, not only the compressor optimum discharge pressure is reduced, but also the cycle efficiency dramatically increases and the power consumption of the cycle decreases. Further, a sensitivity analysis of the exergy efficiency of the 2, 3 and 4 expander cycles is compared to the heat exchangers effectiveness, expander's efficiency and the input flow rate to the expanders. [ABSTRACT FROM AUTHOR]

A cycle analysis has been applied to a model of a advanced ultra-supercritical steam plant with novel steam pipes. The transfer pipes proposed incorporate internal thermal coatings and are externally jacketed to enable cooling. This enables higher temperature working steam, while keeping the pipe wall temperature below the acceptable limit for more conventional steel alloys and avoiding the need to use higher cost austenitic stainless steels and nickel base alloys. The baseline design had a superheat temperature of 700 C ∘ and a reheat temperature of 720 C ∘ . A thermal coating thickness of 2.8 mm is sufficient to keep the wall temperatures of the steam transfer pipe after the supercritical boiler below 600 C ∘ . For the transfer pipe located after the reheater a thicker coating or less ambitious reheat temperature is required to achieve acceptable pipe wall temperatures. Whereas subcritical plant has a calculated cycle efficiency of 42.1%, the elevated temperature and pressure in a customary ultra-supercritical steam boost cycle efficiency to 52.2%. Modifying this design with a thermal barrier lowers the cycle efficiency to 51.4%, still appreciably better than for subcritical plant. Alternative plant cooling arrangements might improve pipe temperatures but have minimal impact on overall cycle efficiency. [ABSTRACT FROM AUTHOR]

• Two methods to allocate electricity in hybrid thermal power plants are proposed. • The first method allocates electricity evaluating extra electricity production. • The first method is based on numerical simulations of power plants. • The second method allocates electricity evaluating efficiency of single cycles. • The second method is usable during power plant operation. In response to global climate target, over the last decade renewable electricity generation from solar energy has grown rapidly and hence measures to deal with its non-dispatchable nature. Integrating concentrating solar plants in conventional fossil power plants is a widely researched solution to tackle solar energy intermittency. This results in hybrid power plants whose total electricity production consists of two different contributions (solar and fuel-electricity) that can be evaluated separately by implementing numerical methods based on the so-called "with and without solar energy" approach. Nonetheless, such evaluation cannot be carried out in actual power plants operation where fossil and renewable contributions are not discernible from each other within the overall production. To overcome this limitation, and consequently allow the total electricity generated to be properly partitioned among energy sources, this study proposes and validates an alternative "on-line and real-time" method to quantitatively assess solar and fuel-electricity by subdividing the overall cycle efficiency into subsequent ones related to the different energy conversion processes during real plant operation. Required input can be derived from available operating data except for factor of internal losses that, however, showing negligible dependence on solar energy and power plant load, can be reasonably assumed constant and estimated in dedicated calculations. [ABSTRACT FROM AUTHOR]

We investigated refrigerant blends as possible low GWP (global warming potential) alternatives for R-134a in an air-conditioning application. We carried out an extensive screening of the binary, ternary, and four-component blends possible among a list of 13 pure refrigerants comprising four hydrofluoroolefins (HFOs), eight hydrofluorocarbons (HFCs), and carbon dioxide. The screening was based on a simplified cycle model, but with the inclusion of pressure drops in the evaporator and condenser. The metrics for the evaluation were nonflammability, low GWP, high COP (coefficient of performance), and a volumetric capacity similar to the R-134a baseline system. While no mixture was ideal in all regards, we identified 16 binary and ternary blends that were nonflammable (based on a new estimation method) and with COP and capacity similar to the R-134a baseline; the tradeoff, however, was a reduction in GWP of, at most, 54% compared to R-134a. An additional seven blends that were estimated to be "marginally flammable" (ASHRAE Standard 34 classification of A2L) were identified with GWP reductions of as much as 99%. These 23 "best" blends were then simulated in a more detailed cycle model. [ABSTRACT FROM AUTHOR]

With the development of compact heat exchangers in the past few decades, S-CO 2 recompression Brayton cycle has attracted much attention. However, the cycle efficiency of the traditional S-CO 2 recompression Brayton cycle is sensitive to the compressor inlet temperature, which limits the application of the cycle. According to the property of S-CO 2 , rapid property change appears in different temperature region under different pressure conditions in pseudocritical area. This feature can be used to reduce recompressing compressor work. To take the advantage of this feature, a modified recompression Brayton cycle based on S-CO 2 recompression Brayton cycle is proposed to decrease the temperature sensitivity of recompression Brayton cycle efficiency. Different minimum pressure and different flow split ratio conditions are investigated under various minimum temperature ranges. In this paper, the temperature sensitivity of the cycle efficiency is investigated by an in-house cycle analysis code in the minimum temperature range of 32–50 °C and the minimum pressure range of 7.6–9.0 MPa. First and second law of thermodynamics are used to analyze the performance of the two kinds of Brayton cycle. Results show that the modified recompression Brayton cycle has better temperature sensitivity while having comparable cycle efficiency as the recompression Brayton cycle. Moreover, high compressor inlet pressure and small flow split ratio can decrease the temperature sensitivity of cycle efficiency. • An integrated thermodynamic analysis code is developed for S-CO 2 Brayton cycle. • Performances of the S-CO 2 recompression power cycle are analyzed. • A modified recompression Brayton cycle is proposed. • Modified Brayton cycle can decrease temperature sensitivity of cycle efficiency. [ABSTRACT FROM AUTHOR]

Highlights • The local pressure drop between inlet and branch tube in T-junctions is clarified. • Parametric studies on the local pressure drop coefficients are carried out with small diameter. • This paper obtains the effects of the T-junction separator on thermodynamic cycle efficiency. Abstract The application of T-junction has already been extended from the petroleum engineering to the emerging advanced thermodynamic cycles. How a T-junction, as a separator in an emerging thermodynamic cycle, affects the cycle efficiency is discussed in this paper. Firstly, based on the Eulerian method, parametric studies on the local pressure drop coefficients are conducted and two new local pressure drop (LPD) coefficients are predicted in this paper. Then, the effects of pressure drop on a composition adjustable organic Rankine cycle efficiency is analyzed. In the process, a composition adjustable organic Rankine cycle with zeotropic mixtures R245fa/R123 is chosen to calculate the effects of pressure drop on thermodynamic cycle efficiency. The quality of the outlet of the evaporator is assumed as 0.7, and the composition ratio as 0.6/0.4. The results show that the pressure variation of T-junction affects the adjustable organic Rankine cycle efficiency, and reasonable phase separation ratio can improve the thermodynamic cycle efficiency. The pressure drop could cause composition diffusion. In addition, two new local pressure drop coefficients are obtained. And the results demonstrate that K 12J declines slowly with the increases of density ratio (ρ 2 / ρ 1) and decreases with the increases of mass fraction of taken off (F). K 13J shows an obvious trend with diameter ratio (d 3 / d 1) and F. This work could push the research of T-junction as a separator in the adjustable organic Rankine cycle. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Engineering for Thermal Energy & Power / Reneng Dongli Gongcheng is the property of Journal of Engineering for Thermal Energy & Power and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Journal of Engineering for Thermal Energy & Power / Reneng Dongli Gongcheng is the property of Journal of Engineering for Thermal Energy & Power and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In this paper, we present a new method to determine the optimal design conditions of a supercritical CO 2 recompression Brayton cycle with dry cooling based on plant location. These power cycles are gathering high interest in concentrated solar thermal power technologies, which are most likely to be deployed in arid areas where dry cooling is a strategic choice. However, the usual high ambient temperature associated with these locations affects negatively the cycle performance. The key selection of two design parameters, the recompression fraction and the compressor inlet temperature, can minimise this negative effect. The method presented here allows the adjustment of these two parameters maximising the annual generation of electricity and cycle efficiency simultaneously. The optimisation process analyses the drop in the cycle performance due to the yearly variation of ambient temperature at the specific location. To reduce the computational effort required, polynomial regressions extrapolate the results from a reduced set of design-point and off-design cycle simulations in a wide range of ambient and compressor inlet temperatures. As an example, the method is applied to three different locations demonstrating the existence of optimal design conditions and justifying the need to adjust these two key parameters for each specific location. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Engineering for Thermal Energy & Power / Reneng Dongli Gongcheng is the property of Journal of Engineering for Thermal Energy & Power and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)