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We have studied the impact of demagnetizing fields on the magnetocaloric effect of commercial-grade gadolinium plates. Adiabatic temperature changes (Δ T) were measured for magnetic fields applied along the parallel and perpendicular directions of the plates. The differences in the obtained Δ T values were accounted for by differences in the internal field due to demagnetizing effects. A combination of calorimetric measurements under a magnetic field and thermometric measurements has enabled us to obtain Brayton cycles for the two different magnetic field orientations. It has been found that the refrigerant capacity for a Brayton cycle working at 1.6 T around room temperature reduces from R C = 9.4 to R C = 5.5 J kg − 1 when the demagnetizing factor changes from N D = 0.035 to N D = 0.928 for the parallel and perpendicular configurations, respectively. It has been shown that it is possible to obtain significant demagnetizing field-induced magnetocaloric effects by rotating the sample in a region of a constant applied magnetic field. The refrigerant capacity of a Brayton cycle around room temperature for a 1.6 T constant applied magnetic field is R C = 0.6 J kg − 1 . The feasibility of these demagnetizing field-induced effects has been confirmed by direct thermometric measurements, which reveal adiabatic temperature changes of 1 K when the sample is rotated between the perpendicular and parallel configurations. [ABSTRACT FROM AUTHOR]

To combat climate change successfully, enhancing existing processes is imperative alongside exploring new regenerative technologies. For this purpose, new components must be considered to improve the efficiency of thermodynamic processes. A promising candidate is the Ranque–Hilsch vortex tube due to its low investment cost and maintenance. Previous research has highlighted the thermodynamic advantages of employing a vortex tube in various applications, such as Brayton cycles or as a replacement for conventional expansion valves. However, to assess the potential of the vortex tube within a thermodynamic process, a computationally efficient but precise model of the vortex tube is required. Existing modeling approaches often fail to accurately predict experimental trends or require information such as geometry data that are not available for potential analyses. Thus, the present study proposes a novel thermodynamic-based black-box modeling approach: the vortex tube efficiency is introduced by incorporating operating and geometrical conditions into a single parameter. The vortex tube efficiency is systematically investigated for different operating conditions and various fluids and compared with available experimental results. The resulting modeling approach allows the qualitative and quantitative prediction of vortex tube behavior for air at various operating pressures and cold gas fractions. Further experimental investigations are required for a comprehensive quantitative description of vortex tubes with different geometries and working fluids. [ABSTRACT FROM AUTHOR]

This study reports the comparative energy and exergy analysis of ortho-para hydrogen and non-ortho-para hydrogen conversion in hydrogen liquefaction process. Two cases were simulated, case A – hydrogen liquefaction with ortho-parahydrogen conversion and case B – hydrogen liquefaction without ortho-parahydrogen conversion. This is the first study that presents a comparative energy and exergy analysis between such two cases. In this research, a hydrogen liquefaction process was designed adopting cascaded five-stage Brayton refrigeration cycle. The process was simulated in Aspen PLUS. The process used a mixed refrigerant (of liquefied natural gas) refrigeration cycle to precool the gaseous hydrogen feed from 26 °C temperature to −192 °C temperature, and mixed refrigerant (of nelium) was subsequently used to further deep-cool the the hydrogen stream from −192 °C temperature to −245.99 °C temperature in the cryogenic section of the process. Liquefaction was achieved by expanding the hydrogen through Joule-Thomson valve at −248.37 °C and 1 bar. The simulated results of the two cases showed the specific energy consumption of case A to be 8.45 kWhr/kg LH , and that of case B to be 15.65 kWhr/kg LH respectively. The results also indicated a total exergy efficiency of 92.42% in case A and 87.18% in case B. The research results showed that the hydrogen liquefaction designed with configuration of ortho-parahydrogen conversion has better performance indicators than the liquefaction without ortho-parahydrogen conversion. Therefore, hydrogen liquefaction with ortho-parahydrogen conversion can be considered in the design and development of new hydrogen liquefaction plants. Process optimization is recommended to further enhance the specific energy consumption and exergy efficiency of both processes. • Comparative analysis of ortho-para and non-ortho-para hydrogen conversion. • Ortho-para Process is more energy efficient than non-ortho-para process. • Average exergy efficiency of 89.8% achieved in the analysed processes. • Integration of three refrigeration cycles to achieve hydrogen liquefaction. [ABSTRACT FROM AUTHOR]

The present investigation proposes an innovative hybrid energy system based on solar energy equipped with a parabolic trough collector, a supercritical CO2 Brayton cycle (SCBC), a recuperative organic Rankine cycle (RORC), a proton exchange membrane electrolyzer (PEME), and a two-tank direct thermal energy storage system. To ensure the stable operation of the system despite fluctuations in the amount of sunlight received during the day, the mass flow rate (MFR) of the heat transfer fluid in the solar collector is regulated to maintain a consistent inlet temperature for the SCBC and RORC. Additionally, the MFR of the HTF from the hot tank to the bottoming cycles also remains constant. This approach allows the entire system to operate around the clock and under stable conditions. The energy and exergy performance of the entire system is evaluated under varying solar irradiance and ambient temperature over a 24-h period. The results revealed that the system could generate 1.5 MW of net power, 4.47 kg of hydrogen per day, and 18.48 kg/s of hot water with a total energy efficiency of 51.30% and exergy efficiency of 55.7%. The solar collector possessed the lowest exergy efficiency of 33.89% due to a high exergy destruction rate. The PEME possessed maximum energy efficiency of 58.85%, followed by RORC and SCBC with 26.38% and 14.84%, respectively. It is concluded the proposed system can provide a reliable and sustainable supply of electricity, hydrogen, and hot water, demonstrating a promising and viable poly-generation technology for both grid-connected and off-grid applications. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Xi'an Jiaotong University is the property of Editorial Office of Journal of Xi'an Jiaotong University 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.)

An axial flow fan is designed for dry cooling of a sCO2 Brayton cycle for a CSP plant, and a scaled model of the fan is manufactured and tested experimentally in an ISO 5801:2017 Type A fan test facility. While the design procedure's estimate of the total-to-static efficiency at the design flow rate is relatively high, at 74.4%, the experimental fan efficiency was found to be only 50.6%. This paper details an investigation into the causes of fan performance degradation, using both experimental and numerical methods. The investigation finds that the hub configuration, tip clearance size, and scale of the test fan is responsible for the reduced performance. Two alternative hub and casing configurations are identified which improve the fan's performance significantly. [ABSTRACT FROM AUTHOR]

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.)

Biogas-fueled decentralized energy systems featuring gas turbines emerge as pivotal players in the quest for more adaptable and eco-friendly energy solutions. This study presents the design of a cutting-edge multigeneration system that harnesses the potential of a gas turbine coupled with ejector-driven dual-loop bi-evaporator technology, reverse osmosis desalination, proton exchange membrane electrolysis, and an organic Rankine cycle. The research encompasses an extensive sensitivity analysis and deploys a genetic algorithm-based optimization technique. Through meticulous Optimization, the system achieves remarkable outcomes, including electricity generation, cooling capacity, heating capacity, desalinated water production, and hydrogen yield, measured at 957.3 kW, 231.4 kW, 272.3 kW, 7.336 kg/s, and 0.99 kg/h, respectively. Notably, this performance surpasses the base case by 2% and 8.9%, yielding exergy efficiency and total unit cost improvements of 33.3% and 16.4 $/GJ. Among the critical decisions made was selecting an organic working fluid for the organic Rankine cycle. Through rigorous evaluation, isobutene emerged as the optimal choice, demonstrating significantly improved output power compared to alternatives. Isobutane as the working fluid led to a substantial increase in overall exergy efficiency and a resultant total unit cost of 18.06 $/GJ, accompanied by an impressive 23.48% exergy efficiency. [Display omitted] • Proposing a novel multi heat recovery for a biogas-fed Brayton cycle in five stages. • Using an ejector-based bi-evaporator cycle in integration with a dual-loop ORC. • Comprehensive energy/exergy/cost study and multi-objective optimization. • Comparing different organic fluids in the MCCP leading to selecting isobutene. • Optimum exergy efficiency and total unit products' cost are 33.33% and 16.44 $/GJ. [ABSTRACT FROM AUTHOR]

The current study examines a novel multigeneration plant that uses geothermal energy to produce clean and sustainable products. The process includes a re-compression supercritical Brayton power plant (re-sBC), an ejector cooling unit (EJCS), a humidifier dehumidifier desalination (HDH) unit, a Proton-Exchange Membrane (PEM) process, and a hot water preparation unit. The designed plant is able to generate hot water, cooling, power, hydrogen, and freshwater using the geothermal source. In the current paper, the thermodynamic analysis, CO 2 emission assessment, and exergoenvironmental index evaluation are executed to determine the system efficiency and the association between the system and the environment. A thorough parametric examination is fulfilled, to show how the system indicators impact efficiency and generated products. According to analysis data, the proposed multigeneration plant is able to generate 1278 kW of heating load, 229.6 kW of refrigeration capacity, and 109.5 kW of net power rate. Additionally, the capacity of the freshwater is 0.1188 kgs − 1 and the hydrogen is 0.001317 kgs − 1 . This developed system emits a total of 117 tonnes of CO 2 emissions per year for these useful outputs. In conclusion, the energetic and exergetic performance of the suggested MG plant are 14.09 % and 23.35 %, respectively. • A sustainable geothermal energy-based MG is proposed. • The thermodynamic, emission, and environmental analysis is conducted. • Design and evaluation of the Green hydrogen production and storage. • Re-compressed sBC integrated into geothermal driven MG plant. • Total energy and exergy efficiency is computed as 14.09 % and 23.35 %, respectively. [ABSTRACT FROM AUTHOR]

Purpose: The purpose of this study is to perform an off-design analysis of the inverted Brayton cycle engine. Design/methodology/approach: The off-design analysis equations of the inverted Brayton cycle engine were first derived in this study and the control parameters of the inverted Brayton cycle engine were first determined and investigated. Findings: It is observed that by controlling the total temperature decrease in cooling section, it is possible to adapt the engine for low specific fuel consumption working conditions or high thrust working conditions. Specific fuel consumption is reduced by 27.1 % by stopping cooling in the cooling section and thrust is increased by 27.6 % by working with full load of the cooling section (500 K temperature decrease in cooling section). It is observed that thrust depending on the flight Mach number increases with an increase in flight Mach number and reaches a peak value at 5.21 flight Mach number and reduces by 80.8 % at 6 flight Mach number relative to the peak value. The specific fuel consumption increases rapidly as the Mach number increases, and the specific fuel consumption is 49.0 g/[kN.s] at Mach 1, reaches 70.4 g/[kN.s] at Mach 5 and increases to 412 g/[kN.s] at Mach 6. The specific fuel consumption increases from 68.1 to 73.0 g/(kN.s) and the thrust decreases from 16.5 to 13.3 kN as the total preburner exit temperature increases from 1,500 to 2,000 K. Specific fuel consumption decreases from 83.1 to 64.8 g/(kN.s) and thrust increases from 4.60 to 11.08 kN depending on afterburner exit total temperature increase from 1,800 to 2,500 K. Research limitations/implications: The cooling section reduces total temperature of the gas flow to lower values to increase the compressor total pressure ratio. The compressor increases the total pressure of the gas flow to the optimum total pressure ratios to increase the nozzle exit Mach number and gain more thrust. The afterburner increases the total temperature of the gas flow to increase the sound speed in the nozzle exit to increase thrust. The nozzle expands the gas flow to reduce the static pressure of the gas flow to near the optimum value, atmosphere pressure, to increase thrust and reduce specific fuel consumption. Practical implications: Hypersonic and supersonic air vehicles can use the current engine model for the its own propulsion systems. Social implications: After first heavier than air flight, aero engines was designed for only used for aero vehicle. Internal combustion engines were used for propelled propeller aircraft at the first term of aircraft. However, propeller-propelled aircrafts are not sufficient to increase aircraft velocity to supersonic Mach numbers due to the shock losses of propeller, so the supersonic era was only introduced by revolution in propulsion systems with new concept. A jet engine was developed to be candidate for supersonic flight. Originality/value: Off-design analysis equations of an inverted Brayton cycle engine were first derived in this study. Furthermore, the control parameters of the inverted Brayton cycle engine were first determined and investigated in this paper. [ABSTRACT FROM AUTHOR]

This paper investigated four different S-CO2 Brayton cycle layouts for nuclear energy conversion: simple recuperation cycle (SR), recompression cycle (RC), re-heating cycle (RH), and intercooling cycle (IC). We compared these S-CO2 Brayton cycle schemes for nuclear energy conversion using the G1+TOPSIS multi-index evaluation method. The evaluation results of different schemes based on their safety, thermodynamics, techno-economic and compactness are given. The results show that for Generation IV reactors with the same designed thermal power, the thermodynamic performance of the S-CO2 system is better for higher reactor exit temperature. Among the schemes, the gas-cooled fast reactor (GFR)+RC scheme has the highest thermal efficiency (47.4%) and exergy efficiency (56.48%). The GFR+IC scheme has the lowest specific cost (1861.3$/W) and the internal rate of return (24.8%). The re-heating cycle (RH) has worse indexes, but it requires the lowest initial investment cost. The intercooling cycle (IC) has the lowest levelized cost of electricity (0.0134 $/KW•h) coupling to GFR. Considering all indexes of four aspects, the reactor's performance ranking is MSR>LFR>SFR>GFR, and the S-CO2 system's performance ranking is RC>SR>IC>RH. For Generation IV nuclear energy conversion technologies, the molten salt reactor (MSR)+RC scheme should be given priority, while GFR+RH schemes should be carefully considered. [ABSTRACT FROM AUTHOR]

Compared with Earth, the lunar surface's environment is more complex, which suggests that the nuclear energy Helium–Xenon closed Brayton cycle (NHCBC), supplying electricity to the lunar base, may operate under off-design conditions. A thermodynamic model coupled with the lunar surface environment is established in this paper to analyze the effects of lunar environment exposure, including solar radiation exposure, lunar dust toxicity, and meteorite impact, on a given NHCBC. The results show that the output capacity of a given NHCBC is suppressed during the daytime and enhanced during the nighttime. The lunar dust will improve the system's output capacity at night but will also significantly inhibit the output capacity of the cycle during the daytime, resulting in a fluctuation of 824 % of the system without lunar dust. The output fluctuation of NHCBC is reduced after meteorite impact, while the output capacity of the NHCBC is suppressed, destroyed even worse. The optimization of cycle parameters can alleviate the influence of the lunar environment exposure on NHCBC to a minimal extent. This paper aims to analyze the impact of lunar surface environment exposure on the cycle parameters and output work characteristics of NHCBC and to provide some guidance for the subsequent application of nuclear energy in the lunar base. • A mathematical model of a nuclear energy cycle for a lunar base was established. • Lunar surface environment threats pose economic and safety risks to the energy cycle. • Optimizing a single-cycle parameter is unlikely to enhance energy cycle robustness. • Reducing radiator area to enhance cycle robustness sacrifices thermal efficiency. [ABSTRACT FROM AUTHOR]

Since the population and economic activities have increased energy demands, researchers and scientists have turned to recover wasted energy in various systems. This study aims to maximize energy recovery from marine diesel engines through heat exchange in four different types of wasted streams (exhaust gas, engine coolant, and engine oil coolant). In this research, four cycles of carbon dioxide critical recovery have been designed and modeled to utilize wasted heat energy from marine diesel engines (MAN B&W L35MC6-TII). The EES engineering software has been used for mathematical calculations. In each cycle, the effect of various parameters such as compressor outlet pressure, compressor inlet temperature, and turbine inlet temperature on output power, exergy efficiency, and compressor power consumption has been investigated. The results of this study indicate that the use of a heat recovery cycle in a diesel engine prevents the loss of a significant amount of energy in the engine. Additionally, increasing the fluid temperature at the compressor inlet reduces the output power and exergy efficiency in all recovery cycles. Increasing the fluid temperature at the turbine inlet reduces the compressor power consumption, increases the output power, and enhances the exergy efficiency in all recovery cycles. When the engine body coolant is used in the recovery cycle, the output power and energy system efficiency increase. Moreover, the cycle includes a generator to recover the heat output of carbon dioxide from the turbine. According to the findings of this study, despite the highest turbine output power (611.5 kW) belonging to the exhaust gas recovery system with two heat exchangers, the recovery system with a single heat exchanger has the highest usable output power (228.3 kW). This system had the highest energy and exergy efficiency of 17.72% and 12.85%, respectively. [ABSTRACT FROM AUTHOR]

This study examined the performance of reversed Brayton cycle heat pumps to supply heat above 300 °C. The aim was to overcome the current temperature limitations faced by heat pump technology in industrial heat supply sectors by examining the viability of the reversed Brayton cycle. In particular, the effects of the operating conditions on the cycle performance, such as the waste and return heat temperatures, were analyzed through thermal performance analysis. The reversed Brayton cycle heat pumps showed improved performance over conventional vapor compression cycle heat pumps when a heat supply above 215 °C was required. Furthermore, integrating additional heat exchangers into the cycle configuration was proposed in this study as a method to enhance waste heat utilization and recover unused heat from industrial processes. By incorporating preheating and recuperated cycles, these modifications broaden the operational range under the same operating conditions. They also improve the coefficient of performance (COP) of the reference cycle by up to 23% and 27.4%, respectively. This study explored the potential of reversed Brayton cycle heat pumps to supply heat above 300 °C and provided fundamental guidelines for the efficient design and operation of reversed Brayton cycle heat pumps. The results are expected to enhance our understanding of the performance characteristics of reversed Brayton cycle heat pump technology and expand its use as an alternative to fossil-fuel-based heat supply systems. [ABSTRACT FROM AUTHOR]

Waste heat recovery from exhaust gas is one of the most convenient methods to save energy in internal combustion engine-driven vehicles. This paper aims to investigate a reduction in waste heat from the exhaust gas of an internal combustion engine of a serial Diesel–electric hybrid bus by recovering part of the heat and converting it into useful power with the help of a split-flow supercritical CO2 (sCO2) recompression Brayton cycle. It can recover 17.01 kW of the total 33.47 kW of waste heat contained in exhaust gas from a 151 kW internal combustion engine. The thermal efficiency of the cycle is 38.51%, and the net power of the cycle is 6.55 kW. The variation in the sCO2 temperature at the shutdown of the internal combustion engine is analyzed, and a slow drop followed by a sudden and then a slow drop is observed. After 80 s from stopping the engine, the temperature drops by (23–33)% depending on the tube thickness of the recovery heat exchanger. The performances (net power, thermal efficiency, and waste heat recovery efficiency) of the split-flow sCO2 recompression Brayton cycle are clearly superior to those of the steam Rankine cycle and the organic Rankine cycle (ORC) with cyclopentane as a working fluid. [ABSTRACT FROM AUTHOR]

• A novel SRBC/ARC using CO 2 -based mixtures as working fluids is investigated. • Thermo-economic comparative studies are carried out for the novel system. • The key parameters are identified that determine the system performance. • The precoolers of the systems are predesigned using a segmented design method. CO 2 –Kr (mass fraction of 0.755/0.245) has enormous development potential as a Brayton cycle working fluid. To reduce the limitation of ambient temperature on the supercritical CO 2 –Kr Brayton cycle, this paper develops a thermo-economic model of a coupled system of a supercritical recompression Brayton cycle (SRBC) and an absorption refrigeration cycle (ARC). The ARC utilizes the waste heat from the SRBC to further reduce the inlet temperature of the main compressor. The influences of ammonia–water ARC and LiBr–H 2 O ARC on the coupled system performance are analyzed and compared. The variations of the thermo-economic performance of the systems under different operating parameters are explored, and the impact of each variable on the cycle efficiency and cost is evaluated using a multiple regression linear method. From the perspective of predesign, mathematical models of precoolers with different systems are established. The results show that the coupled ARC improves the cycle efficiency of SCO 2 –Kr BRC by 9.76 %, reduces system cost by 27.01 % when ambient temperature is 25 °C, in addition, the heat loss and size of the precooler is greatly reduced. The inlet temperature and pressure ratio of the turbine are found to be the dominant parameters in determining the thermo-economic performance of the system. [ABSTRACT FROM AUTHOR]

The excellent electrical properties of graphene have received widespread attention. However, the difficulty of electron transfer between layers still restricts the application of graphene composite materials to a large extent. Therefore, in this study, graphene/polyimide films were subjected to a Joule heating treatment to improve the electrical conductivity of the film by ~76.85%. After multiple Joule thermal cycle treatments, the conductivity of the graphene/polyimide film still gradually increased, but the increase in amplitude tended to slow down. Finally, after eight Joule heat treatments, the conductivity of the graphene/polyimide film was improved by ~93.94%. The Joule heating treatment caused the polyimide to undergo atomic rearrangement near the interface bonded to the graphene, forming a new crystalline phase favourable for electron transport with graphene as a template. Accordingly, a model of the bilayer capacitive microstructure of graphene/polyimide was proposed. The experiment suggests that the Joule heating treatment can effectively reduce the distance between graphene electrode plates in the bilayer capacitive micro-nanostructures of graphene/polyimide and greatly increases the number of charge carriers on the electrode plates. The TEM and WAXS characterisation results imply atomic structure changes at the graphene/polyimide bonding interface. [ABSTRACT FROM AUTHOR]

Reducing the energy consumption of hydrogen liquefaction process is an urgent issue to improve the economy of liquid hydrogen transportation. A novel large-scale hydrogen liquefaction system, with a capacity of 100 TPD, is proposed in this paper. The pre-cooling system is composed of a mixed-refrigerant (MR) refrigeration cycle and a CO 2 –NH 3 cascade refrigeration cycle. Due to the auxiliary pre-cooling effect of the CO 2 –NH 3 cascade cycle, temperature of the pre-cooled hydrogen can be as low as −200.9 °C. A modified MR Joule Brayton cycle with an additional compressor is used as the cryogenic system to cool the hydrogen from −200.9 °C to −252.2 °C. Besides, a four-stage ortho-to-para conversion (OPC) process is utilized. Performance of the novel system is investigated and optimized using the Aspen HYSYS software. According to the results, the lowest specific energy consumption (SEC) of the proposed process is 6.15 kWh/kg LH2 and the exergy efficiency is as high as 67.4%. Based on the energy analysis, the best system coefficient of performance is 0.1751 with a 96.3% of p-H 2 in the liquid hydrogen. In addition, compared to the initial conceptual system, the proposed system exhibits significant performance enhancements, a 20% reduction in SEC and a 27.9% increase in exergy efficiency. A sensitivity analysis is conducted to assess the impact of refrigerant composition and hydrogen pressure on the system, resulting in the determination of the optimal proportions of refrigerant components and the optimal inlet pressure. Results of the study can provide theoretical reference for the further development of large-scale hydrogen liquefaction technology. • A novel large hydrogen liquefaction process is proposed and analyzed. • The process employs mixed refrigerant for pre-cooling and cryogenics. • Performances of the process are simulated and optimized with Aspen HYSYS. • The overall specific energy consumption of the process is 6.15 kWh/kg LH2. [ABSTRACT FROM AUTHOR]

Hypersonic vehicles as next-generation aircraft have broad applications, but existing technologies of onboard power generation are hardly applicable due to the change of engines. In this research, a catalytic steam reforming enhanced closed-Brayton-cycle power generation system based on is developed. This system combines the closed Brayton cycle (CBC) and catalytic steam reformed fuel vapor turbine (CSRFVT) to supply electric power. The zero-dimensional models of CBC and the CSRFVT are established to evaluate system performance. Results indicate the products with a water content of 30% have the strongest working ability, which can reach 330 kJ/kg. Moreover, the thermal efficiency and electric power of the parallel arrangement are higher than that of the series arrangement. Besides, the lower pressure of water is beneficial to the electric power. However, the difference in electric power between various pressures is less than 1 kW. In addition, under the same heat absorption, the total electric power of the system based on fuel and water is higher, and the former's outlet temperature of cooling channels is lower. The maximum total electric power of the novel system is about 120 kW. This research provides an innovative technical solution for the power generation of hypersonic vehicles. • A novel power generation system based on hydrocarbon fuel and water is proposed. • A zero-dimensional model of the system performance is established. • The products with a water content of 30% have the strongest working ability. • The maximum total electric power of this system is 120 kW at Ma 6. Abstract. [ABSTRACT FROM AUTHOR]

Two crucial challenges in energy production are emissions and efficient energy utilization. Renewable energy sources and the harnessing of waste heat are important solutions to address these issues. This study focuses on investigating the applicability of the supercritical CO 2 (S–CO 2) Brayton cycle in conjunction with an intermediate-temperature solid oxide fuel cell (IT-SOFC) as a waste heat source. A system is designed and its performance is analyzed using the first law of thermodynamics. Initially, the operating parameters are determined, and then the effects of variations in compressor inlet parameters and turbine inlet temperature on the efficiency and performance of the Brayton cycle are investigated. The performance of the S–CO 2 cycle and the heat transferred from the waste heat source to the fluid are examined from the thermodynamic point of view at these intermediate-temperature levels. The findings demonstrate the usefulness of considering the waste heat from the commercialized IT-SOFC in the S–CO 2 Brayton cycle. Furthermore, it is observed that the efficiency of the Brayton cycle improves at the critical pressure and temperature points. The system's performance parameters are determined with a turbine inlet temperature of 823 K (550 °C). Through thermodynamic analysis, it is determined that the S–CO 2 cycle generates 125.6 kW of power with a thermal efficiency of 16.34%. It is shown that an IT-SOFC with an electrical power output of 163 kW can supply the necessary heat to this system. • S–CO 2 basic Brayton cycle is used as a bottoming cycle of the SOFC. • IT-SOFC/S–CO 2 Brayton cycle hybrid system is analyzed thermodynamically. • Effects of different operation parameters on efficiency are investigated. • S–CO 2 Brayton cycle thermal efficiency is 16.34% at 550 °C turbine inlet temperature. • The highest cycle efficiency is obtained at the critical point of CO 2. [ABSTRACT FROM AUTHOR]

Small nuclear power plants are a promising direction of research for the development of carbon-free energy in isolated power systems and in remote regions with undeveloped infrastructure. Improving the efficiency of power units integrated with small modular reactors will improve the prospects for the commercialization of such projects. Power cycles based on supercritical carbon dioxide are an effective solution for nuclear power plants that use reactor facilities with an initial coolant temperature above 550 °C. However, the presence of low temperature rejected heat sources in closed Bryton cycles indicates a potential for energy saving. This paper presents a comprehensive thermodynamic analysis of the integration of an additional low-temperature organic Rankine cycle for heat recovery to supercritical carbon dioxide cycles. A scheme for sequential heat recovery from several sources in S-CO2 cycles is proposed. It was found that the use of R134a improved the power of the low-temperature circuit. It was revealed that in the S-CO2 Brayton cycle with a recuperator, the ORC add-on increased the net efficiency by an average of 2.98%, and in the recompression cycle by 1.7–2.2%. With sequential heat recovery in the recuperative cycle from the intercooling of the compressor and the main cooler, the increase in efficiency from the ORC superstructure will be 1.8%. [ABSTRACT FROM AUTHOR]

The shape of fins in flow channels of printed circuit heat exchangers (PCHE) significantly affects the heat exchanger performance. In the pre-cooler condition of the marine supercritical CO2 Brayton cycle power generation system, this study focuses on three typical discontinuous flow channel printed circuit heat exchangers. The investigation involves a numerical analysis of flow and heat transfer performance using CFD method. The comparative consequences illuminate that the rectangular fin channel exhibits the optimal heat transfer performance, and temperature drops are 1.18 times and 1.23 times, exceeding those of airfoil and rhombic fin channels, respectively. All three flow channels show different degrees of temperature drop reduction along the direction of fluid-flow. However, the rectangular fin channel demonstrates the worst flow performance, as pressure drops are 16.6 times and 17.8 times, higher than those of airfoil and rhombic fin channels, respectively. By calculating the values of Nu/f and Q/Δp, the comprehensive performance of each flow channel is ranked from high to low airfoil fin channel, rhombic fin channel, and rectangular fin channel. This research provides guidance for optimizing the design and applying PCHE in engineering for marine supercritical CO2 Brayton cycle pre-coolers. [ABSTRACT FROM AUTHOR]

This work proposes a pumped thermal energy storage (PTES) integrated into the power block of a concentrated solar power plant. The power block operates under a Hybrid Rankine–Brayton (HRB) cycle using propane as the working fluid. During PTES charging, some thermal energy is obtained from a dedicated compressor (additional to that of the HRB cycle), which is stored. During discharge, both compressors (HRB and PTES) are off, restoring the consumed energy and resulting in about a 13% increase in nominal power output. The system is also able to store thermal energy that would otherwise be rejected through the condenser if the PTES were turned off, leading to efficiency improvements in some cases. Considering the 2022 Spanish electricity market prices, the proposed PTES integration with 4 h of storage is feasible. The levelized cost of storage is calculated and compared to those of other PTES systems, achieving around a 40% reduction compared with an equivalent PTES Rankine. These results encourage future studies where the proposed PTES could be integrated into other power cycles that include a recompression process. [ABSTRACT FROM AUTHOR]

The printed circuit heat exchanger (PCHE) has gained significant attention in concentrated solar and nuclear power plant applications due to its small size, high surface area to volume ratio, and ability to function effectively in high-pressure and high-temperature conditions. Ensuring the thermostructural performance of the PCHE remains at a high level is crucial for its safe and effective operation under critical operating environments. At present, PCHE materials primarily consist of alloys because of their outstanding thermal conductivity and great performance. Nevertheless, the durability of these heat exchangers may be restricted based on the specific environmental conditions they encounter, as metals are prone to corrosion. This research presents a numerical model in ANSYS Workbench 17.2 that couples fluid, thermal, and mechanical aspects in a three-dimensional analysis. The model is used to study the behaviour of an Airfoil Fin PCHE made of different composite materials. This study utilised a NACA0021 Airfoil Fin with a staggered pitch design. The numerical results indicated that the Carbon fiber reinforced polymer-GY-70 epoxy and E-Glass fiber reinforced polymer composites have lower equivalent thermal stress and strain compared to conventional alloys under the same operational conditions. So, these materials own an advantage for the supercritical CO2 Brayton cycle application. [ABSTRACT FROM AUTHOR]

The printed circuit heat exchanger (PCHE) has gained significant attention in concentrated solar and nuclear power plant applications due to its small size, high surface area to volume ratio, and ability to function effectively in high-pressure and high-temperature conditions. Ensuring the thermostructural performance of the PCHE remains at a high level is crucial for its safe and effective operation under critical operating environments. At present, PCHE materials primarily consist of alloys because of their outstanding thermal conductivity and great performance. Nevertheless, the durability of these heat exchangers may be restricted based on the specific environmental conditions they encounter, as metals are prone to corrosion. This research presents a numerical model in ANSYS Workbench 17.2 that couples fluid, thermal, and mechanical aspects in a three-dimensional analysis. The model is used to study the behaviour of an Airfoil Fin PCHE made of different composite materials. This study utilised a NACA0021 Airfoil Fin with a staggered pitch design. The numerical results indicated that the Carbon fiber reinforced polymer-GY-70 epoxy and E-Glass fiber reinforced polymer composites have lower equivalent thermal stress and strain compared to conventional alloys under the same operational conditions. So, these materials own an advantage for the supercritical CO2 Brayton cycle application. [ABSTRACT FROM AUTHOR]

The supercritical CO2 power cycle driven by solar as a new generation of solar thermal power generation technology has drawn significant attention worldwide. In this paper, a cogeneration system derived from a supercritical CO2 recompression Brayton cycle is proposed, by considering the recovery of waste heat from the turbine outlet. The absorption refrigeration cycle is powered by the medium-temperature waste heat from the turbine outlet, while the low-temperature waste heat is employed for heating, achieving the cascaded utilization of the heat from the turbine outlet. As for the proposed combined cooling, heating, and power (CCHP) system, a dynamic model was built and verified in MATLAB R2021b/Simulink. Under design conditions, values for the energy utilization factor (EUF) and exergy efficiency of the cogeneration system were obtained. Moreover, the thermodynamic performances of the system were investigated in variable cooling/heating load and irradiation conditions. Compared with the reference system, it is indicated that the energy utilization factor (EUF) and exergy efficiency are 84.7% and 64.8%, which are improved by 11.5% and 10.3%. The proposed supercritical CO2 CCHP system offers an effective solution for the efficient utilization of solar energy. [ABSTRACT FROM AUTHOR]

Biomass-fueled engines are a promising way to reduce the consumption of and dependence on fossil fuels. To create a working prototype, a detailed study of the thermodynamic cycle was developed. The dead volume was revealed to be the most limiting parameter for the engine efficiency. The cycle efficiency is reduced from 51.8% to 30.5% for the given example. The engine needs to be properly designed to minimize energy losses. In addition, the optimal compression ratio of the cycle is very low (about 3.5), losing energy in the exhaust gases and contributing to an inefficient engine. However, using a turbocharger can improve the cycle efficiency, combining the basic cycle with a Brayton cycle. Moreover, a two-stroke engine design is recommended for biomass-fueled engines. It allows minimization of the dead volume, is less sensitive to dirt, and avoids gas exchange with the combustion chamber during scavenging. Finally, the combustion chamber of the initial prototype was redesigned, based on the aforementioned improvements and allowing the successful start-up of the engine. This work demonstrates that biomass is a viable alternative to fossil fuels in applications where internal combustion engines are required. [ABSTRACT FROM AUTHOR]

Small nuclear power plants can provide a stable, carbon-free energy supply to civil infrastructure and industrial enterprises in remote regions isolated from unified energy systems. More than 70 projects of small modular reactors are currently being developed by IAEA member countries; several low-power power units are already supplying thermal and electrical energy to consumers. One of the main limitations standing in the way of widespread dissemination of this technology is the high specific capital cost of a low-power nuclear power plant; therefore, new scientific and technical solutions are needed in this industry. Increasing the thermodynamic efficiency of power cycles of small modular reactors can become a driver for reducing the cost of supplied electrical energy. This paper presents the results of a comprehensive thermodynamic analysis of existing and promising power cycles for small modular reactors. In addition to traditional steam power cycles, cycles using non-traditional working fluids, including carbon dioxide, freons, and helium cycles, are considered. Optimal sets of thermodynamic parameters were determined to ensure maximum net efficiency of electricity production. For water-cooled reactor plants, a maximum efficiency of 33.5% at an initial temperature of 300 °C could be achieved using a steam turbine cycle. It was revealed that for reactor plants with liquid metal and liquid salt coolant in the range of initial temperatures above 550–700 °C, the maximum thermal efficiency was provided by the Brayton recompression cycle with a carbon dioxide coolant: the net electrical efficiency exceeded the level of steam turbine plants, with intermediate superheating of the steam, and could reach a value of 49.4% at 600 °C. This makes the use of these cycles promising for low-power nuclear power plants with a high initial temperature. In small gas-cooled reactor plants with a helium coolant, the use of a binary cycle consisting of a helium Brayton cycle and a steam-powered Rankine cycle provided an efficiency of 44.3% at an initial helium temperature of 700 °C and 52.9% at 1000 °C. This was higher than in the Brayton cycle with a recuperator, with a minimum temperature difference in the heat exchanger of 20 °C: the efficiency was 40.2% and 52%, respectively. Also, the transition to power cycles with non-traditional working fluids will lead to a change in the operating conditions of turbomachines and heat exchangers. [ABSTRACT FROM AUTHOR]

The reliquefaction process of boil‐off gas (BOG) in a propane plant using the reverse Brayton cooling cycle was examined by simulating the operational parameters and system performance of a propane reliquefaction plant in Aspen HYSYS software. The simulation considered various process and design parameters and their effects on the BOG production rate, energy consumption demand, and coefficient of performance (COP) of the cycle. The results demonstrate that the inclusion of methane in the propane product has a considerable impact on the generation of BOG, but this comes at a cost because power consumption increases significantly and the cycle's COP decreases. Furthermore, heat transmission from the surrounding air through the tank insulation and the temperature at which propane is returned from the jetty influence the BOG generation. [ABSTRACT FROM AUTHOR]

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Electricity is one of the most important needs in everyday life due to technological advances. So various efforts are needed to increase electricity production, one way is to build a power plant that can produce productive electricity so that this happens, one way to determine electricity productivity is the value of cycle efficiency. If the value of the cycle efficiency is higher in a generator, then the PLTG performance will be maximized. And if the cycle efficiency value gets smaller, it can be said that the PLTG's performance is not good. Therefore, to maintain PLTG performance, it is necessary to carry out an overhaul to maintain optimal PLTG performance. In this study using cycle efficiency to determine the increase in efficiency before and after overhaul at a load of 100 MW and the causes, after analyzing the efficiency of the brayton cycle increased from 41% to 42%, the cause was a decrease in turbine efficiency from 74 to 91% and compressor efficiency from 73 to 82% after overhaul the increase affected fuel consumption so that the requirement of kcal/kwh decreased to 3196.4 kcal/ Kwh. [ABSTRACT FROM AUTHOR]

This study develops a system simulation model based on the megawatt-class supercritical carbon dioxide Brayton cycle unit in Hengshui, China, to examine the effect of pipe section resistance on system performance. The results indicate that increased pressure loss in pipe sections significantly reduces power generation efficiency and power supply efficiency. Specifically, a 100 % increase in pressure loss results in 3.290 % and 4.377 % decreases in power generation efficiency and power supply efficiency, respectively. Moreover, higher pressure loss leads to increased CO2 mass flow rate at design power generation load. When the pressure loss is doubled, it requires a 17.593 % increase in CO2 mass flow rate to achieve the design power. Pressure loss in high-pressure section has minimal impact on system performance, while resistance in low-pressure section significantly affects it. For instance, a 100 % increase in pressure loss from the compressor outlet to the low temperature regenerator inlet causes a 0.37 % decrease in system power supply efficiency, and a similar increase from the high temperature regenerator outlet to the low temperature regenerator inlet leads to a 0.76 % decrease. These findings provide meaningful guidance for component design and piping layout optimization for similar systems.

One way to protect the environment is to recover waste heat from fossil fuel-powered energy conversion systems. The literature has put forth several systems aimed at harnessing the waste heat generated by solid oxide fuel cells (SOFCs). However, a majority of these systems were cogeneration or tri-generation setups, which exhibited limited exergy efficiency and considerable cost implications. The present research is an attempt to recover the waste heat from an SOFC combined with a gas turbine as the topping system through three subsystems, namely, a supercritical CO 2 Brayton cycle (SCBC), a new ammonia-water cycle (AWC), and a proton exchange membrane electrolysis unit (PEME). In addition, the waste heat of the SCBC and AWC in the heat rejection stages is recuperated by three thermoelectric generators. The output power of the layout is supplied by the topping system, and the power produced in the SCBC and AWC is utilized to produce hydrogen. The other two products of the system are cooling and heating, which are produced in the AWC. At the best operating point, the amounts of electricity, heating, cooling, and hydrogen generated by the configuration are 479.8 kW, 10.32 kW, 8.42 kW, and 0.297 kg h − 1 , respectively. The exergy efficiency and unit cost of poly-generation are 69.29% and 19.5 $ GJ − 1 , indicating the advantages of the suggested configuration over similar systems proposed in the literature. Moreover, the investment cost rate for the proposed configuration is remarkably low, standing at a mere 6.69 $ h − 1 . Thus, the current design allows for the efficient utilization of waste heat from an SOFC in a poly-generation system, achieving high exergy efficiency while keeping costs low. • Proposal of a new configuration for heat loss recovery of a solid oxide fuel cell-gas turbine system. • The exergy efficiency of the system is obtained as 69.29 %. • The unit cost of polygeneration is calculated as 19.5 $ GJ − 1 . • The system has a higher performance than previous similar systems. [ABSTRACT FROM AUTHOR]

The gas turbine is a crucial piece of equipment in the energy and power industry. The exhaust gas has a sufficiently high temperature to be recovered for energy cascade use. The supercritical carbon dioxide (S-CO2) Brayton cycle is an advanced power system that offers benefits in terms of efficiency, volume, and flexibility. It may be utilized for waste heat recovery (WHR) in gas turbines. This study involved the design of a 5 MW S-CO2 recompression cycle specifically for the purpose of operational control. The dynamic models for the printed circuit heat exchangers, compressors, and turbines were developed. The stability and dynamic behavior of the components were validated. The suggested control strategies entail utilizing the cooling water controller to maintain the compressor inlet temperature above the critical temperature of CO2 (304.13 K). Additionally, the circulating mass flow rate is regulated to modify the output power, while the exhaust gas flow rate is controlled to ensure that the turbine inlet temperature remains within safe limits. The simulations compare the performance of PI controllers tuned using the SIMC rule and ADRC controllers tuned using the bandwidth method. The findings demonstrated that both controllers are capable of adjusting operating conditions and effectively suppressing fluctuations in the exhaust gas. The ADRC controllers exhibit a superior control performance, resulting in a 55% reduction in settling time under the load-tracking scenario. [ABSTRACT FROM AUTHOR]

One of the most prominent issues in the transition to net zero emissions without carbon-based fuels today and in forthcoming years is the effective use of sustainable energy sources. In this current research, the pine sawdust biomass sourced innovative multigeneration plant is proposed and planned for the production of beneficial products. The newly arranged system comprises a Brayton cycle, a supercritical CO 2 Brayton cycle, a multi-stages flash desalination part, a PEM component, and a hot water preparation unit that aims the generate power, hydrogen, freshwater, and hot water. The study also deals with performing thermodynamic performance modeling, sustainability index assessment, and environmental impact evaluation to determine the developed system performance. Additionally, the energetic and exergetic performance approaches are operated to separate components and the entire configuration. After that, the comparison of the different energy conversion scenarios is examined on the basis of the energetic efficiency and CO 2 emission rate. The main findings specify that the developed plant can be capable of 2674 kW net power, 0.003679 kg/s of clean hydrogen, and 2.115 kg/s of distilled water. To conclude, it can be stated that the newly developed combined plant has satisfactory performance, with 44.50% energetic performance and 30.01% exergetic performance. • A novel biomass-based combined plant is proposed and examined. • The production of clean power, hydrogen, freshwater, and hot water is analyzed. • Combination and evaluation of the supercritical Brayton cycle is suggested. • A thermodynamic simulation is performed to determine system' performance. • The developed plant has 44.50% of energy efficiency. [ABSTRACT FROM AUTHOR]

The primary scope of the present work is the comprehensive investigation of a novel multigeneration system that exploits renewable energy sources, i.e. solar energy, geothermal energy, and biomass, and produces four useful outputs, i.e. electricity, heating, cooling, and green hydrogen. Solar irradiation is the primary energy source, which is exploited by parabolic trough collectors and powers a supercritical CO 2 regenerative Brayton cycle, while a biomass boiler serves as an auxiliary energy input. In addition, the whole installation includes a proton exchange membrane water electrolyzer, a water heater, as well as an absorption chiller, where a geothermal well is used for heat rejection. Apart from the thermal energy storage tank, which is coupled with the collectors, hydrogen production is used as a secondary energy storage method, as the excess produced renewable electricity feeds the electrolyzer. Consequently, the installation is examined parametrically, and optimized on steady-state conditions. Then, a dynamic simulation study is conducted for the climate data of Athens, Greece. According to the results, at the optimum operation point on steady-state conditions, the energy efficiency is determined at 37.89%, and the exergy efficiency at 20.86%. Moreover, the annual energy and exergy efficiencies are defined at 32.52%, and 18.51%, respectively. The economic evaluation analysis indicates that the payback period is about 11 years, while the internal rate of return, and the net present value are determined at 10.62% and 7,753,905 €, respectively. In addition, the system is estimated to save 3072.6 tons of CO 2 equivalent per annum. In conclusion, the proposed multigeneration system can address the various energy needs and recent environmental challenges, as a totally renewable, economically feasible, and environmentally friendly solution. • A multigeneration system that produces four useful outputs is examined. • The unit exploits three renewable sources, solar, biomass, and geothermal. • Both steady-state and dynamic analyses are carried out. • The annual energy and exergy efficiencies are defined at 32.52% and 18.51%. • The system payback period is found at 11 years, while it saves 3072.6 tn CO2-eq. [ABSTRACT FROM AUTHOR]

This paper proposes a novel solar-based polygeneration system for simultaneous power generation, desalination, hydrogen-production, and refrigeration. The system integrates parabolic trough solar collectors, multi-effect distillation, polymer electrolyte membrane electrolyzer, Kalina cycle, organic Rankine cycle, Brayton cycle, and ejector cooling. Solar energy and waste heat from the Brayton cycle provide energy input. Power generation is achieved via the Brayton, Kalina, and organic Rankine cycles. The multi-effect distillation unit produces freshwater while the electrolyzer generates hydrogen. The ejector system supplies cooling. A comprehensive steady-state energy and exergy analysis evaluates the thermodynamic performance. The system attains 32.269 MW net power output and ejector COP of 0.3193. The overall energy and exergy efficiencies are 38.45% and 35.64%, respectively. The combustion chamber exhibits maximum exergy destruction. Exergoeconomic analysis determines associated costs and investment feasibility. Integrating multiple technologies into a system with solar input enhances efficiency, sustainability, and environmental benefits. • Presents novel solar multi-generation system integrating power, hydrogen, water and cooling generation • Validated methodology analyzes thermodynamic performance providing insights on efficiencies • Exergy destruction analysis identifies optimization opportunities in integrated solar systems • Showcases potential of intricate integration of solar, desalination, hydrogen and power for sustainable energy • Modular and scalable system design enables flexibility for different applications and demands [ABSTRACT FROM AUTHOR]

The global push to reduce greenhouse gas emissions has led to the ban of high global warming potential (GWP) refrigerants in the refrigeration sector, prompting the adoption of low-GWP alternatives. However, as regulations are expected to tighten, technologies like the Reverse Brayton cycles (RBC) are emerging. RBCs can operate with safe fluids and can reach very low temperatures through compressions, regeneration, and expansion, requiring only electricity. This research presents results from an RBC equipped with a radial turbine using natural air (R-729), a hazard-free fluid with zero ozone depletion potential (ODP) and emission potential. The cycle utilizes automotive components, offering a cost-effective, high-tech solution. The study evaluates the cycle COP at a design point and performs an exergetic analysis at 173K. Using a thermal and fluid dynamic model of the cycle, the critical components of the cycle influencing the COP are identified, and potential improvements are explored. [ABSTRACT FROM AUTHOR]

The current work presents a novel conceptual framework for the fluid and gasdynamics that govern the design and performance of an ideal scramjet flowpath. These include a theoretical comparison between ram and scram modes, the physics of thrust loss during inlet unstart, and the design of an optimal scramjet flowpath. We present a unique explicit, closed-form relation for the wall divergence of an ideal scramjet combustor. The accompanying derivations and discussions, which leverage this formulation, seek to address uncertainties and misconceptions regarding the dominant fluid processes present in these engines. It is shown that scram and ram modes exhibit theoretical similitude for maximum thrust potential at conditions beyond the one-dimensional Rayleigh choking limit but can diverge below the global choking threshold. Additionally, it is shown that even for an ideal scramjet heat engine cycle, thermodynamic efficiencies at various flight conditions deviate from those of the classical Brayton cycle. These insights and accompanying theoretical analyses are meant to establish a foundation for the thermodynamics and gasdynamics relevant to the performance of dual-mode scramjet engines. The resulting work offers an intuitive technical perspective on supersonic combustion and the fundamentals of dual-mode scramjet operation that can be applied across a wide range of scramjet-related experimental and computational studies and design efforts in the future. [ABSTRACT FROM AUTHOR]

In this paper, a novel ammonia-hydrogen-electricity cogeneration system is developed. To mitigate the cost associated with hydrogen storage and transportation in later stages, the proposal is to utilize high-temperature ammonia production instead of conventional hydrogen production. A comparative analysis between ammonia and transportation for hydrogen is conducted to assess cost efficiencies. To improve the system efficiency, a supercritical CO 2 Brayton cycle is applied as the power generation cycle. This choice exhibits superior parameter compatibility with the system compared to the Rankine cycle. The study scrutinizes the impacts of different energy utilization sequences and varying process parameters of the power generation cycle on the system's performance to ascertain the most optimal configuration. The results indicate that the Brayton cycle is more suitable for integration with the nuclear-IS thermochemical hydrogen production system, significantly enhancing the power generation capacity of the ammonia-hydrogen-electricity cogeneration system. These improvements result in 18.8 % increase in power generation efficiency and a 9.3 % boost in overall energy efficiency of the system. Subsequent to this enhancement, the system attains an impressive energy efficiency of 47.0 % along with a system exergy efficiency of 63.4 %. This study introduces an innovative approach for optimizing and enhancing the energy efficiency of a cogeneration system by employing nuclear energy as a high-temperature heat source for hydrogen (ammonia) production. • A novel ammonia-hydrogen-electric cogeneration system is developed. • The system bolsters efficiency by 9.3 % through a synergistic Brayton cycle coupling. • Conducted an assessment and comparison of the transportation and storage expenses associated with hydrogen and ammonia. [ABSTRACT FROM AUTHOR]

The supercritical carbon dioxide (S-CO2) Brayton cycle efficiency increases as the compressor inlet condition approaches the critical point. However, the thermodynamic properties of CO2 vary dramatically near the critical point, and phase change is most likely to happen. Both cavitation and condensation bring about significant adverse effects on the performance of compressors. In this paper, the quantitative effects of nonequilibrium condensation and cavitation on the performance of an S-CO2 centrifugal compressor with different inlet-relative entropy values are investigated. The properties of CO2 were provided by the real-gas property table, and the nonequilibrium phase-change model was adopted. The numerical simulation method with the nonequilibrium phase-change model was validated in the Lettieri nozzle and Sandia compressor. Furthermore, simulations were carried out in a two-stage centrifugal compressor under conditions of various inlet-relative entropy values. The type of nonequilibrium phase change can be distinguished by inlet-relative entropy. Cavitation makes the choke mass flow rate decrease due to the drop in the speed of sound. Condensation mainly occurs on the leading edge of the main blade at a large mass flow rate, but cavitation occurs on the splitter. The condensation is more evenly distributed on the main blade, but the cavitation is mainly centered on the leading edge. [ABSTRACT FROM AUTHOR]

In response to the imperative to reduce carbon emissions in power generation, a novel near-zero CO 2 emission power generation system integrating solid oxide fuel cell (SOFC), micro gas turbine (MGT), supercritical carbon dioxide recompression Brayton cycle (SCO 2 BC) and CO 2 capture (CC) is proposed and investigated. The innovation lies in the utilization of oxy-combustion for CO 2 capture from the anode off-gas and the strategic harnessing of waste heat from the cathode off-gas through sequential MGT and SCO 2 BC processes. A comprehensive mathematical model is developed to assess the thermodynamic performance of the integrated system. The results indicate that the electrical efficiencies of the individual components, SOFC, SOFC-MGT, and SCO 2 BC, are 56.52%, 66.00%, and 40.76%, respectively, and the integrated system demonstrates an impressive overall efficiency of 70.15% under a current density of 5000 A/m2. The efficiency penalty incurred by CC on the integrated system is approximately 2%. A sensitivity analysis of key parameters highlights the potential for optimizing individual components to enhance power output or efficiency. Notably, the optimal overall efficiency is achieved when the SOFC operates at 0.25 MPa, the fuel utilization ratio is 85%, and the SCO 2 BC compressor pressure ratio is 2.6. This research not only establishes the viability of the proposed integrated system but also provides insights into optimizing its components for improved performance in power output and efficiency. [Display omitted] [ABSTRACT FROM AUTHOR]

This paper presents the use of sliding pressure inventory control (SPIC) of a 10 MW supercritical carbon dioxide Brayton cycle for concentrated solar power, incorporating printed circuit heat exchangers. Load regulation using SPIC for three representative ambient conditions 45 °C, 30 °C, and 15 °C are considered. While a wide operating range from 10 MW to less than 1 MW part load is obtained, a notable cycle efficiency decline at part load is also seen. Irreversibility analysis reveals that deterioration in recuperator and turbomachinery performance are primarily responsible for cycle performance degradation at part load. Nevertheless, useful inferences are obtained from the 10 MW SPIC irreversibility study. With a slightly increased value of heat exchanger length, a non-condensing 1 MW subcritical CO2 cycle operating between 35 bar/53 bar is found to be as efficient as a 1 MW supercritical CO2 cycle operating between 88 bar/210 bar. The major benefit of choosing the subcritical CO2 cycle for 1 MW scale applications is the significantly reduced turbomachinery speed (~26,000 rpm) in comparison with supercritical CO2 turbomachinery (~67,000 rpm) for the same power scale. These advantages are found to be true for air-based ideal gas cycles operating between 35 bar/53 bar too, with the latter requiring nominally smaller heat exchangers than the subcritical CO2 cycle. The final choice of working fluid, however, for these low-pressure cycles would depend on practical considerations, such as material compatibilities at high temperatures, corrosion considerations, and cost. [ABSTRACT FROM AUTHOR]