Supercritical CO2 Brayton Cycle Research Articles

Performance evaluation of supercritical CO2 Brayton cycle with two-stage compression and intercooling

Performance evaluation of supercritical CO2 Brayton cycle with two-stage compression and intercooling

Part-load performance analysis of a modular biomass boiler with a combined heat and power industrial Rankine cycle and supplementary sCO2 Brayton cycle

Abstract The addition of a supplementary high efficiency cycle integrated with an existing steam power cycle may increase energy efficiency and net generation. In this paper, part load performance and operation of a modular biomass boiler with an existing industrial Rankine steam heat and power cycle and supplementary supercritical CO2 (sCO2) Brayton cycle is analysed. The aim is to leverage the high efficiency of the sCO2 cycle by retrofitting sCO2 heaters in the existing biomass boiler, increasing net power output and thermal efficiency. With nominal load performance previously investigated, understanding part-load performance and operation is vital to determine cycle feasibility. A quasi-steady-state one dimensional thermofluid network model was used to simulate the integrated cycle performance for loads ranging from 100% to 60%. The model solves the mass, energy, momentum, and species balance equations, capturing detailed component characteristics. Two control methodologies are explored for the sCO2 Brayton cycle, namely inventory control and inventory control combined with throttling valve control. Inventory control is selected as the better performing control strategy for load following, maintaining high thermal efficiency across partial loads. At 60% load, the sCO2 compressor operates near the pseudo-critical point, leading to a sharp decrease in sCO2 cycle capacity, which requires careful management of inventory control. Two sCO2 heater configurations are investigated, namely a single convective-dominant heater, and a dual heater configuration with a radiative and a convective heater. The single heater configuration is preferred to minimise adverse impacts on the Rankine cycle superheaters.

Comparative performance analysis of recuperative helium and supercritical CO₂ Brayton cycles for high-temperature energy systems

This study presents a comprehensive comparative analysis of recuperative Brayton cycles utilizing helium (He) and supercritical carbon dioxide (sCO2) as working fluids for high-temperature power generation, focusing on applications in next-generation concentrated solar power (CSP) systems. Thermodynamic cycle simulations were conducted across a temperature range of 1000 K–2000 K, exploring the effects of low-side pressure (1 bar–100 bar) and expansion ratio (1–5) on key performance indicators. These indicators included thermal efficiency, net specific work output, mass flow rate, volumetric flow rate, and system irreversibilities. Results demonstrate that helium-based Brayton cycles exhibit superior thermal efficiency at high temperatures, reaching up to 65 %, compared to sCO2 cycles, which achieve efficiencies up to 55 %. This advantage stems from helium's higher specific heat capacity and lower pressure drops within the cycle. Conversely, sCO2 cycles demonstrate higher net specific work output due to the fluid's higher density, leading to more compact turbomachinery. The study further investigates the impact of irreversibilities, including pressure losses, leakage losses, and heat transfer losses, on cycle performance. A detailed analysis of multi-stage Brayton cycles incorporating intercoolers and reheaters reveals the potential for further efficiency enhancements in both helium and sCO2 systems. This research provides valuable insights for the design and optimization of high-temperature power generation systems, particularly for next-generation CSP plants. The findings highlight the trade-offs between working fluid properties and cycle configurations, guiding the selection of optimal solutions based on specific application requirements and operating conditions.

Study on control strategies of the MW-scale supercritical CO2 recompression Brayton cycle for lead-cooled fast reactor

The supercritical CO2 (sCO2) Brayton cycle for the lead-cooled fast reactor (LFR) is an ideal power generation system for the distributed energy supply in remote islands. To figure out the optimal operating modes of the MW-scale sCO2 LFR unit in different load demands, this work performs a dynamic simulation based on the developed control modules. A parametric analysis is conducted about the effects of rotational speed, split ratio, and main gas temperature on the dynamic characteristics. Control strategies are further studied based on the thermodynamic performance and safety under four variable temperature load regulation modes and three fixed temperature rapid load regulation modes. Results show that the tracking αopt mode has the highest average net efficiency (ηnetav) of 19.13 %. The tracking αsafe mode allows compressors to operate in the safest range by sacrificing a little ηnetav. Excellent load change rates are revealed by using the main circuit regulating valve control mode and the turbine bypass control mode, with −12.48 %Pe/min & 11.92 %Pe/min, and −8.25 %Pe/min & 9.70 %Pe/min, respectively. Though the load change rate of the RS control mode is −3.96 %Pe/min & 3.47 %Pe/min, its ηnetav is higher. Our work guides the efficient, flexible, and safe operation of the sCO2 LFR unit.

Analysis and Optimization of a s-CO2 Cycle Coupled to Solar, Biomass, and Geothermal Energy Technologies

This paper presents an analysis and optimization of a polygeneration power-production system that integrates a concentrating solar tower, a supercritical CO2 Brayton cycle, a double-flash geothermal Rankine cycle, and an internal combustion engine. The concentrating solar tower is analyzed under the weather conditions of the Mexicali Valley, Mexico, optimizing the incident radiation on the receiver and its size, the tower height, and the number of heliostats and their distribution. The integrated polygeneration system is studied by first and second law analyses, and its optimization is also developed. Results show that the optimal parameters for the solar field are a solar flux of 549.2 kW/m2, a height tower of 73.71 m, an external receiver of 1.86 m height with a 6.91 m diameter, and a total of 1116 heliostats of 6 m × 6 m. For the integrated polygeneration system, the optimal values of the variables considered are 1437 kPa and 351.2 kPa for the separation pressures of both flash chambers, 753 °C for the gasification temperature, 741.1 °C for the inlet temperature to the turbine, 2.5 and 1.503 for the turbine pressure ratios, 0.5964 for the air–biomass equivalence ratio, and 0.5881 for the CO2 mass flow splitting fraction. Finally, for the optimal system, the thermal efficiency is 38.8%, and the exergetic efficiency is 30.9%.

Modelling and optimization of combined supercritical carbon dioxide Brayton cycle and organic Rankine cycle for electricity and hydrogen production

Hydrogen as a clean fuel, is key energy carrier for sustainable development, and its production via water electrolysis is most desirable for its carbon free nature. Nuclear power provides good opportunity to satisfy the huge energy demand associated with the process, in addition to electrical power generation. Modelling an efficient and cost effective nuclear based power and Hydrogen cogeneration system and optimizing it to enhance its performance is the core academic problem addressed in the present study. It proposes a power plant cycle aided by a nuclear reactor, providing 300 MW thermal power input. Supercritical CO2 Brayton cycle is used as the main cycle, instead of traditional Helium Brayton cycle or steam Rankine cycle. To increase the cycle efficiency, by reducing the compression work and by reducing the cold source loss, main compression intercooling and waste heat recovery by an Organic Rankine Cycle (ORC) is introduced together with recompression Brayton cycle arrangement. The power coming from recovered waste heat goes to a Proton Exchange Membrane Electrolyzer (PEME), which facilitates the production of Hydrogen by splitting water via electrolysis. Additional attention is given to ORC fluid selection by employing and comparing the performance of widely acknowledged R245fa together with its more eco friendly replacements, R1233Zd(E) and R1234Ze(Z). The evaluation of the system performance is conducted through the lenses of Energy, Exergy, and Economics. Essential parameters are scrutinized to gauge their impact on two pivotal objectives. Overall Exergy Efficiency(ηex) takes care of the thermodynamic performance and the economic aspect is scrutinized by Levelized Cost of Energy (LCOEn). Notably, by employing R245fa as the ORC working fluid, the system attains peak Energy efficiency of 42.13% and Exergy efficiency of 58.32%, and a minimum LCOEn of 0.063 USD/kWh. Of all the components associated with the system nuclear reactor tops the chart for maximum exergy destroyed(40.8% of total) as well as maximum investment cost(65.7% of total). Pump contributes least to exergy destruction(0.03% of the total) and heat exchangers hold least share(1.1% of total) for investment cost. Furthermore, a multiobjective optimization exercise is executed to fine-tune the system’s operational parameters. This optimization results in a 3.12% increase in Overall Exergy Efficiency and a 9.79% decrease in LCOEn compared to the base operating condition with R245fa used as the ORC fluid. The ηex & LCOEn in best possible operating condition are 58.25% & 0.0645 USD/kWh using R245fa as ORC fluid, 58.23% & 0.0645 USD/kWh using R1233Zd(E) as ORC fluid and 58.22% & 0.0644 USD/kWh using R1234Ze(Z) as ORC fluid. If same amount of electrical Power is supplied to PEME for both with and without ORC configuration, having an ORC is advantageous both in terms of superior Exergy Efficiency and lower LCOEn. The proposed configuration is also economically more lucrative with higher Net Present Value(NPV) and Benefit to Cost Ratio(BCR). For example, when PEME power input for both the cases is 10 MW, proposed system has NPV = 201.79 Million USD & BCR = 1.70 compared to NPV = 164.03 Million USD & BCR = 1.58 for without ORC configuration. Even if in without ORC configuration, no electrical power is supplied to the electrolyzer, adding an ORC to produce Hydrogen will still achieve maximum 1.57% Exergy Efficiency increment, compared to only electrical power production by sCO2 Brayton cycle. It is seen that in base condition, the NPV is still superior for the proposed configuration (203.03 to 189.32 Million USD), and the BCR dips only slightly from 1.72 to 1.71.

Thermodynamic analysis of supercritical CO2 power generation system for waste heat recovery with impurities in CO2

Waste heat recovery from gas turbines is an effective method for meeting the demand for a more efficient and cleaner energy system with decreased CO2 emissions and lower environmental pollution. The supercritical CO2 Brayton cycle is a promising power conversion system for waste heat recovery. The advantage of the supercritical CO2 Brayton cycle can be attained based on its physical characteristics. However, when another fluid is mixed as an impurity in a system using pure CO2, physical characteristics of working fluid was changed and operation at the design point can be challenging. Therefore, it is important to verify the purity of CO2 and understand the effect of impurities in CO2 in advance. This study examined the effects of impurities in the working fluid of a supercritical CO2 power generation system for actual demonstration facilities. The effect of impurity, a CO2-based mixture, in a supercritical CO2 power generation system on waste heat recovery from an LM500 gas turbine was investigated. A purity test of industrial grade CO2, which was noted as 99.9 % pure by the supplier, was conducted to verify the composition of the working fluid. The results of the purity test showed that the supplied CO2 consisted of 99.076 % CO2 along with nitrogen, argon, oxygen, water, and methane. Based on the results of the purity test, sensitivity analyses of the CO2-based binary mixtures and industrial mixtures were performed. A design point analysis was conducted for the CO2-based industrial mixture in comparison with pure CO2, which has cycle efficiency of 16.15 %, gross power of 510.03 kW, mass flow rate of 12.55 kg/s, and waste heat recovery of 2119.06 kW. In the case of fixed waste heat with mass flow rate of 14.417 kg/s, the cycle efficiency decreased by 0.39 % and gross power increased by 66.14 kW. In the case of fixed mass flow rate with 1844.598 kW waste heat, the cycle efficiency decreased by 0.32 % and gross power decreased by 9.84 kW. In addition, the influence of the performance of the major components on the system performance was investigated.

Design optimization and off-design performance analysis of one-dimensional supercritical CO2 Brayton cycle

Supercritical carbon dioxide (SCO2) recompression Brayton cycle (RBC) is an encouraging technology for thermal power conversion and heat harvest for a wide range of heat sources due to its high-efficiency, low auxiliary power consumption, and compact size. However, most studies on its design and off-design performance analysis have been limited to the simple zero-dimensional component models without considering aerothermodynamics and ambient conditions. In this study, we developed a set of fully one-dimensional components models for SCO2 compressors, turbines, and heat exchangers, and, then, applied them to the multi-objective design optimization of a SCO2 cycle targeting a 50 MW net power output. The cycle off-design performance analysis methods and the control strategies were developed to countermeasure the performance degradation against the varying cooling water temperatures and part loads. The multi-objective cycle design optimization demonstrates that the cycle thermal efficiency and total product unit cost can be 0.476 and 11.652$/GJ, respectively, for the 50 MW SCO2 RBC cycle. The choke margin of the main compressor is 0.136 less than that of the re-compressor, and condensation can lead to a sharp decline in efficiency under high-flow conditions, causing the earlier onset of choking. The off-design performance analysis shows that the turbine inlet pressure control improves cycle efficiency below the design point of 317 K but does otherwise above the point. In contrast, inventory control strategies can maintain stable cycle efficiency and achieve adjustable net power output between 10 % and 110 %. The findings have the potential to advance further the commercial application of SCO2 cycles in high-temperature thermal energy systems.

A micro-channel cooling system with two-phase looped thermosyphon for a supercritical CO2 Brayton cycle

The supercritical Carbon Dioxide (sCO2) closed Brayton cycle is a promising power generation technology, while the efficient cooling of CO2 and precise control of Compressor Inlet Temperature (CIT) is crucial for the high cycle efficiency and stable compressor operation due to the acute variation of thermophysical properties in the near-critical region. In conventional indirect cooling scheme, an intermediate single-phase water circuit is used to transfer heat from CO2 to water at the precooler, and then from water to the environment at the cooling tower, having the disadvantage of large pumping work consumption and high thermal resistance. In this work, a self-driven two-phase looped thermosyphon that significantly enhances the heat transfer by internal evaporation and condensation, is proposed to replace the water circuit. An experimental ultra-compact cooling system, consisting of a looped thermosyphon combined with micro-channel evaporator and condenser, filled with R134a coolant, is designed, fabricated, and tested. Visualized observation of the two-phase flow pattern and simultaneous measurement of the temperature, pressure and mass flow rates are conducted. A nodal analysis method is adopted, and a MATLAB code is developed for analyzing the internal fluid flow and the coupled sCO2-R134a-Air heat transfer, which is validated by experiment data. The results show that, the CO2 temperature could be accurately maintained at a specified near-critical point with a fluctuation of less than 1 K, and the average heat-releasing temperature can be reduced, while considerable pumping work, usually accounting for 2–5 % of the rated power output can be saved, thus contributing to increased cycle efficiency and system compactness.

Accuracy assessment of the turbomachinery performance maps correction models used in dynamic characteristics of supercritical CO2 Brayton power cycle

The supercritical CO2 Brayton cycle (SCO2BC) has emerged as a promising next-generation power generation technology due to its potential for high thermal efficiency and compact components design. Dynamic modeling of SCO2BC is crucial for understanding and analyzing its performance under design and off-design conditions. Turbomachines are critical components in SCO2BC dynamic models. While turbomachinery components are often modeled using their design-point turbomachinery performance maps (TPM), these maps become less accurate during off-design operations. Despite the existence of various TPM correction methods that ensure model validity, the implementation of the accurate ones within dynamic SCO2BC models remains scarce in the literature. This is crucial as it potentially compromises the accuracy of the obtained results. Therefore, there is a need to investigate the errors in the existing literature TPM correction models (in dynamic SCO2BC simulation) by comparing them against dynamic SCO2BC models employing a highly accurate correction method. Thus, in the current work, the common TPM correction methods from the literature are implemented in SCO2BC dynamic models and compared against a baseline mode, which uses the highly-accurate Pham method (at both the component and cycle levels). To the authors’ knowledge, this is the first work to address this research gap for the SCO2BC dynamic simulations and on both component and cycle levels. Additionally, another novelty is the usage of Simcenter Amesim software to dynamically model the SCO2BC aided with Pham model. Multible dynamic models for both the turbomachines of SCO2BC and the whole cycle are constructed and equipped with the different TPM correction methods found in literature to compare their dynamic behaviour that of Pham model. The Ideal Gas Compressibility factor (IGZ) method demonstrates a better performance than the other tested methods, as it exhibits the lowest discrepancy compared to the Pham model. Many of the other tested methods show significant errors. Furthermore, a popular hybrid correction combining IGZ and Pham (IGZ-Ph) is also investigated. Surprisingly, while seemingly beneficial, this hybrid approach negatively impacts accuracy, even resulting in predictions as if no correction was applied.

Novel solar-based cogeneration system: Parabolic trough integrating supercritical Brayton and organic Rankine cycles with membrane distillation

This research addresses advancements towards third-generation concentrated solar power (CSP) systems, highlighting the critical need for improved system efficiency through advanced power cycles and optimized waste heat utilisation. By integrating a direct parabolic trough solar collector (PTSC) with a supercritical CO₂ (sCO₂) Brayton cycle and direct contact membrane distillation (DCMD), coupled with a bottoming organic Rankine cycle (ORC), this study proposed a novel solution for the co-generation of power and clean water. Innovative design and optimisation methodologies for the integrated system were introduced, and a comprehensive mathematical model was developed and validated, facilitating a comparative analysis of various ORC fluids' techno-economic performance. The investigation revealed that under baseline conditions, neopentane and isobutane demonstrated slightly better cycle's net-work, whereas toluene showed significantly higher water production due to the higher mass flow rate of seawater needed, resulting from the lower condenser inlet temperature. Furthermore, parametric analysis revealed that varying ambient temperatures resulted in different optimal fluids, with cyclohexane, n-octane, n-nonane, and n-heptane achieving the highest thermal efficiency of around 36.52% at 10°C. Additionally, this study highlighted substantial exergy destruction in the DCMD desalination process, accounting for 63.12% of the exergy destruction in the bottoming cycle, predominantly at the membrane where approximately 67% occurred. Moreover, the second compression and expansion stages, especially at higher Direct Normal Irradiance (DNI) levels, contributed the most to exergetic destruction in the topping cycle. Significantly, the double cycle showed exergetic efficiency improvements between 0.12% and 0.35% across different DNI levels while in contrast, single cycles demonstrated marginally superior water production capacity. Economic analyses using bare module costing to assess the levelized cost of electricity and water, along with net present value calculations, revealed that varying ambient temperatures resulted in different optimised fluids. Notably, n-octane achieved the highest net present value, approximately 4.53% above baseline conditions, at an ambient temperature of 10°C. Finally, recommendations for organic fluids for each ambient temperature based on techno-economic optimisation were detailed.

Dynamic heat transfer characteristics of printed circuit precooler in supercritical CO2 Brayton cycle

The dynamic characteristics of heat exchangers are critical in supercritical CO2 Brayton cycle, especially in the precooler where significant thermophysical property variations occur. However, few studies have comprehensively analyzed the dynamic heat transfer characteristics in precooler, particularly with respect to the detailed flow and thermal field evolution. A three-dimensional numerical model was developed to study the dynamic performance of a printed circuit precooler, with an emphasis on the impact of thermophysical properties. The study examines responses to abrupt changes in CO2 and water inlet temperature, as well as mass flux variations. Results show that the precooler exhibits rapid response characteristics with mild fluctuations in heat transfer parameters and flow structure. Notably, the large specific heat near the critical point results in minimal variation in CO2 outlet temperature despite abrupt increases in CO2 inlet temperature, thereby enhancing system stability. Conversely, a decrease in CO2 mass flux causes a transition from forced convection to mixed flow, with strengthened buoyancy effects and decreased entropy production. These variations lead to significant changes in CO2 outlet temperature, posing potential challenges to system stability under CO2 mass flux step change conditions. The heat transfer shows a relatively lower response rate to parameter changes of water compared to CO2. Although variations in water parameters have a negligible effect on CO2 heat transfer, they influence the overall heat transfer coefficient. The dynamic heat transfer characteristics of the precooler presented in this paper address research gaps left by 1D numerical and experimental studies, which have provided limited information on flow and thermal fields during dynamic processes. These insights are essential for understanding the dynamic behavior of the entire system.

Intelligent construction and optimization based on the heatsep method of a supercritical CO2 brayton cycle driven by a solar power tower system

The current progress in tower-based solar thermal concentrators and receivers enables achieving temperatures within the required range of 500–700 °C for the S–CO2 Brayton cycle. Within this temperature range, the efficiency of the S–CO2 Brayton cycle exceeds that of conventional steam power cycles. This study applies the S–CO2 Brayton cycle to concentrated power generation systems, emphasizing structural and parameter optimization. By utilizing the operational parameters of tower-based solar thermal power generation as boundary conditions and maximizing specific power as the optimization objective, various configurations derived from a maximum of two fundamental cycles are systematically enumerated. Subsequently, an intelligent algorithm optimizes the power cycle flow and parameters for each structure, further optimizing the heat exchanger network. The findings reveal that the optimized configuration shares a common heating and cooling process. This optimization yields a specific power increase of 14.62 kJ/kg compared to the reference case, indicating a 13.26 % enhancement. Additionally, the cycle efficiency improves to 47.45 %, marking a 28.52 % increase. The overall system efficiency for the solar power tower system reaches 32.03 %, with an exergy efficiency of 32.19 %.

Thermodynamic analysis of waste heat in a combined super-critical CO2 Brayton cycle for power and hydrogen production

The current investigation aims to propose a novel cycle to generate power and hydrogen using waste heat. For this purpose, super-critical carbon dioxide Brayton cycle, Organic Rankine Cycle (ORC) and proton exchange membrane (PEM) electrolyser systems are consideredin the cycle. Energy, exergy analyses along with parametric study are performed in the research. The best organic working fluid is selected for ORC based on the obtained results. Zero-dimensional modeling for components is performed and results are presented. Results show that the net power generation is 245.5 MW, thermal efficiency is 40.97 %, exergy efficiency is 56.73 %, and hydrogen and oxygen production is 9.04 kg/h and 74.2 kg/h, respectively. The optimum working pressure ratio and evaporator temperature are calculated. The effect of different working parameters on the system performance is obtained. It is shown that increasing the isentropic efficiency of the main and recompression compressors increases power generation, hydrogen production and system efficiency. Furthermore, increasing the turbine’s inlet temperature increases the power generation of the system.

Techno-economic analysis and fuel applicability study of a novel gasifier-SOFC distributed energy system with CO2 capture and freshwater production

This study employs the water-gas-shift membrane reactor and multi-effect distillation with thermal vapor compression technologies to facilitate low-energy carbon capture and large-scale freshwater production in gasifier-solid oxide fuel cell (SOFC) systems. The supercritical CO2 Brayton cycle and double-effect absorption refrigeration cycle are introduced to achieve waste heat cascade recovery. This work expands the fuel selection to 12 biomasses to explore the fuel adaptability and application scenarios of the system, and selects four representative cases to reveal their thermodynamic and economic attributes. The base scheme produces 21,635 ton/year freshwater and 1333 ton/year CO2, and achieves energy and exergy efficiencies of 70.68 % and 30.60 % with total cost rate of 23.21 $/h and levelized cost of products of 43.55 $/GJ. The gasifier and SOFC effort contributes to over 60 % of total irreversibility. Larch wood is preferred in resource-rich regions while wood residue, switch grass and wood chip are also prioritized; rice straw, rice husk, cotton stem and algal biomass are suitable for water-scarce areas. As key parameters change, Case-II consistently excels in power output, efficiencies and economic aspects, but lags in cooling capacity compared with other cases. This work provides a reference for low-carbon transition in the energy sector and large-scale freshwater production.

Potential of solid oxide fuel cells as marine engine assisted by combined cooling and power cogeneration systems

Switching to solid oxide fuel cell-gas turbine in marine applications can contribute to carbon reduction strategy. Integrating waste heat recovery technology can potentially meet the required cooling and power demands. This paper presents four combined cooling and power systems, each combining solid oxide fuel cell-gas turbine, supercritical CO2 cycle, and refrigeration cycle integration. First, the thermodynamic models of the four systems were constructed. Next, the performance of each integrated system was studied based on energy, exergy, economic, and environmental metrics. A multi-objective optimization approach was then applied to each system, balancing efficiency with cost. Results showed that the environmental penalty cost rate was 5.24 $/h at a fuel molar flow rate of 1.4 mol/s. The solid oxide fuel cell-gas turbine, regenerative supercritical CO2 Brayton cycle, and ejector expansion refrigeration cycle system offers the lowest cost rate of 44.40 $/h. Meanwhile, the solid oxide fuel cell-gas turbine, regenerative supercritical CO2 Brayton cycle, and absorption refrigeration cycle system achieves the highest energy efficiency (77.35 %) and cooling capacity (86.39 kW), indicating superior thermodynamic performance. This article provides a reference for the application of the solid oxide fuel cell-waste heat recovery system in marine transportation.

Influence of PCHE size and types on thermodynamic and economic performance of supercritical carbon dioxide Brayton cycle for small modular reactors and its optimization

The supercritical CO2 Brayton cycle is a potential technology in small modular reactors (SMRs), and the overall system efficiency can be significantly improved by optimizing the PCHE design parameters. This study develops a thermodynamic-economic analysis model for a supercritical CO2 simple Brayton cycle cooled SMR, with consideration of the detailed parameters of PCHEs. The impact of the length, channel number and channel type for the recuperator and the precooler on system thermal efficiency and levelized cost of electricity (LCOE) are analyzed. A dual-objective optimization study is conducted at the system level to identify the optimal design of size parameters and types for the heat exchangers. The results indicate that the influence of PCHE size parameters variations on system performance varies across different channel types. Additionally, the selection of the recommended recuperator type is influenced by the recuperator inlet Reynolds number. At the optimum design, the recommended channel type for recuperator and precooler are both S-shaped, resulting in a system efficiency of 39.12% and LCOE of 0.0456 $/kWe. The findings are valuable for enhancing energy utilization and reducing the power generation cost of SMRs.

Multi-objective optimization study of airfoil fin printed circuit heat exchanger with tip gap based on machine learning

The printed circuit heat exchanger (PCHE), a compact and highly efficient device, is capable of operating effectively under demanding conditions, which makes it ideal for supercritical CO2 Brayton cycles. In this study, we present a novel airfoil fin PCHE with tip gap, and conduct multi-objective optimization on the tip gap and arrangement of airfoil fins based on the analysis of the supercritical CO2 flow and heat transfer characteristics. We conduct a parameter design using Design of Experiment to examine the impact of the dimensionless design parameters, including the horizontal number (ζh), staggered number (ζs), vertical number (ζv), and gap number (ζg). To forecast the flow and heat transfer performance, we utilize a neural network model called Particle Swarm Optimization-Back Propagation (PSO-BP). We employ the non-dominated sorting genetic algorithm II to obtain the Pareto optimal front by utilizing ζh, ζs, ζv, and ζg as variables for optimization, and the volumetric heat transfer coefficient (hv) and Fanning friction factor (f) as objectives for optimization. The results find that the utilization of tip gap can enhance heat transfer while reducing flow resistance. The PSO-BPNN model exhibits higher prediction accuracy and excellent generalization ability compared with traditional BPNN model. The VIKOR and TOPSIS methods identify compromise schemes with excellent thermal-hydraulic performance. The mechanism of heat transfer enhancement can be elucidated using the principle of field synergy.

Off-design performance analysis of supercritical CO2 mixture Brayton cycle with floating critical points

The thermodynamic performance of supercritical CO2 (sCO2) Brayton cycle deteriorates significantly due to the mismatch between the cold source temperature and the working fluid’s critical point. Here, we present the first study on the off-design performance of a novel supercritical CO2 mixture Brayton cycle with floating critical points. A distillation based regulation subsystem is integrated into the power cycle to dynamically adjust the circulating composition of the binary CO2 mixture, thereby making its critical point float with the ambient temperature and achieving good temperature matching. The off-design behavior of the system operating with the representative mixture is investigated based on an in-house code. The influence of trigger conditions of critical point regulation on energy consumption of the regulation process is investigated. When the maximum temperature difference of the design points for consecutive days is set to 3 °C, the equivalent power consumption can be limited to 2.34 × 106 MJ per year, which affects the annual efficiency by less than 1 %. The results confirms that using the floating critical point method can improve the annual efficiency by 7 %-10.9 % and improve the specific output power by 6.1 %-9.4 % compared to the sCO2 cycle, depending on the power plant locations.

Characterization of PCM-PCHE and its effect on the suppression of temperature fluctuations in the SCO2 Brayton cycle

Supercritical CO2 Brayton cycles are now widely used in industrial power generation systems based on various energy sources. In order to solve the temperature problem that is prone to occur at the outlet of the turbine, a printed circuit heat exchanger (PCHE) with phase change materials (PCM) incorporated in it is intended to minimize system temperature fluctuations at the cost of extremely low heat exchange loss.. In this paper, a numerical simulation method is used to study this PCM-embedded PCHE to investigate the overall heat exchanger performance. It is found that when the phase shift between the inlet fluctuations of the hot and cold sides is 180°, this PCHE with embedded PCM has the best reduction of the outlet temperature fluctuation amplitude. Then it was put into an overall supercritical CO2 Brayton cycle, and it was found that PCM-PCHE could reduce the amplitude of efficiency fluctuations by roughly 40.8 %, the overall stability of the system was significantly improved, average power generation was increased by about 1.6 kW based on the reduced power consumption of the two-stage compressor.