Supercritical Carbon Dioxide Brayton Cycle Research Articles

Optimization and 4E analysis of integration of waste heat recovery and exhaust gas recirculation for a marine diesel engine to reduce NOx emissions and improve efficiency

This paper proposes an integration of waste heat recovery system and exhaust gas recirculation system to break the inherent trade-offs between oxynitride and carbon emissions of marine low-speed diesel engine. It is significant important to break these trade-offs, because Energy Efficiency Existing Ship Index may not be met, though Energy Efficiency Design Index and Tier III can be already achieved for old ships. The waste heat recovery system consists of supercritical carbon dioxide Brayton cycle and Kalina cycle, where the integration of supercritical carbon dioxide Brayton cycle and Kalina cycle is achieved in the parallel style. This paper uses the classical thermodynamics in terms of engineering approach to carry out the parameter analysis of combined system first. The optimization is conducted in terms of efficiency, energy density and techno-economy with the introduction of global optimal policy. The results showed that the highest efficiency of 52.32% at Tier III mode can be achieved, at which the net power, exergy efficiency, area per unit power output and levelized energy cost can be achieved by 1568.57kW, 45.75%, 0.589m2/kW and 0.114$/kWh at main engine load of 85%. Further, the net power output of waste heat recovery system can reach 1085.76 kW and 2043 kW at Tier II mode and Tier III mode, while the recovering rate of waste heat recovery system can reach over 5% at Tier III mode. Finally, the Energy Efficiency Existing Ship Index of a container ship equipping with such combined system can be reduced from 9.50 to 9.05.

Waste-to-energy poly-generation scheme for hydrogen/freshwater/power/oxygen/heating capacity production; optimized by regression machine learning algorithms

Utilization of machine learning techniques in the analysis and enhancement of poly-generation energy systems improves their efficiency and sustainability. Also, waste-to-energy systems propose a hopeful answer for both waste management and sustainable energy and water production. The production of hydrogen and freshwater through these systems not only provides valuable resources but also contributes to environmental sustainability. This research utilizes artificial intelligence's machine learning algorithms to examine and enhance a waste-to-energy system within a poly-generation energy system that generates hydrogen, freshwater, power, oxygen, and hot air. The integrated system consists of a waste combustion chamber, a proton exchange membrane electrolyzer, a supercritical carbon dioxide Brayton cycle, and a desalination system. Based on the findings, the machine learning algorithms exhibiting R-squared values exceeding 99% are considered strong fits. Additionally, all algorithms with high predicted R-squared values have the capability to accurately forecast new data using the provided training data. The emissions of 669.7 g/kWh and an efficiency of 69.62% are achieved when the pressure ratio is 10.73 and the temperature is 863.6 °C under optimal conditions. The accuracy and validity of the machine learning techniques are further confirmed by the strong agreement with thermodynamic modeling.

Multi-objective performance analysis of different SCO2 Brayton cycles on hypersonic vehicles

To provide the continuous and stable power supply of hypersonic vehicles, this study investigates four candidate cycles on the basis of three critical parameters. Specifically, the effects of cycle pressure ratio (PR), recompression split ratio (x), and cycle intermediate pressure ratio (RPR) on the regenerative, recompression, precompression, and partial cooling supercritical carbon dioxide (SCO2) Brayton cycles (BCs) are emphasized. The analysis is carried on by using an established thermodynamic simulation platform. Using PR as the working condition parameter, the influence laws of x and RPR on each cycle at common working conditions are given. The Non-dominated Solution Genetic Algorithm-II (NSGA-II) performs multi-objective optimization for different cycle types. The performance of these cycles is then compared under optimal conditions. The results show that the regenerative SCO2 BC could maintain relatively high output power while keep the structure simple, compared with other three cycles. The optimum power generation in the study range and the common operating conditions of regenerative SCO2 BC is 203.49 kW and 154.03 kW, respectively. Therefore, the regenerative SCO2 BC preferably satisfies the requirements of the hypersonic vehicles.

Off-design operation of supercritical CO2 Brayton cycle arranged with single and multiple turbomachinery shafts for lead-cooled fast reactor

The lead-cooled fast reactor (LFR) engenders novel requisites for the energy conversion system when applied to maritime ships and distributed energy supply systems. The supercritical carbon dioxide (sCO2) Brayton cycle, with the advantages of high efficiency, space-saving, simplicity, and flexibility, is a promising candidate for LFR. Here, we present the first study on the off-design operation of the sCO2 cycle for LFR, with the turbine and compressor arranged on a single shaft (coaxial-shaft) or two shafts (split-shaft). The off-design performances of the system are investigated using four rotational speed (RS) control-based hybrid control strategies. We showed that the split-shaft system controlled by separate turbine speed and compressor speed has a wider operating space of power load than the coaxial-shaft system. Among the four investigated control strategies, the RS-inventory hybrid control can achieve the best thermal efficiency during load variation by operating at the turbine speed and mass flow rate corresponding to the optimal turbine isentropic efficiency. The maximum operating space of power load (0%–100 %) can be achieved by the RS-turbine inlet pressure hybrid control and the RS-bypass hybrid control. Our study can provide guidance for the flexible and safe part-load operation for small-scale modular Gen-IV nuclear reactors.

Thermal-hydraulic performance study of swiftlet-type fins for supercritical carbon dioxide precooler

ABSTRACT The printed circuit heat exchanger has the advantages of compactness and high efficiency, and is one of the best candidates for precoolers in the supercritical carbon dioxide Brayton cycle. In this paper, for the precooler working condition, the swiftlet-type fin is proposed. The thermal-hydraulic performance of the fin is compared with that of the airfoil fin and the crossed airfoil fin under the same condition by numerical simulation. The flow and heat transfer mechanism of the fin is analyzed based on the field synergy theory and the flow line distribution of the longitudinal section. In the Reynolds number range of 5000 ~ 25000, the Nu of the swiftlet-type fin was improved by 44.5% ~53.0% and 12.1% ~16.6% compared to the airfoil fin and crossed airfoil fin, the f factor increased by 109.1% ~146.3% and 22% ~27%, comprehensive heat transfer performance PEC increased by 6.9% ~19.5% and 6.3% ~11.9%; By studying the effects of different length-to-width ratios (L c ), the widest position of the fin (n), and crossing distances at the tail of the swiftlet-type fin (L e ) on convection heat transfer, the optimal structural parameters are derived, when the Reynolds number is less than 15,000, the optimal structure is L c = 5 mm, n = 0.375, and L e = 1.5 mm; When the Reynolds number is more than 15,000, the optimal structure is L c = 6 mm, n = 0.25, L e = 1.5 mm. This study can provide guidance for the application of printed circuit plate heat exchangers in precooler condition.

Dynamic Modeling and Control of Supercritical Carbon Dioxide Power Cycle for Gas Turbine Waste Heat Recovery

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.

Effects of Near-Critical Condensation and Cavitation on the Performance of S-CO2 Compressor

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.

A review of research on turbines for supercritical carbon dioxide power systems

Supercritical carbon dioxide (S-CO2) Brayton cycle has been known as a potential power cycle technology because of its high efficiency, compact structure and suitability for different heat sources. As one of the key components in the cycle, the turbine has an important impact on the cycle efficiency. Compared with traditional steam and gas turbines, S-CO2 turbines have high working pressure and small size. The internal flow characteristics are significantly different. In this paper, the research progress of S-CO2 turbines in recent years is reviewed. The design and performance evaluation methods for S-CO2 turbines of different types and power levels are summarized, and research on loss correlations and optimization algorithms are introduced. The features of flow field in S-CO2 turbines are discussed. Current studies mainly evaluate the flow field and flow losses through Computational Fluid Dynamics (CFD), and some studies further analyze the influencing mechanism of turbine geometric parameters on flow characteristics. The applications of multi-physical field analysis on S-CO2 turbines are also reviewed. The construction and operation of S-CO2 test loops, and relevant turbine experimental study findings are introduced. Future research directions of S-CO2 turbines are proposed.

Structural optimization of S-CO2 Brayton cycle compressor impeller based on evolutionary algorithm

As the critical components for marine low-speed diesel engine flue gas waste heat recovery (WHR) supercritical carbon dioxide (S-CO2) Brayton cycle system, the structure of the compressor impeller is optimized by the evolutionary algorithm (EA) based on the co-simulation of the CAESES, ANSYS CFX and Opti Slang. The law of impeller pressure ratio, efficiency and power consumption in S-CO2 Brayton cycle (SCBC) as a function of rotational speed, inlet temperature, pressure and impeller structural parameters are revealed, and the method of improving SCBC efficiency for marine low-speed diesel engine flue gas waste heat recovery is studied. The optimized impeller structure is greatly enhanced in aerodynamic performance and safety, and the isentropic efficiency is increased by 2.54%, the pressure ratio is increased by 35.64%, and the temperature rise is increased by only 4.6%. A 100kW S-CO2 compression cycle test bench was set up to verify the simulation-optimized impeller results. The final results show that the optimized impeller structure, aerodynamic performance and safety are greatly improved. It provides theoretical support for selecting and optimising compressor impellers for marine low-speed diesel engine flue gas waste heat recovery S-CO2 Brayton cycle.

Research on the enhanced heat transfer performance of SCO2 caused by vortex generators with different geometric dimensions in novel airfoil channels

The performance of printed circuit heat exchangers (PCHEs) has a significant impact on the heat transfer efficiency and compactness of the supercritical carbon dioxide (SCO2) Brayton cycle system suitable for the fourth-generation nuclear energy system. Compared to PCHEs with other types of channels, the airfoil fin PCHEs have superior flow heat transfer performance. The installation of vortex generators (VGs) in the heat transfer channels can enhance heat transfer efficiently, but the application of them to PCHEs is very limited. In order to improve the performance of PCHE with airfoil fin channels, a novel channel structure combining airfoil fin channels with rectangular VGs is proposed, and the effect of geometric parameters of VGs on the thermal-hydraulic performance of the channels is also investigated. The results show that the VG improves the synergistic effect of velocity field and temperature gradient field, leading to the increase of turbulent kinetic energy and decrease of heat transfer entropy production in the channel, which finally promotes the enhancement of heat transfer. The comprehensive performance of the airfoil fin channel with VGs is 5.95%–19.47% higher than that of the conventional airfoil fin channel. The increase in the height and length of the VGs improves the heat transfer performance of the channel, and the increase in the width of the VGs weakens the heat transfer performance of the channel, and both increase the flow resistance of the channel. By comparing the comprehensive performance, it is found that the VGs have the best height of 0.2 mm, the best length of 0.8 mm and the best width of 0.04 mm. In addition, according to the noise performance statistics (NPS), the height of the VG contributes more to the Nu and Fanning friction coefficients of the airfoil fin channels.

Assessment of a sustainable power generation system utilizing supercritical carbon dioxide working fluid: Thermodynamic, economic, and environmental analysis

Solar energy stands out as one of the most abundant and cost-effective resources for energy conversion systems, playing a pivotal role in addressing the world's growing energy demands and environmental concerns. This study focuses on a power generation system that integrates multiple technologies for efficient energy conversion, including a parabolic solar trough collector unit, a supercritical carbon dioxide Brayton cycle, and two dual-pressure organic Rankine cycles. The goal is to assess this system from various angles, including energy, exergy, exergoeconomic, and exergoenvironmental aspects. The base mode study results reveal an overall energy efficiency of 16.66 %, exergy efficiency of 17.88 %, a total net power generation of 17.32 MW, a payback period of 4.38 years, and a total exergoenvironmental impact rate of 126.75 Pt/h. Additionally, the study conducts a parametric investigation to analyze how the system performs under different conditions and how changes in design parameters affect its main outputs. Furthermore, the study utilizes a multi-objective particle swarm optimization algorithm and a decision-maker method to identify the most desirable condition for the system's performance. Three optimization scenarios are considered, and various specific costs for electricity are evaluated to determine the payback period and net present value.

Dynamic performance of supercritical CO2 Brayton cycle and its relationship to the correction of turbomachinery performance maps: A comparative analysis

Due to its numerous advantages, including the capability to achieve high thermal efficiencies and compactness, the supercritical carbon dioxide Brayton cycle (SCO2BC) has recently been considered as an attractive next-generation heat-to-power conversion cycle. Dynamic modelling of the SCO2BC is essential to simply grasp and analyze its performance in either design or off-design conditions. Turbomachines are key components in the SCO2BC, which are typically modelled by adopting their design-point performance map. However, during off-design operations, the performance maps become inaccurate, and correction relations must be integrated into these models to enhance their validity. Despite the development of multiple performance map correction, reduction, and normalization methods, there is a scarce literature that implemented highly accurate correction relations in SCO2BC transient models, which impacts the validity of the obtained results. Therefore, there is a need to assess the accuracy of these results compared to the results of a SCO2BC model adopting an accurate correction method. However, some information needs to be provided first, which include how turbomachinery correction impacts the dynamic behavior of SCO2BC compared to using uncorrected turbomachinery models, and if the correction of one turbomachine (i.e., the compressor) is more significant than the other. This work aims to provide this data and more by developing dynamic SCO2BC models (CPP models), comprehensively evaluating their transient performance, and comparing them to SCO2BCs with uncorrected turbomachinery models (FPP models). This work possesses novelties of utilizing the most accurate turbomachinery correction model found for SCO2BC and building the model in Simcenter Amesim. It is found that FPP models may be viable when the dynamic responses of the components near the fluctuation source are desired. Otherwise, at least a compressor model correction is required to obtain reliable results. Moreover, all turbomachinery models should be corrected for accurate mass flow rate and power responses.

Study on coupled heat transfer model and enhanced heat transfer law of liquid metals and supercritical fluids

ABSTRACT The supercritical carbon dioxide Brayton cycle system is being considered for application in the power conversion system of advanced liquid metal fast reactors. One important research topic is the coupled heat transfer characteristics and enhanced heat transfer laws between liquid metals and supercritical fluids. However, the traditional Reynolds analogy hypothesis with a constant turbulent Prandtl number is difficult to satisfy the numerical conjugate heat transfer research of liquid metals and supercritical fluids. Therefore, based on the open-source computational fluid dynamics program OpenFOAM, a numerical method suitable for the coupled heat transfer calculation of liquid metals and supercritical fluids was developed, which can achieve precise conjugate heat transfer solutions by applying different turbulence models and heat flux models to liquid metals and supercritical fluids. Subsequently, based on this method, the coupled heat transfer behavior of liquid metals and supercritical fluids in the straight channel of a typically printed circuit heat exchanger was studied. The focus was investigating the conjugate heat transfer characteristics of liquid heavy metal lead-bismuth eutectic and liquid metal sodium with supercritical carbon dioxide. Some sensitive results, including the inlet temperature and Reynolds number of liquid metals and supercritical fluids, were qualitatively and quantitatively analyzed.

Thermoeconomic performance of supercritical carbon dioxide Brayton cycle systems for CNG engine waste heat recovery

The supercritical carbon dioxide (S–CO2) Brayton cycle is a potential technology for recovering waste heat from compressed natural gas (CNG) engines. To choose suitable cycle configurations is important considering the complex operating characteristics of CNG engines. The traditional evaluation models of the S–CO2 cycles configuration are relatively one-sided without the comprehensive considerations of evaluation metrics. On the basis of the analytic hierarchy process and information entropy theory, this paper proposes a multi-dimensional comprehensive evaluation method for S–CO2 cycles from three perspectives: thermodynamic, economic, and environmental performance. A thermoeconomic performance optimization is conducted using a non-dominated genetic algorithm Ⅱ. Unlike most of the existing researches that use a single stable operating condition, this paper considers the full operating conditions of engines. Results show that the recompression cycle has the best overall performance among the investigated cycles with an exergy efficiency and electricity production cost of 67.20 % and 0.45 $/kWh, respectively. The efficiency improvement of the CNG engine coupled with the WHR system can reach up to 6.31 %. This study can provide a new reference for the comprehensive multidimensional evaluation and performance characteristics and optimal performance acquisition under full engine operating conditions of the S–CO2 cycle.

Conceptual design of a novel megawatt portable nuclear power system by supercritical carbon dioxide brayton cycle coupled with heat pipe cooled reactor

In order to meet realistic requirements for flexible and reliable power supply in special scenarios such as remote areas and deep ocean exploration, a novel megawatt portable nuclear power system called SUPERHERO (SUPERcritical carbon dioxide cycle-HEat pipe ReactOr power system) is proposed in this paper. The system consists of a heat pipe-cooled reactor and a closed supercritical carbon dioxide (S–CO2) Brayton power cycle. Different cycle concepts were compared, and the simple recuperated cycle was adopted for compactness and simplicity of the system. The multi-objective optimization is performed to maximize cycle efficiency and minimize system volume, resulting in optimized parameters for a 1MWe system. By utilizing uranium nitride (UN) modular fuel elements and high heat transfer capacity potassium heat pipes, a compact reactor scheme with 3.13MWt is determined that can operate for 15 years without refueling. The neutronics and thermal analysis of the reactor are carried out, and the results show that the reactor has safety features such as a low peak factor, negative temperature feedback coefficient, sufficient reactivity compensation and control, and anti-failure of single heat pipe. The primary heat exchanger is also designed using the CFD method, and the heat exchange tubes combined with ribbed plates and self-supporting structures are used to enhance heat transfer and ensure structural stability. All these studies outline the general features of SUPERHERO, demonstrating that SUPERHERO has great development potential.

Using response surface methodology for multi-objective optimization of an efficient/clean combined heating/power system based on sugarcane bagasse gasification for environmental sustainability

Developing CHP (combined heat and power) systems-based biomass gasification is crucial for achieving environmental sustainability. These systems offer numerous profits, counting abridged greenhouse gas emissions, efficient energy utilization, and sustainable waste management. By investing in and promoting the adoption of biomass gasification-based CHP systems, it can be moved towards a more sustainable and greener energy future. In this regard, a clean CHP system is integrated by comprising a sugarcane bagasse gasifier, a proton conducting solid oxide fuel cell, a supercritical carbon dioxide Brayton cycle, and a heating recovery unit. The system performance is evaluated with respect to input variables from energy and environmental viewpoints. The integrated system performs more efficiently at lower equivalence ratios, higher temperatures, lower utilization factors, and higher pressure ratios. The efficiency initially improves with an increase in current density from 1400 A/m2 to 3000 A/m2, but starts to decline when the current density is pushed beyond this threshold to 5400 A/m2. According to the results, it has been concluded that the most favorable conditions for attaining the optimum goals are an equivalence ratio of 0.4, current density of 5400 A/m2, temperature of 1200 K, utilization factor of 0.7, and pressure ratio of 3.7. The best performance yields a power generation of 344.6 kW, heating generation of 3422.9 g/s, efficiency of 28.60%, and emissions of 1281 g/kWh.

Performance analysis and multi-objective optimization of a novel poly-generation system integrating SOFC/GT with SCO2/HDH/ERC

The SOFC-based poly-generation system is an effective and environmental-friendly technology. To further improve energy efficiency of poly-generation system, a novel poly-generation system is developed based on solid oxide fuel cell/gas turbine (SOFC/GT) as the prime mover and supercritical carbon dioxide (SCO2) Brayton cycle, humidification and dehumidification (HDH) desalination and ejector refrigeration cycle (ERC) as the waste heat recovery units to produce power, cooling and freshwater. In the proposed system, a novel configuration of combining the SCO2 cycle with HDH is applied to recover the waste heat of SOFC/GT hybrid system. A mathematical model is developed to explore the system performances from the energy, exergy and economic perspectives. The effects of key parameters such as fuel flowrate, fuel utilization factor, SOFC operating pressure and temperature, and desalination top temperature on system performances are investigated. Multi-objectives optimization is conducted to obtain the optimal design parameters of the poly-generation system. The results show that the system net power output, cooling capacity and freshwater production are 273.769 kW, 12.997 kW and 24.23 g/s with the total cost being 14.01 $/h under the given condition, respectively. The electrical and exergy efficiencies and total gained output ratio of the system are 68.35 %, 67.23 % and 85.25 %, respectively. The parametric analysis indicates that an appropriate increase in fuel flowrate, fuel utilization factor and SOFC operating pressure and temperature can improve the electrical and exergy efficiency. The optimization results demonstrate that the system exergy efficiency and total cost are 67.48 % and 13.94 $/h.

Analysis on the flow and heat transfer performance of SCO2 in airfoil channels with different structural parameters

As an important component of the system, the performance of the printed circuit heat exchanger (PCHE) has a significant impact on the efficiency and compactness of the supercritical carbon dioxide (SCO2) Brayton cycle system. Optimization of the structural parameters of airfoil fins can improve the performance of PCHE flow channels, but it has not received enough attention. Therefore, it is of great significance to investigate the effects of structural parameters such as the maximum thickness (Wf), the distance from the position where the maximum thickness is located to the leading-edge (Df), and the radius of the leading-edge (Rf) of the airfoil fins on the flow heat transfer performance of SCO2 in the channel of PCHE. A three-dimensional numerical model is developed and validated for performance analysis of the PCHE, meanwhile the thermal-hydraulic performance of channels with different structural parameters of the airfoil fins is compared. The results show that with the increase of the Wf of the airfoil fins, the heat transfer characteristics of the PCHE channel are gradually enhanced, and the flow characteristics are gradually weakened. When the maximum thickness of the airfoil fins is in the front, the heat transfer and flow characteristics of the PCHE channel are better. As the Rf of the airfoil fins increases, the heat transfer characteristics and flow characteristics of the PCHE channel fluctuate. The change of the turbulent kinetic energy, the boundary layer thickness, the synergistic effect of the velocity field and the temperature gradient field, and the local entropy production in the channel can well explain the mechanism of the flow and heat transfer of the SCO2 in the airfoil fin channel. In addition, among the channels with different structural parameters of the airfoil fins, the Fin-5 airfoil fin channel with Wf of 1.5 mm, the Fin-6 airfoil fin channel with Df of 0.6 mm and the Fin-13 airfoil fin channel with Rf of 1.46 mm are recommended. Their comprehensive performance is 2.0–6.3%, 0.9–5.6% and 0.13–1.81% higher than that of the Fin-3 airfoil fin channel, respectively.

Clean and sustainable power/fresh water/hot air production scheme based on solid oxide fuel cell feed by apricot stone biomass: A multi-attribute optimization

Developing novel and low-emission multi-generation systems is attracting considerable critical attention. In this regard, a novel tri-generation of power, fresh water and hot air has been developed in this study based on solid oxide fuel cell. Power has been generated by a solid oxide fuel cell, a gas turbine cycle and a super-critical carbon dioxide Brayton cycle. An air flow has been heated in a heat exchanger and fresh water has been produced through a desalination unit. Super-critical carbon dioxide Brayton cycle, heat exchanger of hot air and desalination unit have been all triggered by a co-combusted gas of apricot stone and synthesis gases of solid oxide fuel cell. Analysis of variance has been utilized to identify the significant influences on power production, fresh water, hot air, emission effect of system and system efficiency. Multi-objective optimization has showed that apricot stone of 200 kg/h, fuel utilization of 0.77, current density of 9697 A/m2 and pressure ratio of 3 in gas turbine system are the optimum conditions. The system has produced 2.10 MW of power, 837 g/h of fresh water and 57 m3/h of hot air with an emission effect of 2069 kg/MW.h and an efficiency of 43.5%.

Fast Calculation of Supercritical Carbon Dioxide Flow, Heat Transfer Performance, and Mass Flow Rate Matching Optimization of Printed Circuit Heat Exchangers Used as Recuperators

Printed circuit heat exchangers (PCHEs) are widely used as recuperators in the supercritical carbon dioxide (S-CO2) Brayton cycle design. The variation of heat sources will have a great impact on the heat transfer effect of the recuperator. It is of interest to study the fast calculation of flow and heat transfer performance of PCHEs under different operating conditions to obtain the optimal comprehensive performance and provide guidance for the operation control strategy analysis. Herein, a fast calculation method is established through a one-dimensional model of a PCHE based on Modelica. The effects of working medium mass flow rate and inlet temperature on the flow and heat transfer process are analyzed from the three aspects of heat transfer rate, flow pressure drop, and comprehensive performance, and the mass flow rate matching optimization is realized. The results show that increased mass flow rate increases heat transfer rate and flow pressure drop. The efficiency evaluation coefficient (EEC) has a maximum value at which the mass flow rate values of the cold and hot channels are best matched, and the comprehensive performance is optimal. When the mass flow rate of the heat channel is 4.8 g/s, the maximum EEC is 1.42, corresponding to the mass flow rate of the cold channel, 4.2 g/s. Compared with the design condition, the heat transfer rate increases by 62.1%, and the total pump power increases by 14.2%. When the cold channel inlet temperature increases, EEC decreases rapidly, whereas EEC increases when the hot channel inlet temperature increases. The conclusions can provide theoretical support for the design and operation of PCHEs.