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Single-stage axial flow turbines are typically used in underground mining machines and underwater vehicles due to their safety and small size. However, the high-pressure ratio and small mass flow rates force the flow inside the turbine to be supersonic. The blade design of such turbines with high-flow velocity leads to high losses and low turbine efficiencies at conventional design values. In this paper, the 1D design of the turbine is carried out using the meanline design method. The results of the design algorithm are compared with both experimental, CFD (Computational Fluid Dynamics), and a well-known commercial software AxSTREAM. After validating the design, Taguchi method is used to analyze 6 different parameters (Blade Shape, Nozzle Shape, Cord Length, Solidity Ratio, Nozzle Angle and Blade Thickness) affecting the turbine performance and the optimum blade profile is compared with the conventional blade design. The optimum design isentropic efficiency (68.267%) outperformed the conventional design turbine isentropic efficiency (61.759%) by about 11%. This paper provides a different insight into the conventional turbine design method. • Single-stage axial turbine design was discussed in detail. • The optimum admission ratio was determined within manufacturing limits. • 1D calculations and CFD results were compared with experimental data. • Nozzle and Rotor blades were optimized with the Taguchi Method. • The effects of Tip Cr on performance were determined. [ABSTRACT FROM AUTHOR]

Obtaining the aerodynamic performance of the turbine blade by Computational Fluid Dynamics (CFD) methods is accurate. However, it consumes time and computational resources. This paper proposes an evaluation method based on Convolutional Neural Network (CNN) and Artificial Neural Network (ANN) to obtain the aerodynamic performance of the turbine blade accurately and quickly. Compared with the existing data-driven modeling methods, this method innovatively introduces the Residual Network (ResNet), employs a transfer learning strategy for network design, and realizes the automatic extraction of blade profile features and non-parametric input. In processing boundary conditions, the ANN is utilized to fuse the blade profile features with the boundary conditions to realize the mapping between blade profile and aerodynamic performance under different conditions. In addition, to minimize the prediction deviation caused by the severely uneven distribution of the data set, we combined ensemble learning with transfer learning and proposed a two-step prediction strategy. The numerical simulations results show that the ResNet-ANN model established in this paper has a prediction relative error of 5 % on turbine blade aerodynamic parameters under various working conditions. The error is reduced by more than 90 % under −40°-10° incidence angle of incoming flow compared with the empirical model. • The method for predicting turbine blade profile loss is non-parametric. • The scheme is effective on both design and off-design conditions. • A two-step strategy is proposed for precise prediction on unevenly distributed data. • The TSP strategy is based on transfer learning and ensemble learning. • The approach is of high accuracy with considerable generalization. [ABSTRACT FROM AUTHOR]

This paper describes the heat transfer performance of plate-fin-tube heat exchangers (PFTHE) using computational fluid dynamics (CFD) simulation. Air-side Nusselt number correlations obtained from CFD simulations are compared to existing empirical correlations found in the literature. The geometries and boundary conditions are presented and compared with previous studies. The results indicate relative differences in mean Nusselt numbers between CFD-based methods and empirical correlations for different Reynolds numbers. Several factors contributing to these differences are discussed, including thermal resistance issues and assumptions about fluid-side heat transfer coefficients. The proposed CFD-based methods provide insight into the heat transfer mechanisms on individual tube rows, with acceptable differences compared to experimental correlations. Comparison of these methods shows consistent results with relatively small average relative errors, indicating the effectiveness of CFD simulations in predicting the heat transfer performance of PFTHE. Moreover, the average relative errors between individual methods range from 5.1% to 6.9%, with some individual errors ranging from 0.1% to even 17.1%. These results demonstrate the potential of CFD simulations to accurately predict heat transfer characteristics in complex heat exchanger systems. • Developed three CFD-based methods for predicting Nusselt numbers in plate fin and tube heat exchanger. • Validated CFD results with experimental data, achieving relative errors of 5.1% to 6.9%. • Identified significant variations in air-side heat transfer coefficients for different tube rows. • Presented a universal methodology applicable to various plate fin and tube heat exchangers' geometries. [ABSTRACT FROM AUTHOR]

In this paper, the concept of partial discharge shrouded impeller is proposed to enhance the performance of supercritical carbon dioxide (S-CO 2) centrifugal compressor under low flow rates, thereby increasing the overall efficiency of the S-CO 2 Brayton cycle. The influence mechanism of the partial discharge shrouded impeller on the flow behavior inside the impeller domain has been revealed by computational fluid dynamics (CFD) simulation. The results indicate a notable enhancement in the pressure ratio and isentropic efficiency of the S-CO 2 centrifugal compressor utilizing the best partial discharge shrouded impeller, showcasing improvements of 0.9% and 10.2% respectively under designed flow rate condition, while the stability parameter (S P) surpasses 0 at lower flow rates when compared to conventional impeller. With the partial discharge shrouded impeller, the flow separation on the blade pressure surface tends to occur nearer the impeller outlet, restricting the wake secondary flow shedding off to the diffuser, thus the flow loss being weakened. Meanwhile, with the optimized compressor by employing the best partial discharge shrouded impeller, the efficiency of S-CO 2 Brayton cycle has been increased by 5% relative to that with full discharge shrouded impeller. • A partial discharge shrouded impeller for S-CO 2 centrifugal compressor was proposed. • The compressor performance was improved by the partial discharge shrouded impeller. [ABSTRACT FROM AUTHOR]

The start-up process is vital to the performance of underwater turbine power system. The current analysis is mostly relied on analytical models established from simplified models and empirical formulas and it cannot accurately predict the start-up process. This paper proposes numerical methods to simulate the startup process of the underwater turbine power system. The results from the analytical and numerical models are compared at different launching depths. It is shown that the analytical model is suitable at the shallow launching depth (30 m), and the maximum difference is 4.3 % compared against the numerical method. However, the difference between analytical and numerical methods is as high as 45.9 % at the large launching depth (300 m). In addition, the closed-loop control strategy of the fuel pump needs to be triggered within 1.2 s after the combustion chamber is fully occupied, the start-up process can then be successful at the large launching depth. The experimental validation is finally performed to test the start-up process of the underwater turbine power system at the launching depths of 300 m. • The simulation method based CFD for underwater turbine power systems is proposed. • Dynamic characteristics of the start-up process of the underwater turbine power system at different depths are investigated. • The control strategy of the underwater turbine power system at large launching depths is designed. [ABSTRACT FROM AUTHOR]

Efficient low wind speed energy harvesting is pivotal in expanding the reach of sustainable wind power to regions with limited wind resources. This paper introduces an innovative approach to enhance wind energy harvesting efficiency in low wind speed environments through the development of a biomimetically inspired design featuring V-shaped attachments on a square bluff body. Drawing inspiration from the swallowtail, these attachments are engineered to manipulate airflow, creating an asymmetrical pressure field that significantly improves the vibration amplitude of the harvesting device. The proposed design is tested in wind tunnel experiments, demonstrating a 32 % reduction in cut-in wind speed and a significant increase in power output at the lowest tested wind speed of 1.7 m/s, compared to traditional designs. Computational fluid dynamics simulations further elucidate the mechanism behind the enhanced energy harvesting, highlighting the role of V-shaped attachments in generating stronger and more stable vortex shedding, crucial for efficient energy harvesting. The proposed attachments not only substantially reduce the cut-in wind speed of galloping but also significantly increase the device's power output, demonstrating the potential of this design for expanding the viability of wind energy in regions with limited wind resources. • Introducing two bionic swallowtail V-shaped attachments boosts output performance. • Compared to traditional designs, it significantly reduces the cut-in wind speed. • The V-shaped attachment's symmetry enhances energy harvesting efficiency. • The harvester exhibits efficient performance in low wind speed environments. [ABSTRACT FROM AUTHOR]

The characteristic curve of a pump-turbine is the essential data for calculating the hydraulic transient processes of a pumped storage power station. However, this curve is often unavailable during the preliminary design stage of pumped storage power stations. The shape of the characteristic curve directly influences the transient guarantee parameters. To date, adjusting the runner geometry to control the characteristic curve's shape for improving hydraulic transients remains a challenging issue. This paper proposes a model for predicting the characteristic curve that correlates its shape with the runner's geometric parameters. Considering the bidirectional flow in pump-turbines, two sets of governing equations are derived separately for the centripetal and centrifugal flow conditions. The governing equations for the unit discharge curve and the unit torque curve are constructed based on the energy equation and torque equation, respectively. Each term in these equations is subsequently organized into the expressions involving the runner's geometric parameters and unit parameters. To make the equations solvable, several sets of feature points are introduced. Based on the approach to obtain the feature points, an experiment/CFD (Computational Fluid Dynamics)-based prediction method and a statistics-based prediction method are proposed. Verifications using manufacturer-measured curves show that the experiment/CFD-based method is well-suited for model test acceleration and characteristic curve repair due to its higher prediction accuracy and availability, while the statistics-based method is more suitable for borrowing similar curve data during the power plant's preliminary design phase or rapidly predicting the corresponding characteristic curves during runner design. This work establishes a theoretical basis for improving hydraulic transient guarantee parameters by runner design optimization. • A novel prediction model for characteristic curves has been introduced. • Two methods are presented for the rapid prediction of characteristic curves. • A foundation for runner design to enhance hydraulic transient parameters. [ABSTRACT FROM AUTHOR]

The paper presents the analysis of the small hydropower plant working at variable speed. The hydro-set that consists of the guide vanes and propeller turbine integrated with the permanent magnet synchronous generator is simulated by using Computational Fluid Dynamics (CFD) in Ansys Fluent v18.0. The important part of the paper is the analysis of the mechanical power losses in the hydro-set gap. The analytical and numerical calculations show that these losses are significant and have to be considered in performance calculations. The k-ε and k-ω SST models, as well as the one-equation Spalart-Allmaras (SA) model, were tested and verified on the experimental hydropower plant of 75 kW power. The comparison showed that the best agreement with experimental results provides the Spalart-Allmaras model. • Integrated water turbine introduces significant mechanical losses. • Steady state turbulence model that initiates transients improves calculations. • Calculation results using k-ε, k-ω SST and SA turbulence models differ significantly. • Best matches with experimental results provides Spalart-Allmaras model. [ABSTRACT FROM AUTHOR]

Abstract Neighbourhood form imposes complex effects on the local microclimate. The overlook of neighbourhood microclimate will lead to miscalculation of building energy performance. In this paper, a neighbourhood-scale building simulation coupled between building energy simulation and CFD is proposed to assess the impact of external convective heat transfer coefficient (CHTC) to the building thermal performance. The co-simulation is run for different types of buildings inside the neighbourhood with different combinations of neighbourhood form parameters. The developed simulation scheme allows the iterations of neighbourhood design parameters and simulation model generation in CFD and EnergyPlus. Five empirical methods are used to predict CHTC, and the results of CHTC values, heating and cooling load intensity are compared in detail with the proposed CFD coupled method. The results suggest that the orientation and multiplier are crucial to the building load intensity in Chicago and the neighbourhood form can affect the thermal load of residential building up to about +27.1% and −18.6%, and +17.2% and −7.7% for office buildings. The proposed method and framework in this paper is capable of generating design guidelines for the optimal energy performance of the buildings in the neighbourhood. Highlights • Neighbourhood-scale building block energy simulation coupled with CFD. • Iterated various neighbourhood design parameters and building model generation. • Empirical methods in evaluating CHTCs are evaluated and compared with CFD method. • Neighbourhood form can affect certain type of building's energy use up to ± 20%. • Neighbourhood design guideline for optimal building thermal load is suggested. [ABSTRACT FROM AUTHOR]

Two-stage ejectors are widely used in multi-effect distillation and refrigeration systems owing to their vacuum and pressurization capabilities. However, most studies on two-stage ejectors are based on the dry-gas hypothesis, which neglects the universal physical phenomenon of condensation. A wet-steam model of two-stage ejectors is established and compared to the dry-gas model in this paper. Simulation results indicate that the proposed wet-steam model more accurately describes the performance and complex flow field characteristics of the two-stage ejector. Moreover, the nonequilibrium condensation mechanism of the fluid within the two-stage ejector under variable conditions is revealed. The results show that as the two-stage main nozzle pressure increases from 300 kPa to 550 kPa, the liquid mass fraction increases, and the droplet nucleation rate of the two stages decreases by 14.17 % and 13.14 %. When the first-stage actuating pressure is increased, the first-stage fluid restricts the expansion state of the second-stage main jet core and weakens the vapor condensation in the region of the shock chain. Furthermore, the experimental results demonstrate that compared with the dry-gas model, the prediction error of entrainment ratio and the secondary flow obtained by the proposed model are reduced by 26.67 % and 43.04 %, respectively. • A wet-steam model of two-stage ejectors is established. • The proposed wet-steam model improves the predictive accuracy compared to the dry-gas model. • The condensation mechanism in the two-stage ejector under variable conditions is revealed. • The validity and reliability of the established wet steam model are verified by experiments. [ABSTRACT FROM AUTHOR]

The submerged arc furnace is widely regarded as one of the most promising ore smelting technologies. However, the real-time monitoring of the multiple physical fields including electric, thermal, and mas, through computational fluid dynamics demands significant computational resources. This paper introduces the spatial-temporal convolutional neural network algorithm to address this challenge. Initially, the influences of various working conditions on these physical fields are analyzed. Subsequently, a prediction model is developed based on the coupling of these multiple physical fields model. The spatial-temporal convolutional neural network algorithm is then employed to elucidate the main parameter distributions, enabling the automatic real-time detection of temperature variation trends and providing a theoretical foundation for intelligent furnace operation. The findings indicate that the electric field is the predominant factor causing non-uniform heat distribution, with localized overheating primarily occurring at the electrode ends. The application of the proposed model facilitates dynamic prediction of the temperature distribution, establishing relationships between historical and future time steps as well as local and global temperature variations. The reliability of the temperature prediction model is confirmed, with the model achieving an accuracy of 99.76 %, surpassing the 98.18 % accuracy of the traditional multi-layer perceptron model. • Multi-physical field coupling model of submerged arc furnace is established. • Temperature prediction model based on residual spatial-temporal convolutional neural network is developed. • The main parameter distributions of the multiple-physical fields are revealed. • The proposed model is verified with compared to the multi-layer perceptron model. [ABSTRACT FROM AUTHOR]

The efflux velocity is the basis for the prediction of turbine wake. A novel energy coefficient is defined to propose a new theoretical equation to predict the efflux velocity of tidal current turbine in this paper. Several CFD cases with different tip speed ratio and solidity is conducted using the DES-SA model. In order to overcome the limitations of the axial momentum theory, the effects of tip speed ratio and solidity on the efflux velocity are studied and the energy coefficients with different tip speed ratio and solidity are determined using the proposed equation based on the CFD results. Several semi-empirical efflux velocity equations are finally proposed by fitting the equation of the energy coefficient with tip speed ratio. The application of these equations in the prediction of wake flow and the power calculation of tidal turbine are also introduced in this paper. [ABSTRACT FROM AUTHOR]

In this paper, the influence of temperature phase change on two-phase ejector is investigated by the computational fluid dynamics (CFD) technique. The working fluids used in this research are LNG as primary fluid and BOG as secondary fluid. The transient behavior in the two-phase ejector is simulated to find the optimal operation conditions for higher ejector performance. The axial velocity, pressure and temperature, entrainment ratio, heating coefficient, volume fractions of gas and liquid are obtained under different operation conditions. The predicted values by CFD simulation prove to be in good agreement with on-site test data. Phase change has a significant effect on the performance of LNG-BOG ejector. The results show that entrainment ratio increases with increasing LNG inlet velocity and decreasing mixture outlet pressure. Too high BOG inlet and mixture outlet pressure can result in abnormal ejection. For the specific two-phase ejector described in this paper, the optimal ejection performance is obtained under the conditions with LNG inlet velocity of 11–12 m/s, BOG inlet pressure of 0.101–0.507 MPa and mixture outlet pressure of 0.101–0.304 MPa. This study may provide a beneficial reference for good performance of LNG-BOG ejector and may be helpful for further applications in LNG transportation. [ABSTRACT FROM AUTHOR]

As the development of turbocompounding and two-stage turbocharging technology, there are increasingly more two-stage turbine systems applied on vehicles. The two-stage turbine recovers waste heat from the exhaust and thus affects the engine performance significantly. However, the interaction pattern and mechanism between the two turbines have not been fully understood. The paper focuses on the characteristic of the two-stage turbine under steady and pulsating flows. Firstly, an analytical model for two-stage turbine is developed to investigate the relationships between the turbines load split and equivalent area ratio under steady condition. The pattern of the load split between the high pressure turbine (HPT) and low pressure turbine (LPT) is disclosed by the model and verified by experimental data. Second, the impact of pulse frequency and amplitude on the two-stage turbine unsteady characteristic is studied by 3D computational fluid dynamics. As frequency increases, the peak values of the HPT expansion ratio and rotor torque increase drastically while those of LPT change little. As the pulse amplitude increases, the cycle-averaged expansion ratio of HPT decreases while that of LPT increases. The cycle-averaged rotor efficiencies of HPT and LPT reduce 3.7% and 8.1% respectively under 1.6 A amplitude condition, when compared with steady condition. In order to understand the phenomenon, the reasons are also discussed in detail in the paper. [ABSTRACT FROM AUTHOR]

This paper introduces a novel coupled model for real-time control of the point absorber wave energy converter (WEC) using parallelized deep reinforcement learning (DRL), where the WEC is situated within a numerical wave tank (NWT) built with the method of computational fluid dynamics (CFD). An in-house solver is developed to couple with the DRL and CFD to solve the interaction between WEC and the fluid environment. Validations on wave generation, wave-floater interaction, and power take-off (PTO) unit are carried out. Then, neglecting the detailed model for the PTO technologies, the DRL-based strategy dynamically adjusts the PTO force as a function of the wave features and floater motion. Based on the interaction data, the model-free DRL is outstanding in adaptability and robustness. Simulation results reveal that DRL control improves the wave energy absorption in irregular wave environments, resulting in improvement of 107.5 % compared to the resistive control, with better device protection performance than the model predictive control (MPC). An additional analysis of model-free characteristics of DRL demonstrates the optimization ability independent of floater modeling. This work is the first in-depth study of DRL control of WECs in CFD simulation, providing a more accurate simulation and an optimization process closer to the reality. • Real-time conversion performance of the point-absorber WEC under DRL control in irregular wave environments is studied. • A CFD-DRL coupled model is developed for the interaction between the DRL-control WEC and the numerical wave tank. • Accelerate the training with paralleled OpenFOAM solvers and emphasizing recent and prioritized experience replay buffer. • Further validate the generalization in the irregular-wave environment generated by JONSWAP spectrum. • Explore the model-free nature of DRL in the control strategy generation of WEC system. [ABSTRACT FROM AUTHOR]

As a kind of energy-saving and micro-hydropower utilization device, pump as turbine (PAT) is simple to construct with low operation and maintenance costs, which is widely used in the energy-consuming industrial processes and micro-hydro power generation. The variation law of blade angle from blade inlet to outlet has the characteristics of uncertainty and diversity, which determines the middle bending shape of the blade and has a direct impact on the fluid. Different blade bending shapes form different wrap angles on the premise of impeller outlet and inlet angles kept invariable. To investigate how the blade angle distribution affects the performance, four different impellers were created and analyzed based on computational fluid dynamics method. This paper investigates the effect of blade bending shapes on the performance characteristics, unsteady characteristics and energy loss of PAT. The numerical result shows due to the small blade wrap angle, the best efficiency of scheme 2 is the lowest among the four schemes, while the best efficiency of scheme 4 is the highest. The appropriate blade bending shape is beneficial to reduce the enstrophy dissipation and improve the efficiency and operating stability of PAT. These findings provide reference points for optimizing the blade profile in PAT. • Different angle distribution profiles from the blade inlet to the blade outlet will form different blade camber shapes. • Four PAT's impellers with different blade bending shapes are designed and investigated by a verified CFD method. • The appropriate blade bending shape can improve the operation stability and the unsteady flow characteristics of PAT. • It is beneficial to improve the PAT's performance that the blade camber shape is mainly concentrated in the blade middle. [ABSTRACT FROM AUTHOR]

The development of novel technical solutions for the efficient recovery of waste heat is crucial for making accessible the large amount of thermal energy released by industrial processes, thus supporting the EU energy strategy. To this end, the EU-H2020 project CO2OLHEAT aims at developing and demonstrating a novel sCO 2 power unit of 2 MW capacity, recovering energy from flue gases at 400 °C. The CO2OLHEAT system features a relatively unconventional multi-shaft configuration where the sCO 2 compressor is driven by a dedicated radial expander, while the electrical power is generated via a separated axial turbine. The present study focuses on the design and fluid-dynamic analysis of the CO2OLHEAT compressor. The thermodynamic optimization of the cycle led to an overall pressure ratio slightly above 2.5, delivered with a two-stage centrifugal compressor. As typically found in sCO 2 power systems, the thermodynamic state of the fluid at the machine intake (P = 85 bar; T = 32 °C) is close to the critical point and to the saturation curve; therefore, the first stage of the machine demands a dedicated aero-thermodynamic design, which can account for the effects of non-ideal thermodynamics and of the potential onset of two-phase flows. The paper discusses the conceptual aero-mechanical design of the compressor and then focuses on its performance assessment over the full operating range via Computational Fluid Dynamics. Two alternative CFD models are applied, the first one based on the barotropic fluid representation and the second one featuring a complete thermodynamic model, both of them assuming homogeneous equilibrium in presence of multi-phase flows. The experimental validation and the application of the two models are presented and discussed. They are shown to provide similar outcomes, and indicate that the compressor fulfills the system requirement and guarantees wide rangeability. A thorough comparison between the CFD results highlights the implications of the underlying physical differences between the models, thus allowing to properly evaluate their use for the aerodynamic design and analysis of sCO2 compressors. • A two-stage sCO 2 radial compressor for waste heat recovery system is presented. • Two alternative CFD formulations are presented and experimentally validated. • The compressor performance and operation are assessed with the two CFD models. • The barotropic model is recommended for design, the full HEM for flow analysis. • The roughness highly influences the compressor performance but not the rangeability. [ABSTRACT FROM AUTHOR]

The temperature field is a critical factor for ensuring the safe combustion and energy conservation in boilers. However, an effective method for reconstructing the temperature field near the water wall is still under exploration. In this paper, a method for online reconstruction of the temperature field distribution near the water wall in a 330 MW tangentially fired coal boiler is proposed, which progresses from a well-established model for the entire furnace. A two-branch fusion network for transfer learning (TBFN-TL) method is proposed, incorporating additional key parameters, heat flux, during the transfer process to enhance the effectiveness. A Bayesian hierarchical neural architecture search (BHNAS) method is proposed to optimize the configuration of the hidden layers in building neural networks. Compared with computational fluid dynamics (CFD) results, the mean absolute percentage error (MAPE) of the reconstruction results for the entire furnace model, traditional transfer learning methods, and the proposed TBFN-TL are 11.57%, 5.738%, and 2.052%, respectively, demonstrating a significant enhancement. The proposed BHNAS method extends the search optimization space, obtaining more excellent configurations for the hidden layer nodes. The proposed methods have significant implications for temperature field reconstruction, the field of transfer learning, and the optimization of hidden layer configurations. • Developed a model for real-time temperature field reconstruction near furnace walls. • Proposed TBFN-TL, enhancing transfer learning with key target domain features. • BHNAS method introduced for optimizing hierarchical neural network configurations. [ABSTRACT FROM AUTHOR]

In the paper, a second order thermodynamic analysis of a small scale alpha-type Stirling engine is presented. The developed mathematical model is based on the Finite Time Thermodynamics (FFT) approach and it is derived from the differential time dependent equations of energy and mass conservation. The engine model consists of three spaces: compression, expansion and regenerator. In contrast to available models, the model presented in this paper assumes polytropic processes in the compression and expansion spaces, which corresponds to the non-ideal heat transfer in these spaces. The results, obtained using the developed second order model, were compared with the results obtained using the Computational Fluid Dynamics (CFD) analysis of the same engine. A very good agreement between the second order model and the CFD model was achieved. Finally, the developed model was applied to analyse potential to recover cryogenic exergy of the Liquefied Natural Gas (LNG). The paper presents the results of the dimensional upscaling of the engine and the influence of the average working pressure. It was revealed that increasing the size of the engine or the average working pressure moves the engine to practically unachievable working conditions. [ABSTRACT FROM AUTHOR]

The existing Chinese solar greenhouse (CSG) had different spatial structure types, which spatial structure can make the greenhouse fully utilize solar energy and obtain the best thermal performance effect is worthy of further research. This paper took the CSG in the Shenyang area as the research object. A mathematical model was established to simulate the three-dimensional dynamic thermal environment of CSG at the crop level by combining experimental and computational fluid dynamics (CFD) numerical simulation. The model can well describe the heat transfer process in the greenhouse. Based on this model, the effects of variation of multiple structural parameters on the temperature distribution, solar energy interception, heat storage and release performance of CSG were quantitatively specified. The simulation results demonstrated that for the CSG with a span of 10 m in the Shenyang area, the optimal ridge height was 6.2 m, the optimal north wall height was 4.4 m and the optimal horizontal projection length of the north roof was 2.0 m. Furthermore, the spatial structure parameters of CSG with an 8 m–12 m span were obtained for the Shenyang area. This paper can provide theoretical guidance for the design and optimization of spatial structure parameters of CSG in the Shenyang area. • A CFD model was established to simulate the thermal environment of crop level in CSG. • The CFD model can accurately depict the dynamic heat and mass exchange process in CSG. • The effect of structural parameters on the thermal environment of CSG was expounded. • The structural parameters of CSG with 8 m–12 m span were obtained for the Shenyang area. [ABSTRACT FROM AUTHOR]

Any technique or method that can improve the efficiency in exploiting renewable wind or marine current energy has got a great significance today. It has been reported that adding a winglet at the tip of the rotor blades on a horizontal axis wind turbine can increase its power performance. The purpose of this paper is to adopt a numerical method to investigate the effects of different winglet configurations on turbine performance, especially focusing on the direction for the winglet tip to point towards (the suction side, pressure side or both sides of the main blade). The results show that the new design of an integrated fusion winglet proposed in this paper can generally improve the main blade's power producing ability, which is further enhanced with the increase of turbine's tip speed ratio with a maximum power augmentation of about 3.96%. No matter which direction the winglet tip faces, the installation angle of the winglet should match well with the real angle of incoming flow. As a whole, the turbine with winglet of two tips facing to both sides of the main blade can produce much more power than the one of winglet configuration whose tip faces only one side for different blade hub pitch angles and vast majority of tip speed ratios. The working principle behind the winglet in improving turbine performance may be that it can block the downwash fluid easily flowing around the tip section of the main blade from the pressure side to suction side, and hence diffuse and spread out the tip vortex. As a result, it finally decreases the energy loss. Besides, the relative projected rotor area in incoming flow direction will also be reduced due to the addition of the winglet, which is also helpful to turbine's power coefficient. [ABSTRACT FROM AUTHOR]

Vortex generators are widely used passive flow-control devices to improve the aerodynamic performance of large wind turbines. In this paper, the aerodynamic performance of the airfoil S809 without and with vortex generators was investigated using a computational fluid dynamic method of simulation. In this paper, the vortex generators in order to control the flow within the boundary layer of the S809 airfoil with the momentum transferring and the vortex trajectory was discussed. The results were obtained with three-dimensional incompressible Reynolds-averaged Navier-Stokes equations, and the turbulence was simulated with the shear stress transport k – ω turbulence model. It is shown that the vortex generators can effectively improve the aerodynamic performance of the airfoil S809 and decrease the thickness of the boundary layer. The stall phenomenon is delayed. Double vortex generator arrangements show better performance in the control of flow separation and further improve the aerodynamic performance of the airfoil S809. According to the results of the vortex generators, the vortex generators can effectively enhance the lift coefficient of the airfoil and control the flow separation. It can provide some instructional meaning to the application of vortex generators on the wind turbine blade, which benefits to the utilization of wind power. [ABSTRACT FROM AUTHOR]

Strengthening the thermal performance of building envelopes is an important direction towards achieving energy efficiency. This paper investigated the thermal performance and energy-saving effect of phase change material (PCM) cool roofs in office buildings during the summer season in Chongqing, leveraging a combination of measurement and simulation techniques. Compared to ordinary and PCM roofs, the PCM cool roof exhibited improved thermal performance, indoor thermal environment, and enhanced building energy savings. Results showed that the inner wall temperature of the PCM cool roof was 6.3 °C lower than that of an ordinary roof, and had a cooling range 65.1% higher than that of a PCM roof. Through computational fluid dynamics (CFD) simulations, this study analyzed the influence of five parameters on the thermal performance and latent heat utilization of the PCM cool roof. Finally, the energy-saving potential and economic benefits of using PCM cool roof in an office building in Chongqing were simulated. This study is helpful to the popularization and application of PCM cool roof. • The thermal performance and energy-saving potential of PCM cool roof are explored. • In summer, the daily energy saving of PCM cool roof ranges from 5.1% to 13.5%. • Analyzed the influencing factors and significance of the roof thermal performance. • The energy saving of PCM cool roof used in office buildings in summer is 6437 kW h. • The CO 2 emission reduction of PCM cool roof is 4115.8 kg/y. [ABSTRACT FROM AUTHOR]

This paper presents a straight-bladed VAWT (vertical axis wind turbine) model for the evaluation of aerodynamic forces and inertial contributions to rotor blade deformation. In this paper, a two-bladed VAWT is proposed and analyzed with CFD (computational fluid dynamics) and wind tunnel experiments in three-dimensional (3D) investigation. In wind tunnel experiments, pressure measurement system is presented to measure the pressure acting on a single blade of straight-bladed VAWT in the spanwise direction. In numerical analysis, 3D CFD models have been performed to simulate the aerodynamic forces characteristics of VAWT with k–ε SST (Shear Stress Transport) ( k–ε ) turbulence model. From comparing the results of the wind tunnel experiments and numerical analysis, it is found that the fluid force decreased with the increase of spanwise positions excluding the position of support structure. Furthermore, according to the result from six-component balance, the waveforms of the power coefficient C pw have similar characteristics and show smaller values than CFD calculations. [ABSTRACT FROM AUTHOR]

In this paper, thermal–hydraulic effects of nanofluid as coolant in VVER-1000 nuclear reactor with annular fuel are investigated. At the first, the core of a VVER-1000 reactor is designed based on the use of internally and externally cooled annular fuels and thermal–hydraulic parameters of the fuel rods are analyzed. From the neutronic viewpoint, Alumina is the best nanoparticle for normal operation at low concentration. In this paper, for this nanoparticle, fuel assembly is simulated in the hot channel using CFD (Computational Fluid Dynamics) simulation codes and thermal–hydraulic calculations (maximum fuel temperature, fluid outlet, MDNBR (Minimum Departure from Nucleate Boiling Ratio), etc.) are done. As one of the most important results of the analysis, using the nanoparticles, the heat transfer coefficient in outer coolant, which was already decreased using annular fuel, is increased. Also, by applying the nanoparticle with smaller size and major concentration, MDNBR is increased. [ABSTRACT FROM AUTHOR]

Circulating Fluidized Bed (CFB) boilers are desirable technology to utilize solid fuels, operate within a wide load range, and promote the high flexibility in burning a wide range of coal and other solid fuels, keeping high efficiency and low gaseous pollution. The paper presents thermal and flow modeling results of steam superheater operated in the large-scale coal-fired CFB boiler, both in steady and transient states. The mathematical model of the superheater wall was developed using Control Volume-based Finite Element Method. The heat transfer coefficient as the sum of radiative and convective heat transfer coefficients was considered in the presented approach to modeling thermal processes in a circulating fluidized bed. The overall heat transfer coefficient was computed for the analyzed type of the boiler at full load and steady-state conditions using available measuring data and results obtained using Computational Fluid Dynamics (CFD) modeling. Depending on the modeling approach adopted in the CFD model, the heat transfer coefficient at full boiler load varies between 159.96 and 189.63 W/(m2·K). In the analyzed period of boiler start-up, results of steam outlet temperature (455 °C–485 °C), heat transfer coefficients on the flue-gas side (100 W/(m2∙K) and 120 W/(m2∙K)), and heat transfer coefficients on the steam-side (925–2008 W/(m2∙K)) vary with time. The methods presented in the paper can be applied to modeling transient flow and thermal processes in superheaters with complicated flow arrangements. The advantage of the proposed method is a short computing time compared to detailed and complex 3D models. The developed model of the superheater with the transfer coefficient determination methods can be used to perform calculations in the full range of boiler load, both during steady and transient boiler operation. • Heat transfer coefficient in CFB boiler was determined using CFD modeling results. • Heat transfer on the flue-gas side in the CFB boiler is calculated considering radiative and convective heat transfer. • A new method for superheater calculations in the transient state is presented. • The simulation of superheater operation in the 100 min CFB boiler startup period was performed. • The developed model can be used to perform simulations in the full range of boiler load. [ABSTRACT FROM AUTHOR]

This paper investigates two furnaces which work under oxy-fuel condition with natural gas. One is a 0.8 MW furnace where detailed inflame measurements are available. The other furnace is an 11.5 kW lab-scale furnace with temperature measurements. The furnaces were investigated by CFD (Computational fluid dynamics) analysis. The main focus was on using combustion models that are not computationally demanding. Therefore the SFM (steady flamelet) approach was used with two detailed mechanisms. The advantage of the SFM is that the calculation time can be reduced from 4 weeks to 4 days on 8 CPU-cores. The applicability of two detailed mechanisms under oxy-fuel condition is pointed out in this paper. The investigation showed that the skeletal25 mechanism and the SFM are in very good accordance with measurements. If the strain rate between CH 4 and O 2 stream is too low, the SFM fails to predict the flame shape correctly. The influence of three different turbulence models was also investigated. Furthermore simulations with the eddy dissipation model and numerically expensive eddy dissipation concept model were conducted. Different WSGGM (weighted sum of grey gases model) were applied. The comparison of the WSGGMs showed that the difference between them is insignificant for small furnaces. [ABSTRACT FROM AUTHOR]

This paper investigates the effect of profile-modifications on a NACA-0015 aerofoil used in VAWTs (vertical axis wind turbines). The profile-modifications being investigated consist of a combination of inward semi-circular dimple and Gurney flap at the lower surface of the NACA-0015 aerofoil. Rather than maximize the lift-coefficient or the ratio of the lift to drag coefficients, this paper choose to maximize the average (or effective) torque of the VAWT as this is a much better measure of the power produced. A fully automated optimization using RSA (Response Surface Approximation) is utilized here to maximize the average torque produced by the wind turbine blade. The data-set used in the optimization is generated using CFD (computational fluid dynamics) simulations. In order to ensure reliability, the computational domain and the turbulence model used in the CFD simulations are validated against previous experimental results. The optimized shape of the modified aerofoil is shown to improve the aerodynamics of the wind turbine blade. [ABSTRACT FROM AUTHOR]

Domestic hot water tanks represent a significant potential demand side management asset within energy systems. To operate effectively as energy storage devices, it is crucial that a stratified temperature distribution is maintained during operation; this paper details experimental and numerical work conducted to understand the influence that wall material specification has on de-stratification within domestic hot water tanks. A 2d axisymmetric CFD (Computational Fluid Dynamic) model was consistent with experiments which showed that switching from copper to stainless steel resulted in a 2.7 fold reduction in useable hot water loss through reduced de-stratification for a 74 L UK domestic hot water tank over a 48 h period. During simulation, a counter rotating convection system, with peak velocities of 0.005 m/s, was observed above and below the thermocline. Minimizing de-stratification, through appropriate wall material selection, increases the performance of hot water tanks and scope for their use in demand side management applications. Given the inconclusive evidence surrounding copper's efficacy as a sanitizing agent, along with the low tensile strength of polyethylene, this paper advocates the use of stainless steel in hot water tank walls and further exploration of alternative materials and composites which have low cost and low thermal conductivity along with high strength and manufacturability. [ABSTRACT FROM AUTHOR]

Understanding the impact of dynamic effects induced by wave-current conditions on the hydrodynamic performance of a floating horizontal axis tidal turbine (HATT) is crucial toward developing floating tidal turbines to harness tidal energy in deep water sites. The complicated of the wake of a HATT has not yet been fully understood. In this paper, a Computational Fluid Dynamics (CFD) model used to study the performance of a turbine supported by a moored floating platform, due to surge only and in wave-current flows. The CFD model is compared against piled turbine tests, providing an error of 1.36% in power coefficients at the studied TSR = 3.9. It was shown that surge motion caused by even a small wave height or wavelength has a significant effect on the thrust and torque of the rotor. The wave height and period have a remarkable effect on the fluctuation of the hydrodynamic performance due to the induced rotor velocity. The surge motion affects the wake velocity recovery and vortex structure development. For a fuller understanding, future work could explore the negative effects such as induced blade fatigue and platform instability arising from surge motion, as to design cost-efficient turbines, supports and arrangements. • A CFD model predicts the coupled motion between the turbine and a moored floating platform under wave-current flows. • Waves alternates both the turbine's hydrodynamic coefficients and motion. • The increasing wave height and period have a positive impact on wake velocity recovery. • The wake vortex structure results more sensitive with wave period, rather than wave height. [ABSTRACT FROM AUTHOR]

As an economical energy recovery device, a pump as turbine (PAT) is widely used in micro hydropower and energy recovery fields. Compared with an original impeller, a special impeller with forward-curved blades can dramatically enhance a PAT's efficiency and broaden its high-efficiency range because the blade angles created by the latter more effectively match the PAT's operating mode. The shape of blade curve and sweep has obvious influence on the performance of a PAT. To investigate how the inlet swept angle of forward-curved blade influences the performance of PAT, five different forward-curved impellers with different inlet swept angle blades were designed and numerically investigated based on a verified computational fluid dynamics (CFD) method. The effects of blade inlet swept angles on the external characteristics, energy loss and unsteady characteristics of PAT are analyzed. Compared with the blade whose inlet swept angle is 0°, the maximum efficiency of back-swept PAT with swept angle of −8° increases by 0.58% while the head decreases by 0.49 m. However, the efficiency of forward-swept PAT of 8° reduces by 0.9%, and the head increases by 0.68 m. The maximum reduction rates of the main frequency amplitude of pressure pulsation in the volute, impeller and draft tube of back-swept PAT are 35.2%, 45.47% and 67.24%, respectively, indicating that the back-swept blade can contribute to improve the operation stability of PAT. Moreover, the vortex in PAT with back-swept blade is greatly improved under partial and design flow rate, which can improve the unsteady flow characteristics of PAT. • This paper introduced swept blade technology in research field of PATs. • The back-swept blade can remarkably improve the PAT's hydraulic performance and widen the high efficiency range of the PAT. • The back-swept blade can effectively suppress the pressure pulsation in PAT. • The back-swept blade can improve the operation stability of PAT and can improve the unsteady flow characteristics of PAT. [ABSTRACT FROM AUTHOR]

Ejectors are widely used as steam power cycle components to recover superfluous water vapor. However, in a system for preparing distilled water used for pharmaceutical injection, the ejector periodically deviates from the design condition owing to fluctuations in steam source pressure. In particular, when the pressure is reduced to approximately 75% of the design value, performance is significantly degraded, affecting water production efficiency. To solve this problem, a two-stage ejector with control switching strategy is proposed in this paper. The performance of a series of two-stage ejector structures with different scale ratios was analyzed, and the optimum scale ratio was determined. Furthermore, an optimal switching strategy is devised to ensure that the two-stage ejector maintains stable performance under different primary flow pressures. The numerical results indicate that the entrainment ratio of the two-stage ejector is 79.4% higher than that of the single-stage ejector when the pressure is 60% of that of the designed primary flow. Moreover, the two-stage ejector can maintain satisfactory entrainment performance when the traditional ejector enters reversed mode under 50% of the designed pressure. The experimental results show that the entrainment performance of the proposed two-stage ejector can be improved significantly when power fluid pressure is insufficient. • A two-stage ejector with variable working conditions was proposed. • The optimal scale ratio of the two-stage ejector in MED-TVC-WFI system was obtained. • An optimal switching strategy of the two-stage ejector was proposed. • The optimal switching pressure of the two-stage ejector is 450 kPa. [ABSTRACT FROM AUTHOR]

Abstract: The objective of the present paper is to study the oil flows from damaged submarine pipelines with different leak sizes. CFD (computational fluid dynamic) simulations with FLUENT software are carried out to investigate the process of oil spill from submarine pipeline to free surface. Effects of oil density, oil leaking rate, leak size and water velocity on the oil spill process are examined. High density, slow leaking, small leak size or fast current brings about long time for oil reaching the maximum horizontal migrate distance when it reaches surface. And this maximum horizontal migrate distance increases with the increase of leak size or water velocity, while increases with the decrease of leaking rate. Then, the dimensionless time required for oil droplets which have the longest horizontal migrate distance when they reach the sea surface and the dimensionless longest horizontal distance the droplets migrate when they reach the sea surface are analyzed and the fitting formulas are obtained. Only the formula for the dimensionless longest horizontal distance versus dimensionless density meets the polynomial, other five formulas meet the natural logarithm distribution. Using the formulas we can obtain when and where to see oil reaching the sea surface, and conduct rapid response. Finally, the maximum horizontal migration distance of oil at certain time is predicted, and a forecasting model is proposed. The using methods of fitting formulas and the forecasting model are shown in the paper by examples. These calculated results provide useful guidance to place the oil containment boom. [Copyright &y& Elsevier]

Abstract: Wind energy represents a very important source of energy for many countries nowadays. Wind energy provides an efficient and an effective solution to reduce fusel fuel consumption as well as pollutant emissions. VAWTs (vertical axis wind turbines) were originally considered as very promising, before being subrogated by the present, horizontal axis turbines. There is now a resurgence of interests for VAWTs, in particular Darrieus turbines. VAWTs (vertical axis wind turbines) like the Darrieus turbine appear to be particularly promising for the conditions of low wind speed, but suffer from a low efficiency compared to horizontal axis turbines. Additionally, VAWTs are not always self-starting, which is a major drawback. The present paper introduces the main problem of the self-stating capability of Darrieus turbine and investigates some techniques to improve this drawback. The effect of the turbine solidity and the usage of hybrid system between drag and lift types have been investigated in this paper numerically using CFD (Computational Fluid Dynamics) technique and experimentally. A considerable improvement of the H-rotor Darrieus turbine self-starting capability can be obtained by these techniques. [Copyright &y& Elsevier]

Abstract: The present paper describes the application of computational fluid-dynamics (CFD) to the design and characterization of a medium scale energy storage unit for district heating systems. The shell-and-tube LHTES unit contains a technical grade paraffin (RT100) as phase change material (PCM) and uses water as heat transfer fluid (HTF). The system has been designed to transfer heat from the district to the building heating networks. After an initial description of the LHTES unit and a wide literature overview on the subject, the paper discusses the need for thermal enhancement to improve the thermal conductivity of the PCM. A solution based on a paraffin-graphite composite with a 15% graphite volume fraction has been found to be well performing in this particular application. Several operating scenarios characterized by heat requests ranging between 130 kW and 400 kW have been explored and the main outputs presented as function of Re and St numbers. The timewise variations of other significant quantities such as liquid fraction, sensible and latent energy content, HFT outlet temperature and heat fluxes have been also presented and discussed. A final discussion on the possible system configurations shows that in comparison to traditional water storage systems for district heating, LHTES systems provide, depending on the chose alternative, higher energy storage densities. [Copyright &y& Elsevier]

The impact of local depth-wise velocity profiles on tidal turbine performance is important. Although the use of standard power laws for predicting velocity profiles is common, these laws may underestimate the magnitude of the depth-wise velocity shear and power attenuation. Predicting the performance of a tidal turbine in a high velocity shear is crucial in terms of power extraction. This paper discusses the dimensional scaling of a turbine using CFD and experimental data. Key performance characteristics (power, torque and thrust coefficients) were studies with increasing diameters and velocities, by generating. a series of non-dimensional curves. This provides a first order approximation for matching turbine performance characteristics to site conditions. The paper also shows that the use of a volume-averaged velocity derived from the upstream velocity profile can be used to determine these key performance characteristics. These are within 2% of those determined assuming a uniform flow. The paper also shows that even changes in the blade pitch angle results in new turbine characteristics under uniform velocity conditions and it is expected that these can be used for profiled flow. [ABSTRACT FROM AUTHOR]

Galloping-based piezoelectric energy harvesting systems are being used to supply renewable electricity for the low-power wireless sensor network nodes. In this paper, a fork-shaped bluff body is presented as the basic system component, and demonstrated by experiments and simulations to improve the harvesting efficiency at low wind speed. For the fork-shaped structure, the fluid simulation results via CFD (Computational Fluid Dynamics) indicate that the ' ⊐ '-shaped region formed by two protruding front blades can help strengthen the vorticity to obtain high air lift force. The ' ⊢ '-shaped region formed by the middle transverse blade and the rear blade can induce a large pressure difference between two sides of the rear blade. The experimental results demonstrate that compared with the traditional bluff bodies such as triangular prism and square prism, the piezoelectric wind energy harvester with the fork-shaped structure can generate much higher output voltages. When the ratio ( l f / W) of the front blade length ( l f ) to the bluff body width (W) is 1/4, the fork structure can induce the best harvesting performance. Further, by adding cover plates on two ends of the bluff body, the energy harvesting efficiency can be further improved in a wider blade length ratio ( l f / W = 0.75 ∼ 1) range. • Fork-shaped structure is proposed to improve performance of wind energy harvester. • Fork-shaped structure consists of two front blades, a middle blade, and a rear blade. • ' ⊐ '-shaped part formed by two protruding front blades helps strengthen vorticity. • ' ⊢ 'shaped part formed by middle and rear blades induces stronger lift force. • Cover plates are added on the structure to further enhance the harvesting efficiency. [ABSTRACT FROM AUTHOR]

This paper investigated the intake flow field of a controllable intake swirl diesel engine using computational fluid dynamics (CFD) methodology. It can be observed that the variation of the intake swirl with the opening of the intake baffle shows the two-stage characteristics, while the baffle opening angle of 48° is as a cut-off point. Through the comprehensive analysis of the influence of valve lift and baffle opening angle on flow coefficient, it is concluded that the influence of valve lift on flow coefficient is more sensitive. A mathematical method is used to fit the formula which can calculate the key characteristics of the controllable intake swirl diesel engine. Meanwhile the influence of the swirl ratio on combustion characteristics is investigated. It can be concluded that the swirl ratio has greater influence on the power performance of the diesel engine. When the swirl ratio increases from 0.4 to 1.2, the power performance is increased by 5.79%, and the fuel consumption was also improved. Finally, according to the actual structure of the intake system of diesel engine, a steady-state intake flow test bed was established to verify the accuracy of CFD study of the intake system. • The swirl ratio of the controllable intake swirl diesel engine has two-stage characteristics. • The diesel engine valve lift is more sensitive to the flow coefficient than the intake baffle. • Two stage characteristics of the intake swirl is the intrinsic property of a diesel engine. • The swirl ratio is more favorable for improving the effective power of a diesel engine. [ABSTRACT FROM AUTHOR]

This paper describes the development of a systematic tool chain capable of automatically extracting accurate and efficient Reduced-Order Models (ROMs) from Computational Fluid Dynamics (CFD) simulations. These ROMs can then be used to support the design and operation of Near-Zero Energy Buildings (NZEB), with a higher accuracy than traditional zonal models but at a fraction of the computational cost of CFD. This study assesses the accuracy and time to solution of these ROMs when solved for appropriate Boundary Conditions (BCs), found in the built environment, in order to define the usability envelope of the automatically extracted ROMs. The parameters used in this study are inlet temperatures (K) and mass flow rates (kg/s). Results demonstrate that the absolute error can be maintained at under 0.5 K for changes in temperature of up to ±15 K, and under 0.25 K for changes in mass flow rates of up to ±45% of the original value. The results show that this method has the potential for applications in the built environment where the ROM accuracy and low computational cost can bridge a gap between low order RC models and high order CFD, further improving the energy efficiency in smart buildings. • A method for extracting zonal models from CFD simulations is presented. • A reduced fluid network model is generated by clustering CFD cells. • The ROM can be solved for different boundary conditions. • The model retains a high level of accuracy and is solved in real time. [ABSTRACT FROM AUTHOR]

Multi-stage Tesla valves in the reversed flow state can be applied during the hydrogen decompression process between the high pressure hydrogen storage vessel and the fuel cell. Under high-pressure turbulent hydrogen flow, severe aerodynamic noise may be caused and large energy loss inside Tesla valves may be generated, which can cause uncomfortable noise in vehicles. In this paper, the valve stage number and the pressure ratio between the inlet and the outlet are analyzed to investigate the possibility of the occurrence of aerodynamic noise and energy loss inside Tesla valves, and Mach number, turbulent dissipation rate, and exergy loss are used and evaluated as the criterion. The results show that both Mach number and exergy loss increase with the increasing of pressure ratio, but with the decrease of valve stage number, Mach number increases and exergy loss decreases. In addition, large turbulent dissipation rate at each valve stage appears near the bifurcation and the confluence between the straight channel and the bend channel of multi-stage Tesla valves. The correlation between the valve stage number, the pressure ratio, and the maximum Mach number is fitted, which can be used to estimate the possibility of the occurrence of aerodynamic noise. • Multi-stage Tesla valves are applicable for hydrogen decompression. • Mach number is used to represent the occurrence of aerodynamic noise. • Impacts of valve stage number under different pressure ratios are investigated. • Small valve stage number results in higher Mach number. • Higher pressure ratio and large valve stage number lead to high exergy loss. [ABSTRACT FROM AUTHOR]

Abstract The studies of supercritical carbon dioxide (S-CO 2) power generation cycles have attracted wide attention from different energy industries in recent years. At present, there is a lack of studies on the dynamic characteristics of S-CO 2 power systems, especially in S-CO 2 coal-fired power plants. In order to further provide the theoretical and technical support for the integration of energy internet and the deep peak-load regulation, it is important to establish the dynamic model of the S-CO 2 power system. Heat exchanger is a key component of the system. Therefore, the dynamic response characteristics of the heat exchanger need to be studied because the related research will lay the foundation of building the dynamic model of the entire S-CO 2 power system. In this paper, the effects of dynamic responses characteristics of thermodynamic parameters (fluid outlet temperature, total surface heat flux and surface heat transfer coefficient of fluid channels) on the printed circuit heat exchanger (PCHE) of 1000 MW S-CO 2 coal-fired power plants are studied in detail. Afterward, a neural network is trained to predict the performance of the PCHE. First, the computational fluid dynamics (CFD) method is adopted to establish the dynamic model of the S-CO 2 /S-CO 2 PCHE. Second, when the fluid inlet temperature or the fluid mass flow rate is changed, the dynamic response trends of thermodynamic parameters on the PCHE of 1000 MW S-CO 2 coal-fired power plants are analyzed. Third, the comparisons of the equilibration time of the PCHE with different boundary conditions (the fluid mass flow rate and the fluid inlet temperature) are investigated. Finally, a neural network is trained to predict the performance of the PCHE. Highlights • The CFD method is adopted to establish the dynamic model of the S-CO 2 PCHE. • The dynamic response trends of key parameters on the PCHE are analyzed. • The equilibration time of the PCHE with different conditions are compared. • A neural network is trained to predict the performance of the PCHE. [ABSTRACT FROM AUTHOR]

Lost circulation of working fluid into formation fractures is one of the most common and costly problems encountered during the development of petroleum and geothermal resources. Fracture plugging strength and efficiency with loss control material determine the effect of lost circulation control. This paper proposes an integrated method for optimal material selection. The key mechanical parameter of loss control material is determined based on mathematical model and simulation on fracture plugging strength and efficiency. The developed fracture plugging strength model accounts for the shear failure of fracture plugging zone. Simulation with coupled computational fluid dynamics and discrete element method is conducted for fracture plugging efficiency accounting for particles transport and capture in fracture. Model and simulation results show that friction coefficient is the key material mechanical parameter for fracture plugging effect. Laboratory experimental results show that rigid particle with lower roundness, fiber with higher tensile strength and elastic particle with higher deformation rate lead to larger friction coefficient and should be selected as loss control material. Reasonable combination of rigid granule, fiber and elastic particle can create a synergistic effect to achieve the optimal friction coefficient and fracture plugging effect. Material selection strategy is determined and has been successfully applied to field case study in Sichuan Basin, China. • Integrated method for LCM selection based on mathematical model, CFD-DEM simulation and laboratory experiments. • Analytical model of fracture plugging strength for lost circulation control in fractured reservoir. • Coupled CFD-DEM simulation of fracture plugging efficiency for lost circulation control in fractured reservoir. • Friction coefficient as the key material mechanical parameter for lost circulation control effect. • Developed material selection strategy for lost circulation control successfully applied to field case study. [ABSTRACT FROM AUTHOR]

The transparent insulation materials (TIM) can effectively improve the performance of flat plate solar collector in cold weather. A three dimension numerical model of flat plate collector with TIM has been developed in this paper. The computational fluid dynamics (CFD) have been used to simulate the model. The Renormalization-group (RNG) k - ε model and Discrete Ordinates (DO) radiation model were adopted. The influences of the environment conditions, mass flow rate, tilt angle and transmittance on the performance of the collector with TIM were analyzed. A good agreement was achieved between the CFD prediction and the previous experiment. The result shows that the collector with TIM is more efficient, when ambient temperature is low. For various wind speeds, the new collector's efficiency has a slightly change. The transmittance of TIM is a key parameter to achieve high performance for the collector. When the transmittance is below 80%, the collector with TIM has no the advantage of being good value. The optimum mass flow rate is 0.06 kg/s under corresponding conditions. The tilt angle of the collector with TIM has less effect compared with the conventional one. • Thermal performance of flat plate collector with TIM is studied by CFD method. • The influences of environmental conditions on performance of the collector with TIM are investigated. • The effects of the flow rate, transmittance of TIM and inclined angle on the collector efficiency are studied. • Optimum value of flow rate is obtained. [ABSTRACT FROM AUTHOR]

Abstract The goal of this work is to perform detailed 3D CFD analysis of heat transfer and flow dynamics inside a commercial gamma-type Stirling engine, including its structural details and variability of the working spaces. The study focuses on an impact of different initial engine parameters, i.e., filling pressures, rotational speeds and heater temperatures, on the engine's characteristics. One of the biggest advantages of using CFD in such kind of problems, is that it allows to reduce models uncertainty resulting from inaccurate assumptions inherent in the low-order models (analytical formulas for heat transfer coefficient or pressure losses etc.). Such empirical formulas are based on the literature data, therefore they are valid only for some range of engines' operational conditions. The results were validated against available experimental data, showing good agreement in terms of overall trends. Comparison of different turbulence and regenerator models demonstrated their little impact on the engine indicated work. The applied CFD model allowed us to accurately and deeply analyse 3D unsteady flow features including the velocity field, vorticity, temperature, friction coefficient and production/dissipation of the turbulent kinetic energy. We focused on identification of recirculation/stagnation regions as well as the regions of increased turbulence intensity. Highlights • The paper presents a multidimensional CFD study of the Gamma Stirling engine. • The simulations are performed using uRANS approach with k−epsilon and k−omega models. • The flow inside the engine has a 3D complex non-uniform character. • The simulations reveal the regions characterized by strong vorticity values. [ABSTRACT FROM AUTHOR]

Abstract This paper aimed to develop a computational fluid dynamics simulation for an industrial boiler. The industrial boiler is used for the sulfuric acid production. A numerical model is carried out using the commercial code "ANSYS-FLUENT". The simulations are developed for the case of the industrial boiler and a new proposed design. A clear understanding of the combustion phenomenon and the fluid flow within the boiler is provided from the simulations. The local characteristics of the fluid flow and the heat transfer such as the temperature; the velocity magnitude and the density distributions are presented and analyzed. The comparison between the numerical results and the experimental data is performed and a good agreement is found. Highlights • A numerical simulation is developed for an industrial boiler. • The fluid flow and the heat transfer characteristics are analyzed and discussed. • The numerical model is validated by comparison between numerical results and industrial measurements. [ABSTRACT FROM AUTHOR]

Abstract Under the pressure of increasingly stringent emission regulations, highly efficient turbocharger turbines are desired to achieve high performance of internal combustion engines. Turbines suffer from significant performance deterioration under realistic inlet conditions distorted with swirls, yet relevant researches are quite limited. Little understanding has been gained about how the inlet swirls influence the turbine performance. This paper investigated turbine performance under swirling inflow conditions through a numerical method. Results show that swirling inflow has a considerable effect on the turbine swallowing capacity and efficiency, and swirling intensity correlates with the efficiency reduction. A simple theoretical analysis reveals that swirling inflow causes high loss of the circumferential velocity in the turbine housing. Consequently, it leads to a reduction of the absolute flow angle at rotor inlet and a large deviation of the relative flow angle at rotor inlet from its optimum value, which are the main causes of the swirling flow effect on turbine swallowing capacity and efficiency respectively. Swirling direction has a remarkable effect on turbine loss mechanisms. Opposite swirl directions result in different vortex movements and deformation around the volute periphery, which leads to different circumferential flow distributions at rotor inlet and inserts distinguishing influence on rotor performance. Highlights • Influence of strength and direction of the swirling inflow on turbine performance is presented. • Swirling inflow conditions lead to reductions in the absolute and relative flow angle at rotor inlet. • Strong circumferential flow non-uniformity is aroused by the swirling inflow. • Flow mechanisms behind the swirling inflow effect are analyzed. [ABSTRACT FROM AUTHOR]

Abstract Wind forecasting holds the key to the management of wind power. Previous vector or matrix wind forecast methods may not best reflect the intrinsic inter relationship among the wind velocity components of a three-dimensional wind field. Alternatively, a tensor-based model is developed to reconstruct the wind velocity distribution within a short period of time, enabling a new way for wind forecasting. A third-order CFD database is established by CFD simulations and the Tucker decomposition is used to obtain the tensor basis off site. Then in real time, the tensor basis can be employed to rapidly reconstruct wind velocity distributions in any direction, which can also form a new way to reconstruct wind velocity distribution in 3-D spaces. A comparison of the maximum and relative reconstruction errors shows that the newly proposed method performs better than the authors' previously published wind field reconstruction method. The influences of sampling rate, noise level and sensor distributions on the reconstruction error are also discussed in this paper. Finally, a wind tunnel experiment is carried out to evaluate the accuracy of the proposed method, and in most cases, the experimental results show that relative errors drop around 0.03%-0.4% and maximum errors drop around 0.02%-1.7% when using the newly proposed method. Highlights • A new tensor-based method is proposed to predict wind velocity distributions. • Tucker decomposition is used to decompose CFD database to obtain tensor bases. • The proposed method can be applied to different geometrical models in 3-D domains. • Wind tunnel experiments are carried out to validate the proposed method. [ABSTRACT FROM AUTHOR]

Abstract In recent years, the world has been experiencing a technological revolution that is transforming the energy sector around the world, and Mexico is no exception. Among these technologies, small wind turbines (SWTs) appear to be promising. This paper presents a methodology according to the specific Task 27 of the International Energy Agency (IEA) in order to improve the wind resource assessment in the urban environment by using computational fluid dynamics (CFD). Many problems that would help boost the use of this technology are still not addressed including wind resource assessment in the urban environment. Among these important issues are the energy yield estimation of SWTs in the urban zones, as well as the effects on the electricity supplied by the turbines in the distribution system. The objective is to present an easy-to-follow methodology, which permits the application of diverse CFD methods and software to assess the installation of SWTs in urban zones. This feasibility study on estimating the wind resource through CFD allows the opportunity to supply local electricity to buildings or public lighting systems. This methodology is based on the insertion of SWTs, in the urban environment; the SWTs are selected based on a market study of these technologies. Highlights • CFD Methodology for micrositing SWTs on buildings. • Wind resource assessment improvement for urban wind applications. • Integration of CAD Modeling and CFD simulations for implement a BUWTs project. • Urban wind harvest studies with CFD techniques. [ABSTRACT FROM AUTHOR]

Abstract Ejector cooling with hydrocarbon as alternative refrigerant promises great application potential in hot climate regions. In order to unleash the potential of these sustainable cooling systems, it is essential to design high-performance hydrocarbon ejectors. In this paper, a computational fluid dynamic (CFD) simulation approach is proposed for detailed ejector modeling. The NIST real gas model is used to incorporate thermophysical properties of actual refrigerants for accurate ejector performance prediction. A hydrocarbon ejector performance is analyzed according to different operating and geometric conditions, where a linear relationship between the expansion ratio and the compression ratio is obtained for Pentane with an accuracy of 0.5%. A set of Pareto Frontier performance curves are also recommended for designing and operating energy-efficient hydrocarbon ejector cooling systems. Our results show that a small area ratio leads to a high ejector compression ratio, which is desired in hot climate applications. The other geometric design parameters have minor effects on the ejector performance. This work also indicates that ejectors with a converging-area chamber can achieve better overall performance compared to conventional ejectors. Highlights • Designing high-performance hydrocarbon ejectors for cooling in hot climate regions. • Axisymmetric CFD simulation of ejector with NIST real gas thermophysical properties. • Pentane ejector having a linear relation between its expansion ratio and compression ratio. • Ejector with converging-area chamber performing better than ejector with constant-area section. • Pareto Frontier performance curves recommended for future hydrocarbon ejector cooling applications. [ABSTRACT FROM AUTHOR]

Abstract This paper presents a novel 1-D mathematical model to determine complete dimensions of an ejector component of Ejector Refrigeration System (ERS). The concepts of Prandtl's mixing length, Prandtl-Meyer expansion wave, Kelvin-Helmholtz instability and Baroclinic effect are introduced in the model to precisely determine the various diameters, mixing length, nozzle exit position etc. for the given conditions of the primary & secondary fluid, cooling capacity and critical condenser pressure. The area ratios obtained using the mathematical model are compared with the experimental/numerical results available in open literature for the same operating conditions and are found to be in good agreement. Moreover, ejector geometry determined from the proposed model is analyzed using CFD for the same input conditions. Average deviation in the entrainment ratio obtained using CFD and that given to the model is found to be less than 2.48% and thus model is validated again. The experimental test rig of ejector refrigeration system is also fabricated and the performance is evaluated while operating at critical condenser pressure. The deviation in the ejector geometry used in the experiment is found to be less than 7% in comparison to the ejector dimensions calculated by the numerical model for the same input conditions. Highlights • 1-D model is proposed to calculate complete geometry of ejector. • Novel concepts are introduced to accurately predict the dimensions of ejector. • Primary and secondary nozzle is influenced by generator and condenser respectively. • Performance and operating range of ejector depend on the geometry of ejector. • Effect of ejector inputs are found on its geometry. [ABSTRACT FROM AUTHOR]