Circulation Flow Research Articles

LES of the upper plenum of the liquid metal fast reactor under the forced flow conditions

A Large Eddy Simulation (LES) of the upper plenum of the E-SCAPE (European SCAled Pool Experiment) facility under the normal operations has been conducted to gain deeper insights into the thermal hydraulics phenomena in liquid metal fast reactors (LMFRs). The results unravel the overall flow features in the upper plenum, the thermal instability in the above core structure region and the impact of the jets from the barrel holes on the large flow circulation and thermal mixing.The above core structure region is represented using a homogeneous porous model. It is shown that during the normal operations, most of the hot stream of the lead bismuth eutectic (LBE) from the core center rises to the top and disperses from the upper barrel holes. Conversely, the cold LBE spread out from the lower barrel holes. Mixing between the two streams only affect the fluids leaving from the middle heights demonstrating limited mixing. These jets help to create a large circulation in the upper plenum region which prevents any thermal stratification. At the interface between the hotter and colder streams, there are unsteady large-scale structures resulting in a mixing layer in the thermal field. This strong mixing is not conventional turbulence and potentially cannot be captured by Reynolds Averaged Navier Stokes average (RANS) modelling.The flow in the upper plenum is dominated by the influences of the different types of jets, which include some free jets issued horizontally or angled upwards and some jets impinging onto the structures in the plenum. The jets overall behave similar to ‘standard’ jets, though significant interactions between the top and bottom jets and the background circulations have strong influences at later stages of the jets, typically after four jet diameters leading to the jets not reaching self-similarity. In addition, the turbulence that is observed in the upper plenum is largely generated by the jet flows and hence the distribution of turbulence is very non-uniform. Away from the jets, turbulence is minimal with the mixing largely driven by the large-scale circulation.

A review of natural circulation flow in integral effect test facilities

The proposed NCFM map was reviewed using natural circulation data identified in the PWR simulated integral effect test (IET) facility with a height (length) scale ratio of 1/1. Based on this, the characteristics of natural circulation flow in the ATLAS and FESTA facilities, which are major IET facilities in Korea, are compared. It was confirmed that the natural circulation flow characteristics were well maintained within the NCFM area even at the half-height test facility of ATLAS. It was also confirmed that the natural circulation flow characteristics were well maintained within the NCFM area at the full-height test facility of FESTA, and the natural circulation flow characteristics were also maintained outside the NCFM region for a relatively small amount of coolant inventories.

Action Mechanism of Film Extraction on Channel Impingement Cooling for Blade Leading Edge Using Large Eddy Simulation

Abstract Various internal cooling techniques combined with external film cooling are applied to cool gas turbine blades, and the coolant extraction can cause variations in internal flow structures and cooling effectiveness. Effects of film extraction under different film hole diameters and coolant mass flow ratio on heat transfer and flow characteristics of channel impingement cooling are presented using large eddy simulation (LES) in this article. The current work was undertaken based on turbine blade dimensions and turbine operating conditions. The results indicate that film extraction coupled with the curvature-induced instability dominates flow patterns and heat transfer in the channel impingement cooling structure with a film hole, especially in the bend region corresponding to the leading edge of turbine blades. Film coolant extraction can disrupt the streamwise counterrotating flow circulation pair. The latter is caused by the curvature-induced instability and is also the major driver of multilongitudinal vortices. The hole edge vortex generated by coolant bleed amplifies heat transfer at the leading edge, and the effect is more significant as the film hole diameter increases. Conversely, heat transfer coefficient downstream of the cooling channel decreases due to a reduction in cooling air. The increasing film bleed flow increases overall total pressure loss, while flow loss in the cooling channel decreases because of the weakened flow circulations and reduced coolant mass flow. This work provides an in-depth insight into the cooling performance of channel impingement cooling with film extraction, contributing to designing film cooling for turbine blades with multichannel wall jet cooling.

Effects of different fire slash artificial promotion regeneration and natural material regeneration on ecological function

IntroductionIn the aftermath of a fire, prompt reforestation of the affected areas is crucial to mitigate economic losses and ecological impacts.MethodsThis paper introduces an ecological function assessment model leveraging the Back Propagation Neural Network (BPNN). The model's efficacy is validated through simulation comparison experiments. Subsequently, an analysis of the ecosystem's material circulation and energy flow capabilities is undertaken.ResultsSimulation outcomes reveal that our proposed model attains convergence by the 10th training iteration, with a loss function value of just 0.28, highlighting minimal training loss. This underscores the model's rapid convergence and impressive training performance. Our method proves superior to the comparison method in both initial and later operational phases. Notably, it offers a significantly faster response speed and boasts an accuracy rate exceeding 95%.DiscussionConsequently, employing this model to analyze ecological function changes is deemed feasible. The analysis of ecosystem material circulation and energy flow capabilities reveals that while initial assessments show minimal change, scores exhibit a clear acceleration as the cycle progresses.

Study on the Separation Performance of a Two Cylindrical Section Hydrocyclone under Various Height Ratios.

Two cylindrical section hydrocyclones can suppress particle misplacement by regulating the circulation flow, but few researchers have investigated the effect of the cylindrical height ratio. In this paper, numerical simulations and physical tests were conducted to investigate the effect of height ratio on the particle motion behavior and separation performance of the two cylindrical section hydrocyclone. According to the numerical simulation results, with increasing height ratio, the separation cut size decreased, the separation accuracy and recovery rate of medium and coarse particles in the underflow increased, the coarse particle misplacement in overflow decreased significantly, and the proportion of medium particle circulation flow gradually increased. According to the test results, the number of misplaced fine particles in underflow could be effectively reduced when H1/H0 = 0.30. With increasing height ratio, the number of misplaced coarse particles in the overflow decreased and the classification efficiency of fine particles increased. The maximum separation efficiencies of medium and coarse particles could be obtained at H1/H0 values of 0.47 and 0.17, respectively. Therefore, increasing the height ratio could inhibit coarse particle misplacement in overflow and improve the separation performance of two cylindrical section hydrocyclones.

Influences of daily solar radiation intensity on the sea-land breeze and pollutant dispersion in coastal areas

Solar radiation plays a crucial role in the formation of sea-land breeze (SLB) circulation in coastal areas, and the SLB circulation in turn influences the atmospheric diffusion of pollutants in coastal cities. Therefore, the characteristics of the SLB and its impacts on the pollutant distributions in Shanghai, China, are numerically investigated for three (low, medium, and high) daily solar radiation intensities (DSRIs). The results show that the pollutant dispersion is affected by both the horizontal flow of SLB circulation and the vertical thermal plume (TP). The SLB only transports pollutants within the near-ground layer, while TP removes pollutants from the boundary layer and then improves near-ground air quality. Both the intensities of the SLB and TP increase with the increase of DSRI, however, the relative strength of the two are different at different DSRIs. When the DSRI is high (28.35 MJ/m2/day) or low (9.45 MJ/m2/day) during the daytime, the sea breeze (SB) is much stronger than the TP, so the prevailing flow direction on the land is horizontal, causing large amounts of pollutants to be blown inland. For the medium DSRI (18.90 MJ/m2/day), the TP is more powerful in the early stage of the SB period, so the airflow across the land is dominated by the rising TP. Pollutants are mainly transported to the upper atmosphere and the best air quality can be achieved in the residential region. At night, the worst air quality occurs at low DSRI, because when the DSRI is low, the speed of the land breeze is also low and this decelerates the diffusion of pollutants to the sea by the wind.

Numerical analysis of rotating scans’ effect on surface roughness in laser-powder bed fusion

The rotating scanning strategy is a critical factor for top surface roughness in laser-powder bed fusion (L-PBF), yet the underlying mechanism remains elusive. This study introduces an integrated L-PBF model, encompassing powder packing and molten pool fluid dynamics analysis, to investigate how surface roughness accumulates across layers with non-rotating scans but is mitigated with rotating scans. To address computational complexity and prediction errors associated with multi-layer simulations, the model utilizes an experimentally built part as substrate and simulates single-layer depositions with varying scanning rotation angles. Additionally, an as-machined surface representing ideal flat substrate is included for comparative analysis. Results indicate that on as-built surfaces featuring alternating peak-valley patterns, both powder packing structure and fusion zone shape are location-dependent. To effectively characterize the packing structure on such non-flat surfaces, an effective packing density is proposed. Specifically, peak locations exhibit a thinner powder layer, a 14.5% increase in effective packing density, and a 7% decrease in penetration depth compared to valley locations. The circulation flow, driven by recoil pressure and Marangoni force, is responsible for the reduced surface roughness with rotating scans. Specifically, the circulation flow intersects with multiple peaks and valleys, effectively promoting material redistribution among these tracks and disrupting the peak-valley patterns. Conversely, the peak-valley patterns are preserved and may propagate to subsequent layers with non-rotating scans.

Mixed convection flow over a horizontal plate and the horizontal wake far downstream

The laminar mixed convection flow over a heated or cooled horizontal plate of finite length is a surprisingly intriguing problem. The hydrostatic pressure jump at the trailing edge and across the wake is to be compensated by induced circulation in the outer potential flow, similar to a plate at a non-zero angle of attack. The mixed convection flows over semi-infinite and finite horizontal plates, respectively, are thus substantially different. As the hydrostatic pressure jump remains finite along the infinitely extended wake, the induced outer potential flow around the plate would grow beyond bounds in a domain extending to infinity. Thus, boundary conditions must be imposed at the boundaries of a finite domain. However, the numerical solution of the Navier-Stokes equations remains a challenging problem due to the lack of appropriate outflow conditions. The traditional outflow condition cannot comply with the finite hydrostatic pressure jump across the wake. Thus, an asymptotic expansion for the wake far downstream from the plate is performed. Remarkably, the perturbation of the flow does not decay with increasing distance from the plate as in a classical wake. The asymptotic solution is implemented as an outflow boundary condition for the numerical solution of the Navier-Stokes equations. The results are compared with a boundary-layer solution obtained in previous work for the limiting case of vanishing Prandtl number.

Assessment of MARS-KS prediction capability for natural circulation flow in passive heat removal system

Considering that system analysis codes are used for the evaluation of the performance of Passive Safety Systems (PSSs), it is important to investigate the capability of the system analysis code to reliably predict the heat transfer and natural circulation flow, which are the main phenomena governing the performance of a PSS. Since MARS-KS has been widely validated for heat transfer models, this study focuses on evaluating its capability to predict the single and two-phase pressure drops and natural circulation flow. The straight pipe simulation results indicate that the pressure drop predictions are reliable within ±5 % error margin for the single-phase flow and the errors of pressure drop up to −30 % for the two-phase flow. Through single-phase natural circulation flow analysis, it is concluded that the use of the appropriate K-factor modeling based on the flow regimes is important since the natural circulation flow rate in MARS-KS is mainly affected by the form loss factor modeling. With two-phase natural circulation flow analysis, this study emphasizes the behavior of the system could change significantly depending on the two-phase wall friction and pressure loss modeling. With the analysis results, modeling considerations for the PSS performance evaluation with the system analysis codes are proposed.

Multi-physics analysis of SBLOCA by coupled Neutronics/Thermal-Hydraulics full plant model

With the development of computational tools, the accident analysis would be performed by best estimate approaches. The employment of multi-physics codes would be considered as new calculation procedure to obtain high valuable results by improving calculations with specialized codes. The small break loss of coolant accident (SBLOCA) is an accident that has typically been analyzed using system codes with a limited number of Thermal-Hydraulics (TH) channels in the core region, neglecting the use of multi-physics calculations. This approach results in insufficient accuracy and resolution in both neutronics and TH calculations within the core zone. To address this issue, this study proposes the implementation of a Neutronics/Thermal-Hydraulics coupling with one-to-one mapping in the core zone, achieved through the development of a comprehensive plant TH model. This approach aims to enhance the accuracy and resolution of calculations, enabling the identification of local phenomena, parameters, and feedback during accident simulations, and the incorporation of these effects on the macroscopic cross-sections at each time step. The results of SBLOCA simulation reveals the effects of conservative/best estimate approach on the sequence of events, the initiation time of the safety systems, the critical controlled parameters of the power plant, and the precise understanding of the accident. Also, it was found that the radial power distribution becomes disrupted and loses its symmetry immediately after the SCRAM leading to different characteristics of steam generators (SGs) and natural circulation flow rate in each loop of primary side.

Study of application of bioclimatic architecture strategy at Citraland Residential House in Palu City

Palu City has a fairly hot air temperature, very high intensity of solar radiation, quite high rainfall, and a fairly large wind speed. When reviewing the climatic conditions of Palu City above, the planners in this case the Citraland housing architect team should be able to apply a bioclimatic architecture strategy to be able to respond to the climatic conditions of the city of Palu. Based on this background, it is necessary to conduct a research study on the application of bioclimatic architecture strategies in Citraland's residences. This study uses a rationalistic approach with an exploratory method. Research shows that Citraland Residence has implemented a bioclimatic architectural strategy in several ways, namely the use of shading or shadow effects in the form of roof canopy, eaves, and lattice made of wood, and protective plants, as well as the use of insulating materials such as natural stone affixed to the outer walls. residential home. In addition, the layout of the residence also plays a role in the flow of air circulation to the maximum. Then the strategy of making wind-catching rooms and the use of glass materials on several sides of the building which acts as a place to enter sunlight into the house

Prediction of liquid circulation flow rate in RH degasser: improvement of decarburization at low atmospheric pressure

Prediction of liquid circulation flow rate in RH degasser: improvement of decarburization at low atmospheric pressure

Bacterial and fungal community structures in Hulun Lake are regulated by both stochastic processes and environmental factors.

Microorganisms are a crucial component of lake ecosystems and significant contributors to biogeochemical cycles. However, the understanding of how primary microorganism groups (e.g., bacteria and fungi) are distributed and constructed within different lake habitats is lacking. We investigated the bacterial and fungal communities of Hulun Lake using high-throughput sequencing techniques targeting 16S rRNA and Internal Transcribed Spacer 2 genes, including a range of ecological and statistical methodologies. Our findings reveal that environmental factors have high spatial and temporal variability. The composition and community structures vary significantly depending on differences in habitats. Variance partitioning analysis showed that environmental and geographical factors accounted for <20% of the community variation. Canonical correlation analysis showed that among the environmental factors, temperature, pH, and dissolved oxygen had strong control over microbial communities. However, the microbial communities (bacterial and fungal) were primarily controlled by the dispersal limitations of stochastic processes. This study offers fresh perspectives regarding the maintenance mechanism of bacterial and fungal biodiversity in lake ecosystems, especially regarding the responses of microbial communities under identical environmental stress.IMPORTANCELake ecosystems are an important part of the freshwater ecosystem. Lake microorganisms play an important role in material circulation and energy flow owing to their unique enzymatic and metabolic capacity. In this study, we observed that bacterial and fungal communities varied widely in the water and sediments of Hulun Lake. The primary factor affecting their formation was identified as dispersal limitation during stochastic processes. Environmental and geographical factors accounted for <20% of the variation in bacterial and fungal communities, with pH, temperature, and dissolved oxygen being important environmental factors. Our findings provide new insights into the responses of bacteria and fungi to the environment, shed light on the ecological processes of community building, and deepen our understanding of lake ecosystems. The results of this study provide a reference for lake management and conservation, particularly with respect to monitoring and understanding microbial communities in response to environmental changes.

Novel high-purity struvite crystallization method for phosphate recovery from simulated swine wastewater using activated talcum

The struvite crystallization method is considered a highly promising approach for phosphate recovery from swine wastewater. However, the utilization of chemicals like magnesium and alkali as sources for struvite crystallization substantially increases the overall cost of this technology. In this study, activated talcum powder (ATP) was used instead of chemical reagents to recover phosphate as struvite from simulated swine wastewater containing 93 mg/L phosphorus and 450 mg/L ammonia nitrogen. The results showed that 93.02 ± 1.56% phosphorus and 14.47 ± 1.89% ammonia nitrogen were removed from simulated wastewater in the continuous flow circulation system. The purity of the struvite collected is as high as 97.24%. Mineralogical analysis showed that mechanical activation destroyed the crystal structure of talcum and increased the reactivity of Mg2+ and OH−, allowing it to be released spontaneously into aqueous solution. The amount of magnesium ions dissolved was affected by factors such as contact time, talcum dose, ammonium concentration and pH. The main components of ATP residue were quartz and magnesite, which will not cause secondary pollution to the environment. The use of ATP to recover phosphate into struvite has the advantages of low chemical cost and no pollution of waste materials, holding broad application prospects.

Decomposition and Variation in Carbon and Nitrogen of Leaf Litter Mixtures in a Subtropical Mangrove Forest

The decomposition of mangrove litter plays a crucial role in material circulation and energy flow within mangrove forests. Evaluating the decomposition-based variation in biogenic elements in litter is important for improving our understanding about their biogeochemical cycling in ecosystems. The main objective of this study was to examine the interaction effect during the decomposition process of mixed Kandelia obovata and Avicennia marina litter. Variations in C and N were also determined in the decomposing leaf litter mixtures. Our findings revealed that the decomposition rates were faster in summer than in winter, and increased with the proportion of A. marina litter. After 35 days of decomposition in summer, the remaining weights for different proportions of K. obovata (KO) and A. marina (AM) were 22.9% (KO:AM = 1:2), 27.2% (KO:AM = 1:1), and 31.2% (KO:AM = 2:1), respectively. Similarly, after 49 days of decomposition in winter, the remaining weights for the different KO:AM proportions were 27.7%, 35.4%, and 44.0%, respectively. Additionally, the decomposition of mixed K. obovata and A. marina litter had an influence on C content and N release dynamics. These results provide a scientific basis for understanding the decomposition of mixed mangrove litter and its implications for material circulation and energy flow within these ecosystems.

A big little fiction form: last decade of production and circulation of made-for-TV movies in Europe

ABSTRACT Made-for-television movies, originating as popular television forms in the 1960s, have historically received scant scholarly attention and faced persistent devaluation within the film industry. However, the contemporary landscape witnesses a resurgence in interest, catalyzed by the focus of VOD services on long-form fiction tailored for streaming, commonly referred to as “originals.” This paper conducts a retrospective examination of the past decade, scrutinizing the presence of made-for-television movies within general television and accentuating their intrinsic value by investigating intra-European circulation flows. Through comprehensive content analysis of general-interest channel schedules in five prominent European countries, this study explores the nuances of production, circulation dynamics, and the influence of public corporations in this scenario. The findings reveal distinctive circulation patterns characterized by continual European exchanges, setting made-for-TV movies apart from TV series, particularly on public channels. Notably, a select cluster of large European countries emerges as pivotal players dominating these intra-European flows.

Research on the separation chamber diameter ratio of the multi-stage hydrocyclone to inhibit particle misplacement

The particle radial settling distance is determined by the separation chamber diameter ratio of multistage hydrocyclones, affecting particle circulation flow and particle misplacement. The effect of the separation chamber diameter ratio on the flow field and separation performance is explored using numerical simulations and physical experiments. The findings indicate that a larger separation chamber diameter ratio increases the particle circulation flow ratio and coarse particle circulation flow proportion, intensifying the particle enrichment ratio. However, smaller separation chamber diameter ratios result in higher turbulence intensity and higher enrichment ratio of coarse particles in the primary separation chamber. Both oversize and undersize separation chamber diameter ratios exacerbate misplaced coarse particles. Physical test results indicate that misplaced fine particles and coarse particles diminish and eventually increase with increasing the separation chamber diameter ratio. The + 150 μm particle content in the overflow reaches the minimum value of 0.32 % in the separation chamber diameter ratio of 0.5. In comparison, the –23 μm particle content in the underflow reaches the minimum value of 3.7 % in the separation chamber diameter ratio of 0.6, and the classification efficiency of −74 μm reaches the maximum of 61.85 %. Consequently, both large and small separation chamber diameter ratios will aggravate particle misplacement and deteriorate classification performance by augmenting the coarse particle circulation flow.

Experimental evaluation of liquid circulation flow rate induced by an air-injection-type aerator

Despite previous research efforts, there is a lack of experimental data on liquid circulation flow rates, particularly in real-scale facilities. The study aims to fill this gap by proposing a momentum transfer model using a gas–liquid separation flow to estimate inner flow in a real-scale air-injection-type aerator. The liquid circulation flow rate was evaluated using velocity measurements. The air supply pressure and dissolved oxygen (DO) were determined. Experiments were performed at depths of 0.90, 1.30, and 1.75 m. The effect of the inner diffuser was investigated at each depth. The inner diffuser reduced the circulation flow rate but increased the vertical upward flow velocity. For the deepest condition (1.75 m), the inner diffuser reduced the air supply pressure and increased the overall oxygen transfer coefficient. Momentum analysis indicated a suppression effect of the air velocity at the aerator exit owing to the inner diffuser. This indicated that an increase in the gas holdup owing to the deceleration of the air velocity at the aerator exit reduced the air supply pressure owing to the reduction in downstream pressure. This study provides valuable insights into aeration system optimization, considering factors such as energy efficiency and oxygen transfer effectiveness.

Free convection at different locations of adiabatic elliptic blockage in a square enclosure

The numerical simulation of free convection flow within a square-shaped enclosure for various orientations of elliptic blockage (EB) is performed in the present study. The bottom wall of the cavity remains uniformly heated, where the left and right (side) walls as well as the boundary wall of the elliptic blockage are insulated and the top wall remains at a cool temperature. As $Pr$ remains constant, the effects of different values of $Ra$ have a great influence on overall fluid flow and temperature gradient for three different locations: bottom elliptic blockage (BEB), center elliptic blockage (CEB) and top elliptic blockage (TEB), as a mass flow circulation has been identified, and a state of equilibrium has been established within the fluid flow simulations along with the isotherm contours. The outcomes of the numerical analysis are presented with the streamlines, isotherms, and variations of the average Nusselt number.

Experimental and numerical study of the interaction between tempered glass fallout and enclosure fire dynamics

Tempered glass, as an important type of safety glazing, is extensively used in high-rise buildings. However, little is known about the fallout behavior of tempered glass in the compartment with different fire locations. Therefore, in this work, the exposed framed glass panes with the dimension of 815 × 815 × 6 mm3 were heated by a pool fire in the compartment. The fuel pans were placed at six different locations in the compartment. It was found that the fallout time of tempered glass increased with a decrease in the distance between the fuel pan and glass panes; when the fire was moved to the wall side, the fallout time of tempered glass was longer. Besides, the temperature gradient of the glass surface at the exposed area was insignificant when the fire source was at the center line of the doorway opening, while there was an evident temperature gradient of the glass surface on the height direction due to the apparent smoke layer in the upper of the compartment for near wall fire locations. In addition, CFD numerical simulations were conducted using FDS software to observe the temperature and velocity fields inside the compartment with different fire locations. It was found that when the fire was moved to the wall side, the circulation flow was formed at both the high-temperature region near the fire source and the low-temperature region on the left of the compartment.