Bed Shape Research Articles

Optimizing waste heat recovery for hydrogen production: Modeling and simulation of ternary size metallic granule flow in a cooling cylinder

In order to recover the waste heat of high temperature metallic granules to produce steam for hydrogen production, a waste heat recovery cooling cylinder with cooling water channel is innovatively developed. The simulation is carried out based on DEM and soft sphere model to study the flow characteristics of ternary size metallic granules. The model of cooling cylinder is established and verified by comparing to the experiment data. The change rule of bed shape in the waste heat recovery cooling cylinder is examined, and the inclination angle, rotational speed and filling rate are assessed to find their influence on the flow characteristics of ternary size metallic granules. The results indicated that, with the increase of inclination angle, the axial velocity increases by 482.76%, which means the reduce of residence time of granules. With the increase of rotational speed, the axial velocity has an increase of 161.54%, the sum velocity increases by 158.49%, leading to a decrease of residence time. As the filling rate increases from 1.5% to 15.5%, the contact number has an increase of 91.53%, which lead to the increase of heat transfer area. The residence time and heat transfer area will directly affect the waste heat recovery efficiency, so a proper arrangement of granule flow is significant for enhancing the heat transfer efficiency.

Minimum spouting velocity of fine particles in fountain confined conical spouted beds using machine learning and least square fitting approaches

AbstractThe present study concerns the development of new models to estimate the minimum spouting velocity (Ums) in various configurations of fountain‐confined conical spouted beds (FC‐CSBs) with fine particles. Existing literature correlations were found to be inaccurate for FC‐CSBs. Therefore, smart modelling techniques were employed to design more accurate predictive tools. The radial basis function (RBF) approach provided the best predictions for systems without draft tubes as well as those with open‐sided draft tubes. Additionally, the Gaussian process regression (GPR) approach yielded the best predictions for systems with nonporous draft tubes. The mean absolute percentage error (MAPE) values for the testing phase were 5.80%, 5.67%, and 5.59%, respectively. These models consider how bed shape and particle properties affect Ums. The sensitivity analysis was conducted to determine the factors with more importance in controlling Ums. Finally, simpler correlations were derived for Ums prediction in different FC‐CSB configurations, with accuracy around 12% error.

STAR-CCM+ simulation of debris bed formation in the unheated DEFCON-S experiment

In a severe accident of light-water reactor, molten corium can be formed and discharged into the reactor cavity. If the resulting debris bed is not adequately cooled, it could threaten the containment integrity by causing a molten core-concrete interaction. This study analyzes a non-heating debris bed formation experiment of DEFCON-S using the STAR-CCM+ code. Relevant CFD models are established to reflect the interaction between particles and fluids to describe the particle behavior and flow of fluids. The shape and size of debris bed are predicted through the CFD calculation. The rolling resistance becomes an important parameter in this simulation. The prediction with the default values of STAR-CCM+ forms a spread shape of particle bed compared to the experimental result. The shape of debris bed obtained with modified rolling resistance coefficients gives consistency with the DEFCON-S experiment, having a deviation in diameter of 4.6 % and a deviation in height of 3.8 %.

Numerical simulation on particle sedimentation in water-filled pool using CFD-DEM method

Numerical calculations of the bed shape formed by particles descending into a water-filled pool have been conducted using the CFD-DEM coupling Eulerian-Lagrangian method, implemented within Fluent code. The mixture model has been employed to simulate the multiphase flows involving water–air fluids. The simulations account not only for the interactions between the fluids and particles but also for collisions, sliding friction and rolling friction between particles (or particles and the wall). The numerical simulations have been performed to investigate the sedimentation shapes for four cases: 4 mm diameter particles (ZrO2 and Stainless Steel) and 6 mm diameter particles (ZrO2 and Al2O3). These particles have been released into a water-filled pool with a diameter of 375 mm. The results indicate that the calculated shapes of the porous bed have been obtained with a reasonable level of accuracy.

Announcement of an approaching death: Glaciar Norte, Citlaltépetl volcano, Mexico

This study shows the dramatic but probable future evolution of Mexico's largest glacier. Mass and energy balances of this glacier have been previously studied, as well as reconstructions of its evolution up to the present time. In this work, for the first time, the real evolution of the glacier is compared with the first years of models of its future evolution.Two dynamic models of glacier thickness evolution have been developed based on a network of stakes and ground penetrating radar complemented by geometrical characterizations of the glacier bed shape. Calculated mean annual mass balance leads the equilibrium line altitude to be increasingly higher and even higher than that of the mountain summit.Two models that complement each other to describe the how and when of the different states and stages in which the glacier front retracts, the thickness decreases causing the separation of the glacier to finally disappear in the middle of the 21st century. This study provides the first view of a glacier that is about to disappear in Mexico, where the cryosphere represents the best climate proxy for future scenarios of related ecosystems, water availability.

Effect of fluidized bed shapes on gas-solid fluidization characters and flow regime transition

The technology of gas-solid dense-phase fluidized bed separation is applied in the separation of fine particles in minerals due to its stable and reliable characteristics. The experiment collected time-domain distribution signals of pressure drop from fluidized beds with different shapes, systematically analyzed the spatiotemporal distribution characteristics of bed density, and studied the effects of bed shape and fluidization number N on the fluidization and flow transition of the bed layer. The results indicate significant differences in Umf among fluidized beds with different shapes, and the tapered bed requires the highest energy for fluidization. When N=1.3, the cylindrical bed layer is the most stable, maintaining an average density of 1.8 g/cm3, with a density fluctuation variance of 0.02 g/cm3. Additionally, when N<1.0, almost no bubbles inside the bed layer. With an increase in gas velocity, the time-domain distribution of pressure drop signals shows different degrees of fluctuation. When N=1.1, Conspicuous non-uniform particle flow is evident in the tapered bed, with a bubble main frequency of 8 Hz, an amplitude of 27.1, and the highest pressure drop energy signal, indicating that the tapered bed enters the bubbling state prematurely. Finally, fine coal separation experiments were conducted, and the results showed that the minimum E value for the cylindrical bed is 0.08 g/cm3, while the maximum E value for the tapered bed is 0.17 g/cm3.

Influence of Right Triangular Prism Rough Beds on Hydraulic Jumps

A hydraulic jump phenomenon is exciting in turbulent flow as it causes large-scale turbulence and high-energy loss. This paper investigates the hydraulic jump characteristics of right triangular prism rough beds. The renormalization group RNG k-ε turbulent model and the volume of fluid (VOF) method in a CFD model are utilized to simulate hydraulic jumps. A total of 210 numerical simulations of four new types of rough beds were performed with an initial Froude number (Fr1) ranging from 4.8 to 9.4, the non-dimensionless wave steepness values of 0.67 ≤ t/s ≤ 1.33, and the distances between roughness elements of 0 ≤ Ls/y1 ≤ 2.67. This study found that arranging the right triangular prism rough elements in a stilling basin increased bed shear stress and energy loss. At the same time, they reduced sequent depth and jump length by about 22% and 50% compared to a smooth bed, respectively. In addition, the entropy production rates are also used to analyze energy dissipation, which clearly shows that the characteristic shape of a rough bed significantly influences the hydraulic jump length. Equations and plots that specify the relationships between the hydraulic jumps and study parameters are helpful guidelines for defining the rough bed dimension when designing or repairing a stilling basin for low-head irrigation works and highway sewers.

Nail bed trauma reconstruction and artificial nail replacement - a case report.

Nail bed reconstruction is crucial after fingertip trauma, impacting both function and aesthetics. In this article, the authors describe a case of partial distal phalanx amputation of the index finger with laceration of the nail bed's remaining part. A traumatically elevated skin-fat flap covered the exposed bone on the fingertip, preserving finger length and sensitivity on the radial side. A full-thickness skin graft from the forearm closed a secondary defect on the finger pulp. Nail bed suturing prevented scarring and nail deformity, and a temporary artificial plastic nail replacement maintained the nail bed's shape. Temporary artificial nail replacements protect the regenerating fingertip bed, promote healing, and prevent nail deformities. Proper adaptation of lacerated nail bed edges, supported by either the patient's own nail or a temporary artificial nail, is crucial for optimal fingertip restoration, including proper nail shape.

Numerical investigation of non-uniform temperature fields for proppant and fluid phases in supercritical CO2 fracturing

The non-uniform temperature distribution in supercritical CO2 (Sc-CO2) fracturing influences the density, viscosity, and volume expansion or shrinkage rate of Sc-CO2, impacting proppant migration. This study presents a coupled computational fluid dynamics-discrete element method and heat transfer model to examine the effects of proppant bed shape and the heat transfers of proppant-wall, proppant-fluid, and fluid-wall on the fluid and proppant temperature fields. The Sc-CO2 volume expansion is assessed under various temperature conditions by evaluating the volume-averaged Sc-CO2 density. Several factors, including proppant size, shape, thermal conductivity, concentration, temperature difference, and injection velocity, are carefully analyzed to elucidate their impacts. The findings elucidate the existence of four distinct zones in the fluid temperature field. Each zone exhibits different magnitudes of temperature change under diverse conditions and undergoes dynamic transformations with the development of the proppant bed. The fluid-wall heat transfer and the fluid temperatures in Zones C and D are significantly subject to the fluid injection velocity (governing the heating duration), the temperature difference between fluid and formation (impacting the magnitude of heat flux), and the proppant bed shape (controlling the effective heating area). Additionally, the proppant-wall and proppant-fluid heat transfers determine the temperatures of both the proppant bed and the fluid within Zone B, showing a strong correlation with proppant thermal conductivity, proppant size, injection velocity, and temperature difference. The proposed coupled model provides valuable insights into the temperature distributions and flow behaviors of temperature-dependent fracturing fluids and proppants.

Estimating the Ballast bed shape using Camcorder video

AbstractTo properly maintain and manage track surfaces, the amount of collapsed settlement of a ballast bed must be determined. However, high maintenance costs make it difficult for railway operators to fully maintain and manage track surfaces. Therefore, we propose a method of estimating the shape of the ballast bed using Dense Inverse Search (DIS) optical flow in images captured using a camcorder, which is inexpensive. This paper describes the outline of the method, an evaluation of its accuracy through simulation and model experiments, and the results of applying the method to actual images captured.

The Role of Bed Morphology and Channel Curvature on the Redistribution of Momentum in a Series of Meander Bends, Pearl River, USA

AbstractThree primary driving factors are responsible for the lateral flux of streamwise momentum within meander bends: topographic steering of the flow related to changes in channel morphology, rapid changes in channel curvature, and curvature‐driven helical motion. While these factors have been studied previously, their relative contributions to the net redistribution of streamwise momentum within a series of consecutive bends have not yet been fully documented. This study explores the relative contributions of these three mechanisms to the redistribution of streamwise momentum using three‐dimensional velocity data obtained along six consecutive meander bends on the Pearl River (Louisiana, USA) for two different discharges. The magnitudes of lateral momentum flux are systematically compared to spatial series of channel width, bed shape, and channel curvature to elucidate the interactions between channel form and flow structure. Results show that the lateral flux of streamwise momentum is primarily driven by topographic steering with values of momentum flux due to curvature‐driven secondary circulation on average an order of magnitude less than values of flux related to topographic steering. The spatial patterns of the lateral flux components show that momentum redistribution due to topographic steering is highest at the entrance to the bend, and momentum redistribution due to secondary circulation is typically highest downstream of the apex. The results of this study emphasize the important role that interaction between process and form plays in dynamics of natural meandering rivers.

Numerical investigation on design optimization of core catcher in sodium cooled fast breeder reactor

Core catcher is a passive prevention device that is designed to prevent damage to the lower head of the reactor vessel caused by direct contact with molten corium. In sodium cooled fast breeder reactors (SCFBRs), the structural design of the core catcher directly affects the shape of the debris bed, which in turn impacts the re-criticality and long-term decay heat removal of the debris bed. In this study, the improved discrete element method (DEM) was used to simulate the formation process of the debris bed below the core catcher, and the influencing mechanism of the structure of the core catcher on the shape of the debris bed was explored. Through numerical simulation, the influence on the shape of the debris bed from the projection area of chimney cap, the inclination angle of chimney cap, and the distance between central chimney and surrounding chimneys of the core catcher was examined. It was found that secondary scattering played a significantly positive role in enhancing the uniformity of the debris bed. This study lays a foundation for analysis of the heat transfer performance and evaluation of long-term decay heat removal of debris bed, and can offer engineering guidance for the design and optimization of sodium cooled fast reactor core catcher.

An experimental investigation on debris bed formation from fuel coolant interactions of metallic and oxidic melts

During postulated severe accidents in a light water reactor (LWR), the core melt (corium) may relocate to the lower head and fail the reactor pressure vessel (RPV). The corium is expected to undergo fuel coolant interactions (FCI) if the reactor cavity is flooded with water. Both FCI energetics and resulting debris bed coolability are of paramount importance to reactor safety, since the ex-vessel corium poses a threat to the containment integrity if steam explosion occurs or the debris bed is uncoolable, leading to release of radioactive fission products to the environment. The present study is intended to quantify the characteristics of a debris bed resulting from FCI, which are crucial to debris bed coolability. Different from the previous studies with only oxidic materials, various materials, including metallic ones of Sn, Sn-Bi and Zn as well as oxidic one of Bi2O3-WO3, were employed as the simulants of corium (mixture of UO2/ZrO2/Zr/Fe) in the present study to investigate the effects of melt materials, melt superheat and coolant subcooling on debris bed formation in a water pool. High-speed photography was applied to visualize melt jet breakup, droplets fragmentation, as well as fragments sedimentation on the pool floor. Other obtained data are debris bed shape (profile) and porosity, as well as morphology and size distribution of debris particles. The comparative results of various tests provided insights toward filling the knowledge gap on debris bed characteristics under different melt materials and compositions.

Empirical modeling of ex-vessel debris bed formation in a pre-flooded reactor cavity

To secure the containment integrity of a nuclear power plant (NPP) in severe accident situation of ex-vessel corium release into the reactor cavity, a pre-flooding strategy of a reactor cavity has been adopted in various NPPs, including Korean PWRs. Molten corium released into the pre-flooded water pool is fragmentized and forms a particulate debris bed at the bottom of the cavity. To prevent the containment failure, it is important to properly remove the heat from the debris bed, which can be accomplished by water ingression into the bed. The water ingression characteristics are highly dependent on the debris bed shape. In this study, several main parameters affecting the debris bed shape were determined with respect to phenomena of free-fall & sedimentation, particle dispersion by steam spike and convection flow, and self-leveling. Then empirical model was developed and validated using the results of DEFCON (Debris bed Formation and COolability experimeNt) experiments. The model’s error was within ±10% when only free-fall & sedimentation were present. When steam-spike or convection was added to free-fall & sedimentation condition, the error increased to within ±20%. When all three were simultaneously present (free-fall & sedimentation, steam-spike, and convection), the model predicted most of the experimental results within ±20% error, except for several cases where convection had a significant impact. The effect of self-leveling itself was within ±10%. Considering all phenomena related to particulate debris bed formation, most cases had an error of ±20%. In addition, the debris bed shape formed by poly-disperse particles was predicted appropriately by the mode using the mass mean diameter of the particle size distribution, with an error range of ±20%. Consequently, it is expected that the proposed model of the debris bed shape can be utilized in an integrated severe accident analysis code for the evaluation on the ex-vessel debris bed coolability in the pre-flooded reactor cavity.

Influence of guide tubes on configuration and heat-up behaviour for PHWR specific suspended debris bed – An analytical assessment

The estimation of accident source term and hydrogen generation is dependent on the core heat-up under postulated accident scenarios. The uncertainty of such estimations increases as the accident severity increases due to complexity in the determination of i) evolving degraded core configurations, and ii) associated suitable physical models for heat-up and degradation simulation. Analysis of postulated severe accidents for PHWR is essential for emergency planning and severe accident management guidelines from a plant licensing perspective. The study presents the order of uncertainty that is present as of today in deciding the size and shape of the suspended debris bed, which in turn decides the exposed core heat up, hydrogen generation as well as fission product release. The study reveals that the location and integrity of reactivity mechanism guide tubes significantly impact the exposed core heat-up, channel disassembly pattern and shape and size of the suspended debris bed. Nevertheless, the experimental study on the guide tube behaviour on asymmetric heat-up condition and their failure will further substantiate the postulation of suspended debris bed configuration.

Numerical investigation of cooling ability in heat-generating porous debris bed after severe accident in PWR

A porous debris bed formed after a severe accident is a structure composed of different sized particles. Due to the fission reaction in the debris bed, decay heat is continuously released. Therefore, the cooling ability should be investigated to determine the safety of the debris bed. In this paper, two-phase conservation equations with closure correlations are proposed for the boiling phenomenon inside the pool. For the flow resistance, the drag force between the gas and liquid in the continuous fluid is considered as well as the flow resistance of the solid to fluid in the porous medium area. The heat transfer model takes into account the heat transfer between solid phase and fluid phases as well as the heat and mass transfer between gas and liquid. All calculations are conducted based on the CFD method, and the related models are written into the CFD calculation program in the form of a User Defined Function (UDF). After the necessary validation of the proposed correlations, the analysis and discussion are based on the effect of the heating type, the non-uniform distribution of structural parameters, and the shape of the geometry. The results show the key effect of natural convection between the different boundary settings of the heating type. The time series of strong natural convection formation and the decay power of heat are the factors that are determined for the position of the boiling crisis. In addition, the limited power density is determined by the top half of the debris bed. The increase in structural parameters and operating pressure leads to a better cooling ability. For the shape of the debris bed, a regular cylinder is a better structure for heat removal, while the conical shape significantly reduces the limited power density, which is dangerous for the long-term cooling of the debris bed. The cooling ability would be improved if a downcomer existed in the porous debris bed. These three research parts are conducive to deepening the understanding of the process of a serious accident.

Effect of Perspective on Eye Movement of Aesthetic Preference Research on Wai Shape of New Chinese Style Arhat Bed

The new chinese style Arhat bed is taken as the research objective to explore the effect of people’s view on people’s aesthetic preferences for Wai shape of new chinese Arhat bed, using the eye movement analysis method through comprehensive analysis on eye movement data from volunteers. Eye movements characteristics of 20 volunteers in watching pictures of different new chinese Arhat bed Wai shape are recorded by SR research Eyelink head mounted eye tracker. Experimental results show that eye movement data of men and women are in the same trend, but there are few data in instability and the male and female have a significant correlation with the time and the number of fixation points, with a obvious regression effect, under two different presented Perspective of products. In all 16 samples selected, samples 12 has the most fixation and fixation times, while samples 15 and samples 13 has the least. Visual fatigue and the difference between 3D model and the real Arhat bed products have some effects on the experimental data. It makes no difference for people to choose products from different perspectives in where the products are placed, and people prefer the Wai shape which contains column and is simple.

Study on the importance of bed shape in combined DEM-CFD simulation of fixed-bed Biomass gasifiers

The extensive utilization of fossil fuels is limited by the environmental problems related to carbon dioxide and other greenhouse gas emissions. As a result, the generation of energy and heat from biomass has become increasingly economically and ecologically important in recent decades. In existing numerical studies, the effect of slope form on airflow within the biomass gasifier was not systematically investigated. To explore the potential impact of the real shape of a fuel bed on local gasification conditions, a small-scale updraft fixed-bed gasifier was modeled in this study with a default lateral feeding position and air supply from below. The discrete element method (DEM) was combined with computational fluid dynamics (CFD) by using two open-source software: LIGGGHTS® and OpenFOAM®. The particle models of two biomasses (olive stone and almond shells) were calibrated and used to investigate qualitatively and quantitatively the airflow patterns, including the resulting uneven pressure and temperature distribution at/over the slope surface. Besides, the effects of operating parameters of the feeding system on slope form were highlighted. Therefore, the real fuel heap shape should be taken into consideration for future simulation studies on side-fed, fixed bed gasifiers. • Material models for DEM simulation are calibrated and validated. • The influences of heap shape and inlet air velocity are explored comprehensively. • Quantitative discussion on the rates of temperature and pressure change. • Suggests that different screw feeding speeds can realize dynamic combustion optimization. • Limitations of a particular DEM-CFD co-simulation model are addressed.

Debris Bed Self-Leveling Mechanism and Characteristics for Core Disruptive Accident of Sodium-Cooled Fast Reactor: Review of Experimental and Modeling Investigations

Evaluations of the Core Disruptive Accident (CDA) are significantly important for safety analysis of Sodium-cooled Fast Reactor (SFR) despite the very low probability of occurrence for CDA. During the material-relocation phase in CDA of SFR, the molten materials are possibly released from the core region into subcooled sodium, subsequently forming the debris bed on the lower part of the reactor vessel after being quenched and fragmented. The accumulated high-temperature debris with decay heat can cause sodium coolant boiling, leading to the so-called “debris bed self-leveling behavior” during which the shape of the debris bed becomes flattered (leveling). It is important to investigate the debris bed self-leveling behavior due to its potential capacity to induce the transfer of debris and affect the ability of cooling and criticality of the debris bed. Thus, in recent years, valuable knowledge concerning the mechanism and characteristics of this behavior was accumulated through lots of experimental results and modeling developments. Aimed at providing a valuable guideline for future investigations on this issue, in this study, the past experimental and modeling investigations on debris bed self-leveling mechanism and characteristics are systematically summarized and reviewed, and some future remarks are also proposed to promote the progression of further research for SFR severe accident analysis.

Experimental investigation of solid particle spreading driven by gas injection into a pool of water

Motivated from the fuel–coolant interaction phenomena in boiling water reactors, in the present work, effect of natural convection flows, set during the melt dripping, on the nature of formation of debris bed, of solidified particles, at the bottom floor is studied. Standard shape solid particles are used to simulate the dripping melt and their paths are tracked using a particle tracking technique to acquire additional data such as particles velocity, travel time and path. The experimental studies performed on PDS-P facility are designed to study the separate effects and generate the data for codes validation. A novel particle tracking technique allowed quantification of kinetic properties for every particle. The results helped in refinement of the particles distribution on the floor, quantifying the debris bed shape. Higher pool depths and natural convection flows rates are seen effective in enhancing the distribution of debris particles, creating shallow and well spread debris bed.