Results of Air Barbotage Experiments Simulating Two-Phase Flow in a CANDU End Shield During In-Vessel Retention

2017 ◽  
Vol 3 (2) ◽  
Author(s):  
Justin H. Spencer
Keyword(s):  
Packed Bed ◽  
Phase Region ◽  
Experimental Investigations ◽  
Wall Region ◽  
Two Phase ◽  
Candu Reactors ◽  
Test Parameters ◽  
Ball Diameter ◽  
The Impact ◽  
Near Wall

This paper presents the results of experimental investigations into two-phase mass transport in a coarse packed bed representing the Canada Deuterium Uranium (CANDU) end shield. This work contributes to understanding of phenomena impacting in-vessel retention (IVR) during postulated severe accidents in CANDU reactors. The air barbotage technique was used to represent boiling at the calandria tubesheet surface facing the inner cavity of the end shield. Qualitative observations of the near-wall two-phase region were made during air injection. In addition, flow visualization was carried out through the addition of dye to the water. Air flow rate, shielding ball diameter, and cavity dimensions were varied within relevant ranges; and the impact of these parameters on the near-wall region was identified. A brief review of the relevant knowledge base is presented, allowing demonstration of the applicability of the test parameters. The observed phenomena are compared to published results involving similar geometries with capillary porous media.

scholarly journals Active control of multiscale features in wall-bounded turbulence

2019 ◽  
Vol 36 (1) ◽  
pp. 12-21 ◽  
Author(s):  
Xiaotong Cui ◽  
Nan Jiang ◽  
Xiaobo Zheng ◽  
Zhanqi Tang
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Turbulent Energy ◽  
Streamwise Velocity ◽  
Discrete Wavelet ◽  
Wall Region ◽  
Mean Velocity ◽  
Pzt Actuator ◽  
The Impact ◽  
Near Wall

Abstract This study experimentally investigates the impact of a single piezoelectric (PZT) actuator on a turbulent boundary layer from a statistical viewpoint. The working conditions of the actuator include a range of frequencies and amplitudes. The streamwise velocity signals in the turbulent boundary layer flow are measured downstream of the actuator using a hot-wire anemometer. The mean velocity profiles and other basic parameters are reported. Spectra results obtained by discrete wavelet decomposition indicate that the PZT vibration primarily influences the near-wall region. The turbulent intensities at different scales suggest that the actuator redistributes the near-wall turbulent energy. The skewness and flatness distributions show that the actuator effectively alters the sweep events and reduces intermittency at smaller scales. Moreover, under the impact of the PZT actuator, the symmetry of vibration scales’ velocity signals is promoted and the structural composition appears in an orderly manner. Probability distribution function results indicate that perturbation causes the fluctuations in vibration scales and smaller scales with high intensity and low intermittency. Based on the flatness factor, the bursting process is also detected. The vibrations reduce the relative intensities of the burst events, indicating that the streamwise vortices in the buffer layer experience direct interference due to the PZT control.

Numerical Study on Near-Wall Natural Convection Over a Microscale Heating Wire

2012 ◽  
Author(s):  
Leping Zhou ◽  
Yunfang Zhang ◽  
Lijun Yang ◽  
Xiaoze Du ◽  
Minami Yoda ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Numerical Study ◽  
Heat Transfer Process ◽  
Brownian Diffusion ◽  
Wall Region ◽  
Two Phase ◽  
Heating Wire ◽  
Transfer Problems ◽  
Near Wall

The study of the natural convection over a very small heat sources is important in the analysis of heat transfer problems in the electronics industry. However, the characteristics of the spatial distribution of the velocity in the near wall region, which is crucial to the mechanisms of heat transfer process in natural convection around a microscale object, is not well understood. In this investigation, the microscale natural convection in the near wall region of a platinum micro heat source was investigated numerically, using FLUENT, a commercially available computational fluid dynamics (CFD) software, and compared with corresponding experimental results. The influence of the nanoparticles on the natural convection was observed using the single-phase or two-phase models available in FLUENT. The temperature and velocity fields were obtained, with which the Brownian diffusion coefficient was deduced. The results indicate that the temperature gradient induced Brownian diffusion and thermophoresis in the near wall region plays an important role in the microscale natural convection in the water/nanoparticle mixture investigated and are in good agreement with the results from a corresponding experimental investigation.

Carbon additives influence on mechanical properties of titanium near-alpha alloy

2019 ◽  
pp. 27-38 ◽  
Author(s):  
O. S. Kashapov ◽  
T. V. Pavlova ◽  
V. S. Kalashnikov ◽  
I. P. Popov
Keyword(s):  
Mechanical Properties ◽  
Titanium Sponge ◽  
Solubility Limit ◽  
Phase Region ◽  
Two Phase ◽  
Carbon Additives ◽  
Negative Effect ◽  
The Impact ◽  
Hammer Forging ◽  
Impact Viscosity

The article considers the influence of carbon in the range from 0.008 to 0.18 mass. % at the temperature of complete polymorphic transformation, microstructure and mechanical properties of near-alphatitanium alloy systems Ti–6.2Al–Sn–Zr–(2.19–3.53) Moeq–(0.18–0.28)Si–(0.008–0.18)С. Alloying with carbon is possible due to special titanium sponge or industrial ligatures. Six experimental forgings performed on bimodal microstructured ingots allowed to establish a rational level of carbon. It is shown that carbon alloying at solubility limit (up to 0.08% by weight) increases the heat resistance of the material, while a similar alloying with silicon gives a greater effect. The carbon effect on the strength at room temperature is negligible. Negative effect of carbon on the impact toughness of the alloys is marked. For the selected carbon alloying level at strength of 1165–1180 MPa, the impact viscosity remains at an acceptable level of KCU = 330–381 kJ/m2 . The alloys of the investigated system allow hot deformation in heavy conditions under hammer forging at relatively low temperatures of the two-phase region.

DEM-CFD Study on Fluid Flow Through Radial Layered Composite Packed Beds

2018 ◽  
Author(s):  
Zehua Guo ◽  
Zhongning Sun ◽  
Nan Zhang ◽  
Ming Ding ◽  
Haozhi Bian ◽  
...  
Keyword(s):  
Fluid Flow ◽  
Packed Bed ◽  
Layered Composite ◽  
Wall Region ◽  
Bypass Flow ◽  
Porosity Distribution ◽  
Container Wall ◽  
The Core ◽  
Core Part ◽  
Near Wall

The radial porosity generally have a higher value at the container wall than that in the core part. Consequently, the fluid flows are mal-distributed in packed bed with significant bypass flow at the wall, which lowers the convective heat transfer performance inside the packed bed. To overcome this drawback of packed bed, we developed an effective way to construct the radial layered composite packed bed, which can easily realize placing small particle at the near wall region and large spheres in the core region. Therefore, smaller pores forms close to the container wall and larger channels presented in the core part. This could result in a much homogenous radial porosity distribution, which is benefit to restrain the bypass flow near the wall. In present paper, the packing procedure is simulated by the discrete element method (DEM). Radial layered composite packed bed and traditional packed bed with uniform spheres are compared on radial porosity distribution. By altering the size of spheres ratios in the near wall region different radial layered packings are also generated and compared. Then, the geometries of these packed bed are imported into the computational fluid dynamics (CFD) simulation. The fluid flow inside the packed bed is investigated. It finds that the radial layered packed bed has a lower pressure drop with the ordered packing structure. And a much homogenous fluid flow distribution is obtained than the traditional, which is benefit for the heat removal inside the packed bed. This would be useful for the optimum design of packed bed in industry applications.

Effects of water–air mixtures on hydraulic transients

2010 ◽  
Vol 37 (9) ◽  
pp. 1189-1200 ◽  
Author(s):  
Oscar Pozos ◽  
Alejandro Sanchez ◽  
Eduardo A. Rodal ◽  
Yuri V. Fairuzov
Keyword(s):  
Bubbly Flow ◽  
Experimental Investigations ◽  
Hydraulic Transients ◽  
Two Phase ◽  
Pressure Transients ◽  
Air Content ◽  
Air Pocket ◽  
Pressurized Pipelines ◽  
Air Pockets ◽  
The Impact

The purpose of this study is to investigate pressurized pipelines and the potential effects on pressure transients of air entrained at the downstream end of large entrapped air pockets followed by a hydraulic jump in pressurized pipelines. The homogeneous two-phase flow model is used to simulate the transient response of the bubbly mixture after a pump shutdown. The results show that pressure transients are significantly reduced with increasing air-pocket volumes and bubbly flow air content. Experimental investigations were carried out to analyze the impact of different air-pocket volumes located at high points of pressurized pipelines. A case study of an existing pumping system was considered to exemplify the impact of the bubbly flow air content on hydraulic transients.

scholarly journals Simulation of Boiling Flow Experiments Close to CHF with the Neptune_CFD Code

2008 ◽  
Vol 2008 ◽  
pp. 1-8 ◽  
Author(s):  
Boštjan Končar ◽  
Borut Mavko
Keyword(s):  
Volume Fraction ◽  
Flow Boiling ◽  
Three Dimensional ◽  
Heated Wall ◽  
Wall Region ◽  
Two Phase ◽  
Subcooled Flow Boiling ◽  
Boiling Flow ◽  
Flow Experiments ◽  
Near Wall

A three-dimensional two-fluid code Neptune_CFD has been validated against the Arizona State University (ASU) and DEBORA boiling flow experiments. Two-phase flow processes in the subcooled flow boiling regime have been studied on ASU experiments. Within this scope a new wall function has been implemented in the Neptune_CFD code aiming to improve the prediction of flow parameters in the near-wall region. The capability of the code to predict the boiling flow regime close to critical heat flux (CHF) conditions has been verified on selected DEBORA experiments. To predict the onset of CHF regime, a simplified model based on the near-wall values of gas volume fraction was used. The results have shown that the code is able to predict the wall temperature increase and the sharp void fraction peak near the heated wall, which are characteristic phenomena for CHF conditions.

Influence of Wall Heating on Turbulent Structure

2007 ◽  
Author(s):  
Shivani T. Gajusingh ◽  
Kamran Siddiqui
Keyword(s):  
Flow Behavior ◽  
Streamwise Velocity ◽  
Wall Region ◽  
Turbulent Regime ◽  
Square Channel ◽  
Wall Heating ◽  
Turbulent Characteristics ◽  
The Mean ◽  
The Impact ◽  
Near Wall

An experimental study was conducted to investigate the impact of wall heating on the flow structure in the near-wall region inside a square channel. PIV was used to measure the two-dimensional velocity fields. The measurements were conducted for a range of mass flow rates that cover laminar and turbulent regimes. The results have shown that when a flow is unstably stratified via heating through a bottom wall, both the mean and turbulent characteristics are affected. The results have shown that the impact of wall heating on the flow behavior is significantly different for laminar and turbulent flow regimes. It was found that when a flow that is originally laminar is heated, the mean streamwise velocity in the near-wall region is significantly increased and turbulence is generated in the flow predominantly due to buoyancy. When the flow is in the turbulent regime, addition of heat reduces the magnitudes of mean streamwise velocity and turbulent properties. The reduction in the magnitudes of turbulent properties in this flow regime is due to the working of turbulence against the buoyancy forces.

scholarly journals Relationship between wear formation and large-particle motion in a pipe bend

2019 ◽  
Vol 6 (1) ◽  
pp. 181254 ◽  
Author(s):  
Yi Li ◽  
Hebing Zhang ◽  
Zhe Lin ◽  
Zhaohui He ◽  
Jialiang Xiang ◽  
...  
Keyword(s):  
Particle Motion ◽  
Mass Concentration ◽  
Granular System ◽  
Wall Region ◽  
Two Phase ◽  
Pipe Bend ◽  
Discrete Element Method Simulation ◽  
Large Particles ◽  
Solid Liquid ◽  
The Impact

Fine and large particles flowing through a bend in a pipe move differently and therefore erode the pipe differently. This paper simulates solid–liquid two-phase flow containing large particles in a bend and analyses the relationship between the wear formation and particle motion. Wear experiments are carried out using 3-mm glass bead particles at a mass concentration of 1–15%. At the same time, the flow field and the motion of the granular system are obtained in computational fluid dynamics–discrete element method simulation. The wear formation mechanism is revealed by comparing experiments with numerical simulations. The wear rate of the wall surface increases with the mass concentration, while the marginal growth rate decreases as the mass concentration increases. As the mass concentration increases to a certain value, the degree of wear reaches a maximum and remains unchanged subsequently because of the formation of a particle barrier along the bend wall. The particles near the wall region will bounce forward because of the periodic disturbance flow around particles. The impact of mass bouncing particles causes the formation of the erosion ripple on the test sheet.

Modeling of Turbulent Swirl Stabilized Flame With Flamelet Generated Manifold and Hybrid LES-RANS Turbulence Model

2019 ◽  
Author(s):  
Ishan Verma ◽  
Rakesh Yadav ◽  
Patrick Sharkey ◽  
Shaoping Li ◽  
Ellen Meeks
Keyword(s):  
Experimental Data ◽  
Operating Conditions ◽  
Scalar Dissipation ◽  
Wall Region ◽  
The Core ◽  
Eddy Simulation ◽  
Flamelet Generated Manifold ◽  
The Impact ◽  
Blending Function ◽  
Near Wall

Abstract Hybrid turbulence modeling is a practical approach to efficiently model the wall-bounded turbulent flows. In this paper, a stress-blended eddy simulation (SBES) model is used with the flamelet generated manifold model (FGM) for modeling turbulent combustion. In the current SBES, the near-wall region is modeled using a two-equation k-ω Reynolds-averaged Navier-Strokes (RANS) formulation, and switches to a large eddy simulation (LES) model in the core region using a blending function. Similarly, the turbulence-related combustion modeling parameters, such as the variances in scalar transport equations and scalar dissipation, are also blended using the same blending function. This combined hybrid FGM-SBES approach is implemented into ANSYS Fluent software and then used to model a swirl-stabilized flame. The flame used is a methane-fueled burner, developed at DLR Stuttgart as the PRECCINSTA combustor. The experimental data for this combustor are available for multiple operating conditions. A stable operating point (φ = 0.83, P = 30 kW) is chosen. The current FGM-SBES results are compared with experimental data as well as with FGM-LES computations. Differences in predictions of mean and variance of reaction progress and mixture fraction in the core versus the near wall region are analyzed and quantified. The impact of the differences in these parameters is then evaluated by comparing temperature and species mass fractions. The findings from the current work, in terms of accuracy, validity and best practices when modeling wall-bounded flows with FGM-SBES are discussed and summarized.

Effect of Austenite Grain Size on Hardenability and Impact Toughness of SCM435H

2016 ◽  
Vol 867 ◽  
pp. 50-54
Author(s):  
Ji Lin Chen ◽  
Shi Peng Ruan ◽  
Li Jun Wang ◽  
Jin Po Zhai ◽  
Chao Liu
Keyword(s):  
Grain Size ◽  
Impact Toughness ◽  
Phase Region ◽  
Material Strength ◽  
Two Phase ◽  
Quenching Temperature ◽  
Austenite Grain Size ◽  
Austenite Grain ◽  
Strength And Plasticity ◽  
The Impact

The effects of austenite grain size on hardenability and impact toughness were investigated. The results show that: Since the beginning of the two-phase region with quenching temperature, the austenite grain size from the initial 4+6 mixed crystal at 740°C, and gradually increased to 10 at 860°C; Austenite grain size and hardenability was directly proportional to the austenite grain size increased from 8μm to 36μm, the biggest change is the hardness 10HRC; Austenite grain size and impact toughness is linear, with the decrease of grain size, the impact energy increases linearly, and the austenite grain size and impact toughness curve fitting. Comprehensive analysis for ensuring the hardenability of cold heading steels should be considered optimal matching of material strength and plasticity.

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