scholarly journals Two-Phase Turbulence Statistics from High Fidelity Dispersed Droplet Flow Simulations in a Pressurized Water Reactor (PWR) Sub-Channel with Mixing Vanes

Fluids ◽  
2021 ◽  
Vol 6 (2) ◽  
pp. 72
Author(s):  
Nadish Saini ◽  
Igor A. Bolotnov
Keyword(s):  
Continuous Phase ◽  
System Level ◽  
Data Repository ◽  
High Fidelity ◽  
Turbulence Statistics ◽  
Two Phase ◽  
Pressurized Water ◽  
Droplet Dynamics ◽  
High Resolution Data ◽  
Spacer Grids

In the dispersed flow film boiling regime (DFFB), which exists under post-LOCA (loss-of-coolant accident) conditions in pressurized water reactors (PWRs), there is a complex interplay between droplet dynamics and turbulence in the surrounding steam. Experiments have accredited particular significance to droplet collision with the spacer-grids and mixing vane structures and their consequent positive feedback to the heat transfer recorded in the immediate downstream vicinity. Enabled by high-performance computing (HPC) systems and a massively parallel finite element-based flow solver—PHASTA (Parallel Hierarchic Adaptive Stabilized Transient Analysis)—this work presents high fidelity interface capturing, two-phase, adiabatic simulations in a PWR sub-channel with spacer grids and mixing vanes. Selected flow conditions for the simulations are informed by the experimental data found in the literature, including the steam Reynolds number and collision Weber number (Wec={40,80}), and are characteristic of the DFFB regime. Data were collected from the simulations at an unprecedented resolution, which provides detailed insights into the continuous phase turbulence statistics, highlighting the effects of the presence of droplets and the comparative effect of different Weber numbers on turbulence in the surrounding steam. Further, axial evolution of droplet dynamics was analyzed through cross-sectionally averaged quantities, including droplet volume, surface area and Sauter mean diameter (SMD). The downstream SMD values agree well with the existing empirical correlations for the selected range of Wec. The high-resolution data repository from the simulations herein is expected to be of significance to guide model development for system-level thermal hydraulic codes.

Phase Inversion in Two-Phase Liquid Systems

1992 ◽  
Vol 57 (7) ◽  
pp. 1419-1423
Author(s):  
Jindřich Weiss
Keyword(s):  
Interfacial Tension ◽  
Phase Inversion ◽  
Continuous Phase ◽  
Considerable Effect ◽  
Weak Dependence ◽  
Dispersed Phase ◽  
Two Phase ◽  
Liquid Systems ◽  
Phase Liquid

New data on critical holdups of dispersed phase were measured at which the phase inversion took place. The systems studied differed in the ratio of phase viscosities and interfacial tension. A weak dependence was found of critical holdups on the impeller revolutions and on the material contactor; on the contrary, a considerable effect of viscosity was found out as far as the viscosity of continuous phase exceeded that of dispersed phase.

Formation of Two-Phase Multiple Emulsions by Inclusion of Continuous Phase into Dispersed Phase

Langmuir ◽  
2002 ◽  
Vol 18 (20) ◽  
pp. 7334-7340 ◽  
Author(s):  
Jong-Moon Lee ◽  
Kyung-Hee Lim ◽  
Duane H. Smith
Keyword(s):  
Continuous Phase ◽  
Dispersed Phase ◽  
Two Phase ◽  
Multiple Emulsions

Direct Coupling of a Two-Dimensional Fan Model in a Turbofan Engine Performance Simulation

2016 ◽  
Author(s):  
Ioannis Templalexis ◽  
Alexios Alexiou ◽  
Vassilios Pachidis ◽  
Ioannis Roumeliotis ◽  
Nikolaos Aretakis
Keyword(s):  
Three Dimensional ◽  
Engine Performance ◽  
System Level ◽  
Design Parameters ◽  
High Fidelity ◽  
Two Dimensional ◽  
Performance Simulation ◽  
Cfd Models ◽  
Component Design ◽  
Complex Phenomena

Coupling of high fidelity component calculations with overall engine performance simulations (zooming) can provide more accurate physics and geometry based estimates of component performance. Such a simulation strategy offers the ability to study complex phenomena and their effects on engine performance and enables component design changes to be studied at engine system level. Additionally, component interaction effects can be better captured. Overall, this approach can reduce the need for testing and the engine development time and cost. Different coupling methods and tools have been proposed and developed over the years ranging from integrating the results of the high fidelity code through conventional performance component maps to fully-integrated three-dimensional CFD models. The present paper deals with the direct integration of an in-house two-dimensional (through flow) streamline curvature code (SOCRATES) in a commercial engine performance simulation environment (PROOSIS) with the aim to establish the necessary coupling methodology that will allow future advanced studies to be performed (e.g. engine condition diagnosis, design optimization, mission analysis, distorted flow). A notional two-shaft turbofan model typical for light business jets and trainer aircraft is initially created using components with conventional map-defined performance. Next, a derivative model is produced where the fan component is replaced with one that integrates the high fidelity code. For both cases, an operating line is simulated at sea-level static take-off conditions and their performances are compared. Finally, the versatility of the approach is further demonstrated through a parametric study of various fan design parameters for a better thermodynamic matching with the driving turbine at design point operation.

RBHT Steam Cooling and Droplet Injection Pre-Test Analysis Using COBRA-TF

2001 ◽  
Author(s):  
C. Frepoli ◽  
A. J. Ireland ◽  
L. E. Hochreiter ◽  
F. B. Cheung
Keyword(s):  
Heat Transfer ◽  
Local Heat Transfer ◽  
Injection System ◽  
Test Facility ◽  
Film Boiling ◽  
Two Phase ◽  
Field Representation ◽  
Dispersed Flow ◽  
Spacer Grids ◽  
Flow Film Boiling

Abstract The droplet injection experiments to be performed in a 7 × 7 rod bundle heat transfer test facility are being simulated using an advanced thermal hydraulics computer code called COBRA-TF. A current version of the code, which provides a three-dimensional, two-fluid, three-field representation of the two-phase flow, is modified to facilitate the simulation of the droplet field produced by the injection system in the test facility. The liquid phase is split into a continuous liquid field and droplet field where a separate momentum and mass equation is solved for each field, with the effects of spacer grids being properly accounted for. Pre-test analyses using the modified COBRA-TF code have been conducted for different injection conditions. Results indicate that there are specific ranges of conditions that can be simulated within the facility constraints to provide for validation of the dispersed flow film boiling models. The numerical results also show important effects of the spacer grids on the local heat transfer in the dispersed flow film boiling regime.

scholarly journals NUMERICAL SIMULATION OF AIR – WATER FLOWS IN AN EVAPORATIVE CONDENSER

2009 ◽  
Vol 8 (1) ◽  
pp. 24 ◽  
Author(s):  
I. C. Acunha Jr ◽  
P. S. Schneider
Keyword(s):  
Turbulent Flows ◽  
Simple Algorithm ◽  
Continuous Phase ◽  
Velocity Fields ◽  
Temperature Fields ◽  
Two Phase ◽  
Equipment Manufacturer ◽  
Functional Aspects ◽  
Water Behavior ◽  
Complex Phenomena

Evaporative condensers present a hard problem for numerical modeling because of the complex phenomena of heat and mass transfer outside of the bundle tubes in turbulent flows. The goal of this work is to study the air and water behavior inside an evaporative condenser operating with ammonia as the refrigerant fluid. A commercial CFD software package (FLUENT) is employed to predict the two-phase flow of air and water droplets in this equipment. The air flow is modeled as a continuous phase using the Eulerian approach while the droplets water flow is modeled as a disperse phase with Lagrangian approach. The coupling between pressure and velocity fields is performed by the SIMPLE algorithm. The pressure, velocity and temperature fields are used to perform qualitative analyses to identify functional aspects of the condenser, while the temperature and the relative humidity evolution contributed to verify the agreement between the results obtained with the numerical model and those presented by equipment manufacturer.

An Experimental Study of Mist/Air Film Cooling With Fan-Shaped Holes on an Extended Flat Plate—Part II: Two-Phase Flow Measurements and Droplet Dynamics

2017 ◽  
Vol 140 (4) ◽  
Author(s):  
Reda Ragab ◽  
Ting Wang
Keyword(s):  
Flow Behavior ◽  
Data Rate ◽  
Main Flow ◽  
Shear Stresses ◽  
Two Phase ◽  
Flow Measurements ◽  
Droplet Dynamics ◽  
Mist Flow ◽  
Film Layer ◽  
Upper Boundary

A phase Doppler particle analyzer (PDPA) system is employed to measure the two-phase mist flow behavior including flow velocity field, droplet size distribution, droplet dynamics, and turbulence characteristics. Based on the droplet measurements made through PDPA, a projected profile describing how the air–mist coolant jet flow spreads and eventually blends into the hot main flow is prescribed for both cylindrical and fan-shaped holes. The mist film layer consists of two layers: a typical coolant film layer (cooling air containing the majority of the droplets) and a wider droplet layer containing droplets outside the film layer. Thanks to the higher inertia possessed by larger droplets (>20 μm in diameter) at the injection hole, the larger droplets tend to shoot across the coolant film layer, resulting in a wider droplet layer than the coolant film layer. The wider droplet layer boundaries are detected by measuring the droplet data rate (droplet number per second) distribution, and it is identified by a wedge-shaped enclosure prescribed by the data rate distribution curve. The coolant film layer is prescribed by its core and its upper boundary. The apex of the data rate curve, depicted by the maximum data rate, roughly indicates the core region of the coolant film layer. The upper boundary of the coolant film layer, characterized by active mixing with the main flow, is found to be close to relatively high values of local Reynolds shear stresses. With the results of PDPA measurements and the prescribed coolant film and droplet layer profiles, the heat transfer results on the wall presented in Part I are re-examined, and the fundamental mist-flow physics are analyzed. The three-dimensional (3D) droplet measurements show that the droplets injected from the fan-shaped holes tend to spread wider in lateral direction than cylinder holes and accumulate at the location where the neighboring coolant film layers meet. This flow and droplet behavior explain the higher cooling performance as well as mist-enhancement occurs between the fan-shaped cooling holes, rather than along the hole's centerline as demonstrated in the case using the cylindrical holes.

scholarly journals Prediction Models of Droplet Characteristics Based on the Locally Convergent Configurations in PMMA Microchips

2021 ◽  
Vol 2097 (1) ◽  
pp. 012027
Author(s):  
Zhongxin Liu ◽  
Zhiliang Wang ◽  
Chao Wang ◽  
Jinsong Zhang
Keyword(s):  
Flow Rate ◽  
Relative Position ◽  
Prediction Models ◽  
Continuous Phase ◽  
Lubricating Oil ◽  
Flow Rate Ratio ◽  
Phase Flow ◽  
Exponential Relationship ◽  
Two Phase ◽  
Relationship Of

Abstract This paper novel designed the local convergence configuration in the coaxial channels to study the two-phase flow (lubricating oil (continuous phase, flow rate Q c)/deionized water (dispersed phase, flow rate Q d)). Two geometric control variables, the relative position (x) and tapering characteristics (α), had the different effects on the droplet formation. The increase of relative position x caused the higher frequency and finer droplets, and the increase of convergence angle α, took the opposite effects. The results indicated that the equivalent dimensionless droplet length Ld/Wout and the flow rate ratio Qd/Qc had an exponential relationship of about 1/2. Similarly, it was found that the dispersed droplets generating frequency and the two-phase capillary number, CaTP = uTPμc/σ, had an exponential relationship. The advantage of the convergent configurations in micro-channel was the size and efficiency of droplet generation was very favorable to be controlled by α and x.

Numerical Simulation and Analysis of Effect of Injection Volume on Biomass Particle Cyclone Venturi Dryer

2021 ◽  
Author(s):  
Guohai Jia ◽  
Guoshuai Tian ◽  
Zicheng Gao ◽  
Dan Huang ◽  
Wei Li ◽  
...  
Keyword(s):  
High Speed ◽  
Optimization Design ◽  
Gas Flow ◽  
Continuous Phase ◽  
Temperature Fields ◽  
Maximum Pressure ◽  
Two Phase ◽  
Velocity Change ◽  
Injection Volume ◽  
Wood Debris

Abstract Cyclone venturi dryer is suitable for drying materials with large particle size and wide distribution. The working process of cyclone venturi dryer is a very complicated three-dimensional and turbulent motion, so it is difficult to be studied theoretically and experimentally. In order to study the internal flow characteristics of the biomass particle cyclone venturi dryer, the computational fluid dynamics (CFD) software was used to simulate the gas-solid two-phase flow field inside the cyclone venturi dryer. The continuous phase adopts the Realizable k-ε turbulence model and the particle phase is discrete. The effects of different injection volume on the pressure, velocity, and temperature fields inside a cyclone venturi dryer were analyzed. The results showed that the maximum pressure drop and velocity change inside the dryer were at the venturi pipe. The wet material of the cyclone venturi dryer was inhaled into the venturi contraction tube by the negative pressure formed after the highspeed airflow was ejected, thus the mixture was completed in the venturi throat. The wood debris material was mixed with the high-speed hot gas flow in the venturi throat and then sprayed into the diffusion pipe. In the diffusion pipe of venturi, the heat and mass transfer process of wet wood debris and heat flow in venturi diffusion tube was completed. It is in good agreement with the simulation results. This study can provide a reference for the optimization design of the related cyclone venturi dryer structure.

scholarly journals Numerical Investigation on the Flow Characteristics in a 17 × 17 Full-Scale Fuel Assembly

Energies ◽  
2020 ◽  
Vol 13 (2) ◽  
pp. 397 ◽  
Author(s):  
Zihao Tian ◽  
Lixin Yang ◽  
Shuang Han ◽  
Xiaofei Yuan ◽  
Hongyan Lu ◽  
...  
Keyword(s):  
Fuel Assembly ◽  
Flow Characteristics ◽  
Full Scale ◽  
Pressurized Water Reactor ◽  
Lateral Velocity ◽  
Pressurized Water ◽  
Spacer Grids ◽  
Rod Bundle ◽  
Real Size ◽  
Cfd Method

In a previous study, several computational fluid dynamics (CFD) simulations of fuel assembly thermal-hydraulic problems were presented that contained fewer fuel rods, such as 3 × 3 and 5 × 5, due to limited computer capacity. However, a typical AFA-3G fuel assembly consists of 17 × 17 rods. The pressure drop levels and flow details in the whole fuel assembly, and even in the pressurized water reactor (PWR), are not available. Hence, an appropriate CFD method for a full-scale 17 × 17 fuel assembly was the focus of this study. The spacer grids with mixing vanes, springs, and dimples were considered. The polyhedral and extruded mesh was generated using Star-CCM+ software and the total mesh number was about 200 million. The axial and lateral velocity distribution in the sub-channels was investigated. The pressure distribution downstream of different spacer grids were also obtained. As a result, an appropriate method for full-scale rod bundle simulations was obtained. The CFD analysis of thermal-hydraulic problems in a reactor coolant system can be widely conducted by using real-size fuel assembly models.

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