Commercial Computational Fluid Dynamics Research Articles

Numerical and experimental study of a thermosyphon closed‐loop system for domestic applications

AbstractA numerical and experimental study has been conducted to enhance the thermal performance of the thermosyphon system. The enhancement response focused on the temperature of both the working fluid within the system loop and water inside the tank. To achieve this, three models were investigated to increase the surface area of the riser pipe without changing the amount of the working fluid. The first one (model A) involved increasing the diameter of the riser pipe and inserting a closed tube inside it to maintain the same amount of working fluid. The second method (model B) involved adding toroidal fins around the riser pipe. However, the third model (model C) combined both models (A and B). The thermal performance of the thermosyphon system for the conventional model has been compared experimentally. Furthermore, numerical simulations for all cases have been done using commercial computational fluid dynamics, ANSYS R 19.3 software. The results show that there is good agreement between the experimental and numerical results. Furthermore, it is found that the thermal responses of models A and B are approximately equal and both are higher than that of the traditional model. Moreover, the thermal performance of model C is found to be higher than those of all the other models under study.

Computational fluid dynamics analysis of ventilation characteristics with various design parameters in single-span greenhouses

ABSTRACT With the advent of the fourth industrial revolution, smart farming technology is being introduced that can properly maintain the growing environment of crops remotely and automatically by grafting information and communication technology (ICT) to greenhouses. To maintain an appropriate growth environment for these crops, the effects of the greenhouse design parameters on these environments need to be evaluated. In this study, the thermal and flow characteristics in the single-span greenhouse were examined with commercial computational fluid dynamics (CFD) code. To validate the numerical method applied herein, the numerical results of the temperature distribution at several monitoring points were compared with the experimental results. The low-average error rate (0.87–1.90%) between them was measured and the numerical results of the temperature distribution exhibited good agreement with the experimental data. In addition, a parametric study was conducted to determine the effects of the various design parameters on the ventilation performance. These study findings will offer appropriate data for design guidelines for greenhouses.

Numerical study of serpentine flow field designs effect on proton exchange membrane fuel cell (PEMFC) performance

Abstract The design of flow field greatly influences Proton Exchange Membrane Fuel Cell (PEMFC) performance, as it not only distributes the reactants, also removes the product (water) from the cell. Improper water removal blocks the reaction sites, which results in mass transport losses. A complete 3-D numerical model of PEMFC with a single serpentine (1-S), double serpentine (2-S),triple serpentine (3-S) and 3-2-1 serpentine flow fields with round corner was designed with the help of commercial Computational Fluid Dynamics (CFD) code ANSYS FLUENT. Simulations were carried out to investigate the effect of four flow fields on distribution of pressure, mass fraction of H2, O2, current flux density distribution, water content of membrane, and liquid water activity in the flow channels as well as the functioning of cells. Performance properties of proposed four designs were evaluated and found that 3-2-1 serpentine flow field performance is better than the 1-S, 2-S, and 3-S flow fields for the given flow rates of reactants and this 3-2-1 serpentine flow field model was validated with literature experimental data. The results also show that the velocity in channels increases with a decrease in the number of flow passes, which improve the reactions in the catalyst layers, reaction product removal from the cell thus reduces the concentration losses and improves the cell performance.

CFD Simulation on Workability of a Seaweed Harvesting Boat Due to Wake-Wash

In the present study, a 2-ton class seaweed harvesting boat was optimized by employing a W-shape hull form to reduce roll motion due to wake-wash from passing boats. A series of numerical simulations were conducted using Star-CCM+, a commercial CFD (computational fluid dynamics) software, to improve workability by optimizing the hull form from the conventional design (original hull form). The 2-dimensional roll decay motion of various hull forms with W-shape midsection were simulated and the hull form with the best performance in free roll decay test was selected. To evaluate stability of each hull in wake-wash, the original or optimized hull was alternately located at the middle of a computational domain as a target ship while an advancing ship (original hull) moved forward generating Kelvin waves which impact the original or optimized boat. Two kinds of working conditions, i.e., ballast and full loading conditions, of the target ship were considered with and without initial roll angle. It was observed through the comparison of motion between the original and optimized hulls a decrement of roll motion for the optimized ship demonstrating the effectiveness of the W-shape hull. Decrement of roll motion was observed for both working conditions. Additionally, the optimized W-shape hull showed an extraordinary performance under the ballast condition without initial roll angle.

Slagging behavior modeling in coal gasifiers using two-way coupled slag model with CFD

In pulverized-coal gasifiers, wall slagging behavior is an important issue associated with ash handling and discharge. Numerical methods have been widely employed to predict the slag flow and heat transfer on the gasifier wall. However, most of the analytical models are only one-way coupled with the simulation of the gasification reactor. In the present study, the slag model was integrated into a commercial computational fluid dynamics (CFD) solver to achieve two-way coupling. The coupled mass, momentum and energy equations were solved iteratively until convergence. The simulations of a simplified gasifier show that the solid slag thickness was seriously affected by the heat flux from gas to slag surface. The proposed two-way coupled slag model was able to give more reasonable predictions compared with other offline slag models since the heat transfer between the gas and the slag could be modeled more accurately. Through analyzing the energy balance in the slag layer, it is found that most of the heat flux from gas was extracted by the cooling water. However, the effect of the heat flux absorbed by the flowing liquid slag became important under high gas temperatures and ash deposition rates.

Thermal-hydraulic analysis of a 7-pin sodium-cooled fast reactor wire-wrapped fuel bundle

The thermal-hydraulic characteristics of 7-pin sodium-cooled fast reactor (SFR) wire-wrapped fuel bundle were numerically investigated by commercial computational fluid dynamics (CFD) code ANSYS Fluent. The sensitivity analyses of mesh size, geometric simplification and Reynolds-Averaged Navier–Stokes (RANS) model were conducted. The turbulent Prandtl number model was adopted. The flow field and heat transfer were analyzed. The results show that the geometric simplification has great influences on friction factor and Nusselt number. The simplification should be taken into consideration seriously. The results of the standard k-ε model, realizable k-ε model and Reynolds stress model (RSM) model are close. The results of the Shear Stress Transport (SST) k-ω model has the maximum error compared with experiment correlation. The strong secondary flows and eddies were observed. The flow velocity near the contact of wire and rod is low and causes high temperature. At the cross section of z=50mm, the difference between the highest and lowest temperatures of the central rod is 13K, and the highest and lowest local Nusselt Numbers are 2.29 and 4.07 respectively, which indicates that the inhomogeneity of heat transfer is considerable. The velocity distribution of the boundary layer agrees well with the law-of-the-wall while the temperature boundary layer is much thicker than that of velocity. At least at y+<100, heat transfer is dominated by molecular heat conduction. At high Peclet number, the default value 0.85 of turbulent Prandtl number overestimates the heat transfer performance and the results of Kays model are closer to the experiment correlation. At very low Peclet number, Kays model has a quite different from experiment correlation. This study provides a reference for SFR design.

Computational optimization of reactivity controlled compression ignition combustion to achieve high efficiency and clean combustion

One of the major limitations of reactivity controlled compression ignition is higher unburned hydrocarbon and carbon monoxide emissions and lower thermal efficiency at part load operating conditions. In the present study, a combined numerical approach using a commercial three-dimensional computational fluid dynamics code CONVERGE along with artificial neural network and genetic algorithm is presented to address the above limitation. A production light-duty diesel engine is modified to run in reactivity controlled compression ignition by replacing an existing mechanical fuel injection system with a flexible electronic port fuel injection and common rail direct injection systems. The injection schedules of port fuel injection and direct injection injectors are controlled using National Instruments port and direct injection driver modules. Upon validation of combustion and emission parameters, parametric investigations are carried out to establish the effects of direct-injected diesel fuel timing start of injection (SOI), premixed fuel ratio and intake charge temperature on the engine performance and emissions in reactivity controlled compression ignition. The results obtained show that the start of injection timing and intake charge temperature significantly influence combustion phasing, while the premixed fuel ratio controls mixture reactivity and combustion quality. By utilizing the data generated with the validated computational fluid dynamics models, the artificial neural network models are trained to predict the engine exhaust emissions and efficiency. The artificial neural network models for gross indicated efficiency and oxides of nitrogen (NOx) are then coupled with genetic algorithm to maximize gross indicated efficiency while keeping the NOx and soot emissions within Euro VI emission limits. By optimizing the start of injection timing, premixed fuel ratio and intake charge temperature simultaneously using the artificial neural network models coupled with genetic algorithm, 19% improvement in gross indicated efficiency, 60% and 64% reduction in hydrocarbon and carbon monoxide emissions, respectively, are obtained in reactivity controlled compression ignition compared to the baseline case.

Reduced kinetic model for the combustion of n-cetane and heptamethylnonane based on a primary reference fuel reduced kinetic model

A reduced kinetic model for the combustion of n-heptane, i-octane, n-cetane and heptamethylnonane was developed based on a prior model designed for use with a primary reference fuel consisting of n-heptane and i-octane. The present model, which can be easily employed in conjunction with a conventional computational fluid dynamics code, contains 59 chemical species and 96 reactions. Predicted ignition delay times under high pressure and temperature conditions were generated using this new kinetic model and compared with those obtained from full kinetic models. The results indicate that the general trends exhibited by the ignition delay times as temperature and pressure are varied are accurately predicted with this reduced model. The present model was also combined with a commercial computational fluid dynamics code and used to simulate the ignition of a diesel spray at high pressure and temperature. Finally, the effects of the cetane number of the fuel on the ignition process were investigated.

진공 청소기 내 PCB 냉각 성능 개선을 위한 히트 싱크 최적화 연구

In the present study, the numerical investigation was carried out for a system in a vacuum cleaner with the heat sinks. Optimization model for the heat sink was developed using the commercial computational fluid dynamics code FLUENT. The cooling performance of the vacuum cleaner was analyzed by a visualization technique of temperature variation. In this study, the porous medium approach was employed to specify the flow resistance and pressure drop in the dust filter. As a result, the data obtained with the numerical method was generally in good agreement with those obtained by the experiments. Detailed effects of the various parameters of heat sinks were discussed, and consequently these parameters had a great influence upon the cooling performance of the vacuum cleaner.

A CFD Investigation of a 2D Balanced Vane Pump Focusing on Leakage Flows and Multiphase Flow Characteristics

Vane pumps are often applied in automatic transmission systems of vehicles. Future applications require the oil pumps to be more efficient and to be able to handle multiphase flow pumping situations to a certain extend. To fulfill these requirements, efficient development tools are needed. Therefore, a less demanding computational 2D model of a fixed-type balanced vane pump was derived and numerically analyzed with the commercial computational fluid dynamics (CFD) software ANSYS CFX. The meshing of the rotating parts was done with TwinMesh, using a moving mesh approach. At first, a mesh convergence study was performed. It was shown that the resolution of the radial clearances in particular had a significant influence on the predicted leakages and the volumetric efficiency. The leakage was further investigated concerning the dependence on rotational speed and delivery pressure. In the next step, multiphase flows were considered. In a first setup, vapor cavitation was analyzed and the influence of the alignment of the suction ports on its onset was derived. In a second setup, the influence of different inlet volume fractions of free air was evaluated. The employed multiphase modeling approach was presented and a sensitivity analysis on modeling parameters was performed. Overall, it was shown that free air in the suction ports changed the pumping characteristic of the vane pump significantly. Pressure and flow ripple increased, and the volumetric efficiency and the mean power demand decreased significantly with an increasing inlet volume fraction.

CFD Simulations of Radiative Heat Transport in Open-Cell Foam Catalytic Reactors

The heat transport management in catalytic reactors is crucial for the overall reactor performance. For small-scale dynamically-operated reactors, open-cell foams have shown advantageous heat transport characteristics over conventional pellet catalyst carriers. To design efficient and safe foam reactors as well as to deploy reliable engineering models, a thorough understanding of the three heat transport mechanisms, i.e., conduction, convection, and thermal radiation, is needed. Whereas conduction and convection have been studied extensively, the contribution of thermal radiation to the overall heat transport in open-cell foam reactors requires further investigation. In this study, we simulated a conjugate heat transfer case of a µCT based foam reactor using OpenFOAM and verified the model against a commercial computational fluid dynamics (CFD) code (STAR-CCM+). We further explicitly quantified the deviation made when radiation is not considered. We studied the effect of the solid thermal conductivity, the superficial velocity and surface emissivities in ranges that are relevant for heterogeneous catalysis applications (solid thermal conductivities 1–200 W m−1 K−1; superficial velocities 0.1–0.5 m s−1; surface emissivities 0.1–1). Moreover, the temperature levels correspond to a range of exo- and endothermal reactions, such as CO2 methanation, dry reforming of methane, and methane steam reforming. We found a significant influence of radiation on heat flows (deviations up to 24%) and temperature increases (deviations up to 400 K) for elevated temperature levels, low superficial velocities, low solid thermal conductivities and high surface emissivities.

Turbulent heat transfer enhancement in an axially rotating pipe fitted with kenics segment mixer

This study reports heat transfer in an axially rotating pipe fitted with Kenics segment mixer. Numerical simulations were processed with the commercial finite volume Computational Fluid Dynamics (CFD) code, ANSYS Fluent 19.2. The rotating domain was modeled with the single rotating reference frame scheme. Natural convection was considered in the numerical procedure. Computations were carried out for axial Reynolds numbers between 5000 and 25,000 ​at different rotation rates. Rotation rate (N) is the ratio of the rotational Reynolds number to the axial Reynolds number. Predictions revealed that the Kenics segment mixer significantly improved the heat transfer of the rotating pipe. This remarkable augmentation in heat transfer was attributed to additional swirl flow created by the inserted tape. By using the Kenics segment mixer with twist ratio of 1.75, the Nusselt number of the plain rotating pipe was augmented by 92–66% at N ​= ​1, 74-55% at N ​= ​3, and 60-44% at N ​= ​5. Reduction in Nusselt number augmentation as the rotating speed of the pipe increased indicated that swirl flows induced by the Kenics segment mixer was more dominant at lower rotation rates.

Experimental and Numerical Investigations of Subcooled Boiling Heat Transfer in a Small-Diameter Tube

Abstract The boiling heat transfer for subcooled water flowing in a small-diameter tube was investigated experimentally and numerically. In the experiment, a platinum tube was used as an experimental tube (d = 1.0–2.0 mm) to conduct joule heating by direct current. The heat generation rate of the tube was controlled with an exponential function. The numerical simulation of boiling heat transfer for subcooled water flowing in the small-diameter tube was conducted using the commercial computational fluid dynamics (CFD) code, phoenics ver. 2013. The small-diameter tube was modeled in the simulation. As the boundary condition, the measured heat flux was given at the inner wall. The inlet temperature ranged from 302 to 312 K. The flow velocities of d = 1.0 mm and d = 2.0 mm were 9.29 m/s and 2.34 m/s, respectively. The three-dimensional analysis was carried out from non-boiling to the critical heat flux (CHF). Governing equations were discretized using the finite volume method in the phoenics. The semi-implicit method for pressure linked equation (SIMPLE) method was applied in the numerical simulation. For modeling boiling phenomena in the tube, the Eulerian–Eulerian two-fluid model was adopted using the interphase slip algorithm of phoenics. The surface temperature difference increased as the heat flux increased in the experiment. The numerical simulation predicted the experimental data well. When the heat flux of the experiment reached the CHF point, the predicted value of the heat transfer coefficient was approximately 3.5% lower than that of the experiment.

Numerical assessment of the vulnerability to impact erosion of a pump as turbine in a water supply system

Abstract Nowadays, the installation of pumps as turbines (PATs) in water supply systems (WSSs) is considered attractive because it is able to effectively combine the pressure regulation with the small-scale hydropower generation. One critical aspect concerns the behaviour of the PAT in the presence of solid particles in the flow which impinge against the inner surface of the device, producing a loss of material termed impact erosion. In this paper, the numerical assessment of PAT erosion is performed, by referring, as a case study, to an existing pressure control station in Southern Italy. The variable operative strategy (VOS) was applied to derive the frequency distribution of flow rates over the PAT operation, under the hypothesis of performing the hydraulic regulation of the hydropower plant. The commercial computational fluid dynamics (CFD) code Ansys Fluent was employed for simulating the liquid–solid flow inside the PAT and then coupled with an in-house code to estimate the erosion. The vulnerability of the PAT to wear was analysed by varying its flow rate, aiming at characterizing the decay of PAT components at a constant rotational speed. Finally, a detailed characterization of the PAT response to the particle impingement at its best efficiency point (BEP) was developed and discussed.

Determination of Drag and Lift Related Coefficients of an AUV Using Computational and Experimental Fluid Dynamics Methods

Determination of hydrodynamic coefficients is a vital part of predicting the dynamic behavior of an Autonomous Underwater Vehicle (AUV). The aim of the present study was to determine the drag and lift related hydrodynamic coefficients of a research AUV, using Computational and Experimental Fluid Dynamics methods. Experimental tests were carried out at AUV speed of 1.5 m s-1 for two general cases: I. AUV without control surfaces (Hull) at various angles of attack in order to calculate Hull related hydrodynamic coefficients and II. AUV with control surfaces at zero angle of attack but in different stern angles to calculate hydrodynamic coefficients related to control surfaces. All the experiments carried out in a towing tank were also simulated by a commercial computational fluid dynamics (CFD) code. The hydrodynamic coefficients obtained from the numerical simulations were in close agreement with those obtained from the experiments.

Flow Past a Circular Cylinder: A Comparison Between Commercial Finite Volume and Finite Element Codes

This study compares the numerical analyzes of two commercial computational fluid dynamics (CFD) software programs: Ansys® CFX 14.5, based on the finite volume method (FVM); and Altair® AcuSolve 13.0, based on the finite element method (FEM). For this purpose, the flow around a circular cylinder inserted into the test section of a low speed wind tunnel was simulated. The same turbulence model, κ–ω SST (shear stress transport), was used in both software, and the numerical results were compared with experimental results. Results of velocity, pressure, static pressure coefficient and skin friction coefficient are presented. A mesh test was carried out to evaluate the mesh convergence and the numerical uncertainties, which indicated greater uncertainties and sensitivity of FVM to the mesh quality. The average computing time for the FEM method was ten times greater than for FVM. Numerical results of both codes showed a good agreement with experimental results and with the literature.

Analysis and Optimization of Unsteady Flow in a Double-Suction Centrifugal Pump for a Cooling-Water Supply System in a Nuclear Reactor

The management of a cooling-water supply system in a nuclear reactor is performed by valve and reactor coolant pump (RCP) control, which regulates both the pressure and the discharge between certain limits. However, the RCP has a significant unsteady flow when operating at different conditions. The unsteady pressure pulsation and radial force vector are difficult to calculate because these are affected by the transient properties of the unsteady flow. This study explores the use of a commercial Computational Fluid Dynamics (CFD) code to comprehensively estimate the unsteady flow of the RCP. The full 3D-URANS equations were solved for different flow rates, and some optimised cases for the unsteady flow were proposed. The results showed that the numerical predictions were validated with the experimental data of a model pump. The code was used to estimate the velocity streamlines, pressure pulsation and radial force vector in the steady and transient conditions. The flow rates were not equal for the inner and outer passage in the double volute casing. Additionally, the pulsation of the pressure and radial force was effectively reduced by optimising the staggered angle α. An optimal case was observed when α =30°.

Internal Ballistics of a Boron-Containing Solid Fuel Ramjet

ABSTRACT The solid fuel ramjet is one of the simplest air-breathing engines, characterized by increased specific impulse. This study focuses on a parametric investigation of the internal ballistics of a boron-containing solid fuel ramjet. A 2-D axisymmetric model of a ramjet combustor flying at Mach 2.5 was developed and solved numerically utilizing a commercial computational fluid dynamics code modified to address the specific issues of the problem. The simulation results were compared to the theoretical performance calculated by the chemical equilibrium code. The solid fuel regression rate was found to depend on the port diameter and thus decreases with time. Thrust regulation of ramjet engine was demonstrated using bypass air. The specific impulse was found to decrease with boron content, probably because of low combustion efficiency caused by either insufficient oxygen supply or short residence time of the boron particles.

A verification of thermophysical properties of a porous ceramic investment casting mould using commercial computational fluid dynamics software

Defects in cast metals remain a common problem in many areas of the foundry industry, particularly in the investment casting of large area, thin-walled components for aerospace applications. During previous research, the thermophysical properties, density and porosity of a fibre reinforced ceramic investment casting mould were determined using several experimental techniques. Without verification, these experimental results remain nothing more than educated guesswork. The purpose of this study is to verify previous results and to more fully characterise the ceramic mould material with complementary measurements. A commercially available computational fluid dynamic (CFD) simulation package, Flow-3D®, was used in conjunction with a full-scale Ni-superalloy (IN718) casting to assess the accuracy of these results. By placing thermocouples strategically across the mould thickness, temperature profiles were determined and compared directly to predicted profiles extracted from the simulation by a custom-written Python script.

Non-Intrusive Visualization of Optically Inaccessible Flow Fields Utilizing Positron Emission Tomography

A technology gap persists in the visualization of optically inaccessible flow fields such as those in integrated systems. Advances in positron emission tomography (PET) technology are enabling its use in the engineering field to address this technology gap. This paper discusses a numerical study performed to characterize a modern PET system’s ability to reconstruct a three-dimensional mapping of the optically inaccessible flow field downstream of an orifice. A method was devised to simulate a ring detector response to a flourine-18 radioisotope/water solution injected into the flow through a standard thickness pipe with orifice. A commercial computational fluid dynamics code and the GEANT4 Applications for the Tomographic Emission Monte Carlo simulation physics package were used to carry out the simulations. Results indicate that geometrical features, such as the pipe internal diameter, can be resolved to within a few millimeters with specific activity levels of 155 Bq/Voxel (91.2 Bq/mm3), and acquisition times as low as 15 s. Results also suggest that flow features, such as the radial extent of the shear layer between the primary and secondary recirculating flow can be resolved to within 5 mm with the same activity level, but with acquisition times of 45 s.