CFD Code FLUENT Research Articles

Physical and Mathematical Modeling of Metal-Slag Exchanges in Gas-Stirred Ladles

AbstractLadle refining plays a key role in achieving the quality of the steel since in this reactor temperature and chemical composition is adjusted, elimination of non-metallic inclusions is performed, and also deoxidation and desulphurization are operations taking place in the refining process. Specifically, the metal-slag mass exchanges have not received much attention through scientific studies. In this work, a rigorous study on the mass exchange between metal and slag is presented through a scaled water physical model. In the model, thymol (playing the role of a solute such as sulfur) is added to the water (playing the role of steel) and silicon oil (playing the role of slag) picks up the thymol, while the ladle is agitated with the central injection of gas. The evolution of thymol concentration in time was measured. Also, a mathematical model was developed and cast into the commercial CFD code Fluent Ansys to represent the fluid flow phenomena and the mass transfer through the solution of the continuity equation, the turbulent momentum conservation equations and the species mass conservation equation. There is a good agreement between the measured and the computed results regarding the thymol concentration evolution in water and consequently the mathematical model was validated regarding the mass species metal-slag exchanges and it may be used to study metal-slag exchanges in the steel ladle such as deoxidation or desulphurization.

Flash recovery system analysis and flashing tank optimization in desalination plants

This study established and calculated the flash system model of 7-effects low-temperature multi-effect distillation (LT-MED) system with an installed capacity of 4500 m3/d. The calculation results showed that the brine and distillate flashing accounts for 6.0% of the total water production, which indicate the significant effect of such flashing heat recovery system. Furthermore, a three-dimensional simulation of water–vapor flow in the flashing tank of a LT-MED plant was conducted by using a FLUENT CFD code coupled with a user-defined function. The factors related to the flash efficiency, including flashing tank diameter, length, and internal platform height, were simulated and analyzed. Finally, an improved scheme for setting a platform inside the flashing tank was proposed. The simulation results revealed that the improved scheme ensures the sufficient flash of water inside the tank. These finds of the present study can serve as a reliable reference for the design of flashing tank in LT-MED plant.

Numerical study and GMDH-type neural networks modeling of plasma actuator effects on the film cooling over a flat plate

In this paper, the film cooling effectiveness for cylindrical and fan-shaped holes is numerically investigated in a 3-D model on the surface of a flat plate with and without the attendance of a plasma actuator. The electric force produced by a plasma actuator is employed as a body force into a finite volume based Navier–Stokes solver. Incompressible, viscous and turbulent flow has been simulated by the Fluent CFD code with the low-Re k-ε turbulence model. The results show that the fan-shaped holes provide higher film cooling effectiveness than cylindrical holes. The influences of flow, geometric and electrical variables on the performance of film cooling have been discussed. Finally, the group method of data handling (GMDH)-type neural networks has been used for presenting a relationship for area weighted average adiabatic film cooling effectiveness. Predicted results for film cooling effectiveness showed that GMDH model can provide beneficial information for simulation of film cooling process.

Analysis of the effects of use of thermal energy storage device (TESD) in solar air heater

In this research work a setup is designed to incorporate Lauric acid as a phase changing material (PCM) in a solar air heater. This phase changing material (PCM) is carefully selected based on the application and manufacturing constraints. A thermal energy storage device (TESD) is manufactured and incorporated in solar air heater and experiments were carried out to compare the solar air heater with and without thermal energy storage device (TESD) to evaluate various parameters such as output temperature and pressure drop. Results revealed that the rise in the output air temperature decreases from 8.67K to 4K with the increase in the mass flow rate of air flowing through the solar air heater from 0.021kg/s to 0.035kg/s. Also with an increase in the mass flow rate, there is a decrease in the friction factor from 0.0119 to 0.00802. There is an average increment of 86.47% in the rise of output air temperature with TESD as compared to rise of the output air temperature without TESD with an average increment of 36.47% in friction factor. A computational analysis is also performed which gives insight into the working of solar air heater with thermal energy storage device (TESD). A computational domain of solar air heater with TESD is analyzed in CFD code FLUENT using various turbulence models such as k-ω SST, k-ω Standard, k-∊ Standard and k-∊ RNG. It is observed that results obtained from turbulence model k-є RNG model are in good agreement with the experimental results and hence used for the analysis of all the cases considered in this work.

Kinetic study of catalytic cracking on the effect of reaction parameters in short-contact cyclone reactors

The paper presented the research and the results obtained by the author concerning the kinetic modeling of the short-contact cyclone reactor of the catalytic cracking unit. It was an effort to model the phenomenon numerically using Euler–Euler two-phase model and 6-lump kinetic model. Geometry, boundary conditions and dimensions of industrial short-contact cyclone reactor for catalytic cracking unit were conferred for 3D simulation using commercial CFD code FLUENT 6.3. The simulated results calculated by the established model in this paper made a reasonable agreement with the experimental findings. The simulated results indicate that the gradient distribution field in the short-contact cyclone reactor is beneficial to increase the contact time between crude oil gas and catalysts, and the short-contact cyclone reactor is also capable of achieving the rapid separation between gas products and catalysts. Simulations were also carried out to determine the effects of operating parameters on product yield. The operating parameters include reaction temperature, catalyst to oil ratio and reaction time, which are helpful for optimizing the yield of desired products.

Numerical Analysis of a Coaxial Impingement Jet and Application for a Laser Welding of AZ91 Magnesium Alloy with Shielding Gas

Abstract A coaxial jet impinging a vertical heated plate is numerically investigated using the Fluent CFD code. The best numerical simulations are carried out using the k-ω SST turbulence model with considered assumptions. Results obtained by the developed numerical model have enabled to determine essentially the average Nu numbers relating to certain Reynolds number for H/D=4 position of the heated plate. A comparison of the accuracy of different turbulent models is proposed in this study. Comparisons with a single jet and with a horizontal disposition are also proposed. Subsequently, an industrial application is proposed; the laser welding process. For that, a moving distributed heat source model has been implemented in order to predict temperature distributions through the welding process of a magnesium alloy with the gas shielding.

Improved numerical algorithm and experimental validation of a system thermal-hydraulic/CFD coupling method for multi-scale transient simulations of pool-type reactors

The paper describes the development and validation of a coupling methodology between the best-estimate system thermal-hydraulic code RELAP5-3D and the CFD code FLUENT, conceived for high fidelity plant-scale safety analyses of pool-type reactors. The computational tool is developed to assess the impact of three-dimensional phenomena occurring in accidental transients such as loss of flow (LOF) in the research reactor MYRRHA, currently in the design phase at the Belgian Nuclear Research Centre, SCK•CEN. A partitioned, implicit domain decomposition coupling algorithm is implemented, in which the coupled domains exchange thermal-hydraulics variables at coupling boundary interfaces. Numerical stability and interface convergence rates are improved by a novel interface Quasi-Newton algorithm, which is compared in this paper with previously tested numerical schemes. The developed computational method has been assessed for validation purposes against the experiment performed at the test facility TALL-3D, operated by the Royal Institute of Technology (KTH) in Sweden. This paper details the results of the simulation of a loss of forced convection test, showing the capability of the developed methodology to predict transients influenced by local three-dimensional phenomena.

Effect of Air Bubbles on Heat Transfer Coefficient in Turbulent Convection Flow

Experimental and numerical studies have been conducted for the effect of injected air bubbles on the heat transfer coefficient through the water flow in a vertical pipe under the influence of uniform heat flux. The investigated parameters were water flow rate of (10, 14 and 18) lit/min, air flow rate of (1.5, 3 and 4) lit/min for subjected heat fluxes of (27264, 36316 and 45398) W/m2. The energy, momentum and continuity equations were solved numerically to describe the motion of flow. Turbulence models k-ε was implemented. The mathematical model is using a CFD code Fluent (Ansys15). The water was used as continuous phase while the air was represented as dispersed. phase. The experimental work includes design, build and instrument a test rig for that purpose. Acircular vertical copper pipe test section of (length=0.7m, diameter= 0.05m, thickness= 1.5mm) is . designed and constructed, heated by an electrical heater fixed on its outer surface. Water . temperature at inlet is kept constant at (32°C). Water inlet and outlet temperatures, as well as radial temperature distribution within the pipe at seven sections along it between pipe surface and its center are measured. The results revealed that the secondary flow created by air bubbles havesignificant effects on heat transfer enhancement and temperature profile. It is observed, that averaged Nusselt number enhancement for low heat flux of 27264 W/m2 and 4 lit/min air bubbles was 33.3 % and 23% in numerical and experimental, respectively.

STH-CFD Codes Coupled Calculations Applied to HLM Loop and Pool Systems

This work describes the coupling methodology between a modified version of RELAP5/Mod3.3 and ANSYS Fluent CFD code developed at the University of Pisa. The described coupling procedure can be classified as “two-way,” nonoverlapping, “online” coupling. In this work, a semi-implicit numerical scheme has been implemented, giving greater stability to the simulations. A MATLAB script manages both the codes, oversees the reading and writing of the boundary conditions at the interfaces, and handles the exchange of data. A new tool was used to control the Fluent session, allowing a reduction of the time required for the exchange of data. The coupling tool was used to simulate a loop system (NACIE facility) and a pool system (CIRCE facility), both working with Lead Bismuth Eutectic and located at ENEA Brasimone Research Centre. Some modifications in the coupling procedure turned out to be necessary to apply the methodology in the pool system. In this paper, the comparison between the obtained coupled numerical results and the experimental data is presented. The good agreement between experiments and calculations evinces the capability of the coupled calculation to model correctly the involved phenomena.

Heat conduction in convectively cooled eccentric spherical annuli: A boundary integral moment method

In this paper heat conduction equation for an eccentric spherical annulus with the inner surface kept at a constant temperature and the outer surface subjected to convection is solved analytically. Eccentric problem domain is first transformed into a concentric domain via formulating the problem in bispherical co-ordinate system. Since an analytical Green?s function for the heat conduction equation in bispherical co-ordinate for an eccentric sphere subject to boundary condition of third type can not be found, an analytical Green's function obtained for Dirichlet boundary condition is employed in the solution. Utilizing this Green's function yields a boundary integral equation for the unknown normal derivative of the surface temperature distribution. The resulting boundary integral equation is solved analytically using method of moments. The method has been applied to heat generating eccentric spherical annuli and results are compared to the simulation results of FLUENT CFD code. A very good agreement was observed in temperature distribution computations for various geometrical configurations and a wide range of Biot number. Variation of heat dissipation with radii and eccentricity ratios are studied and a very good agreement with FLUENT has been observed

Climatic analysis of a passive cooling technology for the built environment in hot countries

The aim of this work was to determine the ventilation and cooling potential of a passive cooling windcatcher operating under hot climatic conditions by replicating the monthly wind velocity, wind direction, temperature and relative humidity (RH) observed in a hot-desert city. The city of Ras-Al-Khaimah (RAK), UAE was used as the location of the case-study and available climatic data was used as inlet boundary conditions for the numerical analysis. The study employed the CFD code FLUENT 14.5 with the standard k–ε model to conduct the steady-state RANS simulation. The windcatcher model was incorporated to a 3×3×3m3 test room model, which was identical to the one used in the field test. Unlike most numerical simulation of windcatchers, the work will simulate wind flows found in sub-urban environment. The numerical model provided detailed analysis of the pressure, airflow and temperature distributions inside the windcatcher and test room model. Temperature and velocity profiles indicated an induced, cooler airflow inside the room; outside air was cooled from 38°C to 26–28°C, while the average induced airflow speed was 0.59m/s (15% lower compared to a windcatcher w/out heat pipes). Field testing measurements were carried out in the Jazira Hamra area of RAK during the month of September. The test demonstrated the positive effect of the integration of heat pipes on the cooling performance but also highlighted several issues. The comparison between the measured and predicted supply temperatures were in good agreement, with an average error of 3.15%.

Thermal–hydraulic analysis of air cooled finned heat transfer tubes

Thermal hydraulics in air cooled finned heat transfer tube banks are analyzed with the ANSYS FLUENT CFD code, by assuming a periodic boundary condition for the region of interest. The Re-normalization Group (RNG) theory based k–ε model is used as a reference turbulence model. Two other turbulence models are used to compare results. They are standard k–ε model and realizable k–ε model. The loss coefficients of the finned heat transfer tube as a function of the Reynolds number are calculated using the RNG k–ε model and the standard k–ε model. Both results are in the band of the measured data in the case of the one pass model. Six-pass finned heat transfer tube banks are calculated using a whole-pass model as well as a one-pass model which transfers the calculated outlet conditions to the next pass calculation. Air temperature distribution along the six passes is compared with the result calculated by a one-dimensional system code. Both results agree each other. However, the evaluated Nu number for each pass is slightly higher than the measured data. The evaluated pressure loss coefficient is in the measured data scattering band.

Enhancement of heat transfer in a rectangular channel with perforated baffles

One problem in using baffles in the channels is the formation of Lower Heat Transfer Areas (LHTA), particularly in the downstream region of baffles (i.e. in baffle-wall corners). The present paper is an investigation of the performance of a new baffle design aiming to enhance the heat transfer phenomenon in the channel. It concerns a perforated baffle having a row of four holes placed at three different positions. These positions are characterized by a ratio called the PAR (Pores Axis Ratio). Three values are taken for the PAR and which are 0.190, 0.425 and 0.660, respectively. The characteristics of fluid flows and heat transfer are presented for Reynolds numbers ranging from 104 to 105. All investigations are achieved with the help of the CFD code Fluent. Some numerical results are validated with available experimental data and a satisfactory agreement is found. The obtained results show that the Pores Axis Ratio (PAR) of 0.190 is the best design that eliminates significantly the LHTAs, giving thus an increase in the heat transfer rate from 2% to 65% compared with the simple baffle.

OWC air chamber performance prediction under impulse turbine damping effects

Oscillating water columns (OWCs) are most widely used in coastal wave energy conversion. The air duct opens into the atmosphere through the air turbine, which is the power take-off device, and this results in a pressure drop across the air chamber. However, because of the complex configure of the impulse turbine and its high rotation speed, it is difficult to install it in the experimental simulator and numerical model. Therefore, the turbine damping effects on the operation of the OWC air chamber are induced to predict its performance more accurately. Orifice plates are used as a substitute for the impulse turbine as it generates a similar pressure drop and power output; the experimental and numerical pressure drops and output powers are compared. A 3D numerical wave tank based on the two-phase VOF model is established using the commercial CFD code Fluent, which can predict air flow and pressure variations in the chamber and duct. Water surface elevations, air flow velocity and pressure variation inside the chamber with the orifice plate are studied numerically, and validated by the corresponding experimental data. The air chamber of the Yongsoo OWC pilot plant is used as the engineering project case. The operating performance of the air chamber installed with a 0.428D orifice plate as the substitute for the designed impulse turbine is computed and analyzed. It is found that the turbine damping effects will cause around 30% reduction in the peak values of the pneumatic energy output of the OWC air chamber in the resonant wave domain.

Numerical simulation of heat transfer enhancement for natural convection in a cubical enclosure filled with Al2O3/water and Ag/water nanofluids

ABSTRACTIn the present study, the natural convective heat transfer in a cube filled with Al2O3/H2O and Ag/H2O nanofluids is investigated numerically. Commercial CFD code FLUENT has been used to simulate water-based nanofluid considering it as a single-phase fluid. The influence of different parameters, such as the Rayleigh number and the nanoparticle volume fraction, is studied. The velocity vectors and the isotherm profiles are plotted. The variation of the Average Nusselt number at the hot wall and the variation of y-component of velocity are presented and discussed. The numerical results show a decrease in the heat transfer with the increase in the particle volume fraction and the same trend in the increase of the Nusselt number with the Rayleigh number.

Experimental and numerical visualizations of swirling flow in a vertical pipe

This paper presents a comparison between the experimental and numerical simulations of turbulent swirling flow induced by twisted tape in vertical pipe. A novel measurement technique, phased array ultrasonic velocity profiler (UVP), has been developed for 2D velocity field visualization in swirling flow. A phased array with basic frequency 4 MHz has been designed, it has eight piezoelectric elements and each element transmits ultrasound beam. The advantage of this sensor is that the ultrasound beam can be controlled easily by changing the time delay of signal transmission for each element. A vector reconstruction algorithm is presented showing how the velocity vector of particles can be calculated from Doppler-shift frequencies taken from the output signals of two receiver elements. Two-dimensional velocity field has been visualized and it is found, as expected, that the presence of swirl cause a significant increase in the magnitude of the measured tangential velocity. Furthermore, a numerical calculation is performed and qualitatively compared with experimental results. The numerical result is obtained by solving three-dimensional, Reynolds-averaged Navier–Stokes equations by the commercial CFD code FLUENT® v.14.5 with RNG k-e turbulence model. The qualitative comparison between phased array UVP and CFD results shows good agreement with the average velocity field. Experimental and numerical findings and parametric trends based on the effects of swirling flow are summarized and discussed.

Research on Flow Field Characteristics Affected by Obstacles of Pull-Push Ventilation System of Plating Tanks through Numerical Simulation

Pull-push ventilation system, with high capture efficiency, is universally used to capture contaminants from containment generation where can’t be enclosed and where the working area is large. When there are obstacles between the pull hood and the push hood, the air jet will disperse, leaving contaminants out of control, causing atmosphere polluted. This paper aims to discuss flow filed of pull-push ventilation system, located in some tank of some plating workshop, with obstacles between pull hood and push hood. Mathematical model, involving physical model, assumptions, governing equations, boundary conditions and grid separation is established. By CFD code FLUENT, flow field, containing velocity field and concentration field, is achieved. To verify the simulation models, velocity field for simulation results is compared with the theory results, while concentration field for simulation results with experimental results. The comparison results show that the results matches well and that mathematical model proposed in this paper is reasonable, helpful and realistic significant in designing this kind exhaust ventilation systems where obstacles presence.

Meshing Effect on the Hydrodynamic Structure Around Water Darrieus Rotor

Turbulent free surface flows are encountered in many hydraulic and water resources engineering problems. In this work, the CFD code Fluent is used to study the meshing effect on the hydrodynamic structure around water Darrieus rotor. This code is based on solving steady Navier-Stokes equations by a finite volume discretization model. The numerical approach used is the multi reference frame (MRF) model. The validation of our computer model is done by the comparison with experimental anterior results.

Simulation of Partial and Supercavitating Flows around Axisymmetric and Quasi-3D Bodies by Boundary Element Method Using Simple and Reentrant Jet Models at the Closure Zone of Cavity

A fixed-length Boundary Element Method (BEM) is used to investigate the super- and partial cavitating flows around various axisymmetric bodies using simple and reentrant jet models at the closure zone of cavity. Also, a simple algorithm is proposed to model the quasi-3D cavitating flows over elliptical-head bodies using the axisymmetric method. Cavity and reentrant jet lengths are the inputs of the problem and the cavity shape and cavitation number are some of the outputs of this simulation. A numerical modeling based on Navier-Stokes equations using commercial CFD code (Fluent) is performed to evaluate the BEM results (in 2D and 3D cases). The cavitation properties approximated by the present research study (especially with the reentrant jet model) are very close to the results of other experimental and numerical solutions. The need for a very short time (only a few minutes) to reach the desirable convergence and relatively good accuracy are the main advantages of this method.

Numerical investigation of combustion of biomass, methane, and gasoil fuels and emissions from a furnace chamber

ABSTRACTThe aim of this study was to compare gaseous emissions from the combustion of conventional fuels (methane and gasoil) and biomass fuels (wood and peat) by the application of the CFD code FLUENT software in a furnace combustion chamber. According to the results, the combustion temperature obtained for conventional fuels was higher than it obtained for biomass fuels. Results also showed significantly lower emissions of CO2, NOx, and soot with the combustion of biomass compared to the methane and gasoil, but SO2 emissions from combustion of the conventional fuels were higher than that of biomass fuels. Also, results showed that the quantity of gaseous emissions is closely related to combustion temperature, molecular structure, and fuel characteristics.