Code FLUENT Research Articles

Thermal and Hydrodynamic Measurements of a Novel Chaotic Micromixer to Enhance Mixing Performance

In this study, three-dimensional simulations were conducted on a new passive micromixer to assess the thermal and hydrodynamic behaviors of Newtonian and non-Newtonian fluids subjected to low generalized Reynolds numbers (0.1 to 50) and shear-thinning properties. To acquire a more profound comprehension of the qualitative and quantitative fluctuations in fluid fraction using the CFD Fluent Code, the mass mixing index, rheological behavior, performance index, mixing energy cost, mass fraction distributions, temperature contours, and pressure drop were compared to illustrate the importance of the mixer geometry in the context of two miscible fluids with varying inlet temperatures. The selected geometry is characterized by a robust chaotic flow that substantially enhances thermal and hydrodynamic performance across all Reynolds numbers. A mass mixing exceeding 72.5% is obtained when Re = 5, reaching 93.5% when Re = 50. Furthermore, the evolution of thermal mixing for all behavior indexes reaches a step of 98% with minimal pressure losses. This work enabled the demonstration of a chaotic geometry in a highly efficient mixing system, leading to enhanced thermal performance for both Newtonian and non-Newtonian fluids. The results of the hydrodynamic and thermal characterization of the mixing of shear-thinning fluids within the micromixers under investigation are conclusive.

Thermal analysis for evaluating the required cooling time of the emergency plan exemption for the Maanshan PWR units

The Maanshan plant is scheduled to be decommissioned in 2025. Taiwan Power Company, the owner of the plant, plans to apply exemption from the emergency plan (EP) while the plant is in decommissioning. One requirement for this exemption is that the fuel rod peak cladding temperature (PCT) must be below 565 °C for the postulated complete loss-of-coolant accident in the spent fuel pool (SFP), assuming cooled by air only. In this study, accident analysis models for the Maanshan SFP are developed. First, the decay heat power is calculated based on the specified cooling time. Second, air temperature entering the fuel assemblies is calculated using GOTHIC code, and then is provided as a boundary condition to the following PCT calculation. Finally, the PCT is calculated from the assembly model using Ansys Fluent code. The specified cooling time is acceptable or not is determined by the criterion that whether the PCT is below the limit. With the cooling time of 54 months, the calculated PCT is about 537 °C. Thus, the shortest cooling time allowed for applying EP exemption would be 54 months for the Maanshan units, which is much longer than that of the reference plants. This is because all the spent fuel assemblies are still stored in the SFP, resulting in a higher total decay power. A suggestion of removing the spent fuel assemblies to the dry storage facility is proposed if the Maanshan plant intends to apply the EP exemption while the plant is in decommissioning.

Four-DOF Maneuvering Motion of a Container Ship in Shallow Water Based on CFD Approach

With the continuous increase in ship size combined with the generally slower increase in the sizes of waterways, the need for the prediction of ship maneuvering in shallow waterways continues to attract attention from the international scientific community. Ship behavior in shallow water is relevant in seabed effects that result in changing the hydrodynamic forces acting on a ship. In this study, the maneuvering characteristics of a container ship with four degrees of freedom in shallow water are analyzed. The Reynolds-Averaged Navier Stokes approach in Ansys Fluent code is used to produce the maneuvering coefficients through the simulations of forward running, static drift, static heel, circular motion, the combined motions, and the pure roll motion of the KRISO container ship. The maneuvering characteristics of the ship are estimated for evaluating the ship behaviors in shallow-water conditions. The obtained results show that the roll has a significant decrease and the ship’s turning diameter has a significant increase when the ship operates in a shallow waterway. The predictions of the maneuvering characteristics of the ship are in good agreement with those of free-running model tests, indicating that the numerical simulation based on the Computational Fluid Dynamics method has compromising capability to predict the maneuvering derivatives and the four-DOF ship maneuvering motion in shallow water as well.

Enhancing performance in solar air channels: A numerical analysis of turbulent flow and heat transfer with novel shaped baffles

Solar air heaters are emerging as a promising solution for sustainable heating, as they harness abundant solar energy to provide heat for a variety of applications. However, their optimum efficiency remains a major challenge. Deflectors have significant potential to improve the performance of solar air heaters by redirecting airflow and optimizing heat transfer, making them more efficient and more suitable for large-scale adoption. This article examines the performance of a new baffle design aimed at improving heat transfer in the channel by increasing the exchange surface between fluid and solid surface. It consists of a “≠” -shaped baffle mounted on the top and bottom walls of the channel. An in-depth analysis of the spacing between these baffles was carried out to assess their impact on the thermal and aerodynamic properties of the solar air channel. Computational Fluid Dynamics (CFD) was used to perform the calculations, using the Finite Volume Method (FVM) in conjunction with the SIMPLE algorithm. All studies are carried out using the CFD code Fluent. Crucial steps in this research include studying the influence of these new baffles at different Reynolds numbers, ranging from 15000 to 35000, as well as varying the separation distance between the two baffles, chosen periodically (DBaffle/2, 3DBaffle/4, DBaffle, 5DBaffle/4 and 3DBaffle/2). Some of the numerical results were validated with the available experimental data and showed satisfactory agreement. The study identified an optimal case for the new baffles, by reducing the distance between the baffles, an improvement in system performance was observed, by increasing the flow strength and widening the recycling cells, which has an impact on dynamic behavior and heat transfer. The presence of this new baffle design, with minimal separation distance between them, demonstrated a significant thermal improvement, with a thermal improvement factor increasing by 44% compared to the simple channel without baffles, thus highlighting the effectiveness of the new solar air channel with “≠” -shaped baffles.

Entropy generation analysis and thermal synergy efficiency in the T-shaped micro-kenics

In this work, three different twist angles of a micro helical insert in a T-shaped are studied numerically in order to evaluate the laminar steady flow behavior of Newtonian fluid in chaotic geometry. In the geometries under consideration, thermal mixing behavior is carried out using fluids having two distinct input temperatures. Under the influence of chaotic advection and low rates of Reynolds number, the second law of thermodynamics is controlled in terms of the entropy generation caused by hydrodynamic and thermal processes. The governing equations are numerically solved using the CFD Fluent code. Thus, the micromixer's configuration demonstrated a very significant improvement in mixing degree while minimizing friction and thermal irreversibilities. The synergy coefficient, which depicts the link between velocity and heat transfer in angle form, is analyzed and the results are provided.

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.

Effect of Vortex Generator on Gas Turbine Blade Cooling

The current numerical study suggests using a vortex generator to lessen the consequences of a counter-rotating vortex pair. For this inquiry, the delta winglet pair in the common-flow-down arrangement is selected. A suitable model for turbulence is examined. The x, y, and z vorticity is studied. Additionally, the effect of variations in turbulent kinetic energy is examined. The outcome is contrasted with the reference scenario. Employing the k-omega SST turbulence model and the commercial code FLUENT, numerical analysis is accomplished.

Wind Velocity Effect on the Aerodynamic and Acoustic Behavior of a Vertical Axis Wind Turbine

In this work we present a numerical study on the effect of wind velocity on the aerodynamic and acoustic behavior of a Savonius-type vertical axis wind turbine (VAWT). The study focuses on the prediction of the torque coefficient for different flow velocities and rotational velocities of the wind turbine. We also present the triggering of the wake zone near the wind turbine blades to see the dynamic effect on the behavior of the wind turbine. The study of the numerical simulation is carried out using a fluent CFD calculation code using the finite volume method for the discretization of the differential equations. The equations governing the flow are solved by the SIMPLE algorithm using two K-epsilon turbulence models.

A between-wall heat transfer simulation approach based on the lattice Boltzmann method and its application in tube heat transfer analysis

Between-wall heat transfer is a fundamental physical process. As a typical coupling heat and mass transfer process, between-wall heat transfer-based problems can be solved conveniently on the basis of advanced computation methods among which the lattice Boltzmann method (LBM) has been widely used in the analysis of simple heat and mass transfer cases. To investigate the applicability of LBM in more complex solid-fluid coupling heat transfer analysis, a 3D fluid-solid-fluid model was established in this work to carry out between-wall heat transfer simulations using the doubled-population LBM. Three independent simulation regions were coupled in the heat transfer model, and the heat flux was taken as the physical quantity that transferred from the region at high temperature to that at low temperature through solid wall. The simulation results satisfactorily agree with that obtained using the commercial code FLUENT. Furthermore, an equivalent fluid-wall-fluid heat transfer model was established for simulation of heat transfer between internal and external fluids through a circular tube. All the boundaries are complete quadrilaterals on which heat transfer boundary conditions can be conveniently applied. The proposed between-wall model based on LBM can be easily established and applied in cases with internal heat source or mass force.

Heat and water recovery from gaseous stream using a flat-sheet ceramic membrane as a transport membrane condenser

Ceramic-membrane technology has been employed to recover waste heat and vapor from moist gases. In addition to the hydrophilicity, pore size, and porosity of separation materials, a membrane condenser can achieve a high recovery rate. In this study, a transport membrane condenser (TMC) was successfully constructed using a flat-sheet ceramic membrane (FCM) with a large pore size of 45.54 μm. The membrane characteristics, including the mean pore size, pore size distribution, and porosity, were investigated to determine their recovery mechanism. Their water and heat fluxes, recovery rates, and thermal resistance were compared under several experimental conditions. The inlet conditions significantly affect the TMC recovery performance. Higher recovery fluxes were obtained at lower water temperatures, higher gas temperatures, and higher gas flow rates. However, when the Reynolds number of water increased, the heat flux increased rapidly, and the recovered water decreased slightly. The highest TMC water recovery rate was 84.1%. In addition, to further analyze the separation mechanisms, a two-dimensional model was developed using ANSYS Fluent code. The simulation results were compared with the experimental data to verify the accuracy of the numerical method. The comparison results showed a high degree of consistency.

CFD Simulation of an Industrial Dust Cyclone Separator: A Comparison with Empirical Models: The Influence of the Inlet Velocity and the Particle Size on Performance Factors in Situation of High Concentration of Particles

The present work is dedicated to the study of multiphase turbulent and three-dimensional rotational flow in dust cyclones, a contribution to air pollution control. Cyclones are widely used devices for the separation of constituents from solid-gas mixtures in industry. In order to improve the filtration efficiency of cyclones, and to reduce the pressure drop, parametric numerical simulation studies using the Fluent code have been conducted to characterise the effects of the parameters affecting the operation of these devices through their performance indicators. In this work, the effect of inlet velocity and the particle size on the turbulent flow air in the cyclone is presented. Numerical simulation of the flow by Fluent code using three numerical models: the first based on the dissipation of kinetic energy by viscosity (RNG) K-epsilon and standard K-epsilon as well as the last based on the solution of Reynolds stress equations (RSM), combined with the multiphase mixing model, gave interesting results in terms of the pressure and flow field in the separator, the variation of inlet velocity, and the variation of particle size. Validation with experimental and empirical results showed the advantage of the Reynolds stress turbulence model (RSM) over the standard K-epsilon and RNG K-epsilon. The RSM model better captures physical phenomena in an intense vortex flow in the presence of walls. But it is characterised by a very long calculation time and requires large machine resources. An alternative to this model is RNG K-epsilon model, which offers a reasonable calculation time with acceptable results (maximum deviation of 5 %) for speed values below 10 m/s. In the absence of numerical resources, certain empirical models such as those of First (for the evaluation of pressure drop) and Iozia and Leith (for evaluation of efficiency) may well be useful for the dimensioning of the cyclone.

Experimental and Numerical Studies on the Efficacy of Water Mist to Suppress Hydrocarbon Fires in Enclosures

Fire is one of the most undesirable events onboard a ship. The engine room is one of the most critical spaces in the ship in terms of fire protection, as it includes machinery, hydrocarbon fuel systems, and different electrical equipment. With the phasing out of Halon 1301 as a fire suppressant over recent decades, there has been an intensive effort to explore the efficacy of water-mist spray in mitigating fires within machinery spaces. This exploration entails a comprehensive investigation through experimental and simulation studies aimed at identifying suppression mechanisms and evaluating their effectiveness. While experimental setups typically encompass measurements of gas temperature, thermal radiation heat flux, oxygen concentration, and fire extinction time, limited attention has been paid to quantifying the heat release rate (HRR), a crucial indicator of fire magnitude. Furthermore, research into shielded fire scenarios remains sparse, despite their significance in maritime fire dynamics. Addressing shielded fires with water mist proves particularly challenging due to the potential obstruction impeding the direct interaction between the fire source and the water droplets. In the existing literature, most of the computational fluid dynamics (CFD) modelling of fires and suppression was performed using a Fire Dynamics Simulator (FDS). Alternate studies were performed using FireFOAM. and very few employed FLUENT and other analogous software codes. In the majority of reported computational studies, the determination of HRR was typically relied upon for its calculation derived from the measured data of fuel mass loss rate. Moreover, certain studies were undertaken for numerical simulations without conducting thorough model validation, either by omitting validation altogether or solely validating against dry fire experiments (i.e., without water-mist suppression). This critical review of the literature has identified several notable research gaps in the context of extinguishing hydrocarbon fires utilising water-mist spray, warranting further investigations. Additionally, this review paper highlights recent advancements in both experimental and numerical investigations pertaining to the efficacy of water-mist fire-suppression systems in enclosed spaces regarding hydrocarbon fires.

Enhancing heat transfer processes in 2U-Rack Servers: A study case employing thermal simulation and the Taguchi method

The data center industry consumes large quantities of energy due to the consumption spawned by Information Technology Equipment (ITE) and air conditioning systems. Servers constitute the predominant portion of ITE within a data center. Relatedly, diverse optimization strategies are required to minimize data centers' energy consumption. This paper used a 2U-Rack Server, specifically, the R261-3C0 server as a study case to enhance heat transfer processes by minimizing the temperature variation in the high thermal-stress components and optimizing airflow patterns. The Taguchi Method is used for this purpose. A thermal simulation is conducted using Computational Fluid Dynamics (CFD) techniques through the Ansys Fluent code. Seven design variables were proposed as control factors, submitting them to the noise factors. New parameters such as the motherboard lifting, the displacement of heatsinks and the CPUs, and the fan speed variation will be introduced among these control factors. Among the noise factors, we considered the fluid velocity at the server inlet region and the Operating Point of the Fan (OPF). After applying the Taguchi Method, the control factors and their optimal levels were obtained. The thermal simulation presented a consistent performance. The optimal configuration of the control parameters generated a 10 °C decrease in the server's overall temperature, an air circulation enhancement by the vector field behavior verification, and a 17.11 % decrease in the server's thermal variation. The optimized model stays in its verification phase, and the validation phase should be accomplished in future work.

Numerical Investigations of a Vertical Axis Wind Turbine with Variable Pitch

In the last decades, the wind energy became more attractive to Romania, and thus many resources are allocated to develop the energetic systems based on wind energy. In this work the performances of a variable-pitch vertical axis wind turbine were investigated using CFD (ANSYS Fluent). A computational methodology has been developed which uses the moving grid option offered by the ANSYS Fluent code, to evaluate amount of energy extracted from the wind. A transient simulation is done for fixed pitch and variable pitch vertical axis wind turbine using a k   SST (Shear Stress Transport) turbulence model. Main parameters like moment coefficient Cm, and power coefficient CP are investigated. The conclusion was that the variable-pitch vertical axis wind turbine has the best power coefficient at low/moderate tip speed ratio.

Effect of Cuo-Water Nanofluid on the Thermal - Hydraulic Behavior of Triangular Corrugated Channel

The aim of this study is to model and simulate laminar flow and heat transfer in a triangular-corrugated duct containing a CuO-water nanofluid. Note that a temperature is imposed on the walls, the considered Reynolds number (Re) and the nanoparticle volume fraction range from 100 to 800 and 0 to 5% respectively. The basic equations were discretized using the finite volume method. Dynamic and thermal fields were obtained, as well as the Nusselt number (Nu). In addition, the influence of certain parameters (Re, nanoparticle volume fraction) was taken into account. It can be observed that the mean Nu increases with increasing Re. Furthermore, raising the nanofluid volume fraction further enhances the heat transfer. For numerical resolution, we used the FLUENT code. Finally, we note that the results are in excellent accord with experimental ones published in the literature.

Optimization analysis of nuclear thermal coupling for a small nuclear thermal propulsion (SNTP) reactor

As a main structure, tie-tube elements are used both in the traditional and modern LEU nuclear thermal propulsion reactors. This complex structure and its corresponding complex convective heat transfer process have been studied, including CFD calculations. But these studies did not effectively evaluate the applicability of the models and typical problems. In this study, a general small nuclear thermal propulsion (SNTP) reactor model is established by using three-dimensional Monte Carlo code and commercial CFD program Fluent. The applicabilities of material properties, turbulence models and grids are clarified by analyzing various influencing factors. The calculation results show that due to the small enthalpy difference and heat transfer, the convection effect of inner flow based on hydrogen can be ignored. There is no factor that can significantly reduce the maximum fuel temperature, but the porosity of the insulator can significantly improve the heat transfer ratio. In terms of thermal safety and overall performance, 2:1 support ratio is still the best choice. Based on the simulation results, the phenomenon of steep temperature rise of outer tie-tubes is found, and the SST k-omega model with Y + <3 is recommended for simulation of similar problems.

Transient behavior of a molten salt fast reactor under two-phase flow conditions with helium bubbling

In the present study, transient behaviors of a chloride molten salt fast reactor without control rods under two-phase flow conditions are analyzed assuming a bypass of the safety protection system. The two-phase flow in the core is caused by helium bubbles injected to remove the gases of the fission product. The void fraction under the rated condition is assumed to be as low as 0.2 %. However, as the fuel flow rate decreases, the void fraction increases inversely proportional to the flow rate and must be considered in any transient analysis. Therefore, analyses with a point reactor kinetics and thermal-hydraulics coupling model have been performed to account for void flow using the CFD code. Comparison between the transient under two-phase flow and the transient under single-phase flow in which the effect of reactivity due to voids is taken into account with the CFD analysis, shows almost the same results, although there are slight differences due to the difference in fuel volume corresponding to the void fraction. When analyzing transients with a system code that has difficulty handling two-component two-phase flow, the void effect has been considered using the above-mentioned single-phase flow analysis. In this way, the entire plant is analyzed using the RELAP5-3D code and the core inlet conditions are passed to the FLUENT code to analyze the transient behavior. The transients analyzed are UTOP, USBO, ULOFF, and ULOHS under the assumption of bypassing the safety protection system. In addition, a transient assuming the loss of helium bubble supply under the decay heat power conditions is analyzed and discussed. The results of the analysis are compared with the results of the same event without voids analyzed using RELAP5-3D. In the case of single-phase flow, the reactor power changes mainly due to temperature feedback. Although the two types of transients have similar appearance, the breakdown of reactivity is quite different. Relating the comparison between the calculated result using the system code and CFD code shows that for the short time behavior until the fuel flow rate shifts to low flow rate, the results of the CFD code, which can analyze the behavior of the helium voids, are more appropriate. However, there are no major problems in the same transient calculation using RELAP5-3D, which calculates the entire plant system.

Flexural–torsional buckling of steel circular arches with I-section under central concentrated load in elevated-temperature environment

This article reports the fire resistance experiments conducted on I-section circular steel arches, as well as the observed out-of-plane flexural–torsional buckling (FTB) behavior and in-depth finite element numerical simulation results. The test was carried out using a large fire test furnace to provide a real fire environment with a nonuniform temperature field. A specially designed loading device allowed for unconstrained out-of-plane deformation of the specimens inside the furnace, thereby achieving effective load conditions and noncoupled response of the components. Numerical analyses were performed using a combination of the general codes Fluent and Abaqus, with the former used for heat transfer analyses, and a structural FE model including the loading device and complex geometric imperfections was established based on the measured data. Thus, accurate simulation of the out-of-plane behavior of the steel arches at elevated temperature was achieved. On this basis, an in-depth parametric study was carried out to investigate the effects of temperature field variations, load ratio (LR), and geometric imperfection. The analysis results show that FTB occurs at nonuniform temperatures for the arches under concentrated load, and the difference in temperature distribution in fire has a minimal effect on the FTB behavior. LR is negatively correlated with critical temperature; the smaller the LR, the more significant the weakening of critical loads by fire. The effect of initial geometrical imperfections on FTB at elevated temperatures is similar to that at ambient temperatures, and the effect on the critical temperature of FTB can almost be ignored when the imperfection amplitude is less than S/400.

Numerical study on the mixed convection with nanofluids in vertical channel asymmetrically heated

Mixed convection heat transfer in cavities is of great interest in many industrial applications, such as the development of crystals, the thermal control of electronic components, the nuclear reactors and various manufacturing processes. Components are generally located on the wall of a channel, that can be also tilted and their thermal control is carried out by the fluid flow. They can be schematized as thermal sources on vertical boards and the heat flux is removed by natural or mixed convection. As to the mixed convection, the interaction between the buoyancy forces and the external flow plays a significant role in the thermal design of systems. When natural convection is not strong enough to remove heat flux, mixed convection is adoptedIn particular, mixed convection due to moving surfaces is very important is these applications. Mixed convection because of buoyancy and motion of one of the channel walls has received little research attention and few guidelines are available for choosing the best performing channel configuration. Moreover, to optimize the transfer through natural convection, it is possible to modify the geometric parameters of the component, thus maximizing the convective heat transfer coefficient. If this is not possible or if one chooses to keep the geometry of the component unchanged for design choices, a possible alternative is the use of nanofluids. The properties of nanofluids exhibit a behaviour ranging between the properties of the base fluid and the properties of the nanoparticles. However, the addition of nanoparticles in the working fluid is considered to enhance the thermal behaviour of the base fluid. In this study a numerical investigation of mixed convection in nanofluids due to the interaction between a buoyancy flow and a moving plate induced flow in a vertical channel is carried out. The moving plate has a constant velocity and moves in the same direction with respect to the buoyancy force. The channel principal walls are heated with uniform heat flux. The numerical analysis is obtained by means of the commercial code Fluent. The effects of the different wall heat fluxes and moving plate velocities are investigated and results in terms of the channel wall and moving plate temperatures and Nusselt numbers are given.

Experimental and numerical investigation of the thermal and dynamic behavior of a heated vortex multijet system impacting a flat plate

This study concerns the experimental and numerical study of the thermal and dynamic behavior of a configuration of a system of vortex jets impacting a flat plate, The objective of this study is to study the behavior of the thermal and dynamic field of vortex blowing of hot air from a multi-jet system impacting a flat plate. The experimental test bench comprising a support of three diffusers of diameter D, impacting the perpendicular plate. A uniform inlet temperature (T, T, T) is imposed such that the impact height H = 4D. The vortex is obtained by a vortex generator made up of 12 fins arranged at 60° from the vertical, placed just at the outlet of the diffuser. A thermo-anemometer device, to measure the blowing temperature at the point in question. The system was numerically simulated by the fluent code using a k-ε RNG turbulence model. It should be noted that the multi-jet system first appears as a free jet: going from the injection orifice to the impact zone, the axial velocity weakens, the jet undergoes considerable deflection, this is the deflection zone the velocities become mainly radial and the thickness of the boundary layer increases radially: this is the parietal flow zone, the structure of the velocity field has two zones of intense deflection with a wall jet on both sides other, favoring a good development of the resulting jet. The results show that this configuration (T, T, T) gave a better optimized distribution of temperature and velocity on the surface of the plate. This homogenization of the temperatures results from a better thermal transfer of the plate.The k-ε RNG model gave acceptable results, which coincide with those of the experimental results.