Code FLUENT Research Articles

Thermo-hydraulic performance of a cryogenic printed circuit heat exchanger for liquid air energy storage

• The nature of local flow and heat transfer was analyzed using vortex identification. • The reverse flow suppresses local heat transfer and increases the flow resistance. • The air side has larger thermal resistance (∼ 58%) in the absence of phase change. • The best comprehensive performance can be achieved at an inclined angle of 45°. • The pressure drop and heat transfer correlations for the best angle were developed. The liquid air energy storage assisted by liquefied natural gas is a promising large-scale storage method, but its development is limited by the lack of thermo-hydraulic data on the cryogenic printed circuit heat exchanger. A simplified model for conjugate heat transfer was built and solved by a commercial code FLUENT 14.5. Model validation was conducted by comparing results with experimental data. The nature of flow and heat transfer was revealed by quantifying the vortex strength and visualizing the vortex core. The influence of the inclined angle was investigated, and the Nusselt number and friction factor correlations for the best angle were developed. The minimum internal temperature approach for optimum system operation is approximately 6 K, located in the middle of the heat exchanger. Results indicate that the evolution of Dean vortices plays a crucial part in the augmentation of heat transfer. The secondary flow caused by elbows forces the fluid cores to strike the windward side periodically, which disturbs the boundary layer and enhances the fluid mixing. Entropy production analysis shows that the thermal entropy generation has a dominant share of total irreversibility. The best performance is achieved at an inclined angle of 45° since the irreversibility is reduced by augmenting the heat transfer.

Aerodynamic Shape Optimization of a NACA0018 Airfoil Using Adjoint Method and Gradient-Based Optimizer

The purpose of this study is to demonstrate the suitability and efficacy of the adjoint method on the aerodynamic shape optimization on a simple symmetrical airfoil NACA0018 at low Reynolds number for wind turbine application. The adjoint method has been used in many pressure-based numerical simulations with various degrees of success leading to optimized geometries in their respective uses. ANSYS Fluent code was used in this simulation. Lift to drag ratio was defined as the observables for which adjoint sensitivities were formulated. The objective function of the optimization was set to maximize the lift to drag ratio of the airfoil by 20%. The optimization regime showed significant increase in lift and drag ratio from the initial baseline NACA0018 value of 0.0211 up to 3.66 for the optimal NACAOpt. The results demonstrate the potential of the adjoint solver paired together with the gradient-based optimizer to improve the geometry for shape optimization in many CFD applications.

Numerical simulation and optimization of steel tube billet heating process in rotary hearth furnace using computational fluid dynamics

Billet reheating is an important part of the steel production process. Since the production process will adopt different tube billet arrangement strategies, and the condition of the furnace hearth will also change due to long-term operation and accumulation of iron oxide scales, these factors will inevitably affect heating efficiency and temperature distribution uniformity of the tube billet, thereby affecting the quality of the final product. In this study, a physical and mathematical model was established for a 48 m diameter rotary hearth furnace of the seamless steel pipe production-line and typical 300 mm diameter tube billets of different lengths. Commercial FLUENT code was used to carry out CFD numerical simulation research on the influence of the aforementioned factors. Optimizing and adjusting strategies under different arrangement strategies were proposed, and the influence of furnace hearth condition change on heating effect was studied. The methods and simulation approach of this paper also have guidance for the billet heating control in similar continuous heating furnaces.

Numerical Investigation on the Thermal-Hydraulic Characteristics near a Corroded Lower Head of the Reactor Vessel During IVR-ERVC

Third-generation advanced pressurized water reactors adopt the external reactor vessel cooling (ERVC) strategy to ensure the pressure vessel is not at risk of melt-through in severe accidents, thereby completely controlling radioactive materials in the pile. However, due to its long-term service, vessel aging, steel corrosion, and oxidation may lead to deformation at different locations on its outer surface, forming various shapes of sawtooth structures, thus affecting the heat transfer behavior of the high-temperature walls during ERVC. In this paper, the Fluent code, coupled with boiling heat and mass transfer equations based on user-defined functions (UDFs) was used to simulate the thermal-hydraulic processes on the lower head with three typical sawtooth structures. The distribution of the stagnation zone for vapor buildup was the main focus. By varying the heat flux installed on the lower head and the inlet velocity of the flow channel, the onset time of critical boiling and the development of the location of critical heat flux over time were further investigated. It was found that a long period of unstable bubble generation and detachment before the onset of critical boiling may occur on the lower head. These findings can provide technical support for the safety design of advanced nuclear reactors.

Numerical Investigation of the Use of Boron Nitride/Water and Conventional Nanofluids in a Microchannel Heat Sink

The purpose of this paper is to study the effects of the use of boron nitride (BN) and other conventional nanoparticles (Al2O3, CuO and TiO2) on pressure drop and heat transfer in a microchannel. The governing equations for forced fluid flow and heat transfer were worked out by using fluent computational fluid dynamics (CFD) code. Computational results collected from fluent CFD code for Al2O3 as the nano-particle were compared with numerical values used in the literature for validation. The basis of a water-cooled (pure water, Al2O3/Water, CuO/Water, TiO2/Water and BN/Water) smooth microchannel was outlined, and then the corresponding laminar flow and heat transfer were evaluated numerically. The results from the numerical tests (NT) express good agreement with the values found in the literature. These results also indicate, through the comparison which was performed by taking the heat transfer and pressure loss parameters between BN and other widely used conventional nanoparticles (Al2O3, CuO and TiO2) into consideration, that BN is the more favorable nanoparticle. In comparison to other common nanoparticles (Al2O3, CuO and TiO2), BN enhances heat transfer and slightly raised pressure losses owing to its high thermal conductivity and high velocity profile because of low density. It is also chemically stable at the highest temperature relative to most solid materials. Thus, it has a structure that can be used in cooling systems for a long time without causing a problem of agglomeration.

Designing a molten core collection chamber for Bushehr-1 nuclear power plant using MELCOR 1.8.6 and ANSYS-FLUENT codes

The Bushehr-1 nuclear power plant (BNPP-1) is not actually planned to include a core catcher for mitigating molten corium in severe accidents. The feasibility analysis of designing a multi-layers core catcher next to the reactor cavity is presented in this study. In fact, the main purpose of this paper is to design a space to increase the surface to the volume of the molten material and create conditions for retention and maintaining coolability of the molten material.In this design, the molten material is first discharged to the main reactor cavity (cavity1) after LB-LOCA with SBO accident and then passed through the secondary reactor cavity (cavity2) to the collection chamber (cavity3). In the secondary reactor cavity, the first layer is sacrificial concrete with a thickness of 10 cm, the second layer is zirconium-dioxide with a thickness of 10 cm, and finally the third layer is serpentine concrete with a thickness of 40 cm. In the collection room, the first layer is sacrificial concrete with a thickness of 10 cm, the secondary layer is zirconium-dioxide with a thickness of 20 cm, and finally the thickness of the serpentine concrete is 20 cm. In order to study and simulate the design, MELCOR 1.8.6 and ANSYS-FLUENT codes are used. The conditions of the molten core are calculated using MELCOR code in the passing channel and collection room including: the total volume of molten material, the temperature of the upper part of the molten material pool, the rate of the heat of decomposition of molten material, the heat transferred to concrete in areas of molten material and also the displacement time. The FLUENT code is used to estimate the temperature and thermal strength of the embedded layers. After comparing the results obtained from MELCOR and ANSYS-FLUENT code, it could be concluded that it is possible to preserve the molten material up to 24 h after entering the molten material into the cavity and the design area without water injection. Furthermore, by injecting water in the collection chamber, the possibility of long-term and permanent storage of molten materials is possible.

Thermal control of lithium-ion batteries for electric cars by metal foam partially filled with Phase Change Material

A viable solution to environmental problems related to pollutant emissions from internal combustion engine vehicles is electric cars. The main problem with electric vehicles, which also limits their widespread use, is due to lithium batteries and in particular their thermal control. Thermal control of lithium batteries is an extremely topical issue since it is not only related to the performance of the vehicles on which they are mounted, but also to the safety of the vehicles and drivers. For this purpose, both factors internal to the battery itself and external causes such as environmental conditions must be considered.In this work, a thermal control system based on metal foams partially filled by the phase change material (PCM) was numerically investigated as a possible application for cooling lithium batteries. For this purpose, a two-dimensional numerical model was constructed in which the PCM partially fills the metal foam. The finite volume method used through the ANSYS Fluent code was used for the governing equations, which are written assuming local thermal equilibrium. Several cases were simulated for different values of the external convective heat transfer coefficient. The results obtained, are reported in terms of temperatures and liquid fractions. Comparisons with partially filled and totally filled cases by PCM in the thermal control system are reported to show the advantage obtained, in terms of thermal control, with a composite system of metal foam and PCM.

Numerical analysis of a developing turbulent flow and conjugate heat transfer for molten salt and liquid sodium in a solar receiver

• Temperature uniformity within a solar receiver using guide vanes was investigated. • Friction coefficient and Nu number were reported for liquid sodium and molten salt. • The effect of wall heat flux on fluid flow and heat transfer was studied. A numerical analysis of the developing flow and conjugate heat transfer in a solar receiver tube with a three-blade guide vane at the tube inlet was performed to investigate the effect of guide vane and working fluid on the flow and temperature distribution in a solar receiver tube subjected to the boundary condition of the non-uniform wall heat flux. Three dimensional Navier-Stokes, energy, and Laplace equations were solved numerically using Fluent code for the molten solar salt and liquid sodium as the working fluids. The SST k-ω turbulence model was used to predict the flow behavior inside the tube. The values of the friction coefficient and Nu number predicted by the numerical analysis were compared to and validated against experimental correlations from the literature. The numerical results show that a significantly lower pressure drop, and more uniform temperature distribution in the receiver tube are achievable by using the liquid sodium, compared to the molten solar salt. Application of a three-blade guide vane improves temperature uniformity across the receiver tube cross-section, but increases pressure drop in the developing flow region and, thus the overall pressure drop in the tube. The increase in the pressure drop is attributed to the swirling flow and higher friction coefficient compared to the fully developed flow for both working fluids studied in this work.

Neutronics and thermal-hydraulics coupling analyses on transient and accident behaviors of molten chloride salt fast reactor

ABSTRACT Neutronics and thermal-hydraulics coupling transient analyses have been carried out to investigate the intrinsic safety characteristics and fuel temperature ranges of a molten chloride salt fast reactor. The analysis system includes a primary heat transport system and a secondary heat transport system connected by aheat exchanger and a decay heat removal system connected to the secondary system. The neutronics and thermal-hydraulics coupling analysis was performed with the RELAP5-3D code to analyze the entire plant behavior of each event, the temperature and velocity of the reactor inlet flow were obtained, and the reactor power was analyzed in detail following the FLUENT code. Through these analyses, the most severe events for the reactor were revealed. Analysis using the two codes showed that the reactor power calculated by RELAP5-3D was in good agreement with that of FLUENT although the detailed flow inside the core could not be reproduced.

Investigation on precursor flow of cased telescoped ammunition coupling interior ballistic process

The Cased Telescoped Ammunition (CTA) adopts a new launching technology, which has the advantages of short projectile feeding distance, fast launching speed, compact structure. In the process of weapon launching, due to the continuous acceleration of the projectile, the gas in front of the projectile is compressed to form a shock wave. After the shock wave exits the muzzle, it expands rapidly and forms a precursor flow. In order to study the characteristics of shock waves and the formation of precursor flow, the two-dimensional axisymmetric muzzle flow field model of a 6mm CTA bullet is established. Based on the charge characteristics of CTA, a two-stage zero-dimensional interior ballistic mathematical model is established. The zero-dimensional interior ballistic model is coupled with the muzzle flow field model by the user-defined functions (UDF) of CFD code FLUENT. The model is numerically calculated and the mesh independence is verified. The numerical results are in good agreement with the experimental results, which shows the accuracy of the model. From the numerical results, it can be found that compared with conventional ammunition, the shock wave formation process of CTA is later, and the muzzle velocity is increased by 4.2%.

Heat Transfer Enhancement in Pipe Using Al2O3/Water Nanofluid

Convection heat transfer is widely used in many industrial heat and cooling systems. The heat convection can be enhanced passively by adding metal nanoparticles in the water that have been adequately consumed. Small solid metals or nanoparticles of metal oxides floating in the base liquid increase the efficiency of thermal transmission in the system. Commercial CFD code FLUENT is used to simulate water-based nanofluids and is considered to be a single-phase fluid. The effects of various parameters such as Nusselt number and friction factor are studied as a function of Reynolds number and particle volume fraction. The volume fraction of 0.5, 1.0, and 2.0 percent of the Al2O3 nanoparticles was investigated, with Reynolds numbers between 6000 and 12,000. The numerical results show that nanofluids have a higher efficiency in convection heat than basic fluid and an improved thermal transfer efficiency with Reynolds numbers and volume concentrations.

Numerical simulation of natural convection and heat transfer in a molten pool with embedded cooling tubes

This study described the natural circulation and heat transfer of a molten pool in a specifically designed core catcher conceived for a pressurized water reactor. In addition to external cooling, the core catcher features internal cooling tubes embedded in the molten pool. To investigate the coolability in such a configuration, first, a full-scale core catcher simulation is conducted to give a preliminary study under a real SA situation. Results illustrated that cooling efficiency can be remarkably enhanced due to the inner tubes. Then a test facility of the 2D slice with the geometrical scaled factor of 1:4 has been developed, and molten salt (NaNO3–KNO3) experiments will be implemented in the near future. This study also performed a pre-test simulation using molten NaNO3–KNO3 as a stimulant to study the heat transfer and flow characteristics of the salt pool. The melt convection in the test section was represented by a two-dimensional mesh with a WMLES turbulence model using the FLUENT code. The simulation captured the heat transfer enhancement by the cooling tubes as expected, and the results would help decide the proper test matrix and improvement of instrumentation required to obtain the necessary data for code validation.

Three-dimensional modeling of sputtered materials transport in diagnostic ducts of fusion devices

Migration of plasma erosion products in plasma facilities is studied experimentally and numerically within the framework of modeling transport of plasma-facing materials in the diagnostic ducts of fusion devices. Material transport simulation is discussed for two cases of low and high background neutral gas pressures. Monte Carlo software KITe was used to simulate transport at a neutral gas background pressure 0.1–0.5 Pa—typical during steady-state tokamak operation and during pressure pulses caused by edge localized modes (ELMs). The simulation approach was implemented to describe experiments at the MAGNUM-PSI facility. Fluid dynamic code FLUENT is used to simulate transport during pressure surges as high as 1000 Pa, which can occur in the case of severe disruptions in tokamak plasma discharges, such as vertical displacement events (VDE) or accidental events. The hydrodynamic approach was verified in simulation of target sputtering in the QSPA plasma gun facility.

Numerical simulation and experimental validation of an ultra-low head hydro turbine

The huge energy potential is available at ultra-low heads with high-flow rates.The cost-effective prototype hydro turbine was designed for the application at an ultra-low head site, ranging between 1 and 1.30 m. The leading and trailing edges of guide vanes are shaped to give a better aerodynamic performance in a turbulent flow. The cambered airfoil section (NACA 66 mod.) with a uniformly varying cross-section from hub to tip was selected for rotor blades. The cascade effect on the turbine's performance was studied for two different rotors having three and four identical blades. The computation of three-dimensional flow through the turbine was done using ANSYS Fluent code. The calibrated five-hole probes were used to measure absolute velocity along a radial direction at upstream and downstream of the rotor. The results of experimental tests, design and numerical simulations were plotted and compared. The cascade combination of a three-blade rotor and nine guide vanes gave optimum results. This combination at the design flow rate reduced the axial thrust on the shaft. Experimental results of three rotor blade and nine guide blade combination showed good agreement with numerical results.

Numerical and experimental investigation of heat and mass transfer performance of pool boiling type shell and plate evaporator

Computational fluid dynamics is critical for promoting understanding of evaporation heat transfer in chevron plate heat exchangers. In this study, the volume of fluid method is employed in the FLUENT code to solve two-phase flow. The Lee model is employed to simulate the phase change of the refrigerant R134-a. Validation is performed by comparing the predicted heat transfer coefficient and experimental data. The effects of surface roughness, saturation temperature (Ts) of the refrigerant, heat flux, and spacing between the plates (S) on the heat transfer coefficient and flow field are studied. The predicted and experimental results indicate that surface roughness has a significant effect on the heat transfer coefficient, nucleation site density, and size of the detached bubbles. The value of S of the evaporator was varied (S = 17, 12, and 7 mm) to predict the optimal heat transfer performance. The predicted results show that at S = 12 mm, the plate heat exchanger exhibits good performance. The saturation temperature of R-134a exhibits a considerable effect on heat transfer coefficient when Ts increased from 4.4 to 7°C, but shows no effect on increasing Ts to 10°C.

Film Cooling Holes Performance on A Flat Plate

The present study aims to evaluate numerically the influence of film cooling holes configuration. Five models of holes configuration were studied to examine the effectiveness of a single film cooling hole (8 mm diameter). A cylindrical hole, square hole, rotated square, triangle hole and rotated triangle hole was employed to eject the coolant air with constant cross sectional area at 350 angle of injection. A 3-D finite-volume method was utilized to describe the turbulent flow over flat plate surface (as a model of a turbine blade surface). The mainstream domain (40d x10d x4d) had been represented in ANSYS FLUENT 16 with a standard turbulence model. So far, in term of effective cooling, the numerical results elucidate noticeable enhancement realized at BR=0.5 due to a reduction in plate surface temperature compared with BR =0.25 and 1 for cylindrical hole model. Moreover, the holes configuration performance demonstrate a better surface effectiveness about 1.6 % and 1.2 % for rotated triangle and square models respectively compared with the cylindrical holes model at BR=1. It was found that the numerical results had an excellent matching with related published results which show the solidity of ANSYS FLUENT code to predict the cooling efficiency with varying blowing ratio.

CFD‐based analysis of entropy generation due to mean and fluctuating fields during turbulent natural convection in a square enclosure

AbstractThe current study aims to numerically investigate the entropy generation during the natural convection flow of air in a square cavity. The governing equations for the conservation of mass, momentum, energy, and turbulence are solved using a control volume‐based technique employing the commercial code Fluent. Runs have been performed for both laminar and turbulent flow regimes by varying the Rayleigh number (Ra) from 103 to 1010. On the other hand, various viscous distribution coefficients (ϕ = 10−4, 10−3, and 10−2) and constant Prandtl number (Pr = 0.71) were considered. Given the conflicting perspectives in the literature regarding the entropy generation under turbulent regimes, more research is needed to better understand the impact that the fluctuating flow has on entropy production. The four terms of entropy generation inherent to turbulent natural convection (entropy generation due to dissipation in the mean and the fluctuating velocity fields in addition to the heat flux due to the mean and the fluctuating temperature) are computed in the present work and compared to calculations based on only mean values of temperature and velocity gradients. It was found that taking into account the fluctuating terms of temperatures and velocities augment the total entropy generation by 10.10%, 14.43%, and, 17.70%, up to 32.60%, respectively, for Ra = 5 × 108, Ra = 109, Ra = 1.58 × 109, and Ra = 1010. The gain shows the tendency to increase with the Rayleigh number. Thus, the fluctuating terms cannot be neglected particularly for high Rayleigh numbers. Furthermore, unlike entropy production due to the mean flow field, numerical outcomes reveal that the generated irreversibilities due to fluctuating flow are located around the upper hot and the lower cold corners of the heated walls. In addition, a numerical relationship between the first and the second laws of thermodynamics has been derived. A promising result that emerged from this study has shown that the Nusselt number and therefore the first law of thermodynamics is sufficient to estimate the heat part of entropy generation without the necessity of using the second law.

CFD simulation of partial channel blockage on plate-type fuel of TRIGA-2000 conversion reactor core

A nuclear reactor cooling system that has been operating for a long time can carry some debris into a fuel coolant channel, which can result in a blockage. An in-depth two-dimensional simulation of partial channel blockage can be carried out using FLUENT Code. In this study, a channel blockage simulation is employed to perform a safety analysis for the TRIGA-2000 reactor, which is converted using plate-type fuel. Heat generation on the fuel plate takes place along its axial axis. The modelling of the fuel-plate is in the form of a rectangular sub-channel with an inlet coolant temperature of 308 K with a low coolant velocity of 0.69 m/s. It is assumed that blockage is in a form of a thin plate, with the blockage area being assumed to be 60 %, 70 %, and 80 % at the sub-channel inlet flow. An unblocking condition is also compared with a steady-state calculation that has been done by COOLOD-N2 Code. The results show that a partial blockage has a significant impact on the coolant velocity. When the blockage of 80 % occurs, a maximum coolant temperature locally reaches 413 K. While the saturation temperature is 386 K. From the point of view of the safety aspect, the blockage simulation result for the TRIGA-2000 thermal-hydraulic core design using plate-type fuel shows that a nucleate boiling occurs, which from the safety aspect, could cause damage to the fuel plate.

Research on decay heat removal effectiveness in pool-type fast reactor CEFR based on system code SAC-DRACS coupled with CFD software

In station blackout(SBO) accident, the establishment and maintenance of natural circulation in the China Experimental Fast Reactor(CEFR) mainly relies on the decay heat removal system(DHRS). However, due to the complex structure of the reactor, it’s very difficult to model the full-scale CEFR. In the present work, DHRS and the primary circuit system of the CEFR are modeled by the System Analysis Code for Direct Reactor Auxiliary Cooling System (SAC-DRACS) code and three-dimensional CFD software FLUENT, respectively. Then the long-term transient simulation of 4000 s is calculated by coupling SAC-DRACS and CFD codes. The overall temperature stratification and local core temperature variations in the pool caused by DHRS are analyzed. Meanwhile, the residual heat removal capacity of DHRS is evaluated, the average core outlet temperature does not exceed 500.3 °C under the action of DHRS. This work provides an extension of the research method for the pool-type fast reactor safety analysis.

The Impact of Nanofluid on Natural Convection in an Isosceles Rectangular Container with a Heat Source

The development of modern technology in microelectronics and power engineering requires the creation of efficient cooling systems. This is made possible by the use of special fin technology inside the cavity or special heat transfer Ethylene glycol-copper nanofluids to intensify the heat removal from the heat-generating elements. A numerical study of the natural convection of stationary laminar heat transfers in a closed rectangular cavity with a local source of internal volumetric heat generation. For different Rayleigh numbers and different volume fractions of nanoparticles. The system of equations governing the problem was solved numerically by the fluent computer code based on the method of finite volumes. Based on the Boussinesq approximation. Interior and exterior surfaces are maintained at a constant temperature. The study is carried out for Rayleigh numbers ranging from 104 to 106. The effects of different Rayleigh numbers and volume fractions of nanoparticles on natural convection have been studied. The results are presented as isotherms, isocurrents, and local and mean Nusselt numbers. The aim of this study is to see the influence of the thermal Rayleigh number and the volume fraction of the nanoparticles on the rate of heat transfer.