Fluent Model Research Articles

Pairing Directional Solar Inputs From Ray Tracing to Solar Receiver/Reactor Heat Transfer Models on Unstructured Meshes: Development and Case Studies

Abstract A novel method for pairing surface irradiation and volumetric absorption from Monte Carlo ray tracing to computational heat transfer models is presented. The method is well-suited to directionally and spatially complex concentrated radiative inputs (e.g., solar receivers and reactors). The method employs a generalized algorithm for directly mapping absorbed rays from a Monte Carlo ray tracing model to boundary or volumetric source terms in the computational mesh. The algorithm is compatible with unstructured, two and three-dimensional meshes with varying element shapes. Four case studies were performed on a directly irradiated, windowed solar thermochemical reactor model to validate the method. The method was shown to conserve energy and preserve spatial variation when mapping rays from a Monte Carlo ray tracing model to a computational heat transfer model in ansys fluent.

Simulation of binary particle segregation for bubbling fluidized beds using polydispersed structure‐based drag model extended from a monodispersed model

AbstractA bubble structure‐based drag model developed for the monodispersed system has been extended to simulate bi‐dispersed bubbling fluidized beds. Both dense phase and dilute phase are considered to be comprised of two types of particles with different sizes. The derivation of the structure‐based drag coefficient for individual particle based on the force equilibrium principle is proved to be independent of the volume fractions (εsi) of particle i. The multi‐fluid model in the commercial software Ansys Fluent is employed to evaluate the polydispersed drag model for the segregation of binary gas‐particle flows in a bubbling fluidized bed. It is shown that the simulation results predicted by the new structure‐based drag model are in reasonable agreement with experimental data with a 6.34% root mean square error (RMSE). The new structure‐based model can capture the particle distribution at the top region of the fluidized bed well. The bubble behaviour can also be captured by the new model well.

The Influence of Groove Structure Parameters on the Maximum Flow Resistance of a Rectangular Narrow Channel

In the hydraulically suspended passive shutdown assembly, in order to prevent the liquid suspension rod falling too fast and the outer tube from violent impact, it is necessary to study the way to increase flow resistance. This study added grooves to the wall of the narrow channel to increase its flow resistance. Using the RNG k-ε turbulence model in Fluent, the influence of the groove structure parameters and the Reynolds number on the flow resistance of the narrow channel was discussed to find the optimal groove structure parameters. The results showed that the flow resistance of the narrow channel increased with the increase in the concave–convex ratio, and when the concave–convex ratio was small, the flow resistance decreased with increased groove thickness, while when the concave–convex ratio exceeded a certain critical value, the flow resistance increased with increased groove thickness. Additionally, the growth rate slowed down when the concave–convex ratio was greater than 3:1. As the unit length decreased, the flow resistance first increased and then decreased. When the unit length was 6 mm, the flow resistance reached the maximum. With the increase in the Reynolds number, the intensity of the local high-turbulence kinetic energy clearly increased.

Transition Delay and Drag Reduction using Biomimetically Inspired Surface Waves

This paper explores the use of Two-Dimensional sinusoidal surface features to delay transition and/or reduce drag. The authors, in this paper demonstrated that the presence of low amplitude sinusoidal surface features might damp the disturbances in the laminar boundary layer, reduce wall shear stress and maintain laminar flow for longer than a conventional flat plate. The hypothesis of the paper is inspired by the simplification of the dermal denticle on the surface of the shark-skin. Simulations are carried out using the Transition SST model in FLUENT based on the evidences of the transition model being suitable for a wider variety of high curvature scenarios. The surface waves are simulated for different amplitudes and wavelengths and their impact on transition onset and drag reduction are quantified at different velocities. Results presented in this paper indicate that a transition delay of 10.8% and a drag reduction of 5.2% are achievable. Furthermore, this paper adds credence to the notion that biomimicry is a very promising avenue for future drag reducing methods.

Simulation of micro plastic filtration for existing filters

This paper uses DPM model in Fluent to divide the mesh and conduct fluid analysis for the existing family filter, by using the Rosin - Rammler distribution simulated reality of different diameter of the plastic particles’ distribution in the water. Secondly, using particle tracking algorithm to calculate the distribution of particle diameter of the export, so as to check the existing household filter’s ability for the different plastic particle diameter.

МОДЕЛИРОВАНИЕ СЖИГАНИЯ БИОГАЗА В ИНЖЕКЦИОННОЙ ГОРЕЛКЕ С ТЕПЛОВЫМ РАССЕКАТЕЛЕМОГАЗА В ИНЖЕКЦИОННОЙ ГОРЕЛКЕ С ТЕПЛОВЫМ РАССЕКАТЕЛЕМ

The purpose of this work is to develop a design of a biogas combustion equipped with a thermal divider and study the process of burning biogas of different composition. To study the biogas combustion process in the burner of the developed design, the Ansys Fluent modeling software package is used. An injection burner for biogas combustion with a cone-shaped thermal divider and primary air regulator has been developed. Studies of the process of burning biogas of different composition in burners of 5 designs were carried out: without a divider, with a divider with a length of L = 6 mm, with a divider L = 12 mm, with a divider L = 18 mm and a divider L = 24 mm. As a result of modeling, it is found that the placement of a divider with a length of 6 mm and 12 mm does not affect the temperature of the gas-air mixture in the burner body. Increasing the length of the divider to 18 mm allows to increase the temperature of the flow of the gas-air mixture passing along the divider. A further increase in the length of the divider to 24 mm leads to a slight increase in the temperature of the gas-air mixture. The dependences of the flame temperature on the length of the divider during the combustion of biogas with a methane content of 60% and 70% are obtained. When a divider with a length of 6 mm and 12 mm is placed in the burner body, the flame temperature decreases, with an increase in the length of the divider to 18 mm, the flame temperature increases, and with an increase in the length of the divider to 24 mm, the flame temperature remains practically unchanged. Consequently, the placement of a divider with a length of 18 ... 24 mm in the burner body ensures preliminary heating of the gas-air mixture and allows increasing the efficiency of the biogas combustion process.

Performance investigation on twisted elliptical tube heat exchangers with coupling-vortex square tube layout

The twisted elliptical tube heat exchangers with the novel coupling-vortex chessboard tube layout (TETHXs-CV) were simulated with the RNG k-ε model in software Fluent 15.0. The shell-side flow pattern at the tangential points between adjacent tubes in traditional TETHX is countercurrent while that in TETHX-CV is concurrent, which helps enhance heat transfer capability without any extra manufacturing cost. The impacts of the ratio A/B of the major axis to the minor axis and the twist pitch S were also investigated. The results indicate that with the increase of A/B and the decrease of S, the secondary flow behaves more intensely, the Nusselt number Nu and the friction factor f increase, while with the increase of A/B and S, the comprehensive evaluation index Nu∙f−1/3 increases. The Nu, f and Nu∙f−1/3 of all twisted tube schemes are higher than those of the smooth round tube schemes R10.8. Compared with corresponding parallel-vortex schemes, the coupling-vortex schemes possess more uniform temperature fields, and the average Nu, f and Nu∙f−1/3 of the coupling-vortex schemes C12.3S50/C12.3S100 increase by 12.8%/9.9%, 15.2%/10.5% and 7.6%/6.3%, respectively; the smaller S or the closer A/B is to 1, the more advantageous the TETHX-CV.

Simulation of Tidal Energy Extraction, Using Fluent Model

This study has been performed to develop our knowledge about marine sources energy extraction. Water in the channel has been simulated in laboratory scale by means of FLUENT software. The turbine tidal flow is generated by a moving disk which applies a pressure decrement with energy dissipation. Free water surface is estimated by means of fluid volume in the model which changes freely. The numerical results illustrate that eddy sequence has been generated after the tidal flow of turbine and a flow acceleration is generated nearby, especially beneath the energy extraction devise. Free water surface drop due to energy extraction is considered in model results that seems a to improve the turbine eddy sequence.

Hydrate-Induced Vibration in an Offshore Pipeline

Summary Gas-hydrate plugging poses an operational challenge to offshore petroleum production and transportation. In this study, a computational-fluid-dynamics (CFD) model that uses ANSYS Fluent (ANSYS 2019) multiphase-flow-modeling techniques to simulate and analyze the effect of gas-hydrate flow in pipelines is proposed. For this purpose, the study attempted to integrate the ANSYS Fluent model with an existing commercial subsea-pipeline-visualization tool. To validate the simulation results, two case studies were conducted. The first study was about a pipeline whose dimensions are based on the specifications in existing literature (Balakin et al. 2010a). The second study was about a pipeline with more-complex geometry (M-shaped jumper with six elbows). The Eulerian/Eulerian method was used to model the multiphase hydrate flow. The population-balance method (PBM) was then used to model hydrate agglomeration and its breakup mechanism in the flow. A parametric study of the stresses in the pipelines resulting from flow-induced vibration (FIV) was conducted to identify the regions that underwent the maximum stresses and deformations under various flow conditions. The tool can be used in the petroleum industry to identify the operational hazards in offshore structures and to take necessary safety measures to avoid any potential catastrophic events.

Features of Mass Transfer of Noncondensable Gases by Primary Coolant of Nuclear Icebreaker Reactors

To study the characteristics of the mass transfer of noncondensable gases in the primary loop of the nuclear icebreaker reactors, models of the core and the up-core space were developed using the Relap5 (USA) and Fluent (USA) codes and modeling of interphase mass transfer and transport of the gas phase by the water coolant was performed on these sections. Spatial non-uniformity of the content of undissolved gases, which arises as a result of vapor-gas bubbles concentrating in the vortex structures of the flow and resulting in a significant reduction of their dissolution rate, was revealed. This must be taken into account in the analysis of the operation of the primary loop equipment of nuclear icebreakers (hydrogen absorption in the titanium alloys of steam-generator piping, nodular corrosion of the zirconium cladding of the fuel rods).

Numerical investigation of heat transfer in a helically coiled tube using copper/water nano-fluid under constant heat flux and prediction of the results using perceptron and radial basis function networks

This study investigated the numerical analysis of Nusselt number and entropy generation of copper/water nano-fluid under turbulent flow conditions at volume fraction ranges of 1–5% within a helical coil under constant heat flux. The nano-fluid behavior was modeled through a single-phase model. Flow and heat transfer governing equations were discretized using finite volume method, and the SIMPLE algorithm was used to solve pressure-velocity coupling equations. The turbulence modelling was done by k-e turbulence model in ANSYS FLUENT 15. Then, the examination and prediction of the resulted data were carried out using perceptron and radial basis function networks. The innovation of the present study was the application of an unsupervised method (namely, SOM) to specify the winner neuron. Input data of the artificial network included Reynolds number, input temperature, constant heat flux, nano-fluid thermal conductivity coefficient and nano-fluid volume fraction, while output parameters included Nusselt number and total entropy generation. The results showed that Nusselt number, entropy generation yielded from heat transfer, and friction increased as the Reynolds number increased. With an increase in the volume fraction, entropy generation yielded from heat transfer and friction decreased and increased, respectively. The results of artificial networks revealed that self-organizing map (SOM) model had 25 neurons, possessing the highest amount of data. Moreover, Mean Squared Error (MSE), correlation coefficient, and maximum error, Nusselt number and total entropy generation for perceptron neural network were 5.0103,0.996,9.1865, 4.389 × 10−5, and 0.998,0.0259, respectively, confirming a successful prediction. In addition to radial basis function networks, the values of Mean Squared Error (MSE), Root Mean Squared Error (RMSE), standard deviation(σ) and a kind of Error(μ) for Nusselt number and entropy generation total were 8.2255 × 10−8,0.0002868,0.00028718,4.741 × 10−6 and 6.0157 × 10−8,0.00024527,0.00024549,7.9006 × 10−6, respectively.

CFD modeling of industrial cold box with plate-fin heat exchanger: Focusing on phase change phenomenon

Cold box with plate-fin heat exchanger (PFHE) is extensively used in liquefied natural gas (LNG) refinery plants. In the present study, a CFD model in ANSYS FLUENT is developed for better understanding the transport phenomena, especially the phase change, in a quite complex plate-fin heat exchanger operated in a gas refining company. The flow channels, ducts and passes of the cold box, are considered in the computational geometry. The porous media technique is introduced in the computational domain due to the excessive increase in the number of computational grids when the fins accounted for in the numerical domain. The flash calculations (FC) technique is coupled with CFD in evaluation of chemical species in the cold box by a user defined function. This study examines the importance of local thermal equilibrium between the porous medium and fluid flow without mass transfer (LTE-non mass), local thermal equilibrium between the porous medium and fluid flow with mass transfer (LTE), and local thermal non equilibrium between the porous medium and fluid flow with mass transfer (LTNE) in simulation of an industrial cold box. Numerical results are compared with the corresponding operational data and the best agreement is obtained by the LTNE approach. The calculated mean relative errors of the LTNE approach for the outlet vapor fraction of streams A, hot stream, B and C, sided cold streams, are 0.15, 0.352, and 0.173%, respectively.

Simulation of aggregation effects on co-fired biomass-coal ash in an electrostatic precipitator

Aggregation of fine ash into larger particles benefits fly ash removal in an electrostatic precipitator. Thermal aggregation, turbulent aggregation, and electrical aggregation of fine ash (derived from co-firing of biomass fuel and anthracite coal) was simulated under different conditions in an electrostatic precipitator. A population balance model and user-defined function in Fluent were assumed to obtain aggregation kernel functions and calculate the aggregation effects on the co-combusted particles. The results show that electrical aggregation had an obvious effect on both micron- and submicron-sized particles. For submicron particles, the effect of thermal aggregation is about ten times greater than turbulent aggregation. Meanwhile, for micron-sized particles, turbulent aggregation is about seven times greater than thermal aggregation. Therefore, particle aggregation in the electrostatic precipitator mainly occurs because of electrical aggregation, supplemented by thermal aggregation and turbulent aggregation. When the flow velocity is 1.0m/s, particle volume fraction is 1.4%, and biomass co-firing ratio is 10%, the effects of all three aggregation processes on ash particles are optimized.

Study on Quantitative Sewage Blowing-Off and Real-Time Sewage Level Detection of Submarine Storage Tank

Aiming at the problems of huge exhaust noise and air bubbles caused by sewage blowing-off at an inappropriate time for a submarine ST, a sewage level detection system is designed, which can detect in real-time the sewage level using a weighing sensor to achieve quantitative sewage blowing-off. Therefore, the theoretical analysis of the sewage blowing-off is carried out, and the process of the sewage blowing-off is simulated by a VOF model of Fluent. From the simulation, the gas-liquid volume distribution diagram, the volume curve of the sewage, and the flow rate curve of the outlet sewage are obtained. Furthermore, the installation and detection method of the weighing sensor are described in detail. Finally, an experimental test system for simulating the sewage blowing-off is established, and an ultrasonic liquid level sensor, capacitance level sensor, and weighing sensor are tested. By comparing the effects of the three sensors, the result shows that the weighing sensor is the most effective for real-time sewage level detection during the process of sewage blowing-off and can effectively reduce the exhaust noise of the sewage blowing-off system.

Spread of hydrogen vapor cloud during continuous liquid hydrogen spills

The spread of hydrogen vapor cloud during continuous liquid hydrogen spills is numerically investigated. Comparison between terminated and continuous spills has also been carried out. The two-phase flow is predicted by Mixture model and Realizable k-ε turbulence model in ANSYS FLUENT. The flammable vapor cloud reaches a steady state with little changes in dimension and volume during continuous spills. Spill rate and wind speed is positively related with the maximum length of the flammable cloud, while the influence of ambient ground temperature is not obvious. Since the moment of spill termination, the length and height of the flammable cloud continue to develop along the continuous trajectory for certain duration, while the volume of the hydrogen vapor cloud deviates instantly. The present work deepens the understanding on continuous liquid hydrogen spills, and provides guidance for determining the safe stand-off distance.

Effects of dynamic changes in inlet temperature on proton exchange membrane fuel cell

To examine the effects of the inlet temperature on a proton exchange membrane fuel cell (PEMFC), this study proposes a dynamic temperature (DT) model by considering the dynamic variation in temperature that influences the water content of the cell and its performance. A three-dimensional model featuring the geometry and nonconformal mesh of the PEMFC is first formulated. An experiment was then conducted featuring a 34-cm2 single-cell and test system. Following this, a simulation and another experiment were carried out at a working temperature of 333 K with 100% relative humidity (RH) at inlet temperatures of 316 K, 323 K, and 328 K (at 50%, 60%, and 80% RH, respectively). The contours, which included hydrogen in the channels and water in the membrane, were then described. The results show that the proposed DT model can more accurately predict the performance of the PEMFC than the FLUENT model. In particular, when the inlet temperature was 328 K (80% RH), the maximum relative difference between the DT model and FLUENT was 13.8% compared to the results of the experiment. The hydrogen content in the channels decreased and the water content in the membrane increased as the reaction continued. The proposed model provides a new means for studying the effects of dynamic temperature on the PEMFC.

Numerical and experimental investigation of flow around a balloon-shaped bluff body

Air accumulator is a critical component in Underwater Compressed Air Energy Storage systems and Buoyancy Energy Storage systems. In order to bridge the gap between the CFD simulations and experiment verification of flow around air accumulator, in this study, the force characteristics and flow structures around a balloon-shaped air accumulator bluff body model have been investigated using a computational-experimental dual prong method for the first time. The three-dimensional Unsteady Reynolds Averaged Navier-Stokes (URANS) closure is achieved through the k-ω SST turbulence model in FLUENT. The force characteristics and flow structures are measured in a low-speed closed-loop wind tunnel to verify the simulation results. The free end and shape effects are investigated by comparing the flow structure of three different but interconnected bluff bodies at the equivalent Reynolds number of 7.0 × 104. The results show that the k-ω SST turbulence model can correctly predict the time-averaged force characteristics of the balloon-shaped bluff body and flow structures in the wake. Besides, the distinct vortex structures are induced due to the free end and tapered shape effects.

Computational fluid dynamic and thermal stress analysis of coatings for high‐temperature corrosion protection of aerospace gas turbine blades

AbstractThe current investigation presents detailed finite‐element simulations of coating stress analysis for a three‐dimensional, three‐layered model of a test sample representing a typical gas turbine component. Structural steel, titanium alloy, and silicon carbide are selected for main inner, middle, and outermost layers respectively. ANSYS is used to conduct three types of analysis—static structural, thermal stress analysis, and also computational fluid dynamic erosion (via ANSYS FLUENT). The specified geometry, which corresponds to corrosion test samples exactly, is discretized using a body‐sizing meshing approach, comprising mainly of tetrahedron cells. Refinements were concentrated at the connection points between the layers to shift the focus toward the static effects dissipated between them. A detailed grid independence study is conducted to confirm the accuracy of the selected mesh densities. The momentum and energy equations were solved, and the viscous heating option was applied to represent the improved thermal physics of heat transfer between the layers of the structures. A discrete phase model (DPM) in ANSYS FLUENT was used, which allows for the injection of continuous uniform air particles onto the model, thereby enabling an option for calculating the corrosion factor caused by hot air injection. Extensive visualization of results is provided. The simulations show that ceramic (silicon carbide) when combined with titanium clearly provide good thermal protection; however, the ceramic coating is susceptible to cracking and the titanium coating layer on its own achieves significant thermal resistance. Higher strains are computed for the two‐layer model than the single layer model (thermal case). However even with titanium only present as a coating the maximum equivalent elastic strain is still dangerously close to the lower edge. Only with the three‐layer combined ceramic and titanium coating model is the maximum equivalent strain pushed deeper towards the core central area. Here the desired effect of restricting high stresses to the strongest region of the gas turbine blade model is achieved, whereas in the other two models, lower strains are produced in the core central zones. Generally, the CFD analysis reveals that maximum erosion rates are confined to a local zone on the upper face of the three‐layer system which is in fact the sacrificial layer (ceramic coating). The titanium is not debonded or damaged which is essential for creating a buffer to the actual blade surface and mitigating penetrative corrosive effects. The present analysis may further be generalized to consider three‐dimensional blade geometries and corrosive chemical reaction effects encountered in gas turbine aero‐engines.

Heat transfer enhancement of charging and discharging of phase change materials and size optimization of a latent thermal energy storage system for solar cold storage application

Abstract In this work, phase change material (PCM) is considered as thermal energy backup system for solar cold storage applications when there is peak power demand or power failure or no sun shines situations. A numerical study of solidification (charging) and melting (discharging) of PCM validated by experimental data is performed to explore the performance of a unique latent heat thermal energy storage (LHTES) system. The LHTES unit (PCM pack) occupied with PCM acts as a heat exchanger made up from evaporator tube along with rectangular metal fins which enhance the heat transfer during phase changing of PCM. Evaporator with 5, 8, 10, and 12 longitudinal aluminum fins, and without fin inside the PCM pack of six different thicknesses (4.5 cm, 5.0 cm 5.5 cm, 6.0 cm, 6.5 cm, and 7.0 cm) are considered to investigate the charging and discharging characteristics of PCM in our present study. To obtain the best performance from the PCM pack, heat transfer characteristics and temperature distributions of PCM, and the effect of variation of thickness of the PCM pack are studied through computational fluid dynamics (CFD) simulation. Solidification and melting model of ANSYS Fluent 15.0 package employing enthalpy-porosity technique is used to develop 3-D simulation models. Faster solidification, as well as a higher energy storage capacity and heat flux during melting is found for the PCM pack of 6.5 cm thickness with higher number of fins. A lab scale experimental set-up is fabricated to compare the present simulation results which shows reasonably well validation during both the charging and discharging.

Development of a math module of shell and tube phase-change energy storage system used in TRNSYS

Due to the lack of phase-change energy storage modules in the TRNSYS software, this paper applies the numerical simulation method to develop a TRNSYS module. Research has been conducted on the characteristics of the shell-and-tube phase-change energy storage system in order to provide a reasonable basis for its application in practical engineering. According to the principles of energy conservation, a numerical model has been proposed to calculate the temperature field and fluid temperature field of the phase-change unit, and a mathematical model is applied to guide the editing of the TRNSYS module. A Fluent model was established to compare the TRNSYS simulation results and verify the physical validity of the module. In terms of the thermal outlet temperature of the HTF, the maximum relative error between the two in the melting phase is noted to be 1.17%, and the maximum relative error at the solidification stage is 1.83%.Different flow parameters of the system have been studied. The results of the study indicate that differences in inlet temperatures have a greater influence on the average temperature and outlet temperature of the PCM, whereas differing inlet flows have a negligible influence on the phase-change unit.