Flow Field Distribution Research Articles

Simulation and study of the flow field in a kettle-type reactor for ethylene polymerization

Abstract Addressing the complexities inherent in the polymerization process for solution method polyethylene production, particularly the challenges in describing the turbulent three-dimensional flow field within the reactor and the precise design of reactor structural parameters, this research leverages computational fluid dynamics (CFD) methods integrated with polymerization reaction kinetics equations. We have formulated User-Defined Functions (UDFs) for a quantitative representation of the polymerization process. Employing the Realizable k-epsilon turbulence model and Sliding Grid (SG) technique, we analyzed the flow dynamics and field distribution within the reactor, elucidating the distribution patterns of temperature, pressure, and concentration fields. A comparative assessment of simulation outcomes against experimental data revealed that the average deviation of the simulated temperature field from actual operating conditions falls within the permissible error range, thereby affirming the simulation model’s validity. Utilizing local sensitivity analysis, we investigated the impact of impeller structural parameters on mixing time and stirring power. Our analysis of the most sensitive structural parameters indicated that impeller diameter and the number of impellers are pivotal in reducing mixing time and stirring power, respectively. Notably, the stirring power escalates with an increase in the number of impellers, while the mixing time exhibits a trend of initial decrease followed by an increase with varying impeller diameters. The methodologies and patterns discerned in this study provide insightful design references for the design and optimization of reactors across different tonnages.

Numerical investigation of vehicle water entry with angle of attack

This paper investigates the water entry of a vehicle with angle of attack (AOA) through numerical methods, employing the volume-of-fluid multiphase flow model and overset grid technique. The validity of the numerical model is confirmed through experimental verification. Building upon this, the study analyzes the motion characteristics, cavity evolution, and flow field distribution of the vehicle during water entry, considering the influence of AOA and falling velocity. Numerical findings indicate that the collapse of the right side of the cavity induces a transient lateral force on the vehicle, resulting in vehicle tilting. Moreover, an increase in initial velocity delays vehicle tilt, while an increase in AOA reduces vehicle motion stability, leading to earlier tilting. Initially, the vehicle rotates counterclockwise around the Oz axis of the projectile coordinate system. Subsequent to cavity collapse, the vehicle experiences an opposing moment, leading to a reduction in rotation speed and eventual rotation in the opposite direction. Water impact triggers sudden changes in the vehicle's lift and drag coefficients, while cavity sticking induces a minor abrupt change in the lift coefficient. Following cavity collapse, both lift and drag coefficients exhibit significant oscillations. Unlike typical cavity collapse phenomena, the flow field on the right side of the vehicle undergoes alternating high-pressure and low-pressure regions.

Mechanisms of fluid–structure interaction in an underwater muzzle brake

A fluid–structure interaction (FSI) mechanism of a shock-type underwater muzzle brake is examined. A bidirectional coupling interior ballistic approach is employed to achieve accurate projectile velocity. A velocity–pressure separation solution algorithm, semi-implicit method for pressure-linked equations and the Schnerr–Sauer cavitation model are used to address the volume of fluid multiphase Navier–Stokes equations with compressible cavitation. The full ballistic muzzle flow field distribution is comprehensively modeled. Analyzing the force and flow parameters of the T-shaped underwater muzzle brake based on the numerical solution reveals detailed insights. The underwater muzzle brake provides significant braking force in the interior ballistic period due to the presence of the water medium, which is quite different from air launch. Moreover, while both the internal and intermediate ballistic periods utilize the kinetic energy of the fluid against the wall, the muzzle brake principle in the interior ballistic period is a positive kinetic impact of water, mainly dependent on the flow velocity inside the barrel, and provides 17% recoil impulse. The side holes are significantly affected by cavitation phenomena. In contrast, during the intermediate ballistic period, the kinetic impact of gas, primarily dependent on the high-pressure gas expansion, decreases exponentially with time and provides 36% recoil impulse.

Machine learning assisted mechanism modeling for gas phase electrohydrodynamic system

In this paper, a hybrid physics-data driven model for electrohydrodynamic gas system (EHDGS) was developed by combining artificial neural network (ANN) with mechanism modeling method. ANN was used to correlate the relationship between the variables (electrode distance, diameter of grounding cylinder, applied voltage, electric field gradient, etc.) in a needle-cylinder EHDGS and the initial space charge density. The results showed that the ANN model of nine neurons can well predict the initial space charge density. The coefficient of determination (R2) reaches 0.9874, and the mean absolute error is as low as 0.0067. Subsequently, a hybrid mechanism model where the initial space charge density was predicted from the ANN model was constructed to simulate the needle-cylinder EHDGS. The experiment with the needle-cylinder EHDGS was carried out. The simulation results were in good agreement with the experimental data, demonstrating the reliability of the proposed hybrid model. The electric field distribution, space charge distribution, and flow field distribution behavior of the EHDGS were then analyzed in detail. The effects of key parameters on the flow characteristics of EHDGS were systematically studied, showing that higher voltage and shorter distance give higher flow rate up to 2.5 m/s. The diameter of the cylinder also significantly influences the breakdown voltage. Three dimensionless groups were defined and their effects on spatial charge density distribution were investigated. This study provides both insights and an efficient tool for the design and optimization of EHDGS.

Effect of oyster shell filling in artificial reefs on flow field environment and assessing the potential of carbon fixation

Artificial reefs are basic fishery facilities for marine habitat conservation and construction. In order to enhance fishery resources and restore the ecological environment in Laizhou Bay, where is an important fishing ground in China, an assembly-type oyster reef was designed based on the biological community, water depth and sea current in Laizhou Bay. This paper studied the effect of filling oyster shell in the assembly-type oyster reef on the flow field distribution by computational fluid dynamics (CFD), optimized the structure of reef, and presented the construction deployment of reef habitat and assessed potential of carbon fixation of oyster reefs. Indexes of upwelling, slow flow and vortex were chosen to describe the flow field effect of oyster reefs. The distribution characteristics of flow field under three types of filling oyster shell were analyzed: filling no shell (UAR), filling shells with an 83.6 void ratio (OAR), and filling shells with a 0 void ratio (FAR). The results showed that the upwelling, vortex and slow flow efficiency indicators of the OAR had obvious advantages compared with the other two filling methods, and the efficiency indicators of OAR with the spacing between basic elements of 280 m and deployment angle of 0° were higher than the others. Finally, according to the study result of filling method, spacing and deployment of oyster reef, the assessment showed that reefs could fix 2178.9 t carbon by themselves on the basis of national marine ranching demonstration area regulations in China.

Research on Constant-Flow Water-Saving Device Based on Dynamic Mesh Transient Flow Field Analysis

For the control of the outlet flow rate of a constant-flow water-saving device under different water pressures, this study developed and implemented a custom User-Defined Function (UDF) program to simulate the dynamic motion of the water-saving valve within the Fluent environment. This simulation realistically represents the valve’s behavior under varying water pressures, thereby accurately predicting the valve opening height to comply with national regulatory standards. Firstly, a dynamic grid transient CFD simulation model of the water-saving valve was established using a Fluent UDF program written in C language. The parameters of the elastic elements in the water-saving device flow control system were designed to achieve control of the outlet flow rate. Then, the benchmarking analysis of the aforementioned simulation model was completed based on the flow rate test results of the water-saving device. Finally, the relationship between physical quantities and flow field distribution characteristics of the water-saving valve was analyzed under three different water pressures specified in the national standard. Based on the optimization calculations, the valve opening heights under three different water pressures were obtained, ensuring that the outlet flow rates meet the regulatory standards set by the national authorities. Compared with traditional methods that rely solely on steady-state simulations or empirical data, the method proposed in this paper represents a significant advancement.

Numerical Simulation of the OFA Effect on Combustion in a 600 MWe Boiler with Centrally Fuel Rich Burners

ABSTRACT With the rapid development of renewable energy, the traditional coal-fired power generation plays an important role in peak regulation, which requires the boilers to operate at low load or even ultra-low load. In order to investigate the effect of over-fire air (OFA) ratio on the flow, temperature and component concentration distribution and the furnace exit parameters for utility boilers at ultra-low loads, a 600 MWe utility boiler with centrally fuel rich (CFR) burner technology is taken as the object of study, and numerical simulations are carried out for five operating conditions with different OFA ratios (0%–40%) at 25% of the boiler’s maximum continuous rating (BMCR) load. The results show that no obvious high-temperature region is formed in the furnace and the flow field distribution in the furnace exit area is not conducive to the stable combustion of pulverized coal when the OFA ratio is 0% and 10%. When the OFA ratio is 30%, the area of the high-temperature region in the furnace reaches its maximum. When the OFA ratio is 40%, the furnace exit NO concentration is only 94.54 ppm. With the increase of the OFA ratio from 0% to 40%, the temperature of the flue gas at the furnace exit decreases by more than 100 K, which may affect the stable operation of the Selective Catalytic Reduction (SCR) denitrification equipment. Taking into consideration the flow in the furnace, the combustion, the NO x emission, and other factors, the recommended OFA ratio is 20% ~30%.

The influence of the guide vane positioning on the flow field of a turbo air classifier

AbstractAs the important component to guide the airflow in the classifier, installation position of the guide vane determines the width of the classification annular region and influences the flow field distribution. The influence of the guide vane positioning on the flow field in the annular region is analyzed through numerical simulation. The simulation results show the tangential velocities near the inner edge of the guide vanes increase, and the tangential velocity gradient decreases with decrease of the width of the annular region. The increases of turbulent dissipation rate near the guide vanes are beneficial to powder dispersion. However, the increases of turbulent dissipation rate near the rotor cage aren′t conducive to uniformity of the flow field. In case of the narrow annular region, the cut size gradually increases when the width of the annular region increases. However, when the width of the annular region continues to increase, the particle′s residence time become long, and the solid concentration increases significantly to increase the probability of particle aggregation. The reasonable range of the installation diameter of the guide vane in the classifier is between 504 mm and 524 mm.

Effect of High-Voltage Electrostatic Precipitator Dust Collection Plate Structure on Collection Efficiency.

To investigate the effect of changes in the dust collector structure on the flow field and electric field distribution resulting from the secondary flow generated by the corona discharge in the collector coupled with the main flow and to improve the dust collection efficiency of the ESP, a folding plate design has been adopted. A multiphysics-coupled corona discharge and flow field numerical model was analyzed to analyze the internal flow and electric field characteristics of linear flat plates and folded plates with three different pole configurations. The study indicates that the dust collecting plate's structure significantly affects the dust collector's internal flow field and electric field distribution within the dust collector. The near-plate electric field and flow field inside the folded plate type are superior to those of the linear flat electrostatic precipitator. With the augmentation of the inlet velocity, the ionic wind disturbance on the flow field inside the electrostatic precipitator channel gradually decreases. Additionally, the folding plate has a certain inhibitory effect on the influence of the ionic wind. At an inlet velocity of 0.5 m/s, the speed near the folding plate is approximately 20% lower than that of the traditional linear flat plate. The folding plate can effectively reduce the flow velocity near the dust collection plate, thereby reducing the occurrence of particle re-entrainment and improving dust removal efficiency. By comparing the speed at the center line of the plate and near the plate, it is obvious that the speed of model B decreases significantly, and as the number of discharge electrodes increases, the speed decreases more obviously. At the same time, when the dust collection efficiency of the two models was compared, it was found that the working efficiency of the B model has been significantly improved, among which the B3 model has the best dust collection effect.

Simulation Analysis Based on Sodium-Cooled Fast Reactor Fuel Assembly Under Blockage Accident

This paper employs computational fluid dynamics to investigate the fuel assemblies within a sodium-cooled fast neutron reactor. To begin with, we developed computational models for seven wire spacer fuel rods under both normal operating conditions and transient blockage conditions. We conducted separate analyses to assess the impacts of normal operation, blockage thickness, and blockage area. This work allowed us to acquire data on the heat transfer properties and the flow field variations for the coolant, blockages, and fuel rods across different conditions. Subsequently, we leveraged these flow field alterations to examine the resulting temperature distributions. Analyses were conducted to evaluate the effects of normal operation, blockage thickness, and blockage area. The research acquired the heat transfer characteristics and flow field distribution variations of the coolant, blockages, and fuel rods under different operational conditions and utilized these variations to analyze the temperature distribution. Through research analysis, the following conclusions have been reached. Under normal operating conditions, the temperature and flow fields of the fuel components exhibit cyclic variations along the axial length, corresponding to the pitch of the wire spacers. Heat exchange between the internal and external subchannels occurs independently, which further substantiates that the incorporation of wire spacers strengthens lateral flow disturbances. This effect is more pronounced within the internal subchannels, thereby leading to a marked difference in the flow fields on either side of the wire spacers. In the case of blocked conditions, an increase in blockage thickness and area both lead to higher temperatures for the coolant, the blockages themselves, and the fuel rods. The temperature in the recirculation zone behind the blockages also rises with increasing blockage thickness and area, although the magnitude of this increase is not significant. After the onset of blockage conditions, the instantaneous temperature tends to increase. As time progresses, the instantaneous temperature fields following the blockage do not display greater fluctuations in temperature change than those observed after the system has stabilized. For the temperature parameters of the convective field, differences arising from an increase in blockage area are more significant than those caused by an increase in blockage thickness. When blockage area and blockage thickness are increased by the same multiple, an increase in blockage area results in a higher temperature peak. Increasing the area of blockage necessitates a longer duration for both the temperature and the velocity fields to revert to equilibrium.

Numerical study on the flow characteristics of an integrated fish cage based on the monopile offshore wind turbine foundation

The integration of net cages and offshore wind turbines can effectively develop and utilize marine resources and is one of the important ways of intensive use of the sea. The numerical simulation of the hydrodynamics of an integrated fish cage based on the monopile offshore wind turbine foundation in currents is carried out. The realizable k-ε model is adopted and the porous media model is used to simulate the net. To verify the validity of the numerical model, the numerical result is compared with the data of the corresponding literature. The results show that the numerical method is effective. On this basis, the flow field distribution results of the integrated structure at different velocities are calculated. At the center of the downstream zone of the integrated structure, the time-average velocity is lower than 80 % of the initial velocity. The effects of the net solidity and the cage draught on the flow field characteristics of the integrated structure are analyzed. The results show that the increase of net solidity will significantly reduce the velocity inside the net cage and in the downstream zone of the cage. As the net solidity increases from 0.14 to 0.32, the average velocity attenuation inside the net cage increased by 13.9 %. The change of cage draught will affect the velocity distribution in the horizontal and vertical directions. When the cage draught increases, the velocity on both sides in the downstream zone of the integrated structure increases more than 5 %. It is expected that the results of this study can provide data support for the design of integrated structure of net cages and offshore wind turbines.

Simulation study of flow and heat transfer in wavy microchannel heat sink with manifolds and secondary channels composite

With the continuous increase in power density of electronic devices, traditional cooling methods have gradually shown their limitations. Microchannel heat sinks (MCHSs) have enormous potential in thermal management for electronic devices due to their excellent heat dissipation performance. To improve the flow and heat transfer performance of MCHSs, a numerical study was conducted on 56 types of wavy microchannel heat sinks with manifolds and secondary channels composite (WMCHS-MSCs). The results indicate that compared to the original manifold wavy microchannel heat sink (MWMCHS), the optimal WMCHS-MSC increases the thermal enhancement factor by 45.1 % when the inlet volume flow rate Q = 1.0 × 10−6 m³/s. At the same time, the overall thermal resistance, the maximum temperature difference on the bottom wall, and the pressure drop of the optimal WMCHS-MSC are reduced by 7.6 %, 21.9 %, and 10.6 %, respectively. Compared to the original MWMCHS, the increase in Q for WMCHS-MSCs results in an overall trend of increased thermal performance, decreased temperature non-uniformity and hydraulic performance, and initially increased and then decreased overall performance. The flow field distribution of the secondary channels of WMCHS-MSCs intuitively demonstrates the improved hydraulic and thermal performance brought about by disrupting the thermal boundary layer and mixing the flow. The study presents a novel approach for the design of wavy MCHSs, potentially paving the way for enhanced thermal management solutions in electronic devices.

Thermal flow and thermoelectricity characteristics in a sandwich flat plate thermoelectric power generation device under diesel engine exhaust conditions

Thermoelectric power generation (TEG) technology can be used to recover exhaust waste heat, but its effective application is restricted by bulky size and low thermoelectric conversion efficiency. The compactness evaluation of thermoelectric devices characterized by the power density is lacking. In this paper, a three-dimensional thermal flow and thermoelectricity multi-physics field model of a sandwich flat plate TEG device with multi-layer thermoelectric modules (TEMs) was established. An engine thermoelectric recovery bench test was carried out to verify the model and present the thermal parameters and output performance. The thermal, flow and electrical field distributions of the TEG device, as well as voltage, power and conversion efficiency with engine loads, and power density, were presented. The results show that the hot side temperatures, voltages and powers for each thermoelectric module (TEM) are greatly affected by the position occupied by the TEMs and engine loads. At full load and the coolant flow of 8.5 L/min, the device achieves the peak values of the power of 80.9 W and thermoelectric efficiency of 2.1 %, respectively. The device shows good compactness with the power density of 19.8 kW/m3, attributed to the reasonable arrangement of the collectors, coolers, and TEMs. This work can provide some insights of the relationship between the structural form and size, thermal parameters, electrical parameters and conversion efficiency of the sandwich type TEG device.

Experimentation and simulation of gas flow field distribution during the growth of carbon nanotubes in a horizontal reactor

Carbon nanotubes (CNTs) were grown in a horizontal reactor by chemical vapor deposition, and it was found in the experiments that different heating temperatures and the position of the porcelain boat affect the morphology and yield of CNTs. Computational fluid dynamics (CFD) software is used to simulate the gas flow field distribution in the horizontal reactor under different operating parameters, and the results revealed that the gas flow in the horizontal reactor was advancing with vortex, and this gas circulation is induced by the difference in density due to the existence of temperature difference between the gas streams. As the heating temperature and nitrogen gas velocity increase, this vortex distorts the laminar flow, which in turn weakens the growth of CNTs.

Numerical Simulation and Flow Field Analysis of Porous Water Jet Nozzle Based on Fluent

The water jet nozzle is a penetrating drilling tool, which sends the pumped water to the nozzle through a high-pressure hose. It can work in a variety of working environments. When it dredges the blockage in the pipeline, its structural parameters will affect the jet flow field in the pipeline. Taking the self-propelled water jet nozzle as the research object, SolidWorks was used to establish the nozzle model with different parameter structures. Based on Fluent, the k-ε turbulence model was used to simulate the jet of nozzles with different nozzle sizes and arrangements in the pipeline. The distribution of the jet flow field and the change in velocity and displacement of nozzles with different parameters in the pipeline were compared, and then computational fluid dynamics (CFD) were used to process the simulation data for further research. The results show that when the inclination angle of the rear nozzle is 35°, the attenuation of the front jet velocity and the fluctuation of the wall fluid velocity are the smallest. When the nozzle aperture is increased from 2 mm to 3.5 mm, the vortex area inside the pipe is reduced, and the velocity attenuation of the front jet is also reduced, with the velocity attenuation rate decreasing by about 10%. This study provides a reference for the design and parameter optimization of self-propelled water jet nozzles.

Simulation and Analysis of Hydrodynamic Behavior in Different Nozzles and Its Corresponding Fluidized Beds

Uniform air distribution is the basic condition for the stable operation of circulating fluidized beds and closely related to the hole layout of nozzles and the air outlet conditions. In this paper, CAD modeling software is used to establish different opening types for nozzles and the corresponding gasifier models, and Fluent simulation software for numerical simulations (k-ε model) is introduced to the hydrodynamic behavior of the upper opening, the side opening and the combined opening types of nozzles, as well as the corresponding single-nozzle fluidized bed gasifiers. The flow field distribution under the above opening modes is obtained, including the velocity distribution, static pressure distribution, and total pressure distribution, and the influence of the boundary conditions, including the inlet gas velocity and outlet pressure, on the flow field distribution inside the nozzle and in the single-nozzle fluidized bed gasifier is also investigated. The simulation results show that the suitable optimal operating conditions for the coal gasifier can be achieved with an inlet velocity of 30 m/s and an outlet pressure of 25 kPaG. Under the above conditions, the local fluidization dead zone at the elbow and top of the nozzle is narrower, the uniformity of the wind velocity can be improved, the pressure drop of the inner core tube of the nozzle is gentle, and the pressure distribution tends to be stable. Theoretically, the anti-slag performance of the nozzle is improved, which will enhance the stability and reliability of the operation of the gasification unit.

A Study on the Influence of Radial Spoiler Arrangement on the Combustion Process of Wankel Rotor Engines

Wankel rotor engines are widely used in various fields due to their high power density and simple structure. This paper presents the optimisation of the Wankel rotor engine by simple modifications of the structure. We propose a radial spoiler arrangement scheme that can affect the flame propagation speed and reaction severity by altering the flow field distribution and pre-reaction distribution in the cylinder. By comparing the effects of four layout schemes on flame propagation speed and reaction intensity, including no spoilers, radial spoilers deflected at an angle of 10° in the negative direction of the Z-axis, radial spoilers deflected at an angle of 10° in the positive direction of the Z-axis, and radial spoilers arranged at the centre of the rotor combustion chamber, the benefits of different layout schemes were evaluated. We conducted a study on the influence of the arrangement of radial spoilers on the combustion process of a Wankel rotary engine through theoretical calculations. This helps to reduce engine vibration, improve engine operation stability, and enhance engine performance.

Optimizing the design of parallel busbars to suppress the Taylor Instability in large-scale liquid metal batteries

Abstract In this study, we utilize the open-source software OpenFOAM to numerically simulate the Tayler instability in liquid metal batteries. The simulation depicts the dynamic evolution of the electrolyte layer, fluid flow, and magnetic field distribution in the battery at different operating times. Special attention is paid to the influence of optimizing the parallel busbar configuration on Tayler instability and battery capacity. It is found that the additional magnetic field generated by the busbars can effectively alter the magnetic field distribution inside the battery, thereby significantly reducing the Lorentz force and suppressing the Tayler instability within the battery. Therefore, by optimizing the parallel busbar configuration, the stable operating time of the battery is prolonged, and the battery capacity is enhanced. This study provides theoretical support and practical guidance for the application of liquid metal batteries in large-scale grid-level energy storage systems and offers new insights into the development of energy storage technology.

Drag of Rankine bodies embedded in porous media at small Darcy numbers

This paper studies the flow over a solid inclusion embedded in a porous medium of low permeability. We study Rankine bodies which represent circular cylinders and spheres when the aspect ratio is one, and thin plates and almost uniform rods when the aspect ratio is small. Using boundary layer theory, the flow field and pressure distribution are determined. It is found that the pressure drag dominates the shear drag except for small aspect ratios. Thus, geometry plays a decisive role in the choice of using the Darcy equation or the Darcy-Brinkman equation. The results are important for the determination of flow resistance of a non-homogeneous porous medium which has solid inclusions.

Numerical analysis of heat transfer and flow characteristics of the satellite thermal flowmeter and exploration of high-precision calibration methods

The performance of the thermal flowmeter for satellites is numerically studied to optimize. Flow patterns and temperature distributions, affected by buoyancy convection, significantly influence the accuracy of flow-rate measurements in inclined thermal flowmeters. The present study delves into the thermal flowmeter’s flow field and temperature distribution influenced by gravitational effects. When the Reynolds number is low, buoyancy convection causes a significant inconsistency in the measurement result between ground and space. By eliminating the constraint of the symmetrical arrangement of thermocouples and introducing additional thermocouples for high-precision calibration, the measurement accuracy is remarkably improved. Ultimately, arranging the thermocouples asymmetrically reduces the error by 62%. Additionally, integrating two more thermocouples is even more beneficial, reducing the error by 83% compared to the previous study. These improvements would be potential solutions of flow-rate measuring inconsistency between ground and space, aiding the development of a high-precision thermal flowmeter for satellites.