Gas Flow Field Research Articles

Effects of the inlet duct length on the flow field and performance of a cyclone separator with a contracted inlet duct

The inlet duct length may affect the gas flow field and performance of a cyclone separator with a contracted inlet duct. In this study, a numerical simulation using the Eulerian-Lagrangian approach with a one-way coupling method was conducted to evaluate the gas flow field and separation efficiency of the cyclone separators with contracted inlet ducts of different lengths. The simulation results indicated that increasing the inlet duct length led to higher gas tangential velocity in the cyclone body. The effect of the inlet duct length on gas axial velocity was inferior to that on gas tangential velocity. A longer inlet duct reduced both the pressure drop and the separation efficiency. The reductions of the expansion loss at the inlet of the cylinder and friction loss inside the cyclone body contributed the most reduction of the pressure drop as the inlet duct length increased. Generally, when the inlet duct was 1.5 times longer than the cylinder diameter, the effect of inlet duct length on the gas flow field and performance of a cyclone separator became slight.

Gas outflow into vacuum over a forward- and backward-facing step in a wide range of rarefaction

The direct simulation Monte Carlo method has been applied to investigate the outflow of rarefied gas into vacuum over a forward- and backward-facing step. The non-equilibrium effects at the ends of the step channel have been taken into account by considering the geometry of sufficiently large regions directly adjacent to the inlet and outlet of the channel. The mass flow rate through a step channel as well as the gas flow field both inside the step channel and in the upstream and downstream regions have been calculated over a wide range of gas rarefaction. The calculation results have been compared with the corresponding data for a channel of constant cross-section. The system configuration has been found to have a pronounced effect on the simulation findings. The so-called Knudsen minimum has been established in the dependence of the mass flow rate on the gas rarefaction, and a gas circulation zone has been found in the flow field.

Simulation Study on Centrifugal Spray Evaporation Characteristics and Process Optimization of Desulfurization Wastewater

As an advanced treatment of desulfurization wastewater, centrifugal spray drying technology, which can achieve a zero liquid discharge target, has attracted wide attention and great interest in recent years. However, the results of previous studies were based on the laboratory-scale centrifugal spray dryer. In order to study the evaporation characteristics of desulfurization wastewater and the parameter optimization of the dryer, the evaporation model of wastewater droplets was established. The effects of parameters such as the angle of the deflectors, gas–liquid ratio and atomizer speed on droplet evaporation were studied by numerical simulation. The results show that with the increase in the angle of the deflectors, the swirl effect of flue gas flow field is more obvious and the time and axial distance required for the complete evaporation of the droplets are shorter. Reducing the gas–liquid ratio will make the average evaporation time longer. Moreover, a higher atomizer speed is helpful for the evaporation of the droplets. The optimum gas–liquid ratio and rotational speed are found to be 9300 m3/Nm3 and 16,000 rpm, respectively.

CFD Investigation of Different Flow Field Designs for Efficient PEMFC Performance

Proton exchange membrane (PEM) fuel cell performance depends substantially on the geometry, configuration of the flow channels, and size. A right gas flow field pattern requires a homogeneous reactant distribution, low-pressure drop, and good water management. This paper outlines a numerical study, investigated the influence of the U-type, Z-type, and serpentine flow field configuration on the steady-state cell performance using the CFD technique ANSYS FLUENT PEMFC module. The main goal of this study focuses on a novel perspective for enhancing the design of the PEMFC resulting in better performance. The results indicate that the PEMFC with serpentine flow field configuration yields a significantly higher power density compared to the other designs.

A numerical study on the performance of PEMFC with wedge-shaped fins in the cathode channel

The gas flow field design has a significant influence on the overall performance of a proton exchange membrane fuel cell (PEMFC). A single-channel PEMFC with wedge-shaped fins in the cathode channel was proposed, and the effects of fin parameters such as volume (0.5 mm3, 1.0 mm3, and 1.5 mm3), number (3, 5, and 9), and porosity of the gas diffusion layer (GDL) (0.2, 0.4, 0.6, and 0.8) on the performance of PEMFC were numerically examined based on the growth rate of power density (GRPD) and polarization curve. It was shown that wedge-shaped fins could effectively improve the PEMFC performance. With an increase in fin volume, the distributions of oxygen mass fraction in the outlet area of the cathode channel were lower, the drainage effect of the PEMFC improved, and GRPD also increased accordingly. Similar results were obtained as the number of fins increased. The GDL porosity had a greater effect than the wedge-shaped fins on the improvement in PEMFC performance, but the influence of GDL porosity weakened and the GRPD of porosity decreased as the porosity increased. This study provides an effective guideline for the optimization of the cathode channel in a PEMFC.

Study on the evolution law of the gas flow field based on the distribution characteristics of voids in the overlying strata in a goaf

Study on the evolution law of the gas flow field based on the distribution characteristics of voids in the overlying strata in a goaf

Modeling of hydrogen shaft injection in ironmaking blast furnaces

Hydrogen, as a carbon-free fuel and reducing agent, has the potential to mitigate carbon dioxide emission in BF ironmaking and the shaft injection is one of the promising and feasible processes; however, its effects on non-renewable fossil fuels saving in ironmaking process and the in-furnace phenomena are still not clear. In this study, a multi-fluid BF model is adopted to study hydrogen shaft injection's influence on in-furnace phenomena and BF performance, including flow-thermal-chemical behaviors and fossil fuel rate saving. The computational domain includes the industrial-scale BF regions from the slag surface in the hearth to the stock line near the furnace top, and the study is carried out under a fixed bosh gas flow rate. The simulation results show that compared with regular BF operation, hydrogen shaft injection can considerably affect BF performance, including the gas flow field, thermal field, and reduction behaviors. It is found that, as the injection rate increases, the penetration depth of hydrogen shows an increasing trend; the apex of cohesive zone shifts to a higher position with a more concave-shaped profile; moreover, both the reduction degree of iron oxides and thermal conditions in the shaft can be improved, which are accompanied with a significantly decreased fossil fuel rate. This study provides a quantitative tool to understand and optimize the hydrogen shaft injection into BFs towards a low-carbon ironmaking process.

Modeling of gas jet flow into a liquid bath using the inhomogeneous poly-dispersed method

Precise modeling of gas injection into a liquid bath is essential for both determining the enormous interaction mechanisms between phases and promoting its better utilization in nuclear industry. For this purpose, an investigation on three CFD methods was performed and compared with the experimental results from air injected vertically into a water pool through a circular nozzle with diameter of 1.58 mm in this work. An inhomogeneous poly-dispersed method based on a bubble-size-dependent lift force model was integrated into the traditional gas-liquid two-fluid model for the simulation of gas-liquid jet flow with air injected vertically in a water bath. Results show that the computer resources consumption can be kept at a low level using the method. Compared with the mono-dispersed and homogeneous poly-dispersed models, the predicted results of the void fraction distribution obtained by using the inhomogeneous poly-dispersed model considering the adjustable coefficients for the break up and coalescence models show good agreements with those of the experiment, with a maximum deviation less than 20%. Hence, the model should be more reliable to predict two-phase flow parameters. Bubble distributions analyses of varying scales were also demonstrated, indicating that the adoption of both inhomogeneous gas flow field and lift force model able to change sign of its coefficient play an important role for predicting the gas injection into liquid bath correctly.

Effect of Carrier Gas Flow Field on Chemical Vapor Deposition of 2D MoS2 Crystal

The carrier gas flow field plays a vital role in the chemical vapor deposition (CVD) process of two dimensional (2D) MoS2 crystal, which was studied by simulations and experiments. Different carrier gas flow fields were studied by utilizing three types of precursor carrier which affected the local gas flow field significantly. The experiment results showed that the appropriate precursor vapor concentration could be achieved by local carrier gas flow field conditioning, resulting in single 2D MoS2 crystals of a large size and a high coating rate of 2D MoS2 crystal on the target substrate surface. The carrier gas flow also contributed to the growth of the 2D MoS2 crystal when it flew towards the target surface. The size of deposited single 2D MoS2 crystal reached tens of micrometers and a few layers of 2D MoS2 crystal were characterized and confirmed.

Gas Expansion Energy Model and Numerical Simulation of Outburst Coal Seam under Multifield Coupling

Due to the insufficient understanding of the outburst mechanism, the coal and gas outburst disasters in China are more serious. Gas expansion energy is the main source of energy that causes outburst. In order to explore the distribution law of gas expansion energy in outburst coal seams, a gas-solid coupling equation of outburst coal seams was established. The distribution law of coal stress field, deformation field, gas flow field, and gas expansion energy were simulated and analyzed by using COMSOL Multiphysics. The results showed that from the excavation face to the deep part of coal seam, the stress presented unloading zone, stress concentration zone, and original stress zone. The volumetric strain and permeability reached the minimum, while the gas pressure reached the maximum at the peak value of vertical stress. As time goes on, the gas pressure in the fracture near the working face gradually decreased and was less than the pressure in coal matrix. The total gas expansion energy consists of free gas and desorption gas expansion energy. Affected by the excavation, free gas expansion energy maintained a constant value in the original coal seam and gradually decreased in the area close to the working face. The expansion energy provided by desorption gas was zero in the original coal seam. And it first increased and then decreased rapidly near the working face. Compared with stress and coal seam thickness, gas pressure and initial diffusion coefficient had significant influence on gas expansion energy of coal seam. When the diffusion coefficient was greater than 1e-9 m2/s, the gas expansion energy of the coal seam near the working face was significantly higher than that of the original coal seam, which had the risk of inducing outburst.

Hydrodynamics in bubble columns with helically-finned tube Internals: Experiments and CFD-PBM simulation

Experiments and CFD-PBM simulation were performed in this study to investigate the effects of helically-finned tube (HFT) internals on the gas-liquid flow in a laboratory-scale bubble column. Hydrodynamic parameters, including gas holdup, bubble size and flow field as well as turbulence properties, were compared for an empty column and other two columns with bare-tube (BT) or HFT internals. We found that bare rods promote the stability of two-phase flow, whereas helical fins destabilize the flow. Meanwhile, the spatial distribution of gas holdup or bubble size becomes more uniform in the presence of HFT internals, whereas liquid velocity or turbulent dissipation rate evidently decreases. The fin-induced spiral movement, flow resistance and bubble accumulation are the mechanisms underlying these experimental observations. Integration of rod and helical fin may be promising for process intensification in bubble columns.

A volume of fluid simulation of the steady deformation and the drag of a single droplet in a flowing gas

A method is proposed to investigate the steady deformation and the drag of a single droplet in a flowing gas at a high Reynolds number. The volume of fluid (VOF) method is used to model the droplet surface structure. The direct numerical simulation (DNS) method is used to model the gas flow field. In order to avoid the effect of the droplet acceleration on the drag and reduce the computation cost, a body force is added to the droplet to make it fixed at a constant position. The body force is determined by using the Newton iteration procedure. The simulated droplet aspect ratio and the drag coefficient agree well with the published experimental data. Meanwhile, the sources of the drag are analyzed and the effect of the Reynolds number and the Weber numbers on the droplet deformation and the drag are studied. The drag mainly comes from the pressure difference between the droplet-leading zone and the trailing zone, and the turbulence wake would increase the drag.

Influence of the Surface Microstructure of Conductive Polymer Composite Bipolar Plate on the Fuel Cell Performance

AbstractAll components contribute to the total electrical resistance in the fuel cell including the bipolar plates (BP). Contact interface between BP and gas diffusion layers (GDL) can influence the voltage losses. It is usually assumed the real contact area of two metal surfaces is determined by the plastic deformation of their highest asperities. The contact deformation of the polymer composite BP and GDL made of graphite paper or graphite cloth, is depending on the complex topography of the surfaces which touch elastically and plastically and on the clamping force the stack. This paper presents the analysis of the influence of microstructures of the BP surfaces on the voltage losses and directly affecting the performance of the fuel cells. For same model of the BP made by injection molding in a conductive poly(propylene) matrix composite, the mold cavities surface microstructure of the gas flow fields have been manufactured by micro‐milling at two different roughness Ra of 0.77 µm (first type) and then, laser ablation at respectively Ra of 9.9 µm (second type). Voltage loss through the BP and membrane electrodes assembly have been investigated at different clamping forces the stack.

Stabilization of liquid instabilities with ionized gas jets.

Impinging gas jets can induce depressions in liquid surfaces, a phenomenon familiar to anyone who has observed the cavity produced by blowing air through a straw directly above a cup of juice. A dimple-like stable cavity on a liquid surface forms owing to the balance of forces among the gas jet impingement, gravity and surface tension1,2. With increasing gas jet speed, the cavity becomes unstable and shows oscillatory motion, bubbling (Rayleigh instability) and splashing (Kelvin-Helmholtz instability)3,4. However, despite its scientific and practical importance-particularly in regard to reducing cavity instability growth in certain gas-blown systems-little attention has been given to the hydrodynamic stability of a cavity in such gas-liquid systems so far. Here we demonstrate the stabilization of such instabilities by weakly ionized gas for the case of a gas jet impinging on water, based on shadowgraph experiments and computational two-phase fluid and plasma modelling. We focus on the interfacial dynamics relevant to electrohydrodynamic (EHD) gas flow, so-called electric wind, which is induced by the momentum transfer from accelerated charged particles to neutral gas under an electric field. A weakly ionized gas jet consisting of periodic pulsed ionization waves5, called plasma bullets, exerts more force via electrohydrodynamic flow on the water surface than a neutral gas jet alone, resulting in cavity expansion without destabilization. Furthermore, both the bidirectional electrohydrodynamic gas flow and electric field parallel to the gas-water interface produced by plasma interacting 'in the cavity' render the surface more stable. This case study demonstrates the dynamics of liquids subjected to a plasma-induced force, offering insights into physical processes and revealing an interdependence between weakly ionized gases and deformable dielectric matter, including plasma-liquid systems.

An Experimental Study on Performance and Structural Improvements of a Novel Elutriator

During the transportation and packaging of low density polyethylene (LDPE) granular materials, fine dusts such as floccules, powder and fiber will be produced, which pollute the environment, affect product quality and generate fire hazards. In this work, the separation performance of fine dust and optimal operating conditions of an improved elutriator were investigated experimentally. Experiments were carried out to investigate the effects of air speed, feeding speed, and grid layout on the removal efficiency of fine particles. Experimental data showed that the separation efficiency of the novel elutriator ranged from 96% to 98.50%, which was more stable and an average of 51.44% higher than that of the original elutriator. By setting internals and improving the structure, the gas flow field in the equipment was regulated, the particle dispersion was intensified, and the static electricity was eliminated, which significantly improved the separation efficiency of fine dust.

Loss mechanism of micro-carbon ferromanganese during RH refining

ABSTRACT It is of great significance to improve the yield of ferroalloy for steelmaking to reduce cost and save energy. In this paper a kind of loss mechanism of micro-carbon ferromanganese which has micro content of carbon during RH refining of interstitial free steel was investigated. The flow field of argon gas in the RH degassing vessel was investigated through numerical simulation. Through force analysis and particle tracking of the micro-carbon ferromanganese, it was found that micro-carbon ferromanganese with size smaller than the critical value of 1.01 millimeters has a large probability to be carried away into the RH vacuum pipeline. The micro-carbon ferromanganese of small particle was easily lost into the vacuum pipe by the upward flow of argon gas. Industrial experiment was conducted and a novel mechanism was confirmed that increasing the vacuum pressure during addition of the micro-carbon ferromanganese could improve the yield greatly.

A MEMS flow sensor based on fish lateral line sensing system

The artificial lateral line is a bionic sensor developed in recent years to detect physical parameters of gas and liquid flow field, which has great application prospects in underwater target detection, microfluidic velocity detection and smart skin. However, these sensors generally have only one kinocilium, resulting in inability to identify directions. Moreover, the kinocilium exposed directly in fluid shows performance of low sensitivity. This paper presents a flexible, lightweight, and sensitive piezoresistive sensor inspired by lateral line. The sensor presented comprises a cluster of micropillars arranged in stepwise distribution to detect fluid direction and a hydrogel cap to realize high-sensitive and low-speed threshold detection. The experiment of direction detection shows that the output signal in inhibitory direction of the sensor is smaller than the signal in excitatory direction and lagging behind, which can be used in orientation identification. The results show that the sensitivity of the sensor without hydrogel cap is 0.57 mV/(mm/s), while the sensor with hydrogel cap is 1.18 mV/(mm/s), which indicates that the hydrogel cap can increase the sensitivity by 107%. The sensor developed in this paper has a broad application prospect in biomedicine devices and micro-fluid equipment.

Numerical Analysis of the Activated Combustion High-Velocity Air-Fuel Spraying Process: A Three-Dimensional Simulation with Improved Gas Mixing and Combustion Mode.

Owing to its low flame temperature and high airflow velocity, the activated combustion high-velocity air-fuel (AC-HVAF) spraying process has garnered considerable attention in recent years. Analyzing the velocity field, temperature field, and composition of AC-HVAF spray coatings plays a vital role in improving the quality of coatings. In this study, an actual spray gun is adopted as a prototype, and the radial air inlets are introduced to improve the reaction efficiency so that the chemical reaction can be completed in the combustion chamber. Furthermore, a complete three-dimensional (3D) model is established to examine the effects of radial inlets and porous ceramic sheet on the combustion and flow fields. The hexahedral cells are used to discretize the entire model for reducing the influence of false-diffusion on the calculation results. The gas flow field is simulated by the commercial Fluent software, and the results indicate that the porous ceramic sheet effectively reduces the turbulent dissipation of the airflow with a good rectification effect (the ceramic sheet ensures a consistent airflow direction). The radial inlets and the porous ceramic sheet promote the formation of vortex in the combustion chamber, increase the residence time and stroke of the gas in the combustion chamber, and improve the probability of chemical reactions. In addition, it is observed that the stability of velocity for the airflow is strongly related to the airflow density.

Numerical investigation of the effect of blocked gas flow field on PEM fuel cell performance

Proton exchange membrane fuel cell (PEMFC) systems are up and coming power source for transportation and stationary applications and sustainable energy conversion sources in the near future if optimal cell performance is provided. PEMFCs operating parameters, new design, or a new arrangement are critical issues affecting cell performance. They have to be considered carefully. In this paper, a three-dimensional, one-phase computational fluid dynamics (CFD) model of PEM fuel cell with blocked gas flow field has been developed by using CFD tool to observe the effects of blockage on the cell performance. It is mainly to reach the maximum cell performance, and an appropriate gas flow field should be supplied to the PEMFC. Hence, it is supplied a novel gas flow field along with two different patterns (rectangular and semi-cylindrical form) to the PEMFC. Polarization curves are generated for each new pattern to investigate the blockage effect on the cell performance compared to the traditional gas flow field. Consequently, rectangular and semi-cylindrical patterns increase the gas flow velocity in the channel and hence improve the effective mass transport from the channel center to the catalyst layer in the proton exchange membrane (PEM) fuel cell. It is recorded that, compared to a straight PEMFC, the rectangular gas flow field and semi-cylindrical gas flow field improve approximately 49.3%, 49.9% of current density, respectively.

Multiphysics Coupling Simulation and Parameter Study of Planar Solid Oxide Fuel Cell.

In this paper, a numerical model of gas flow, heat transfer, mass transfer and electrochemical reaction multi-physics field coupling of a planar SOFC is established and solved. According to the calculation results, the distribution of velocity, temperature and concentration inside the SOFC cell is analyzed. The influence of cathode inlet flow rate, porosity, rib width and other parameters on the performance of SOFC is also discussed. The results show that within a certain range, increasing the cathode inlet flow rate can significantly increase the average current density of the cell. Increasing the porosity of the electrode can improve the gas diffusion of the porous electrode, thereby increasing the rate of the electrochemical reaction. Increasing the width of the ribs will result in a significant decrease in cell performance. Therefore, the rib width should be reduced as much as possible within the allowable range to optimize the working performance of the cell.