Flow Field Uniformity Research Articles

Cathode optimization and multi-physics simulation of pulse electrochemical machining for small inner-walled ring grooves

The small inner-walled ring grooves of the injector nozzles of hard-to-cut metallic materials are difficult to machine in aerospace and aviation field. Nowadays, electrical discharge machining (EDM) technology is often employed to machine this kind of structures. However, a time-consuming process of removing the metamorphic layer is needed after EDM process for some important workpieces. To solve this problem, electrochemical machining (ECM) technology for the inner-walled ring grooves of 1J116 corrosion-resistant material is studied. First, four basic tool cathode structures are designed with equal-clearance method and flow field simulations are performed with k-e turbulence model to optimize their structures to ensure flow field uniformity and machining stability. Simulation results show that the uniformity of flow field distribution and machining stability of structure IV cathode are the best among the four types of cathode structures. Then, electric field characteristics in different machining states between the structure IV cathode and the workpiece are analyzed with multi-physics simulation based on the flow field analysis. Simulation results show that current density can meet the machining requirements of the inner-walled ring grooves of the injector nozzles when voltages vary from 12 to 18 V. Finally, a verification experiment is conducted with the optimized tool cathode and machining parameters. The experimental results show that good machining quality is achieved at voltage of 14 V with structure IV cathode.

A microfluidic platform culturing two cell lines paralleled under in-vivo like fluidic microenvironment for testing the tumor targeting of nanoparticles

Nanoparticles are attractive in medicine because their surfaces can be chemically modified for targeting specific disease cells, especially for cancer. Providing an in-vivo like platform is crucial to evaluate the biological behaviours of nanoparticles. This paper presents a microfluidic device that could culture two cell lines in parallel in in-vivo like fluidic microenvironments and be used for testing the tumor targeting of folic acid - cholesterol - chitosan (FACC) nanoparticles. The uniformity and uniformity of flow fields inside the cell culture units are investigated using the finite element method and particle tracking technology. HeLa and A549 cells are cultured in the microfluidic chip under continuous media supplementation, mimicking the fluid microenvironment in vivo. Cell introducing processes are presented by the flow behaviours of inks with different colours. The two cell lines are identified by detecting folate receptors on the cellular membranes. The growth curves of the two cell lines are measured. The two cell lines cultured paralleled inside the microfluidic device are treated with FITC-FACC to investigate the targeting of FACC. The tumor targeting of FACC are also detected by in vivo imaging of HeLa cells growth in nude mice models. The results indicate that the microfluidic device could provide a dynamic, uniform and stable fluidic microenvironment to test the tumor targeting of FACC nanoparticles.

Optimization of MOCVD Hardware Configuration and Process for Growth of High Quality (Gd,Y)BCO Superconducting Tapes Based on CFD Modeling

A systematic computational fluid dynamic (CFD) study was performed to investigate the effects of hardware configuration and process parameters on flow field and temperature profile above the film growth surface for (Gd,Y)BCO superconducting tapes in a metalorganic chemical vapor deposition (MOCVD) reactor. Significant improvement in the uniformity of flow field and temperature profile was achieved by optimizing the gap between showerhead and susceptor, showerhead length, gas flow rate, and chamber pressure. As results of the improvement in hardware configuration based on CFD modeling, high quality (Gd,Y)BCO superconducting films were achieved and the limit on growth rate was increased. The improvement was not only in the surface morphology (achieving more clean and smooth surface with less outgrowth grains and impurity phase particles), but also in the cross sectional microstructure view (more uniform from the bottom to the top) for thick films processed by the reel-to-reel MOCVD. A 1.76-μm-thick (Gd,Y)BCO film in a 284-m-long tape yielded a self-field critical current of 769 A/12 mm width at 77 K.

Numerical Study on Enhancing Heat Transfer of the Belt-type Resistance Heater in the Hypersonic Wind Tunnel

Numerical studies of Heat transfer enhancement of belt-type Electric-resistance Heater is reported in this paper. The effect of different kinds of belt arrangements is studied in detail. Results show that, for changing m and n, which is the spacing between adjacent belts both in vertical and horizon, the comprehensive Performance Evaluation Criterion(PEC) increases as belt spacing decreases; For the case of model adding several baffles, the PEC reaches 1.6, with Nu/Nuo and f / f0 comes to 3.38 and 9.51; For the staggered arrangement belt geometry, the PEC attains 1.18 and the flow field uniformity improves significantly compared with the aligned arrangement one.

Study on Flow Field Optimization for SCR System of Coal-fired Power Plants

Coal-fired power plants are undergoing ultra-low emission retrofits. When the flue structure of the SCR denitrification system of the existing unit is fixed, the internal baffles and static mixers need to be optimized to ensure the flow field uniformity, thus ensuring the denitrification efficiency and controlling the ammonia escape rate. For a 660 MW SCR system, numerical simulation of flue gas flow uniformity and cold state test of physical model were carried out. The results show that the uniformity of the flow field distribution and the mixing effect of ammonia and gas in the SCR denitrification system are effectively improved by adding deflectors and optimizing the static mixers. The research in this paper provides reference for similar engineering design and construction in the future.

Study on ammonia injection and mixed element of SCR denitrification system

Selectivce Catalytic Reduction (SCR) denitrification is the most widely used flue gas denitrification technology for coal-fired power plants due to its excellent comprehensive performance. The key to the denitrification efficiency is the uniform mixing of the reducing agents NH3 and NOX in the flue gas. In this paper, the linear controlled ammonia injection grid, partition-controlled ammonia injection grid and mixed element of type ammonia injection grid are compared. The advantages and disadvantages of various gas flow field uniformity adjustment techniques are analysed. It is pointed out that the mixed element of type ammonia injection grid technology is the main direction of the current ammonia injection technology development. Finally, the future development trend of the ammonia injection mixing device is pointed out.

Study on a New Gasoline Particulate Filter Structure Based on the Nested Cylinder and Diversion Channel Plug

Increasingly stringent emission regulations have imposed strict requirements on the particulate matter (PM) from gasoline direct injection (GDI) engines, and the gasoline particulate filters (GPFs) are considered one of the most promising devices for meeting these requirement. To reduce the flow resistance of the GPF, a type of nested cylinder and diversion channel plug (NC-DCP) GPF is designed. It is composed of nested foam metal cylinders and annular diversion channel plugs. The pressure drop and its influencing factors were theoretically studied. The results show that the structural parameters, such as the cylindrical layer spacing and the length-to-diameter ratio, and the pressure drop have trade-off relationships. Moreover, the filtration efficiency is analyzed, and the calculation formula is summarized. The internal flow field distribution and its influencing factors are discussed based on a 2-D axisymmetric simulation. The results show that the exhaust velocity affects the flow field uniformity but does not affect the flow field structure. The pressure drop gradually decreases as the number of nested layers increases, and the positive direction is beneficial to reduce the overall pressure drop. Under different velocities, there is an optimal length-to-diameter ratio to minimize the pressure drop, and the simicircular diversion plug greatly improves the flow uniformity index for the internal flow field of the filter element.

Workpiece reciprocating movement aided wire electrochemical machining using a tube electrode with an array of holes

Parts with a ruled surface manufactured to high accuracy and good surface integrity are widely used in industry. Wire electrochemical machining (WECM) has great advantages and potential in the processing of these parts because there is no residual machining stress, the surface is free of burrs and has no recast layer, and there is no tool wear. In this paper, WECM using a tube electrode with an array of holes was introduced to further improve the machining efficiency and capability for thick workpiece. Additionally, the reciprocating movement of the workpiece was used to change the spraying position of the electrolyte on the machining surface. The simulation results indicate that this method can improve the velocity and uniformity of the electrolyte flow field in the machining gap. Experiments verified that when the amplitude of the reciprocating movement is greater than the spacing of holes, machining efficiency and accuracy are greatly improved. Finally, using optimized machining parameters, an array of slits with a width of 550 μm (standard deviation of 5.99 μm) was fabricated on 10-mm-thick stainless steel 304 at a cutting rate of 3 mm²/min.

Development of a Nose-only Inhalation Toxicity Test Chamber That Provides Four Exposure Concentrations of Nano-sized Particles

Using a numerical analysis based on computerized fluid dynamics, a nose-only inhalation toxicity chamber with four different exposure concentrations is designed and validated for flow field uniformity and cross-contamination among the exposure ports for each concentration. The designed flow field values are compared with the measured values from exposure ports located horizontally and vertically. For this purpose, nanoscale sodium chloride particles are generated as test particles and introduced to the inhalation chamber to evaluate the cross-contamination and concentration maintenance among the chambers, for each concentration group. The results indicate that the designed multiconcentration inhalation chamber can be used in animal inhalation toxicity testing without cross-contamination among concentration groups. Moreover, the designed multiconcentration inhalation toxicity chamber can also be converted to a single-concentration inhalation chamber. Further testing with gas, organic vapor, or non-nanoscale particles will ensure the use of the chamber in the inhalation testing of other test articles.

Optimization analysis of the internal structure of flow-assisted zinc-nickel battery driven by a propeller

This study established a three-dimensional analysis model of the internal flow field of the battery stack with a rotating propeller by using the flow-assisted zinc-nickel battery stack driven by a propeller. The flow of electrolyte in the battery stack was simulated and analyzed. The key design parameters of the battery stack were analyzed and optimized by adjusting the baffle and blade heights, blade speed, and blade number based on the uniformity of the internal flow field of the battery stack. The final simulation results show that the flow field distribution is the most uniform when the baffle and blade are 100 and 140 mm, respectively; from the top of the battery stack, the number of blades is five leaves, and the speed is 600 r/min. This article serves as the basis for the structural design of flow-assisted zinc-nickel battery driven by a propeller.

Effects of modifying the blade trailing edge profile on unsteady pressure pulsations and flow structures in a centrifugal pump

In the present work, the effects of modifying the blade pressure side (EPS profile) on unsteady pressure pulsations and flow structures in a low specific speed centrifugal pump are carried out by experimental and numerical methods. Results are compared to the original trailing edge (OTE profile). Unsteady pressure signals are captured at twenty measuring points at flow rate of 0–1.6Qd. It is observed that the pump head of the EPS profile is improved for all the concerned working conditions. Pressure amplitudes at the blade passing frequency are compared and discussed in detail. It is found that the EPS profile contributes to pressure pulsation reduction obviously. For all the measured flow rates, pressure amplitudes are attenuated evidently at major measuring positions, especially at high flow rates. As for the mean pressure amplitude of twenty measuring points, pressure amplitude is reduced more than 20% at the nominal flow rate using the EPS profile. From relative velocity distribution, it is found that the uniformity of flow field at the blade outlet region would be improved significantly by the EPS profile. Besides, the corresponding vorticity magnitude at the blade outlet would be reduced compared to the OTE profile. The combined effects contribute to the reduction of pressure amplitude using the EPS profile.

Numerical Simulation of Internal Flow Field in Blast Furnace Slag Dry Granulating Device

In this paper, CFD numerical simulation method was adopted to study the internal flow field of experimental dry granulating device of blast furnace slag and to research the impact of equipment structure and wind speed on cooling effectiveness. Main content included the internal flow field uniformity under different blade type and number of inlets. The results showed that the internal flow field in strip-blades device was more uniform than fan-shaped blades device. With the increase of air inlets quantity, the internal flow field in device became more uniform and stable, especially when there were 8 air inlets in the equipment.

Microfluidic device for generating regionalized concentration gradients under a stable and uniform fluid microenvironment

A relative stable microenvironment is essential for in vitro cell culture. This paper presents a novel cell culture device with multiple arrays of perfusion channels (PCs) to maintain the stability and uniformity of flow fields. Besides, a series of regionalized concentration gradients can be generated by adjusting the relative positions of inlets. The number of circular arrays of PCs have been optimized based on the simulation results. The particle tracking technology has been used to evaluate the changes of flow fields inside the culture chamber as the variation of velocity in medium inlet. The Hela cells, L929 mouse fibroblast cells and HUVEC cells are cultured dynamically in the optimized device. The culture device without PC is used as a comparison. The results of normalized cell density and cell viability indicate that the device with multiple arrays of PCs is more favorable to cell growth. The effects of adjacent position and opposite position of two inlets on generating regionalized concentrations have been demonstrated by FEM simulation analysis and fluorescence distribution. The densities and attachment areas of L929 cells inside one chamber with regionalized concentration gradient have also shown the validity of the designed device.

Numerical simulation of bypass evaporation system treating FGD wastewater using high temperature flue gas

ABSTRACTA novel zero-liquid discharge (ZLD) technology for desulfurization wastewater treatment is put forward in this paper. A ZLD reconstruction project performed on 2 × 320 MW desulfurization system was taken as the research object, to study the evaporator structure and the key factors affecting spray evaporation through CFD numerical simulation. The result shows that when the evaporator diameter is 2.4 m, the central density difference and the temperature difference of evaporator outlets are 0 kg/L and 0°C, under this condition, the wall sticking can be avoided effectively, and the uniformity of evaporator's outlet flow field is improved. As for the same amount of wastewater, small atomized particle size, high flue gas flow rate and high flue gas temperature are conducive to complete evaporation, and the optimum atomized particle size is 100–150 μm, flue gas velocity is 3–4 m/s and flue gas temperature is 250–260°C. In order to reduce adverse impact on the main flue duct, the optimized design scheme that extracting flue gas before and after the air preheater is put forward in the purpose of energy saving.

Fabrication and release of silicon nitride micro string array by convection freeze sublimation method at atmospheric pressure

A convection freeze sublimation (CFS) method was developed to release silicon nitride strings with a high aspect ratio and high tensile stress, which are widely applied as electromechanical resonators. This method is cost-efficient and easy to operate for its implementation at atmospheric pressure and no vacuum or cryogenic equipment is needed. The CFS system is composed of cyclohexane, nitrogen gas, a freezer and a drying chamber. Cyclohexane with low surface tension (24.38 mN m−1) and high phase transition temperature (6.5 °C) was chosen as the medium in the CFS method. Nitrogen gas was introduced into the drying chamber to facilitate the sublimation of solid cyclohexane by enhancing heat convection at the solid–air interface. A convective mass transfer model was calculated to quantitatively analyze the influence of convective parameters on the sublimation rate. The silicon nitride string array were successfully released with the aid of 3 ml min−1 flow of nitrogen gas. However, when the nitrogen flow rate exceeded 6 ml min−1, the strings adhered in some points because solid cyclohexane is prone to melt instead of sublimating under excessive heat introduced by nitrogen gas. Furthermore, a finite element model was built to explore the influence of different outlet parameters on the magnitude and uniformity of flow field on the surface of solid cyclohexane. To evaluate the mechanical property of the released string, we measured the natural frequency of a single string and confirmed the influence of tensile stress on its natural frequency. The results showed that the CFS method is able to serve as a general tool for ultra-weak structure releasing, which makes this method applicable in fields such as optomechanics and metamaterials.

Numerical research on vapor splitter in divided wall column

In order to lower the difficulty to control the vapor split ratio of divided wall column (DWC) and to optimize auto-allocated vapor flow rate on the both side of the divided wall in real industry, this paper presents a new vapor ratio regulator. The splitter, which is based on the Coanda effect, is installed in the bottom section of the DWC to control vapor flow rate on both sides of the DWC and solve the problem of vapor allocation in the DWC. In this research, Auto-cad, computational, Tecplot, and Origin are used to do data analysis. By tracking the vapor flow trajectory and analyzing the splitter’s allocation rule, it is shown that the RV can be effectively regulated by adjusting the velocity of the gas inlet. In order to achieve a high uniformity of the vapor flow field of regulator, the installation location of the device is optimized.

Low NOx combustion and SCR flow field optimization in a low volatile coal fired boiler

Low NOx burner redesign and deep air staging have been carried out to optimize the poor ignition and reduce the NOx emissions in a low volatile coal fired 330 MWe boiler. Residual swirling flow in the tangentially-fired furnace caused flue gas velocity deviations at furnace exit, leading to flow field unevenness in the SCR (selective catalytic reduction) system and poor denitrification efficiency. Numerical simulations on the velocity field in the SCR system were carried out to determine the optimal flow deflector arrangement to improve flow field uniformity of SCR system. Full-scale experiment was performed to investigate the effect of low NOx combustion and SCR flow field optimization. Compared with the results before the optimization, the NOx emissions at furnace exit decreased from 550 to 650 mg/Nm³ to 330–430 mg/Nm³. The sample standard deviation of the NOx emissions at the outlet section of SCR decreased from 34.8 mg/Nm³ to 7.8 mg/Nm³. The consumption of liquid ammonia reduced from 150 to 200 kg/h to 100–150 kg/h after optimization.

Uniform, stable supply of medium for in vitro cell culture using a robust chamber

A uniform, stable supply of medium is important for in vitro cell culture. In this paper, a microfluidic device is presented for culturing cells inside a robust chamber with continuous perfusion of medium. The device consists of a main channel, two bifurcated channels and a culture chamber. The culture chamber connects to the bifurcated channels via multiple paths, and distributes symmetrically on the main channel, to improve the efficiency of medium exchange. Furthermore, regular polygonal chambers with various numbers of edges have been designed, to study the effects of chamber shape on flow fields. The finite element method has been employed to predict the effects of multiple paths on the uniformity and stability of flow fields in the culture chamber. Particle tracking technology has been used to evaluate the flow fields in the chambers, and PC-12 cells have been cultured using the microfluidic device, to test its validity. The results of simulation and experiment indicate that the microfluidic design could provide a continuous interstitial-like flow microenvironment, with a relatively stable and uniform supply of medium.

Parameter Optimization on the Forced Ventilation of Symmetric Tunnel Construction Based on the Super-Short Bench-Cut Method

To exploit the influence of the tunnel face and the distance between the diameter and the orifice of a blast pipe on the ventilation effect in symmetric tunnel construction, this paper uses Fluent to establish a three-dimensional model and numerical simulation. Firstly, the accuracy of the numerical simulation is tested and then the distance between the orifice and tunnel face and the influence of the air duct diameter on the ventilation effect are studied, respectively. The results show that the ventilation effect is best when the wind pipe is arranged on one side of the tunnel wall (an asymmetrical layout), although the space in the tunnel is axisymmetric, and that the error of the numerical simulation is less than 5% of the measured value. When the distance between the orifice and tunnel face is 5 m, the uniformity of the air flow field near the tunnel face is poor; when the distance is 10 m and 12 m, an obvious vertex area appears in the tunnel. Furthermore, the uniformity of the wind velocity flow field is optimal when the distance is 8 m. When the air duct diameter is less than 1.4 m, there is a uniformity of the flow field near the tunnel face of the upper and lower benches; when the air duct diameter is more than 1.4 m, the tunnel face of the upper bench near the ground shows more obvious backflow. Therefore, it was determined that taking the air duct diameter as 1.4 m and the distance between the orifice and tunnel face as 8 m was the best combination for the design of ventilation in this project. It was also found that a better ventilation effect can be achieved when the distance between the nozzle of the ventilator and the tunnel face is 6 m–9 m and the wind speed of the nozzle is 6 m/s–8 m/s. In practical engineering, the wind speed and the required air volume should be taken into consideration to determine the diameter of the ventilator.

Flow Field Design and Experiments on Pulse ECM of Large-lead Ball Nut Raceway During Tool Cutting-out Stage

A novel process of pulse electrochemical machining (PECM) using a spherical tool cathode with inner slant jet has been proposed and preliminary verified for the machining of large-lead ball nut raceway, in which the electrolyte flow field uniformity plays a very important role in achieving high machining accuracy and process stability. This paper is focusing on the flow field design during tool cutting-out stage, which is considered necessity for realizing one-pass PECM of raceway. Difficulties of flow field design lie in the nonuniform flow field distribution caused by the sudden change of electrolyte flow and the possible deformation or movement of the spike. The method using sacrifice metal was adopted and two novel types of fastening way (the welding type and the magnetic attraction type) were presented to solve the problems existing in conventional methods using sacrifice metal. Verification experiments were conducted and the results show that stable PECM can be achieved using these two types of method. It's also found that the magnetic attraction type of method has better performance of process stability and adaptability than that of the welding type.