Flow Field Distribution Research Articles

Alkaline electrolyzer-improving electrocatalytic oxidation of landfill leachate coupling with hydrogen production

A hybrid electrolytic water system was constructed including the anodic electro-oxidation treatment of the leachate from a waste incineration plant as well as the coupled cathodic electrolysis for hydrogen production. Four types of electrolyzers were designed with different flow channels and investigated the effect of different electrolysis parameters on the coupled reactions. The results indicate that the pin-type electrolyzer is superior to the other three electrolyzers in term of the degradation performance and energy consumption. At high current density of 4000 A/m2 and the flow rate of 100 ml/min, the pin-type electrolyzer shows the lowest potential of 6.09 V, the COD removal rate of 98.17% for the leachate and the energy consumption of 200.14 W h. The mass transfer mechanism was further explored under different flow channels and current densities, illustrating that the excellent performance of the pin-type electrolyzer is due to its largest mass transfer area and the most uniform inside flow field distribution. The apparent COD degradation kinetic behaviors were studied, indicating that the maximum degradation rate was 0.033 min-1 at the electric density of 4000A/m2. Such electrocatalytic oxidation of waste leachate coupled with hydrogen production would provide a promising route to construct new hybrid electrolytic water systems.

Thermal-flow characteristics analysis of a novel resilient capacity ceramic insulated winding dry type transformer

With the increasing demand for the resilient capacity of transformers in high-proportion renewable energy grids, the overload capacity of transformers and the thermal conductivity of winding insulation materials have been put forward as important requirements. In response to these requirements, a novel ceramic high temperature tolerance insulation winding is proposed in this paper and is applied in a ceramic insulated winding transformer. A combination of simulation and experimentation is used to analyze the thermal-flow characteristics of this transformer. The temperature and flow field distribution characteristics of transformers with both winding insulation methods (ceramic and Nomex paper) are compared. The internal mechanism of reflux near the iron core and high voltage winding under forced air cooling is clarified. A superior outside cooling condition is obtained. A prototype ceramic insulated winding transformer is developed and tested to verify the accuracy of the simulation model. The results show that the hotspot temperature of the ceramic insulated winding transformer under natural cooling is 10.7% lower than that of the Nomex paper insulated winding transformer. With forced air cooling of 2, 3, 4, 5, and 6 m/s applied at the bottom, the hotspot temperature of the ceramic insulated winding transformer is 11.4%, 10.5%, 9.7%, 14.0%, and 17.8% lower than that of the Nomex paper insulation winding transformer, respectively. Under forced air cooling, a reflux phenomenon is observed in both transformers in the vicinity of the iron core and high voltage winding due to the formation of adverse pressure gradient region and wall viscous force blocking. The strength of the reflux is affected by the magnitude of the forced air cooling flow velocity and the construction of the transformer. The optimal range of the external cooling flow velocity for the ceramic insulated winding transformer is 3–4 m/s. The errors between the simulated temperature and the measured temperature at the nine monitoring points of the prototype are all less than 5%, which verifies the effectiveness of the simulation model. The experimental and theoretical basis for the design and application of resilient capacity dry type transformers is provided by this research.

Influence of Partition Wall Length on Inlet Flow Regime of a Pumping Station Arranged in Parallel with a Sluice Gate

When a sluice gate is arranged in parallel with pumping station units, biased flow occurs in the forebay when the units are operating. The transverse flow velocity in front of the channel inlet is relatively high, and, in severe cases, it may lead to the formation of suction vortices, impacting the stable operation of pump units. Taking the Liushan Pumping Station project of the Eastern Route of the South-to-North Water Diversion Project as a case study, this paper investigates the effect of the partition wall length on the inlet flow regime of pumping station units arranged in parallel with the sluice gate to reduce the transverse flow velocity in front of the channel inlet. Using numerical simulations, the inlet flow regimes for different partition wall lengths were compared. Moreover, the flow field distributions in the forebay under different operating conditions were analyzed alongside the transverse flow velocity in front of the channel inlet and the uniformity of flow velocity distribution in the section behind the channel inlet. Hydraulic model tests were then conducted to validate the simulation results. The results indicate that in the original design, there existed a vortex zone in the forebay in front of the inlet of the channel where the transverse flow was relatively high. However, the introduction of partition walls significantly reduced the transverse flow velocity in front of the inlet of the channel in the forebay. The optimal effect was achieved when the length of the partition wall was twice the width of the inlet channel. Furthermore, the uniformity of velocity distribution at the inlet of the channel increased by an average of 7.4%, leading to a substantial improvement in the inlet flow regime of the pumping station. The addition of partition walls in the forebay effectively resolved the issues related to the flow regime in the forebay, providing valuable references for similar engineering studies in the future.

A Combined Model of Diffusion Model and Enhanced Residual Network for Super-Resolution Reconstruction of Turbulent Flows

In this study, we introduce a novel model, the Combined Model, composed of a conditional denoising diffusion model (SR3) and an enhanced residual network (EResNet), for reconstructing high-resolution turbulent flow fields from low-resolution flow data. The SR3 model is adept at learning the distribution of flow fields. The EResNet architecture incorporates a long skip connection extending from the input directly to the output. This modification ensures the preservation of essential features learned by the SR3, while simultaneously enhancing the accuracy of the flow field. Additionally, we incorporated physical gradient constraints into the loss function of EResNet to ensure that the flow fields reconstructed by the Combined Model are consistent with the direct numerical simulation (DNS) data. Consequently, the high-resolution flow fields reconstructed by the Combined Model exhibit high conformity with the DNS results in terms of flow distribution, details, and accuracy. To validate the effectiveness of the model, experiments were conducted on two-dimensional flow around a square cylinder at a Reynolds number (Re) of 100 and turbulent channel flow at Re = 4000. The results demonstrate that the Combined Model can reconstruct both high-resolution laminar and turbulent flow fields from low-resolution data. Comparisons with a super-resolution convolutional neural network (SRCNN) and an enhanced super-resolution generative adversarial network (ESRGAN) demonstrate that while all three models perform admirably in reconstructing laminar flows, the Combined Model excels in capturing more details in turbulent flows, aligning the statistical outcomes more closely with the DNS results. Furthermore, in terms of L2 norm error, the Combined Model achieves an order of magnitude lower error compared to SRCNN and ESRGAN. Experimentation also revealed that SR3 possesses the capability to learn the distribution of flow fields. This work opens new avenues for high-fidelity flow field reconstruction using deep learning methods.

Transient Flow Characteristics of a Pressure Differential Valve with Different Valve Spool Damping Orifice Structures

Lubrication system failure is a significant cause of in-flight shutdown incidents in aviation engines. The pressure differential valve, an essential component of a certain type of aviation engine lubrication system, is responsible for controlling the flow rate and pressure of the lubricating oil. Comprehending the transient flow characteristics of the pressure differential valve is of paramount importance for the secure operation of lubrication systems. This paper establishes a transient flow model of a pressure differential valve based on a transient computational fluid dynamics (CFD) method, and the experimental validation demonstrates the effectiveness of the computational model. The internal flow characteristics of the differential pressure valve at different stages during the opening process were studied. Additionally, four transient lubricating oil flow models with different valve spool damping orifice were established to analyse the impact of damping orifice structure on valve spool movement characteristics, pressure control characteristics, and flow field distribution. The results indicate that when the diameter of the valve spool damping orifice increases from 0.3 mm to 1.0 mm, the valve spool displacement and fluid force increase by 88 % and 20 %, respectively. Meanwhile, the peak valve spool velocity, peak oil supply pressure, and steady-state value decreased by 15 %, 29 %, and 34 %, respectively. As the length of the valve spool damping orifice increases from 0.894 mm to 4.0 mm, the growth rate of valve spool displacement and fluid force gradually decreases, with the peak valve spool velocity decreasing by 7 %. This study has potential significance for the structural optimization and application of pressure differential valve in lubrication systems.

Discussion on the influence of internal components on the flow field distribution of a new gas–solid non-catalytic fluidized bed (NRFB)

Discussion on the influence of internal components on the flow field distribution of a new gas–solid non-catalytic fluidized bed (NRFB)

Calculation of noise field in main transformer room of indoor substation based on thermal-acoustic coupling

In order to calculate the noise field distribution in the main transformer room of an indoor substation accurately, a thermal-acoustic coupling idea was introduced, and a noise field solving the algorithm based on thermal-acoustic coupling was proposed in view of the noise quality loss caused by the effect of ambient temperature changes. Firstly, the fluid-structure coupling model of the main transformer room is established, and the computational fluid dynamics method is used to calculate the flow field distribution and temperature boundary conditions under the action of the heat source; Then, extracting the rheological equation of the environmental boundary conditions in the flow field calculation, and use the difference function to couple the rheological equation to the sound grid to obtain the sound field coupling model under the condition of variable temperature; Finally, the modified parameter acoustic integral equation under the sound field coupling model is calculated based on the conventional Gauss numerical integration method, and the sound field of the main transformer room considering the effect of variable temperature is obtained. The algorithm has been successfully applied in the analysis of the noise field of Xi'an 110 kV Zhenxing Substation, and the error with the measured value is 2.083%.

Flow field optimization for performance enhancement of planar solid oxide fuel cells

The flow field design is very essential to the material distribution uniformity and overall output performance of planar solid oxide fuel cells. In this paper, the structure of the external manifold and cathode side interconnect is optimized to solve the uneven flow field distribution problem. The effects of crucial geometric parameters on the internal mass transfer, component transport, electrochemical reaction, temperature field and overall output performance of the fuel cell are studied by three-dimensional multi-physics numerical simulation. It is found that the combination of the three-inlet-two-outlet external manifold and cylindrical ribbed interconnect significantly reduces the uneven gas distribution between different channels and greatly improves the diffusion of oxygen under the ribs, thus enhancing the overall output performance of SOFC. Increasing the number of cylindrical ribs is beneficial to the transport and uniform distribution of oxygen. However, the excessive number of cylindrical ribs will hinder oxygen diffusion to the end of the flow channel, resulting in increased concentration polarization along the flow channel. Moreover, reducing the total contact area of the ribs enhances oxygen diffusion beneath the ribs but also raises the contact resistance and may deteriorate the cell performance.

Development of novel high anti-pollution polyamide/polysulfate disk tubular reverse osmosis membrane modules and their application in simulated space bathing wastewater

Water is a precious resource in space stations, and wastewater recycling is necessary to meet the needs of astronauts. In that respect, applying the high anti-pollution disk tubular reverse osmosis (DTRO) technique is a reliable way to remove pollutes from wastewater. Thin film composite (TFC) membrane treatment is the most frequently employed solution for purifying wastewater in industry; however, the intrinsic weaknesses of polymer membrane substrates, e.g., poor mechanical property, foulant adsorption and low resistance to acidic/basic conditions, greatly hamper their applications. In this study, the novel polysulfate (PSE) membrane substrates were prepared via non-solvent induced phase separation (NIPS) method. The microstructure and performance of PSE membrane substrates were comprehensively investigated at varying polymer concentration and nanoparticle types. The results showed that adding nanosilver to the support layer significantly enhanced the TFC- PSE/Ag membrane performance (up to 57 %) and tensile strength (by 4.57 ± 0.13). According to computational fluid dynamics (CFD) simulations, the optimized geometric design of deflectors would have noticeably improved the flow field distribution and strength, which was consistent with experimental data. The DTRO modules enabled the effective management of wastewater using simulated space bathing wastewater. The effluent met the water reuse criteria in terms of COD concentration, NH3-N concentration, conductivity and turbidity whose respective values were 15 mg/L, 0.21 mg/L, 60 μS/cm, and 0.9 NTU. The proposed DTRO modules own antifouling and acid/alkaline-resistance, indicating their remarkable application potential in the large-scale recovery of bathing wastewater from the earth or space station.

Study on the mechanism of vibration signal generation in water supply pipeline leaks

This study addresses water supply network leakage by employing numerical simulations to overcome challenges related to too small orifice hindering sensor deployment. Utilizing computational fluid dynamics and finite element methods, coupled with large eddy simulation, flow field distribution within pipes and at leakage orifice is investigated. The formation of leakage flow fields is categorized into three stages: leakage formation, unstable leakage, and stable leakage. During the leakage stage, the flow field is analyzed, and four regions—bottom central, bottom vortex, upper central, and upper vortex—are identified based on spatial characteristics. Detailed variable distribution patterns (velocity, pressure, vorticity) are provided in various planes. Understanding these distribution characteristics, six excitation sources responsible for generating leakage vibration signals are identified: pulsating velocity, pulsating pressure, bubble rupture, cavity pulsation, vortex-induced vibration, and gas expansion. The relationships among these excitation sources and their intensities concerning pipeline pressure and leak orifice radius are analyzed. Notably, a positive correlation between pressure and the intensity of all excitation sources is observed, while the impact of leak orifice size on these sources is found to be intricate. This research significantly contributes to an enhanced understanding of the physical processes associated with pipeline leakage.

Influence of a hemispherical bulge on a flat wall upon the collapse jet of cavitation bubbles

Uneven sections along a wall cause local flow deterioration and can result in severe cavitation erosion. This paper investigates the influence of a hemispherical bulge on a flat wall upon the collapse dynamics of a cavitation bubble in terms of the Kelvin impulse theory and high-speed photography based on the Weiss theorem and the image method. The evolution and characteristics of the bubble collapse morphology, the flow field distribution, and the Kelvin impulse (in terms of strength, direction, and directional sensitivity) are analyzed for symmetric and asymmetric configurations. The results show that the bubble collapse jet can be divided into three scenarios: mainly induced by the hemispherical bulge, mainly induced by the flat wall, and broadly equivalent effects of both. Additionally, as the dimensionless distance between the bubble and the flat wall increases, the range of the jet attraction zone induced by the bulge initially increases, subsequently decreases, and ultimately converges to the diameter of the bulge. The maximum width of the attraction zone can reach 3.45 times the radius of the bulge. Finally, the spatial sensitivity of the jet direction is found to be significant near the junction between the flat wall and the bulge.

Improving the hydraulic performance of a high-speed submersible axial flow pump based on CFD technology

The hydraulic performance of a high-speed submersible axial flow pump is investigated to reduce its energy consumption. A more efficient and stable optimization method that combines parametric design, computational fluid dynamics, and a computer algorithm is proposed. The main aim is to broaden the high-efficiency operating zone, so the average efficiency under multiple conditions is optimized while considering rotor–stator matching. The design-of-experiments method and a radial-basis-function neural network are combined to form the optimization platform, and automatic optimization of the pump design is realized through repeated execution of design and simulation. The flow loss mechanism inside the pump is studied in depth via the entropy generation rate, and regression analysis shows that the pump efficiency is influenced mainly by the blade angles. After optimization, the target efficiency is increased by 8.34%, and the flow field distribution shows that the channel vortex and hydraulic loss are controlled effectively. Finally, the results are validated by experiment. The proposed optimization approach has advantages in saving manpower and obtaining globally optimal solutions.

대규모 와 모사를 통한 운전부하가 튜브 축류홴의 난류유동장 분포양상에 미치는 영향 분석

대규모 와 모사를 통한 운전부하가 튜브 축류홴의 난류유동장 분포양상에 미치는 영향 분석

Numerical study on transport and deposition characteristics of particles associated with heat setting process in opposed jet flow field

The transport and deposition of particles accompanying the heat setting process in the opposed jet air supply system have a significant impact on the equipment safety. This paper used the Realizable k–ε model to simulate the flow field distribution of the impinging jet and the Lagrange method to track the trajectory of particles, by considering factors, such as jet velocity (7–13 m/s), oven temperature (413–473 K), and particle size (1–30 μ m ) changes, the instantaneous force process of particles was analyzed and their deposition mechanism was revealed. The numerical results have been well validated, with the root mean square error of within 10%. The results indicate that the flow field form of the opposed jet significantly affects particle placement on the surface of the air duct, the maximum turbulent vortex structure appears at the inlet of the air duct on both sides of the protruding nozzle, enhancing the capture of particles. Under the influence of gravity, the lower surface of the air duct becomes the main deposition surface, this phenomenon becomes more pronounced as the particle size increases and the maximum deposition rate difference between the upper and lower layers is 37%. The number of particles deposited on the rear end of the air duct is greater than that on the front end, and the deposition rate decreases with the increase in jet velocity. In the initial stage, a temperature gradient appeared in the machine room, which provided upward lift for the particles, resulting in more small diameter particles ( d p < 10 μ m ) depositing on the upper surface of the air duct. The results can provide theoretical support for the fire prevention and pollutant purification of equipment, such as heat setting machines.

Thermal-Hydraulic Analysis of Pebble Bed High Temperature Gas-Cooled Reactor After Shutdown Based on FLUENT Software

In order to provide a reliable tool for thermal-hydraulic simulation of pebble bed high temperature gas-cooled reactors (HTGRs), a two-dimensional model was developed based on the porous media model and user-defined scalar (UDS) function of FLUENT software. Then, the model was applied to the numerical simulation of the shutdown test of the 10 MW high temperature gas-cooled test reactor (HTR-10) at 9 MW power level, and the temperature distribution and flow field distribution in the reactor were obtained and compared with the results of the experimental data. The reliability of the model in this paper was verified. Based on the model, the effects of the water-cooled panel temperature and the initial core temperature on the thermal-hydraulic characteristics of HTR-10 after shutdown were further explored. The results show that there is a decoupling phenomenon between the residual heat transfer within the core and the heat dissipation of the pressure vessel. The initial core temperature has relatively little effect on the heat dissipation and maximum temperature of the pressure vessel, but it has a significant impact on the thermal characteristics of the core area.

Research on the Characteristics of Stirring Flow Field of Flotation Separator Based on PIV Technology

In order to explore the distribution characteristics and characteristics of the internal flow field of the flotation machine, and to understand the variation law of the flow field parameters in the process of the internal flow field of the flotation machine, particle image velocimetry was used to measure the flow field of the flotation machine, and four groups of sections were designed, each group of sections had four different revolutions, and there were 16 experimental groups in total. The results show that the vertical plane of the flow field of flotation machine can be roughly divided into four areas. The flow field level of the flotation machine can also be divided into three areas. The effect of rotating speed on the average circulating speed of flotation machine was studied. This paper analyzes the statistical law of vorticity distribution in the internal flow field of flotation machine and the relationship between average speed and rotating speed, and establishes the probability model and influence analysis model related to it.

Effect of inlet velocity on the hydraulic and filtering performance of a Y‐type screen filter

AbstractUneven sediment distribution affected by inlet velocity, particle size distribution and flow field characteristics leads to local clogging in a Y‐type screen filter. This study revealed the detailed flow field characteristics and distribution of sediments on the screen via computational fluid dynamics combined with the discrete element method (CFD–DEM) simulations and experimental tests. The results showed that the distribution of the flow rate on the filter screen was extremely uneven, with the maximum flow rate being 11.72 times greater than the minimum rate. The flow rate was distributed symmetrically on the two sides along the outlet centreline, as shown by the unfolded drawing of the filter core. Numerical simulation and experimental tests using sandy water showed that the number and average particle diameter on the screen decreased, and the number and average particle diameter in the plug increased, with increasing inlet velocity. The sediments on the screen were distributed intensively, and the plugging extent coefficient and the anti‐clogging performance improved. However, this process was more likely to cause local clogging and worsen the filtration performance. Therefore, low‐speed filtering should be applied if the filtering effect is needed, and high‐speed filtering should be applied if the filtering efficiency is favourable but the flushing frequency increases.

Numerical simulation of the influence of gear-type combustion stabilizer on the flow field distribution and combustion products of swirl burner

The gear-type combustion stabilizer (GCS) installed in the burner can effectively disturb the flow field. However, there is a lack of research on the impact of GCS's position on NOx production. This study aims to design the optimal GCS position to enable stable combustion of pulverized coal (PC) and reduce NOx emissions. In comparison to the prototype burner, the extension of the central air pipe (CAP) resulted in delayed mixing of the central air with the primary air, delayed ignition of the PC, and a 2.93% reduction in the burnout rate (BR). Furthermore, the installation of a GCS in the primary air pipe (PAP) reduced the cross-sectional area of the flow path, increased the flow velocity, and delayed the ignition. The GCS disturbed the axial velocity at radial positions less than 0.5 m and formed a backflow, which led to an increase in the BR. At the burner outlet of the burner equipped with an internal-external gear-type combustion stabilizer (IEGCS), the PC gas stream formed a significant rich/lean separation. The CO content generated by the external gear-type combustion stabilizer (EGCS) burner is the highest, which is beneficial to inhibiting the formation of NOx. As a result, the NOx production was reduced by 17.02% compared to the prototype burner.

The influence of ring clearance on the performance of a double-suction centrifugal pump

Due to the complex structure of a double-suction pump's suction chamber, the flow in the pump's cavity is often ignored in numerical simulations because of difficulties in structured hexahedral meshing. However, the wear ring clearance interlinking the pump chamber leads the fluid at the impeller inlet directly to the impeller area. This significantly impacts the pump's internal flow field, so the influence of the clearance on the internal flow of a double-suction pump cannot be ignored. This paper develops four three-dimensional double-suction pump models with different wear ring clearances to investigate their influence on pump performance, and structured hexahedral meshes were used for all the computational domains. The clearances varied from 0.2 to 0.5 mm in 0.1 mm increments. The influences of the clearance on the energy loss, external characteristics, and internal flow field distribution of the pump were simulated via a verified computational fluid dynamics method. The results show that the wear ring leakage decreases with the flow rate and increases with wear ring clearance. The increase in backflow leads to an internal flow disorder inside the impeller, resulting in a decreased head and efficiency. Energy loss is mainly caused by increasing the turbulence entropy production with an increasing wear ring clearance. Also, the low-pressure region in the pump cavity expands to the volute with increasing clearance, and the impeller outlet pressure decreases. This study's research on wear ring clearance provides a reference for the design and application of double-suction centrifugal pumps.

Study of aerosol dispersion and control in dental practice.

In this study, we investigated the dispersion patterns of aerosols and droplets in dental clinics and developed a suction device to evaluate its effectiveness in reducing aerosols during dental procedures. Firstly, the continuous images of oral aerosols and droplets were photographed with a high-speed camera, and the trajectories of these particles were recognized and processed by Image J to determine key parameters affecting particle dispersion: diffusion velocity, distance, and angle. Secondly, based on the parameter data, the flow field of aerosol particles around the oral cavity was simulated using computational fluid dynamics (CFD), and the flow field under adsorption conditions was simulated to demonstrate the aerodynamic characteristics and capture efficiencies of the single-channel and three-channel adsorption ports at different pressures. Finally, according to the simulated data, a three-channel suction device was developed, and the capture efficiency of the device was tested by the fluorescein tracer method. The dispersion experimental data showed that aerosol particles' maximum diffusion velocity, distance, and angle were 6.2m/s, 0.55m, and 130°, respectively. The simulated aerosol flow-field distribution was consistent with the aerosol dispersion patterns. The adsorption simulation results showed that the outlet flow rate of single-channel adsorption was 184.5 L/s at - 350Pa, and the aerosol capture efficiency could reach 79.4%. At - 350Pa and - 150Pa, the outlet flow rate of three-channel adsorption was 228.9 L/s, and the capture efficiency was 99.23%. The adsorption experimental data showed that the capture efficiency of three-channel suction device was 97.71%. A three-channel suction device was designed by simulations and experiments, which can capture most aerosols in the dental clinic and prevent them from spreading. Using three-channel suction devices during oral treatment effectively reduces the spread of oral aerosols, which is essential to prevent the spread of epidemics and ensure the health and safety of patients and dental staff.