scholarly journals A Coupled, Semi-Numerical Model for Thermal Analysis of Medium Frequency Transformer

Energies ◽  
2019 ◽  
Vol 12 (2) ◽  
pp. 328 ◽  
Author(s):  
Haonan Tian ◽  
Zhongbao Wei ◽  
Sriram Vaisambhayana ◽  
Madasamy Thevar ◽  
Anshuman Tripathi ◽  
...  
Keyword(s):  
Numerical Model ◽  
Analytical Model ◽  
Electromagnetic Analysis ◽  
Medium Frequency ◽  
Fluid Analysis ◽  
Fluid Behavior ◽  
Proposed Model ◽  
Computational Fluid Dynamics Cfd ◽  
Cfd Method ◽  
Thermal Fluid Analysis

Medium-frequency (MF) transformer has gained much popularity in power conversion systems. Temperature control is a paramount concern, as the unexpected high temperature declines the safety and life expectancy of transformer. The scrutiny of losses and thermal-fluid behavior are thereby critical for the design of MF transformers. This paper proposes a coupled, semi-numerical model for electromagnetic and thermal-fluid analysis of MF oil natural air natural (ONAN) transformer. An analytical model that is based on spatial distribution of flux density and AC factor is exploited to calculate the system losses, while the thermal-hydraulic behavior is modelled numerically leveraging the computational fluid dynamics (CFD) method. A close-loop iterative framework is formulated by coupling the analytical model-based electromagnetic analysis and CFD-based thermal-fluid analysis to address the temperature dependence. Experiments are performed on two transformer prototypes with different conductor types and physical geometries for validation purpose. Results suggest that the proposed model can accurately model the AC effects, losses, and the temperature rises at different system components. The proposed model is computationally more efficient than the full numerical method but it reserves accurate thermal-hydraulic characterization, thus it is promising for engineering utilization.

Numerical Investigation of Dusts Removal from Tramway Surface by Street Vacuum Sweeper

2011 ◽  
Vol 236-238 ◽  
pp. 1619-1622 ◽  
Author(s):  
Bo Fu Wu ◽  
Jin Lai Men ◽  
Jie Chen
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Numerical Model ◽  
Pressure Drop ◽  
Removal Efficiency ◽  
Pressure Drops ◽  
Operational Safety ◽  
Airflow Field ◽  
Computational Fluid Dynamics Cfd ◽  
Cfd Method

In order to enhance the operational safety of tram vehicle and reduce the wear of guide wheels mounted on the vehicle, it is necessary to remove particles such as dusts and silts from tramway surface. The aim of this paper is to evaluate the effectiveness of street vacuum sweeper for sucking up dusts from tramway surface. A numerical model was developed based on dusts removal process. Under different pressure drops across the pickup head of the street vacuum sweeper, the flow field and dusts removal efficiency were analyzed with computational fluid dynamics (CFD) method. The numerical results show that a higher pressure drop can improve the airflow field in the pickup head and results in higher dusts removal efficiency, but higher pressure drop definitely need more energy. Therefore, a balance should be taken into consideration.

scholarly journals Numerical Analysis of Woltman Meter Accuracy under Flow Perturbations

Water ◽  
2019 ◽  
Vol 11 (12) ◽  
pp. 2622
Author(s):  
Carmen V. Palau ◽  
Iban Balbastre ◽  
Juan Manzano ◽  
Benito M. Azevedo ◽  
Guilherme V. Bomfim
Keyword(s):  
Numerical Model ◽  
Measurement Errors ◽  
Gate Valve ◽  
Experimental Tests ◽  
Butterfly Valve ◽  
Balance Equations ◽  
Straight Pipe ◽  
Proposed Model ◽  
Computational Fluid Dynamics Cfd ◽  
Water Measurement

One of the unknowns in the instrumentation for water measurement is what degree of influence other hydraulic elements exert on the velocity profile and, consequently, on the measurement errors. In this work, the measurement errors of a horizontal-axis Woltman meter produced by a gate valve and by a butterfly valve in different hydraulic configurations were studied using a simplified numerical model. The gate valve was installed beside the meter and three pipe diameters upstream of the meter and were operated with closures of 75%, 50% and 25%, while the butterfly valve was installed at three pipe diameters upstream of the meter with closures of 0° (open) and 30°. The numerical model based on the rotor’s torque balance equations and Computational Fluid Dynamics (CFD) was validated by experimental tests. According to the results, it was concluded that the proposed model is valid and capable of estimating the errors caused by the hydraulic fittings arranged next to the meter. In addition, it is evident that for the analysed operating range, both valves must be installed at least three diameters of straight pipe upstream of the meter.

Bifunctionally Graded Electrode Supported SOFC Modeling and Computational Thermal Fluid Analysis for Experimental Design

2010 ◽  
Vol 8 (1) ◽  
Author(s):  
Junxiang Shi ◽  
Xingjian Xue
Keyword(s):  
Porous Electrode ◽  
Functionally Graded ◽  
Operating Conditions ◽  
Hydrogen Distribution ◽  
Fuel Gas ◽  
Ion Migration ◽  
Fluid Analysis ◽  
Porous Microstructure ◽  
Computational Fluid Dynamics Cfd ◽  
Thermal Fluid Analysis

A comprehensive 3D computational fluid dynamics (CFD) model is developed for a bi-electrode supported cell (BSC) solid oxide fuel cell (SOFC). The model includes complicated transport phenomena of mass/heat transfer, charge (electron and ion) migration, and electrochemical reactions. The uniqueness of the modeling study is that functionally graded porous electrode property is taken into account, including not only linear but also nonlinear porosity distributions. The model is validated using experimental data from open literature. Numerical results indicate that BSC performance is strongly dependent on both operating conditions and porous microstructure distributions of electrodes. Using the proposed fuel/gas feeding design, the uniform hydrogen distribution within the porous anode is achieved; the oxygen distribution within the cathode is dependent on porous microstructure distributions as well as pressure loss conditions. Simulation results also show that fairly uniform temperature distribution can be obtained with the proposed fuel/gas feeding design. This modeling work can provide a pre-experimental analysis and guide experimental designs for BSC test.

An Investigation for the Usability of K-K Equations for Nano Porous Membranes

2009 ◽  
Author(s):  
Junfeng Lu ◽  
Yang Chu ◽  
Wen-Qiang Lu
Keyword(s):  
Fluid Dynamics ◽  
Molecular Dynamics ◽  
Porous Membranes ◽  
Permeable Membrane ◽  
Filtration Membrane ◽  
Fluid Behavior ◽  
Ultra Filtration ◽  
Computational Fluid Dynamics Cfd ◽  
Nano Filtration ◽  
Cfd Method

As physical model used to interpret the fluid behavior when it passes through a semi-permeable membrane, Kedem-Ketchalsky’s (K-K) equations [1, 2] were successfully used in a bunch of filtration processes. However, because they were developed and dedicated to normal ultra- and micro-filtration systems, their limitations were obviously observed in some sort of nano-filtration processes that the pore size of the filtration membrane is only several nanometers. This paper analyzed the feasible utilization scopes of K-K equations. And two methods, Molecular Dynamics (MD) method and Computational Fluid Dynamics (CFD) method, used respectively to analyze nano- and ultra-filtration processes are introduced in this paper.

Research on Flow Field Simulation and Experiment of Numerical Control Electrochemical Machining

2010 ◽  
Vol 458 ◽  
pp. 63-68 ◽  
Author(s):  
Xiu Qing Fu ◽  
Min Kang ◽  
Q.Y. Zheng
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Numerical Model ◽  
Flow Field ◽  
Optimization Design ◽  
Electrochemical Machining ◽  
Numerical Control ◽  
Simulation And Experiment ◽  
Computational Fluid Dynamics Cfd ◽  
Cfd Method

To design the flow field of inner-spraying ball-end cathode in NC-ECM, the numerical model was bulit according to the physical model of the cathode flow channal, and the computational fluid dynamics (CFD) method was applied to slove the numerical model. The velocity and pressure distributations were obtained. The influences of the cathode internal structure and the outlet shape on the velocity of electrolyte were analyzed on the basis of the numerical simulation. The relatively good simulation results were obtained by means of the optimization design of the cathode. Based on the experiment results, the accuracy of simulation was verified, and the correction number of the design of the flow field was reduced in NC-ECM. It is indicated that the computational fluid dynamics (CFD) method can be applied to simulate the flow field, and the optimization design of the cathode can be guided according to the results of simulation.

Effect Investigation of the Circumferential Grooves on the Static Characteristics of Hydrodynamic Journal Bearing Using CFD Method

2014 ◽  
Vol 643 ◽  
pp. 316-321
Author(s):  
Qing Zheng Meng ◽  
Lin Cai ◽  
Miao He
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Numerical Model ◽  
Cfd Simulation ◽  
Journal Bearing ◽  
Static Characteristics ◽  
Computational Fluid Dynamics Cfd ◽  
Hydrodynamic Journal Bearing ◽  
Good For ◽  
Cfd Method

The performance of a hydrodynamic journal bearing with different center circumferential grooves (CGs) is investigated using Computational fluid dynamics (CFD) simulation. The influences of the CG extended angel have been investigated based on the numerical model. The results show that the CG of millimeter range depth in load zone is not good for the bearing performance but it is opposite in unload zone.

scholarly journals A Semi-Empirical Model for Predicting Frost Properties

Processes ◽  
2021 ◽  
Vol 9 (3) ◽  
pp. 412
Author(s):  
Shao-Ming Li ◽  
Kai-Shing Yang ◽  
Chi-Chuan Wang
Keyword(s):  
Thermal Conductivity ◽  
Linear Programming ◽  
Numerical Model ◽  
Empirical Model ◽  
Quantitative Method ◽  
Predictive Ability ◽  
Dimensionless Temperature ◽  
Crystal Shape ◽  
Proposed Model ◽  
Semi Empirical

In this study, a quantitative method for classifying the frost geometry is first proposed to substantiate a numerical model in predicting frost properties like density, thickness, and thermal conductivity. This method can recognize the crystal shape via linear programming of the existing map for frost morphology. By using this method, the frost conditions can be taken into account in a model to obtain the corresponding frost properties like thermal conductivity, frost thickness, and density for specific frost crystal. It is found that the developed model can predict the frost properties more accurately than the existing correlations. Specifically, the proposed model can identify the corresponding frost shape by a dimensionless temperature and the surface temperature. Moreover, by adopting the frost identification into the numerical model, the frost thickness can also be predicted satisfactorily. The proposed calculation method not only shows better predictive ability with thermal conductivities, but also gives good predictions for density and is especially accurate when the frost density is lower than 125 kg/m3. Yet, the predictive ability for frost density is improved by 24% when compared to the most accurate correlation available.

scholarly journals Computational fluid dynamics (CFD) simulation analysis on retinal gas cover rates using computational eye models

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Makoto Gozawa ◽  
Yoshihiro Takamura ◽  
Tomoe Aoki ◽  
Kentaro Iwasaki ◽  
Masaru Inatani
Keyword(s):  
Cfd Simulation ◽  
Simulation Analysis ◽  
Fluid Dynamic ◽  
Fluid Analysis ◽  
Intraocular Gas ◽  
Pars Plana ◽  
Computational Fluid Dynamics Cfd ◽  
Multiple Breaks ◽  
Gas Volume ◽  
Wall Wettability

AbstractWe investigated the change in the retinal gas cover rates due to intraocular gas volume and positions using computational eye models and demonstrated the appropriate position after pars plana vitrectomy (PPV) with gas tamponade for rhegmatogenous retinal detachments (RRDs). Computational fluid dynamic (CFD) software was used to calculate the retinal wall wettability of a computational pseudophakic eye models using fluid analysis. The model utilized different gas volumes from 10 to 90%, in increments of 10% to the vitreous cavity in the supine, sitting, lateral, prone with closed eyes, and prone positions. Then, the gas cover rates of the retina were measured in each quadrant. When breaks are limited to the inferior retina anterior to the equator or multiple breaks are observed in two or more quadrants anterior to the equator, supine position maintained 100% gas cover rates in all breaks for the longest duration compared with other positions. When breaks are limited to either superior, nasal, or temporal retina, sitting, lower temporal, and lower nasal position were maintained at 100% gas cover rates for the longest duration, respectively. Our results may contribute to better surgical outcomes of RRDs and a reduction in the duration of the postoperative prone position.

scholarly journals Numerical Investigation for the Resin Filling Behavior during Ultraviolet Nanoimprint Lithography of Subwavelength Moth-Eye Nanostructure

Coatings ◽  
2021 ◽  
Vol 11 (7) ◽  
pp. 799
Author(s):  
Yuanchi Cui ◽  
Xuewen Wang ◽  
Chengpeng Zhang ◽  
Jilai Wang ◽  
Zhenyu Shi
Keyword(s):  
Simulation Model ◽  
Nanoimprint Lithography ◽  
Cfd Simulation ◽  
Boundary Slip ◽  
Accurate Analysis ◽  
Inlet Velocity ◽  
Filling Height ◽  
Proposed Model ◽  
Good Consistency ◽  
Computational Fluid Dynamics Cfd

Accurate analysis of the resin filling process into the mold cavity is necessary for the high-precision fabrication of moth-eye nanostructure using the ultraviolet nanoimprint lithography (UV-NIL) technique. In this research, a computational fluid dynamics (CFD) simulation model was proposed to reveal resin filling behavior, in which the effect of boundary slip was considered. By comparison with the experimental results, a good consistency was found, indicating that the simulation model could be used to analyze the resin filling behavior. Based on the proposed model, the effects of process parameters on resin filling behavior were analyzed, including resin viscosity, inlet velocity and resin thickness. It was found that the inlet velocity showed a more significant effect on filling height than the resin viscosity and thickness. Besides, the effects of boundary conditions on resin filling behavior were investigated, and it was found the boundary slip had a significant influence on resin filling behavior, and excellent filling results were obtained with a larger slip velocity on the mold side. This research could provide guidance for a more comprehensive understanding of the resin filling behavior during UV-NIL of subwavelength moth-eye nanostructure.

A method for predicting Mach stem height in steady flows

2021 ◽  
pp. 095441002110015
Author(s):  
Song-Guk Choe
Keyword(s):  
Analytical Model ◽  
Slip Line ◽  
Flow Region ◽  
Rocket Engines ◽  
Steady Flows ◽  
Mach Stem ◽  
Stem Height ◽  
Mach Numbers ◽  
Relative Errors ◽  
Cfd Method

The prediction of Mach stem height can be important in the design of supersonic intake in supersonic and hypersonic flows. It is also important because of the progress in aircraft and rocket engines. An analytical method of predicting the Mach stem height is necessary in theoretical field of shock reflection and is the basis of the comparable computational fluid dynamics (CFD) method. A method for predicting the Mach stem height in steady flows is performed based on the earlier models. In this article, an analytical model for predicting the Mach stem height is improved based on two main assumptions: one is the calculation of the triple point deflection angle when the Mach stem is an oblique shock and the other is about the shape of the free part of the slip line. Under these assumptions, the relations predicting of Mach stem height in two-dimensional steady flow are derived based on the advanced averaging method of the subsonic flow region. The Mach stem heights are decided solely for the incoming flow Mach numbers and the wedge angles by the improved analytical model. As a result, the Mach stem heights by the model of this article are found to agree well with experimental results at lower Mach numbers, but there are relative errors at higher Mach numbers. The convexity of the slip line is also considered.

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