Analytical and Numerical Investigations of Friction Number for Laminar Flow in Microchannels

2018 ◽  
Vol 141 (3) ◽  
Author(s):  
Mohamed S. El-Genk ◽  
Mahyar Pourghasemi
Keyword(s):  
Slip Length ◽  
Fully Developed Flow ◽  
Inlet Velocity ◽  
Pressure Losses ◽  
Numerical Investigations ◽  
Apparent Slip ◽  
Flow Development ◽  
Computational Fluid Dynamics Cfd ◽  
The Difference ◽  
Cfd Analyses

Analytical and computational fluid dynamics (CFD) analyses confirmed the presence of apparent slip for water flow in microchannels with equivalent hydraulic diameter, Dh < 103μm, markedly decreasing the friction number, fRein. The determined values of the slip length, β, from reported measurements of pressure losses in microchannels with aspect ratio, α = 1, 1.74, 2, and 40, are 0.9, 3.5, 1.6, and 0.125 μm, respectively. For Dh > 103μm, the apparent slip in microchannels diminishes, and the friction number approaches the theoretical Hagen–Poiseuille with no slip. The analytical solution for fully developed flow successfully benchmarked the CFD approach, which is subsequently used to investigate fRein and the flow development length, Le, for uniform inlet velocity in microchannels. For fully developed flow, the analytical and CFD values of fRein are in excellent agreement. For microchannels with Dh < 103μm, fRein decreases below that of the theoretical Hagen–Poiseuille with no slip, almost exponentially with decreased Dh. The difference increases with decreased Dh, but increased α and β. The friction number for uniform inlet velocity is identical to that for fully developed flow when Dh ≤ 100 μm, but is as much as 9% higher for larger Dh. For uniform inlet velocity, Le negligibly depends on α and β, but increases with increased Rein. The obtained values are correlated as: Le/Dh = 0.068 Rein.

Yaw Galloping of a TLWP Platform Under High Speed Currents by Analytical Methods and its Comparison With Experimental Results

2017 ◽  
Author(s):  
Francisco Lamas ◽  
Miguel A. M. Ramirez ◽  
Antonio Carlos Fernandes
Keyword(s):  
High Speed ◽  
Production Systems ◽  
Experimental Tests ◽  
Experimental Results ◽  
Analytical Methodology ◽  
New Approach ◽  
Laboratory Facilities ◽  
Polynomial Curve ◽  
Computational Fluid Dynamics Cfd ◽  
Cfd Analyses

Flow Induced Motions are always an important subject during both design and operational phases of an offshore platform life. These motions could significantly affect the performance of the platform, including its mooring and oil production systems. These kind of analyses are performed using basically two different approaches: experimental tests with reduced models and, more recently, with Computational Fluid Dynamics (CFD) dynamic analysis. The main objective of this work is to present a new approach, based on an analytical methodology using static CFD analyses to estimate the response on yaw motions of a Tension Leg Wellhead Platform on one of the several types of motions that can be classified as flow-induced motions, known as galloping. The first step is to review the equations that govern the yaw motions of an ocean platform when subjected to currents from different angles of attack. The yaw moment coefficients will be obtained using CFD steady-state analysis, on which the yaw moments will be calculated for several angles of attack, placed around the central angle where the analysis is being carried out. Having the force coefficients plotted against the angle values, we can adjust a polynomial curve around each analysis point in order to evaluate the amplitude of the yaw motion using a limit cycle approach. Other properties of the system which are flow-dependent, such as damping and added mass, will also be estimated using CFD. The last part of this work consists in comparing the analytical results with experimental results obtained at the LOC/COPPE-UFRJ laboratory facilities.

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.

Development of the DLE Combustor for L30A Gas Turbine

2015 ◽  
Author(s):  
Toshiaki Sakurazawa ◽  
Takeo Oda ◽  
Satoshi Takami ◽  
Atsushi Okuto ◽  
Yasuhiro Kinoshita
Keyword(s):  
Gas Turbine ◽  
Gas Turbines ◽  
Nox Emission ◽  
Test Facility ◽  
Exhaust Temperature ◽  
Main Burner ◽  
Harmful Emissions ◽  
Emission Regulation ◽  
Computational Fluid Dynamics Cfd ◽  
Cfd Analyses

This paper describes the development of the Dry Low Emission (DLE) combustor for L30A gas turbine. Kawasaki Heavy Industries, LTD (KHI) has been producing relatively small-size gas turbines (25kW to 30MW class). L30A gas turbine, which has a rated output of 30MW, achieved the thermal efficiency of more than 40%. Most continuous operation models use DLE combustion systems to reduce the harmful emissions and to meet the emission regulation or self-imposed restrictions. KHI’s DLE combustors consist of three burners, a diffusion pilot burner, a lean premix main burner, and supplemental burners. KHI’s proven DLE technologies are also adapted to the L30A combustor design. The development of L30 combustor is divided in four main steps. In the first step, Computational Fluid Dynamics (CFD) analyses were carried out to optimize the detail configuration of the combustor. In a second step, an experimental evaluation using single-can-combustor was conducted in-house intermediate-pressure test facility to evaluate the performances such as ignition, emissions, liner wall temperature, exhaust temperature distribution, and satisfactory results were obtained. In the third step, actual pressure and temperature rig tests were carried out at the Institute for Power Plant Technology, Steam and Gas Turbines (IKDG) of Aachen University, achieving NOx emission value of less than 15ppm (O2=15%). Finally, the L30A commercial validation engine was tested in an in-house test facility, NOx emission is achieved less than 15ppm (O2=15%) between 50% and 100% load operation point. L30A field validation engine have been operated from September 2012 at a chemical industries in Japan.

Effect of Divergence Angle on Flow Through Inlet Section of Diffuser of a Gas Turbine Combustion Chamber: The CFD Approach

2006 ◽  
Author(s):  
Digvijay B. Kulshreshtha ◽  
S. A. Channiwala ◽  
Jitendra Chaudhary ◽  
Zoeb Lakdawala ◽  
Hitesh Solanki ◽  
...  
Keyword(s):  
Combustion Chamber ◽  
Gas Turbine ◽  
Total Pressure ◽  
Divergence Angle ◽  
Velocity Head ◽  
Turbine Engine ◽  
Inlet Velocity ◽  
Pressure Losses ◽  
Flow Through ◽  
Mach Numbers

In the combustor inlet diffuser section of gas turbine engine, high-velocity air from compressor flows into the diffuser, where a considerable portion of the inlet velocity head PT3 − PS3 is converted to static pressure (PS) before the airflow enters the combustor. Modern high through-flow turbine engine compressors are highly loaded and usually have high inlet Mach numbers. With high compressor exit Mach numbers, the velocity head at the compressor exit station may be as high as 10% of the total pressure. The function of the diffuser is to recover a large proportion of this energy. Otherwise, the resulting higher total pressure loss would result in a significantly higher level of engine specific fuel consumption. The diffuser performance must also be sensitive to inlet velocity profiles and geometrical variations of the combustor relative to the location of the pre-diffuser exit flow path. Low diffuser pressure losses with high Mach numbers are more rapidly achieved with increasing length. However, diffuser length must be short to minimize engine length and weight. A good diffuser design should have a well considered balance between the confliction requirements for low pressure losses and short engine lengths. The present paper describes the effect of divergence angle on diffuser performance for gas turbine combustion chamber using Computational Fluid Dynamic Approach. The flow through the diffuser is numerically solved for divergence angles ranging from 5 to 25°. The flow separation and formation of wake regions are studied.

scholarly journals Hydrodynamic analysis of a liquid-solid fluidized bed via cfd-dem simulations, stability analysis, and tomography

2021 ◽  
Author(s):  
Hussein Zbib
Keyword(s):  
Stability Analysis ◽  
Fluidized Bed ◽  
Volume Fraction ◽  
Particle Volume Fraction ◽  
Percentage Error ◽  
Particle Interactions ◽  
Particle Volume ◽  
Computational Fluid Dynamics Cfd ◽  
The Difference ◽  
Dem Model

A coupled computational fluid dynamics (CFD) and discrete element method (DEM) model was developed to analyze the fluid-particle and particle-particle interactions in a 3D liquid-solid fluidized bed (LSFB). The CFD-DEM model was validated using the Electrical Resistance Tomography (ERT) experimental method. ERT was employed to measure the bed-averaged particle volume fraction (BPVF) of 0.002 m glass beads fluidized with water for various particle numbers and flow rates. It was found that simulations employing the combination of the Gidaspow drag model with pressure gradient and virtual mass forces provided the least percentage error between experiments and simulations. It was also found that contact parameters must be calibrated to account for the particles being wet. The difference between simulations and experiments was 4.74%. The CFD-DEM model was also employed alongside stability analysis to investigate the hydrodynamic behavior within the LSFB and the intermediate flow regime for all cases studied.

Application of CFD in Designing Spacers: A Novel Approach

2000 ◽  
Author(s):  
Vahid Jalili ◽  
Mayur K. Patel ◽  
Christopher Bailey
Keyword(s):  
Experimental Data ◽  
Optimum Size ◽  
Large Area ◽  
Optimum Time ◽  
Actual Length ◽  
Inlet Velocity ◽  
Biomedical Device ◽  
Novel Approach ◽  
Computational Fluid Dynamics Cfd ◽  
Inlet Boundary Condition

Abstract The aim of this paper is to report on a novel approach used in designing spacer (a biomedical device used to aid inhalation of the drug). The Computational Fluid Dynamics (CFD) technique has been around for some years, but to date has not been used in designing spacers. In the present study the commercial CFD engines used were FLUENT-5.1.1 and PHOENICS. The study covered a large area taking into account various parameter changes such as the inlet boundary condition i.e. changing the velocity at inlet, varying the jet angle at entry to the spacer and the actual length of the spacer. The results were possible were compared to the experimental data available and generally the comparison was good. The findings from this research have highlighted, that there is an optimum size of 6cm and inlet velocity of 30m/s which result in an increased efficiency. It was also found that there is an optimum time of 0.4 sec. For which the highest drug concentration appears to be present.

scholarly journals Pressure-Driven Thermal Slip Flow in the Elliptical Channel with Radial Oscillatory Wall

2020 ◽  
Vol 2020 ◽  
pp. 1-9
Author(s):  
Nattawan Chuchalerm ◽  
Benchawan Wiwatanapataphee ◽  
Wannika Sawangtong
Keyword(s):  
Slip Length ◽  
Ritz Method ◽  
Slip Flow ◽  
Temperature Fields ◽  
Thermal Slip ◽  
Fully Developed Flow ◽  
Navier Slip ◽  
Heat Transfer Phenomenon ◽  
Flow Heat ◽  
Velocity And Temperature Fields

This paper is aimed at presenting thermal slip flow driven by oscillatory pressure gradient in a deformable microchannel of elliptic cross-section. The fully developed flow of Newtonian fluid is considered, and Navier slip is applied on the boundary. The boundary value problem is formulated and applied to the coronary blood flow-heat transfer phenomenon during thermotherapy treatment. Its semianalytical solutions of velocity and temperature fields are carried out by the Ritz method. The effects of oscillatory wall and slip length on velocity and temperature fields of blood are investigated.

The Impact of Volute Versus Collector on Centrifugal Compressor Performance

2002 ◽  
Author(s):  
Y. I. Biba
Keyword(s):  
3D Model ◽  
Internal Flow ◽  
Performance Measurements ◽  
Cross Sectional ◽  
Flow Rates ◽  
Computational Fluid Dynamics Cfd ◽  
Compressor Performance ◽  
The Subject ◽  
Cfd Analyses ◽  
The Impact

As part of a revamp or rerate study, an investigation was undertaken to assess the impact of a collector design versus a volute on compressor performance. The subject compressor was a single stage, axial inlet configuration with a discharge collector rather than the more commonly used scroll volute. The primary distinction between the collector and volute is that the collector cross sectional area is constant at all circumferential locations. A complex 3D model containing the inlet, impeller, low solidity diffuser (LSD), and collector was built. A similar model was also created where the volute was substituted for the collector. Computational Fluid Dynamics (CFD) analyses were performed using these models with results generated at different flow rates. Computational results are presented and compared to test data for collector configuration. The test included standard performance measurements as well as more detailed internal flow data, allowing a credible comparison with the CFD results. Conclusions are drawn with respect to potential compromises in choosing a collector versus a volute.

The Aerodynamic Attributes and Flight Trajectories of a Tail Fin-Stabilized Projectile

2013 ◽  
Vol 415 ◽  
pp. 544-547
Author(s):  
Chun Chi Li ◽  
Chang Sheng Tai ◽  
Cheng Chyuan Lai ◽  
Shang Min Fu ◽  
Yen Chun Tsai
Keyword(s):  
Degrees Of Freedom ◽  
Angle Of Attack ◽  
Field Testing ◽  
Maximum Height ◽  
Firing Range ◽  
Calculation Results ◽  
Computational Fluid Dynamics Cfd ◽  
Flight Trajectories ◽  
The Difference ◽  
Low Speed Wind Tunnel

Combined with low-speed wind tunnel experiments, this study adopted computational fluid dynamics (CFD) and the MATLAB/Simulink control software to analyze the aerodynamic attributes of a tail fin-stabilized projectile and subsequently simulate its flight trajectory with four degrees of freedom under a flight condition (M) of 0.6 and an angle of attack (α) between-60° and 60°. Comparing the CFD calculation results with the revised experiment data using the Karman-Tsien Rule showed that the aerodynamic coefficients CD, CL, and CM were similar within an angle of attack between-30° and 30°. The projectile further demonstrated excellent aerodynamic attributes within an angle of attack between-60° and 60°, maintaining stable flight. Furthermore, comparing the four-degrees-of-freedom simulation results with data from the firing table showed that the maximum height difference of trajectories at varying angles of elevation (mil) ranged from 3.07% to 4.68%, and the difference in the firing range distance ranged from 0.15% to 5.72%. To reduce the costs of field testing, this study establishes a method to design aerodynamic systems, analyze and compare flow fields, and simulate flight trajectories.

scholarly journals Cold Flow Computations for the Diffuser-Combustor Section of an Industrial Gas Turbine

1996 ◽  
Author(s):  
Dadong Zhou ◽  
Ting Wang ◽  
William R. Ryan
Keyword(s):  
Gas Turbine ◽  
Total Pressure ◽  
Reverse Flow ◽  
Three Dimensional ◽  
Complex Flow ◽  
Pressure Losses ◽  
Structured Grid ◽  
Computational Fluid Dynamics Cfd ◽  
Enhance Efficiency ◽  
Industrial Gas Turbine

In the first part of a multipart project to analyze and optimize the complex three-dimensional diffuser-combustor section of a highly advanced industrial gas turbine under development, a computational fluid dynamics (CFD) analysts has been conducted. The commercial FEA code I-DEAS was used to complete the three-dimensional solid modeling and the structured grid generation. The flow calculation was conducted using the commercial CFD code PHOENICS. The multiblock method was employed to enhance computational capabilities. The mechanisms of the total pressure losses and possible ways to enhance efficiency by reducing the total pressure losses were examined. Mechanisms that contribute to the nonuniform velocity distribution of flow entering the combustor were also identified. The CFD results were informative and provided insight to the complex flow patterns in the reverse flow dump diffuser, however, the results are qualitative and are useful primarily as guidelines for optimization as opposed to firm design configuration selections.

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