Numerical Study of Gaseous Microchannel Flows on the Dimensional and Physical Effects

2009 ◽  
Author(s):  
Kuan-Hung Lin ◽  
Jiunn-Chi Wu
Keyword(s):  
Friction Factor ◽  
Numerical Study ◽  
Pressure Ratio ◽  
Slip Flow ◽  
Applied Pressure ◽  
Flow Characteristics ◽  
Velocity Slip ◽  
Analytic Solutions ◽  
Transition Flow ◽  
Aspect Ratios

In this article, we perform a series of simulations to analyze the gaseous flow in two-dimensional (2D) and three-dimensional (3D) microchannels. The geometry effects of entrance and exit, applied pressure ratios and rarefaction effects on the flow characteristics are thoroughly investigated. In addition, a modified Poiseuille number correlation for air flows is obtained. This calculation solves the compressible Navier-Stokes and energy equations under velocity slip and temperature jump conditions with varying inlet to outlet pressure ratios (from 1.76 to 20), the outlet Knudsen numbers (from 0 to 0.22) and the aspect ratios (from 0 to 0.47). The calculated mass flow rate, pressure distribution and friction factor are compared with analytic solutions and experimental data in both the slip flow and earlier transition flow regimes. In the case of higher applied pressure ratio, both experiments and numerical modeling show pressure drop at upstream and downstream. Finally, we discuss the adequacy of the friction factor correlation for the 2D flow and the 3D flow in microchannels with both inlet and outlet chambers.

scholarly journals 2D Numerical Study of Heat Transfer Enhancement Using Fish-Tail Locomotion Vortex Generators

2021 ◽  
Vol 8 (3) ◽  
pp. 386-392
Author(s):  
Ahmed Hashim Yousif ◽  
Hakim T. Kadhim ◽  
Kadhim K. Idan Al-Chlaihawi
Keyword(s):  
Heat Transfer ◽  
Friction Factor ◽  
Numerical Study ◽  
Rectangular Channel ◽  
Flow Characteristics ◽  
Vortex Generators ◽  
Transfer Enhancement ◽  
Number Range ◽  
Maximum Value ◽  
Fluid Flow Characteristics

In this paper, a numerical simulation is performed to study the effect of two types of concave vortex generators (VGs), arranged as fish-tail locomotion in a rectangular channel. The heat transfer and fluid flow characteristics with and without VGs are examined over the Reynolds number range 200≤Re≤2200.The two proposed types of the VGs are selected based on the speed of the fish movement which is arranged in different distances between them (d/H=0.6, 1, 1.3). The results show that the use of VGs can significantly enhance the heat transfer rate, but also increases the friction factor. The heat transfer performance is enhanced by (4-21.1%) reaching the maximum value by using the first type of the VGs at (d/H=1.3) due to better mixing of secondary flow and the new arrangement of the VGs which lead to decreasing the friction factor with an easy flow of fluid.

Slip Flow in the Hydrodynamic Entrance Region of Circular and Noncircular Microchannels

2009 ◽  
Vol 132 (1) ◽  
Author(s):  
Zhipeng Duan ◽  
Y. S. Muzychka
Keyword(s):  
Friction Factor ◽  
Slip Flow ◽  
Velocity Slip ◽  
Mean Free Path ◽  
Momentum Equation ◽  
Linearization Method ◽  
Asymptotic Results ◽  
Cross Sectional ◽  
Practical Applications ◽  
Continuum Flow

Microscale fluid dynamics has received intensive interest due to the emergence of micro-electro-mechanical systems (MEMS) technology. When the mean free path of the gas is comparable to the channel’s characteristic dimension, the continuum assumption is no longer valid and a velocity slip may occur at the duct walls. Noncircular cross sections are common channel shapes that can be produced by microfabrication. The noncircular microchannels have extensive practical applications in MEMS. The paper deals with issues of hydrodynamic flow development. Slip flow in the entrance of circular and parallel plate microchannels is first considered by solving a linearized momentum equation. It is found that slip flow is less sensitive to analytical linearized approximations than continuum flow and the linearization method is an accurate approximation for slip flow. Also, it is found that the entrance friction factor Reynolds product is of finite value and dependent on the Kn and tangential momentum accommodation coefficient but independent of the cross-sectional geometry. Slip flow and continuum flow in the hydrodynamic entrance of noncircular microchannels has been examined and a model is proposed to predict the friction factor and Reynolds product f Re for developing slip flow and continuum flow in most noncircular microchannels. It is shown that the complete problem may be easily analyzed by combining the asymptotic results for short and long ducts. Through the selection of a characteristic length scale, the square root of cross-sectional area, the effect of duct shape has been minimized. The proposed model has an approximate accuracy of 10% for most common duct shapes.

Experimental and Numerical Studies on Gas Flow Through Silicon Microchannels

2017 ◽  
Vol 139 (8) ◽  
Author(s):  
K. Srinivasan ◽  
P. M. V. Subbarao ◽  
S. R. Kale
Keyword(s):  
Boundary Condition ◽  
Gas Flow ◽  
Stokes Equations ◽  
Pressure Ratio ◽  
Flow Characteristics ◽  
Slip Boundary Condition ◽  
Second Order ◽  
Navier Stokes ◽  
Slip Boundary ◽  
Aspect Ratios

The present work investigates the extension of Navier–Stokes equations from slip-to-transition regimes with higher-order slip boundary condition. To achieve this, a slip model based on the second-order slip boundary condition was derived and a special procedure was developed to simulate slip models using FLUENT®. The boundary profile for both top and bottom walls was solved for each pressure ratio by the customized user-defined function and then passed to the FLUENT® solver. The flow characteristics in microchannels of various aspect ratios (a = H/W = 0.002, 0.01, and 0.1) by generating accurate and high-resolution experimental data along with the computational validation was studied. For that, microchannel system was fabricated in silicon wafers with controlled surface structure and each system has several identical microchannels of same dimensions in parallel and the processed wafer was bonded with a plane wafer. The increased flow rate reduced uncertainty substantially. The experiments were performed up to maximum outlet Knudsen number of 1.01 with nitrogen and the second-order slip coefficients were found to be C1 = 1.119–1.288 (TMAC = 0.944–0.874) and C2 = 0.34.

Analytical Modeling of Gaseous Slip Flow in Parabolic Microchannels

2014 ◽  
Vol 136 (7) ◽  
Author(s):  
Farzad Tahmouresi ◽  
Samir K. Das
Keyword(s):  
Pressure Distribution ◽  
Friction Factor ◽  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Analytical Modeling ◽  
Separation Of Variables ◽  
Slip Flow ◽  
Aspect Ratios ◽  
Gaseous Slip Flow

The paper presents an analytical solution of velocity, mass flow rate, and pressure distribution for fully developed gaseous slip flow in nonsymmetric and symmetric parabolic microchannels. The flow is considered to be steady, laminar, and incompressible with constant fluid properties. Fully developed gaseous slip flow in microchannels of parabolic cross section is solved analytically for various aspect ratios using a parabolic cylindrical coordinate system on applying the method of separation of variables. Prior to apply separation of variables, Arfken transform [Arfken, 1970, Mathematical Methods for Physicists, Academic Press, Orlando, FL, Ch. 2] was used on momentum equations and first-order slip boundary conditions at each channel wall were imposed. A simple model is proposed to predict the friction factor and Reynolds number product fRe for slip flow in parabolic microchannels. Through the selection of a characteristic length scale, the square root of cross-sectional area and the effect of duct shape have been minimized. The results of a normalized Poiseuille number for symmetric parabolic microchannels (ɛ=1) shows good agreement with the previous results [Morini et al., 2004, “The Rarefaction Effect on the Friction Factor of Gas Flow in Micro/Nano-Channels,” Superlattices Microstruct., 35(3–6), pp. 587–599; Khan and Yovanovich, 2008, “Analytical Modeling of Fluid Flow and Heat Transfer in Microchannel/Nanochannel Heat Sinks,” J. Thermophys. Heat Transf., 22(3), pp. 352–359] for rectangular microchannels. The developed model can be used to predict mass flow rate and pressure distribution of slip flow in parabolic microchannels.

Effect of Aspect Ratios on the Performance Characteristics of Air Amplifier

2015 ◽  
Author(s):  
Jeong-Min Lee ◽  
Yi-Seul Jo ◽  
Sung-Min Kim ◽  
Youn-Jea Kim
Keyword(s):  
Shear Stress ◽  
Total Pressure ◽  
Applied Pressure ◽  
Flow Characteristics ◽  
Operating Conditions ◽  
Compressed Air ◽  
Turbulent Model ◽  
Aspect Ratios ◽  
Ansys Cfx ◽  
Induced Flow

In this study, the flow characteristics of the Coandă nozzle were studied with various values of the aspect ratio of induced flow inlet to outlet. Furthermore, four different applied pressure conditions of compressed air were also considered. Numerical analysis was performed using the commercial CFD code, ANSYS CFX with a shear stress transport (SST) turbulent model. The results of total pressure and velocity distributions were graphically depicted with various geometrical configurations and operating conditions.

Numerical Study of Friction Factor and Heat Transfer Characteristics for Single-Phase Turbulent Flow in Tubes with Helical Micro-Fins

2012 ◽  
Vol 59 (4) ◽  
pp. 469-485 ◽  
Author(s):  
Piotr Jasiński
Keyword(s):  
Heat Transfer ◽  
Turbulent Flow ◽  
Numerical Simulations ◽  
Friction Factor ◽  
Numerical Study ◽  
Flow Characteristics ◽  
Thermal Characteristics ◽  
Pressure Drops ◽  
Experimental Stand ◽  
Helical Angle

The paper presents a numerical study on the heat transfer and pressure drop, related to flow in pipes with helical micro-fins. For all tested geometries, one applied a constant wall heat flux and fully developed 3D turbulent flow conditions. The influence of the angle of micro fins (referred to the tube axis) on thermal-flow characteristics were tested. The value of this angle was varied - with a step of 10 degrees - from 0 to 90 degrees (representing grooves parallel and perpendicular to the axis, respectively). Before numerical investigation, the pipe with helical angle of 30 degree was tested on an experimental stand. The results obtained from experiment and numerical simulations were compared and presented on the charts. As an effect of the numerical simulations, the friction factor f and Nusselt number characteristics was determined for the range of Re=104 ÷ 1.6 × 106. The analysis of the results showed high, irregular influence of the helical angle on thermal characteristics and pressure drops. Additionally, the ratios: f / fplain, Nu/Nuplain and efficiency indexes (Nu/Nuplain)/( f / fplain) as a function of the Reynolds number for every helical angle were shown on the charts.

Analytical Modeling of Fluid Flow and Heat Transfer in Micro/Nano-Channel Heat Sinks

2007 ◽  
Author(s):  
Waqar A. Khan ◽  
Michael M. Yovanovich
Keyword(s):  
Heat Transfer ◽  
Slip Flow ◽  
Velocity Slip ◽  
Fluid Friction ◽  
Closed Form Solutions ◽  
Aspect Ratios ◽  
Nano Channel ◽  
Accommodation Coefficients ◽  
Wall Interaction ◽  
Energy Equations

Laminar forced convection in two-dimensional rectangular micro and nano-channels under hydrodynamically and thermally fully developed conditions is investigated analytically in the slip flow regime (0.001 < Kn < 0.1). Closed form solutions for fluid friction and Nusselt numbers are obtained by solving the continuum momentum and energy equations with the first-order velocity slip and temperature jump boundary conditions at the channel walls. Isoflux thermal boundary condition is applied on the heat sink base. Results of the present analysis are presented in terms of channel aspect ratio, hydraulic diameter, momentum and thermal accommodation coefficients, Knudsen number, slip velocity, Reynolds number and Prandtl number. It is found that fluid friction decreases and heat transfer increases, compared to no-slip flow conditions, depending on aspect ratios and Knudsen numbers that include effects of the channel size or rarefaction and the fluid/wall interaction.

scholarly journals Numerical Study on the Effect of the Pipe Groove Height and Pitch on the Flow Characteristics of Corrugated Pipe

Energies ◽  
2021 ◽  
Vol 14 (9) ◽  
pp. 2614
Author(s):  
Ki-Bea Hong ◽  
Dong-Woo Kim ◽  
Jihyun Kwark ◽  
Jun-Seok Nam ◽  
Hong-Sun Ryou
Keyword(s):  
Aspect Ratio ◽  
Velocity Distribution ◽  
Friction Factor ◽  
Numerical Study ◽  
Flow Characteristics ◽  
Main Flow ◽  
Secondary Vortex

For corrugated pipes with a square groove, it is known that there is no interaction between the main flow and groove flow when the aspect ratio is less than four. When the groove length and height are different, the interaction occurs in the pipe. In previous studies, it was investigated whether this interaction is dependent on groove length. However, when changing the groove height, the shape of the vortex generated inside the groove changes, which may cause the interaction to occur. Therefore, in this paper the interaction between the main and groove flow of corrugated pipes is investigated when changing both groove height as well as groove pitch, corresponding to an aspect ratio of less than four. For the groove height, the flow out of the groove after impingement changes with the shape of the secondary vortex in the groove. This flow deforms the velocity distribution in the main flow, and thus the friction factor is different. For the groove pitch, there is no difference in v-velocity distribution at the interface at the 5th and 20th groove. This means there is no interaction between the grooves, and, the friction factor differs as the number of grooves differs.

Microscale Flow Through Channels With a Right-Angled Bend: Effect of Fillet Radius

2008 ◽  
Vol 130 (10) ◽  
Author(s):  
V. Raghavan ◽  
B. Premachandran
Keyword(s):  
Flow Regime ◽  
Knudsen Number ◽  
Pressure Ratio ◽  
Slip Flow ◽  
Flow Characteristics ◽  
Velocity Profiles ◽  
Exit Velocity ◽  
Fillet Radius ◽  
Flow Through ◽  
Slip Flow Regime

Microscale gas flow through channels with a right-angled bend has been numerically analyzed to study the effect of the fillet radius on flow characteristics. The flow is assumed to be incompressible, laminar, and hydrodynamically developing. The fillet radius has been varied from zero, representing a sharp corner, to 0.6 times the height of the channel. The Knudsen number has been varied from zero, representing no-slip at the boundary, to 0.1, which is the limiting case for the slip-flow regime. A low Reynolds number of value 1 has been considered in the present study, which makes the flow to be within the incompressible slip-flow regime. The flow characteristics in terms of velocity profiles, velocity vectors, and the pressure ratio between the inlet and outlet of the channel have been presented for several cases. Results show that for the case of the fillet radius equal to zero, the flow separation occurs after the bend and due to this, the exit velocity profile changes significantly. The highest pressure ratio between the inlet and the outlet is required to maintain a specific mass flow rate for this case. The cases with a nonzero fillet radius exhibit exit velocity profiles identical to that of a straight channel. The pressure ratio decreases when the fillet radius and the Knudsen number are increased.

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