Experimental Analysis of Microchannel Entrance Length Characteristics Using Microparticle Image Velocimetry

2010 ◽  
Vol 132 (4) ◽  
Author(s):  
Tariq Ahmad ◽  
Ibrahim Hassan
Keyword(s):  
Reynolds Number ◽  
Flow Field ◽  
Entrance Region ◽  
Working Fluid ◽  
Parallel Plates ◽  
Entrance Length ◽  
Number Range ◽  
Micro Piv ◽  
Image Velocimetry ◽  
Microparticle Image Velocimetry

The study of the entrance region of microchannels and microdevices is limited, yet important, since the effect on the flow field and heat transfer mechanisms is significant. An experimental study has been carried out to explore the laminar hydrodynamic development length in the entrance region of adiabatic square microchannels. Flow field measurements are acquired through the use of microparticle image velocimetry (micro-PIV), a nonintrusive particle tracking and flow observation technique. With the application of micro-PIV, entrance length flow field data are obtained for three different microchannel hydraulic diameters of 500 μm, 200 μm, and 100 μm, all of which have cross-sectional aspect ratios of 1. The working fluid is distilled water, and velocity profile data are acquired over a laminar Reynolds number range from 0.5 to 200. The test-sections were designed as to provide a sharp-edged microchannel inlet from a very large reservoir at least 100 times wider and higher than the microchannel hydraulic diameter. Also, all microchannels have a length-to-diameter ratio of at least 100 to assure fully developed flow at the channel exit. The micro-PIV procedure is validated in the fully developed region with comparison to Navier–Stokes momentum equations. Good agreement was found with comparison to conventional entrance length correlations for ducts or parallel plates, depending on the Reynolds range, and minimal influence of dimensional scaling between the investigated microchannels was observed. New entrance length correlations are proposed, which account for both creeping and high laminar Reynolds number flows. These correlations are unique in predicting the entrance length in microchannels and will aid in the design of future microfluidic devices.

Entrance Length Characteristics in Microchannels Using Micro-Particle Image Velocimetry

2007 ◽  
Author(s):  
Tariq Ahmad ◽  
Ibrahim Hassan ◽  
Roland Muwanga
Keyword(s):  
Particle Image Velocimetry ◽  
Flow Field ◽  
Particle Image ◽  
Working Fluid ◽  
Entrance Length ◽  
Number Range ◽  
Micro Particle Image Velocimetry ◽  
Micro Piv ◽  
Aspect Ratios ◽  
Image Velocimetry

An experimental study has been carried out to explore the laminar hydrodynamic development length in the entrance region of adiabatic square microchannels. Flow field measurements are acquired through the use of micro-Particle Image Velocimetry (micro-PIV), a non-intrusive particle tracking and flow observation technique. With the application of micro-PIV, entrance length flow field data is obtained for two different microchannel hydraulic diameters of 500 μm and 100 μm, both of which have cross-sectional aspect ratios of one. The working fluid is distilled water, and velocity profile data is acquired over a laminar Reynolds number range from 0 to 200. The test sections were designed as to provide a sharpedged microchannel inlet from an infinitely sized reservoir, at least 100 times wider and higher than the microchannel hydraulic diameter. Also, all microchannels have a length-to-diameter ratio of at least 100, to assure fully developed flow at the channel exit. The micro-PIV procedure is validated in the fully developed region with comparison to Navier-Stokes momentum equations. Good agreement was found with comparison to conventional entrance length correlations for ducts, and no influence of scaling was observed.

scholarly journals Experimental and Numerical Investigations on the Flow Characteristics within Hydrodynamic Entrance Regions in Microchannels

Micromachines ◽  
2019 ◽  
Vol 10 (5) ◽  
pp. 317 ◽  
Author(s):  
Haiwang Li ◽  
Binghuan Huang ◽  
Min Wu
Keyword(s):  
Stokes Equations ◽  
Flow Characteristics ◽  
Simulated Data ◽  
Working Fluid ◽  
Separation Flow ◽  
Entrance Length ◽  
Number Range ◽  
Numerical Investigations ◽  
Micro Piv ◽  
Strong Agreement

Flow characteristics within entrance regions in microchannels are important due to their effect on heat and mass transfer. However, relevant research is limited and some conclusions are controversial. In order to reveal flow characteristics within entrance regions and to provide empiric correlation estimating hydrodynamic entrance length, experimental and numerical investigations were conducted in microchannels with square cross-sections. The inlet configuration was elaborately designed in a more common pattern for microdevices to diminish errors caused by separation flow near the inlet and fabrication faults so that conclusions which were more applicable to microchannels could be drawn. Three different microchannels with hydraulic diameters of 100 μm, 150 μm, and 200 μm were investigated with Reynolds (Re) number ranging from 0.5 to 50. For the experiment, deionized water was chosen as the working fluid and microscopic particle image velocimetry (micro-PIV) was adopted to record and analyze velocity profiles. For numerical simulation, the test-sections were modeled and incompressible laminar Navier–Stokes equations were solved with commercial software. Strong agreement was achieved between the experimental data and the simulated data. According to the results of both the experiments and the simulations, new correlations were proposed to estimate entrance length. Re numbers ranging from 12.5 to 15 was considered as the transition region where the relationship between entrance length and Re number converted. For the microchannels and the Reynolds number range investigated compared with correlations for conventional channels, noticeable deviation was observed for lower Re numbers (Re < 12.5) and strong agreement was found for higher Re numbers (Re > 15).

scholarly journals Numerical and Experimental Analyses of Three- Dimensional Unsteady Flow around a Micro-Pillar Subjected to Rotational Vibration

Micromachines ◽  
2018 ◽  
Vol 9 (12) ◽  
pp. 668 ◽  
Author(s):  
Kanji Kaneko ◽  
Takayuki Osawa ◽  
Yukinori Kametani ◽  
Takeshi Hayakawa ◽  
Yosuke Hasegawa ◽  
...  
Keyword(s):  
Flow Field ◽  
Moving Boundary ◽  
Three Dimensional ◽  
Steady Streaming ◽  
Micro Piv ◽  
Piv Measurement ◽  
Image Velocimetry ◽  
Measurement Tools ◽  
Rotational Vibration ◽  
Induced Flow

The steady streaming (SS) phenomenon is gaining increased attention in the microfluidics community, because it can generate net mass flow from zero-mean vibration. We developed numerical simulation and experimental measurement tools to analyze this vibration-induced flow, which has been challenging due to its unsteady nature. The validity of these analysis methods is confirmed by comparing the three-dimensional (3D) flow field and the resulting particle trajectories induced around a cylindrical micro-pillar under circular vibration. In the numerical modeling, we directly solved the flow in the Lagrangian frame so that the substrate with a micro-pillar becomes stationary, and the results were converted to a stationary Eulerian frame to compare with the experimental results. The present approach enables us to avoid the introduction of a moving boundary or infinitesimal perturbation approximation. The flow field obtained by the micron-resolution particle image velocimetry (micro-PIV) measurement supported the three-dimensionality observed in the numerical results, which could be important for controlling the mass transport and manipulating particulate objects in microfluidic systems.

Experimental Study of Advanced Convective Cooling Techniques for Combustor Liners

2008 ◽  
Author(s):  
Michael Maurer ◽  
Uwe Ruedel ◽  
Michael Gritsch ◽  
Jens von Wolfersdorf
Keyword(s):  
Heat Transfer ◽  
Experimental Study ◽  
Reynolds Number ◽  
Heat Transfer Coefficient ◽  
Flow Field ◽  
Transfer Coefficient ◽  
Heat Transfer Enhancement ◽  
Transfer Enhancement ◽  
Number Range ◽  
Convective Cooling

An experimental study was conducted to determine the heat transfer performance of advanced convective cooling techniques at the typical conditions found in a backside cooled combustion chamber. For these internal cooling channels, the Reynolds number is usually found to be above the Reynolds number range covered by available databases in the open literature. As possible candidates for an improved convective cooling configuration in terms of heat transfer augmentation and acceptable pressure drops, W-shaped and WW-shaped ribs were considered for channels with a rectangular cross section. Additionally, uniformly distributed hemispheres were investigated. Here, four different roughness spacings were studied to identify the influence on friction factors and the heat transfer enhancement. The ribs and the hemispheres were placed on one channel wall only. Pressure losses and heat transfer enhancement data for all test cases are reported. To resolve the heat transfer coefficient, a transient thermocromic liquid crystal technique was applied. Additionally, the area-averaged heat transfer coefficient on the W-shaped rib itself was observed using the so-called lumped-heat capacitance method. To gain insight into the flow field and to reveal the important flow field structures, numerical computations were conducted with the commercial code FLUENT™.

Extending “Assessment of Tesla Turbine Performance” Model for Sensitivity-Focused Experimental Design

2017 ◽  
Vol 140 (3) ◽  
Author(s):  
Matthew J. Traum ◽  
Fatemeh Hadi ◽  
Muhammad K. Akbar
Keyword(s):  
Reynolds Number ◽  
Power Output ◽  
Performance Model ◽  
Nozzle Geometry ◽  
Design Parameters ◽  
Working Fluid ◽  
Extended Model ◽  
Number Range ◽  
Nozzle Height ◽  
Turbine Performance

The analytical model of Carey is extended and clarified for modeling Tesla turbine performance. The extended model retains differentiability, making it useful for rapid evaluation of engineering design decisions. Several clarifications are provided including a quantitative limitation on the model’s Reynolds number range; a derivation for output shaft torque and power that shows a match to the axial Euler Turbine Equation; eliminating the possibility of tangential disk velocity exceeding inlet working fluid velocity; and introducing a geometric nozzle height parameter. While nozzle geometry is limited to a slot providing identical flow velocity to each channel, variable nozzle height enables this velocity to be controlled by the turbine designer as the flow need not be choked. To illustrate the utility of this improvement, a numerical study of turbine performance with respect to variable nozzle height is provided. Since the extended model is differentiable, power sensitivity to design parameters can be quickly evaluated—a feature important when the main design goal is maximizing measurement sensitivity. The derivatives indicate two important results. First, the derivative of power with respect to Reynolds number for a turbine in the practical design range remains nearly constant over the whole laminar operating range. So, for a given working fluid mass flow rate, Tesla turbine power output is equally sensitive to variation in working fluid physical properties. Second, turbine power sensitivity increases as wetted disk area decreases; there is a design trade-off here between maximizing power output and maximizing power sensitivity.

scholarly journals Flow Characteristics of the Entrance Region with Roughness Effect within Rectangular Microchannels

Micromachines ◽  
2019 ◽  
Vol 11 (1) ◽  
pp. 30
Author(s):  
Haiwang Li ◽  
Yujia Li ◽  
Binghuan Huang ◽  
Tiantong Xu
Keyword(s):  
Reynolds Number ◽  
Aspect Ratio ◽  
Stokes Equations ◽  
Critical Role ◽  
Flow Characteristics ◽  
Entrance Region ◽  
Working Fluid ◽  
Asymmetric Distribution ◽  
Rectangular Microchannels ◽  
Aspect Ratios

We conducted systematic numerical investigations of the flow characteristics within the entrance region of rectangular microchannels. The effects of the geometrical aspect ratio and roughness on entrance lengths were analyzed. The incompressible laminar Navier–Stokes equations were solved using finite volume method (FVM). In the simulation, hydraulic diameters ( D h ) ranging from 50 to 200 µm were studied, and aspect ratios of 1, 1.25, 1.5, 1.75, and 2 were considered as well. The working fluid was set as water, and the Reynolds number ranged from 0.5 to 100. The results showed a good agreement with the conducted experiment. Correlations are proposed to predict the entrance lengths of microchannels with respect to different aspect ratios. Compared with other correlations, these new correlations are more reliable because a more practical inlet condition was considered in our investigations. Instead of considering the influence of the width and height of the microchannels, in our investigation we proved that the critical role is played by the aspect ratio, representing the combination of the aforementioned parameters. Furthermore, the existence of rough elements obviously shortens the entrance region, and this effect became more pronounced with increasing relative roughness and Reynolds number. A similar effect could be seen by shortening the roughness spacing. An asymmetric distribution of rough elements decreased the entrance length compared with a symmetric distribution, which can be extrapolated to other irregularly distributed forms.

Wavy-Channel for Microscale Heat Transfer in Macro Geometries

2017 ◽  
Author(s):  
Kai Xian Cheng ◽  
Zi Hao Foo ◽  
Kim Tiow Ooi
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Performance Index ◽  
Heat Transfer Performance ◽  
Cnc Machining ◽  
Hydrodynamic Performance ◽  
Working Fluid ◽  
Transfer Performance ◽  
Number Range ◽  
Reynolds Number Range

Microscale heat and fluid flow in macro geometries have been made practical in terms of cost and fabrication, by superimposing two macro geometries which are fabricated using readily-available CNC machining methods. Wavy-profile has been proposed to enhance heat transfer performance in the microchannel owing to the simplicity of geometry and feasibility to be fabricated using simple turning process. Experimental studies were conducted on single-phase, forced convective heat transfer using water as the working fluid for the Reynolds number range of 1300 to 4600, for a constant heat flux of 53.0 W/cm2. Three sinusoidal waves with different wavelength and same amplitude are studied to examine the effect of the total number of waves on the heat transfer and hydrodynamic performance within constant microchannel length. The maximum performance index, which evaluates heat transfer performance per unit pumping power, is 1.39, achieved by wavy profile with the shortest wavelength at Reynolds number of 2800. The performance index for all the enhanced microchannels peaks at the Reynolds number range of 2500 to 2800. Beyond that, the performance index is not a strong function of the wavelength. At lower Reynolds numbers, profile with the shortest wavelength achieves substantially higher performance indices, as the increment in pressure drop is accompanied by a comparable increment in heat transfer. Future work includes the introduction of correlations for the implementation of such geometries in industrial heat exchangers.

Measurements and simulations of time-dependent flow fields within an electrokinetic micromixer

2011 ◽  
Vol 676 ◽  
pp. 265-293 ◽  
Author(s):  
DOMINIK P. J. BARZ ◽  
HAMID FARANGIS ZADEH ◽  
PETER EHRHARD
Keyword(s):  
Flow Field ◽  
Base Flow ◽  
Complex Flow ◽  
Flow Topology ◽  
Electrical Field ◽  
Image Velocimetry ◽  
Microparticle Image Velocimetry ◽  
Meander Bends ◽  
Dependent Flow ◽  
Meander Channel

We investigate the flow field in an electrokinetic micromixer. The concept of the micromixer is based on the combination of an alternating electrical field applied to a pressure-driven base flow in a meander–channel geometry. The presence of the electrical field leads to an additional electro-osmotic velocity contribution, which results in a complex flow field within the meander bends. The velocity fields within the meander are measured by means of a microparticle-image velocimetry method. Furthermore, we introduce a mathematical model, describing the electrical and fluid-mechanical phenomena present within the device, and perform simulations comparable to the experiments. The comparison of simulations and experiments reveals good agreement, with minor discrepancies in flow topology, obviously caused by small but crucial differences between experimental and numerical geometries. In detail, simulations are performed for sharp corners of the bends, while in the experiments these corners are rounded due to the microfabrication process.

Numerical and Experimental Prediction of Transitional Characteristics of Flow and Heat Transfer in an Array of Heated Blocks

1999 ◽  
Vol 121 (3) ◽  
pp. 202-208 ◽  
Author(s):  
Y. Asako ◽  
Y. Yamaguchi ◽  
M. Faghri
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Fluid Flow ◽  
Parallel Plate ◽  
Three Dimensional ◽  
Parallel Plates ◽  
Number Range ◽  
Flow And Heat Transfer ◽  
Numerical Predictions ◽  
Experimental Prediction

Three-dimensional numerical analysis, for transitional characteristics of fluid flow and heat transfer in periodic fully developed region of an array of the heated square blocks deployed along one wall of the parallel plates duct, is carried out by using Lam-Bremhorst low-Reynolds-number two equation turbulence model. Computations were performed for Prandtl number of 0.7, in the Reynolds number range of 200 to 2000 and for two sets of geometric parameters characterizing the array. The predicted transitional Reynolds number is lower than the value for the parallel plate duct and it decreases with increasing the height above the module. Experiments were also performed for pressure drop measurements and for flow visualization and the results were compared with the numerical predictions.

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