Experimental Investigations of Laminar, Transitional to Turbulent Gas Flow in a Micro-Channel

2010 ◽  
Author(s):  
Chungpyo Hong ◽  
Toru Yamada ◽  
Yutaka Asako ◽  
Mohammad Faghri ◽  
Koichi Suzuki ◽  
...  
Keyword(s):  
Mach Number ◽  
Flow Regime ◽  
Gas Flow ◽  
Flow Characteristics ◽  
Channel Length ◽  
Transitional Flow ◽  
Experimental Investigations ◽  
Compressibility Effect ◽  
Micro Channels ◽  
Wide Range

This paper presents experimental results on flow characteristics of laminar, transitional to turbulent gas flows through micro-channels. The experiments were performed for three micro-channels. The micro-channels were etched into silicon wafers, capped with glass, and their hydraulic diameter are 69.48, 99.36 and 147.76 μm. The pressure was measured at seven locations along the channel length to determine local values of Mach number and friction factor for a wide range of flow regime from laminar to turbulent flow. Flow characteristics in transitional flow regime to turbulence were obtained. The result shows that f·Re is a function of Mach number and higher than incompressible value due to the compressibility effect. The values of f·Re were compared with f·Re correlations in available literature.

Experimental Investigations of Laminar, Transitional to Turbulent Gas Flow in Rib-Patterned Micro-Channels

2011 ◽  
Author(s):  
Chungpyo Hong ◽  
Toru Yamada ◽  
Yutaka Asako ◽  
Mohammad Faghri ◽  
Ichiro Ueno
Keyword(s):  
Mach Number ◽  
Friction Factor ◽  
Gas Flow ◽  
Flow Direction ◽  
Channel Length ◽  
Experimental Investigations ◽  
Patterned Surfaces ◽  
Micro Channels ◽  
Wide Range ◽  
Turbulent Gas Flow

The effects of rib-patterned surfaces on laminar, transitional to turbulent gas flow in micro-channels were experimentally investigated in the present study. The experiments were performed for two micro-channels having either smooth or rib-patterned surfaces. The micro-channels were etched into silicon wafers and capped with glass substrates. The micro-ribs were patterned on the microchannel surfaces and oriented perpendicular to the flow direction. The pressure was measured at seven locations along the channel length to determine local values of Mach number and friction factor for a wide range of flow regime from laminar to turbulent flow. The friction factors with the hydraulic diameter based on the rib-to-upper-wall height were compared with that for incompressible theory on Moody chart. The values of the product of friction factor and Reynolds number (f·Re) as a function of Mach number were also compared with those of smooth micro-channels and incompressible theory.

Experimental Investigation of Gaseous Flow in a Micro-Tube

2009 ◽  
Author(s):  
Yasuhiro Yoshida ◽  
Chungpyo Hong ◽  
Yutaka Asako ◽  
Koichi Suzuki
Keyword(s):  
Mach Number ◽  
Gas Flow ◽  
Electrical Discharge Machining ◽  
Tube Length ◽  
Experimental Investigations ◽  
Arbitrary Lagrangian Eulerian ◽  
Atmospheric Conditions ◽  
Compressibility Effect ◽  
Wide Range ◽  
Tube Exit

Experimental investigations on nitrogen gas flow characteristics were performed for a micro-tube. The micro-tube was fabricated in a stainless steel block by electrical discharge machining (EDM). The tube diameter was 326 μm and the ratio of length to diameter was 200. The stagnation pressure was chosen in such a way that the exit Mach number ranged from 0.1 to 1.4. The outlet pressure was fixed at atmospheric conditions. The pressure was locally measured at five locations along tube length to determine local values of Mach number and friction factor for a wide range of flow regime from laminar to turbulent flow. The result shows that f·Re is a function of Mach number and higher than incompressible value, 64 due to the compressibility effect. The values of f·Re were compared with f·Re correlation in literature. In additional experiments, Mach number at the micro-tube exit was measured by using a Shadowgraph system which visualizes the shock wave of the gas. The micro-tube with 400 μm in diameter was used for the experiment. The super sonic flow was observed since Mach number at the micro-tube exit was beyond unity. The experimental results for laminar flow were compared with the numerical results obtained by the arbitrary-Lagrangian-Eulerian method. The both results are in excellent agreement.

DSMC simulation of rarefied gas flow over a 2D backward-facing step in the transitional flow regime: Effect of Mach number and wall temperature

2020 ◽  
pp. 095441002095987
Author(s):  
Deepak Nabapure ◽  
Ram Chandra Murthy K
Keyword(s):  
Mach Number ◽  
Flow Regime ◽  
Surface Properties ◽  
Wall Temperature ◽  
Gas Flow ◽  
Rarefied Gas ◽  
Transitional Flow ◽  
Flow Properties ◽  
Rarefied Gas Flow ◽  
Backward Facing Step

Rarefied gas flow over a backward-facing step (BFS) is often encountered in separating flows prevalent in aerodynamic flows, engine flows, condensers, space vehicles, heat transfer systems, and microflows. Direct Simulation Monte Carlo (DSMC) is a powerful tool to investigate such flows. The purpose of this research is to assess the impact of Mach number and wall temperature on the flow and surface properties in the transitional flow regime. The Mach numbers considered are 5, 10, 25, 30, and the ratio of the temperature of the wall to that of freestream considered are 1, 2, 4, 8. The Reynolds number for the cases studied is 8.6, 17.2, 43, and 51.7, respectively. Typically the flow properties near the wall are found to increase with both Mach number and wall temperature owing to compressibility and viscous dissipation effects. The variation in flow properties is more sensitive to Mach number than the wall temperature. The surface properties are found to decrease with Mach number and increase with wall temperature. Moreover, in the wake of the step, the vortex’s recirculation length is reasonably independent of both free stream Mach number and wall temperature, whereas it decreases with Knudsen number.

Results of the Study Rotor Wheels Supersonic Microturbines with a Large Angle of Rotation of the Flow

2015 ◽  
Vol 752-753 ◽  
pp. 884-889 ◽  
Author(s):  
Andrey Yu. Fershalov ◽  
Mikhail Yu. Fershalov ◽  
Yuriy Ya. Fershalov ◽  
Timofey V. Sazonov
Keyword(s):  
Mach Number ◽  
Gas Flow ◽  
Large Angle ◽  
Experimental Investigations ◽  
Flow Rates ◽  
Ratio Speed ◽  
Supersonic Gas Flow ◽  
Angle Of Rotation

The article presents the results of experimental investigations of rotor wheels supersonic microturbines with a large angle of rotation of the flow. The characteristics of the studied rotor wheels. The analysis of the results of the study ratio speed of rotor wheels, depending on the Mach number. Recommendations for the design working wheels microturbines operating at high supersonic gas flow rates.

Multiphase Fluid Structure Interaction in Bends and T-Joints

2010 ◽  
Author(s):  
Marcos F. Cargnelutti ◽  
Stefan P. C. Belfroid ◽  
Wouter Schiferli ◽  
Marlies van Osch
Keyword(s):  
Flow Regime ◽  
Slug Flow ◽  
Gas Flow ◽  
Single Phase ◽  
Scaling Factor ◽  
Operating Conditions ◽  
Phase Flow ◽  
Large Radius ◽  
Single Phase Flow ◽  
Wide Range

Air-water experiments were carried out in a horizontal 1″ pipe system to measure the magnitude of the forces induced by the multiphase flow. Forces and accelerations were measured on a number of bends and T-joint configurations for a wide range of operating conditions. Five different configurations were measured: a baseline case consisting of straight pipe only, a sharp edged bend, a large radius bend, a symmetric T-joint and a T-joint with one of the arms closed off. The gas flow was varied from a superficial velocity of 0.1 to 30 m/s and the liquid flow was varied from 0.05 to 2 m/s. This operating range ensures that the experiment encompasses all possible flow regimes. In general, the slug velocity and frequency presented a reasonable agreement with classical models. However, for high mixture velocity the measured frequency deviated from literature models. The magnitude of the measured forces was found to vary over a wide range depending on the flow regime. For slug flow conditions very high force levels were measured, up to 4 orders of magnitude higher than in single phase flow for comparable velocities. The annular flow regime resulted in the (relative) lowest forces, although the absolute amplitude is of the same order as in the case of slug flow. These results from a one inch pipe were compared to data obtained previously from similar experiments on a 6mm setup, to evaluate the scaling effects. The results for the one inch rig experiments agreed with the model proposed by Riverin, with the same scaling factor. A modification of this scaling factor is needed for the model to predict the forces measured on the 6mm rig. The validity of the theories developed based on the 6mm experiments were tested for validity at larger scales. In case of slug flow, the measured results can be described assuming a simple slug unit model. In annular and stratified flow a different model is required, since no slug unit is present. Instead, excitation force can be estimated using mixture properties. This mixture approach also describes the forces for the slug regime relatively well. Only the single phase flow is not described properly with this mixture model, as would be expected.

Mach Number on Outlet Plane of a Straight Micro-Tube

2013 ◽  
Author(s):  
Y. Asako ◽  
D. Kawashima ◽  
T. Yamada ◽  
C. Hong
Keyword(s):  
Mach Number ◽  
Turbulent Flow ◽  
Gas Flow ◽  
Flow Characteristics ◽  
Ideal Gas ◽  
Computational Domain ◽  
Arbitrary Lagrangian Eulerian ◽  
Downstream Region ◽  
Laminar And Turbulent Flow ◽  
Energy Equations

The Mach number and pressure on the outlet plane of a straight micro-tube were investigated numerically for both laminar and turbulent flow cases. The numerical methodology is based on the Arbitrary-Lagrangian-Eulerian (ALE) method. The LB1 turbulence model was used for the turbulent flow case. The compressible momentum and energy equations with the assumption of the ideal gas were solved. The computational domain is extended to the downstream region from the micro-tube outlet. The back pressure was given to the outside of the downstream region. The computations were performed for a tube whose diameter ranges from 50 to 500 μm. The average Mach number on the outlet plane of the fully under-expanded flow depends on the tube diameter and ranges from 1.16 to 1.25. The flow characteristics of the under-expanded gas flow in a straight micro-tube were revealed.

scholarly journals Numerical Investigation of Liquid–Liquid Mixing in Modified T Mixer with 3D Obstacles

2021 ◽  
pp. 25-32
Author(s):  
Md. Readul Mahmud
Keyword(s):  
Numerical Investigation ◽  
Stokes Equations ◽  
Three Dimensional ◽  
Flow Characteristics ◽  
Reynolds Numbers ◽  
Channel Length ◽  
Navier Stokes ◽  
Mixing Efficiency ◽  
Mixing Performance ◽  
Wide Range

The fluids inside passive micromixers are laminar in nature and mixing depends primarily on diffusion. Hence mixing efficiency is generally low, and requires a long channel length and longtime compare to active mixers. Various designs of complex channel structures with/without obstacles and three-dimensional geometries have been investigated in the past to obtain an efficient mixing in passive mixers. This work presents a design of a modified T mixer. To enhance the mixing performance, circular and hexagonal obstacles are introduced inside the modified T mixer. Numerical investigation on mixing and flow characteristics in microchannels is carried out using the computational fluid dynamics (CFD) software ANSYS 15. Mixing in the channels has been analyzed by using Navier–Stokes equations with water-water for a wide range of the Reynolds numbers from 1 to 500. The results show that the modified T mixer with circular obstacles has far better mixing performance than the modified T mixer without obstacles. The reason is that fluids' path length becomes longer due to the presence of obstacles which gives fluids more time to diffuse. For all cases, the modified T mixer with circular obstacle yields the best mixing efficiency (more than 60%) at all examined Reynolds numbers. It is also clear that efficiency increase with axial length. Efficiency can be simply improved by adding extra mixing units to provide adequate mixing. The value of the pressure drop is the lowest for the modified T mixer because there is no obstacle inside the channel. Modified T mixer and modified T mixer with circular obstacle have the lowest and highest mixing cost, respectively. Therefore, the current design of modified T with circular obstacles can act as an effective and simple passive mixing device for various micromixing applications.

On the Stability of the Flow of Gas out of a Compressor

1953 ◽  
Vol 57 (509) ◽  
pp. 345-346
Author(s):  
J. M. Stephenson
Keyword(s):  
Mach Number ◽  
Flow Characteristic ◽  
Flow Characteristics ◽  
Negative Slope ◽  
Pressure Flow ◽  
Damped Oscillations ◽  
Wide Range ◽  
High Mach ◽  
The Stability ◽  
Stable Flow

It is often supposed that the flow of gas from a compressor is, or should be, stable if the pressure-flow characteristic has a negative slope. It is shown here that this is only true if the Mach number is zero, i.e. if the machine is pumping a liquid. As the Mach number is increased towards one, a third regime becomes more and more important, wherein disturbances give rise to damped oscillations. The flow in this regime is stable in the mathematical, but not in the physical sense, since disturbances can occur all the time.Two conclusions can be drawn. First, although compressors with “flat” pressure-flow characteristics have a wide range of stable flow at low speeds, they are poor at high Mach numbers, where the flat part cannot be used. Next, the actual points on the characteristics at which the flow becomes unstable are not fixed, but depend to a large extent on the steadiness of the entry flow.

Interaction of Shock and Expansion Wave With Solid Particles in Supersonic Flows

2002 ◽  
Author(s):  
Ali Dolatabadi ◽  
Javad Mostaghimi ◽  
Valerian Pershin
Keyword(s):  
Mach Number ◽  
Flow Regime ◽  
Drag Force ◽  
Gas Flow ◽  
Volume Fraction ◽  
Supersonic Flows ◽  
Operating Conditions ◽  
Solid Particles ◽  
Process Efficiency ◽  
Two Phase

Interaction of solid particles with shock and expansions in supersonic flows is analyzed. In this analysis, a dense cloud of solid particulates is modeled by using a fully Eulerian approach. The dispersed flow and the gas flow were considered in the Eulerian frame whereby most of the physical aspects of the gas-particle flow can be incorporated. In addition to the momentum and energy exchanges in the form of source terms appearing in the governing equations, the two phases were strongly coupled by considering the volume fraction of the particulate phase in the equations. The simulation performed for a High Velocity Oxy-Fuel (HVOF) process under typical operating conditions in which the powder loading is high and the two-phase flow is not dilute near the injection port. The simulations showed large variations in the flow regime in the region that most of the particles exist. Unlike the results corresponding to the Lagrangian approach, the flow becomes subsonic near the centerline and the drag force decreases significantly since the relative Mach number is small. The validation experiments showed that the variation of flow regime by changing the relative Mach number could significantly change the particle drag force, and consequently process efficiency.

Friction Factor Correlations for Gas Flow in Slip Flow Regime

2007 ◽  
Vol 129 (10) ◽  
pp. 1268-1276 ◽  
Author(s):  
Chungpyo Hong ◽  
Yutaka Asako ◽  
Stephen E. Turner ◽  
Mohammad Faghri
Keyword(s):  
Friction Factor ◽  
Flow Regime ◽  
Gas Flow ◽  
Slip Flow ◽  
Channel Height ◽  
Inlet Temperature ◽  
Arbitrary Lagrangian Eulerian ◽  
Knudsen Numbers ◽  
Wide Range ◽  
Slip Flow Regime

Poiseuille number, the product of friction factor and Reynolds number (fRe) for quasi-fully-developed gas microchannel flow in the slip flow regime, was obtained numerically based on the arbitrary-Lagrangian-Eulerian method. Two-dimensional compressible momentum and energy equations were solved for a wide range of Reynolds and Mach numbers for constant wall temperatures that are lower or higher than the inlet temperature. The channel height ranges from 2 μm to 10 μm and the channel aspect ratio is 200. The stagnation pressure pstg is chosen such that the exit Mach number ranges from 0.1 to 1.0. The outlet pressure is fixed at atmospheric conditon. Mach and Knudsen numbers are systematically varied to determine their effects on fRe. The correlation for fRe for the slip flow is obtained from that of fRe of no-slip flow and incompressible theory as a function of Mach and Knudsen numbers. The results are in excellent agreement with the available experimental measurements. It was found that fRe is a function of Mach and Knudsen numbers and is different from the values by 96/(1+12Kn) obtained from the incompressible flow theory.

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