Experimental Study on Roughness Effect for Laminar Micro-Channel Gas Flow

2001 ◽  
Author(s):  
Jih-Hsing Tu ◽  
Fangang Tseng ◽  
Ching-Chang Chieng
Keyword(s):  
Experimental Study ◽  
Surface Roughness ◽  
Friction Factor ◽  
Gas Flow ◽  
Micro Channel ◽  
Micro Machining ◽  
Roughness Effect ◽  
Relative Roughness ◽  
Smooth Channel ◽  
Micro Channels

Abstract Present study investigates the roughness effect on laminar gas flow for microchannels ranging from 40 to 600 μm with various roughness heights (40–82 nm) by systematical experiments. The micro-channels are manufactured by micro-machining technology and KOH anisotropic etching is employed to achieve various roughness patterns. Experimental results shows that higher product levels of Reynolds number (Reh) and friction factor (f) are obtained for microchannels of larger size and smaller relative roughness and friction factor f approaches to laminar flow theory value f0 for very smooth channel but the ratio of (f/f0) decreases as the surface roughness increases.

Visual Experimental Study of Flow Field in Rectangular Microchannels With Different Surface Roughness

2007 ◽  
Author(s):  
Chunping Zhang ◽  
Dawei Tang ◽  
Peng Han ◽  
Xuegong Hu
Keyword(s):  
Experimental Study ◽  
Surface Roughness ◽  
Reynolds Number ◽  
Flow Field ◽  
Friction Factor ◽  
Transitional Flow ◽  
Traditional Values ◽  
Relative Roughness ◽  
Laminar To Turbulent Transition ◽  
Poiseuille Number

A new visual experimental study is performed on flow field for laminar to turbulent transition in three different roughness microchannels with almost the same aspect ratio. The red trace is a thin straight line in microchannels at the low Reynolds number. The exit, middle and entrance region become diffuse and transitional flow occurs successively with increasing Reynolds number. The transition Reynolds number is about 1700 for relative roughness smaller than 3%, but the transition Reynolds number is about 1500 with relative roughness is 3.15%, which show that transition occurs earlier than the traditional values. The friction factor and Poiseuille number were also measured in microchannels. It is found that the friction factor and Hagen-Poiseuille number increased with surface roughness, and were significantly greater than the classical values.

Prediction of Heat Transfer in Turbulent Decaying Swirling Flow

1999 ◽  
Author(s):  
Yusuf A. Uskaner
Keyword(s):  
Heat Transfer ◽  
Fluid Dynamics ◽  
Experimental Study ◽  
Friction Factor ◽  
Loss Factor ◽  
Swirling Flow ◽  
Swirling Flows ◽  
Heat Transfer Augmentation ◽  
Relative Roughness ◽  
Inlet Swirl

Abstract This paper presents an aproach for the prediction of heat transfer augmentation in decaying swirling flow in a pipe by making an analogy between the increase in friction factor due to swirl and increase in heat transfer due to swirl. The proposed method can be used to predict heat transfer for decaying swirling flow in smooth and rough pipes which can be applied to different swirl generators based on the known inlet swirl conditions. An experimental study is performed regarding the swirling flow of air in smooth and rough pipes. The experimental study covered only the fluid dynamics of swirling flow. No heat transfer experiments were done. It is determined experimentally that in swirling flows degree of swirl decays continuously along the smooth and rough pipes and the total loss factor is the sum of friction factor for non-swirling flow and the swirl loss factor. Swirl loss factor is found to be a function of the degree of swirl and pipe relative roughness. Using the relations obtained experimentally for the variation of swirl strength and loss factor along the pipe, an equation is proposed to be used for the prediction of heat transfer in turbulent decaying swirling flows.

ROUGHNESS EFFECT OF DIFFERENT GEOMETRIES ON MICRO GAS FLOWS BY LATTICE BOLTZMANN SIMULATION

2009 ◽  
Vol 20 (06) ◽  
pp. 953-966 ◽  
Author(s):  
CHAOFENG LIU ◽  
YUSHAN NI ◽  
YONG RAO
Keyword(s):  
Surface Roughness ◽  
Lattice Boltzmann ◽  
Experimental Studies ◽  
Resistance Coefficient ◽  
Lattice Boltzmann Model ◽  
Gas Flows ◽  
Fractal Boundary ◽  
Roughness Effects ◽  
Roughness Effect ◽  
Relative Roughness

The roughness effects of the gas flows of nitrogen and helium in microchannels with various relative roughnesses and different geometries are studied and analyzed by a lattice Boltzmann model. The shape of surface roughness is simulated to be square, sinusoidal, triangular, and fractal. Numerical computations compared with theoretical and experimental studies show that the roughness geometry is an important factor besides the relative roughness in the study of the effects of surface roughness. The fractal boundary presents a higher influence on the velocity field and the resistance coefficient than other regular boundaries at the same Knudsen number and relative roughness. In addition, the effects of rarefaction, compressibility, and roughness are strongly coupled, and the roughness effect should not be ignored in studying rarefaction and compressibility of the microchannel as the relative roughness increases.

An Experimental Study of the Abrasive Water Jet Micro-Machining Process for Quartz Crystals

2012 ◽  
Vol 565 ◽  
pp. 339-344 ◽  
Author(s):  
H. Qi ◽  
J.M. Fan ◽  
Jun Wang
Keyword(s):  
Experimental Study ◽  
Removal Rate ◽  
Water Jet ◽  
Machining Process ◽  
Bottom Surface ◽  
Micro Machining ◽  
Abrasive Water Jet ◽  
Process Variables ◽  
Jet Impact ◽  
Micro Channels

An experimental study of the machining process for micro-channels on a brittle quartz crystal material by an abrasive slurry jet (ASJ) is presented. A statistical experiment design considering the major process variables is conducted, and the machined surface morphology and channelling performance are analysed to understand the micro-machining process. It is found that a good channel top edge appearance and bottom surface quality without wavy patterns can be achieved by employing relatively small particles at shallow jet impact angles. The major channel performance measures, i.e. material removal rate (MRR) and channel depth, are then discussed with respect to the process parameters. It shows that with a proper control of the process variables, the abrasive water jet (AWJ) technology can be used for the micro-machining of brittle materials with high quality and productivity.

Friction Factor Directly From Roughness Measurements

2001 ◽  
Author(s):  
Elling Sletfjerding ◽  
Jon Steinar Gudmundsson
Keyword(s):  
Reynolds Number ◽  
Pressure Drop ◽  
Power Spectrum ◽  
Friction Factor ◽  
High Reynolds Number ◽  
Gas Flow ◽  
Relative Roughness ◽  
High Reynolds ◽  
Friction Factor Correlation ◽  
Roughness Measurements

Abstract Pressure drop experiments on natural gas flow in 150 mm pipes at 80 to 120 bar pressure and high Reynolds number were carried out for pipes smooth to rough surfaces. The roughness was measured with an accurate stylus instrument and analyzed using fractal methods. Using a similar approach to that of Nikuradse the measured friction factor was related to the measured roughness values. Taking the value of the relative roughness and dividing it by the slope of the power spectrum of the measured roughness, a greatly improved fit with the measured friction factor was obtained. Indeed, a new friction factor correlation was obtained, but now formulated in terms of direct measurement of roughness.

E-08 Effect of Surface Roughness on Friction Factor of Gas Flow in Micro-tubes

2016 ◽  
Vol 2016.69 (0) ◽  
pp. 187-188
Author(s):  
Goku Tanaka ◽  
Chungpyo Hong ◽  
Yutaka Asako ◽  
Hiroshi Katanoda ◽  
Minoru Fukuhara ◽  
...  
Keyword(s):  
Surface Roughness ◽  
Friction Factor ◽  
Gas Flow ◽  
Effect Of Surface

Measurement of Semi-Local Friction Factor of Gas Flow in Micro-Tube

2013 ◽  
Author(s):  
D. Kawashima ◽  
Y. Asako
Keyword(s):  
Surface Roughness ◽  
Turbulent Flow ◽  
Friction Factor ◽  
Gas Flow ◽  
Flow Region ◽  
Nitrogen Gas ◽  
Gaseous Flow ◽  
Flow Through ◽  
Local Pressures ◽  
Measured Pressure

This paper presents experimental results on friction factor of gaseous flow in a PEEK micro-tube with relative surface roughness of 0.04 %. The experiments were performed for nitrogen gas flow through the micro-tube with 514.4 μm in diameter and 50 mm in length. Three pressure taps holes with 5 mm interval were drilled and the local pressures were measured. Friction factor is obtained from the measured pressure differences. The experiments were conducted for turbulent flow region. The friction factor obtained by the present study are compared with those in available literature and also numerical results. The friction factor obtained is slightly higher than the value of Blasius formula.

Experimental investigations of nanosecond-pulsed Nd:YAG laser beam micromachining on 304 stainless steel

2018 ◽  
Vol 1 (1) ◽  
pp. 62-75 ◽  
Author(s):  
Rasmi Ranjan Behera ◽  
Mamilla Ravi Sankar ◽  
Prahlad Kumar Baruah ◽  
Ashwini Kumar Sharma ◽  
Alika Khare
Keyword(s):  
Surface Roughness ◽  
Stainless Steel ◽  
Laser Beam ◽  
Nd:Yag Laser ◽  
Research Work ◽  
Scanning Speed ◽  
304 Stainless Steel ◽  
Experimental Investigations ◽  
Micro Channel ◽  
Micro Channels

The demand for miniaturized components is increasing day by day as their application varies from industry to industry such as biomedical, micro-electro-mechanical system and aerospace. In the present research work, high-quality micro-channels are fabricated on 304 stainless steel by laser beam micromachining process with nanosecond Nd:YAG laser. The laser pulse energy (LPE), scanning speed (SS) and scanning pass number (SP No.) are used as the process parameters, whereas the depth and width of the kerf as well as the surface roughness are used to characterize the micro-channels. It is found that the kerf depth, width and surface roughness decrease with increase in the SS. The kerf depth sharply increases with increase in the SP No. The kerf width is minimum at 30 mJ LPE, 400 µm s‒1 SS and 10 SP No. The minimum surface roughness is observed at 30 mJ LPE, 500 µm s‒1 SS and 10 SP No. The oxygen content is found to gradually decrease with the distance from the centre of the micro-channel. Based on the experimental results, optimized input parameters can be offered to control the micro-channel dimensions and improve their surface finish effectively on stainless steel.

Turbulence Model Investigation of Water Flow in Rough Micro Channels

2009 ◽  
Author(s):  
Shobeir Aliasghar Zadeh ◽  
Rolf Radespiel
Keyword(s):  
Reynolds Number ◽  
Friction Factor ◽  
Rectangular Cross Section ◽  
Turbulence Models ◽  
Reynolds Numbers ◽  
Micro Channel ◽  
Conventional Theory ◽  
Roughness Elements ◽  
Micro Channels ◽  
Experimental Values

Three-dimensional laminar and turbulent water flows in smooth and rough micro channels with rectangular cross-section were numerically simulated. The hydraulic diameter of the smooth micro channel is 190 μm and 191 μm for the rough one. The roughness inducing surfaces, which were modelled by three rectangular elements placed on the sidewall of the micro channel, are 50 μm high and 50 μm wide. The simulations were conducted for Reynolds numbers between 100 and 4000. The effects on the friction factor and flow characteristics due to the roughness elements, varying Reynolds numbers and low-Reynolds number turbulence models were investigated and compared with the experimental values reported by Hao et al. [1]. Furthermore, the velocity profiles in various Reynolds number and flow regimes have been compared with μPIV measurements. At Reynolds numbers less than 2100 the computed friction factors in the smooth micro channel agree well with the measurements and the values of the conventional theory. For the micro channel with roughness elements, the friction factor approaches the value of measurements and conventional theory, when Re < 900. Transition from laminar to turbulent flow occurs at about Reynolds numbers of 2100 and 900 in smooth and rough micro channel, respectively. Comparison of simulated results using the Spalart-Allmaras and SST K-ω turbulence models with experimental values show good agreement. By contrast, the K-ε model overestimates the pressure loss in micro channels.

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