Effects of Low Uniform Relative Roughness on Single-Phase Friction Factors in Microchannels and Minichannels

2007 ◽  
Author(s):  
Timothy P. Brackbill ◽  
Satish G. Kandlikar
Keyword(s):  
Large Diameter ◽  
Reynolds Numbers ◽  
Transition To Turbulence ◽  
Roughness Effects ◽  
Relative Roughness ◽  
Flow Parameters ◽  
Friction Factors ◽  
Turbulent Flow Regime ◽  
Critical Reynolds Numbers ◽  
Large Diameter Pipes

Nikuradse’s [1] work on friction factors focused on the turbulent flow regime in addition to being performed in large diameter pipes. Laminar data was collected by Nikuradse, however only low relative roughness values were examined. A recent review by Kandlikar [2] showed that the uncertainties in the laminar region of Nikuradse’s experiments were very high, and his conclusion regarding no roughness effects in the laminar region is open to question. In order to conclusively resolve this discrepancy, we have experimentally determined the effects of relative roughness ranging from 0–5.18% in micro and minichannels on friction factor and critical Reynolds numbers. Reynolds numbers were varied from 30 to 7000 and hydraulic diameters ranged from 198μm to 1084μm. There is indeed a roughness effect seen in the laminar region, contrary to what is reported by Nikuradse. The resulting friction factors are well predicted using a set of constricted flow parameters. In addition to higher friction factors, transition to turbulence was observed at decreasing Reynolds numbers as relative roughness increased.

Effects of Roughness on Turbulent Flow in Microchannels and Minichannels

2008 ◽  
Author(s):  
Timothy P. Brackbill ◽  
Satish G. Kandlikar
Keyword(s):  
Experimental Study ◽  
Laminar Flow ◽  
Turbulent Flow ◽  
Roughness Parameter ◽  
Reynolds Numbers ◽  
Turbulent Regime ◽  
Roughness Effects ◽  
Relative Roughness ◽  
Roughness Elements ◽  
Moody Diagram

The effect of roughness ranging from smooth to 24% relative roughness on laminar flow has been examined in previous works by the authors. It was shown that using a constricted parameter, εFP, the laminar results were predicted well in the roughened channels ([1],[2],[3]). For the turbulent regime, Kandlikar et al. [1] proposed a modified Moody diagram by using the same set of constricted parameters, and using the modification of the Colebrook equation. A new roughness parameter εFP was shown to accurately portray the roughness effects encountered in laminar flow. In addition, a thorough look at defining surface roughness was given in Young et al. [4]. In this paper, the experimental study has been extended to cover the effects of different roughness features on pressure drop in turbulent flow and to verify the validity of the new parameter set in representing the resulting roughness effects. The range of relative roughness covered is from smooth to 10.38% relative roughness, with Reynolds numbers up to 15,000. It was found that using the same constricted parameters some unique characteristics were noted for turbulent flow over sawtooth roughness elements.

Determining critical flow parameters for the Poiseuille, Couette and Taylor – Couette flows

2020 ◽  
Author(s):  
A.S. Kondratiev ◽  
K.F. Ogorodnikov
Keyword(s):  
Couette Flow ◽  
Critical Reynolds Number ◽  
Reynolds Numbers ◽  
Critical Parameters ◽  
Physical Conditions ◽  
Flow Parameters ◽  
Critical Reynolds Numbers ◽  
Taylor Couette ◽  
Mathematical Justification ◽  
Analytical Expressions

Based on a detailed analysis of the known Dou method for determining the critical parameters of a Newtonian fluid flow during the transition of a laminar flow regime to a turbulent one, an alternative to determining the critical Reynolds number for the Poiseuille and Couette flows in cylindrical, coaxial and flat channels, the article proposes a new mathematical justification of the Dou method leading to simpler calculation relations, while preserving the initial ideas about the physical conditions of the transition. New computing expressions for determining the critical Dou number for the generalized Poiseuille – Couette flow in a flat channel not considered by Dou are obtained. Analytical expressions for calculating critical parameters for the Taylor – Couette flow approximating experimental results for critical Reynolds numbers are given, as well as calcula-ted values of critical Dou numbers.

Computational Analysis of Wall Roughness Effects for Liquid Flow in Micro-Conduits

2004 ◽  
Vol 126 (1) ◽  
pp. 1-9 ◽  
Author(s):  
C. Kleinstreuer ◽  
J. Koo
Keyword(s):  
Surface Roughness ◽  
Darcy Number ◽  
Data Sets ◽  
Roughness Effects ◽  
Flow Area ◽  
Flow Parameters ◽  
Friction Factors ◽  
Medium Layer ◽  
Actual Flow ◽  
Cutting Processes

Fluid flow in microchannels or microtubes may differ in terms of wall frictional effects, and hence flow rates, when compared to macrochannels. Focusing on steady laminar fully developed flow of a liquid in different micro-conduits, relative surface roughness is captured in terms of a porous medium layer (PML) model. The new approach allows the evaluation of microfluidics variables as a function of PML characteristics, i.e., layer thickness and porosity, uncertainties in measuring hydraulic diameters as well as the inlet Reynolds number. Specifically, realistic values for the PML Darcy number, relative surface roughness, and actual flow area are taken into account to match observed friction factors in micro-conduits. The model predictions compared well with measured data sets for systems with significant relative roughness values. Although other surface effects may have influenced the experimental results as well, surface roughness is found to affect the friction factor and hence the flow parameters in relatively rough channels, e.g., those which are made of aluminum or stainless steel by way of micro-cutting processes.

Numerical and Experimental Analysis of Turbulent Flow in Corrugated Pipes

2010 ◽  
Vol 132 (7) ◽  
Author(s):  
Henrique Stel ◽  
Rigoberto E. M. Morales ◽  
Admilson T. Franco ◽  
Silvio L. M. Junqueira ◽  
Raul H. Erthal ◽  
...  
Keyword(s):  
Reynolds Number ◽  
Pressure Drop ◽  
Turbulent Flow ◽  
Friction Factor ◽  
Turbulence Models ◽  
Reynolds Numbers ◽  
Velocity Magnitude ◽  
Geometric Configurations ◽  
Corrugated Surfaces ◽  
Friction Factors

This article describes a numerical and experimental investigation of turbulent flow in pipes with periodic “d-type” corrugations. Four geometric configurations of d-type corrugated surfaces with different groove heights and lengths are evaluated, and calculations for Reynolds numbers ranging from 5000 to 100,000 are performed. The numerical analysis is carried out using computational fluid dynamics, and two turbulence models are considered: the two-equation, low-Reynolds-number Chen–Kim k-ε turbulence model, for which several flow properties such as friction factor, Reynolds stress, and turbulence kinetic energy are computed, and the algebraic LVEL model, used only to compute the friction factors and a velocity magnitude profile for comparison. An experimental loop is designed to perform pressure-drop measurements of turbulent water flow in corrugated pipes for the different geometric configurations. Pressure-drop values are correlated with the friction factor to validate the numerical results. These show that, in general, the magnitudes of all the flow quantities analyzed increase near the corrugated wall and that this increase tends to be more significant for higher Reynolds numbers as well as for larger grooves. According to previous studies, these results may be related to enhanced momentum transfer between the groove and core flow as the Reynolds number and groove length increase. Numerical friction factors for both the Chen–Kim k-ε and LVEL turbulence models show good agreement with the experimental measurements.

scholarly journals Unsteady forces on a circular cylinder at critical Reynolds numbers

2014 ◽  
Vol 26 (12) ◽  
pp. 125110 ◽  
Author(s):  
O. Lehmkuhl ◽  
I. Rodríguez ◽  
R. Borrell ◽  
J. Chiva ◽  
A. Oliva
Keyword(s):  
Circular Cylinder ◽  
Reynolds Numbers ◽  
Unsteady Forces ◽  
Critical Reynolds Numbers

Stability of Hagen-Poiseuille flow with superimposed rigid rotation

1976 ◽  
Vol 73 (1) ◽  
pp. 153-164 ◽  
Author(s):  
P.-A. Mackrodt
Keyword(s):  
Poiseuille Flow ◽  
Pipe Flow ◽  
Stokes Equations ◽  
Three Dimensional ◽  
Reynolds Numbers ◽  
Neutral Curve ◽  
Rigid Rotation ◽  
Transition To Turbulence ◽  
Navier Stokes ◽  
Navier Stokes Equations

The linear stability of Hagen-Poiseuille flow (Poiseuille pipe flow) with superimposed rigid rotation against small three-dimensional disturbances is examined at finite and infinite axial Reynolds numbers. The neutral curve, which is obtained by numerical solution of the system of perturbation equations (derived from the Navier-Stokes equations), has been confirmed for finite axial Reynolds numbers by a few simple experiments. The results suggest that, at high axial Reynolds numbers, the amount of rotation required for destabilization could be small enough to have escaped notice in experiments on the transition to turbulence in (nominally) non-rotating pipe flow.

Loss Characteristics of Orifices and Nozzles

1978 ◽  
Vol 100 (3) ◽  
pp. 299-307 ◽  
Author(s):  
S. H. Alvi ◽  
K. Sridharan ◽  
N. S. Lakshmana Rao
Keyword(s):  
Reynolds Number ◽  
Turbulent Flow ◽  
Flow Regime ◽  
Discharge Coefficient ◽  
Critical Reynolds Number ◽  
Reynolds Numbers ◽  
Center Line ◽  
Laminar Regime ◽  
Variation Of Parameters ◽  
Turbulent Flow Regime

Loss characteristics of sharp-edged orifices, quadrant-edged orifices for varying edge radii, and nozzles are studied for Reynolds numbers less than 10,000 for β ratios from 0.2 to 0.8. The results may be reliably extrapolated to higher Reynolds numbers. Presentation of losses as a percentage of meter pressure differential shows that the flow can be identified into fully laminar regime, critical Reynolds number regime, relaminarization regime, and turbulent flow regime. An integrated picture of variation of parameters such as discharge coefficient, loss coefficient, settling length, pressure recovery length, and center line velocity confirms this classification.

Measurement and Prediction of the Effects of Nonuniform Surface Roughness on Turbulent Flow Friction Coefficients

1988 ◽  
Vol 110 (4) ◽  
pp. 380-384 ◽  
Author(s):  
R. P. Taylor ◽  
W. F. Scaggs ◽  
H. W. Coleman
Keyword(s):  
Turbulent Flows ◽  
Rough Surfaces ◽  
Reynolds Numbers ◽  
Base Diameter ◽  
Friction Coefficients ◽  
Friction Factors ◽  
Random Rough Surfaces ◽  
The Status ◽  
Uniform Array ◽  
Prediction Approach

The status of prediction methods for friction coefficients in turbulent flows over nonuniform or random rough surfaces is reviewed. Experimental data for friction factors in fully developed pipe flows with Reynolds numbers between 10,000 and 600,000 are presented for two nonuniform rough surfaces. One surface was roughened with a mixture of cones and hemispheres which had the same height and base diameter and were arranged in a uniform array. The other surface was roughened with a mixture of two sizes of cones and two sizes of hemispheres. These data are compared with predictions made using the previously published discrete element prediction approach of Taylor, Coleman, and Hodge. The agreement between the data and the predictions is excellent.

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