scholarly journals Roughness-induced critical phenomenon analogy for turbulent friction factor explained by a co-spectral budget model

2021 ◽  
Vol 33 (10) ◽  
pp. 105127
Author(s):  
Shuolin Li ◽  
Gabriel Katul
Keyword(s):  
Friction Factor ◽  
Critical Phenomenon ◽  
Turbulent Friction ◽  
Budget Model

Turbulent Friction Factor for a Rod Bundle in Consideration of a Subchannel Geometry

2002 ◽  
Author(s):  
Joo Hwan Park ◽  
Chang Joon Jeong ◽  
Myung Seung Yang ◽  
Dong Suk Oh
Keyword(s):  
Friction Factor ◽  
Measurement Data ◽  
Experimental Results ◽  
Flow Area ◽  
Theoretical Derivation ◽  
Turbulent Friction ◽  
Law Of The Wall ◽  
Rod Bundle ◽  
Two Parameters ◽  
Geometry Parameter

A generalized turbulent friction factor for a rod bundle was developed based on “Law of the Wall” for a tube. It was included two parameters which are one parameter of hydraulic diameter and flow area of a subchannel and rod bundle and another parameter (called geometry parameter hereinafter) of subchannel configuration and pitch-to-diameter ratio (P/D) for a single subchannel. The turbulent geometry parameter for a single subchannel has been used as a constant on the previous works but it was found to be dependent on subchannel shapes and P/D from the present work. Hence, it was modeled as a function of the subchannel shapes and P/D from 1.0 to 1.5. The turbulent geometry parameters for single subchannels were validated by the theoretical derivation of a triangular and square subchannel. Those are compared and agreed well with the previous measurement data for 4 kinds of subchannel types such as a triangular, a square, a wall and a corner subchannel. The present model of turbulent friction factor for a rod bundle included the turbulent geometry parameter has been compared with the various experimental results for circular tubes and hexagonal tubes with various rod numbers. The predicted turbulent friction factors for those rod bundles were agreed excellently with experimental results.

The Effect of a Longitudinal Magnetic Field on Pipe Flow of Mercury

1961 ◽  
Vol 83 (4) ◽  
pp. 445-453 ◽  
Author(s):  
Samuel Globe
Keyword(s):  
Magnetic Field ◽  
Reynolds Number ◽  
Friction Factor ◽  
Pipe Flow ◽  
Longitudinal Magnetic Field ◽  
Hartmann Number ◽  
Characteristic Length ◽  
Axial Magnetic Field ◽  
Turbulent Friction ◽  
The Magnetic Field

An experimental investigation has been made of the effect of an axial magnetic field on transition from laminar to turbulent flow and on the turbulent friction factor for pipe flow of mercury. Magnetic-flux densities up to 5700 gauss were obtained with a water-cooled solenoid. Pipes of glass and aluminum were used of approximately 0.1 to 0.2 in. diam. The maximum Hartmann number, with the hydraulic radius (half the actual radius) taken as the characteristic length, was about 20. Measurements were made of the pressure gradient and velocity of flow. The transition Reynolds number was determined from the curve of friction factor against Reynolds number. The results show an increasing value of minimum transition Reynolds number with Hartmann number. The magnetic field also brought about a decrease in the turbulent friction factor and corresponding shear force at the wall.

Laminar, Transitional and Turbulent Friction Factors for Gas Flows in Smooth and Rough Microtubes

2008 ◽  
Author(s):  
Marco Lorenzini ◽  
Gian Luca Morini ◽  
Sandro Salvigni
Keyword(s):  
Reynolds Number ◽  
Friction Factor ◽  
Turbulent Regime ◽  
Turbulent Friction ◽  
Compressibility Effect ◽  
Flow Acceleration ◽  
Friction Factors ◽  
Macro Scale ◽  
Fully Developed Turbulent Flow ◽  
Microscale Transport

Theoretical and experimental works on microscale transport phenomena have been carried out in the past decade in the attempt to analyse possible new effects and to assess the influence of scaling on the classical correlations which are used in macro-scale heat and fluid flow, following the need to supply engineers with reliable correlations to be used in the design of micro-scale devices. These results were sometimes in mutual contrast, as is the case for the determination of the friction factor, which has been found to be lower, higher or comparable to that for macroscopic channels, depending on the researchers. In this work the compressible flow of nitrogen inside circular microchannels from 26 μm to 508 μm in diameter and with different surface roughness (<1%) is investigated for the whole range of flow conditions: laminar, transitional and turbulence. Over 5000 experimental data have been collected and analysed. The data confirmed that in the laminar regime the agreement with the conventional theory is very good in terms of friction factors both for rough and smooth microtubes. For the smaller microchannels (<100 μm) when Re is greater than 1300 the friction factor tends to deviate from the Poiseuille law because the flow acceleration due to compressibility effect gains in importance. The transitional regime was found to start no earlier than at values of the Reynolds number around 1800–2000. Both smooth and sudden changes in the flow regime have been found, as reported for conventional tubes. Fully developed turbulent flow was attained with both smooth and rough tubes, and the results for smooth tubes seem to confirm Blasius’s relation, while for rough tubes the Colebrook’s correlation is found to be only partially in agreement with the experimental friction factors. In the turbulent regime the dependence of the friction factor on the Reynolds number is less pronounced for microtubes with respect to the prediction of the Colebrook’s correlation and the friction factor tends only to depend on the microtube relative roughness.

Turbulent friction factor and velocity profile in smooth annuli

1971 ◽  
Vol 23 (1) ◽  
pp. 446-458
Author(s):  
D. N. Roy ◽  
U. Gangopadhay
Keyword(s):  
Velocity Profile ◽  
Friction Factor ◽  
Turbulent Friction

Analytical Prediction of Turbulent Friction Factor in Circular Pipe Under Supercritical Conditions

2012 ◽  
Author(s):  
Jinguang Zang ◽  
Xiao Yan ◽  
Shanfang Huang ◽  
Zejun Xiao ◽  
Yanping Huang
Keyword(s):  
Friction Factor ◽  
Viscous Sublayer ◽  
Circular Pipe ◽  
Main Role ◽  
Analytical Prediction ◽  
Flow Area ◽  
Algebraic Form ◽  
Supercritical Conditions ◽  
Turbulent Friction ◽  
Law Of The Wall

An analytical method was proposed for the prediction of the turbulent friction factor in a circular pipe under supercritical conditions. The friction factor equation was based on the new wall function by Van Direst transformation which is widely used in compressed flow. The law of the wall of two layers was used and integrated over the entire flow area to obtain the algebraic form of the turbulent friction factor. The new turbulent friction formula was first adjusted to Colebrook equation in isothermal flow at supercritical pressures. And then it was validated in heated supercritical flow by several existing correlations. Similar trends were found between them, which confirms the physical validity of the new frictional formula. The theoretical analysis also shows that the friction factor due to the variation of fluid property at supercritical pressures is mainly caused by the density and viscosity variation. In viscous sublayer, both the viscosity play the main role, while in turbulent sublayer, only the density do.

Analytic Prediction of the Friction Factor for Turbulent Flow in Internally Finned Channels

1981 ◽  
Vol 103 (3) ◽  
pp. 423-428 ◽  
Author(s):  
M. J. Scott ◽  
R. L. Webb
Keyword(s):  
Turbulent Flow ◽  
Friction Factor ◽  
Analytical Model ◽  
Analytical Models ◽  
Turbulent Friction ◽  
Law Of The Wall ◽  
Finned Tubes ◽  
Rectangular Channels ◽  
Factor Data ◽  
Analytic Prediction

This work develops an analytical model for the friction factor with turbulent flow in internally finned channels. Such channels are an important class of enhanced heat transfer surfaces. Until this work, no analytical models for the turbulent friction factor have been proposed. The present model assumes the validity of the Law of the Wall and applies the logarithmic velocity distribution to the interfin and core regions of the flow. Theoretically based friction factor equations are developed for internally finned circular tubes and rectangular channels. The model predicts Carnavos data for 21 internally finned tubes within ± 10 percent. Friction factor data were taken for five internally finned, rectangular channels. The analytical model predicts these data within ± 10 percent, except for the case of a very high fin.

Analytical prediction of turbulent friction factor for a rod bundle

2011 ◽  
Vol 38 (2-3) ◽  
pp. 348-357 ◽  
Author(s):  
Jun Ho Bae ◽  
Joo Hwan Park
Keyword(s):  
Friction Factor ◽  
Analytical Prediction ◽  
Turbulent Friction ◽  
Rod Bundle
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