Proposed Correlations for Laminar, Transition, and Turbulent Friction Factors in Micro-fin Tubes with Different Inlet Configurations

2022 ◽  
pp. 73-82
Author(s):  
Afshin J. Ghajar
Keyword(s):  
Turbulent Friction ◽  
Friction Factors ◽  
Fin Tubes

Analytic Prediction of the Friction and Heat Transfer for Turbulent Flow in Axial Internal Fin Tubes

1993 ◽  
Vol 115 (3) ◽  
pp. 553-559 ◽  
Author(s):  
Nae-Hyun Kim ◽  
R. L. Webb
Keyword(s):  
Heat Transfer ◽  
Turbulent Flow ◽  
Analytic Model ◽  
Algebraic Form ◽  
Law Of The Wall ◽  
Finned Tubes ◽  
Nusselt Numbers ◽  
Friction Factors ◽  
Transfer Equations ◽  
Fin Tubes

An analytic model is developed to predict the friction factors and Nusselt numbers for turbulent flow in axial internal fin tubes. The present model uses the Law of the Wall and applies the logarithmic universal velocity and temperature profile to the interfin and core regions of the flow. The fin shape is assumed trapezoidal, and the fin parameters such as fin height, fin root thickness and fin tip thickness are determined from the tube dimensional data. Theoretically based friction and heat transfer equations are developed for internally finned tubes in an algebraic form. The analytic model predicts Carnavos friction data for 11 axial internal fin tubes within ± 10 percent, and heat transfer data of air, water, and water-glycol within ± 15 percent when proper velocity and temperature profiles are used.

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.

Transport of Oils as Oil-in-Water Emulsions

1979 ◽  
Vol 101 (1) ◽  
pp. 100-104 ◽  
Author(s):  
J. L. Zakin ◽  
R. Pinaire ◽  
M. E. Borgmeyer
Keyword(s):  
Oil Viscosity ◽  
Turbulent Friction ◽  
Specific Energy Loss ◽  
Friction Factors ◽  
Oil In Water ◽  
Viscoelastic Effects ◽  
Oil Concentration ◽  
Flow Pressure ◽  
Friction Factor Correlation ◽  
Newtonian Behavior

Turbulent flow pressure drop measurements were made for various concentrated oil-in-water emulsions which exhibit non-Newtonian behavior. The effects of oil viscosity, temperature and oil concentration on specific energy loss were evaluated. Measured turbulent friction factors consistently fell below those predicted by the Dodge and Melzner friction factor correlation, probably due to viscoelastic effects of the emulsion. Several polymer and surfactant drag reducers were tested in these emulsions, and high molecular weight polyacrylamides were found to be the most effective in further reducing pumping energy losses. The effectiveness of the polymer additives decreased with time during pump circulation.

The Effect of Journal Misalignment on the Operation of a Turbulent Flow Hydrostatic Bearing

1993 ◽  
Vol 115 (3) ◽  
pp. 355-363 ◽  
Author(s):  
Luis San Andres
Keyword(s):  
Turbulent Flow ◽  
Load Capacity ◽  
Surface Condition ◽  
Dynamic Force ◽  
Turbulent Friction ◽  
Flow Equations ◽  
Hydrostatic Bearing ◽  
Friction Factors ◽  
Static Misalignment ◽  
Journal Misalignment

An analysis for calculation of the dynamic force and moment response in turbulent flow, orifice compensated hydrostatic journal bearings is presented. The fully developed flow of a barotropic liquid is described by variable properties, bulk-flow equations and local turbulent friction factors based on bearing surface condition. Bearing load and moments and, dynamic force and moment coefficients are calculated for perturbations in journal center displacements and misaligned journal axis rotations. Numerical results for the effect of static misalignment angles in the plane of the eccentricity vector are presented for a water lubricated hydrostatic bearing. The predictions show that journal axis misalignment causes a reduction in load capacity due to loss in film thickness, increases the flow rate and produces significant restoring moments (couples). Force and moment coefficients due to dynamic journal axis rotations are also discussed.

Flow and Heat Transfer in Convectively Cooled Underground Electric Cable Systems: Part 1—Velocity Distributions and Pressure Drop Correlations

1978 ◽  
Vol 100 (1) ◽  
pp. 30-35 ◽  
Author(s):  
J. C. Chato ◽  
R. S. Abdulhadi
Keyword(s):  
Pressure Drop ◽  
Noticeable Effect ◽  
Turbulent Friction ◽  
Electric Cable ◽  
Flow And Heat Transfer ◽  
Friction Factors ◽  
Wide Range ◽  
Order Of Magnitude ◽  
Cable Systems ◽  
Small Channels

Velocity distributions and pressure drop correlations have been obtained experimentally for a wide range of physical, flow, and thermal parameters in three models of oil-cooled underground electric cable systems. The flow can be considered as consisting of several, interconnected, parallel channels. If one of these is significantly larger in cross section, it will dominate the behavior of the entire system with velocities up to an order of magnitude greater than in the other channels. Laminar, fully developed flow exists at a dimensionless entrance length as low as x/DH = 100. The turbulent velocity profiles are essentially uniform in the larger, main channel, but not in the small channels with lower velocities. Laminar friction factors can be correlated with an equivalent Reynolds number, based on the main flow channel alone, as fe·Ree = 30. Turbulent friction factors increase with increasing skid wire roughness ratios and approach the asymptotic values of 0.013 and 0.021 for roughness ratios 0.0216 and 0.0293, respectively. Cable heating had no noticeable effect on the friction factor correlations.

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