Effect of Triangular Roughness Elements on Pressure Drop and Laminar-Turbulent Transition in Microchannels and Minichannels

2006 ◽  
Author(s):  
Timothy P. Brackbill ◽  
Satish G. Kandlikar
Keyword(s):  
Turbulent Flow ◽  
Reynolds Numbers ◽  
Subject Area ◽  
Internal Flows ◽  
Local Pressure ◽  
Flow Area ◽  
Friction Factors ◽  
Roughness Elements ◽  
Initial Work ◽  
Constricted Flow

Roughness elements affect internal flows in different ways. One effect is a transition from laminar to turbulent flow at a lower Reynolds number than the predicted Re = 2300. Initial work at RIT in the subject area was performed by Schmitt and Kandlikar (2005) and Kandlikar et al. (2005), and this study is an extension of these efforts. The channel used in this study is rectangular, with varying separation between walls that have machined roughness elements. The roughness elements are saw-tooth in structure, with element heights of 107 and 117 μm for two pitches of 405 μm and 815 μm respectively. The resulting hydraulic diameters and Reynolds numbers based on the constricted flow area range from 424 μm to 2016 μm and 210 to 2400 respectively. Pressure measurements are taken at sixteen locations along the flow length of 88.9 mm to determine the local pressure gradients. The results for friction factors and transition to turbulent flow are obtained and compared with the data reported by Schmitt and Kandlikar (2005). The roughness elements cause an early transition to turbulent flow, and the friction factors in the laminar region are predicted accurately using the hydraulic diameter based on the constricted flow area.

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.

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.

scholarly journals Transition From the Turbulent to the Laminar Regime for Internal Convective Flow With Large Property Variations

1970 ◽  
Vol 92 (3) ◽  
pp. 506-512 ◽  
Author(s):  
C. W. Coon ◽  
H. C. Perkins
Keyword(s):  
Laminar Flow ◽  
Turbulent Flow ◽  
Circular Tube ◽  
Reynolds Numbers ◽  
Bulk Temperature ◽  
Heating Rates ◽  
Nusselt Numbers ◽  
Friction Factors ◽  
High Heating ◽  
Flow Situation

The results of a primarily experimental study of the transition from turbulent flow to laminar flow as a consequence of high heating rates are presented. Results are reported for hydrodynamically fully developed, low Mach number flows of air and helium through a vertical, circular tube. The electrically heated section was 100 diameters in length; entering Reynolds numbers ranged from 1700–40,000, and maximum wall-to-bulk temperature ratios reached 4.4. As a means of predicting the occurrence of a transition from turbulent flow to laminar flow, the experimental results are compared to the acceleration parameter suggested by Moretti and Kays and to a modified form of the parameter that is appropriate to a circular tube. It is suggested that the variable property turbulent flow correlations do not provide acceptable predictions of the Nusselt number and the friction factor if the value 4μq′′G2DTcp≃1.5×10−6 based on bulk properties, is exceeded for an initially turbulent flow situation. It is further suggested that Nusselt numbers and friction factors at locations down-stream from the point xDlaminar≃(2×10−8)(Tinlet)(Reb,inlet)2TwTbmax−1 for bulk temperatures in degrees Rankine may be obtained from the laminar correlation equations even though the flow is initially turbulent.

Application of an Intermittency Model for Laminar, Transitional, and Turbulent Internal Flows

2019 ◽  
Vol 141 (7) ◽  
Author(s):  
J. P. Abraham ◽  
E. M. Sparrow ◽  
J. M. Gorman ◽  
Yu Zhao ◽  
W. J. Minkowycz
Keyword(s):  
Slight Modification ◽  
Reynolds Numbers ◽  
Internal Flows ◽  
Circular Tubes ◽  
Flow Problems ◽  
Turbulent Transition ◽  
Turbulence Intermittency ◽  
Friction Factors ◽  
External Flows ◽  
Laminar And Turbulent Regimes

A turbulent transition model has been applied to fluid flow problems that can be laminar, turbulent, transitional, or any combination. The model is based on a single additional transport equation for turbulence intermittency. While the original model was developed for external flows, a slight modification in model constants has enabled it to be used for internal flows. It has been successfully applied to such flows for Reynolds numbers that ranged from 100 to 100,000 in circular tubes, parallel plate channels, and circular tubes with an abrupt change in diameters. The model is shown to predict fully developed friction factors for the entire range of Reynolds numbers as well as velocity profiles for both laminar and turbulent regimes.

A Comparison of Predicted and Measured Friction Factors for Turbulent Flow Through Rectangular Ducts

1962 ◽  
Vol 84 (1) ◽  
pp. 82-88 ◽  
Author(s):  
J. P. Hartnett ◽  
J. C. Y. Koh ◽  
S. T. McComas
Keyword(s):  
Friction Coefficient ◽  
Turbulent Flow ◽  
Reynolds Numbers ◽  
Square Duct ◽  
Aspect Ratios ◽  
Friction Factors ◽  
Rectangular Channels ◽  
Laminar And Turbulent Flow ◽  
Flow Through ◽  
Predicted Values

The friction coefficient for both laminar and turbulent flow through rectangular channels was analytically and experimentally studied. The analytic expression for the pressure loss in fully established laminar flow was verified by experiment. In turbulent flow, the method of Deissler and Taylor was used to calculate the friction coefficient. The calculated and measured results were in agreement for ducts having large aspect ratios. At aspect ratios less than 5:1, the predicted values of the friction factors were lower than the experimental data, with a maximum difference of 12 per cent evident for the square duct. It was found that the circular-tube correlation accurately predicts the friction coefficient for flow through rectangular ducts of any aspect ratio for Reynolds numbers between 6 × 103 and 5 × 105. Hydrodynamic entrance-length results are also presented in the laminar and turbulent flow ranges for both a smooth and an abrupt entrance configuration.

Geometry Effects on Turbulent Flow and Heat Transfer in Internally Finned Tubes

2001 ◽  
Vol 123 (6) ◽  
pp. 1035-1044 ◽  
Author(s):  
Xiaoyue Liu ◽  
Michael K. Jensen
Keyword(s):  
Heat Transfer ◽  
Turbulent Flow ◽  
Reynolds Numbers ◽  
Helix Angle ◽  
Turbulence Energy ◽  
Finned Tubes ◽  
Nusselt Numbers ◽  
Flow And Heat Transfer ◽  
Geometric Conditions ◽  
Friction Factors

A parametric study has been performed on turbulent flow and heat transfer in internally finned tubes. For a rectangular fin profile, the effects of fin number N, fin width s, fin height H, and helix angle γ were numerically investigated for the conditions of N=10∼40,H=0.03∼0.1,s=0.05∼0.22,γ=10 deg∼40 deg, and Re=40,000. In addition, the performance of three fin profiles—rectangle, triangle, and round crest—with the same fin heights, width, and helix angles were compared for Reynolds numbers between 10,000 and 70,000. Rectangular and triangular fins behave similarly; for some geometric conditions the round crest fin has lower friction factors and Nusselt numbers (17 and 10 percent, respectively) than the rectangular fin. However, when the number of fins is large, the round crest fin can have larger friction factors (about 16 percent). Damping of turbulence energy in the interfin region is credited for the reversal of the typical trends.

Turbulent flow between counter-rotating concentric cylinders: a direct numerical simulation study

2008 ◽  
Vol 615 ◽  
pp. 371-399 ◽  
Author(s):  
S. DONG
Keyword(s):  
Turbulent Flow ◽  
Large Scale ◽  
Outer Cylinder ◽  
Three Dimensional ◽  
Reynolds Numbers ◽  
Taylor Vortex ◽  
Small Scale ◽  
Mean Flow ◽  
Concentric Cylinders ◽  
High Reynolds

We report three-dimensional direct numerical simulations of the turbulent flow between counter-rotating concentric cylinders with a radius ratio 0.5. The inner- and outer-cylinder Reynolds numbers have the same magnitude, which ranges from 500 to 4000 in the simulations. We show that with the increase of Reynolds number, the prevailing structures in the flow are azimuthal vortices with scales much smaller than the cylinder gap. At high Reynolds numbers, while the instantaneous small-scale vortices permeate the entire domain, the large-scale Taylor vortex motions manifested by the time-averaged field do not penetrate a layer of fluid near the outer cylinder. Comparisons between the standard Taylor–Couette system (rotating inner cylinder, fixed outer cylinder) and the counter-rotating system demonstrate the profound effects of the Coriolis force on the mean flow and other statistical quantities. The dynamical and statistical features of the flow have been investigated in detail.

Local Heat Transfer Measurements in Turbulent Flow Around a 180-deg Pipe Bend

1987 ◽  
Vol 109 (1) ◽  
pp. 43-48 ◽  
Author(s):  
J. W. Baughn ◽  
H. Iacovides ◽  
D. C. Jackson ◽  
B. E. Launder
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Turbulent Flow ◽  
Transfer Coefficient ◽  
Secondary Flow ◽  
Local Heat Transfer ◽  
Reynolds Numbers ◽  
Local Heat ◽  
Pipe Bend ◽  
Streamline Curvature

The paper reports extensive connective heat transfer data for turbulent flow of air around a U-bend with a ratio of bend radius:pipe diameter of 3.375:1. Experiments cover Reynolds numbers from 2 × 104 to 1.1 × 105. Measurements of local heat transfer coefficient are made at six stations and at five circumferential positions at each station. At Re = 6 × 104 a detailed mapping of the temperature field within the air is made at the same stations. The experiment duplicates the flow configuration for which Azzola and Humphrey [3] have recently reported laser-Doppler measurements of the mean and turbulent velocity field. The measurements show a strong augmentation of heat transfer coefficient on the outside of the bend and relatively low levels on the inside associated with the combined effects of secondary flow and the amplification/suppression of turbulent mixing by streamline curvature. The peak level of Nu occurs halfway around the bend at which position the heat transfer coefficient on the outside is about three times that on the inside. Another feature of interest is that a strongly nonuniform Nu persists six diameters downstream of the bend even though secondary flow and streamline curvature are negligible there. At the entry to the bend there are signs of partial laminarization on the inside of the bend, an effect that is more pronounced at lower Reynolds numbers.

Heat Transfer and Friction in Channels With Very High Blockage 45° Staggered Turbulators

2003 ◽  
Author(s):  
Jeremy C. Bailey ◽  
Ronald S. Bunker
Keyword(s):  
Heat Transfer ◽  
Reynolds Numbers ◽  
Transfer Coefficients ◽  
Flow Area ◽  
Test Technique ◽  
Heat Transfer Coefficients ◽  
Smooth Channel ◽  
Constant Pitch ◽  
Transfer Behavior ◽  
Very High

Heat transfer and friction coefficients have been measured within a rectangular passage of aspect ratio 0.4 containing 45-degree staggered turbulators of very high blockage. Using a constant pitch-to-height ratio of 10 for all geometries, turbulator height-to-channel hydraulic diameter ratios from 0.193 to 0.333 were investigated. This range of e/D creates actual channel blockage ratios e/H from 0.275 to 0.475, presenting significant flow area restrictions. A liquid crystal test technique is used to obtain both detailed heat transfer behavior on the surfaces between turbulators, as well as averaged fully developed heat transfer coefficients. Reynolds numbers from 20000 to 100000 were tested. Nusselt number enhancements of up to 3.6 were obtained over that of a smooth channel, with friction coefficient enhancements of as much as 65. In contrast to low-blockage turbulated channels, the 45-degree turbulated Nu is found to be lower than that at 90-degree orientation, given very similar e/D and e/H values.

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