Flow Friction Behavior in Porous Channels

2005 ◽  
Author(s):  
T. M. Jeng ◽  
T. Y. Wu ◽  
P. L. Chen ◽  
S. F. Chang ◽  
Y. H. Hung
Keyword(s):  
Reynolds Number ◽  
Friction Factor ◽  
Rectangular Channel ◽  
Experimental Studies ◽  
Darcy Number ◽  
Metallic Foam ◽  
Friction Behavior ◽  
Cross Sectional ◽  
Porous Flow ◽  
Flow Friction

A series of experimental studies on the flow friction behavior in a rectangular channel filled with various porous metallic foam materials have been performed. The rectangular channel has a cross-sectional area 60mm × 25.4mm with a length of 60mm. The parameters and conditions of interest in the study are the Reynolds number (Re) and medium porosity/pore density (ε/PPI). The ranges of the above-mentioned parameters are: Re=2058-6736 and ε=0.7-0.93/5-40PPI. Their effects on flow friction characteristics in such porous metallic foam channels have been systematically explored. In the study, the porous flow parameters including the Darcy number (Da), inertia coefficient (CF) and Darcy friction factor (f) are investigated. The combined effects of foam porosity and Reynolds number are examined in detail. From the results, the relevant new empirical correlations of Da and CF are proposed, respectively; and a new correlation of the friction factor in terms of ε, Da and Re is presented. Besides, the results reveal that all the ratios of f/fε=1 are much greater than unity and reach the orders of around hundreds to thousands. This manifests that it needs more pumping power to maintain the same flow rate as in a hollow channel. Finally, the experimental data of f/fε=1 is correlated in the study.

Heat Transfer And Pressure Drop Of An Angled Discrete Turbulator At Elevated Reynolds Numbers Up To 900,000

2021 ◽  
pp. 1-29
Author(s):  
Sam Ghazi-Hesami ◽  
Dylan Wise ◽  
Keith Taylor ◽  
Peter Ireland ◽  
Étienne Robert
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Pressure Drop ◽  
Friction Factor ◽  
Rectangular Channel ◽  
Reynolds Numbers ◽  
Enhance Heat Transfer ◽  
Near Surface ◽  
Number Range ◽  
Smooth Channel

Abstract Turbulators are a promising avenue to enhance heat transfer in a wide variety of applications. An experimental and numerical investigation of heat transfer and pressure drop of a broken V (chevron) turbulator is presented at Reynolds numbers ranging from approximately 300,000 to 900,000 in a rectangular channel with an aspect ratio (width/height) of 1.29. The rib height is 3% of the channel hydraulic diameter while the rib spacing to rib height ratio is fixed at 10. Heat transfer measurements are performed on the flat surface between ribs using transient liquid crystal thermography. The experimental results reveal a significant increase of the heat transfer and friction factor of the ribbed surface compared to a smooth channel. Both parameters increase with Reynolds number, with a heat transfer enhancement ratio of up to 2.15 (relative to a smooth channel) and a friction factor ratio of up to 6.32 over the investigated Reynolds number range. Complementary CFD RANS (Reynolds-Averaged Navier-Stokes) simulations are performed with the κ-ω SST turbulence model in ANSYS Fluent® 17.1, and the numerical estimates are compared against the experimental data. The results reveal that the discrepancy between the experimentally measured area averaged Nusselt number and the numerical estimates increases from approximately 3% to 13% with increasing Reynolds number from 339,000 to 917,000. The numerical estimates indicate turbulators enhance heat transfer by interrupting the boundary layer as well as increasing near surface turbulent kinetic energy and mixing.

Heat Transfer in a Rotating Two-Pass Rectangular Channel Featuring Reduced Cross-Sectional Area After Tip Turn (Aspect Ratio = 4:1 to 2:1) With Profiled 60 deg Angled Ribs

2019 ◽  
Vol 141 (7) ◽  
Author(s):  
Andrew F Chen ◽  
Chao-Cheng Shiau ◽  
Je-Chin Han ◽  
Robert Krewinkel
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Aspect Ratio ◽  
Flow Direction ◽  
Rectangular Channel ◽  
Secondary Flows ◽  
Transfer Coefficients ◽  
First Passage ◽  
Cross Sectional ◽  
Internal Surfaces

The present study features a two-pass rectangular channel with an aspect ratio (AR) = 4:1 in the first pass and an AR = 2:1 in the second pass after a 180-deg tip turn. In addition to the smooth-wall case, ribs with a profiled cross section are placed at 60 deg to the flow direction on both the leading and trailing surfaces in both passages (P/e = 10, e/Dh ∼ 0.11, parallel and in-line). Regionally averaged heat transfer measurement method was used to obtain the heat transfer coefficients on all internal surfaces. The Reynolds number (Re) ranges from 10,000 to 70,000 in the first passage, and the rotational speed ranges from 0 to 400 rpm. Under pressurized condition (570 kPa), the highest rotation number achieved was Ro = 0.39 in the first passage and 0.16 in the second passage. The results showed that the turn-induced secondary flows are reduced in an accelerating flow. The effects of rotation on heat transfer are generally weakened in the ribbed case than the smooth case. Significant heat transfer reduction (∼30%) on the tip wall was seen in both the smooth and ribbed cases under rotating condition. Overall pressure penalty was reduced for the ribbed case under rotation. Reynolds number effect was found noticeable in the current study. The heat transfer and pressure drop characteristics are sensitive to the geometrical design of the channel and should be taken into account in the design process.

Analyses of Liquid Flow in Micro-Conduits

2004 ◽  
Author(s):  
Junemo Koo ◽  
Clement Kleinstreuer
Keyword(s):  
Reynolds Number ◽  
Aspect Ratio ◽  
Friction Factor ◽  
Viscous Dissipation ◽  
Wall Slip ◽  
Reynolds Numbers ◽  
Darcy Number ◽  
Low Reynolds Numbers ◽  
Dissipation Effect ◽  
Liquid Flows

Experimental observations of liquid microchannel flow are reviewed and results of computer experiments concerning channel entrance, wall slip, non-Newtonian fluid, surface roughness, viscous dissipation and flow instability effects on the friction factor are discussed Specifically, based on numerical friction factor analyses, the entrance effect should be taken into account for any microfluidic system. It is a function of channel length, aspect ratio and the Reynolds number. Non-Newtonian fluid flow effects are expected to be important for polymeric liquids and dense particle suspension flows. The wall-slip effect is negligible for liquid flows. For relatively low Reynolds numbers, i.e., Re > 1,200, onset to instabilities may have to be considered because of possible geometric non-uniformities, including a contraction and/or bend at the microchannel inlet as well as substantial surface roughness. Significant roughness effects, described with a new porous medium layer (PML) model, are a function of the Darcy number, the Reynolds number and cross-sectional configurations. This model was applied to micro-scale liquid flows in straight channels, tubes and rotating cylinders, and validated with experimental data sets. In contrast to published models, PML model simulations yield both an increase and decrease of the friction factor depending on the Darcy number. Viscous dissipation in microchannels is a strong function of the channel aspect ratio, Reynolds number, Eckert number, Prandtl number, and conduit hydraulic diameter. Specifically, viscous dissipation effects are quite important for fluids with low specific heat capacities and high viscosities, even for very low Reynolds numbers, i.e., ReD < 1. The viscous dissipation effect was found to decrease as the fluid temperature increases. As the aspect ratio deviates from unity, the viscous dissipation effect increases. It was found that ignoring the viscous dissipation effect could ultimately affect friction factor measurements for flows in micro-conduits. This could imply a significant amount of viscous heat generation and, for example, may diminish a projected micro-heat-exchanger performance.

scholarly journals Solution of the Implicit Colebrook Equation for Flow Friction Using Excel

2017 ◽  
Author(s):  
Dejan Brkić
Keyword(s):  
Reynolds Number ◽  
Friction Factor ◽  
Hydraulic Resistance ◽  
Iterative Solution ◽  
Pipe Surface ◽  
Implicit Equation ◽  
Flow Friction ◽  
Relative Roughness ◽  
Additional Task ◽  
Accepted Standard

Empirical Colebrook equation implicit in unknown ow friction factor (λ) is an accepted standard for calculation of hydraulic resistance in hydraulically smooth and rough pipes. e Colebrook equation gives friction factor (λ) implicitly as a function of the Reynolds number (Re) and relative roughness (ε/D) of inner pipe surface; i.e. λ0=f(λ0, Re, ε/D). e paper presents a problem that requires iterative methods for the solution. In particular, the implicit method used for calculating the friction factor λ0 is an application of xed- point iterations. e type of problem discussed in this "in the classroom paper" is commonly encountered in uid dynamics, and this paper provides readers with the tools necessary to solve similar problems. Students’ task is to solve the equation using Excel where the procedure for that is explained in this “in the classroom” paper. Also, up to date numerous explicit approximations of the Colebrook equation are available where as an additional task for students can be evaluation of the error introduced by these explicit approximations λ≈f(Re, ε/D) compared with the iterative solution of implicit equation which can be treated as accurate.

scholarly journals Analysis of Aspect Ratio in a Miniature Rectangle Channel for Low Frictional Resistance

Micromachines ◽  
2021 ◽  
Vol 12 (12) ◽  
pp. 1580
Author(s):  
Takashi Fukuda ◽  
Makoto Ryo Harada
Keyword(s):  
Surface Roughness ◽  
Reynolds Number ◽  
Aspect Ratio ◽  
Rectangular Channel ◽  
Frictional Resistance ◽  
Experimental System ◽  
Cross Sectional ◽  
Friction Resistance ◽  
Calculation Results ◽  
Volume Range

We conducted a theoretical investigation of the cross-sectional aspect ratio of a rectangular channel to have sufficiently low frictional resistance under less than 150 of the Reynolds number. From the theoretical consideration, it was clarified that 3.40 or more is recommended as a criterion for determining the aspect ratio. This addresses the problem of determining the interval of rectangle channels, installed in a plate reactor. There is a concern that the real system does not follow the analytical solution, assuming laminar flow, since the higher aspect ratio leads to disturbances of the flow such as the emergence of vortices. However, in the channel’s volume range of (W × H × L) = (7.0 mm × 0.38 mm × 0.26 m), such a turbulence was not observed in the detailed numerical calculation by CFD, where both calculation results were in agreement to within 3% accuracy. Moreover, even in an experimental system with a surface roughness of ca. 7%, friction resistance took agreement within an accuracy of ±30%.

Experimental Studies on Hydrodynamic Resistance and Flow Pattern of a Narrow Flow Channel With Dimples on the Wall

2004 ◽  
Author(s):  
J. B. Zhao ◽  
Y. T. Chew ◽  
B. C. Khoo
Keyword(s):  
Reynolds Number ◽  
Flow Visualization ◽  
Friction Factor ◽  
Experimental Studies ◽  
Flow Channel ◽  
Hydrodynamic Resistance ◽  
Test Channel ◽  
Single Vortex ◽  
Smooth Channel ◽  
Water Proof

A systematic flow visualization study on flow structures inside dimples with different relative depths (h/d) and with round or sharp edges is carried out in the first part of this investigation; three flat test plates are made and each one has two dimples with the same print diameter (d) at 40 mm and the same h/d, which is set at 4%, 20% and 50% respectively. Then friction factor is measured on a test channel with two types of test plates. One has dimples array with h/d at 4% and round edge and the second is a flat plate used as reference; surface roughness can be changed for both test plates by painting and covering with water-proof paper. Flow visualization is also done on a dimple located at the center of the plate in the channel. Results show that shallow dimple (h/d=4%) produces non-separated flows at Reynolds number Reδ&lt;1000 and there exists a rather small separation cavity flow at Reynolds number Reδ&gt;1500. Dimple with h/d at 20% produces two symmetric vortices at Reδ&lt;850, single vortex at Reδ ≈ 1000–1600 and symmetric horseshoe-liked vortex at Reδ&gt;1700. Round edged dimple changes its fl pattern at different Reynolds number comparing to its sharp edged counterpart. For the dimple with h/d at 50%, at Reδ &lt;1200 there is only one stable vortex; at Reδ&gt;1800, it is unstable with its rotating direction changing frequently. In this part of preliminary work, dimpled plate with roughness reduces the friction factor by at least 2% in the flow channel comparing to the reference plate at Reynolds number ReDh ≈ 8,500~24,000. The friction factor curve of the channel with roughened dimpled plate approaches a hydraulically smooth channel with the increase of Reynolds number. No increase in friction factor is observed on the channel with dimpled plate having smooth surface in the comparison to the reference channel without dimples.

Experimental Study on Thermal-Hydraulic Performance of Single-Phase Water Flow in Narrow Rectangular Channel

2009 ◽  
Author(s):  
Mei Wang ◽  
Yan Wen ◽  
Suizheng Qiu ◽  
Guanghui Su ◽  
Weifeng Ni
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Laminar Flow ◽  
Friction Factor ◽  
Water Flow ◽  
Single Phase ◽  
Rectangular Channel ◽  
Flow Region ◽  
Phase Water

The purpose of this study is to discover the differences of pressure drop and heat transfer of single-phase water flow between conventional channels and narrow rectangular channels. Furthermore, the differences between the level and the vertical channel have been studied. The gap of the test channel is 1.8mm. Compared with conventional channels, the narrow rectangular channel showed differences in both flow and heat transfer characteristics. The critical Reynolds number of transition from laminar flow to turbulent flow is 900∼1300, which is smaller compared with conventional channels. The friction factor is larger than that of the conventional channels and the correlation of friction factor with Reynolds number was given by experimental results. From the relation graph of Nusselt number and Reynolds number, the demarcation of the laminar flow region and turbulence flow region is obvious. In laminar region, Nusselt number almost remained constant and approximately consistent with numerical simulation results. While in turbulent region, Nusselt number increased significantly with increasing Reynolds number. A new Nusselt number correlation was obtained based on Dittus-Boelter equation, and the coefficients were less about 13% than that of Dittus-Boelter equation.

Heat Transfer in Thin, Compact Heat Exchangers With Circular, Rectangular, or Pin-Fin Flow Passages

1992 ◽  
Vol 114 (2) ◽  
pp. 373-382 ◽  
Author(s):  
D. A. Olson
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Pressure Drop ◽  
Friction Factor ◽  
Heat Exchangers ◽  
Rectangular Channel ◽  
Fluid Temperature ◽  
Compact Heat Exchangers ◽  
Pin Fin

We have measured heat transfer and pressure drop of three thin, compact heat exchangers in helium gas at 3.5 MPa and higher, with Reynolds numbers of 450 to 36,000. The flow geometries for the three heat exchanger specimens were: circular tube, rectangular channel, and staggered pin fin with tapered pins. The specimens were heated radiatively at heat fluxes up to 77 W/cm2. Correlations were developed for the isothermal friction factor as a function of Reynolds number, and for the Nusselt number as a function of Reynolds number and the ratio of wall temperature to fluid temperature. The specimen with the pin fin internal geometry had significantly better heat transfer than the other specimens, but it also had higher pressure drop. For certain conditions of helium flow and heating, the temperature more than doubled from the inlet to the outlet of the specimens, producing large changes in gas velocity, density, viscosity, and thermal conductivity. These changes in properties did not affect the correlations for friction factor and Nusselt number in turbulent flow.

scholarly journals Numerical Scrutiny on Friction Factor Characteristics for Protruded Channel under Turbulent Cross-Flow Condition

2019 ◽  
Vol 8 (6S4) ◽  
pp. 146-150
Keyword(s):  
Reynolds Number ◽  
Friction Factor ◽  
Rectangular Channel ◽  
Cross Flow ◽  
Working Fluid ◽  
Nozzle Flow ◽  
Duct Flow ◽  
Enhancement Of Heat Transfer ◽  
Energy Equations ◽  
Volume Method

In the present study, the effect of protrusion pitch, protrusion height, and duct Reynolds number on friction factor characteristics of small rectangular channel with protrusions in cross-flow scheme is analyzed to obtain a suitable configuration of protrusion pattern. Cross-flow is obtained by combining main duct flow (along the direction of length of duct) and nozzle flow which ejects air normal to the protruded bottom wall for the enhancement of heat transfer rate. Finite volume method is used to solve conservation of mass, momentum, and energy equations along with k-ω turbulence model for the analysis of hydraulic performance of protruded channel. Reynolds number from 8360 to 33950 for duct flow and 5120 for nozzle flow are considered with air as working fluid. It is predicted that the friction factor is increased with the increase in protrusion pitch.

scholarly journals Experimental Investigation of Heat Transfer of Nanofluid in Elliptical and Circular Tubes

2021 ◽  
Vol 8 (4) ◽  
pp. 665-671
Author(s):  
Ammar M. Al-Tajer ◽  
Abdulhassan A. Kramallah ◽  
Ali M. Mohsen ◽  
Nabeel Sameer Mahmoud
Keyword(s):  
Reynolds Number ◽  
Nusselt Number ◽  
Friction Factor ◽  
Volume Concentration ◽  
Pressure Change ◽  
Experimental Comparison ◽  
Distilled Water ◽  
Cross Sectional ◽  
Pressure Drops ◽  
Circular Tubes

The paper presents experimental comparison of forced convection for steady state turbulent flow of nanofluid (Al2O3-distilled water) inside circular and elliptical (aspect ratio of 0.75) cross section tubes of identical circumference and tube surface area. Convection coefficient, pressure change, and fiction factor were compared at different Reynolds number (3,000-9,230) with different nanoparticles volume concentration (0.5%, 1.0%, and 1.5%). The results showed that Nusselt number increases with increasing Reynolds number and nanoparticle volume concentration. The pressure drops and friction factor of nanofluid are higher than the distilled water and are increasing as the volume concentration increases. Furthermore, the elliptical tube provided small increase in Nusselt number compared to that of circular cross sectional tube. However, the friction factor in the elliptical tube was slightly higher.

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