Measurement of Steady-Flow Instability and Turbulence Levels in Dacron Vascular Grafts

1992 ◽  
Vol 114 (4) ◽  
pp. 521-526 ◽  
Author(s):  
D. G. Shombert
Keyword(s):  
Reynolds Number ◽  
Pressure Drop ◽  
Steady Flow ◽  
Flow Instability ◽  
Dynamic Properties ◽  
Fluid Dynamic ◽  
Vascular Grafts ◽  
Turbulent Regime ◽  
Number Range ◽  
Measured Transition

Fluid dynamic properties of Dacron vascular grafts were studied under controlled steady-flow conditions over a Reynolds number range of 800 to 4500. Knitted and woven grafts having nominal diameters of 6 mm and 10 mm were studied. Thermal anemometry was used to measure centerline velocity at the downstream end of the graft; pressure drop across the graft was also measured. Transition from laminar flow to turbulent flow was observed, and turbulence intensity and turbulent stresses (Reynolds normal stresses) were measured in the turbulent regime. Knitted grafts were found to have greater pressure drop than the woven grafts, and one sample was found to have a critical Reynolds number (Rc) of less than one-half the value of Rc for a smooth-walled tube.

Pressure Drop Measurements for Air Flow Through Open-Cell Aluminum Foam

2004 ◽  
Author(s):  
Nihad Dukhan ◽  
Angel Alvarez
Keyword(s):  
Reynolds Number ◽  
Pressure Drop ◽  
Flow Rate ◽  
Aluminum Foam ◽  
Flow Direction ◽  
The Other ◽  
Turbulent Regime ◽  
Thick Sample ◽  
Open Cell ◽  
Two Samples

Wind-tunnel pressure drop measurements for airflow through two samples of forty-pore-per-inch commercially available open-cell aluminum foam were undertaken. Each sample’s cross-sectional area perpendicular to the flow direction measured 10.16 cm by 24.13 cm. The thickness in the flow direction was 10.16 cm for one sample and 5.08 cm for the other. The flow rate ranged from 0.016 to 0.101 m3/s for the thick sample and from 0.025 to 0.134 m3/s for the other. The data were all in the fully turbulent regime. The pressure drop for both samples increased with increasing flow rate and followed a quadratic behavior. The permeability and the inertia coefficient showed some scatter with average values of 4.6 × 10−8 m2 and 2.9 × 10−8 m2, and 0.086 and 0.066 for the thick and the thin samples, respectively. The friction factor decayed with the Reynolds number and was weakly dependent on the Reynolds number for Reynolds number greater than 35.

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.

Prediction of Pressure Drop for Incompressible Flow Through Screens

1993 ◽  
Vol 115 (2) ◽  
pp. 239-242 ◽  
Author(s):  
E. Brundrett
Keyword(s):  
Reynolds Number ◽  
Pressure Drop ◽  
Incompressible Flow ◽  
Pressure Loss ◽  
Effective Porosity ◽  
Local Damage ◽  
Number Range ◽  
Flow Through ◽  
Careful Specification ◽  
Cosine Law

A new pressure loss correlation predicts flow through screens for the wire Reynolds number range of 10−4 to 104 using the conventional orthogonal porosity and a function of wire Reynolds number. The correlation is extended by the conventional cosine law to include flow that is not perpendicular to the screen. The importance of careful specification of wire diameter for accurate predictions of porosity is examined. The effective porosity is influenced by the shape of the woven wires, by any local damage, and by screen tension.

Hydrogen Combustion Within a Gas Turbine Reheat Combustor

2012 ◽  
Author(s):  
Madhavan Poyyapakkam ◽  
John Wood ◽  
Steven Mayers ◽  
Andrea Ciani ◽  
Felix Guethe ◽  
...  
Keyword(s):  
Pressure Drop ◽  
Natural Gas ◽  
Gas Turbine ◽  
Dynamic Properties ◽  
Fluid Dynamic ◽  
Fold Increase ◽  
Inlet Temperature ◽  
Turbine Performance ◽  
Auto Ignition ◽  
Operating Window

This paper describes a novel lean premixed reheat burner technology suitable for Hydrogen-rich fuels. The inlet temperature for such a combustor is very high and reaction of the fuel/oxidant mixture is initiated through auto-ignition, the delay time for which reduces significantly for Hydrogen-rich fuels in comparison to natural gases. Therefore the residence time available for premixing within the burner is reduced. The new reheat burner concept has been optimized to allow rapid fuel/oxidant mixing, to have a high flashback margin and to limit the pressure drop penalty. The performance of the burner is described, initially in terms of its fluid dynamic properties and then its combustion characteristics. The latter are based upon full-scale high-pressure tests, where results are shown for two variants of the concept, one with a pressure drop comparable to today’s natural gas burners, and the other with a two-fold increase in pressure drop. Both burners indicated that Low NOx emissions, comparable to today’s natural gas burners, were feasible at reheat engine conditions (ca. 20 Bars and ca. 1000C inlet temperature). The higher pressure drop variant allowed a wider operating window. However the achievement of the lower pressure drop burner shows that the targeted Hydrogen-rich fuel (70/30 H2/N2 by volume) can be used within a reheat combustor without any penalty on gas turbine performance.

Mixing Enhancement in a Chaotic Micromixer Using Pulsating Flow

2014 ◽  
Author(s):  
Mohammad Karami ◽  
Mojtaba Jarrahi ◽  
Ebrahim Shirani ◽  
Hassan Peerhossaini
Keyword(s):  
Reynolds Number ◽  
Lyapunov Exponent ◽  
Steady Flow ◽  
Concentration Distribution ◽  
Pulsating Flow ◽  
Chaotic Advection ◽  
Mixing Enhancement ◽  
Mean Flow ◽  
Number Range ◽  
Velocity Amplitude

This study determines the simultaneous effects of spatial disturbance and flow pulsation on micromixing by using three different metrics: concentration distribution, Lyapunov exponent and axial vorticity. Numerical simulations are performed for both steady and pulsating flows through a microchannel made up of C-curved repeating units. Moreover, a straight microchannel is analyzed to compare the effects of chaotic advection and molecular diffusion, the main mechanisms of transverse mixing in the chaotic and straight mixer respectively. Simulations are carried out in the steady flow for the Reynolds number range 1≤Re≤50 and in the pulsating flow for velocity amplitude ratios 1≤β≤2.5, and the ratio of the peak oscillatory velocity component to the mean flow velocity, Strouhal numbers 0.1≤St≤0.5. It was found that chaotic advection improves mixing without significant increase in pressure drop. The analysis of concentration distribution implied that full mixing occurs after Reynolds number 50 in the steady flow. When the flow is pulsatile, small and moderate values of the Strouhal number (0.1≤St≤0.3) and high values of velocity amplitude ratio (β ≥ 2) are favorable conditions for mixing enhancement. Moreover, mixing has an oscillating trend along the microchannel due to the coexistence of regular and chaotic zones in the fluid. These results correlate closely with those obtained using two other metrics, analysis of the Lyapunov exponent and axial vorticity.

Local Flow and Heat Transfer Behavior in Convex-Louver Fin Arrays

1999 ◽  
Vol 121 (1) ◽  
pp. 136-141 ◽  
Author(s):  
N. C. DeJong ◽  
A. M. Jacobi
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Reynolds Number ◽  
Pressure Drop ◽  
Shear Layer ◽  
Local Flow ◽  
Number Range ◽  
Flow And Heat Transfer ◽  
Transfer Behavior ◽  
Strip Geometry

Local and surface-averaged measurements of convection coefficients and core pressure-drop data are provided for an array of convex-louver fins. For a Reynolds number range from 200 to 5400, these data are complemented with a flow visualization study and contrasted with new measurements from a similar offset-strip geometry. The results clarify the effects of boundary layer restarting, shear-layer unsteadiness, spanwise vortices, and separation, reattachment, and recirculation on heat transfer in the convex-louver geometry.

Steady flows in rectangular cavities

1967 ◽  
Vol 28 (4) ◽  
pp. 643-655 ◽  
Author(s):  
Frank Pan ◽  
Andreas Acrivos
Keyword(s):  
Reynolds Number ◽  
Steady Flow ◽  
Creeping Flow ◽  
Large Reynolds Number ◽  
Steady Flows ◽  
Viscous Effects ◽  
Number Range ◽  
Infinite Depth ◽  
Aspect Ratios ◽  
High Reynolds

This paper deals with the steady flow in a rectangular cavity where the motion is driven by the uniform translation of the top wall. Creeping flow solutions for cavities having aspect ratios from ¼ to 5 were obtained numerically by a relaxation technique and were shown to compare favourably with Dean & Montagnon's (1949) similarity solution, as extended by Moffatt (1964), in the region near the bottom corners of a square cavity as well as throughout the major portion of a cavity with aspect ratio equal to 5. In addition, for a Reynolds number range from 20 to 4000, flow patterns were determined experimentally by means of a photographic technique for finite cavities, as well as for cavities of effectively infinite depth. These experimental results suggest that, within finite cavities, the high Reynolds number steady flow should consist essentially of a single inviscid core of uniform vorticity with viscous effects being confined to thin shear layers near the boundaries, while, for cavities of infinite depth, the viscous and inertia forces should remain of comparable magnitude throughout the whole domain even in the limit of very large Reynolds number R.

Mixing Analysis of Laminar Flow in Static Mixers with Circle Grid Fractal Perforated Plate Elements

2014 ◽  
Vol 607 ◽  
pp. 417-421
Author(s):  
Bukhari Manshoor ◽  
Izzuddin Zaman ◽  
Azwan Sapit ◽  
Amir Khalid
Keyword(s):  
Reynolds Number ◽  
Pressure Drop ◽  
Laminar Flow ◽  
Flow Pattern ◽  
Coefficient Of Variation ◽  
Fluid Dynamic ◽  
Perforated Plate ◽  
Static Mixers ◽  
Plate Elements ◽  
Flow Splitting

The static mixers are widely used in many industries to obtain the desired type of mixing. In the context of mixing process, two different fluids and have a different properties will mix in a single equipment to produce an another fluid with a new property. In this research, a new approach of static mixers was proposed for pipeline mixing. The flow pattern, pressure drop and mixing characteristics (coefficient of variation) were carried out by means of computer simulations. The static mixers introduced here consists of a series of perforated plate with circle grids fractal pattern elements. The simulations work were carried out by using a commercial package of Computational Fluid Dynamic (CFD), ANSYS CFX 14.0 software. Three levels of laminar flow with Reynolds numbers (Re) of 100, 200 and 400 respectively had been used to investigate the performance of the static mixers introduced here. The effectiveness of circle grid perforated plate static mixer had been evaluated by comparing the homogeneity level of mixing fluids for each flow simulated. The simulations gave a new insights in the flow pattern in circle grids fractal perforated plate elements. The pressure drop predictions compare favorably with literature data and the coefficient of variation (COV) value for circle grid perforated plate with 50% porosity at Reynolds number 100 was 0.0744 which is out of the range meanwhile at Reynolds number 200 and 400 was 0.0483 and 0.0247 respectively which are in the range of reasonable target for many applications. Mixing in the elements occurs through a combination of flow splitting and shearing at the junctions of successive elements. Besides that, simple installation and manufacturing of this type of static mixers makes the fractal perforated plate’s element an excellent static mixing device.

The Effect of Inner Surface Roughness and Heating on Friction Factor in Horizontal Micro-Tubes

2011 ◽  
Author(s):  
Lap Mou Tam ◽  
Hou Kuan Tam ◽  
Afshin J. Ghajar ◽  
Wa San Ng ◽  
Ieok Wa Wong ◽  
...  
Keyword(s):  
Surface Roughness ◽  
Reynolds Number ◽  
Pressure Drop ◽  
Boundary Conditions ◽  
Friction Factor ◽  
Transition Region ◽  
Isothermal Condition ◽  
Tube Diameter ◽  
Number Range ◽  
Inner Surface

According to Krishnamoorthy et al. [1], pressure drop measurements for horizontal micro-tubes under isothermal condition have been conducted by various researchers in recent years. From their literature review, it was shown that the friction factor in micro-tubes could unanimously be predicted by using macro-scale theory and that there is a need to investigate certain issues like (a) the effect of micro-tube diameter on the transition Reynolds number range and (b) the effect of the inner surface roughness on the friction factor and transition region. Regarding to the point (a), Ghajar et al. [2] measured the pressure drop for a horizontal mini- and micro-tubes with various diameters in the transition region under isothermal condition. Their experimental results indicated the influence of the tube diameter on the friction factor profile and on the transition Reynolds number range. However, regarding to the point (b), the effect of roughness on friction factor profile and transition was still not fully understood. Moreover, only a few studies have investigated the effect of heating on friction factor in micro-tubes, especially, in the transition region. Therefore, in this study, an experimental setup was built to measure pressure drop for horizontal micro-tubes under the isothermal and uniform wall heat flux boundary conditions. Water was used as the test fluid and the test section was glass and stainless steel micro-tubes with various roughness and diameters. From the measurements, the effect of roughness and heating on friction factor and transition region was clearly observed. For friction factor under isothermal condition, compared to the macro-tube, the micro-tube had a narrower transition region due to the roughness and the decrease in the tube diameter delayed the start of transition. For friction factor under heating condition, the laminar and transition data were different from the isothermal case. Heating also delayed the start of transition. The effect of heating was not seen on the turbulent region. For isothermal and heating boundary conditions, the increase of inner surface roughness induced a narrower transition region.

Numerical solutions for steady flow past a circular cylinder at Reynolds numbers up to 100

1970 ◽  
Vol 42 (3) ◽  
pp. 471-489 ◽  
Author(s):  
S. C. R. Dennis ◽  
Gau-Zu Chang
Keyword(s):  
Reynolds Number ◽  
Circular Cylinder ◽  
Steady Flow ◽  
Numerical Solutions ◽  
Equations Of Motion ◽  
Reynolds Numbers ◽  
Reliable Data ◽  
Time Dependent ◽  
Cylinder Surface ◽  
Number Range

Finite-difference solutions of the equations of motion for steady incompressible flow around a circular cylinder have been obtained for a range of Reynolds numbers from R = 5 to R = 100. The object is to extend the Reynolds number range for reliable data on the steady flow, particularly with regard to the growth of the wake. The wake length is found to increase approximately linearly with R over the whole range from the value, just below R = 7, at which it first appears. Calculated values of the drag coefficient, the angle of separation, and the pressure and vorticity distributions over the cylinder surface are presented. The development of these properties with Reynolds number is consistent, but it does not seem possible to predict with any certainty their tendency as R → ∞. The first attempt to obtain the present results was made by integrating the time-dependent equations, but the approach to steady flow was so slow at higher Reynolds numbers that the method was abandoned.

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