scholarly journals Parametric Experiments on Coaxial Airblast Jet Atomization

1990 ◽  
Author(s):  
Zoltan Farago ◽  
Norman Chigier
Keyword(s):  
Reynolds Number ◽  
Flow Rate ◽  
High Speed ◽  
Liquid Sheet ◽  
Velocity Range ◽  
Air Flow Rate ◽  
Flow Conditions ◽  
Number Range ◽  
Reynolds Number Range ◽  
Air Stream

Experiments using high speed, high magnification, and high contrast photography on airblast coaxial atomizers were carried out to study the wave characteristics of liquid surfaces, ligament breakup, and droplet formation. Liquid flow rate was changed from 4 to 50 kg/h, corresponding to a velocity range of 1.5 to 18 m/s, and a Reynolds number range of 1400 to 18000. Air flow rate was varied from 8 to 70 kg/h, corresponding to a velocity range of 22 to 180 m/s, and a Reynolds number range of 13000 to 105000. Tube wall thicknesses of 145 and 320 microns were used. Under different flow conditions, different jet instabilities (capillary, helical and Kelvin-Helmholtz) and different dominant mechanisms of ligament formation were observed. One of the most surprising experimental results is that, under certain flow conditions, the coaxial round liquid jet, surrounded by an axisymmetric annular air stream, forms a flat curling liquid sheet. This liquid sheet breaks into droplet clouds with a frequency of a few thousand Hertz and emits strong oscillations and fluctuating, highly non-axisymmetric vibrations.

Experimental Results of Flow Nozzle Based on PTC 6 for High Reynolds Number

2014 ◽  
Author(s):  
Noriyuki Furuichi ◽  
Kar-Hooi Cheong ◽  
Yoshiya Terao ◽  
Shinichi Nakao ◽  
Keiji Fujita ◽  
...  
Keyword(s):  
Reynolds Number ◽  
High Reynolds Number ◽  
Discharge Coefficient ◽  
Experimental Results ◽  
Flow Conditions ◽  
Number Range ◽  
Discharge Coefficients ◽  
Reynolds Number Range ◽  
Lower Reynolds Number ◽  
High Reynolds

Discharge coefficients for three flow nozzles based on ASME PTC 6 are measured under many flow conditions at AIST, NMIJ and PTB. The uncertainty of the measurements is from 0.04% to 0.1% and the Reynolds number range is from 1.3×105 to 1.4×107. The discharge coefficients obtained by these experiments is not exactly consistent to one given by PTC 6 for all examined Reynolds number range. The discharge coefficient is influenced by the size of tap diameter even if at the lower Reynolds number region. Experimental results for the tap of 5 mm and 6 mm diameter do not satisfy the requirements based on the validation procedures and the criteria given by PTC 6. The limit of the size of tap diameter determined in PTC 6 is inconsistent with the validation check procedures of the calibration result. An enhanced methodology including the term of the tap diameter is recommended. Otherwise, it is recommended that the calibration test should be performed at as high Reynolds number as possible and the size of tap diameter is desirable to be as small as possible to obtain the discharge coefficient with high accuracy.

The effects of surface roughness and tunnel blockage on the flow past spheres

1974 ◽  
Vol 65 (1) ◽  
pp. 113-125 ◽  
Author(s):  
Elmar Achenbach
Keyword(s):  
Surface Roughness ◽  
Reynolds Number ◽  
Drag Coefficient ◽  
Critical Reynolds Number ◽  
Measurement Techniques ◽  
Flow Conditions ◽  
Number Range ◽  
Flow Past ◽  
Reynolds Number Range ◽  
Shedding Frequency

The effect of surface roughness on the flow past spheres has been investigated over the Reynolds number range 5 × 104 < Re < 6 × 106. The drag coefficient has been determined as a function of the Reynolds number for five surface roughnesses. With increasing roughness parameter the critical Reynolds number decreases. At the same time the transcritical drag coefficient rises, having a maximum value of 0·4.The vortex shedding frequency has been measured under subcritical flow conditions. It was found that the Strouhal number for each of the various roughness conditions was equal to its value for a smooth sphere. Beyond the critical Reynolds number no prevailing shedding frequency could be detected by the measurement techniques employed.The drag coefficient of a sphere under the blockage conditions 0·5 < ds/dt < 0·92 has been determined over the Reynolds number range 3 × 104 < Re < 2 × 106. Increasing blockage causes an increase in both the drag coefficient and the critical Reynolds number. The characteristic quantities were referred to the flow conditions in the smallest cross-section between sphere and tube. In addition the effect of the turbulence level on the flow past a sphere under various blockage conditions was studied.

On Separation of a Divergent Flow at Moderate Reynolds Numbers

1976 ◽  
Vol 43 (2) ◽  
pp. 227-231 ◽  
Author(s):  
Yuji Matsuzaki ◽  
Yuan-Cheng Fung
Keyword(s):  
Reynolds Number ◽  
Flow Rate ◽  
Flow Separation ◽  
Reynolds Numbers ◽  
Pressure Differential ◽  
Divergence Angle ◽  
Number Range ◽  
Divergent Flow ◽  
Reynolds Number Range ◽  
Mean Pressure

Flow separation in a divergent channel was investigated in connection with problems of instability and oscillations in physiology at a Reynolds number range much smaller than that usually considered in engineering diffuser design. Experimental data on a divergent flow through a two-dimensional water tunnel in the Reynolds number range Re = 1000 to 6000 are presented. The quantities measured are flow rate, divergence angle, and mean pressure differential between two fixed points at the throat and downstream. In a lower range of divergence angle flow separation is characterized by a sharp decrease in the mean pressure differential when the flow rate is increased continuously and gradually; whereas recovery from separation is signaled by a discontinuous increase in pressure when the flow rate is decreased again. The critical Reynolds numbers for separation and reattachment are detectably different. Some discussion is given about flow separation in external and internal flows.

scholarly journals Net-exergetic, hydraulic and thermal optimization of coaxial heat exchangers using fixed flow conditions instead of fixed flow rates

2021 ◽  
Vol 9 (1) ◽  
Author(s):  
Tobias Blanke ◽  
Markus Hagenkamp ◽  
Bernd Döring ◽  
Joachim Göttsche ◽  
Vitali Reger ◽  
...  
Keyword(s):  
Reynolds Number ◽  
Laminar Flow ◽  
Mass Flow ◽  
Flow Rate ◽  
Heat Exchangers ◽  
Circular Ring ◽  
Flow Conditions ◽  
Flow Rates ◽  
Mass Flow Rates ◽  
Pipe Radius

AbstractPrevious studies optimized the dimensions of coaxial heat exchangers using constant mass flow rates as a boundary condition. They show a thermal optimal circular ring width of nearly zero. Hydraulically optimal is an inner to outer pipe radius ratio of 0.65 for turbulent and 0.68 for laminar flow types. In contrast, in this study, flow conditions in the circular ring are kept constant (a set of fixed Reynolds numbers) during optimization. This approach ensures fixed flow conditions and prevents inappropriately high or low mass flow rates. The optimization is carried out for three objectives: Maximum energy gain, minimum hydraulic effort and eventually optimum net-exergy balance. The optimization changes the inner pipe radius and mass flow rate but not the Reynolds number of the circular ring. The thermal calculations base on Hellström’s borehole resistance and the hydraulic optimization on individually calculated linear loss of head coefficients. Increasing the inner pipe radius results in decreased hydraulic losses in the inner pipe but increased losses in the circular ring. The net-exergy difference is a key performance indicator and combines thermal and hydraulic calculations. It is the difference between thermal exergy flux and hydraulic effort. The Reynolds number in the circular ring is instead of the mass flow rate constant during all optimizations. The result from a thermal perspective is an optimal width of the circular ring of nearly zero. The hydraulically optimal inner pipe radius is 54% of the outer pipe radius for laminar flow and 60% for turbulent flow scenarios. Net-exergetic optimization shows a predominant influence of hydraulic losses, especially for small temperature gains. The exact result depends on the earth’s thermal properties and the flow type. Conclusively, coaxial geothermal probes’ design should focus on the hydraulic optimum and take the thermal optimum as a secondary criterion due to the dominating hydraulics.

Vortex shedding from a circular cylinder in moderate-Reynolds-number shear flow

1980 ◽  
Vol 101 (4) ◽  
pp. 721-735 ◽  
Author(s):  
Masaru Kiya ◽  
Hisataka Tamura ◽  
Mikio Arie
Keyword(s):  
Reynolds Number ◽  
Circular Cylinder ◽  
Shear Flow ◽  
Vortex Shedding ◽  
Transverse Velocity ◽  
Number Range ◽  
Uniform Shear ◽  
Reynolds Number Range ◽  
Moderate Reynolds Number ◽  
Shear Parameter

The frequency of vortex shedding from a circular cylinder in a uniform shear flow and the flow patterns around it were experimentally investigated. The Reynolds number Re, which was defined in terms of the cylinder diameter and the approaching velocity at its centre, ranged from 35 to 1500. The shear parameter, which is the transverse velocity gradient of the shear flow non-dimensionalized by the above two quantities, was varied from 0 to 0·25. The critical Reynolds number beyond which vortex shedding from the cylinder occurred was found to be higher than that for a uniform stream and increased approximately linearly with increasing shear parameter when it was larger than about 0·06. In the Reynolds-number range 43 < Re < 220, the vortex shedding disappeared for sufficiently large shear parameters. Moreover, in the Reynolds-number range 100 < Re < 1000, the Strouhal number increased as the shear parameter increased beyond about 0·1.

scholarly journals Asymmetrical Split-and-Recombine Micromixer with Baffles

Micromachines ◽  
2019 ◽  
Vol 10 (12) ◽  
pp. 844 ◽  
Author(s):  
Wasim Raza ◽  
Kwang-Yong Kim
Keyword(s):  
Reynolds Number ◽  
Geometrical Parameters ◽  
Mixed Species ◽  
Mixing Index ◽  
Number Range ◽  
Mixing Performance ◽  
Curved Channels ◽  
Advection Diffusion Equation ◽  
Advection Diffusion ◽  
Reynolds Number Range

The present work proposes a planar micromixer design comprising hybrid mixing modules of split-and-recombine units and curved channels with radial baffles. The mixing performance was evaluated numerically by solving the continuity and momentum equations along with the advection-diffusion equation in a Reynolds number range of 0.1–80. The variance of the concentration of the mixed species was considered to quantify the mixing index. The micromixer showed far better mixing performance over whole Reynolds number range than an earlier split-and-recombine micromixer. The mixer achieved mixing indices greater than 90% at Re ≥ 20 and a mixing index of 99.8% at Re = 80. The response of the mixing quality to the change of three geometrical parameters was also studied. A mixing index over 80% was achieved within 63% of the full length at Re = 20.

An Experimental Procedure for Determining Both the Density and Flow Rate From Pressure Drop Measurements in a Cylindrical Pipe

2008 ◽  
Vol 130 (9) ◽  
Author(s):  
Ghislain Michaux ◽  
Olivier Vauquelin ◽  
Elsa Gauger
Keyword(s):  
Reynolds Number ◽  
Flow Rate ◽  
Pressure Change ◽  
Gas Mixture ◽  
Gas Extraction ◽  
Cylindrical Pipe ◽  
Flow Area ◽  
Number Range ◽  
Experimental Procedure ◽  
Pressure Drops

An experimental procedure was developed for determining both the density and flow rate of a gas from measurements of pressure drops caused by an abrupt flow area contraction in a cylindrical pipe. Experiments were carried out by varying the density and flow rate of a light gas mixture of air and helium, spanning a Reynolds number range from 0.2×104 to 3.4×104. From experimental results, a procedure was then proposed for evaluating the density from pressure change measurements in the scope of light gas extraction experiments.

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