On the Calibration of Irwin Probes for Flow in Rectangular Ducts With Different Aspect Ratios

2017 ◽  
Vol 139 (10) ◽  
Author(s):  
Raquel Faria ◽  
Almerindo D. Ferreira ◽  
A. M. G. Lopes ◽  
Antonio C. M. Sousa
Keyword(s):  
Experimental Data ◽  
Friction Coefficient ◽  
Turbulent Flow ◽  
Flow Region ◽  
Reynolds Numbers ◽  
Hydraulic Diameter ◽  
Equivalent Diameter ◽  
Aspect Ratios ◽  
Cross Section Area ◽  
Section Area

In this work, the suitability of pressure probes, commonly known as Irwin probes, to determine the local wall shear stress was evaluated for steady turbulent flow in rectangular ducts. Pressure measurements were conducted in the fully developed flow region of the duct and both the influence of duct aspect ratio (AR) (from 1:1.03 to 1:4.00) and Reynolds number (from 104 to 9 × 104) on the mean characteristics of the flow were analyzed. In addition, the sensitivity of the longitudinal and transversal placement of the Irwin probes was verified. To determine the most appropriate representation of the experimental data, three different characteristic lengths (l*) to describe Darcy's friction coefficient were investigated, namely: hydraulic diameter (Dh), square root of the cross section area (√A), and laminar equivalent diameter (DL). The comparison of the present experimental data for the range of tested Re numbers against the results for turbulent flow in smooth circular tubes indicates similar trends independently of the AR. The selection of the appropriate l* to represent the friction coefficient was found to be dependent on the AR of the duct, and the three tested scales present similar performance. However, the hydraulic diameter, being the commonly employed to compute turbulent flow in rectangular ducts, is the selected characteristic length scale to be used in the present study. A power function-based calibration equation is proposed for the Irwin probes, which is valid for the range of ARs and Reynolds numbers tested.

Enhancement of Fluid Mixing in a Double T-Shaped Micromixer by Periodic Disturbances of Pressure

2011 ◽  
Vol 339 ◽  
pp. 118-123 ◽  
Author(s):  
Huan Chao Chiu ◽  
Jerry M Chen
Keyword(s):  
Reynolds Numbers ◽  
Mixing Efficiency ◽  
Low Reynolds Numbers ◽  
Periodic Disturbances ◽  
Side Channels ◽  
Aspect Ratios ◽  
Cross Section Area ◽  
Section Area ◽  
Channel Aspect Ratio ◽  
Phase Angles

This paper presents numerical simulations of mixing phenomena in a double T-shaped micromixer to which periodic pressure disturbances are added to enhance the mixing efficiency. The fluids were brought in contact at the upper T-junction. The pressure disturbances of various frequencies (0-50 Hz) and phase angles were introduced through the side channels of the lower T-structure. The simulations were carried out for microchannels having the same cross-section area but with different aspect ratios (1.6-10) at low Reynolds numbers (2.9-8.8). It is found that the mixing efficiency rapidly increases with an increase of the oscillation frequency in the lower range (0-8 Hz) to reach a maximum and then decreases in the higher frequency range except for the in-phase disturbance. The mixing is enhanced most significantly as the two pressure disturbances oscillate exactly out of phase. The effects due to channel aspect ratio and inlet velocity are also discussed.

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.

Heat Transfer for High Aspect Ratio Rectangular Channels in a Stationary Serpentine Passage With Turbulated and Smooth Surfaces

2013 ◽  
Author(s):  
Matthew A. Smith ◽  
Randall M. Mathison ◽  
Michael G. Dunn
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Aspect Ratio ◽  
Flow Behavior ◽  
Reynolds Numbers ◽  
Hydraulic Diameter ◽  
Internal Cooling ◽  
Number Range ◽  
Aspect Ratios ◽  
Parallel Configuration

Heat transfer distributions are presented for a stationary three passage serpentine internal cooling channel for a range of engine representative Reynolds numbers. The spacing between the sidewalls of the serpentine passage is fixed and the aspect ratio (AR) is adjusted to 1:1, 1:2, and 1:6 by changing the distance between the top and bottom walls. Data are presented for aspect ratios of 1:1 and 1:6 for smooth passage walls and for aspect ratios of 1:1, 1:2, and 1:6 for passages with two surfaces turbulated. For the turbulated cases, turbulators skewed 45° to the flow are installed on the top and bottom walls. The square turbulators are arranged in an offset parallel configuration with a fixed rib pitch-to-height ratio (P/e) of 10 and a rib height-to-hydraulic diameter ratio (e/Dh) range of 0.100 to 0.058 for AR 1:1 to 1:6, respectively. The experiments span a Reynolds number range of 4,000 to 130,000 based on the passage hydraulic diameter. While this experiment utilizes a basic layout similar to previous research, it is the first to run an aspect ratio as large as 1:6, and it also pushes the Reynolds number to higher values than were previously available for the 1:2 aspect ratio. The results demonstrate that while the normalized Nusselt number for the AR 1:2 configuration changes linearly with Reynolds number up to 130,000, there is a significant change in flow behavior between Re = 25,000 and Re = 50,000 for the aspect ratio 1:6 case. This suggests that while it may be possible to interpolate between points for different flow conditions, each geometric configuration must be investigated independently. The results show the highest heat transfer and the greatest heat transfer enhancement are obtained with the AR 1:6 configuration due to greater secondary flow development for both the smooth and turbulated cases. This enhancement was particularly notable for the AR 1:6 case for Reynolds numbers at or above 50,000.

First approximations to the energy release of giant dikes at Cerberus Fossae, Mars 

2021 ◽  
Author(s):  
Sam Rivas-Dorado ◽  
Javier Ruiz ◽  
Ignacio Romeo
Keyword(s):  
First Episode ◽  
Aspect Ratios ◽  
Cross Section Area ◽  
Section Area ◽  
Induced Fractures ◽  
Seismic Moment Release ◽  
Rock Mechanical Properties ◽  
Lower Size ◽  
Insight Mission ◽  
Cerberus Fossae

<p>Historical dike intrusions in the vicinity of volcanic edifices on Earth are known to produce swarms of seismic activity with cumulative seismic moments between 1·10<sup>12</sup> and 1·10<sup>20</sup> Nm, equivalent to moment magnitudes between 2 and 7. On Mars, long linear graben systems are likely to host giant dike complexes at depth, which possibly produced significant seismicity during their intrusion. Not only this, but dike intrusions are also candidates to produce crustal seismicity at present day, which may be detected during the lifespan of the InSight mission. In this work we infer the possible geometry of dikes underneath Cerberus Fossae, and make estimations of the energy released during their intrusion.</p><p>We used cross section area balancing on topographic profiles orthogonal to several of the Cerberus Fossae graben to estimate proxies for the geometry of the underlying dikes (aperture, height, depth, etc.). This technique has already been used to approximate dike properties at the nearby Elysium Fossae, with successful results. At Cerberus Fossae, the obtained dike aspect ratios are consistent with sublinear scaling, which is characteristic of fluid-induced fractures (as expected for dikes). These results support the presence of giant dikes underneath Cerberus, which may be up to 700 m thick, 140 km long, and have heights of up to 20 km.</p><p>Additionally, we used the inferred geometries and assumptions about the host rock mechanical properties to estimate various energy quantities related to dike intrusion, and compared them with the energy releases in terrestrial diking episodes. Two calculations are of special interest; M<sub>d</sub>, the energy associated to dike inflation, and M<sub>s</sub>, an approximation to the cumulative seismic moment release. The obtained M<sub>d</sub> values are between 3.1·10<sup>20</sup> and 5.0·10<sup>21</sup> Nm, and are 1 to 2 orders of magnitude larger than the equivalent moments in terrestrial events. M<sub>s</sub> was calculated from M<sub>d</sub> with two key assumptions; 1) that all aseismic energy was released by the dike, and 2) values of seismic efficiency (the percentage of seismic relative to the total energy released) based on terrestrial examples. The obtained M<sub>s</sub> are between 6.3·10<sup>19</sup> and 2.2·10<sup>21</sup> Nm, which are equivalent to moment magnitudes of 6.5 and 7.9. These are comparable to, albeit slightly larger than, the cumulative moments of some of the largest terrestrial diking events, such as the first episode in the Manda-Hararo sequence (Ethiopia, 2005, M<sub>s </sub>= 6.2) or the Miyake-jima event (Japan, 2000, M<sub>s </sub>= 6.8).</p><p>The Elysium volcanic province is thought to have been active until very recent times, and possibly even at present day. If this is the case, then intrusions in the lower size of the spectrum investigated at Cerberus, and smaller-sized events, may be detected by InSight as a series of crustal seismic events with cumulative moment magnitudes <6. Further research is needed to fully assess the validity of the comparisons between terrestrial and Martian events, and the possible energy releases of dike-induced marsquakes.</p>

A Study of Flow of Plastics Through Pipes

1946 ◽  
Vol 13 (2) ◽  
pp. A101-A105
Author(s):  
R. C. Binder ◽  
J. E. Busher
Keyword(s):  
Experimental Data ◽  
Reynolds Number ◽  
Friction Coefficient ◽  
Laminar Flow ◽  
Turbulent Flow ◽  
Dynamic Viscosity ◽  
Apparent Viscosity ◽  
Turbulent Viscosity ◽  
Yield Value

Abstract The pipe friction coefficient for true fluids is usually expressed as a function of Reynolds number. This method of organizing data has been extended to tests on the flow of different suspensions which behaved as ideal plastics in the laminar-flow range and as true fluids in the turbulent-flow range. In the laminar-flow range, Reynolds number below about 2100, the denominator in Reynolds number is taken as the apparent viscosity. The apparent viscosity can be determined from the yield value and the coefficient of rigidity. In the turbulent-flow range, the denominator in Reynolds number is an equivalent or turbulent viscosity equal to the dynamic viscosity of a true fluid having the same friction coefficient, velocity, diameter, and density as that of the plastic. The various experimental data on plastics correlate well with this extension of the method for true fluids.

Heat Transfer Characteristic Inside Two-Pass Variable Cross-Section Channels With Ribs and Bleed Holes

2004 ◽  
Author(s):  
Xiangyun Liu ◽  
Shuiting Ding ◽  
Zhi Tao ◽  
Guoqiang Xu
Keyword(s):  
Heat Transfer ◽  
Cross Section ◽  
Transfer Characteristic ◽  
Reynolds Numbers ◽  
Variable Cross Section ◽  
Heat Transfer Process ◽  
Variable Cross ◽  
Relative Roughness ◽  
Cross Section Area ◽  
Section Area

Heat transfer characteristics were experimentally studied for two-pass channels with variable cross-section with and without ribs. Rectangular ribs were placed symmetrically on two opposite walls with attack angles of 90° and 60° to the main flow. The bleed holes were only distributed on the rib roughened surface along the second pass. The cross-section area of the channel varied in the way that it increased along the first pass and decreased along the second. The relative roughness heights were 0.092 and 0.123; the relative roughness pitches were 10 and 20. The experiments were carried out at Reynolds numbers from 7100 to 60000. Analysis of the experimental results may lead to the following conclusions: (1) The heat transfer was enhanced by the presence of variable cross section. (2) The 60° ribs was not necessarily the optimistic option as published in the literature, test showed that 90° ribs produced a hither heat transfer for the relative roughness height of 0.092. (3) For up to 30% of bleeding were outlet, the existence of bleed holes enhanced the heat transfer process.

On Identification of Leaky Pipeline Parameters via Monte Carlo Simulation

2011 ◽  
Author(s):  
Kamal A. F. Moustafa ◽  
Samir A. Emam ◽  
Yousef S. Haik
Keyword(s):  
Monte Carlo Simulation ◽  
Monte Carlo ◽  
Friction Coefficient ◽  
Pressure Head ◽  
Localization Accuracy ◽  
Cross Section Area ◽  
Section Area ◽  
Leaky Pipeline ◽  
Minimum Number ◽  
Leak Localization

In this study, a numerical simulation using inverse pipeline analysis is conducted for the localization and quantification of leak using minimum number of measurement points of a leaky pipeline. The friction coefficient and leak cross section area were also identified by window marching technique using only the pressure head at one end of the pipeline and the flow rate measurements at the other end of the pipeline. The Monte Carlo simulation approach is applied to identify the pipeline parameters by minimizing an objective function that represents the mismatch between the measured and numerically modeled pipeline variables. The simulation results are able to identify and localize the leak location as well as the friction coefficient and leak across section area. The effect of additive measurement noise on the leak localization accuracy is also investigated.

scholarly journals Use Of Pulsed IR Thermography For Determination Of Size And Depth Of Subsurface Defect Taking Into Account The Shape Of Its Cross-Section Area

2015 ◽  
Vol 60 (2) ◽  
pp. 615-620 ◽  
Author(s):  
O. Wysocka-Fotek ◽  
M. Maj ◽  
W. Oliferuk
Keyword(s):  
Cross Section ◽  
Rectangular Cross Section ◽  
Time Derivative ◽  
Equivalent Diameter ◽  
Ir Thermography ◽  
Flat Bottom ◽  
Surface Distribution ◽  
Cross Section Area ◽  
Section Area

Abstract The paper is devoted to reconstruction of size and depth (distance from the tested surface) of artificial defects with square and rectangular cross-section areas using the pulsed IR thermography. Defects in form of flat-bottom holes were made in austenitic steel plate. The defect size was estimated on the basis of surface distribution of the time derivative of the temperature. In order to asses the depth of defects with considered geometries on the basis of calibration relations (i.e. dependence of time of contrast maximum vs. defect depth for given defect diameter) obtained for circular defects, the ‘equivalent diameter’ describing not only the defect cross-section area but also its shape was assigned. It has been shown that presented approach gives satisfactory results.

CFD Study on the Effects of Nozzle Number on Turbulent Flow and Energy Separation in a Ranque-Hilsch Vortex Tube

2013 ◽  
Vol 465-466 ◽  
pp. 505-509
Author(s):  
Nilotpala Bej ◽  
Kalyan Prasad Sinhamahapatra
Keyword(s):  
Turbulent Flow ◽  
Cross Section ◽  
Vortex Tube ◽  
Internal Flow ◽  
Energy Separation ◽  
Counter Flow ◽  
Cross Section Area ◽  
Section Area ◽  
Compressible Turbulent Flow ◽  
Nozzle Cross Section

In this paper, the effects of nozzles number on the internal flow in a counter flow Ranque-Hilsch vortex tube (RHVT) are studied. A 3D structured discretized model of a counter flow multi nozzle RHVT is developed to study the dynamic behaviour of the highly swirling, compressible turbulent flow. Simulations of the turbulent flow are performed using standardk-ε model with 2, 4, 6 and 8 number of nozzles at the computational inlet. Total temperature profiles and total energy separations are studied as a function of nozzle number and total nozzle cross section area. It is observed that cooling effect increases as the nozzle number increases irrespective of total nozzle cross section area.

Turbulent Flow in D-Type Corrugated Pipes: Flow Pattern and Friction Factor

2012 ◽  
Vol 134 (12) ◽  
Author(s):  
H. Stel ◽  
A. T. Franco ◽  
S. L. M. Junqueira ◽  
R. H. Erthal ◽  
R. Mendes ◽  
...  
Keyword(s):  
Reynolds Number ◽  
Turbulent Flow ◽  
Flow Pattern ◽  
Friction Factor ◽  
Reynolds Numbers ◽  
Important Change ◽  
Groove Width ◽  
Simple Method ◽  
Pressure Drag ◽  
Aspect Ratios

Turbulent flow in d-type corrugated pipes of various aspect ratios has been numerically investigated in terms of flow pattern and friction factor, for Reynolds numbers ranging from 5000 to 100,000. The present numerical model was verified by comparing the friction factor with experimental and numerical results from the literature. The numerical analysis suggested that d-type behavior exists for groove aspect ratios up to w/k = (groove width/rib height) = 2 independent of the pitch. However, for a ratio of w/k = 3 an important change in the flow pattern occurs so that the pressure drag exerted by the groove walls becomes important. It is shown that the friction factor is independent of the groove height as long as the flow is similar to a flow in a d-type corrugated pipe. Moreover, the friction factor curve for d-type pipes shows a logarithmic behavior as function of the Reynolds number, so that a simple method can be used to derive an expression for the friction factor as a function of the Reynolds number and the relative groove width only. The results may be useful to engineering projects that require a better prediction of the friction factor in d-type corrugated pipes.

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