Head recovery at submerged abrupt conduit outlets

1988 ◽  
Vol 15 (2) ◽  
pp. 272-274 ◽  
Author(s):  
James A. Kells ◽  
C. D. Smith
Keyword(s):  
Pipe Flow ◽  
Open Channel ◽  
Classical Problem ◽  
Head Loss ◽  
Area Ratio ◽  
Shape Effect ◽  
Velocity Head ◽  
Flow Area ◽  
Downstream Flow ◽  
Primary Variable

The question of an abrupt expansion in a pipeline from one diameter to a larger diameter is a classical problem dealt with in most undergraduate fluid mechanics texts. A problem not dealt with, but which is far more common in practice, is the abrupt expansion at the terminal end of a pipe where the flow expands into an open channel downstream. It is often assumed that the entire velocity head for the pipe flow is lost. This is not necessarily true. In this paper, the experimental study of an abrupt expansion into an open channel is reported. Several different channel shapes are used in an attempt to determine shape effect, if any. It is concluded that the primary variable affecting the head loss is the ratio of the upstream to downstream flow area, called the area ratio. Key words: abrupt expansion, conduit outlet, head recovery, head loss, area ratio.

The Influence of Confinement on the Hydrodynamic Characteristics of a Cylindrical Pillar Within a Microchannel

2015 ◽  
Author(s):  
John O’Connor ◽  
Jeff Punch ◽  
Nicholas Jeffers ◽  
Jason Stafford
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Flow Regime ◽  
Power Law ◽  
Open Channel ◽  
Head Loss ◽  
Heat Fluxes ◽  
Hydrodynamic Characteristics ◽  
Data Set ◽  
Number Range

Microfluidic cooling technologies for future electronic and photonic microsystems require more efficient flow configurations to improve heat transfer without a hydrodynamic penalty. Although conventional microchannel heat sinks are effective at dissipating large heat fluxes, their large pressure drops are a limiting design factor. There is some evidence in the literature that obstacles such as pillars placed in a microchannel can enhance downstream convective heat transfer with some increase in pressure drop. In this paper, measured head-loss coefficients are presented for a set of single microchannels of nominal hydraulic diameter 391μm and length 30mm, each containing a single, centrally-located cylindrical pillar covering a range of confinement ratios, β = 0.1–0.7, over a Reynolds number range of 40–1900. The increase in head-loss due to the addition of the pillar ranged from 143% to 479%, compared to an open channel. To isolate the influence of the pillar, the head-loss contribution of the open channel was extracted from the data for each pillar configuration. The data was curve-fitted to a decaying power-law relationship. High coefficients of determination were recorded with low root mean squared errors, indicating good fits to the data. The data set was surface-fitted with a power law relationship using the Reynolds number based on the cylinder diameter. This was found to collapse the data well below a Reynolds number of 425 to an accuracy of ± 20%. Beyond this Reynolds number an inflection point was observed, indicating a change in flow regime similar to that of a cylinder in free flow. This paper gives an insight into the hydrodynamic behavior of a microchannel containing cylindrical pillars in a laminar flow regime, and provides a practical tool for determining the head-loss of a configuration that has been demonstrated to improve downstream heat transfer in microchannels.

Recirculation in an Annular-Type Jet Pump

1994 ◽  
Vol 116 (4) ◽  
pp. 735-740 ◽  
Author(s):  
Donald F. Elger ◽  
Sam. J. Taylor ◽  
Chyr P. Liou
Keyword(s):  
Recirculation Zone ◽  
Area Ratio ◽  
Secondary Flows ◽  
Jet Pump ◽  
Flow Area ◽  
Pump Design ◽  
A Value

For some annular-type jet pump applications, it is important to avoid formation of a recirculation zone in the mixing region. The goals of this research were to find (i) when recirculation occurs and (ii) the size and location of the resulting recirculation zone. Experiments were performed using air in a straight-walled, annular-type, ducted jet. Area ratio Aj/As varied from 0.39 to 0.89; here, A is flow area, and j and s identify the jet and secondary flows, respectively. Data showed that recirculation correlates with J, where J ≈ Pj/(Pj + Ps), and P is rate of momentum. For the area ratios studied, recirculation begins when J exceeds a value ranging from 0.89 to 0.94. This paper also presents data showing the recirculation zone boundaries and presents a discussion of jet pump design.

Head losses at manholes with a 90° bend

1988 ◽  
Vol 15 (5) ◽  
pp. 851-858 ◽  
Author(s):  
J. Marsalek ◽  
B. J. Greck
Keyword(s):  
Key Words ◽  
Channel Flow ◽  
Open Channel ◽  
Open Channel Flow ◽  
Head Loss ◽  
Pipe Diameter ◽  
Head Losses ◽  
Junction Geometry ◽  
Pressure Changes

Head and pressure changes were studied at manholes with a 90° bend. For pressurized flow, such changes depend only on junction geometry. Among junction parameters, the benching was found particularly important. Full benchings reaching to the pipe crown produced the lowest head losses, particularly when combined with an enlarged pipe diameter at the junction. Head changes in open-channel flow were significantly smaller than those in pressurized flow. Key words: head loss, manholes, sewer junctions, sewer design, sewer hydraulics.

Flow Past a Permeable Manipulator Ring Placed in a Turbulent Pipe Flow

2011 ◽  
Author(s):  
Koji Utsunomiya ◽  
Suketsugu Nakanishi ◽  
Hideo Osaka
Keyword(s):  
Turbulent Flow ◽  
Shear Layer ◽  
Pipe Flow ◽  
Area Ratio ◽  
Turbulent Pipe Flow ◽  
Wall Region ◽  
Open Area ◽  
Mean Flow ◽  
Flow Past ◽  
The Mean

Turbulent pipe flow past a ring-type permeable manipulator was investigated by measuring the mean flow and turbulent flow fields. The permeable manipulator ring had a rectangular cross section and a height 0.14 times the pipe radius. The experiments were performed under four conditions of the open area ratio β of the permeable ring (β = 0.1, 0.2, 0.3 and 0.4) for Reynolds number of 6.2×104. The results indicate that as the open-area ratio increased, the separated shear layer arising from the permeable ring top became weaker and the pressure loss was reduced by increasing fluid flow through the permeable ring. When β was less than 0.2, the velocity gradient was steeper over the permeable ring and in the shear layer near the reattachment region. When β was greater than 0.3, the width of the shear layer showed a relatively large augmentation and the back pressure in the separating region increases. Further, the response of the turbulent flow field to the permeable ring was delayed compared with that of the mean velocity field, and these differences increased with β. The turbulence intensities and Reynolds shear stress profiles near the reattachment point increased near the wall region as β increased, while those peak values that were taken at the locus of the manipulator ring height decreased as β increased.

Partially filled pipes: experiments in laminar and turbulent flow

2018 ◽  
Vol 848 ◽  
pp. 467-507 ◽  
Author(s):  
Henry C.-H. Ng ◽  
Hope L. F. Cregan ◽  
Jonathan M. Dodds ◽  
Robert J. Poole ◽  
David J. C. Dennis
Keyword(s):  
Reynolds Number ◽  
Free Surface ◽  
Turbulent Flow ◽  
Pipe Flow ◽  
Large Scale ◽  
Open Channel ◽  
Streamwise Velocity ◽  
Flow Depth ◽  
Secondary Motion ◽  
Laminar And Turbulent Flow

Pressure-driven laminar and turbulent flow in a horizontal partially filled pipe was investigated using stereoscopic particle imaging velocimetry (S-PIV) in the cross-stream plane. Laminar flow velocity measurements are in excellent agreement with a recent theoretical solution in the literature. For turbulent flow, the flow depth was varied independently of a nominally constant Reynolds number (based on hydraulic diameter, $D_{H}$; bulk velocity, $U_{b}$ and kinematic viscosity $\unicode[STIX]{x1D708}$) of $Re_{H}=U_{b}D_{H}/\unicode[STIX]{x1D708}\approx 30\,000\pm 5\,\%$. When running partially full, the inferred friction factor is no longer a simple function of Reynolds number, but also depends on the Froude number $Fr=U_{b}/\sqrt{gD_{m}}$ where $g$ is gravitational acceleration and $D_{m}$ is hydraulic mean depth. S-PIV measurements in turbulent flow reveal the presence of secondary currents which causes the maximum streamwise velocity to occur below the free surface consistent with results reported in the literature for rectangular cross-section open channel flows. Unlike square duct and rectangular open channel flow the mean secondary motion observed here manifests only as a single pair of vortices mirrored about the vertical bisector and these rollers, which fill the half-width of the pipe, remain at a constant distance from the free surface even with decreasing flow depth for the range of depths tested. Spatial distributions of streamwise Reynolds normal stress and turbulent kinetic energy exhibit preferential arrangement rather than having the same profile around the azimuth of the pipe as in a full pipe flow. Instantaneous fields reveal the signatures of elements of canonical wall-bounded turbulent flows near the pipe wall such as large-scale and very-large-scale motions and associated hairpin packets whilst near the free surface, the signatures of free surface turbulence in the absence of imposed mean shear such as ‘upwellings’, ‘downdrafts’ and ‘whirlpools’ are present. Two-point spatio-temporal correlations of streamwise velocity fluctuation suggest that the large-scale coherent motions present in full pipe flow persist in partially filled pipes but are compressed and distorted by the presence of the free surface and mean secondary motion.

scholarly journals A Non-Dimensional Conceptual Design Procedure for the Vaneless Volutes of Radial Inflow Turbines

1991 ◽  
Author(s):  
A. Whitfield ◽  
A. B. Mohd Noor
Keyword(s):  
Mach Number ◽  
Conceptual Design ◽  
Swirling Flow ◽  
Design Procedure ◽  
Area Ratio ◽  
Working Fluid ◽  
Flow Area ◽  
Cross Sectional ◽  
The Absolute ◽  
Inlet Conditions

The requirements for the volute of a radial inflow turbine are that it should collect the working fluid, deliver it to the turbine rotor as efficiently as possible and provide the desired rotor inlet conditions. The overall performance requirements of the turbine leads to the rotor design and the identification of the desired flow conditions at rotor inlet in terms of the magnitude and direction of the absolute Mach number, see Whitfield (1990). The volute must then be designed to ensure that the desired rotor inlet conditions are attained. A non-dimensional conceptual design procedure for a vaneless turbine volute is described. Based on a knowledge of the magnitude and direction of the absolute Mach number at rotor inlet the overall dimensions of the volute in terms of the radius ratio and flow area ratio are first established. The overall design is then developed to provide the variation of the volute centroid radius and area ratio with azimuth angle. A trapezoidal cross-sectional shape is then used to establish the outer dimensions of the volute. The non-dimensional design procedure assumes a one-dimensional compressible flow and as such relies on the empirical specification of the dissipation of angular momentum, the dissipation of energy, and the deviation of the swirling flow from that of a free vortex. The effect of the uncertainties associated with the empirical data on the volute design geometry is assessed.

scholarly journals The Study on Internal Flow Characteristics of Disc Filter under Different Working Condition

2021 ◽  
Vol 11 (16) ◽  
pp. 7715
Author(s):  
Yanbing Chi ◽  
Peiling Yang ◽  
Zixuan Ma ◽  
Haiying Wang ◽  
Yuxuan Liu ◽  
...  
Keyword(s):  
Irrigation System ◽  
Flow Characteristics ◽  
Head Loss ◽  
Main Flow ◽  
Horizontal Direction ◽  
Macroscopic Model ◽  
Hydraulic Characteristics ◽  
Flow Area ◽  
Micro Irrigation ◽  
Filter Bed

A disc filter (DF) is an important component in a micro irrigation system. However, it has a high head loss and low filtration efficiency, which can lead to the inoperability of micro irrigation systems. To improve the filtration ability and to decrease the pressure loss of the irrigation system, it is necessary to internalize the hydraulic characteristics of DFs. In this study, the filter bed of a DF was divided into three parts, i.e., upper, middle, and lower, which were wrapped with a transparent film. The wrapped part was completely blocked. The purpose was to analyze the hydraulic characteristics of different clogged conditions in three types of filters under four types of flows. In addition, we attempted to simulate the filter operation process with computational fluid dynamics, based on two aspects—a macroscopic model and a simplified model. The results showed that the patterns of head loss among all of the DFs was consistent, and the macroscopic model that treated filter bed as a porous medium could express the measured results. The macroscopic models observed that there was a circular flow in the DF, and the flow velocity presented a symmetrical distribution in a horizontal direction. The middle of the filter element appeared in a high-pressure area and demonstrated the highest head loss, which may be the main flow area of the DF, and the inner flow characteristics of the DF were consistent under different conditions. The simplified models showed that the main flow area is near the filter bed in the inner DF, and the flow is tangent to the filter bed between 45 and 90 degrees in a horizontal direction. The uneven distribution of velocity and pressure on the filter bed might be necessary factors to impact filter efficiency.

Decline of residual chlorine in artificial stream flow sustained by reclaimed wastewater: field study in Sapporo

2003 ◽  
Vol 3 (3) ◽  
pp. 79-84
Author(s):  
N. Funamizu ◽  
T. Iwamoto ◽  
T. Takakuwa
Keyword(s):  
Mathematical Model ◽  
Pipe Flow ◽  
Open Channel ◽  
Wastewater Reuse ◽  
Chlorine Concentration ◽  
Residual Chlorine ◽  
Flow Section ◽  
Reclaimed Wastewater ◽  
Environmental Application ◽  
Hourly Variation

Among several applications of urban wastewater reuse, use of reclaimed wastewater to sustain stream flows has become attractive especially in urban areas. This environmental application of reclaimed wastewater occupies about 32% of total wastewater reuse in Japan. In this paper, residual chlorine in the full-scale project for environmental application in Sapporo was discussed. The field survey of residual chlorine showed that there was the hourly variation of residual chlorine concentration in the river and this variation depended on the hourly variation in composition of chlorine species in the effluent of the WWTP, and that the rate of decline of residual chlorine in the open channel section was greater than that in the pipe flow section. The simple mathematical model was developed for describing the decline process on the basis of the dispersion model including two reactions: interaction of residual chlorine and organic matter in reclaimed water and interaction of chlorine and pipe surface or bio-film. The expressions for these two reaction rates were obtained by lab-scale experiments and these calibration results showed that consumption rate of residual chlorine in the aqueous phase was comparable to the rate on the pipe wall in the pipe flow section, and that residual chlorine in the open channel was consumed mainly by bio-film. The calibrated mathematical model yielded a good estimation of the chlorine concentration profile.

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