Experimental Study of the Influence of Different Weir Types on the Rate of Air Entrainment

2003 ◽  
Vol 38 (4) ◽  
pp. 769-783 ◽  
Author(s):  
M. Emin Emiroglu ◽  
Ahmet Baylar
Keyword(s):  
Experimental Study ◽  
Air Entrainment ◽  
Entrainment Rate ◽  
Empirical Correlations ◽  
Air Entrainment Rate ◽  
Maximum Penetration Depth ◽  
Longitudinal Slope ◽  
Maximum Penetration ◽  
Labyrinth Weirs ◽  
Better Than

Abstract Aeration is used in water treatment to alter the concentration of dissolved gases, to strip volatile organics, and to reduce tastes and odours. This can be obtained by creating turbulence in the water. One method of producing such turbulence is via the overflow jets downstream of weir structures. This paper investigates the effect of varying weir types on the air entrainment rate. Empirical correlations predicting the maximum penetration depth and air entrainment rate were developed for different weir types. It is demonstrated that the air entrainment rate of the broad-crested weirs is generally much better than for the sharp-crested weir and the labyrinth weirs. The air entrainment rate increased as the weir longitudinal slope of the broad-crested weirs and the weir sill slope of the labyrinth weirs became larger.

scholarly journals An Investigation on the Use of Venturi Weirs as an Aerator

2003 ◽  
Vol 38 (4) ◽  
pp. 753-767 ◽  
Author(s):  
Ahmet Baylar
Keyword(s):  
Air Entrainment ◽  
Gas Transfer ◽  
Entrainment Rate ◽  
Unit Discharge ◽  
Air Entrainment Rate ◽  
Throat Width ◽  
Better Than ◽  
Rectangular Notch ◽  
Good Agreement ◽  
Free Overfall

Abstract The most classic example of a hydraulic structure where gas transfer occurs is a weir. Transfer of gases between the atmosphere and river water can occur in a free overfall jet from a weir. A free overfall jet from a weir plunging into downstream water causes entrainment of air bubbles if the free overfall jet velocity exceeds the critical value where aeration occurs. This paper investigates the free overfall jets from Venturi and rectangular notch weirs and their effect on air entrainment rate. A Venturi weir was placed at the upstream channel end in order to increase the flow velocity of the free overfall jet and, in turn, to increase air entrainment. It was demonstrated that the air entrainment rate of the Venturi weir is significantly better than the rectangular notch weir, and this advantage becomes more pronounced as the throat width of the Venturi weir is decreased. These results demonstrated that Venturi weirs can be used as highly effective aerators in streams, rivers, constructed channels, fish hatcheries, water treatment plants, etc. Moreover, a regression equation was obtained for the Venturi weirs, relating air entrainment rate to unit discharge, weir crest width, drop height and throat width of Venturi weir. There was good agreement between the measured air entrainment rates and the values computed from the predictive equation.

Role of Nozzles with Air Holes in Air Entrainment by a Water Jet

2003 ◽  
Vol 38 (4) ◽  
pp. 785-795 ◽  
Author(s):  
M. Emin Emiroglu ◽  
Ahmet Baylar
Keyword(s):  
Experimental Study ◽  
Nozzle Exit ◽  
Negative Pressure ◽  
Air Entrainment ◽  
Water Jet ◽  
Entrainment Rate ◽  
Air Bubbles ◽  
Air Entrainment Rate ◽  
Plunging Water Jet

Abstract When a water jet impinges a pool of water at rest, air bubbles may be entrained and carried a distance below the pool's surface. This process is called plunging water jet entrainment and aeration. This paper describes an experimental study of the air entrainment rate of circular nozzles with and without air holes, and in particular, the effect of varying numbers and positions of air holes and distance between the location of the air holes and nozzle exit. A negative pressure occurred due to the air holes on the circular nozzles. This phenomenon affected air entrainment. The differences in air entrainment rate were related to changes in the jet shape. It was demonstrated that the air entrainment rates of the circular nozzles with air holes were significantly higher than those of circular nozzles without air holes.

scholarly journals Air entrainment by inclined circular plunging water jets with various impingement heights

2020 ◽  
Vol 20 (8) ◽  
pp. 3478-3486
Author(s):  
Yiyi Ma ◽  
Luchen Zhang ◽  
Yu Yang ◽  
Ping Wei
Keyword(s):  
Experimental Study ◽  
Surface Roughness ◽  
Water Surface ◽  
Jet Impingement ◽  
Air Entrainment ◽  
Entrainment Rate ◽  
Water Jets ◽  
Air Entrainment Rate ◽  
Jet Breakup ◽  
Early Increase

Abstract This paper presents an experimental study on air entrainment by inclined circular plunging water jets issued from long nozzles with various jet impingement heights up to 6.1 m. Particular attention was paid to the jets having a large impingement height, and which disintegrated into small droplets before reaching the water surface. The dominant sizes and velocities of the droplets generated by jet breakup were 1–4 mm and 4–9 m/s. The results show that for plunging water jets having the same hydraulic head, the air entrainment rate increased as the jet impingement height at first grew, then dropped as the jet impingement height kept increasing. The early increase in the air entrainment rate was due to the growth of jet surface roughness, while the later decrease was caused by the water jet disintegration. The momentum of the plunging jet decreased dramatically due to the reduced mass and the significant energy dissipation through the atmosphere caused by jet disintegration. This led to a much smaller penetration depth and air entrainment rate compared to with a continuous jet.

The effect of sharp-crested weir shape on air entrainment

2002 ◽  
Vol 29 (3) ◽  
pp. 375-383 ◽  
Author(s):  
Ahmet Baylar ◽  
M Emin Emiroglu
Keyword(s):  
Air Entrainment ◽  
Entrainment Rate ◽  
Air Bubbles ◽  
Cross Sectional ◽  
Aquatic Life ◽  
Plunge Pool ◽  
Air Entrainment Rate ◽  
Rivers And Streams ◽  
Entrained Air ◽  
Better Than

Aeration in the waters of rivers and streams is very important to the quality and existence of aquatic life. If the overfall jets downstream of weir structures plunges into a plunge pool, entrained air bubbles will contribute to aeration. This paper investigates sharp-crested weirs having different cross-sectional geometry and their effect on the air entrainment rate. It is demonstrated that the air entrainment rate of a 30° triangular sharp-crested weir is better than that of the other sharp-crested weirs tested. Moreover, variation in the number of V-notches over the width of the weir plate was studied for 30° triangular sharp-crested weirs. The 30° triangular sharp-crested weir with two V-notches was found to have higher values of air entrainment rate.Key words: aeration, air entrainment rate, plunging overfall jet, sharp-crested weir.

The Effect of Nozzle Type on Air Entrainment by Plunging Water Jets

2002 ◽  
Vol 37 (3) ◽  
pp. 599-612 ◽  
Author(s):  
Tamer Bagatur ◽  
Ahmet Baylar ◽  
Nusret Sekerdag
Keyword(s):  
Penetration Depth ◽  
Oxygen Transfer ◽  
Free Water ◽  
Air Entrainment ◽  
Water Jet ◽  
Transfer Efficiency ◽  
Entrainment Rate ◽  
Water Jets ◽  
Air Entrainment Rate ◽  
Oxygen Transfer Efficiency

Abstract In this study, for the plunging water jet aeration system using various inclined nozzle types, bubble penetration depth, air entrainment rate, water jet expansion, effect of water jet circumference at impact point, oxygen transfer coefficient and oxygen transfer efficiency which changed depending on the water jet velocity, were researched in an air-water system. Numerous studies were conducted with circular nozzles. The present study describes new experiments performed with different nozzle types. Three types of nozzles were examined, i.e., those with circular, ellipse and rectangle duct with rounded ends. Experimental results showed that water jets produced with ellipse and rectangle duct with rounded ends nozzles have very different flow characteristics, entrainment patterns on free water jet surface, and submerged water jet region within the receiving tank. Higher air entrainment rate and oxygen transfer efficiency was observed in the rectangle duct with rounded ends nozzle due to water jet expansion. Bubble penetration depth, however, is lower for the rectangle duct with rounded ends nozzle than for the other nozzles. The ellipse nozzle provided the highest bubble penetration depth. These results showed that it is appropriate to use ellipse nozzle in aeration of deep pool and rectangle duct with rounded ends nozzle in the applications where high bubble concentration is desirable.

scholarly journals Estimating Flow Characteristics of Different Weir Types and Optimum Dimensions of Downstream Receiving Pool

2010 ◽  
Vol 58 (4) ◽  
pp. 245-260 ◽  
Author(s):  
M. Emiroglu
Keyword(s):  
Penetration Depth ◽  
Open Channel ◽  
Flow Characteristics ◽  
Channel System ◽  
Maximum Penetration Depth ◽  
Jet Trajectory ◽  
Maximum Penetration ◽  
Labyrinth Weirs ◽  
Bubble Zone ◽  
Free Overfall

Estimating Flow Characteristics of Different Weir Types and Optimum Dimensions of Downstream Receiving PoolThis paper presents the results of a laboratory study on the flow characteristics of sharp-crested weirs, broad-crested weirs, and labyrinth weirs. The variation of the maximum bubble penetration depth for different weir types is investigated depending on overfall jet expansion, discharge, and drop height. Moreover, most efficient depth, length and width of the downstream receiving pool in an open channel system are studied by considering the penetration depth, overfall jet expansion, jet trajectory and the bubble zone. The results show that overfall jet expansion at the labyrinth weirs is significantly wider than the rectangular sharp-crested weirs and the trapezoidal sharp-crested weir. It is demonstrated that the labyrinth weirs have the lowest values of bubble penetration depth among the weirs tested. Furthermore, it is found that the rectangular and the trapezoidal weirs are observed to have the highest bubble penetration depth among all weirs. Consequently, empirical equations are obtained for predicting the maximum penetration depth of bubbles, trajectory of free overfall nappe, jet expansion of free overfall nappe, and the length of the bubble zone.

Estimation of the air entrainment characteristics of a transient high-pressure diesel spray

2005 ◽  
Vol 219 (8) ◽  
pp. 1025-1036 ◽  
Author(s):  
W Choi ◽  
B-C Choi
Keyword(s):  
High Pressure ◽  
Particle Image Velocimetry ◽  
Particle Image ◽  
Air Entrainment ◽  
Diesel Spray ◽  
Entrainment Rate ◽  
Recirculating Flow ◽  
Air Entrainment Rate ◽  
Image Velocimetry ◽  
Ambient Gas

The air entrainment characteristics of a transient high-pressure diesel spray were investigated with respect to time and location for injection pressures ( Pinj = 76 or 137 MPa) and ambient density (ρa = 15.6 kg/m3) under the non-evaporating condition (303 K). A particle image velocimetry analysis was introduced and some parameters were defined to express air entrainment characteristics. The air entrainment rate increased greatly as the flow moved downstream owing to a larger contact surface area and a recirculating flow. Higher pressure led to a greater entrainment rate with higher effectiveness. The speed (spray tip and front ambient gas) and volume (spray and laterally entrained gas) relations suggested the possibility for the renewal against the lateral-dominant entrainment mechanism.

Air entrainment rate and holdup in the Jameson cell

2007 ◽  
Vol 20 (8) ◽  
pp. 761-765 ◽  
Author(s):  
T. Taşdemir ◽  
B. Öteyaka ◽  
A. Taşdemir
Keyword(s):  
Air Entrainment ◽  
Entrainment Rate ◽  
Air Entrainment Rate
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