scholarly journals Experimental Study on Shape and Rise Velocity of Small Bubbles in Stagnant Water

2015 ◽  
Vol 9 (2) ◽  
pp. 1397-1403
Author(s):  
A Mitra ◽  
P Bhattacharya ◽  
S Mukhopadhyay ◽  
K K Dhar
Keyword(s):  
Experimental Study ◽  
Rise Velocity ◽  
Stagnant Water ◽  
Small Bubbles

Fragmentation of acoustically levitating droplets by laser-induced cavitation bubbles

2016 ◽  
Vol 805 ◽  
pp. 551-576 ◽  
Author(s):  
Silvestre Roberto Gonzalez Avila ◽  
Claus-Dieter Ohl
Keyword(s):  
Shock Wave ◽  
Experimental Study ◽  
Surface Tension ◽  
Cavitation Bubble ◽  
High Speed ◽  
Size Range ◽  
Sound Field ◽  
Negative Pressures ◽  
Impulsive Pressure ◽  
Small Bubbles

We report on an experimental study on the dynamics and fragmentation of water droplets levitated in a sound field exposed to a single laser-induced cavitation bubble. The nucleation of the cavitation bubble leads to a shock wave travelling inside the droplet and reflected from pressure release surfaces. Experiments and simulations study the location of the high negative pressures inside the droplet which result into secondary cavitation. Later, three distinct fragmentation scenarios are observed: rapid atomization, sheet formation and coarse fragmentation. Rapid atomization occurs when the expanding bubble, still at high pressure, ruptures the liquid film separating the bubble from the surrounding air and a shock wave is launched into the surrounding air. Sheet formation occurs due to the momentum transfer of the expanding bubble; for sufficiently small bubbles, the sheet retracts because of surface tension, while larger bubbles may cause the fragmentation of the sheet. Coarse fragmentation is observed after the first collapse of the bubble, where high-speed jets emanate from the surface of the droplet. They are the result of surface instability of the droplet combined with the impulsive pressure generated during collapse. A parameter plot for droplets in the size range between 0.17 and 1.5 mm and laser energies between 0.2 and 4.0 mJ allows the separation of these three regimes.

scholarly journals Shapes and Rise Velocities of Single Bubbles in a Confined Annular Channel: Experiments and Numerical Simulations

Fluids ◽  
2021 ◽  
Vol 6 (12) ◽  
pp. 437
Author(s):  
Andrea Cioncolini ◽  
Mirco Magnini
Keyword(s):  
Numerical Simulations ◽  
Complex Shape ◽  
Annular Channel ◽  
Qualitative Behavior ◽  
Air Bubbles ◽  
Volume Of Fluid Method ◽  
Rise Velocity ◽  
Limited Evidence ◽  
Stagnant Water ◽  
Circular Tubes

Shapes and rise velocities of single air bubbles rising through stagnant water confined inside an annular channel were investigated by means of experiments and numerical simulations. Fast video imaging and image processing were used for the experiments, whilst the numerical simulations were carried out using the volume of fluid method and the open-source package OpenFOAM. The confinement of the annular channel did not affect the qualitative behavior of the bubbles, which exhibited a wobbling rise dynamic similar to that observed in bubbles rising through unconfined liquids. The effect of the confinement on the shape and rise velocity was evident; the bubbles were less deformed and rose slower in comparison with bubbles rising through unconfined liquids. The present data and numerical simulations, as well as the data collected from the literature for use here, indicate that the size, shape, and rise velocity of single bubbles are closely linked together, and prediction methods that fail to recognize this perform poorly. This study and the limited evidence documented in the literature indicate that the confinement effects observed in non-circular channels of complex shape are more complicated than those observed with circular tubes, and much less well understood.

Experimental Study of Particle Clouds in Stagnant Water

2017 ◽  
Vol 143 (9) ◽  
pp. 04017082 ◽  
Author(s):  
Mohamad Moghadaripour ◽  
Amir Hossein Azimi ◽  
Siamak Elyasi
Keyword(s):  
Experimental Study ◽  
Stagnant Water ◽  
Particle Clouds

Lift Force Effects on the Behavior of Bubbles in Homogeneous Isotropic Turbulence

2005 ◽  
Author(s):  
Mustapha Abbad ◽  
Benoiˆt Oesterle´
Keyword(s):  
Relative Velocity ◽  
Lift Force ◽  
Isotropic Turbulence ◽  
Stokes Number ◽  
Rise Velocity ◽  
Homogeneous Isotropic Turbulence ◽  
Preferential Concentration ◽  
Coupling Approximation ◽  
Lagrangian Tracking ◽  
Small Bubbles

The influence of lift forces on the dispersion of small bubbles is numerically studied in a homogeneous isotropic turbulence generated by random Fourier modes, under one-way coupling approximation. The effects of bubble Stokes number and mean relative velocity are investigated by computing the statistics from Lagrangian tracking of a large number of bubbles in many flow field realizations, and comparison is provided between the results obtained with and without taking the lift force into account. The effects of preferential concentration, which are known to reduce the terminal rise velocity of bubbles, are also investigated. The lift force is found to drastically modify the correlations and integral time scales of the fluid seen by the bubbles in their fluctuating motion, and to significantly enhance the accumulation of bubbles in high vorticity regions.

scholarly journals Experimental Effect of the Impact of Stagnant Water on Solar Modules

2020 ◽  
Vol 9 (3) ◽  
pp. 2095-2100
Keyword(s):  
Experimental Study ◽  
Power Output ◽  
Output Voltage ◽  
Operating Temperature ◽  
Output Current ◽  
Stagnant Water ◽  
Pv Module ◽  
Pv Modules ◽  
Experimental Effect ◽  
The Impact

In this research, an experimental study of the impact of stagnant water on solar modules is investigated. Two different experiments using two identical photovoltaic (PV) modules S1 and S2 were used for the study. In the first experiment, the PV module S1 was covered with stagnant water and the second PV module was unshielded with water. In the second experiment, the PV modules were swapped with S2 covered with stagnant water and S1 unshielded with water. The experiments were carried out under normal operating temperature of PV cells at the Department of Electrical Engineering, University of Nigeria, Nsukka on latitude 6:52 degrees north, longitude 7:23 degrees. Results obtained from the first experiment show that the efficiency and power output of S1 PV module decreased by 9.3% and 8.0% respectively when compared with that of S2 PV module. In the case of output voltage and current, it was found that shielding of PV module S1 with stagnant water caused an increase in the output voltage by 1.93% and a decrease in the output current by 10.26%. In the second experiment, the efficiency and Output power of PV module S2 decreased by 9.21% and 8.18% respectively when compared with the unshielded PV module S1. In the case of voltage and current, it was found that shielding of PV module S2 with stagnant water caused an increase in the Output voltage by 1.63% and decrease in the output current by 10.91%.

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