scholarly journals Experimental Investigations on the Wall-attached Bubble Growth Process in Water With Supersaturated Total Dissolved Gas

2021 ◽  
Author(s):  
Lu Lin ◽  
Ran Li ◽  
Jingjie Feng ◽  
Qin Zou ◽  
Xiaolong Cheng ◽  
...  
Keyword(s):  
Growth Rate ◽  
Bubble Growth ◽  
Prediction Method ◽  
Growth Period ◽  
Experimental Investigations ◽  
Dissolved Gas ◽  
Release Process ◽  
Environmental Pressure ◽  
Total Dissolved Gas ◽  
Vacuum Degree

Abstract Due to dam discharge, waterfalls, sudden increases in water temperature and oxygen production by photosynthesis, the total dissolved gas (TDG) in water is often supersaturated, which may have serious effects on aquatic ecology. When the atmospheric pressure is lower than the TDG pressure in water, the supersaturated dissolved gas in water will slowly release into air. Wall-attached bubbles were formed during the TDG release process. The generation and departure of wall-attached bubbles influence the release process of TDG in water. To simulate the growth period of the wall-attached bubbles under different pressures, a decompression experimental device was designed to record the supersaturated TDG release process. Based on experimental data and mathematical calculations, the quantitative relationship between the bubble growth rate and environmental pressure was obtained. The supersaturated TDG dissipation rate increases monotonically with increasing relative vacuum degree. Based on the wall-attached bubble growth rate calculation method applied in this paper, a formula of the supersaturated TDG adsorption flux based on wall-attached bubbles was proposed, and a prediction method of the TDG release coefficient was established. The simulation results show that with increasing relative vacuum degree, the TDG coefficient increases correspondingly, and the adsorption mechanism of vegetation surface area can be obviously promoted under lower environmental pressure. This study provides an important theoretical basis for the accurate calculation of the TDG release process and provides a scientific basis for the accurate prediction of the spatial and temporal distribution of supersaturated TDG under different environmental conditions.

Understanding gas bubble trauma in an era of hydropower expansion: how do fish compensate at depth?

2020 ◽  
Vol 77 (3) ◽  
pp. 556-563 ◽  
Author(s):  
Naomi K. Pleizier ◽  
Charlotte Nelson ◽  
Steven J. Cooke ◽  
Colin J. Brauner
Keyword(s):  
Bubble Growth ◽  
Gas Bubble ◽  
Hydroelectric Dams ◽  
Dissolved Gas ◽  
Empirical Relationships ◽  
Lethal Effects ◽  
Exposed Fish ◽  
Total Dissolved Gas ◽  
Rainbow Trout Oncorhynchus Mykiss ◽  
The Relationship

Hydrostatic pressure is known to protect fish from damage by total dissolved gas (TDG) supersaturation, but empirical relationships are lacking. In this study we demonstrate the relationship between depth, TDG, and gas bubble trauma (GBT). Hydroelectric dams generate TDG supersaturation that causes bubble growth in the tissues of aquatic animals, resulting in sublethal and lethal effects. We exposed fish to 100%, 115%, 120%, and 130% TDG at 16 and 63 cm of depth and recorded time to 50% loss of equilibrium and sublethal symptoms. Our linear model of the log-transformed time to 50% LOE (R2 = 0.94) was improved by including depth. Based on our model, a depth of 47 cm compensated for the effects of 4.1% (±1.3% SE) TDG supersaturation. Our experiment reveals that once the surface threshold for GBT from TDG supersaturation is known, depth protects rainbow trout (Oncorhynchus mykiss) from GBT by 9.7% TDG supersaturation per metre depth. Our results can be used to estimate the impacts of TDG on fish downstream of dams and to develop improved guidelines for TDG.

scholarly journals Energy dissipation efficiency as a new variable in the empirical correlation of total dissolved gas

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Jingying Lu ◽  
Xiaolong Cheng ◽  
Zhenhua Wang ◽  
Ran Li ◽  
Jingjie Feng ◽  
...  
Keyword(s):  
Energy Dissipation ◽  
Standard Error ◽  
Air Entrainment ◽  
Empirical Equations ◽  
Generation Process ◽  
Field Observations ◽  
Dissolved Gas ◽  
Total Dissolved Gas ◽  
Future Work ◽  
Hydropower Stations

AbstractTotal dissolved gas (TDG) supersaturation, which occurs during dam spilling, may result in fish bubble disease and mortality. Many studies have been conducted to identify the factors pertaining to TDG generation, such as the spilling discharge and tailwater depth. Additionally, the energy dissipation efficiency should be considered due to its effect on the air entrainment, which influences the TDG generation process. According to the TDG field observations of 49 cases at Dagangshan and Xiluodu hydropower stations, the TDG was positively related to the energy dissipation efficiency, tailwater depth and discharge per unit width. A correlation between the generated TDG level and these factors was established. The empirical equations proposed by the USACE were calibrated, and the TDG level estimation performance was compared with the established correlation for 25 spillage cases at seven other dams. Among the considered cases, the standard error of the TDG estimation considering the energy dissipation efficiency was 5.7%, and those for the correlations obtained using the USACE equations were 13.0% and 10.0%. The findings indicated that the energy dissipation efficiency considerably influenced the TDG level, and its consideration helped enhance the precision of the TDG estimation. Finally, the generality of this approach and future work were discussed.

In-Situ Dual-Wavelength Ellipsometry and Light Scattering Monitoring of Si/Si1−xGex Heterostructures and Multiuantum Wells

1993 ◽  
Vol 324 ◽  
Author(s):  
C. Pickering ◽  
D.A.O. Hope ◽  
W.Y. Leong ◽  
D.J. Robbins ◽  
R. Greef
Keyword(s):  
Growth Rate ◽  
Light Scattering ◽  
Laser Light ◽  
Growth Period ◽  
Laser Light Scattering ◽  
Heterojunction Bipolar Transistor ◽  
Dual Wavelength ◽  
Multi Quantum Well ◽  
Refractive Index Data

AbstractIn-situ dual-wavelength ellipsometry and laser light scattering have been used to monitor growth of Si/Si1−x,Gex heterojunction bipolar transistor and multi-quantum well (MQW) structures. The growth rate of B-doped Si0 8Ge0.2 has been shown to be linear, but that of As-doped Si is non-linear, decreasing with time. Refractive index data have been obtained at the growth temperature for x = 0.15, 0.20, 0.25. Interface regions ∼ 6-20Å thickness have been detected at hetero-interfaces and during interrupted alloy growth. Period-to-period repeatability of MQW structures has been shown to be ±lML.

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