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Environmental Impact Studies for Dams and Reservoirs
Published in Larry Canter, Environmental Impact of Water Resources Projects, 1985
Professional knowledge and judgment is based on the general effects of impoundments on water quality (Canter, 1977). Considering water quality only, it is known that impoundment of water will lead to beneficial effects in terms of turbidity reduction, hardness reduction, oxidation of organic material, coliform reduction, and flow equalization. Detrimental effects include lower reaeration, buildup of inorganics, algae blooms, stratified flow, and thermal stratification. Perhaps the most significant impact is due to thermal stratification with the following additional changes in water quality: decreased dissolved oxygen in hypolimnion; anaerobic conditions in hypolimnion; and dissolution of iron and manganese from bottom deposits. In addition to changes in water quality resulting from thermal stratification, changes in mixing patterns also occur. Thermal stratification can result in overflow (warmer water flowing over the surface of colder water), interflow (cool water flowing between upper layers of warmer water and lower layers of colder water), or underflow (cooler water flowing underneath warmer surface water). An additional concern of water impoundment is the reduction in waste assimilative capacity of the body of water being impounded. In general, water impoundment decreases the reaeration ability of a body of water, thus reducing the waste loading that the body of water can receive without having the dissolved oxygen concentration decreased below a prescribed water quality standard.
CFD study of oil-water segregated and dispersed flow coalescence in horizontal pipes
Published in Chemical Engineering Communications, 2021
Juan Carlos Berrio, Andres Pinilla, Nicolas Ratkovich
In general terms, flow patterns can be classified into three categories: (i) stratified or segregated, (ii) dispersed, and (iii) intermittent flow. A representation of these three categories is shown in Figure 1. In stratified flows, is when the two phases (oil and water) are segregated by gravity, where the high dense fluid (water) flows below the less dense fluid (oil), with interphase between water and oil, this flow pattern mainly appears at low mixture velocities. Nevertheless, this interphase can be smooth, wavy, or mixed with droplets of both water-in-oil and/or oil-in-water. A non-stratified flow can occur with the presence of phase droplets of either within the oil or water phase that exists continuously as the mixture flows throughout the pipe. Non-stratified flow also is known as a dispersed flow. Furthermore, the latter, the intermittent flows are characterized by having large oil droplets separated by water slugs, generated when the mixture velocity increases (Bannwart et al. 2004).
Investigation of the interfacial instability in a non-Boussinesq density stratified flow using linear stability theory
Published in Cogent Engineering, 2019
Ehsan Khavasi, Pouriya Amini, Javad Rahimi, Mohammad Hadi Mohammadi
Interfacial instabilities affect the behavior of stratified flows. An improved understanding of the interfacial instabilities in stratified shear flows can aid to forecast exchange flow rates and vertical mixing rates. The importance of this forecasting is because of its control on the vertical transfer of salt, heat, nutrients, pollutants and momentum in stratified flows. A noteworthy quantity of mixing in the interior ocean and atmosphere is produced by the formation of shear instabilities in density stratified flows (Nourmohammadi, Afshin, & Firoozabadi, 2011). It is probable to predict instabilities using linear stability analysis. The results of such tool provide a theoretical estimation of initial instability frequency or wavelength, the instability growth rate, knowledge that is serious for understanding and controlling shear flows (Khavasi & Firoozabadi, 2018, 2019).