جستجوی مقالات مرتبط با کلیدواژه "deposition rate" در نشریات گروه "فنی و مهندسی"

Cohesive sediments are composed primarily of clay-sized material, which have strong interparticle forces due to their surface ionic charges. As particle size decreases, the interparticle forces dominate the gravitational force, and the settling velocity is no longer a function of only particle size. When, under certain conditions, the attractive forces exceed the repulsive ones, colliding particles stick together, forming agglomerations known as "flocs" with size and settling velocities much higher than those of the individual particles. This phenomenon is known as "flocculation" (Baldock et.al, 2004). In a flocculated cohesive sediment suspension, the settling unit is the floc rather than the individual particle. The settling velocity of cohesive sediment particles, also is called the fall velocity, is one of the key variables in the study of sediment transport and is important in understanding suspension, deposition, mixing and exchange processes (Partheniades, 2009). Adding a chemical solution in a mixture of water and sediment changes the physicochemical of the sediments and the flocculation of the clay particles may increase or decrease. Today, in many countries the wastewater is used for irrigation sector as an additional water resource. Wastewater in combination with other water resources change the physicochemical characteristics of the water and it causes changing in hydrodynamic behaviors which one of them is the effect of wastewater concentration on the fall velocity of cohesive sediments in channels and water transfer Systems (khastar-Boroujeni, 2018). Therefore this study focuses on the effect of urban wastewater on cohesive sediments transport to improve water quality and manage the irrigation systems. For this purpose, some experiments were carried out in an annular flume using a mixture of cohesive sediment and water with combination of three levels of wastewater for evaluating their effects on the fall velocity of cohesive sediments.

Sedimentation in water conveyance channels is one of the main problems in the operation of irrigation systems. In recent years, wastewater has been used in agriculture. This may affect the rate of the channel sedimentation. In order to assess this matter, some experimental tests were conducted in an annular flume. In these experiments the velocity and the shear stress profiles were measured using an Acoustic Doppler Velocimeter (ADV). During the experiments, deposition rate of the sediments were determined by using the measured suspended sediment concentration. The results showed that adding 30% to 60% wastewater caused deposition rate of the sediments to be increased at a rate of 39%. In this work a significant difference between the effect of 30% and 60 % wastewater concentration was not observed. For all experiments, it was observed that the arrival time for deposition of a certain amount of suspended sediment in a fluid- containing wastewater occurred in a shorter period of time.

Effect of hypophosphite anion on morphology, deposition rate, composition, and corrosion behavior of trivalent chromium coatings, as a complexing agent in trivalent chromium electrolyte, was investigated. For this purpose, the concentration of hypophosphite anion in trivalent chromium electrolyte was changed from 0-0.75 M. Morphology and composition of the coatings were evaluated by using scanning electron microscopy (SEM) equipped with energy dispersive spectrometry (EDS). Corrosion behavior of the coatings was investigated using Tafel extrapolation method and electrochemical impedance spectrometry (EIS) technique in 3.5 wt% NaCl solution. Results show that the deposition rate was decreased by addition of hypophosphite anion to the bath. However, further increasing of its concentration to 0.525 M, results in increased deposition rate. Moreover, the incorporation of phosphorous in the trivalent chromium coatings caused higher micro cracks density and increase in porosity, and thus the corrosion resistances of these coatings were decreased.