| مستخلص: |
Rivers, as water resources, are considered an origin of supply for many requirements of urban communities. River networks consist of many branches that connect at river confluences. Because pollutants usually enter the river in different situations from the upstream branches of river intersections, it is essential to investigate the mixing process through the river network. For this purpose, precise analytical and numerical models should be used to evaluate this phenomenon quantitatively. Based on the cell concept and separation of advection and dispersion operations, this study developed a new analytical relationship through the confluences of rivers. A physical model of the Y-shaped junction was created in the laboratory, and four inlet flow discharges 25, 21, 12, and 9 l/s and three initial concentrations of sodium chloride solution 80, 160, and 200 g/L were selected as study parameters. Then, the concentration-time curves along the sub-branches, the intersection, and the downstream of the river's main channel were taken at 2-second intervals. In order to evaluate the efficiency of the analytical model, the parameters of the model were first calculated by coding based on its framework and using the least squares method. Then the analytical curves were outlined versus the experimental results. It was observed that the presented model could produce double-peaked curves and also cover experimental data series precisely. The dispersion coefficients and the related time parameter in the presented model (T) were found to increase by moving downstream of the river junction. It was also observed that the Peclet numbers (Pe = xu/D ) are increased like dispersion coefficients by increasing the distance downstream of the confluence. In addition, the research results showed that increasing the residence time parameter in dispersion cells (T) causes growth in the dispersion coefficient, despite increasing the residence time in advection cells (β), compelling the movement of the pollutant breakthrough curves. [ABSTRACT FROM AUTHOR] |
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