Estudo da reaeração da água em canal com fundo deslizante

• Autor(a) principal: Queiroz, Flávia Martins de
• Data de Publicação: 2013
• Tipo de documento: Tese
• Idioma: por
• Título da fonte: LOCUS Repositório Institucional da UFV
• Texto Completo: http://locus.ufv.br/handle/123456789/755
• topic: Recursos hídricos; Reareação; Water resources; Reaeration; CNPQ::CIENCIAS AGRARIAS::ENGENHARIA AGRICOLA

This work aimed to study the reaeration of clean water in shallow channel process, to evaluate the main factors intervening and to propose predictive equations, which could allow the estimation of the reaeration coefficient (K2) from hydraulic and other variables representing the process of mass transfer of oxygen from air to flowing water. To implement the experiment was necessary to build a water channel, with the length, width and height dimensions of 5.00 mx 1.60 mx 0.80 m, and a conveyor belt, which was positioned at the bottom of the channel, whose function was to move the water at different velocities and to promote turbulence. To conduct reaeration tests, initially, the oxygen dissolved, present in the water supply network, was removed by adding sodium sulfite. The reintroduction of oxygen in the water was due to physical phenomenon of mass transfer, which was favored by the water motion. The tests were conducted by subjecting the belt slide at the speeds of 0.54, 0.67, 0.74, 0.84, 0.94, 1.14 and 1.35 ms-1, with of water depths in range 0.11 to 0.25 m. These conditions provided the water an average speed in the range of 0.05 ms-1 to 0.20 ms-1. To the experimental data, previously treated and converted into a deficit of dissolved oxygen, were fitted to first-order kinetics model and determined the parameter named reaeration coefficient (K2) of water for all 27 tests conducted. With the hydraulic channel data, the value of K2 was estimated using various predictive theoretical, empirical and semiempirical equations available in the literature. The suitability of the equations have been evaluated by analyzing the coefficient of determination (R²) and error estimation such as standard error (SE), normal mean error (NME) and mean multiplicative error (MME). Estimated K2 values using predictive equations were compared to those calculated from data obtained in the tests (measurement of absorbed oxygen), having been found that the best adjustments occurred in semiempirical equations proposed by Krenkel and Orlob (1962), Cadwallader and McDonnell (1969), Parkhurst and Pomeroy (1972), although some empirical also have provided good fit. Twenty combinations of variables were tested to obtain a predictive general equation that produce a good fit to experimental data. The equation involving the variables shape factor channel, slope and Reynolds number was considered the most appropriate because it presented a high determination coefficient and significant parameters, and also variables showed a similar degree of importance in the sensitivity analysis of the mathematical model. It was also analyzed a model based on surface renewal theory and the phenomenon of turbulence, which indicated that large vortices were the principal agents in the transport of oxygen from air to water. Therefore, another equation was proposed, adjusted using data obtained in this work and the Moog and Jirka (1999), with which the adequate estimation of physical phenomenon was obtained.