Regulador automático de vazão para condutos livres: desenvolvimento e avaliação

• Autor(a) principal: Amaral, Luis Gustavo Henriques do
• Data de Publicação: 2007
• Tipo de documento: Tese
• Idioma: por
• Título da fonte: LOCUS Repositório Institucional da UFV
• Texto Completo: http://locus.ufv.br/handle/123456789/621
• topic: Irrigação agrícola; Hidráulica; Equipamentos e acessórios; Canais; Irrigation; Hydraulics; Equipments and accessories; Channels; CNPQ::CIENCIAS AGRARIAS::ENGENHARIA AGRICOLA::ENGENHARIA DE AGUA E SOLO::IRRIGACAO E DRENAGEM

The development of irrigated agriculture depends on the rational use of water resources. Hence, it is necessary to reduce the water loss that occurs from reservation to application of water in the irrigated areas. In open channel irrigation schemes, frequent water level fluctuations combined to high sensitivity of water delivery structures cause large variations on supplied discharge. The main objective of this work was to develop and evaluate a flow regulator able to minimize the effect of water level fluctuations upstream from delivery structures on supplied discharge, using rectangular orifices in curved plate to control the water passage from the main to the derivation channel. The specific objectives were: to design and construct the flow regulator; to obtain discharge coefficients for rectangular orifices in vertical curved thin plate; to determine the regulator supplied discharge variation for the entire operational range; and to obtain the characteristic curves of the equipment. The flow regulator, built from fiberglass, was conceived to keep a constant hydraulic head on the orifices, even if the water level varies expressively. The equipment is composed of a cylindrical tube with rectangular orifices around its circumference. This tube slides within a fixed tube, which works as a guide, and is fastened to a float that adjusts the orifices position according to water level in the main channel. The set operates within a collection box installed close to the channel offtake. The flow regulation is made by adjusting the hydraulic head and altering the flow area. The evaluation of the automatic flow regulator was accomplished in a concrete channel belonging to the Hydraulic Laboratory of the Department of Agricultural Engineering of the Federal University of Viçosa, in Viçosa, Minas Gerais state, Brazil, using clean water. The discharge coefficient was determined for rectangular orifices 0.08 m long and 0.04 m high using four different angles between the orifice axis and its plate: 1.57, 1.75, 1.80 and 1.89 rad. The relative variation in the discharge supplied by the automatic flow regulator was determined for a variation of 0.15 m in the main channel s water level, for all discharge regulation options. Additionally, it was determined the characteristic curves of the automatic flow regulator by relating the discharge and the hydraulic head over the orifices gravity center. The equipment presented an excellent performance. It is adequate for operating channel networks as it minimizes the effect of water level fluctuations over the supplied discharge. It was verified a reduction of 3.5% in the discharge coefficient against the increase of 0.32 rad in the angle between the orifice axis and its plate and a mean discharge variation supplied by the automatic flow regulator of ± 2.3%. The main cause for this discharge variation was attributed to the static friction between the walls of the guide and the sliding tubes that was not overcome when there was a small variation in the buoyancy force over the float. According to the analysis of the equipment s characteristic curves, the automatic flow regulator developed can supply discharges between 3.3 and 30.7 L s-1, enabling its application in small and medium irrigated areas. The automatic flow regulator is a good alternative to the regulation and measuring of discharges in open channels, since the discharge variation of the developed equipment is smaller than the discharge variation of the structures commonly used to control the discharge in channels.