Local head loss caused in connections used in micro-irrigation systems/ Perda de carga localizada em conexoes utilizadas em sistemas de microirrigacao

Information about local head loss caused by connections employed in micro-irrigation systems is hard to be found in literature. The objective of this research was to experimentally determine the local head losses in connections commonly used in micro-irrigation and propose mathematical models using the theorem of Buckingham. The methodology of tests was based on international standards. The tests were carried out under controlled inlet pressure, at 150 kPa, and five to ten units of each connection model were tested. The curves relating flow and head losses were drawn based on 15 flow conditions, obtained under increase and decrease of flow rate. For each condition, 30 points were collected resulting in a sample size of 900 points in each test. For each connection model evaluated, the following information was obtained: curves of local head loss as a function of flow rate and of local head loss coefficient ([K.sub.L]). The obtained values of [K.sub.L] ranged from 2.72 to 24.16, which become constant for Reynolds number higher than 10,000. The sensitivity of the coefficient related to a ratio of the internal sections in the connections was also verified. The flow exponents presented values close to the one applied by the Darcy-Weisbach equation (m = 2). The models developed for the connections presented a satisfactory performance. Key words: hydraulics, dimensional analysis, Buckingham Pi theorem Informacoes sobre perda de carga localizada em conexoes utilizadas em sistemas de microirrigacao sao dificeis de serem encontradas na literatura. O objetivo desta pesquisa foi determinar experimentalmente as perdas de carga localizada em conexoes comumente empregadas nesses sistemas e propor modelos matematicos utilizando o teorema de Buckingham. A metodologia dos ensaios foi baseada em recomendacoes de normas tecnicas internacionais. Os ensaios foram realizados sob pressao de entrada controlada em 150 kPa, com cinco a dez unidades testadas para cada modelo de conexao. As curvas relacionando vazao e perda de carga localizada foram plotadas com base em 15 condicoes de vazao, obtidas sob incremento e decrescimo de vazao. Para cada condicao, foram coletados 30 pontos, resultando num conjunto de 900 registros de dados a cada ensaio. Em cada modelo de conexao avaliado, foram obtidas as seguintes informacoes: curvas de perda de carga localizada em funcao da vazao e do coeficiente de perda de carga localizada ([K.sub.L]). Os valores de [K.sub.L] variaram de 2,72 a 24,16, o