LOCAL HEAD LOSS OF NON-COAXIAL EMITTERS INSERTED IN POLYETHYLENE PIPE

The design of a lateral line for drip irrigation requires accurate evaluation of head losses in not only the pipe but in the emitters as well. A procedure was developed to determine localized head losses within the emitters by the formulation of a mathematical model that accounts for the obstruction caused by the insertion point. These localized losses can be significant when compared with tire total head losses within the system due to the large number of emitters typically installed along the lateral line. Air experiment was carried out by altering flow characteristics to create Reynolds numbers (R) from 7,480 to 32,597 to provide turbulent flow and a maximum velocity of 2.0 m s(-1). The geometry of the emitter was determined by an optical projector and sensor An equation was formulated to facilitate the localized head loss calculation using the geometric characteristics of the emitter (emitter length, obstruction ratio, and contraction coefficient). The mathematical model was tested using laboratory measurements on four emitters. The local head loss was accurately estimated for the Uniram (difference of +13.6%) and Drip Net (difference of +7.7%) emitters, while appreciable deviations were found for the Twin Plus (-21.8%) and Tiran (+50%) emitters. The head loss estimated by the model was sensitive to the variations in the obstruction area of the emitter However, the variations in the local head loss did not result in significant variations in the maximum length of the lateral lines. In general, for all the analyzed emitters, a 50% increase in the local head loss for the emitters resulted in less than an 8% reduction in the maximum lateral length.Federal Department of Science and Technology - MCT Ministerio de Ciencia e TecnologiaNational Scientific and Technological Development Council (CNPq)Sao Paulo State Scientific Foundation (FAPESP)National Institute of Science and Technology in Irrigation Engineering (INCTEI

Perda de carga em microtubos e conectores utilizados em microaspersão Head loss in microtubes and connectors used in microsprinkler systems

Este trabalho foi desenvolvido com o objetivo de ajustar equações que estimam a perda distribuída de carga em microtubos utilizados em microaspersão e a perda localizada de carga na passagem lateral do fluxo por meio dos conectores na linha lateral. A perda distribuída de carga foi determinada em quatro diâmetros de microtubos com nove a dez repetições para 15 vazões, por meio da aplicação do teorema de Bernoulli. O fator de atrito (f) foi estimado fixando-se o valor de m = 0,25 e calibrando-se o valor do parâmetro c (0,290). A perda localizada de carga foi determinada por diferença entre perda de carga no microtubo mais conector e perda de carga no microtubo. Dois modelos de conectores foram utilizados e caracterizados quanto ao diâmetro interno e dimensões. Uma aproximação matemática foi proposta para calcular a perda localizada de carga com base em coeficiente de carga cinética do conector (K'), que leva em consideração as dimensões do conector e do microtubo e independência das forças viscosas para Re > 5.000. As variações de vazão e de pressão entre os emissores situados nos extremos da linha lateral mostraram-se sensíveis à perda de carga na passagem lateral pelo conector mais a perda de carga no microtubo.<br>This work was carried out aimed at presenting equations to estimate the continuous head loss in microtubes and the local head loss in the connector used on microsprinklers lateral lines. The continuous head loss was determined using Bernoulli's theorem for four microtubes diameters, each one with nine to ten replications for 15 flowrates. The Darcy-Weisbach friction factor was estimated by setting m to 0.25 and by calibrating the parameter value c to 0.290. The local head loss was determined by subtracting the head loss on the connector and microtube from the head loss on the microtube. Two types of connectors were used and characterized by its internal diameters and its dimensions. A mathematical approach to compute the local head loss was proposed based on a kinetic head connector coefficient (K'). This coefficient is a function of connector and microtube dimensions and independent of viscous forces up to Re > 5,000. Flowrate and pressure at emitters located at the far end of the lateral line were sensitive the head losses at the connectors and in the microtube