Osvaldo Rettore Neto

Local head loss for uncoaxial drippers inserted in polyethylene pipes

In this paper, the results of an experimental investigation on local head losses from uncoaxial in-line emitters inserted into the pipe line are reported. Local losses corresponding to four different pipe-emitter combinations, with ten replications, were measured for a range of discharge values. For each discharge, the amount of local losses was calculated as the difference between the total measured head losses and the corresponding friction losses evaluated by the Darcy-Weisbach equation. Mathematical approaches were tested to calculate hfe based on the kinetic head coefficient (K) and constant equivalent length (Le). For the drip-line models examined, the amount of local losses, expressed as a percentage of the total losses, was found to grow with an increase in the obstruction degree. The percentage increased to 24.5% and 50.8%, respectively, for Ag/At = 0.221 and 0.429. The results of this experimental investigation indicated the practical validity of using a constant equivalent length (Le) to estimate the local head losses in a drip lateral line. The percentage variation between total head loss calculated by a step-by-step procedure and the Le approximation method was 5.5% for non-compensating pressure emitters and less than 1.7% for the pressure compensating emitters.

Perda de carga localizada em gotejadores integrados em tubos de polietileno

Este trabalho foi desenvolvido para analisar as perdas de carga localizadas em gotejadores coaxiais integrados em tubos de polietileno. A perda de carga para diferentes vazoes foi determinada em quatro modelos de tubos gotejadores, com sete repeticoes. Para cada vazao, a perda de carga localizada foi calculada pela diferenca entre a perda de carga no tubo com emissor e a perda de carga continua no tubo uniforme, estimada pela equacao de Darcy-Weisbach. Aproximacoes matematicas foram sugeridas para calcular a perda de carga com base no coeficiente de carga cinetica (K) e em um valor constante de comprimento equivalente (Le). A desconsideracao da perda de carga localizada levou a superestimativa do comprimento maximo da linha lateral de ate 25,7%, para os gotejadores autocompensados, e de 9,5%, para os nao autocompensados. O calculo da perda de carga localizada, utilizando o modelo potencial para estimar o valor de K em funcao do indice de obstrucao, mostrou bons resultados, comparaveis aqueles obtidos com o valor de K ajustado pelos dados observados em laboratorio, o que resultou em pequenas variacoes na estimativa do comprimento maximo da linha lateral por esses dois procedimentos.

Quantificação do erro na determinação da perda contínua de carga em tubos elásticos

The plastics industry and its derivatives, with the help of engineering have improved the quality of materials used for manufacturing pipes, mainly polyethylene. The elasticity of polyethylene tubes allows diameter increases as pressure rises, which is not taken into account by the mathematical equations used to determine the head loss. The purpose of this research was to quantify the errors on head loss determining in elastic tubes as a function of inlet pressure on the lateral line, comparing observed and estimated values by equations recommended in the technical literature. Three samples of polyethylene pipe were evaluated under 9 inlet pressures and 3 flow rate conditions, which corresponds to velocities of 1.0, 1.5 and 2.0 m s-1. Measurements for determining the outside diameter of the tubes were carried out under pressures from 0 to 588.4 kPa incrementing 49.05 kPa each step. For all evaluated conditions it was verified that pressure affects the continuous head loss in elastic tubes and the equations of Darcy-Weisbach, Hazen-Williams, and Flamant overestimate the results.

Estimating Local Head Loss of Non Coaxial Emitters

The design procedure of a lateral line of trickle irrigation needs to be evaluated accurately, by accounting for head losses distributed in the piping as well as within the emitters. A methodology was developed for determining localized head losses by the formulation of a mathematical model using the concept of an obstruction index. These localized losses can be significant when compared with the total head losses, due to the great number of emitters installed along the lateral line. The experiment was carried out with values for Reynolds Number (R) in the interval from 7480 to 32597 to provide turbulent flow and maximum velocity of 2,0 m s-1. The geometry of the emitter was determined by an optic projector HB 400. An equation was formulated that computes the localized head loss calculation using the geometric characteristics of the emitter (emitter length, obstruction index and the contraction coefficient). The model provided satisfactorily results for 2 irrigation systems.