Head loss in laser-perforated thin-walled polyethylene pipes for irrigation/ Perda de carga em tubos de polietileno de parede fina para irrigacao perfurados a laser

• Published in: Revista brasileira de engenharia agrícola e ambiental 2019-05, Vol.23 (5), p.317
• Main Authors: de Melo, Veronica G.M.L, Frizzone, Jose A, de Camargo, Antonio P, Bombardelli, Wagner W.A
• Format: Article
• Language: English
• ISSN: 1415-4366
• DOI: 10.1590/1807-1929/agriambi.v23n5p317-323

For reducing fixed and operational costs in pressurized irrigation systems, thin-walled polyethylene pipes with laser-perforated orifices are manufactured to operate under low pressure (up to 100 kPa). Hydraulic characterization of these materials is essential for designing irrigation systems. Considering the material elasticity and the thin wall thickness (about 200 [micro]m), the internal diameter of these pipes may vary according to the operating pressure, resulting in changes of head losses. The purpose of this study was to analyze the head loss in flexible pipes with laser-perforated orifices, and to estimate the maximum length of laterals based on criteria of water distribution uniformity. Non-perforated pipe samples were tested to obtain equations of friction loss. Equations were fitted as a function of flow rate and pressure head at the pipe inlet, and, alternatively, the Darcy-Weisbach equation was modified considering the diameter expressed as a power-law function of pressure head. The equation of head loss as a function of flow rate and pressure head provided proper estimations and considered effects related to changes in the diameter of plastic pipes due to variations in the pressure head. The Darcy-Weisbach equation can be employed for estimating head loss in flexible pipes, whose diameter varies due to pressure, but the diameter must be calculated as a function of the pressure head at the lateral inlet. Key words: operating pressure, diameter change, design, lateral line Para reduzir custos fixos e operacionais em sistemas de irrigacao pressurizados sao produzidos tubos de polietileno com pequena espessura de parede, com orificios de descarga perfurados a laser, que operam a baixas pressoes (ate 100 kPa). A caracterizacao hidraulica desses materiais e essencial para o dimensionamento dos sistemas de irrigacao. Dada a elasticidade do material de fabricacao e a fina espessura de parede (aproximadamente 200 [micro]m) dos tubos, o diametro interno pode ser alterado em funcao da pressao de operacao, provocando variacoes na perda de carga. O objetivo deste trabalho foi analisar a perda de carga em tubos de polietileno flexiveis perfurados a laser e expressar o comprimento maximo dessas tubulacoes em funcao de criterios de uniformidade de distribuicao de agua. Utilizaram-se amostras de tubos nao perfurados para determinar as equacoes de perda de carga. Ajustaram-se equacoes em funcao da vazao e da carga de pressao na entrada do tubo e, alternativame