Pressure drop across sand and recycled glass media used in micro irrigation filters

Filtration is necessary for avoiding emitter clogging in micro irrigation systems. The pressure drop across different granular media, such as silica sand, crushed recycled glass, surface modified glass and glass microspheres of selected grain sizes ranging from 0.63 to 1.50 mm, was studied in a laboratory filter scaled from a commercial filter using tap water. Real and bulk densities, porosity, sphericity and the equivalent diameter of these media were measured. The pressure loss was also measured at filter surface velocities from 0.004 to 0.025 m s−1. The pressure losses for the silica sand, crushed glass and modified glass were 39%, 27% and 10% lower than that for microspheres. The experimental results were compared with predicted values calculated using Ergun and Kozeny-Carman equations, as well as other multiple linear equations obtained with the stepwise methodology. Although the Ergun equation was the most accurate for predicting pressure drop, a newly developed equation that requires only grain size as the physical parameter of each medium also showed good performance and it may be of interest for use by irrigation engineers.