Reducing energy requirements for sand filtration in microirrigation: Improving the underdrain and packing

• A scaled media filter was tested using different porous materials and pressures.
• Pressure drop was measured across filter media.
• Experimental results were used to calibrate a CFD model.
• Results showed that most of the pressure drop was produced in the underdrain.
• A new underdrain design was proposed that greatly reduced pressure drop.

Energy consumption in pressurised irrigation systems has become a major issue, even when microirrigation is used. Although the emitters used in microirrigation operate at low pressures, their filters require higher pressures and there is therefore no reduction in energy consumption. Part of the pressure drop found in filters is produced by the porous medium itself and this cannot be avoided. However, a large part of the pressure dissipated is caused by auxiliary elements of the filter and this could potentially be reduced without reducing the effectiveness of the filtration process. The auxiliary elements that produced most of the pressure drop in a sand filter were identified. The pressure drop in a scaled sand filter was measured at different points. A computational fluid dynamics (CFD) model of the filter was developed and validated using experimental data. Good agreement was observed between the measured and predicted pressures at the different locations. The CFD model was then used to analyse the regions and elements that produced most pressure drop in the filter and a new underdrain designed to reduce pressure drop was developed. It was predicted that the total pressure drop produced by the underdrain could be halved. In view of these results, a new underdrain design and packing strategy was proposed which could reduce the overall pressure drop in the filter by 35%.