Effect of wand-type underdrains on the hydraulic performance of pressurised sand media filters. (April 2020)

• Record Type: Journal Article
• Authors: Pujol, Toni; Puig-Bargués, Jaume; Arbat, Gerard; Duran-Ros, Miquel; Solé-Torres, Carles; Pujol, Joan; Ramírez de Cartagena, Francisco
• Is Part Of: Biosystems engineering. Volume 192(2020)
• Page Start: 176
• Page End: 187
• Publication Date: 2020-04
• Subjects: Filtration -- Granular bed -- Drip irrigation -- Computational fluid dynamics -- Modelling; Bioengineering -- Periodicals; Agricultural engineering -- Periodicals; Biological systems -- Periodicals; Génie rural -- Périodiques; Systèmes biologiques -- Périodiques; 631
• DOI: 10.1016/j.biosystemseng.2020.01.015
• Languages: English
• ISSNs: 1537-5110

Abstract

Abstract : Sand media filtration is frequently used in drip irrigation systems. Commercial filter designs may use different underdrain models but wand-type designs provide a large ratio of horizontal area covered by underdrains and are expected to provide a uniform flow of water through the medium. The complexity of these designs makes it difficult to analyse the effects of changing the position of wand and the slot open area. These underdrain effects were studied by means of a computational fluid dynamics (CFD) model assuming clean water conditions. The backwashing process was not considered. The CFD results were validated using experimental data from a commercial sand media filter with 10 wands. Unbalanced flows between underdrains were observed in the original configuration. Two new designs were proposed: (1) a design that uses the same type of wands as the original filter but distributes them so as to have an equal horizontal area served by each wand; (2) a design that uses the same spatial distribution as the original filter but with longer wands in those regions of the original filter with lower volumetric flow. CFD simulations indicate that design (1) can reduce the pressure drop through the filter at nominal volumetric flow rates by up to 5.8% with a more uniform flow inside the medium and design (2) could improve the performance of the filter by achieving an up to a 4.9% reduction of pressure drop. Thus, the spatial distribution of underdrains is a key parameter in the hydraulic performance of sand media filters. Highlights: Hydraulic performance of wand underdrain for sand media filter was assessed. A computational fluid dynamics model was developed and experimentally validated. Volumetric flow is higher in upper slots than in bottom ones. Volumetric flow was imbalanced between wands. With equal surface area per wand more uniform flow is achieved.