Water Supply Vol 4 No 5-6 pp 131–138 © IWA Publishing 2005
Prediction of filter expansion during backwashing
Ö. Akgiray*, E. Soyer** and E. Yüksel***
*Marmara University, Faculty of Engineering, Department of Environmental Engineering, Goztepe 34722, Istanbul, Turkey (E-mail: akgiray@eng.marmara.edu.tr)
**Istanbul Technical University, Faculty of Civil Engineering, Department of Environmental Engineering, Maslak 80626, Istanbul, Turkey (E-mail: esoyer@ins.itu.edu.tr)
***Istanbul Technical University, Faculty of Civil Engineering, Department of Environmental Engineering, Maslak 80626, Istanbul, Turkey (E-mail: esoyer@ins.itu.edu.tr)
ABSTRACT
The application of the Ergun equation to predict the expansion of filter media during backwashing is investigated. Fluidization data from the literature have been analyzed and the values k1=3.519 and k2=0.266 have been found to give a very good fit to the data in the range of Reynolds numbers of interest in filter backwashing. An empirical equation that is applicable over a wider range of Reynolds numbers than the Ergun equation is also developed. New experiments have been carried out with glass spheres, plastic spheres, silica sand, and crushed glass. The effect of particle shape on expansion behaviour is investigated. It is found that the influence of particle shape is larger than previously recognized. Furthermore, the shape effect depends on the Reynolds number based on the backwash velocity. The advantages, limitations, and range of applicability of each method of calculation are delineated.
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