R. Floris en P. van Thienen recently published 'Experimental investigation of turbulent particle radial transport processes in DWDS using optical tomography' in: Drinking Water Engineering and Science Discussions 4 (2011)1, p.61-83

Abstract

Several transport mechanisms govern the cross-sectional particle distribution in fully developed turbulent flow in a pipe. These transport mechanisms affect particle load deposition as well as particle resuspension, which are identified as principal protagonists in the build-up of potential discolouration risk in drinking water distribution systems (DWDS). Both are to a large degree controlled by particle size and flow conditions. However, so far, these relationships are not completely understood in the context of DWDS.

In this research we have attempted to identify under which conditions particles suspended in water are transported towards the pipe wall, which generate favourable conditions for deposition. Experimental results are reported and then compared, qualitatively and quantitatively, to the theoretical predictions in the regime transport map for turbulent flow proposed by van Thienen et al. (2011a). The research was conducted by completing a series of experiments in a laboratory test facility with different hydraulic regimes and different particle size ranges. A newly developed optical tomography measurement system was used in order to produce cross-sectional images of particle concentration in water flowing inside a pipe. The experimental results allowed us to identify flow conditions and particles sizes under which gravitational settling and turbophoresis dominated the radial particle transport. These findings show a good correspondence between experimental data and theoretical predictions on the occurrence of turbophoresis and lead to a better understanding of the processes that increase the potential discolouration risk in DWDS. More >> 

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This year's edition of the main international meeting for drinking water distribution specialists, the Water Distribution Systems Analysis conference, is organized as part of the World Environmental & Water Resources Congress in Palms Springs, California, from May 22 to 26, 2011. It has about 750 oral presentations, of which about 75 concern water distribution systems. Two researchers of KWR's water distribution team, Jan Vreeburg and myself (Peter van Thienen), are here to be updated about the latest developments in the field, meet people working in the field, and to present our own research. The topic which receives most attention is water security, which mostly focuses on detecting deliberate or accidental contamination of the drinking water distribution system with a chemical or biological agent. In a review presentation on the subject, Avi Ostfeld (Technion), who is an authority in this field, identified a distinction between research on design decisions, i.e. where to place sensors, and real-time processing and interpretation of sensor data, including event detection and the correct response to events. In his opinion, the former has reached a saturation point, and it is important to focus research on the latter aspect.

Other topics which have several presentations in the conference include network models, network optimization, network hydraulics, reliability, asset management, and water quality. In the latter track, Jan Vreeburg has presented his work (with Melanie Tankerville) on particles in the distribution network. Their field measurements suggest a correlation between particle load and biological activity (ATP), which Jan interprets as an indication for an important role of particles as a substrate for biofilms.

Tomorrow, on the final day of the conference, I will present my work on the development of a technique to image particle concentrations in a moving body of water using optical tomography. This technique is very similar to medical imaging techniques such as CT and PET, and contributes to understanding processes which lead to the accumulation of particles in the drinking water distribution system which may ultimately lead to unwanted discoloration of the water.

Peter van Thienen,
Scientific researcher