Impact of Transition Flow Regime on Contaminants Propagation in Pressurised Pipes

In recent years, the scientific community has focused a lot of attention on the problem of water quality within the distribution networks in order to prevent and identify any presence of contaminants that might insist within it. In literature, several numerical models are available able to identify, position, represent and simulate the propagation of contamination in pressurized pipe networks. Unfortunately, these models adopt simplified approaches that do not lead to significant errors when dealing with fully developed turbulent motion regimes, but which could lead to relevant overestimation of contaminant concentrations in transition flow regime with low velocity. Such errors can be relevant if flow regime is near to laminar taking to unreliable interpretation of the contamination in complex networks. For this reason, the diffusive - dispersive processes have to be investigated in order to make the models more realistic.

With this aim in mind, the present paper aims to investigate the effect that the different flow regimes impose on a conservative contaminant (NaCl) in order to better understand the diffusive - dispersive phenomenon within the water networks. To do this, experimental tests were carried out on a laboratory network in which contamination experiments were carried out in a controlled environment (Enna, Italy). The monitoring campaign was performed through conductivity sensors positioned in specific nodes of the network functioning in real - time. Several tests have been carried out for different values of the Reynolds number, maintaining the constant pressure, both through laboratory experiments and through the use of the EPANET hydraulic simulator. The results were compared and it was noticed that the diffusion - dispersion processes are relevant for the low Reynolds numerical values. Furthermore, the EPANET simulator does not reflect the true behavior of the system as all the contaminants move rigidly from one node to another in the network regardless of the flow regime.