Air intrusion in water distribution network (WDN) modelling

A new criterion for water distribution network (WDN) modelling is proposed, according to the assumption of pipe permeability to the air and zero minimum pressure in all the WDN nodes. The two sets of pipes and internal nodes are divided into four sub-sets, corresponding to nodes with zero pressure (DN), nodes with pressure greater than zero (PN), pipes with channel flow (UP) and pipes with fully pressurized flow (SP). An iterative procedure, based on Newton–Raphson and Linear Theory methods, is available for the solution of both diffusive and convective problems, holding respectively for PN + SP unknowns and DN unknowns, when the sub-set decomposition is known. A practical procedure is also provided for the solution of the general problem when the decomposition is not known. Applications show the difference between the solutions obtained assuming a head-driven demand with and without the application of the minimum pressure criterion.