Ahmad Malekpour

The Challenge of Air Valves: A Selective Critical Literature Review

AbstractOne key alternative for removing, preventing, and effectively coping with the often vexing presence of air in water pipelines is the combination air-vacuum valve. Despite their often effective role, such valves can be highly problematic if not well designed and maintained. This paper critically reviews the current design, application, functionality, and simulation of air valves and the associated shortcomings, with a primary focus on air/vacuum valves (AVVs). It is argued that the efficient number of air valves along undulating pipelines is yet to be fully articulated. Air-valve simulations should expressively consider their dynamic behavior, the physical behavior of any air pockets that might form below an air valve, and the varying character of the water surface at the air valve location. There is a pressing need for a comprehensive and systematic study on the proper sizing and location of AVVs for the transient protection of systems. Overall, the efficient application of AVVs requires broad res...

Column separation and rejoinder during rapid pipeline filling induced by a partial flow blockage

ABSTRACT A new mechanism for inducing column separation and rejoinder during rapid filling of gravity pipe systems is numerically and conceptually identified. A shock-fitting model is combined with the discrete gas cavity model to compute the resulting water hammer due to column rejoinder. Numerical explorations show that column separation may be induced during rapid filling when the water column encounters a flow restriction such as a partially open valve followed by a “V-shaped” pipe profile. Interestingly, the resulting pressure spikes are sometimes capable of inducing a new or secondary column separation event near the front of the advancing water column front, an event associated with the sudden jump in velocity carried by the propagating rejoinder shock wave. A physical interpretation of the captured events is provided and model results are shown to compare favourably to a previously published set of experimental data involving column separation and rejoinder.

Encouraging Effective Air Management in Water Pipelines: A Critical Review

AbstractAir can be entrapped in water and wastewater systems under a variety of conditions, and if such air is not managed properly, it can impose considerable operational penalties. To avoid these problems and the dangers associated with air pockets, several air management strategies have been routinely suggested. However, the devastating consequences of air pockets frequently documented in the literature imply the need for further development in this area. Improving air management obviously requires a thorough understanding of the current strategies and their shortcomings. This paper overviews the sources of air in pipes and key consequences associated with its presence. Current measures for managing air in water pipes are reviewed and critiqued. Finally, knowledge gaps that limit the efficient application of current air management strategies to real world problems are identified, and suggestions for future development are presented.

Understanding of the Risks of High Pressures Following Rapid Pressurization in Pipelines Containing Entrapped Air Pockets: A Novel Energy Auditing Approach

Rapid pressurization of liquid pipelines containing entrapped air may result in extreme overpressures. Both experimental and numerical studies have shown that the magnitude of the induced pressure has important sensitivities to many physical parameters even though the complex nature of the system’s transient responses has tended to obscure the physical mechanisms themselves. To provide insight and guidance to key design issues, this paper proposes an energy auditing approach to elucidate the physics of the transient events leading to the extreme pressure rise during pipe rapid pressurization events. The proposed approach is then utilized to provide physical understanding of the features of the flow and the system parameters affecting the maximum pressure rise during rapid pressurization of pipe system. Both rigid column and elastic numerical models are then employed to verify the results obtained from the proposed approach.Copyright

Numerical investigation of rapid filling in bypass pipelines

ABSTRACT The rapid filling behaviour of a bypass pipeline is analysed numerically using an elastic model combined with the polytropic law for the air phase. These explorations show that the system can be readily filled when the entrapped air in the bypass line could be released into the atmospheric air, but that large pressure surges are predicted due to the collision of the filling fronts coming from the opposite ends of the bypass line. As expected, both the distance to the upstream reservoir and the size of the bypass line influence the magnitude of resulting overpressures. The magnitude of these predicted surges is naturally reduced by modelling the presence of the compressible air, the presence of which tends to cushion the impact of the filling fronts. A decrease in the volume of initially entrapped air increases the magnitude of the pressure surge and decreases the period of oscillation. In general, entrapped air is beneficial during rapid filling; however, such air is certainly problematic for conditions of normal flow and thus should be routinely removed using air valves.

Comparing Unsteady Modeling Approaches of Surges Caused by Sudden Air Pocket Compression

The entrapment and compression of air in closed conduits is a relevant problem in pipeline systems that experience unsteady flow regimes. Severe surging result…