Discretized Air Phase Modeling in the Simulation of Pipeline Refilling Operations
This chapter focuses in the numerical simulation of the filling of water mains, and how to incorporate the effects of air phase in those computations. Water mains are part of an aging urban infrastructure, and maintenance procedures are becoming more frequent; some maintenance procedures require the emptying and subsequent refilling of pipelines. Water main refilling is also observed in water main commissioning or following power outages. In any condition, the refilling process is performed very cautiously due to the possible interactions between water and the air initially present in the pipes, as explained below. Because of the gradualness, pipeline refilling may be a time consuming process, which may adversely affect water users.
During the filling process, at a certain inflow rate one cannot exactly predict whether, or at what locations, air pockets will form. If such pockets are compressed during the filling events, severe pressure surges may appear. On the other hand, if the filling cannot eliminate all the air pockets within the pipeline, other issues can arise as air pockets may block the flow, create additional energy losses, reduce pipe conveyance or increase pumping electricity demand. The problem of air pockets in water mains has raised the interest of different researchers, for example with regard to the development of a criterion of hydraulic removal of air pockets by the water flow. Some of these investigations were directed towards the development of numerical models to simulate the filling process in water mains. However, as it will be shown, there is a knowledge gap in terms of what is the most appropriate way to incorporate air phase pressurization in the water filling modeling.
Current investigation at Auburn University aims to address this gap and propose an improved numerical modeling tool, designed for water works to simulate the refilling of water mains. The final goal is to transform the filling process into an engineered and predictable process, decreasing the uncertainties associated with such events and possibly reducing downtime in pipelines caused by lengthy refilling.
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