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Pipe network analysis is a calculation of fluid flows and pressure drops in complex piping systems. Analysis of piping systems is important for public utilities supplying water to consumers, natural gas distribution planning, or any system of piping where consistent delivery pressures and flow rates are important. It is unlikely that a supplier knows specific demands and flow rates throughout the network, so pipe network analysis provides a method where system loops are chosen and calculations are performed.
Calculations needed for pipe network analysis are available in commercial software packages, but the fundamental equations can also be calculated manually. The analysis uses a relaxation method where piping loops are chosen, pressure drops and delivery points are estimated. The amount of material passing through the system is then determined, and a series of calculations are performed.
At this point, corrections are made to the estimates and calculations are repeated when necessary. This is known as an iterative method. The process continues with smaller and smaller changes in the assumptions, until conservation of mass and energy is satisfied. Conservation of mass and energy means the inlet pressures and flows at the supply point equal the system pressure losses and required customer delivery flow rates and pressures.
Pipe network analysis uses the same iterative method regardless of the fluid being delivered. The importance and complexity of these calculations increases as a pipe network grows, and customers expect uninterrupted delivery. Fluid dynamics and pressure drops can be measured experimentally, but laboratory measurements do not always translate well to real-world systems of overlapping loops, many delivery points and a constantly changing pipe network.
Utility planners can use the results of a pipe network analysis to modify and upgrade their systems. New customer demands may require additional pump or compressor stations to supply adequate flows. Growing subdivisions or neighborhoods may require a re-analysis of the network, because the addition of new piping loops changes the calculation assumptions.
Water piping can develop internal scale, or roughness, as it ages. This may require additional pumping energy to overcome. Pipe network analysis typically needs to be a dynamic process with constantly changing variables, rather than a single analysis with no allowance for changes over time.
A computational method traditionally used for manually calculating a pipe network analysis is the Hardy Cross method. This method assumes that all pipe sizes and lengths are fixed variables. The Hardy Cross method becomes less accurate as the piping system becomes more complex. Results from a Hardy Cross calculation may be less accurate than software applications, but the results can be used as assumptions for more complex software calculations.
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