NPSHr is a property of the pump and is a function of the flow. This value is determined by testing done by the manufacturer and is usually presented as one of the pump characteristic curves. You want to ensure that the available NPSH (NPSHa) is greater than the required NPSH (NPSHr), or the water will vaporize in the pump and damage the pump.
Picking the right number of pumps and which ones to run at any time without wasting energy is tricky. The problem gets especially tricky when you have the potential to mix constant and variable speed pumps, and there is no storage in the system, so you canāt simply run pumps efficiently and turn them off when a tank is full.
A key input to any model with pumps is some form of pump head curve showing flow vs. pump head. Given the curve, the model can tell the user the exact point on the pump curve at which the pump will operate.
The fixture unit method (in some places called fixture value method) was developed by Roy B. Hunter from the US Bureau of Standards, based on research conducted by Hunter in the 1920s and 30s (Hunter, 1940). Every fixture in a building was assigned a fixture unit value. For example, a flush tank toilet uses 6, and a shower was 2.5, and a kitchen sink 1.5 (AWWA, 2014). For nearly the last 100 years, determining the peak flow in a pipe has been determined by the fixture unit method.
They are nonlinear, partial differential equations which are about the worst kinds of equations to solve. About the only things that can make them worse are changes in state (e.g. steam condensing) or non-Newtonian fluids (e.g. mudflows). Numerous researchers have shown that it is impossible to arrive at a closed-form, analytical solution in the form v(r, Ļ, z) =ā¦ When people work with these equations these days, they almost always use numerical solutions. I heard a story once that Albert Einstein started his research in solving the Navier-Stokes equations but gave up because it was too difficult. He moved on to easy topics like quantum physics and relativity. I havenāt been able to verify this, but it makes for a good story.
One of the most important inputs to transient analysis is the speed of the pressure wave (called celerity) moving through the pipes. The speed depends on the fluid properties and pipe properties and has a significant impact on the magnitude of the transient pressure wave and the speed at which it moves through the pipes.
Flushing water mains is one of the accepted methods for cleaning a water main and reduce water quality complaints due to color and turbidity, or to bring fresh water with a high disinfectant residual into an area with low disinfectant residual.Ā
In order to do any kind of hydraulic modeling, whether it is for water distribution, sewage or stormwater, it is necessary to determine the head loss over a range of flow rates. Much of the early days of hydraulic engineering were consumed with engineers trying to come up with the right equation to do these calculations.