However some local losses such as those produced by a part open valve are often very signifcant and can never be termed a minor loss, and these must always be included. The dissapation of the lost energy occurs over a finite but not necessarily short section of the pipeline, however for hydraulic calculations it is accepted practice to consider the entire amount of this loss at the location of the device.įor pipe systems with relatively long pipes, it is often the case that fitting losses will be minor in relation to the the overall pressure loss in the pipe. Our Pipe Flow software automatically calculates the friction loss in pipes using the Darcy-Weisbach equation since this is the most accurate method of calculation for non-compressible fluids, and it is also accepted as industry accurate for compressible flow provided certain conditions are met.Įnergy loss due to valves, fittings and bends is caused by some localized disruption of the flow.
We now need to calculate each of the items that is required to determine the friction loss in the pipe. The following sections consider each calculation in turn.
Summing these losses/gains will give us the overall pressure drop in the pipe. Working backwards we must know the fluid density and viscosity properties, know the pipe diameter and roughness properties, calculate the Reynold's number, use this to calculate the friction factor using the Colebrook-White equation, and finally plug in the friction factor to the Darcy-Weisbach equation to calculate the friction loss in the pipe.Īfter calculating the pipe friction loss we then need to consider possible fitting losses, change in elevation and any pump head added. There are therefore a number of sub-calculations that must take place to calculate the overall friction loss. The friction factor itself is dependent on internal pipe diameter, the internal pipe roughness and the Reynold's number which is in turn calculated from the fluid viscosity, fluid density, fluid velocity and the internal pipe diameter. However to calculate the friction loss in a pipe for example, it is necessary to calculate the friction factor to use in the Darcy-Weisbach equation which determines the overall friction loss. To calculate the pressure loss in a pipe it is necessary to compute a pressure drop, usually in fluid head, for each of the items that cause a change in pressure. Pressure gain due to any fluid head that is added by a pump.Pressure loss due to a change in elevation of the fluid (if the pipe is not horizontal).Friction loss as the fluid passes through any pipe fittings, bends, valves, or components.Friction between adjacent layers of the fluid itself.Friction between the fluid and the wall of the pipe.This overall pressure difference across the pipe is related to a number of factors: There may also be a pressure gain/loss due a change in elevation between the start and end of the pipe. When fluid flows through a pipe there will be a pressure drop that occurs as a result of resistance to flow.
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