Pipe Flow Expert User Guide
We recommend using the Compressible Flow Calculation Engine to calculate gas systems
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| We recommend using the Compressible Flow Calculation Engine to calculate gas systems,
however see the next section for considerations when using the non-compressible Darcy-Weisbach equation to calculate a compressible gas system. Using Non-Compressible Darcy-Weisbach Equation Important Note: We would always recommend using the Compressible Flow Calculation Engine to solve compressible gas systems (rather than using the non-compressible calculation engine with the Darcy-Weisbach equation). The following notes in this section are included for completeness only. The Darcy-Weisbach equation is normally applicable to incompressible Newtonian fluids, since the density of these fluids can be considered to be constant even with changes in pressure, however this equation is also sometimes used for compressible systems provided that they operate within certain criteria. When the Non-Compressible Calculation Engine is selected on the Calculations tab in Configuration Options then Pipe Flow Expert uses the Colebrook-White equation to calculate friction factors and the Darcy-Weisbach equation to calculate the friction loss in a pipe. These equations assume a constant fluid density & viscosity and they provide a very accurate solution when working with non-compressible fluids (liquids) and they are sometime used for low velocity gas systems where there is a relatively small amount of pressure loss. Working with Compressible Fluids 199 If the user select the Non-Compressible Calculation Engine when using the software to model gas systems then there are certain criteria that the model must operate within to ensure the solution is of acceptable accuracy. Changes in pressure and temperature will affect the gas density and viscosity. These property changes affect the actual pressure drop and are not automatically accounted for in the Darcy- Weisbach equation, therefore some limitations must be applied to ensure that the calculated results are within an acceptable accuracy. Generally systems which involve gases fall into two categories: tải về 4.95 Mb. Chia sẻ với bạn bè của bạn:
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