Pipe Flow Expert User Guide
Net Positive Suction Head available
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- Điều hướng trang này:
- Two Phase Flow
- 196 Pipe Flow Expert User Guide Working with Compressible Fluids
| Net Positive Suction Head available
Pipe Flow Expert is able to calculate the pressure available at a pump inlet. This pressure will change if the mounting position of the pump along a pipe is changed. The vapor pressure of the fluid being pumped is subtracted from the pump inlet pressure to obtain the Net Positive Suction Head available. The NPSHa must be higher than the pump manufacturer’s NPSHr (Net Positive Suction Head requirement for the flow rate) in order to prevent gas bubbles forming in the fluid. Two Phase Flow Pipe Flow Expert is not able to model two phase flow, such as gas/liquid mixtures. When two different fluids are mixed together it is possible that two-phase flow may occur at some point in a system. Pipe Flow Expert does not calculate the pressure drop for two-phase flow. Two-phase flow can produce an extremely high pressure drop many times greater than the pressure drop of either individual fluid. The user should make due allowance for the two-phase flow pressure drop by using a component to add an appropriate additional pressure loss. Slurries Slurries which have a constant density and a constant viscosity are able to be modeled, provided the minimum velocity to keep the solids in suspension is maintained throughout the pipeline system. The density and viscosity of the slurry mixture must be entered as the fluid data. 196 Pipe Flow Expert User Guide Working with Compressible Fluids The Pipe Flow Expert software now contains a Compressible Isothermal Flow Calculation Engine (from version 7 and later). In a gas system, as pressure loss occurs along a pipe, the gas density will decrease and the volume of the gas will expand. As the volume of gas increases, the velocity of the gas in the pipe will increase. Although the volume of gas and velocity in the pipe changes, the mass flow (weight of flow) in the pipe will remain constant. Gas flow rates are therefore often referred to in terms of mass flow (weight of flow) or standard volume (which is the volume of gas at standard conditions, normally atmospheric pressure and some common temperature reference, since this standard volume also define a constant mass flow). Pipe Flow Expert provides a choice of standard volume units for gas flow rate which include: SCCM (Standard Cubic Centimeters per Minute), SLM (Standard Liters per Minute), SCMH (Standard Cubic Meters per Hour) MMSCMH ( Million Standard Cubic Meter per Hour) MMSCMD ( Million Standard Cubic Meter per Day) SCFM (Standard Cubic Feet per Minute) SCFH (Standard Cubic Feet per Hour) SCFD (Standard Cubic Feet per Day) MMSCFH (Million Standard Cubic Feet per Hour) MMSCFD (Million Standard Cubic Feet per Day) Each of the standard volume units for gas flow relate to the gas at a standard condition, however there are a number of slightly different standard reference conditions that are used worldwide depending on country and location. Pipe Flow Expert provides a choice of standard reference conditions to be used when referring to the standard volume flow rate of gas and these include: 0 °C, 100.000 kPa.a 0 °C, 101.325 kPa.a 15 °C, 101.325 kPa.a 20 °C, 101.325 kPa.a 25 °C, 101.225 kPa.a 60 °F, 14.696 psi.a 68 °F, 14.696 psi.a Mass flow can also be used to refer to an amount of gas flow and the units for mass flow include: Kgs/sec Kgs/min Kgs/hour Lb/sec Lb/min Lb/hour |