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FLUIDA library examples
Water-hammer in a liquid line
This example shows the FLUIDA library capabilities concerning water-hammer analysis in a pipe using a real properties fluid (two phase flow). The pipe is simulated by the "Pipe" component, which takes into account inertia forces, pressure losses, and phase changes.
The model represents a pipe between two boundaries. The left one imposing P-T (5 bar, 300 K) and the right one forces the mass flow circulating through the pipe.
The pipe data are:
- Working fluid: water (NIST_H2O).
- Internal diameter: 48 mm.
- Roughness: 50 µm.
- Nodes: 25.
- Length: 10 m.
A previous steady state is calculated to determine the pipe conditions at a constant mass flow of 5 kg/s. The transient will be started by a sudden flow reduction on the right side; that is, the time dependant mass flow is set to zero in 1 millisecond after 0.05 seconds.
Some result plots are given below. The following phenomena can be seen:
- Pressure rises (pcv) are due to the wave trips caused by a sudden stop of the fluid. This wave is reflected in the open end as a negative flow.
- When this backflow is stopped again at the closed end, the "negative" pressures that should be created are limited to the vapour pressure.
- The corresponding vapour bubble formation then takes place, this causes a water column separation, and the column enters the tank.
- Bubble collapse begins when this liquid column is stopped by the tank pressure and begins to enter the pipe causing the vapour to collapse.
- A new cycle starts when the liquid column is stopped at the closed end when the vapour is eliminated.
The following plots illustrate pressure evolution in pipe nodes, mass flow at pipe ends, quality evolution in pipe nodes, and density evolution in pipe nodes.
