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FLUIDA library examples
Vacuum network
This example shows most of the FLUIDA capabilities and the use of several different components. It contains two tanks, a pressure regulator, a vacuum pump, some pneumatic valves, calibrated orifices, etc. The aim of the simulation is to control the pressure level in the tanks "Tank1" and "Tank2" by switching the valves "V1" and "V2".
The model represents a system that deals with the extraction of polluted air from several places where high cleaning conditions are required ("Tank1" and "Tank2", 0.01 m3 each with a wall heat capacity of 100 J/K)). The working fluid is air and it is set by the component "WorkingFluid1".
Low vacuum is achieved by means of a water-ring pump. This pump has a strong non-linear characteristic, which should normally be given by the supplier of the pump (a table for pump displacement versus rotational speed and vacuum pressure is implemented in the model).
The pressure-regulator keeps the vacuum-level at a certain value. It is a valve with variable throat section driven by the upstream/downstream pressure difference according to opening/closing settings (the allowable pressure difference is set to 10 kPa). The maximum throat section is 1 · 10-5 metres.
The circuit contains a porous filter. The pressure loss in this component is calculated as a linear relation between flow and pressure-drop for given reference conditions. For this model, the conditions are a pressure drop of 80 kPa for 0.0002 kg/s mass flow (reference pressure: 0.1 MPa).
Two on-off valves ("V1" and "V2") control the incoming atmospheric air, either from the pressure regulator branch or the filter branch. Additionally, there are two calibrated holes "R2" and "R3" (quadratic restrictors). The diameter considered in all these items are: 0.005 metres for valves "V1" and "V2", 0.001 metres for restrictor "R2", and 0.0001 metres for restrictor "R3".
Some other elements are used to connect all the parts of the circuit, such as pipes, junctions, and tee joints. The diameter considered in all these items is 0.030 metres.
Finally, the environmental conditions such as ambient pressure and temperature are simulated using constant pressure tanks ("HP_tank", "Ambient1", "Ambient2", and "Pump_exit") and thermal boundary nodes ("Wall_BT1" and "Wall_BT2"). They are set to 0.1 MPa and 300 K respectively.
At the beginning of the simulation, valve "V1" is opened and "V2" is closed, permitting a direct air flow from the external atmosphere "HP_tank" to "Tank1". In this first stage, the air in the low pressure area is pumped out reaching the desired pressure conditions in "Tank1" in less than 5 seconds. The pressure drops until the pressure difference in the regulator is enough to open it. After this, the pump maintains the pressure level in the tanks by pumping out the incoming air flow from the regulator, filter branches and tank leaks.
The valves are kept in their initial status for up to 25 seconds, at which point "V1" is closed and "V2" is opened. The air coming from the pressure regulator then reaches "Tank1" after passing through "Tank2". The change of valve status can be clearly seen in the mass flow plots. The pressure level of the tanks is kept in the same way, as in the previous stage. Finally, the simulation is stopped at 100 seconds.
The following plots illustrate pressure evolution in the tanks, temperature evolution in the tank walls, mass flow through the valves "V1" and "V2", mass flow through the vacuum pump, and the regulation signal of the pressure regulator.
