Reply To: Mass conservation vs inflow and outflow

[SRP]

Hi,

When modeling an extract fan in a room with a very small natural opening, if the fan is set to remove air at a rate of 3m³/s, in a real-world scenario, the small opening would not realistically accommodate a 3m³/s inflow due to physical limitations. In CFD, however, the simulation must adhere to the conservation of mass, so it would show an inflow of 3m³/s if no other inflow or outflow boundaries are defined. This is because the simulation assumes that the mass entering a system equals the mass leaving the system. In the case where there is no natural opening and the extract fan is removing 3m³/s, the conservation of mass would still apply. In reality, the room would develop a negative pressure.