Pressure type flow rate control device, and flow rate calculating method and flow rate control method for same

A pressure-type flow rate control device for calculating a flow rate Q of a mixed gas that passes through an orifice from a flow factor FF, while an upstream pressure P1 of the orifice is maintained at approximately at least twice a downstream pressure P2 of the orifice,

• the mixed gas consisting of a first gas and a second gas and having a mixture ratio representing the volume ratio of X:(1−X) between the first gas and the second gas,
• the pressure-type flow rate control device comprising:
• a first processor calculating an average density ρAV, average specific heat ratio κAV, and average gas constant RAY of the mixed gas, respectively, by:
• ρAV=X·ρ(A)+(1−X)·ρ(B),
• κAV=X·κ(A)+(1−X)·κ(B), and
• RAV=X·R(A)+(1−X)·R(B)
• using a density ρ(A) of the first gas, a density ρ(B) of the second gas, a specific heat ratio κ(A) of the first gas, a specific heat ratio κ(B) of the second gas, a gas constant R(A) of the first gas, and a gas constant R(B) of the second gas;
• a second processor calculating the flow factor FF of the mixed gas by:
• FF=(k/ρAV){2/(κAV+1)}1/(κAV−1)[κAV/{(κAV+1)RAV}]1/2
• using the average density ρAV, the average specific heat ratio κAV, and the average gas constant RAV, where k is a constant;
• a third processor calculating the flow rate Q of the mixed gas that is output from the orifice by:
• Q=FF·S·P1(1/T1)1/2
• using the flow factor FF of the mixed gas, where S is an orifice cross section, and T1 is a temperature of the gas on an upstream side of the orifice;
• an adjuster disposed on the upstream side of the orifice and adjusting a supply amount of the mixed gas that is supplied to the orifice;
• and
• a controller controlling the supply amount adjusted by the adjuster such that the flow rate Q of the mixed gas that is calculated becomes a predetermined target flow rate Q0.