Method and apparatus using turbine flow meter to measure fluid flow therethrough without reference to viscosity

A method of calculating a mass flow through a duct, the method comprising the steps of:

• providing a dual rotor turbine volumetric flow meter operably connected to a duct having fluid flowing therethrough, the dual rotor turbine having a temperature gauge, a first rotor and a second rotor, at least one of said first rotor and said second rotor having a non-linear response to fluid flow,
• calibrating the dual rotor turbine volumetric flow meter by deriving a Rosbko/Strouhal number curve therefor,
• determining a first rotor frequency and a second rotor frequency,
• dividing the second rotor frequency by the first rotor frequency to derive a frequency ratio,
• calculating a combined Roshko number using the frequency ratio,
• determining a combined Strouhal number using the combined Roshko number and the Roshko/Strouhal number curve,
• calculating the volumetric flow rate using the combined Strouhal number,
• providing a density meter operably connected to the duct, the density meter determining the density of the fluid,
• multiplying the density by the volumetric flow rate to calculate the mass flow moving through the duct.

An apparatus for calculating a mass flow through a duct, the apparatus comprising:

• a dual rotor turbine volumetric flow meter operably connected to a duct having fluid flowing therethrough, the dual rotor turbine having a temperature gauge, a first rotor and a second rotor, at least one of said first rotor and said second rotor having a non-linear response to fluid flow, the dual rotor turbine volumetric flow meter adapted to be calibrated with a Roshko/Strouhal number curve therefor,
• the first rotor having a first frequency and the second rotor having a second frequency, means for calculating a frequency ratio by dividing the first rotor frequency by the second rotor frequency, means for calculating a combined Roshko number using the frequency ratio, means for calculating a combined Strouhal number by using the combined Roshko number and the Roshko/Strouhal number curve, means for calculating the volumetric flow rate by using the combined Strouhal number,
• a density meter operably connected to the duct, the density meter determining the density of the fluid,
• means for calculating the mass flow moving through the duct by multiplying the density by the volumetric flow rate.