This master's thesis deals with the gas flow measuring method according to the Venturi critical nozzle model. The physical starting points of the critical nozzle operation are presented, on which the adapted mathematical model for calculating the mass flow is based. A test site is presented, where measurements were performed to determine the effect of a change in the type of gas on the mass flow forecast if the system is calibrated to dry air and only the change in material properties is taken into account in the calculation model. It was found that the measurements of the model calibrated for dry air cannot be used to calculate the mass flow for argon and nitrous oxide and can be used for the measurement with oxygen and nitrogen.
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