Method for Ascertaining Flow by Means of Ultrasound

A method for ascertaining flow of a gas mixture through a circularly cylindrical measuring tube having a straight, measuring tube, longitudinal axis and an inner diameter DI, wherein at least one component i of the gas mixture is a hydrocarbon, comprising the steps of:

• ascertaining a first average flow velocity vL by means of travel-time difference measurement of acoustic signals along a signal path;
• ascertaining a modified Reynolds number Remod according to the formula Remod=(vL*DI)/vkin, wherein the kinematic viscosity vkin of the gas mixture is known;
• and
• ascertaining a second average flow velocity vA by means of a known function vA=f(Remod) as a function of the modified Reynolds number Remod, wherein the method step of ascertaining the modified Reynolds number Remod precedes the method step of ascertaining the kinematic viscosity vkin of the gas mixture;
• and
• ascertaining the kinematic viscosity vkin of the gas mixture occurs taking into consideration the material fractional amounts xi of the individual components i of the gas mixture.