METHOD AND VORTEX FLOW METER FOR DETERMINING THE MASS FLOW RATIO OF A MULTIPHASE FLOW

摘要

The present invention relates to a vortex flow meter and to a method for determining the mass flow ratio (x) of an at least temporarily two-phase or multiphase medium flowing in a measurement tube, having a gaseous first phase flowing with a first mass flow rate mG and having a liquid second phase flowing with a second mass flow rate mL, using a vortex flow meter which has a bluff body projecting into the flow medium and a vortex sensor placed in particular downstream of or within the bluff body, wherein the gaseous phase has a first density (&rgr;G) which differs from a second density (&rgr;L) of the liquid phase, comprising: producing Karman vortices in the flow medium at least in the region of the vortex sensor using the bluff body, wherein the vortices are shed from the bluff body with a vortex shedding frequency (fV) which is dependent on an instantaneous flow velocity of the flow medium; capturing periodic pressure variations caused by the Karman vortices in the flow medium using the vortex sensor to generate a sensor signal (S) corresponding to the pressure variations; selecting a useful signal component (M) from the sensor signal, which useful signal component (M) has a particularly narrow frequency band containing the vortex shedding frequency, in particular with a relative bandwidth of less than 50% of the instantaneous vortex shedding frequency, wherein preferably the instantaneous vortex shedding frequency corresponds to the central frequency of the frequency bandwidth; using the useful signal component (M) for determining a mass flow ratio (x) of the flow medium, wherein the mass flow ratio (x) is defined as the ratio of the first mass flow rate mG to a total mass flow rate at which the medium flows, in particular according to a calculation specification (AA).