Measuring and testing – Volume or rate of flow – By measuring vibrations or acoustic energy
Patent
1993-12-03
1995-06-06
Chilcot, Jr., Richard F.
Measuring and testing
Volume or rate of flow
By measuring vibrations or acoustic energy
7386128, G01F 100
Patent
active
054212120
DESCRIPTION:
BRIEF SUMMARY
The invention concerns a method for acoustic flow measurement for measurement of the flow velocity of gases and/or of quantities derived from same, in which method a long-wave sound is transmitted into the measurement pipe and, by means of two sound detectors placed at a certain distance from one another in connection with the measurement pipe, the sound signals that propagate in the gas flow downstream and/or upstream are detected, the flow velocity of the gas that flows in the measurement pipe being determined by means of said sound signals, preferably with correlation.
Further, the invention concerns a device for measurement of the gas flow velocity and/or of quantities derived from same, such as volumetric flow and/or mass flow, which device comprises a measurement pipe, in which the gas flow to be measured runs, which device comprises a loudspeaker or loudspeakers as the transmitters of the sound signals and microphones as the sound detectors, said microphones being placed in connection with the measurement pipe at a certain known distance from one another, and which device comprises a signal generator or equivalent, by whose means electric signals are fed to said loudspeaker or loudspeakers, and which device comprises a correlator, to which the signals received from said microphones are fed.
From the FI Patent No. 76,885 of the Technical Research Centre of Finland (Valtion teknillinen tutkimuskeskus VTT), a method and a device of acoustic flow measurement are known for measurement of the flow velocities, volumetric flows, and/or mass flows of gases, liquids, and/or multi-phase suspensions in a pipe or in an equivalent wave tube by making use of acoustic waves propagating downstream and upstream. In this prior-art method and device, the wide-band acoustic signal coming from the sound sources is made to propagate in the measurement pipe or equivalent wave tube in the plane-wave mode both downstream and upstream, and the flow velocity is determined on the basis of the sound transit times obtained from the maxima and/or the minima of the correlation functions of the measured sound signals and on the basis of the mutual distance between the measurement points.
In one technical solution described in said FI patent, the sound is fed into the measurement pipe in the form of a frequency sweep, and the transit time of sound is determined from the signals of the microphones placed at the ends of the measurement interspace by means of a polarity correlator. From the transit times measured downstream and upstream, it is possible to measure both the average flow velocity and the sound speed in a medium at rest with high accuracy. Moreover, if necessary, from the flow velocity and from the cross-sectional area of the pipe, it is possible to calculate the volumetric flow rate. A gas flow velocity measured in accordance with said FI patent or in some other way is, as a rule, used as starting information, together with the temperature and the pressure of the gas, for computing of the mass flow rate. Thus, measurement of the flow velocity is, as a rule, combined with measurement of the temperature and of the pressure of the gas.
It is well known that the sound speed in a gas mainly depends on the composition and temperature of the gas. The composition affects the sound speed mainly by the intermediate of the average molecular weight, and to some extent also by the intermediate of the number of degrees of freedom in the molecules, i.e. of the number of atoms present in a molecule.
In the applicant's FI Patent Applications Nos. 916102 and 916103, a method and a device are described for measurement of the flow velocity of a gas and/or of quantities that can be derived from same. In the latter FI application, a method and a device are described for monitoring of a gas flow, in particular of a natural-gas flow, in particular for monitoring of the composition of the gas. In the method of the FI Pat. Appl. 916103, it has been considered novel that, in the method, an oscillation of sound frequency is applied to the gas flow pi
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Koukkari Sauli
Mayranen Tarmo
Biegel R.
Chilcot, Jr. Richard F.
Instrumenttitehdas Kytola Oy
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