ACOUSTIC method of FLOW rates MEASUREMENT

The group of specialists from the Moscow State Mining University and the University of Mississippi has developed an ultrasonic spirometer for monitoring of breathing regime in various reviving and sustaining apparatuses as respirator and artificial lungs including testing and control systems. This device can also be used for the performance of similar applications in medical equipment. The device is based on the new physical principle. The electronics fulfilled with the usage of US element base.

The careful analysis of publications and preliminary laboratory estimation have showed that on the one hand acoustical methods in flow measurements have not realized their potential possibilities, and on the other hand none of the existing acoustics means of flow measurement allows to create  anemometer, which should be able:

• - to measure speeds of flow in the range of (0.05 ... 30) m/s;

• - not to have moving parts;

• - to measure high frequency pulsations;

• - to measure average flow speed in the working cross section;

• - to have stabile characteristics, allowing to decrease error.

The suggested measurement method satisfies all mentioned here demands. The method is based on the air-acoustics interaction and involves vibrations excitation in the cylindrical wave guide-air duct, their reception at some distance from the excitation point and a comparative analysis of radiated and received vibrations as a result of which an informative signal (e.g., vibration phase or time difference) is singled out, which serves as a flow rate measure. It differs from others known in that definite mode waves are being radiated and received by excitement of the air conduit elements, acoustically isolated from each other. This method provides accuracy and exception of air conduit effect upon the aerodynamics field of air-gas flow.

"We are encourage proposes for cooperative production of the new spirometry devices"
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The description of wave propagation process in the tubes without flow was suggested by E.Scuchic. From this description we made the conclusion which waves can spread in the round channel of the given diameter. The spread rate of the zero mode wave fronts of these vibrations is equal to one of sound velocity in open space with the same medium For the analytic description of the air-acoustic interaction, which is the base of acoustical anemometry, it is necessary to solve the boundary problem for the equation with partial derivatives. For the first approach the anemometer channel may be performed of unlimited length. For better correspondence with real physical phenomenon in the mathematics model it is necessary to take into consideration the error, coursed by the acoustical waves reflection from the open ends of the anemometer. The means of the correction determination, corresponding to the reflected waves field with the help of normal modes reflection coefficient calculation is offered. The analytic dependencies of the velocities upon the dimensions, channel walls material and air-gas medium characteristics have been got using G. Gohnson's and K. Ogimoto's work

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