Acoustic Flow Measurement Research Articles

Asymmetric viscothermal acoustic propagation and implication on flow measurement for SOFC

In the applications of heating generation based on the solid oxide fuel cells (SOFC) technology, a high-accuracy performance of flow measurement is of great importance. Due to the advantage of non-invasive no-moving-parts construction and bi-direction measurement, ultrasonic flow meter, where viscothermal dissipation and asymmetric acoustic modes cannot be overlooked, may be a promising method in the SOFC-based applications. The present paper mathematically formulates asymmetric linear disturbance dynamics in terms of velocity and temperature disturbances based on the conservations of mass, momentum and energy. An iterative calculation procedure, which is similar to Galerkin method, is presented. Numerical analysis of asymmetric acoustic features (phase velocity and attenuation coefficient) are comprehensively given under the effects of viscothermal dissipation and shear flow convection. In the end, flow measurement performance of asymmetric acoustic modes is literally discussed. Numerical study shows that viscothermal dissipation affects the cut-on frequency of acoustic modes and couples nonlinearly with shear convection when the flow Mach number is large. These parameters impose significant influences on measurement performance. Each acoustic mode has inherent measurement derivation which can be theoretically used to compensate the acoustic flow measurement error. Apparent prediction error may occur if the viscothermal dissipation is taken out of consideration.

Determination of an equivalent pore size from acoustic flow measurements

The hydraulic radius, rh, is defined as the ratio of a channel’s cross-sectional area to its perimeter. This parameter is important for specification of the performance of a porous medium that can be used as a regenerator in a Stirling engine or refrigerator. It is easy to calculate rh for pores of regular geometry, but difficult in more complex media. Two techniques which use oscillating flow to determine this parameter will be presented and compared. One technique extracts rh by finding the low velocity limit of the standard expression for viscous pressure drop in the Poiseuille flow regime. The other involves a plot of the nondimensional viscous flow resistance, Δpvis/Δxωρu, versus the reciprocal of the viscous penetration depth, 1/δν, in the laminar flow regime. When rh<δν, the flow behavior is frequency independent and the dynamics is characterized by rh only. When rh>δν, the flow resistance is frequency dependent and the dynamics is characterized by both rh and δν. It is possible to identify an effective hydraulic radius by equating it to the value of δν where that transition occurs. [Work supported by ONR.]

On the theory of acoustic flow measurement

The motivation for this paper arises from problems frequently encountered in acoustic flow measurement. Of primary concern is that acoustic flow meters, rather than directly measuring the volume flow rate, measure some biased average of fluid velocity in a duct. That is, the average is usually not equal to the volume flow rate divided by the duct cross-sectional area, and is influenced by alterations in the flow profile. In this paper perturbation analysis is used to characterize nontrivial situations under which a sound field may be convected to first order by the unbiased cross-sectionally averaged flow. Perturbation analysis previous to this paper has considered only the plane-wave approach to the problem. This paper will examine the use of higher-order duct modes. It will be shown that under certain circumstances these modes are less prone to distortion by the flow field than the plane wave, and will still average the flow to an approximation which improves with mode order. The study is restricted to the consideration of rectangular section ducts and cylindrical ducts with axisymmetric flow fields. As an aside, the two-dimensional viscous convective wave equation by Mungur and Gladwell [J. Sound Vib. 9, 28–48 (1969)], has been extended to three dimensions in this paper. In deriving this form it was noticed that an error existed in the original equation. This error has been corrected in the present three-dimensional version of the equation.

5421212 Method and device in acoustic flow measurement for ensuring the operability of said measurement : Mayranen Tarmo; Koukkari Sauli Muurame, Finland assigned to Instrumenttitehdas Kytola Oy

5421212 Method and device in acoustic flow measurement for ensuring the operability of said measurement : Mayranen Tarmo; Koukkari Sauli Muurame, Finland assigned to Instrumenttitehdas Kytola Oy