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.