Separation of thermoviscous losses in Celcor™ ceramic

A series of three papers by Sabatier and coauthors reported successive improvements to both the theory and measurement of excess attenuation due to the wall porosity of Celcor™. We report an independent measurement of excess attenuation due to wall porosity of Celcor conducted to study the attenuation due to viscous and thermal effects separately for a thermoacoustic refrigeration application. A 38-mm-long sample was placed at the center of a 700-mm-long electrodynamically driven plane wave resonator. The location of the Celcor within the standing wave would select different contributions from viscosity and thermal conductivity. As per the technique described by Moldover et al. [Modern Acoustical Techniques for the Measurement of Mechanical Properties (Academic, San Diego, 2001)], the quality factors Q were measured between 230 Hz and 1.6 kHz in air at atmospheric pressure on a pristine sample. Wall pores were then blocked by an in situ polymerization sealing process. There was no observed decrease in attenuation of even modes (dominated by thermal loss) for the coated sample below 1.0 kHz. The volume exclusion due to pore sealing was inferred by the increase in even mode resonance frequencies in good agreement with other determinations of wall porosity. Thermoviscous losses were computed with DELTAE and compared to measured losses.