DOI: 10.1007/s10765-005-5581-7 International Journal of Thermophysics, Vol. 26, No. 3, May 2005 (© 2005) High-Precision and High-Resolution Measurements of Thermal Diffusivity and Infrared Emissivity of Water–Methanol Mixtures Using a Pyroelectric Thermal Wave Resonator Cavity: Frequency-Scan Approach A. Matvienko 1 and A. Mandelis 1,2 Received January 21, 2005 The thermal diffusivity and effective infrared emissivity of water–methanol mix- tures were measured at atmospheric pressure and ambient temperature using a pyro- electric thermal-wave resonator cavity. The applied frequency-scan method allows keeping the cavity length fixed, which eliminates instrumental errors and substan- tially improves the precision and accuracy of the measurements. A theoretical model describing conduction and radiation heat transfer in the cavity was developed. The model predictions and the frequency-scan experimental data were compared, show- ing excellent agreement. The measurements were performed for methanol volume fractions of 0, 0.5, 1, 2, 5, 10, 20, 40, 75, and 100%. The fitted thermal diffusivity and effective emissivity vs. concentration results of the mixtures were compared to literature theoretical and experimental data. The maximum resolution of 0.5% by volume of methanol in water by means of the thermal-wave cavity method is the highest reported to date using thermophysical techniques. Semi-empirical expres- sions for the mixture thermal diffusivity and infrared emissivity as functions of methanol concentration have been introduced. The expression for infrared emissiv- ity is consistent with the physical principle of detailed balance (Kirchhoff’s law). The expression for thermal diffusivity was found to describe the data satisfactorily over the entire methanol volume-fraction range. KEY WORDS: infrared emissivity; methanol; mixtures; photopyroelectric tech- nique; thermal diffusivity; thermal-wave resonator cavity; water. 1 Center for Advanced Diffusion Wave Technologies, Department of Mechanical and Indus- trial Engineering, University of Toronto, 5 King’s College Road, Toronto, Ontario M5R 3G8, Canada. 2 To whom correspondence should be addressed. E-mail: mandelis@mie.utoronto.ca 837 0195-928X/05/0500-0837/0 © 2005 Springer Science+Business Media, Inc.