https://doi.org/10.1140/epjst/e2008-00402-0
Application of the diffraction theory for photothermal deflection to measurements of thermophysical and mass-diffusion properties of gases
1
National Research Council of Canada, Institute for Fuel Cell Innovation, 4250 Wesbrook Mall, Vancouver, British Columbia, V6T 1W5, Canada
2
Institute of Modern Optical Technologies, Suzhou University, Suzhou, Jiangsu, 215006, P.R. China
The application of recently developed diffraction theory for cw transverse photothermal deflection spectroscopy (normal deflection only) to the measurements of thermophysical and mass-diffusion properties of gases is presented. Compared with the traditional ray-optics theory, the diffraction theory has one more term in the phase signal. This term quantitatively exhibits the probe-beam size effect on the phase signal. Experimental results demonstrated that even if the ratio of the probe-beam radius to the thermal diffusion length of a deflecting medium was as low as about 0.22, the probe-beam size effect could not be ignored when measuring the distance between the probe beam and a solid sample using the phase signal. With the measured distance, the thermal diffusivity αg and the temperature coefficient of the refractive index dn/dT of pure gases (O2, N2, and CO2) and binary gas mixtures (CO2-O2 and CO2-O2) were precisely measured, resulting in good agreement with literature values. Furthermore the measured dn/dT values of the pure gases had one more significant figure than the literature ones. The concentration dependences of αg and dn/dT were employed for the determination of mass-diffusion coefficients of CO2-O2 and CO2-N2, and the results were consistent with literature values.
© EDP Sciences, Springer-Verlag, 2008
