Gas phase thermal diffusivities by a thermal lens technique |
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Authors: | RT Bailey FR Cruickshank D Pugh A McLeod W Johnstone |
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Institution: | Department of Pure and Applied Chemistry, University of Strathclyde, 295 Cathedral Street, Glasgow G1 1XL, UK |
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Abstract: | A simplified design of thermal lens apparatus is presented in which a chopped cw argon laser beam produces a transient thermal lens in a cylindrical gas cell. The axial intensity variation of a cw helium-neon laser probing this lens is analysed to yield the thermal diffusivities and thus the thermal conductivity coefficients of Kr, CO2, CH4, C2H6, C3H8, C3H6 and C4H10 as 9.4 × 10?3 ± 4%, 1.6 × 10?2 ± 3%, 2.98 × 10?2 ± 4%, 2.03 × 10?2 ± 4%, 2.05 × 10?2 ± 7%, 1.6 × 10?2 ± 8% and 1.9 × 10?2 ± 8% respectively in W m?1 K?1 at 300 K. The method is rapid, requiring only that the sample be transparent at both laser frequencies used. A simplified mathematical analysis is shown to be adequate for this system. For the conditions specified, self-lensing of the argon laser beam is shown to be compensated by using an effective laser beam diameter. |
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