| Description |
x, 45 pages, 20 unnumbered leaves : illustrations ; 28 cm. |
| Summary |
"The thermal accommodation coefficient plays an important role in low density thermal energy transfer measurement. The object of this investigation was to measure the thermal energy transfer between a heated test surface and a water cooled reference surface (flat black lacquer) consisting of two infinite concentric cylinders separated by dry air. Two machined and sanded steel cylinders with mean surface roughnesses of 25 microinches and 7.5 microinches were used as the test surfaces . Measurements were made in the pressure range of 1.2 x 10⁻⁶ mm Hg. to 1.8 x 10⁻⁶ mm Hg. and temperature range for test cylinders of 110°- 200. 2°F. in determining the emittance. The pressure range was 1.0 x 10⁻³ mm Hg. to 1.35 x 10⁻³ mm Hg. and the temperature range 115.5° -197.6° F. in determining the thermal accommodation coefficients. The thermal accommodation coefficient for dry air on a steel surface with an average mean surface roughness of 25 microinches was 0.835 (emittance was 0.174) while for the 7.5 microinches surface condition, the thermal accommodation coefficient was 0.693 (emittance was 0.123). The experimental data indicated that for the same material, the rougher surface will have a higher value of thermal accommodation coefficient and emittance. The experimental results agree closely with those of classical theory (roughness causes more than one collision at the surface) and with some other investigators (2 & 7). The accuracy of the results as well as the experimental deviations are within the accepted engineering limits for this type of measurement"--Abstract, leaves ii-iii. |
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