Measurement of Thermophoretic Velocity in Surrounding Gas of Nitrogen or Carbon Dioxide

摘要

Several experiments are conducted under the microgravity condition, which is achieved by a free-fall, for measuring the thermophoretic velocity in surrounding gas of nitrogen and carbon dioxide. PMMA spheres are used as measured particles, which are 2.91μm in mean diameter. The temperature gradient is 10 K/mm and the pressure is the range between 20 kPa and 100 kPa. Velocities of particles are individually measured during 0.25 s of the microgravity condition and the measurements are repeated in order to attain the accuracy by accumulating data. Comparison between obtained experimental results and theoretical predictions are done; the result for nitrogen is consistent with prediction, while a notable discrepancy is found for carbon dioxide. The disagreement is fixed by modifying the tangential momentum accommodation coefficient.