Experimental and theoretical study of photophoresis in a low-density gas

Results are presentedfrom a refinement of the kinetic theory of photophoresis for the entire range of Knudsen numbers. Allowance is made for the optical, thermophysical, and accommodation properties of the particles. Experiments are performed to measure the photophoretic force acting on model microscopic particles in air, helium, and argon within a broad range of gas pressure. The experiments confirm the theory's prediction of the dependence of the force on the Knudsen number and the heat-conduction parameter. Values of the asymmetry factor and accommodation coefficient are determined by comparing the experiment and theory. The results of experiments conducted on actual aerosols agree with the data used to model their macroscopic particles.