Numerical study of diffusion coefficient measurements with sinusoidal varying accelerations

The effect of periodic gravitational acceleration on diffusion coefficient measurements was analyzed in terms of material properties in the specimen s uch as viscosity, density, and specimen configuration. We found that convec tion is induced in microgravity with sinusoidal varying accelerations becau se a concentration difference exists even under isothermal conditions. g-ji tter with lower frequency produced large error in the accuracy of the diffu sion coefficient measurement. The errors increased abruptly with a decrease in the frequency below 0.1 Hz. The error increased monotonously with a dec rease in the density ratio of elements in diffusion materials. In order to obtain optimized experimental conditions for experiment planning, the predi cted error due to gravitational disturbances was plotted as a function of m aterial properties such as the viscosity, the density ratio, and the specim en configuration. (C) 1999 American Institute of Physics. [S0021-8979(99)02 812-1].