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 such as viscosity, density, and specimen configuration. We found that convection is induced in microgravity with sinusoidal varying accelerations because a concentration difference exists even under isothermal conditions. g-jitter with lower frequency produced large error in the accuracy of the diffusion coefficient measurement. The errors increased abruptly with a decrease in the frequency below 0.1 Hz. The error increased monotonously with a decrease in the density ratio of elements in diffusion materials. In order to obtain optimized experimental conditions for experiment planning, the predicted error due to gravitational disturbances was plotted as a function of material properties such as the viscosity, the density ratio, and the specimen configuration. (C) 1999 American Institute of Physics. [S0021-8979(99)02812-1].