A Comparative Study of G-jitter Effect on Thermal Diffusion aboard the International Space Station

Fluid science research including thermal diffusioninfluids benefitsfrom thequies- cent low-gravity environment provided by the In- ternational Space Station (ISS). However, resid- ual gravities (or g-jitters) aboard the ISS impact the overall environment in which experiments are being performed. The impact of these resid- ual gravities needs to be assessed to ensure that they are appropriately accounted for when results are being reported for experiments performed on- board the ISS. In this paper we study the ther- mal diffusion process in a ternary mixture of n- butane, dodecane and methane. Measured data from the Space Acceleration Measurement Sys- tem (SAMS) acceleration systemonboard the ISS and related influence on fluid flow are compared with the ideal zero-gravity simulation to illustrate the effect of reduced gravity (small accelerations) on thermal diffusion. A three-dimensionalnumer- ical model is implemented forthestudyofvarious g-jitter scenarios. It is found that the ISS micro- gravity environment can cause the diffusion pro- cess to depart from the ideal behaviour in some circumstances. Such departure varies with the magnitudeoftheg-jittersandmay beinsignificant when the g-jitter magnitude is below a threshold value around 10μg. Furthermore, the magnitude of the g-jitters is not the only factor affecting the diffusion process. It has to be evaluated together with the frequency and alignment of the g-jitters. In general, this comparative study indicates that the ISS is an effective reduced gravity platform for experimental diffusion studies.

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