Frequency response of natural convection of nanofluids under microgravity with gravity modulation

What is it about?

The International Space Station, which orbits the earth, is not in a completely weightless state. A minute residual gravity from 0.0001g0 to 0.001g0 is generated compared to the gravity acceleration g0 on the ground. The residual gravity includes steady and periodic accelerations. Its amplitude is approximately 0.001g0, and its frequency varies widely due to the vibration factors. The fluctuating periodical gravity acceleration is called gravity modulation and is caused by unavoidable vibrations such as mechanical operations and human activities in spacecraft. Since natural convection is unlikely to occur under a microgravity field, it is considered that the same heat transfer characteristics as in the gravity field on the ground cannot achieve. We consider using nanofluids with high thermal conductivity to improve heat transfer fundamentally. In this study, we investigate the possibility of applying nanofluids to thermal management systems in the space environment. However, when nanofluids are used in space, the effect of gravity modulation on the behavior and heat transfer characteristics of nanofluids is unclear. Therefore, it is necessary to conduct a fundamental investigation for heat transfer in the presence of gravity modulation. From the above points of view, this study focuses on three-dimensional natural convection by nanofluids to improve the heat transfer characteristics under microgravity fields. We investigated the influences of frequency and volume fractions of nanoparticles on heat transfer.

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Photo by Norbert Kowalczyk on Unsplash

Photo by Norbert Kowalczyk on Unsplash

Why is it important?

Various damping devices have been considered to reduce the influences of gravity modulation under microgravity. The vibration-damping devices devised so far can suppress gravity modulation at frequencies higher than 1.0 Hz but not at lower frequencies. Research on nanofluids under a microgravity environment is mostly two-dimensional analysis, and three-dimensional thermal convection structures have not been investigated. Furthermore, the effects of gravity modulation on three-dimensional thermal convection and heat transfer have not been clarified. This study focuses on such an unexplained research area. A detailed three-dimensional numerical simulation clarified the time variation of three-dimensional thermal convection structures in the presence of gravity modulation and the frequency response of the heat transfer characteristics to the gravity modulation.

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