#2683 Quantifying Water Content and Equilibration Timescale of Wind Tunnel Materials Xinting Yu1, Sarah M. Hörst1, Chao He1, Nathan T. Bridges2, and Devon Burr3 1Department of Earth and Planetary Sciences, Johns Hopkins University ([email protected]) 2Applied Physics Laboratory, Johns Hopkins University, 3Department of Earth and Planetary Sciences, University of Tennessee

Conclusion Materials summarization and the methods of measuing Water content measurement results for various wind water content . tunnel materials. To improve our understanding of the e ect of 1. Low-density materials tend to have higher water interparticle forces, we measured water In addition to low-density materials, materials with higher content (>5%) compared to high-density materials content and equilibration timescales for density (basalt, quartz sand and beach sand) are used for (0.05-0.1%). various wind tunnel materials. comparison. 2. Low-density materials take >6 hrs to equilibrate, while high density materials only need <30 mins. Material Density (kg/m3) Size Range (µm) The low-density materials used in the wind 3. The water content of materials grows linearly with Basalt 3000 150-1000 2 tunnel have: increasing relative humidity (RH=15-60%), with R >0.8. Quartz Sand 2650 105-125 1. high water content, ~6%; Beach Sand 2650 500-1000 2. long equilibration timescales, >6 hrs. Walnut Shells 1100 125-1000 The high water content of these materials may Activated Charcoal 250-550 400-841 [1] increase the interparticle forces and thus GC 350 37-175 signicantly increase the threshold wind Iced Tea 100-200 N/A speed. Iced Coffee 100-200 N/A

Low density materials are widely used in planetary wind The water content of the materials is determined through gravimetric measurement. tunnels but are not well characterized. 1. The materials are dried for 24 hrs in a 120˚C and weighed

Aeolian processes are found on many worlds including: on an analytical balance (mdry). Earth, Venus, Mars, Titan, Triton, Pluto and comet 67p[2]. 2. After drying, they were removed from the oven and weighed again (m ). While wind tunnels are very e ective at simulating aeolian wet The water content is then given by: processes with di erent planetary parameters, the robust- u(%)=(m -m )/m *100% ness of the results depends on both the experimental con- wet dry dry The equilibration timescales are acquired by measuring the ditions and understanding of experimental materials. weight as a function of time. Low-density materials are widely used in planetary wind tunnels, e.g., Titan and Mars Wind Tunnel (TWT and the MARSWIT), to simulate the lower gravity on Titan and Mars.

Previous studies[3,4] have shown e ect of water content on threshold wind speed for high-density sand (~2650 kg/m3):

water content change threshold change

0.1%—>0.2% 10%

0–>0.3~0.6% 100% Similar data for low-density materials are missing, thus water content and equilibration timescale is the focus of the study.

References [1] C.L. McKenna-Neuman. Boundary-Layer Meteorology, 108(1):61-89, 2003. [2] D.M. Burr, et al. Aeolian Research, 18:205-214, 2015. [3] P-Y Belly. Technical report, USACE, 1964. [4] J.N. Svasek & J. H. J. Terwindt. Sedimentology, 21(2), 311-322. [5] D.M. Burr, et al. Nature, 517:60-63, 2015. Titan Wind Tunnel (TWT) with important components labelled [5].

Xinting Yu, Department of Earth and Planetary Sciences, Johns Hopkins University, MD, Baltimore, USA