17:15 〜 19:15
[AGE34-P15] Evaporation from Soil Surface under Low/Microgravity Environment
キーワード：micro-gravity、evaporation、water holding capacity、hydraulic conductivity
In recent years, there has been a lot of research aimed at long-term stays in space. In the future, it will be necessary to be self-sufficient in terms of food, but one issue in plant cultivation is understanding the dynamics of water in the soil in different gravitational environments. Therefore, in this study, we conducted experiments with the aim of clarifying the evaporation of water in microgravity environments.
In order to create a microgravity environment, we used a 3D clinostat and conducted experiments under four conditions: 1G, 1/3G, 1/6G, and 0G. We used three types of soil: Toyoura standard sand, clay soil, and Akadama soil, and the initial volumetric water content of the soil was set at 20%. In previous experiments, there was a problem where the soil moved due to the rotation of the clinostat, so we first constructed an experimental system where the soil did not move. We filled a 50 ml centrifuge tube with soil, covered the soil surface with a 77 µm nylon mesh, and fixed the soil in place by holding it down from above with an aluminum pipe. We also made a hole in the lid of the centrifuge tube with a diameter similar to that of the aluminum pipe, to allow for evaporation. Using this, we conducted an evaporation experiment for 48 hours and measured the mass change. Next, we prepared three types of soil structure: normal packed soil, soil with vertical pores, and aggregate structure soil, and measured the change in evaporation amount due to differences in soil structure.
As results, the evaporation experiment was able to continue without the soil spilling out while rotating. For all soil types, the smaller the gravity, the less the evaporation amount, and we obtained a different finding than before. We thought this was because in a microgravity environment, the buoyancy added to the evaporated water molecules becomes smaller. When buoyancy decreases, the movement of evaporated water vapor becomes less likely to occur, and the relative humidity of the air near the soil surface is maintained at a high level. We thought that this would make it less likely for further evaporation to occur, and that the amount of evaporation would consequently decrease. There was almost no difference in the amount of evaporation depending on the type of soil or the soil structure, but we thought that this was because the evaporation period was short, at 48 hours. Unlike drop experiments and flight experiments, the 3D clinostat makes it possible to conduct long-term experiments, so we would like to develop experiments that make use of this characteristic.
In order to create a microgravity environment, we used a 3D clinostat and conducted experiments under four conditions: 1G, 1/3G, 1/6G, and 0G. We used three types of soil: Toyoura standard sand, clay soil, and Akadama soil, and the initial volumetric water content of the soil was set at 20%. In previous experiments, there was a problem where the soil moved due to the rotation of the clinostat, so we first constructed an experimental system where the soil did not move. We filled a 50 ml centrifuge tube with soil, covered the soil surface with a 77 µm nylon mesh, and fixed the soil in place by holding it down from above with an aluminum pipe. We also made a hole in the lid of the centrifuge tube with a diameter similar to that of the aluminum pipe, to allow for evaporation. Using this, we conducted an evaporation experiment for 48 hours and measured the mass change. Next, we prepared three types of soil structure: normal packed soil, soil with vertical pores, and aggregate structure soil, and measured the change in evaporation amount due to differences in soil structure.
As results, the evaporation experiment was able to continue without the soil spilling out while rotating. For all soil types, the smaller the gravity, the less the evaporation amount, and we obtained a different finding than before. We thought this was because in a microgravity environment, the buoyancy added to the evaporated water molecules becomes smaller. When buoyancy decreases, the movement of evaporated water vapor becomes less likely to occur, and the relative humidity of the air near the soil surface is maintained at a high level. We thought that this would make it less likely for further evaporation to occur, and that the amount of evaporation would consequently decrease. There was almost no difference in the amount of evaporation depending on the type of soil or the soil structure, but we thought that this was because the evaporation period was short, at 48 hours. Unlike drop experiments and flight experiments, the 3D clinostat makes it possible to conduct long-term experiments, so we would like to develop experiments that make use of this characteristic.