Microgravity Effects on Water Movement in Capillary Tubings.

Knowledges of growing crops in space are needed to achieve long duration space missions, such as manned Mars explorations. For successful space agriculture, it is important to understand water movement in porous media under microgravity. Capillary force may be a major factor for water move in porous media under microgravity. Previous studies reported that water hardly infiltrated into soil, implying that capillary force might be smaller under microgravity than under 1G. As the capillary rise theory involves a gravity term in the denominator, the height of capillary rise is supposed to be nearly infinite under microgravity. To understand microgravity effects on the capillary rise, we conducted capillary rise experiments with different sizes of capillary tubings (0.4, 0.6, and 0.8 mm in dia.) under microgravity made with parabolic flights. The water surface in the capillary tubings rose up to the end of the tubings as the gravitational force decreased. Our experiments revealed that capillary force might become nearly infinity under microgravity as the capillary rise theory implied water move in a capillary tubing. We also found that capillary rise velocity was larger in the first parabolic flight than that in the other flights. This velocity differences might be resulted from the inner surface condition of the capillary tubings whether it was dry or wet, affecting the contact angle and surface tension. We will discuss about this velocity differences and will compare with the previous research that carried out capillary rise experiments in horizontal capillary tubings under 1G.