抄録
Precipitation of dissolved materials during the mixing by a gravity current is investigated in the laboratory. The experiment includes the physical process as well as the chemical process of two miscible fluids of slightly different density. Ammonium carbonate and calcium chloride solutions are used for these fluids, and sodium chloride is also dissolved into the former solution to control the density difference between these fluids accurately. When these solutions are mixed during the physical process of the advancement of a gravity current generated by lock-exchange flows, the chemical reaction takes place to make calcium carbonate which hardly dissolves in water to be visible as white substance. The behavior of this visible suspended substance is analyzed by digital image processing.
The results show that the white substance made by the mixing of the two fluids appears most clearly in the upper region of the current head. The substance remains stationary and elongated downstream along the density interface. After a while it collects in masses of clouds in a three-dimensional way, and eventually sinks to the bottom. It is found that this chemical process depends on the dynamics of the gravity current, and that the chemical reaction is suppressed with increasing density difference.
