Аuthors
1*, 1, 1, 2, 21. Joint Institute for High Temperatures of the Russian Academy of Sciences, 13, Izhorskaya str., Moscow, 125412, Russia
2. Baumann Moscow State Technical University, 105005, Moscow, 2nd Baumanskaya St., b. 5, c. 1
*e-mail: nikvikvas@mail.ru
Abstract
In the study of vapor explosions (a dangerous, destructive phenomenon that occurs when superheated melt interacts with cold water, potentially occurring during accidents at nuclear reactors, in the metallurgical and pulp and paper industries), research into the poorly understood, fast-moving subprocess of triggering (initiation) plays a crucial role. The initiation of a vapor explosion is associated with direct contact between the coolant and a drop of melt, caused by the vibrations of the thin vapor film covering it. Therefore, experimental studies of triggering are often conducted on a small scale, using single droplets melted in special crucibles and then falling in air into a container of water. The paper presents the results of a study of spontaneous fine fragmentation of tin melt droplets interacting with water by visualizing the process using high-speed video filming and the structure and size of solidified products (debris). To visualize the process, high-speed video filming was used with a Vi-deoSprint/C/G4 camera at a frame rate of 500 Hz through a special transparent window on the side of the water container. Images obtained with a Bresser LCD 50x-2000x microscope were used to assess the size and structure of the solidified tin fragments. The experiments were conducted in the following parameter ranges: tin melt mass mSn = 1–3 g, water temperature Twater = 18–23 °C, melt temperature 400 °C < TSn < 1000 °C. Fine fragmentation of tin droplets was observed in the approximate melt temperature range of 500 °C < TSn < 850 °C. With increasing melt temperature in this range, the power of vapor explosions and the degree of droplet fragmentation increased. The solidified fragmentation pro-ducts had a porous-mesh structure with a branched increased surface area with overall dimensions of several mm. To estimate the change in the temperature of a melt droplet during free fall in the air after exiting the melting crucible, a mathematical model was developed, which takes into account cooling due to convection and radiation. It is shown that the change in the temperature of the droplet before entering the container with water for typical conditions of the experiments is less than 1 % of the temperature of the melt in the crucible.
Keywords:
vapor explosion, fine fragmentation, melt droplet, tin, high-speed video filming, air cooling, mathe-matical modelingReferences
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