Experimental Study On Bubble Departure In Natural Circulation Under Rolling Condition

A study on vapor bubble departure in natural circulation subcooled-boiling under rolling condition is performed with theory and experiment in this dissertation.In the theoretical study, the forces acting on the departing bubbles under rolling condition are analyzed. The variety of the forces under rolling condition are caused by the fluctuation of flow rate. A model of forces acting on the departing bubbles under rolling condition is established.Under natural circulation, a visualized experiment on vapor bubble departure is carried on. The range of parameters: the system pressure between 0.12MPa and 1.1 MPa, the rolling angle 10°, the rolling periods 10s, 12s and 15s, the subcooled degree of water between 10°C and 50°C, the heating power between 0 and 493.4 kW/m~2.The results comparing rolling condition with non-rolling condition are shown as follow. The fluctuation of flow rate is caused by rolling, and other parameters like outlet temperature, wall temperature etc., follow the fluctuation. Under rolling condition, the position of vapor bubble departure is moving along the heating wall, and there are two stable positions, the highest one and the lowest one. Under the same thermal hydraulic condition, the corresponding positions of non-rolling distribute between the highest and the lowest of rolling. The fact is that the nucleation sites are activated and extinguished, which cause the position moving. The phenomenon of position moving in substance is caused by the fluctuation of flow rate.