Abstract
Plate type fuel element is widely used in integral and test reactor cores with the advantages of higher power density, deeper fuel burnup and more compact structure. In the semi-closed narrow gap rectangular channel, physics-structure coupling effect under low pressure condition will lead to very complex coolant flow and heat transfer phenomena. Knowledges of the bubble movement and deformation regime are important for studying the mechanism of gas-liquid two-phase flow. In this work, a visual experimental investigation was carried out for the bubble rising characteristics and bubble three-dimensional (3D) reconstruction in a rectangular channel. The process of the bubbles motion was observed by two vertically placed high-speed cameras. By controlling the power of the oxygen pump and the aperture of the air outlet respectively, the rate of bubble formation can be controlled, which eliminated the effects of bubble-to-bubble interactions by increasing the distance between the bubbles. Based on the extracted parameters obtained by digital image processing and assumption that each cross section along the height of bubble to be an ellipse, a new method for reconstructing bubble shape was proposed, using 3D modeling method which can more closely simulates objects to connect bubble elliptic cross sections smoothly under the condition that the cross sections of bubble were not changed as much as possible. Then the bubble shape and trajectory were reconstructed. The results showed that the 3D trajectory of bubble was oscillating and the reconstructed bubble shape not only conformed to the projected contour but also satisfied the effect of surface tension which lead to smooth shape of the bubbles in any time.
