ICONE11-36304 The Experimental Study for the Characteristics of Steam Bubbles in Subcooled Boiling Flow

Abstract

On a design and a safety numerical analysis for light water reactors (LWRs), Two-fluid model and Three-fluid model have been used. As for the numerical analysis, the information about the steam bubbles, which are interfacial area concentration, interfacial heat transfer and interfacial shear stress, were based on the experimental data of a single steam bubble flowing upward in a stagnant liquid condition. Therefore, the difference of the result between the numerical analysis and the experimental data in a forced convection flow was occurred. In other word, the characteristics of the steam bubbles in a subcooled boiling flow have not been inspected enough. Since the behavior of the steam bubbles in a subcooled boiling flow was complicated, it was difficult to measure the motion of the steam bubbles experimentally. Consequently, it has been important to clarify the characteristics of steam bubble in a subcooled boiling flow. On the other hand, the development of measurement method was also important for clarifying the steam bubbles motion in a subcooled boiling flow. In present work, the characteristics of steam bubbles in a subcooled boiling flow under an vertical circular channel were investigated by applying a digital image processing method assembling a digital high-speed video camera, a stroboscope, and a personal computer. As a result, the profiles of void fraction, interfacial area concentration and interfacial heat transfer coefficient along the flow direction could be measured. For the steam bubbles whose diameter were less than 8mm, the interfacial area concentration and the mean bubble diameter had a correlation with void fraction despite the variation of liquid flow rate and subcooling. In case the collapse of steam bubble occurred due to an irregular bubble condensation, the interfacial heat transfer coefficient with the bubble collapse was about twice of that without a bubble collapse. And the interfacial heat transfer coefficient without bubble collapse showed a good agreement with the correlation supposed by Akiyama. In addition, the supposed image processing method could be applied to the present experimental condition.