Experimental Investigation On Flow Characteristics And Heat Transfer Of Falling Water Film Of Passive Containment Cooling System (PCCS)

To enhance nuclear safety with passive features, the passive containment cooling system (PCCS) has been suggested by Westinghouse in the AP1000 to remove heat in the containment during postulated accidents by evaporation of the falling water film with high heat transfer coefficient and low power consumption. For an analysis of the PCCS cooling capability, it is extremely necessary to research the properties and mechanisms of the hydrodynamics, flow stability, heat transfer and breakdown of water film.This paper experimentally investigates the statistical characteristics, horizontal spread and longitudinal flow development on the experimental facility WAFSEA (Water Film Stability Experiment Apparatus), and researches the properties of heat transfer and breakdown on the water film heat transfer experiment apparatus. In this paper, the correlation of the mean film thickness based on Reynolds number (Re) and the variation rules of wave velocity, horizontal spread and longitudinal flow development were obtained by analyzing the data of maximum, minimum and mean film thickness, wave velocity and coverage of water film. The results show it is laminar flow for water film when Re is lower, and wave will be found with the Re increasing, the form of wave remains in this process before the Re reaches to 200. The solitary wave with large fluid will be discovered after the Re is 400, the wave velocity and amplitude of the solitary wave will remain with the Re increasing. The way how the film extends horizontally is obtained, with the flow rate increasing, the coverage will enlarge but the thickness will remain after the critical film thickness is achieved, and the longitudinal characteristics show that the flow may be fully developed at 2.6m from the origin.Finally, the variation of the dimensionless heat transfer coefficient with Reynolds number is obtained, and it is found that the local heat transfer coefficient will be remain along the flow direction and be larger at bottom because the flow is violent. The experimental results show the wave velocity is larger when heating, and variation of the critical heat flux when permanent breakdown occurs with Reynolds number is obtained.