Studies On Bubble Behaviors In Natural Circulation

In this paper, by using the de-ionized water as the working fluid, photographic method and experiment are used to research the bubble behaviors in annular channel under subcooling natural circulation in low pressure.On the basis of photographic method, an experiment is designed to test the void fraction with photographic method and some optical corrections are discussed to the bubbles. Experimental results show that the method has the capacity of measuring of volumetric quality and section void fraction at low fraction, and match the valve cut-off method. At high fraction, bubbles are existing in great amount with random shapes and overlap each other. Thus, it's hard to differentiate a single bubble in admissible error, and emendation would improve the measuring precision.On single bubble, the results show that growing sliding bubbles are accord to the Mihic function, which is belong to thermal phase. This means the growth at nucleate sites belong to the inertial phase. In the conditions of this paper, Ivey relationships gave higher results than experiment. Compared with experiment data, an implicit function for frequency is gotten, which is fit to the data well. Theoretical and experimental analysis proved that the rising velocity is in proportion to bubble diameter's square root and independent of conditions. About resistance coefficient, two formulas of low Reynolds number flow are tested. Compared with data, the flow velocity should be minus by rising velocity in calculation of coefficient.The main factors which influence bubble shape are viscosity and surface tension. The viscosity and surface tension are lower, the bubble distortion is higher.On bubbles behaviors, aggregation and void distribution in axial direction are main research contents. In experiment, a departure phase is observed after tumbling phase, which is different from Fortes chart. From the experiment, the process of big bubbles coalesced small bubbles is the main mode of bubble growing to big bubble, and a way to enhance the heat transfer near the heat rod. As a whole, the axial distribution of void fraction is the same as the existing theory and experiment.