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Experimental study on flow resistance in a vertical 3 × 3 rod bundle channel under natural circulation conditions ZHUZhiqiang1, TIAN Chunping1, REN Tingting1, YAN Changqi1, and WANG Jianjun1   1.        Fundamental Science on Nuclear Safety and Simulation Technology Laboratory, Harbin Engineering University, Harbin150001, China (zhuzhiqiang@hrbeu.edu.cn; wangjianjunheu@163.com) Abstract: In order to study and analyze flow resistance characteristics in a 3 × 3 rod bundle channel, a natural circulation loop was set up and a series of experiments were conducted. For single-phase flow, the flow regime is divided and the transition Reynolds number is considered as 800. The flow transition is recognized by the slope change of friction factor curve since the flow transition in the rod bundle channel is not as obvious as that in round pipe. There is a slight change at Reynolds number 800 for the grid spacer local resistance coefficient. For two-phase flow resistance, the boiling flow phases are identified to obtain stable two-phase flow. The ONB during the experiment is determined by the wall temperature drop. The variation of pressure drop components, including the gravity pressure drop, the frictional pressure drop and the acceleration pressure drop, is given. For high mass quality conditions, the mass flow rate is observed declining with the increasing heat flux when the frictional pressure drop grows fast. Based on the Chisholm correlation, a new correlation is fitted by experimental results. The comparison against experimental results shows the new correlation can well predict the two-phase frictional pressure drops under given flow conditions. Keywords: rod bundle; natural circulation; flow transition; frictional resistance; flow boiling
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