| Rectangular channel has been widely used in ship-based nuclear power plant because of its high specific surface area and high heat transfer efficiency.As opposed to land-based nuclear reactor,ship-based nuclear reactor always suffers fromthe ocean conditions of heaving,inclining and rolling.Besides,natural circulation has become to be the important operation mode for the nuclear reactors in order to improve the inherent safety and simplify the system design.In this thesis experimental studies on the flow characteristics of the rectangular channel in the natural circulation loop were performed in both single phase and two phase flow conditions.In the experiments,the deinoized water was selected as the working fluid and the system pressure,inlet water temperature and heat flux on the heated section were selected as controlling parameters.The effects of the rolling motion condition on the characteristics of flowing resistance of the channel were analyzed by comparing the data against the data for the system not in any of ocean conditions.Furthermore,high speed camera and visualization study were used to study the transition of the flow pattern in single phase with or without the influence of rolling motion.The transition Reynolds number in the rectangular channel without rolling motion was determined by the results from the recording of the high speed camera and the observation of the tracer in the visual window.The transition Reynolds number was about 2600 under forced circulation and free of heat supply conditions and about 2900 under natural circulation condition,which fit the curve of frictional coefficient accordingly.In the cases of rolling motion,the transition Reynolds number increased and was approximately determined in this work.For the single-phase flow in rectangular channel,the effect of rolling motion on the time average frictional coefficient is different in laminar region and turbulent region.It increased inlaminar region with increase of the rolling intensity,and remained almost unchanged in turbulent region.There was not obvious phase difference between instantaneous frictional pressure drop and the flow rate.The time average Renolds number and angular acceleration of the rolling motion decided the value of instantaneous frictional coefficient.The existing formula developed for the static condition could be used with good agreement with the experimental data when the time average Reynolds number lied around the transition area from laminar to turbulent.Reynolds number is the main factor for the instantaneous two phase friction pressure drop.Depending on experimental data,a relational expression for instantaneous frictional resistance coefficient was advanced under rolling condition,whose maximum relative error was with 22.4%.For the cases of two-phase flow in vertical state condition,the correlations based both homogeneous and separated flow model were evaluated against the experimental data,in which the correlations based on homogeneous flow model showed worse performance with mean relative error(MRE)of around 50% than those based on separated flow model with MRE of around 26.4%.Among all the correlations evaluated,the correlation based on Mishima model showed the best performance with MRE of 26.4%.The improved correlation on the basis of Mishima model was developed with the consideration of the effects of mass flux and the capillary force in this study,whose MRE was within 19.4%.In the cases of subcooling,the time average two-phase frictional pressure drop increased with the increase of the rolling intensity and the superficial Reynolds number with whole liquid phase.The maximum acceleration of the rolling motion has little influence on the instant frictional pressure drop and the superficial Reynolds number with whole liquid phase was the dominant factor for the instant frictional pressure drop... |
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