| Narrow Rectangular Channel?NRC?has the advantages of compact structure and high heat transfer efficiency,and is widely used in engineering field,such as nuclear-powered shipes,marine nuclear-powered platforms,spacecraft cooling systems,and so on.NRC`s hydraulic diameter is small,therefor it has narrow-space effect.When fluid flows within the NRC,the flow instability is more easy to occur.Natural circulation?NC?has become the main circulation model of heat transfer during normal operation and cooling system in advanced nuclear reactor,due to its passive inherent safety,.However,because of its complex and coupled flow-heat-transfer characteristics,flow stability under NC is weaker.To improve the safety of small integrated nuclear reactor operating,it is necessary to carry out the experiment of“Flow Instabilities in Narrow Rectangular Channel under Natural Circulation”and systematically analyze it.Firstly,the device and the instrument in the experimental system are introduced.Methods of instrument detection,preparatory work and experimental procedure are also given as well as the data-processing.Besides,the uncertainty of measure-parameters which is measured during the investigation are also analyzed.Subsequently,the onset of flow instability?OFI?is studied.The reliability of models is verified by experimental data,which are commonly applied to predict the onset of significant void?OSV?or the onset of flow instability?OFI?.The result shows that the model of Levy,Wang and Xu are applicable for the test,and could be used to predict working condition of OFI conservatively.Futhermore,according to experimental data,a new empirical correlation is put forward:qOFI?28?0.663qsat1.045.Utilizing other researcheres`experimental data to verify the practicability,it is found the correlation is more suitable for heat channels whose heat flux exceeds 265kW·m-2.Thirdly,flow states occurres in the test are classified by the change regulations of macro flow rate that combined with the graph shot by high-speed camera.Typical phenomenons of flow instabilities are described in detail,as well as the cause of phenomenons.Based on the change of gas-phase distribution during the experiment,mechanism of instabilities is also analyzed.At last,the boundary of instabilities are found out by using the standard deviation curve of flow-rate,and the dimensionless boundary map is drawn with the dimensionless data.Effects of different operating conditions on the boundary as well as shortages of this experiment.are discussed.At the end of the article,future work and prospect are put forward. |
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