Study Of Natural Circulation Heat Transfer Characteristics In A Rectangular Channel Under Rolling Motion Conditions

In marine nuclear power plants,natural circulation is important for improving the inherent safety of the reactor,reducing noise and simplifying the system.In order to achieve the miniaturization of equipment,marine reactor often use plate-type fuel elements,which form a narrow rectangular channel,as the coolant flow channel.However,when the reactor under Ocean conditions keeps in the normal operation or the accident condition,whether the coolant can safely and efficiently derive the heat produced by the reactor core is extremely important for the safety of the reactor.Therefore,it is necessary to study the natural circulation heat transfer characteristics in a narrow rectangular channel under ocean conditions.This paper uses deionized water as the working fluid and uses the high speed camera to study the natural circulation heat transfer characteristics in narrow rectangular channels with a single heating plate under ocean conditions.The natural circulation experiments in a narrow rectangle channel are investigated in a swinging experimental platform.The main contents of the study includ the single-phase natural circulation heat transfer characteristics,onset of nucleate boiling(ONB)and subcooled boilingheat transfer characteristics,respectively,in the vertical,incline and rolling motion conditions.For the single-phase natural circulation heat transfer characteristics,the Re range in the transition regime in vertical conditions is 2900 ~ 4000.The Yang-correlationestablished in the pipe flow condition can well predict the single-phase natural circulation heat transfer characteristics in this experiment and the prediction error is within 15%.In the incline condition,by the influence of the orientation of the heating plate,the positive inclination angle will increase the local heat transfer coefficient in the fully developed region of the laminar flow regime.The rolling motion will decrease the cycle-averaged natural flow rate,and only in the transition regime the rolling can enhance the natural circulation heat transfer characteristics.For the onset of nucleate boiling characteristics,the particularity of the shape of the narrow rectangular channel in the vertical condition causes the bubble generated at the ONB to be rapidly condensed or to slide along the channel for a distance,and the bubbles at the ONB in the channel are not generated at the same cross-section.It is found that the change of wall temperature with the heat flux can correctly reflect the generation of ONB.By modifying the Su-model based on the experimental data,the Su-modified-model can well predict the ONB in a narrow rectangular channel.In addition,the incline condition and the rolling motion have little effect on the time-averaged ONB,which can be predicted by the Su-modified-model,and the prediction error is within 20%.For the subcooled boiling characteristics,the Yan-correlation established in the forced circulation of a pipe can well predict the natural circulation subcooled boiling characteristics in a narrow rectangular channel,and the prediction error is within 30%.In addition,the incline condition and the rolling motion have little effect on the time-averaged subcooled boiling characteristics,and the time-averaged subcooled boiling characteristics can be predicted by Yan-correlation.