Experimental Study On Boiling Heat Transfer Of C Type Passive Residual Heat Removal Heat Exchanger

AP1000 Passive Residual Heat Removal System(PRHRS)as part of the AP1000 Passive Core Cooling System(PXS),can discharge the core residual heat to ensure the reactor safety under emergency accident conditions.AP1000 PRHRS is using C type heat exchanger as the main equipment.Under emergency conditions,the natural circulation in the C type passive residual heat removal heat exchanger needs to be established for long time running so as to export the core residual heat.When the system is in the long-term operating state,the heat transfer is mainly in nucleate pool boiling condition outside the heat exchanger tubes.With the reduction of the water level in In-containment Refueling Water Storage Tank due to the evaporation,the heat transfer in the low lever condition might occur and the heat transfer tubes would be exposed in the air.Experimental methods are used to study of the boiling heat transfer outside the C type heat exchanger tubes.The boiling heat transfer characteristic outside the C type heat exchanger is studied in different conditions.The experimental equipment is designed and built which is called C type passive residual heat removal heat exchanger principle experiment on boiling and condensation heat transfer.Experiments include the C type single tube boiling heat transfer experiment,the C type tube bundle boiling heat transfer experiment and the C type tube boiling heat transfer experiment in low level condition.Based on the analysis of the experimental results,this paper studies of the pool boiling heat transfer characteristics of the C type tube as well as C type tube bundle.This paper also analyzed the bundle effect on characteristics of C type heat exchanger in nucleate pool boiling.By verifying the five nucleate pool boiling heat transfer correlations for calculation of boiling heat transfer outside the experimental tube,it is found that the boiling heat transfer coefficient calculated by Rohsenow correlation agrees well with experimental values,and it is appropriate to be used to predict the boiling heat transfer coefficients under this experimental conditions.There is a full discussion and verification on the processing method of experimental data in this paper and it is proved that the processing method in the paper is effective and feasible.The calculated heat flux of the equivalent pool boiling heat transfer area in the low level condition is in good agreement with that of pool boiling heat transfer area in the normal liquid level condition.The relative deviation of the heat flux above is less than 5%.Compared with the pool boiling heat transfer coefficient of pool boiling heat transfer area in the normal liquid level condition,the pool boiling heat transfer coefficient of the equivalent pool boiling heat transfer area in the low level condition is slightly smaller.However,the difference of the two heat flux calculated is almost negligible and the boiling heat transfer capacity of the C type heat exchanger in the low level condition has not been significantly reduced.