The Investigation Of Crucial Model For Predicting Departure From Nucleate Boiling Critical Heat Flux Based On CMFD Method

The high heat transfer coefficient of nucleate boiling can remove the heat produced by pressurized water reactor(PWR)core effectively.This efficient heat transfer mechanism,however,is limited by a critical heat flux(CHF).In the case of PWR,it is named departure from nucleate boiling(DNB).When this phenomenon happens,bubbles crowd near the heated surface,leading to the heat transfer deterioration and wall temperature excursion,which may cause the meltdown of core.Hence,the prediction of DNB type of CHF is a significant task in the thermal hydraulic analysis of PWRs.At present,the most commonly used methods are empirical correlations and look-up table.Recently,with the development of twophase computational fluid dynamics(CMFD),the use of this method becomes another potential option.In the work done before,the commercial CFD software STAR-CCM+ was used to predict DNB type of CHF.But the result was not ideal.In order to improve the result,the crucial models are investigated in this paper.The two models that have great influence on the accuracy of result are bubble departure diameter model and wall function model.So,in this paper,at first,the most commonly used bubble departure diameter models are listed and are evaluated according to the experimental data of Sugrue.The result shows that Klausner’s force balance model performances well and is used in this paper.As for the improvement of wall function,the wall rough model which treats the influence of bubbles on flow field as wall roughness is used.Then,in order to assess the applicability of the models,DEBORA tests are simulated and the predicted value of related parameters are compared with experimental data.The results shows that the use of force balance model and rough wall model can improve the result significantly.After that,the prediction of DNB type of CHF of water in a round tube is done in this paper.By comparing the value with the look-up table one,it is found the models used can predict the DNB type of CHF under subcooled condition well.But for saturated condition,the models still need to be improved.At last,the steady-state subchannel test-case of PWR subchannel and bundle tests(PSBT)international benchmark is simulated,which can lay a foundation for the prediction of DNB in rod bundles.