CFD Simulation Of Flow And Heat Transfer In Secondary Passive Residual Heat Removal Exchanger

In order to ensure the safety of the nuclear reactor under station blackout accident,passive residual heat removal system was adopted by the third generation nuclear reactor.Secondary side passive residual heat removal system cools the steam produced by steam generator through the C-type heat exchanger and the cooling water tank,finally it discharges core heat.The system makes full use of the driving force of fluid’s natural circulation,so it reduces the level of human intervention and improves the inherent security of the system.In this paer,the software ANSYS CFX was used to compute and analyse the C-type heat exchanger which was made of the single tube,the 3×3 tubes and the 5×5 tubes separately.The in-tube model was condensation two-phase flow model and the external tube model was subcooled boiling model,wall model of tube was heat conduction model.Setting interfaces to accomplish the heat transfer coupling among the in-tube and external tube.The article analysed and proved the wall condensation model and subcooled boiling model.Then analysis and research of the single tube was carried out.On the basis of this,the paper compared conditions of three different steam inlet flow rate and three different steam inlet temperature.Finally,more complex thermal-hydraulic analysis of 5×5 tubes was proceed.Analysis shows that,the steam in the tube condensates and releses heat along the flow direction,the gas condensation rate,the heat transfer and the heat transfer coefficient are the biggest in the entrance of the tube,then they gradually reduce along the flow direction.The fluid in the pool occurs subcooled boiling phenomenon,the gas generated by heating mainly spreads on the top of the tube and forms natural circulation.In the case of heat exchanger’s consistant inlet gas temperature,the more inlet flow rate,the higher fluid temperature,stronger heat transfer and more obvious subcooled boiling phenomenon in the same position.When the inlet flow rate isunchanged, the higher inlet fluid temperature,the stronger heat transfer.Pool’s natural cycle mixes the hot and cold fluid fully and improved the heattransfer. The exit of three working conditions’ pipes barely generate bubbles,it shows that the heat exchanger plays an important role in removing heat.We can find that the heat exchanger exhausts more heat when increasing the number of tubes.So the design of multi-tubes spacing arrangement can maximize the heat removal.The results not only provide basis for design of PRHR exchanger,but also are of great guiding significance on the stable operation of the heat exchanger.