CFD-based Numerical Research On Passive Residual Heat Removal Heat Exchanger

The heat exchanger of passive residual heat removal system(PRHR HX)is put in use when the nuclear plant meets accidents,such as blackout,loss of main feedwater.It is able to remove the residual heat generated in the reactor core in time,and prevent the reactor from significant accidents.The passive means of altitude difference,temperature difference are as driving forces in passive residual heat removal heat exchanger,so that the coolant within the heat exchanger could turn out natural circulation.The system enables the dependence on nuclear power plant pumps,valves and other active devices is greatly reduced,but also makes the impact of human factors on the safety of nuclear power plants be greatly reduced.In nuclear power plants,the introduction of passive systems can effectively increase safety of the reactor core in the incidents.This subject applies ANSYS fluid dynamics soft wares for passive residual heat removal heat exchanger heat transfer characteristics in the numerical simulation,mainly related to the study are as the follows:(1)Analysis the physical model of the PRHR HX,and appropriate simplify the physical model of PRHR HX,applying DesignModeler to complete the establishment of the entire PRHR HX model.(2)Discuss the shell side and tube side temperature's field of the PRHR heat exchanger separately,then focus research on the heat transfer process of the PRHR HX tubes,and analysis the temperature field inside the heat transfer tubes.Analysis difference between outlet mean temperature and the inlet temperature under different inlet temperatures,and assess the heat transfer performance of PRHR HX.(3)Analysis the velocity field of the PRHR heat exchanger shell side.From the analysis,the influence of the heat exchanger structure to the natural circulation could be recognized,and then make suitable comments to optimize the design of the PRHR heat exchanger.(4)Define a dimensionless parameter "?" to do sensitivity analysis of the heat exchanger performance under typical heat transfer conditions.The major factors involved mainly include tube bundle inlet temperature,initial temperature of coolant in the IRWST and the flow of heat transfer tube bundle,etc.After the analysis on the simulation results,we conclude that,the tube bundle inlet section of the passive residual heat exchanger studied in this issue has large temperature difference between its inside and outside.That is why this section transfers heat much more intensively,and the temperature of the shell side increased significantly.In the IRWST,the upper partial fluid flows much more severely compared with the lower portion.The fluid around the upper bend of the tube bundle flows most violent.PRHR HX tube side'temperature turns out obvious stratification along the tube side distance.At the same time,there is an obvious temperature stratification along the height direction in the shell side coolant.With the increase of tube bundle's inlet temperature,heat exchanger's heat transfer ability strengthen gradually,the PRHRs' heat discharge effect becomes more significant.Through the sensitivity analysis of the heat exchanger,we can summarize as follows:(1)With the heat transfer tube bundle inlet temperature rising from 550 K to 615 K,? is also a trend of increase gradually,the passive heat removal effect becomes more apparent.(2)With the increase of the initial coolant temperature in IRWST,the average outlet temperature of heat transfer tube bundle shows a trend of obvious rise,and ? gradually reduces,so residual heat removal heat exchanger's cooling capacity gradually decreases.(3)When inlet velocity increases in a certain range,? gradually reduce,and the cooling effect is gradually decline.But when the inlet velocity increases to a certain extent,the outlet temperature of the tube bundle and ? becomes stable,the cooling effect of the heat exchanger is not affected by the effects of inlet velocity's increase gradually.