Investigation On Natural Convection In A Vertical Annulus

Control rod drive mechanism(CRDM) is a key component in nuclear power reactors, which takes function of controlling the power of the reactor during normal operation and shutting down the reactor during accidents. In order to guarantee the normal operation of CRDM, the temperature of yoke coil should be kept under a limited value. The axial heat transfer in a vertical annulus between the drive rod and the pressure-bearing shell is mainly relying on the natural convection. Thus, a simplified test section was developed for modeling the vertical annulus which keeps closed at the top and open at the bottom, so as to analyze the inlet water temperature effect and outside wind speed effect on its heat transfer. The experimental results show that the natural convection heat transfer coefficient is closely related with both Gr and the forced convection heat transfer coefficient outside. So a correlation using Nug to modify Gr is proposed. In addition, the corresponding numerical simulation based on STAR-CCM+ is performed to investigate the characteristics of natural convection phenomenon coupling with external forced-air cooling. Unfortunately, the simulated results by the numerical model of STAR-CCM+ could not match well with the experimental results. Then, a theoretical thermosyphon model is developed to simulate experimental cases and the simulated results show a good agreement with the experimental values. Therefore, the developed thermosyphon model is proposed for future design calculation.