Establishment of reasonable 2-D model to investigate heat transfer and flow characteristics by using scale model of vessel cooling system for HTTR

In this study reasonable 2D model was established by using FLUENT for start-up of analysis and evaluation of heat transfer flow characteristics in 1/6 scale model of VCS for HTTR. The pressure vessel temperature was set around 200 ℃, in which the ratio of heat transfer via natural convection has been numerically predicted to be around 20-30% of total heat removal in previous studies. This temperature is useful for the analysis code validation in the prediction of temperature distribution of components such as pressure vessel which is heated up by turbulent flow of natural convection. The numerical results of upper head of pressure vessel by the k-ω-SST intermittency transition model, which can adequately reproduce the separation, re-attachment and transition, reproduced the test results including temperature distribution well in contrast to those by the k-ε model in both cases that helium gas is evacuated or filled in the pressure vessel. It was emerged that any local hot spot did not appear on the top of upper head of pressure vessel where natural convection flow of air is separated in both cases. In addition, the plume of high temperature helium gas generated by the heating of heater was well mixed in the upper head and uniformly heated the inner surface of upper head without generating hot spots. (author)