(407f) Effect of Cooling on Natural Circulation Velocity and Temperature Measurements inside Vertical Heated Channel Representing Prismatic Modular Reactor Core

Presently available computational fluid dynamics (CFD) commercial codes alone are not able to capture all gas dynamic phenomena for natural circulation in prismatic modular reactors (PMRs). Therefore, multiphase reactors engineering and applications laboratory (mReal) research team at Missouri S&T designed and constructed a scaled down PMR with two plena and only two channels, representing the reactor core natural circulation loop, as the initial design for high temperature testing and data collection. Natural circulation within the facility is imitated by electrically heating one channel and cooling both the other channel and the upper plenum. Natural circulation intensity can be varied by either controlling the heat supplied to the riser or cooling of the down-comer. In this study, the effect of cooling (chilled water temperature namely; 5, 15, 25, and 35 ^oC) on gas velocity and temperature measurements inside the heated channel was investigated by implementing hot wire anemometry (HWA) technique, micro-foil sensors and thermocouples. Measurements were obtained at three axial locations along the channel (i.e., z/L = 0.044, 0.591, and 0.956). For each location, radial measurements were obtained from the inner wall (r/R = 1) to the centerline (r/R = 0.0) of the channel. For all cooling intensities, it is found that both temperature and velocity are increasing as distance increase from the inlet to the mid-channel. At the outlet, however, a sudden drop in temperature and gas velocity was observed. This sudden drop was reported previously and is attributed to end losses effects. Present study indicated this loss is due partly because of flow reversal and primarily due to conjugate heat conduction through the channels material itself and the cold upper plenum. Gas velocity change was found to increase by 30% maximum with decreasing chilled water temperature from 35 to 5 ^oC. On the other hand, air temperature is found to decrease by 6.4% near the outlet while no significant change is observed for downstream positions. These results, for the first time provide detailed velocity and temperature variation which can be used for validating CFD codes.