Effect of non-uniform heating on temperature and velocity profiles of buoyancy driven flow in vertical channel of prismatic modular reactor core

Abstract

To overcome the lack of experimental results of buoyancy-driven flow fields in vertical core channels of prismatic modular reactors, hot wire anemometry; micro foil sensors; and T-type thermocouples were integrated simultaneously at six axial positions along an electrically heated stainless steel channel of a test facility designed and developed with a representative geometry of prismatic modular gas-cooled reactor. At each axial position, nine radial measurements were obtained from the wall to the centerline of the channel. Fluid measurements display typical temperature and velocity profiles throughout the inlet- and mid-section of the channel. However, wall-to-fluid temperature differences along with axial variation of velocity fields indicate flow instabilities at the top section of the channel. This could be attributed to heat losses by conduction through the thickness of channel’s wall in addition to interactions occurring between heated air jets exiting the core channel and cooled air plumes cooled in the upper plenum which is anticipated to take place more rigorously in real prismatic facilities. Additionally, a new definition of the characteristic temperature difference is proposed to calculate a modified Grashof number that can be used to indicate such flow instabilities. Distortion factors between the developed facility and reference modular gas-cooled reactor are found to range from 18% to 24%. Current results are crucial for guiding and validating the commercial computational fluid dynamics codes.