Experimental study of natural circulation phenomena in a micro prismatic modular reactor core channel

• A horizontal dual channel plenum-to-plenum facility have been designed and tested to represent the prismatic micronuclear reactor core. • Innovative measurement techniques have been implemted to study the gas thermal hydraulics in a horizontal dual channel P2PF. • Air flows in the P2PF from the left plenum to the right plenum through the hot channel then it circulates back through the cold channel. • The maximum hot channel surface temperature location is shifted in the direction of air flow. Motivated by the need to experimentally investigate natural circulation thermal–hydraulic behavior in horizontal prismatic gas-cooled microreactors, this study examines the effect of varying cooling water temperatures (5–20 °C) on flow characteristics within a dual-channel plenum-to-plenum facility (P2PF). An integrated experimental setup was developed, incorporating micro-foil heat flux sensors, T-type thermocouples, and advanced thermal gas flow sensors to simultaneously measure surface temperature, gas temperature, heat flux, and flow direction at multiple axial and radial locations. Results indicate that stable natural circulation of air is established when the temperature gradient is sufficiently high. However, at lower temperature differences, the flow becomes unstable and non-unidirectional. Radial temperature asymmetries and buoyancy-induced flow reversal were observed, leading to enhanced heat transfer at the channel outlet. The local convection heat transfer coefficient exhibited a non-monotonic trend, decreasing initially along the channel and increasing near the outlet. These measurements offer valuable data for validating computational fluid dynamics (CFD) models and contribute to a deeper understanding of natural circulation and passive cooling mechanisms in advanced microreactor designs.