An experimental investigation on penetration of buoyancy-driven cold liquid into a vertical channel with hot, forced-flow Original Research Article

An experimental investigation on penetration of cold liquid into a modeled subassembly channel under mixed convection, from the hot plenum of a prototypical fast breeder reactor (FBR) design has been conducted. The penetration phenomenon occurs under certain natural circulation conditions during the operation of the direct reactor auxiliary cooling system (DRACS) for decay heat removal and can influence the natural circulation head that determines the core flow rate and consequently the core cooling rate. In the present experiment, a simplified test section simulating the upper plenum and a subassembly channel was constructed wherein both temperature and velocity measurements were made to investigate the penetration of cold water into a vertical channel with upward flowing hot water. Upon comparing temperature and velocity data we found an overall similarity in their respective spatio-temporal distributions as expected. The data suggested correlations describing the onset of flow penetration and penetration depth into the channel, expressed as a combination of Reynolds and Grashof numbers for a given Prandtl number. Flow penetration was identified based on the temperature and velocity data. This work suggests a dimensionless grouping based on an order of magnitude analysis that satisfactorily casts the experimental data while noting the subtle differences with other investigations.