Reversed Flow Phenomenon Taking Place In The Natural Air Draft Heat Removal System

This paper qualitatively discusses the discovery of buoyancy induced reversed flow (BIRF) phenomenon accurs during gap-width effect and flow blockage effect experiment in the stack-enhanced natural air draft heat removal (NADHRS) experimental apparatus. Such an experiment was intended to research the basic nature of natural air circulation mechanism currently considered in the design of the decay and residual heat removal system (Reactor Cavity cooling System RCCS) for MHTGR 450 MWt under developed by GA Technology. The apparatus is a simple model of RCCS, equipped with inlet port, lower upper plenum, hear source, cooling channel, and twin stacks at the upper part serves as outlet port. The onset of BIRF Phenomenon has been made visible and observable with the aid of smoke, supported with a Pen Recorder used to display the measured air temperature at the stacks outlet. As the flow being gradually blocked, the incoming air mass flow rate decreases such that will be overheated in the cooling channel. This overheated air results in higher buoyancy force inside the system, which needs further supply of fresh air. This condition was suspected to trigger the occurrence of mass-deficit (minimum pressure) region inside the system into which outside ambient air was drawn in through one side stack to conserve the mass flow, i.e. BIRF phenomenon. It still needs further research on the impact of BIRF phenomenon on the system coolability, and possibilities of its occurrence on the actual RCCS