On the Location and Mechanisms of Dryout in Top-Fed and Bottom-Fed Particulate Beds

Dryout experiments with inductively heated particulate beds and water were performed. The beds were up to 0.5 m deep and consisted of 3-mm particles. For bottom-fed conditions, the liquid was driven by natural convection from a downcomer annulus and entered the bed through a permeable base. Dryout started near the top of the bed, and the dryout heat flux was more than twice as high as in a comparable top-fed bed. For top-fed conditions, the base of the bed was impermeable. In this case, the elevation of incipient dryout depended on the heat flux. The appearance of the first dry spot was found to be preceded by a remarkable decrease of the liquid inventory in the bed, which delayed dryout and which is interpreted as a boil-off transient of reservoir liquid in the bed. A proposed model for predicting the dryout elevation that is based on the observed dryout mechanism is in qualitative agreement with the experimental data.