Two-Phase Interactions in Countercurrent Flow Studies of the Flooding Mechanism.

摘要

During a loss of coolant accident in a pressurized water reactor countercurrent flow,flooding and upflow are all expected to take place. Predicting the transition from counter to upflow requires a reliable model for the flooding process. The first phase of a study is reported here which has the objective of evolving the mechanism for the flow reversal process and of developing sound productive models. This report includes a description of the experimental test loop constructed and the experimental measurements made during the first eleven months of the project. Measurements were made of liquid flowing downward as a film as well as upflow in the film entrained droplets as the system was carried through flow reversal. Time variation of pressure and pressure gradients were measured at four stations along the axis. The measurements demonstrated that the onset of flooding was associated with the onset of entrainment and that wave closure and blocking did not occur. Two types of flooding were observed. When entrainment takes place at the point of liquid entry,then flooding is characterized by a slugging or churning. When entrainment initiates well below the entry,then flow reversal occurs by droplet transport above the feed. Criteria for the existence of these two types of flooding are proposed.