Mechanical Engineering, Sharif University of Technology
Abstract
This work concerns dryout experiments in which a tube, initially containing water, filled up or partially filled and at 1,2 or 3 atmosphere pressures, is heated. The initial water column experience three thermal regions. The first region, called the first period, involves heating of the tube until saturation conditions are obtained in the water. Boiling of the water in the tube causes swelling with overflow at the top of the tube. which happens during the second period. The second period ends when the overflow ceases. Hereafter, the liquid content of the tube diminishes because of evaporation, its level falls and exposes the tube wall to vapor, and the temperature of the exposed tube rises. This occurrence is called dryout; the period in which it occurs is called the third period. The experimental results of 44 dryout experiments are the histories of dry-out level collapsed liquid level, and tube wall temperatures. The analytical objective is the prediction of the temperature~ collapsed liquid level and the dryout histories during the three periods. The temperature history of the first period is predicted according to a result of Jaeger [4]. The collapsed liquid level, quench front and the transient height of the two-phase level during the second period are predicted by a model developed by Lahey [6]. Once dryout begins, a drift flux model by Sun et al [10] predicted the hisotory of the dry-out and the collapsed liquid level. The wall temperature above the dryout level is predicted using a model by Yeh et al. [5]. Good agreements between the experimental results and the predictions were found for the first and third periods hut the duration of the second period could not he correctly predicted.
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