THE MECHANISM OF BURNOUT IN INITIALLY SUB-COOLED FORCED CONVECTIVE SYSTEMS (thesis)
An analysis is made of burnout in convective two-phase systems with particular emphasis directed toward understanding the physical mechanisms. Various aspects of twophase flow were examined including flow regimes, film flow and entrainment, and two-phase heat transfer as well as diTect burnout experiments. The information on two-phase heat transfer indicates that there are two distinct types of burnout, the first due to breakdown of nucleate boiling, and the second due to transition from convection-dominated heat transfer to a liquid-deficient heat transfer region. This analysis is concerned only with this second type of burnout. The analysis indicates that the pre-burnout conditions are dominated by the flow of liquid in a thin film on the heated surface, and that burnout occurs when this film flow dries up. The rate of supply of liquid to the heated surface by diffusion of droplets from the core may be considered negligibly small when a heat flux is present. This means there is a great difference between systems which are initially subcooled, and those in which a dispersed twophase feed is used. The postulate that burnout conditions for dispersed feed systems are determined in the entrance region before the start of the heated section allows a qualitative prediction of several effects observed in these systems. The film flow mechanism was used to derive equations for burnout in initially subcooled systems based on a model considering removal of liquid from the film by evaporation and entrainment. This model gives a reasonably good correlation of burnout data. The results indicate that a model which is not based on droplet diffusion can correlate burnout data quite well, and that in fact droplet diffusion in the heated section has little effect on burnout. (auth)
- Research Organization:
- Minnesota. Univ., Minneapolis
- DOE Contract Number:
- AT(11-1)-926
- NSA Number:
- NSA-18-006926
- OSTI ID:
- 4143359
- Report Number(s):
- TID-19845
- Resource Relation:
- Other Information: Orig. Receipt Date: 31-DEC-64
- Country of Publication:
- United States
- Language:
- English
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