| It is well known that boiling heat transfer yields heat transfer rates several orders of magnitude higher than most other mechanisms of heat transfer. One of the most important characteristics of nucleate boiling is that, while the heat flux is high, the temperature difference between the heater surface and the liquid is low; however, there is an upper limit to the heat flux during nucleate boiling beyond which the surface temperature increases very rapidly and boiling undergoes a transition to a totally different mode of heat transfer called film boiling. The maximum heat flux has important application in the design of nuclear reactors, large electronic equipments, and modern electronic devices.;This thesis presents a new mathematical model that predicts the CHF in a narrow heated channel a common configuration in the new generation of compact nuclear reactors. This new mathematical model builds on the analysis by Trevor and Elkassabgi (1995) for predicting the critical velocity for two fluid sheet surrounded by a solid wall. This critical velocity was used as the trigger mechanism for the collapse of the vapor escape route leaving the heated surface. The collapse of the vapor escape route signals the onset of the burn out phenomenon. A new predictive correlation for the critical heat flux was derived &parl0;qmaxqmax ,LS=0.7148+0.0553H '2R'14 1+R'H'2 &parr0; . The new correlation predicted the experimental data of Elkassabgi (1986) within 1%. However an additional data is needed to be included to confirm the validity and the error bound of our new correlation. |
