ICMS ' 2000 The Physics of Boiling at Burnout
The basic elements of a new experimental approach for the investigation of burnout in pool boiling are presented. The approach consists of the combined use of ultrathin (nano-scale) heaters and high speed infrared imag|ng of the heater temperature pattern as a whole, in conjunction with highly detailed control and characterization of heater morphology at the nano and micron scales. It is shown that the burnout phenomenon can be resolved in both space and time. Ultrathin heaters capable of dissipating power levels, at steady-state, of over 1 MW/m 2 are demonstrated. A separation of scales is identified and it is used to transfer the focus of attention from the complexity of the two-phase mixing layer in the vicinity of the heater to a micron-scaled microlayer and nucleation and associated film-disruption processes within it.
A Theoretical Analysis of Heat Transfer in Natural Convection and in Boiling

 A theoretical analysis of natural convection and of boiling heat transfer is presented. Instead of approaching these problems according to a conventional concept, a short-cut method is introduced by the application of wave motion. Above the heating surface a boundary layer is assumed whose thickness depends upon the heat flow. Inside this layer there is wave motion, stable in the lower part but unstable in the upper. It has been recognized that, if there is a temperature gradient across a stratum of liquid, a wave motion will occur. Each loop of this wave can initiate vortexes in the natural-convection process and also can facilitate the formation of bubbles in boiling. A unified formula is thus obtained for convection and for boiling. The calculated results agree excellently with experiments as conducted by previous investigators. This paper does not profess to be a complete treatise, but shows how the concept of wave motion can be made of use in giving a new picture of these heat-transfer processes.
Ex-vessel boiling experiments: laboratory- and reactor-scale testing of the flooded cavity concept for in-vessel core retention Part II: Reactor-scale boiling experiments of the flooded cavity concept for in-vessel core retention
This paper summarizes the results of a reactor-scale ex-vessel boiling experiment for assessing the flooded cavity design of the heavy water new production reactor. The simulated reactor vessel has a cylindrical diameter of 3.7 m and a torispherical bottom head. Boiling outside the reactor vessel was found to be subcooled nucleate boiling. The subcooling mainly results from the gravity head, which in turn results from flooding the side of the reactor vessel. The boiling process exhibits a cyclic pattern with four distinct phases: direct liquid-solid contact, bubble nucleation and growth, coalescence, and vapor mass dispersion. The results show that, under prototypic heat load and heat flux distributions, the flooded cavity will be effective for in-vessel core retention in the heavy water new production reactor. The results also demonstrate that the heat dissipation requirement for in-vessel core retention, for the central region of the lower head of an AP-600 advanced light water reactor, can be met with the flooded cavity design.