[en] The film boiling liquid-solid contacts of saturated ethanol and water to horizontal flat gold plated copper are examined by using electric conductance probe. It is observed that the liquid-solid contacts occur over a wide temperature range, and generally, induced by hydrodynamic instabilities. The area of contact decreases exponentially with interface temperature and is liquid depth dependent. The averaged duration of contacts is strongly influenced by the dominant nucleation process, and thus, depends on the interface temperature and the wettability of the solid during the contact. The frequency of major contacts is about 1.5 times the bubble detaching frequency. It is found that the liquid-solid contacts may account for a large percentage of the film boiling heat transfer near the low temperature end of film boiling and decreases as the interface temperature increases

[en] The rate of removal of coolant is examined by means of quasi-steady film boiling from a jet of fuel falling into a water pool during a core meltdown accident in a light water reactor. A two-layer turbulence model in the vapor film is used. Entrainment of droplets due to the high vapor velocity is taken into account, which, for a jet of diameter 0.5 m, increases the removal rate by factor of 5 at 0.7 m behind the leading edge. However, the water removal rate is only of the order of kilograms/second, and the total amount of coolant removal is still small compared to the coolant inventory in the lower plenum. (orig.)

[en] A mechanistic droplet deposition model has been developed to quantify the direct contact heat transfer present in dispersed flow film boiling. Lagrangian subscale trajectory calculations utilizing realistic velocity and temperature distributions in the momentum boundary layer are used to determine the number of dispersed droplets able to achieve contact with the heated wall. Coupling the droplet deposition model with a physical direct contact heat transfer coefficient model allows the total direct contact heat transfer to be determined based upon the local vapor mass flux, wall superheat, and vapor superheat. Comparisons to the existing models highlight the more mechanistic nature of the proposed model. (author)

[en] A method for predicting film boiling heat transfer in tubes, consisting of the film boiling look-up table and a correction factor to account for the developing film boiling effect, is introduced in this paper. The film boiling look-up table has been derived previously to predict the fully developed filmboiling heat-transfer coefficient in tubes of 8-mm inside diameter. In this paper, the correction factor has been derived using a carefully selected tube-film-boilin g database covering both developing and fully developed regions; it extends the application of the look-up table to developing film-boiling conditions. The developing film-boiling correlation in conjunction with the latest film-boiling lookup table predicts the selected film-boiling database with an average error of -1.67% and a root-meansquare error of 11.57% for about 6,000 data points. The proposed methodology has been compared against six other prediction methods using an extended film-boiling database. This methodology is shown to be superior to other methods in terms of applicable parametric ranges and prediction accuracy

No abstract available

No abstract available

[en] The pressure oscillations during different film boiling modes in He II are studied in this paper. In the sub-cooled film boiling state, a flame-shaped vapour bubble can be seen to be quivering on the planar heater accompanied by a little audible noise, and the pressure oscillation, resulting from both vapour bubble oscillation and liquid column oscillation of bulk He II in a cryostat, is detected. In the noisy film boiling state in saturated He II, a big vapour bubble expands and crushes repeatedly on the planar heater accompanied by a loud acoustic noise, and the pressure oscillation is mainly caused by the crushing and formation of the vapour bubble. There are two possibilities for the occurrence of transition boiling. A theoretical analysis of the pressure oscillation was also carried out, which agreed well with the experimental results. (author)

[en] A minimum film boiling mechanism is suggested, based on the adsorption characteristics of the system. The wetting process is characterized by a precursor, non-evaporating film. As the surface temperature increases the film thickness decreases, with a sharp decrease at a temperature threshold determined by the heat of adsorption. The minimum film boiling temperature is assumed to be the temperature at which only the monolayer exists. The predicted values are in fair agreement with experimental results for different systems. (author)

[en] In order to prevent the burn-out of a heating element immersed in a liquid, it has hitherto been a common practice to detect a temperature rise of the heating element or the attendant increase in resistance. However, unless the temperature of the heating element becomes considerably higher than that of the liquid, detection cannot be made and it is possible that the heating element will burn-out. In general, a liquid which boils under the application of heating by a heating element generates a boiling sound. When the heat flux of the heating element is further increased, a film boiling state is attained and gives forth a peculiar sound wave. It has been experimentally verified that burn-out of the heating element usually arises when the heat flux is further increased under this condition. On the basis of this fact, the present invention arranges at least one sound detector on the surface of the heating element immersed in the liquid or in the vicinity of the heating element within the liquid. By detecting the peculiar sound wave in the film boiling state, the heating element is prevented from burning out. This device can be mounted on, for example, a fuel element in a reactor. (Takasuka, S.)

[en] To give a more accurate interpretation of experimental results on the of surface boiling instability, conditions of initiation of interfacial waves are theoretically analyzed. The equations obtained will permit to more completely use experimental data when developing calculation techniques