THIN-LAYER BOILOVER: PREDICTION OF ITS ONSET AND INTENSITY

摘要

Although in the burning of liquid fuel floating on water the fuel burning itself is similar to that of the simple fuel, the presence of the water underneath introduces a number of effects that are caused by the transfer of heat from the fuel to the water. One of the main effect is the disruptive burning of the fuel known as boilover that is caused by the water boiling and splashing, which results in the explosive burning of the fuel. From a practical point of view, it appears that there are two important aspects of the problem, one is the onset of boilover, the second its intensity. In the present work, the liquid heating is analyzed as a semi-infinite conduction problem with a surface suddenly increased to a constant temperature (boiling point), the penetration of the thermal wave being a function of time (of the order of (αt)~(1/2), where α is the thermal diffusivity of the liquid). This analysis provides predictions for the times at which the nucleation of the water starts (assumed to occur when the water/fuel interface reaches a constant level of superheat approx = 120℃). They are in satisfactory agreement with the measurements. These measurements were conducted in two laboratories and address the major issues of the thin layer boilover process by analyzing the effect of the variation of the key parameters of the problem (fuel layer thickness, pool diameter and fuel type). Knowing that the fuel layer remaining before nucleation is closely related to the thickness of the superheated water layer (water that gasifies), it is shown that the boilover intensity can be estimated on the basis of the pre-boilover fuel mass ratio. The thicker these layers, the more intense is the boilover. Fuels used as support of the proposed analysis include single-component fuels and multicomponent fuels.