BOILING AND CRISIS OF BOILING OF A TWO-PHASE LIQUID IN SPHERICAL MICROFUEL FILLS

摘要

Heat transfer from microfuel fill to a two-phase coolant by means of a phase transition can occur in two forms: evaporation and bubble boiling. The evaporation regime proceeds on menisci along the lines of triple contact of phases. This regime is stable and promising for technical applications. Bubble boiling occurs when the surface of the microfuel is overheated relative to the saturation temperature. In the presence of boiling, the bubbles in the fill can be large (relative to the pore size) and small. Evaporation and boiling with small bubbles occur simultaneously, the process is characterized by a high coefficient of heat transfer, and the regime is stable and promising for applications. Several paths lead to a crisis of boiling. The most dangerous process is one which gives rise to systemic instability of the uniform distribution of the phases in the fill. Superheating of microfuel surfaces in this case is not an accident, but the mechanical action of the accompanying pressure oscillations can be dangerous. Microfuel surfaces can become dry inside large volumes of steam, which arise in regions where the fill porosity is elevated.