水中における金属細線の超高速加熱と衝撃波の発生

抄録

Heat transfer, vapor formation and pressure generation when a metal wire is heated very rapidly in water were investigated experimentally and theoretically for comprehensive understanding of highly transient, highly non-equilibrium thermofluid phenomena related to the physical process of vapor explosions. A small stainless steel or platinum wire, the diameter of which ranges from 0.lmm to 0.55mm, was electrically heated in water with a heating rate (wire temperature increasing rate) of l0⁶K/s to 10¹0K/s. Water temperature was changed from 20°C to 100°C to elucidate the effect of subcooling. Aspects of the phenomena were observed using high speed motion pictures with a frame speed of l00 000 fps to 20 000 000 fps. It was found that spontaneous vapor formation takes place, resulting in shock wave and high pressure when the wire surface temperature reaches the homogeneous nucleation temperature of water. It was also found that the maximum heat flux at the instant of spontaneous vapor formation is around several hundreds MW/m². A theoretical model is presented for the pressure generation, which is in good agreement with experiments.