Experimental observations of shock-wave-induced bubble collapse and hot-spot formation in nitromethane liquid explosive

Abstract

We studied the collapse of individual helium gas bubbles in the homogeneous explosive nitromethane (NM) to investigate effects of hot-spot formation on the detonation process. A bubble was injected into a NM sample, and a shock wave from an explosive detonator compressed the bubble, creating a localized hot spot. We measured shock and detonation wave speeds with optical velocimetry, and we used a high-speed camera to image the shock propagation and the pre- and post-bubble collapse processes. An infrared camera image showed the residual radiance temperature distribution after the bubble collapse, and an optical fiber pyrometer measured the time-resolved thermal radiance. We measured the optical spectra of light emitted from detonating NM without a bubble and from a collapsing bubble in shocked, undetonated NM. We estimated temperatures of the detonation fronts and of the hot spots formed by bubble collapse. To study the incipient detonation process, we performed all bubble collapse experiments at pressures below the threshold for creating a sustained detonation. Where the bubble collapsed, we observed an opaque, thermally emissive region believed to be chemical reaction products. Chemical reactions in NM can be produced with lower shock pressures (∼1 GPa) when a helium bubble is present than without a bubble (∼10 GPa). We used hydrodynamic modeling to predict shock wave propagation, extent of chemical reaction, and subsequent temperature rise from the collapsing bubble. Simulations using a temperature-dependent Arrhenius burn model gave much better results than reactive burn models that depend only on pressure and density.

Rayleigh Problem in Superfluid Helium

“…The discussed approach was used in [5], where the authors applied relation (14) to express v n via the heat flux Q released by the heater. Since, however, the total mass flow j is not equal to zero, part of the total energy released by the heater is converted into mechanical energy, associated with the motion of the helium as a whole.…”

“…The dynamics of "acoustic" bubbles generated by ultrasound [9] or by cavitation due to negative pressure [10] is under active study. Research on the collapse of vapor bubbles [11,12], as well as sonoluminescence [13,14] or sonofusion [15,16], is also of importance.…”