Papers by Keyword: Microexplosion

Abstract: Understanding the evaporation and combustion mechanisms of single droplets of gel propellant is the first stage to predict the burning characteristics in the combustion chamber. This paper, taking into account convection heat for freely falling gelled fuel droplets under normal gravity conditions, as well unsteady mass diffusion and thermal diffusion inside droplet, a theoretical model was developed to understand mass and heat transport mechanisms, and bubble growth within the gel droplet during processes of droplet combustion. The results show that at the first stage, shrinkage of the radius obeys the d2-law; steep temperature gradient and fuel mass concentration gradient appear within droplet, especially region near droplet surface. At the second stage, liquid fuel near the gellant layer within droplet starts to boiling, gellant layer formation resist the vaporizing fuel gas flow to extent; the vapor region appears between gellant layer and vaporizing surface within the droplet, and the droplet expands, swells, the layer thickness decreases until it ruptures.

Abstract: By focusing femtosecond laser pulses in the bulk of a quartz wafer, sub-surface waveguides were microexploded. The material around the femtosecond laser induced microexplosive zone was densified, which altered local refractive index. Changes in material density can take corresponding variations in nanomechanical properties, which were proved by the depth dependent modulus and hardness variations tested by nanoindentation in the area around the microexplosive zone. Changes in refractive index were correlated with residual strains along radial direction of the waveguide cross section. An equation of residual strain in such area that based on nanoindentation data was set up, so as to discover density and refractive index variations in the adjacent areas of femtosecond laser microexplosive zone indirectly.