The present study investigates bubble nucleation in liquid oxygen with dissolved impurities (nitrogen or helium molecules) using molecular dynamics simulations. When the mole fraction of impurities is 0.05, there is a fundamental difference in the bubble nucleation mechanism between the two dissolved impurities cases; vaporization in the homogeneous bulk makes a bubble in the case of a nitrogen-dissolved liquid while phase separation of impurities and liquid molecules makes a nucleus in the case of a helium-dissolved liquid. Fluctuations can cause local voids, which in turn can grow to be bubbles, and this effect is stronger in the case of a helium-dissolved liquid with a lower mole fraction (0.01) than in the case of a nitrogen-dissolved liquid with a higher mole fraction (0.05). From these results, we conclude that helium molecules have a much stronger action to raise the bubble formation pressure compared with nitrogen. In this paper, the kinetically-defined critical nucleus, which is a very important factor in quantitatively evaluating the nucleation mechanism, is also estimated through the calculation of the size change rate of each nucleus.
- Molecular dynamics