High pressure nucleation in water/nitrogen systems

Abstract

Nucleation rate measurements of water in the presence of nitrogen as a carrier gas are reported at total pressures near 10, 25, and 40 bar, and temperatures of 230 and 250 K. The results were obtained using our pulse-expansion wave tube, particularly suited for high pressure nucleation research. Enhanced fugacity of water vapor in the mixture, due to the presence of nitrogen, was quantitatively taken into account. Values of the enhancement factors as a function of pressure and temperature were correlated from accurate gravimetric measurements available in literature. The results demonstrate a strong influence of nitrogen pressure on the nucleation behavior of water, when temperature and supersaturation are kept fixed. The effect is associated with a decrease of the surface tension of water, due to the adsorption of nitrogen onto the liquid surface. A tentative model is presented that qualitatively describes this decreasing surface tension with pressure. The competition between the opposing effects of enhanced fugacity and decreasing surface tension is identified as a complicating factor in detecting pressure effects on nucleation. This conclusion is expected to hold for other vapor/carrier gas systems as well.

Effect of carrier-gas pressure on barrier to nucleation: Monte Carlo simulation of water/nitrogen system

“…Experimental evidence has already demonstrated that the carrier-gas effect is more pronounced at relatively low temperatures. 6 To confirm the experimental finding, we carried out Monte Carlo simulation for the system at a lower temperature, i.e., Tϭ240 K. Figure 2 shows the ⌬G i curves at carrier-gas pressure pϭ0 and 60 bar. We set the supersaturated-vapor density of water, ⍀zϭ0.2 ϫ10 Ϫ7 Å Ϫ3 .…”

“…In fact, this reduction alone would give rise to a smaller barrier height of nucleation, opposite to our results. However, this apparent contradiction can be resolved by using an argument of Luijten et al, 6,12,13 who suggested that the carrier-gas effect in water /nitrogen system can be viewed as a result of two competing factors: the enhancement of equilibrium vapor pressure which lowers the supersaturation, and the reduction of surface tension due to the surface adsorption of carrier-gas molecules. Our results therefore suggest that the increased barrier height of 4.…”

“…In diffusion cloudchamber experiments, [1][2][3][4][5] for example, marked effects of carrier-gas pressure on the rate of nucleation and the critical supersaturation were seen. For a water/nitrogen system, however, a recent experiment 6 using a high pressure pulseexpansion wave tube demonstrated that when the nucleation rate is plotted as a function of conventional supersaturation ͑i.e., the ratio of the partial vapor pressure of the supersaturated vapor to the equilibrium vapor pressure of the pure component͒, the carrier-gas pressure effect is hardly discernible.…”

“…Luijten et al 6,12,13 proposed that the carrier-gas effect can be explained by two competing factors: the enhanced vapor pressure which hampers nucleation and the reduced surface tension which facilitates nucleation. Based on the nucleation theorem for binary nucleation, Oxtoby and Laaksonen 14 showed that the carrier-gas effect is generally small.…”

Molecular dynamics simulation of supersaturated vapor nucleation in slit pore

“…The inclusion of carrier gas particles in the simulation is to mimic real experiments of nucleation [15][16][17][18] where the carrier gas plays a major role in releasing the latent heat generated from nuclei formation. The interaction potential of target-target is a Lennard-Jones ͑LJ͒ type, i.e., a͒ Author to whom correspondence should be addressed.…”