Homogeneous Bubble Nucleation Driven by Local Hot Spots: A Molecular Dynamics Study† (original) (raw)

Comparison of heterogeneous and homogeneous bubble nucleation using molecular simulations

Physical Review B, 2007

NPT and NP zz T molecular dynamics simulations of Lennard-Jones atoms were used to compare homogeneous and heterogeneous nucleation. In the heterogeneous cases, the attraction between the fluid and a smooth fcc ͑100͒ surface was varied. Multiple simulations were used to determine nucleation times from which nucleation rates were estimated using a transient nucleation model. Calculations demonstrated a clear enhancement in nucleation rates in the heterogeneous cases compared to the homogeneous case. To obtain homogeneous nucleation rates similar to the heterogeneous cases required temperatures about 10 K higher. It was also found that void formation was favored as the attraction between the liquid and solid was decreased. Varying the system size, thermostatting method, and barostat time constant affected quantitative results, but not the qualitative trends.

The birth of a bubble: A molecular simulation study

The Journal of Chemical Physics, 2005

We study the nucleation of a bubble in a metastable Lennard-Jones ͑LJ͒ fluid, confined to a spherical pore with wetting walls, by a combination of grand canonical, canonical ensemble, and gauge cell Monte Carlo simulation methods complemented by the Voronoi-Delaunay tessellation analysis of statistical geometry of intermolecular cavities. We construct the isotherm of confined fluid in the form of a continuous van der Waals' loop, in which the unstable backward trajectory between the spinodals corresponds to bubble states. We show that as the degree of metastability increases and the fluid becomes progressively stretched, the decrease of fluid density is associated with the evolution of a population of interstitial intermolecular cavities. At the spinodal, the fluid becomes mechanically unstable: Interstitial cavities partly coalesce into a larger cavity located due to the system symmetry around the pore center. This cavity represents a bubble embryo, which grows at the expense of interstitial cavities. The nucleation barrier is calculated by direct thermodynamic integration along the isotherm. We compare our simulation results to the predictions of the classical nucleation theory and experiments on capillary condensation-evaporation of nitrogen in pores of hybrid organic-inorganic mesoporous molecular sieve HMM-3.

Activated Instability of Homogeneous Bubble Nucleation and Growth

Physical Review Letters, 2007

For the superheated Lennard-Jones liquid, the free energy of forming a bubble with a given particle number and volume is calculated using density-functional theory. As conjectured, a consequence of known properties of the critical cavity [S. N. Punnathanam and D. S. Corti, J. Chem. Phys. 119, 10 224 (2003)], the free energy surface terminates at a locus of instability. These stability limits reside, however, unexpectedly close to the saddle point. A new picture of homogeneous bubble nucleation and growth emerges from our study, being more appropriately described as an ''activated instability.''

THE CLASSICAL THEORY OF HOMOGENEOUS BUBBLE NUCLEATION REVISITED

2000

The classical theory of homogeneous bubble nucleation is reconsidered by employing a phenomenological nucleation barrier in the capillarity approximation that utilizes the superheat threshold achieved in experiments. Consequently, an algorithm is constructed for the evaluation of the superheat temperatures in homogeneous boiling (tensile strengths in cavitation), the critical radii and steady-state nucleation rates. The correlations for the superheat temperatures show

Bubble nucleation and growth in fluids

Chemical Engineering Science, 2007

The present paper reports an original study which for the most part is predominantly experimental, investigates the nucleation and growth of CO 2 bubbles in non-Newtonian and Newtonian fluids that were initially supersaturated under different pressures. Quantitative information by means of two cameras reveals that at an immobile nucleation site the bubble grows rapidly followed by a linear increase. After reaching a critical size, the bubble detaches from the stagnant site to rise in liquids with an exponential temporary increase for both the diameter and distance. A simple physical reasoning was proposed to qualitatively explain these observed phenomena. Recently, the growth rate and flow fields around a CO 2 micro-bubble were measured in a microdevice by a micro-Particle Image Velocimetry in water. This information at microscale gives new insight into the complex mechanism of bubble nucleation and growth in fluids and could help to develop a rigorous theoretical modelling and numerical simulation such as the Lattice Boltzmann approach.

Computer simulation of fluid phase change: vapor nucleation and bubble formation dynamics

Computational Materials Science, 1999

Using large scale molecular dynamics (MD) simulation techniques, two types of¯uid±¯uid phase changes were investigated. One is a homogeneous nucleation process from supersaturated vapor, in which we compare a Lennard± Jones system and water system. Another is a bubble formation (cavitation) process in stretched liquid, in which we compare one-component and two-component systems.

Bubble formation and dynamics in a quiescent high-density liquid

AIChE Journal, 2015

Gas bubble formation from a submerged orifice under constant-flow conditions in a quiescent high-density liquid metal, lead-bismuth eutectic (LBE), at high Reynolds numbers was investigated numerically. The numerical simulation was carried out using a coupled level-set and volume-of-fluid method governed by axisymmetric Navier-Stokes equations. The ratio of liquid density to gas density for the system of interest was about 15,261. The bubble formation regimes varied from quasi-static to inertia-dominated and the different bubbling regimes such as period-1 and period-2 with pairing and coalescence were described. The volume of the detached bubble was evaluated for various Weber numbers, We, at a given Bond number, Bo, with Reynolds number Re) 1. It was found that at high values of the Weber number, the computed detached bubble volumes approached a 3/5 power law. The different bubbling regimes were identified quantitatively from the time evolution of the growing bubble volume at the orifice. It was shown that the growing volume of two consecutive bubbles in the period-2 bubbling regime was not the same whereas it was the same for the period-1 bubbling regime. The influence of grid resolution on the transition from period-1 to period-2 with pairing and coalescence bubbling regimes was investigated. It was observed that the transition is extremely sensitive to the grid size. The transition of period-1 and period-2 with pairing and coalescence is shown on a Weber-Bond numbers map. The critical value of Weber number signalling the transition from period-1 to period-2 with pairing and coalescence decreases with Bond number as We $ Bo 21 , which is shown to be consistent with the scaling arguments. Furthermore, comparisons of the dynamics of bubble formation and bubble coalescence in LBE and water systems are discussed. It was found that in a high Reynolds number bubble formation regime, a difference exists in the transition from period-1 to period-2 with pairing and coalescence between the bubbles formed in water and the bubbles formed in LBE.