Comparison of heterogeneous and homogeneous bubble nucleation using molecular simulations (original) (raw)

Homogeneous Bubble Nucleation Driven by Local Hot Spots: A Molecular Dynamics Study†

The Journal of Physical …, 2008

We report a Molecular Dynamics study of homogenous bubble nucleation in a Lennard-Jones fluid. The rate of bubble nucleation is estimated using forward-flux sampling (FFS). We find that cavitation starts with compact bubbles rather than with ramified structures as had been suggested by Shen and Debenedetti ( J. Chem. Phys. 111, 3581 (1999)). Our estimate of the bubblenucleation rate is higher than predicted on the basis of Classical Nucleation Theory (CNT). Our simulations show that local temperature fluctuations correlate strongly with subsequent bubble formation -this mechanism is not taken into account in CNT.

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.

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

Computer simulation study of homogeneous nucleation in a Lennard-Jones fluid

Abstract In the absence of nucleation centers, moderately supercooled liquids are metastable but after a finite time undergo homogeneous nucleation. This is usually described in terms of classical nucleation theory (CNT) in which spontaneous fluctuations lead to the formation of small crystallites. When a crystallite exceeds a critical size, i.e. when it overcomes the nucleation free energy barrier, the whole system crystallizes. In this picture the critical nucleus is assumed spherical and the nucleation barrier, which depends only on its size, is determined by a balance between surface and volume free energy terms. Several computer simulations have helped to elucidate the microscopic aspects of crystal nucleation for mod- erate supercooling and allowed free energy barriers and nucleation rates to be computed for model systems such as hard-spheres, and Lennard-Jones (LJ). These models are repre- sentative of real systems, e.g. colloids or globular proteins, and the theoretical pred...

Multiscale Simulation of Surface Nanostructure Effect on Bubble Nucleation

Volume 2: Heat Transfer Equipment; Heat Transfer in Multiphase Systems; Heat Transfer Under Extreme Conditions; Nanoscale Transport Phenomena; Theory and Fundamental Research in Heat Transfer; Thermophysical Properties; Transport Phenomena in Materials Processing and Manufacturing, 2017

Effects of nanostructured defects of copper solid surface on the bubble growth in liquid argon have been investigated through a hybrid atomistic-continuum method. The same solid surfaces with five different nanostructures, namely, wedge defect, deep rectangular defect (R-I), shallow rectangular defect (R-II), small rectangular defect (R-III) and no defect, have been modeled at molecular level. The liquid argon is placed on top of the hot solid copper with superheat of 30 K after equilibration is achieved with CFD-MD coupled simulation. Phase change of argon on five nanostructures has been observed and analyzed accordingly. The results showed that the solid surface with wedge defect tends to induce a nano-bubble relatively more easily than the others, and the larger the size of the defect is the easier the bubble generate.

18. Bubble Creation in Water and Water Mixtures – Consequences of the Extended Theory of Nucleation

Tunnelling and Underground Space Technology, 2004

The objective of this article is to examine the consequences raised from the extension of the classical theory of homogeneous nucleation presented in the preceding publications. The theory takes into account the real properties of fluids (liquid mixtures) and assumes that non-equilibrium (dissipative) effects associated with irreversible processes involved in nucleus formation are responsible for changing the nucleation barrier predicted by the classical theory. These effects can increase the nucleation work for condensation and decrease the nucleation work for boiling and cavitation. This article focuses on bubble nucleation in water rather than droplet nucleation. After the basics of the theory are given, some of the fundamental relations of the theory are examined to obtain the relations for bubble growth controlled by evaporation or gas diffusion processes.

Molecular dynamics simulations of nucleation from vapor to solid composed of Lennard-Jones molecules

The Journal of Chemical Physics, 2011

We performed molecular dynamics (MD) simulations of nucleation from vapor at temperatures below the triple point for systems consisting of 10 4 -10 5 Lennard-Jones (L-J) type molecules in order to test nucleation theories at relatively low temperatures. Simulations are performed for a wide range of initial supersaturation ratio (S 0 10 − 10 8 ) and temperature (kT = 0.2 − 0.6ε), where ε and k are the depth of the L-J potential and the Boltzmann constant, respectively. Clusters are nucleated as supercooled liquid droplets because of their small size. Crystallization of the supercooled liquid nuclei is observed after their growth slows. The classical nucleation theory (CNT) significantly underestimates the nucleation rates (or the number density of critical clusters) in the low-T region. The semi-phenomenological (SP) model, which corrects the CNT prediction of the formation energy of clusters using the second virial coefficient of a vapor, reproduces the nucleation rate and the cluster size distributions with good accuracy in the low-T region, as well as in the higher-T cases considered in our previous study. The sticking probability of vapor molecules onto the clusters is also obtained in the present MD simulations. Using the obtained values of sticking probability in the SP model, we can further refine the accuracy of the SP model.

Molecular dynamics of homogeneous nucleation in the vapor phase. I. Lennard-Jones fluid

Journal of Chemical Physics, 1998

Molecular dynamics computer simulation was carried out to investigate the dynamics of vapor phase homogeneous nucleation at the triple point temperature under supersaturation ratio 6.8 for a Lennard-Jones fluid. To control the system temperature, the 5000 target particles were mixed with 5000 soft-core carrier gas particles. The observed nucleation rate is seven orders of magnitude larger than prediction of a classical nucleation theory. The kinetically defined critical nucleus size, at which the growth and decay rates are balanced, is 30-40, as large as the thermodynamically defined value of 25.4 estimated with the classical theory. From the cluster size distribution in the steady state region, the free energy of cluster formation is estimated, which diminishes the difference between the theoretical prediction and the simulational result concerning the nucleation rate.