New criterion for comparison of classical theory of nucleation in superheated liquids with experimental data

We have obtained inequality $ 1 - {{\Delta \bar \tau } \mathord{\left/ {\vphantom {{\Delta \bar \tau } {\bar \tau }}} \right. \kern-\nulldelimiterspace} {\bar \tau }} < \left( {J \cdot V \cdot \bar \tau } \right)^{ - 1} < 1 + {{\Delta \bar \tau } \mathord{\left/ {\vphantom {{\Delta \bar \tau } {\bar \tau }}} \right. \kern-\nulldelimiterspace} {\bar \tau }} $ 1 - {{\Delta \bar \tau } \mathord{\left/ {\vphantom {{\Delta \bar \tau } {\bar \tau }}} \right. \kern-\nulldelimiterspace} {\bar \tau }} < \left( {J \cdot V \cdot \bar \tau } \right)^{ - 1} < 1 + {{\Delta \bar \tau } \mathord{\left/ {\vphantom {{\Delta \bar \tau } {\bar \tau }}} \right. \kern-\nulldelimiterspace} {\bar \tau }} , where J is the frequency of homogeneous nucleation, V and $ \bar \tau $ \bar \tau are, respectively, volume and average lifetime of the superheated liquid, and $ {{\Delta \bar \tau } \mathord{\left/ {\vphantom {{\Delta \bar \tau } {\bar \tau }}} \right. \kern-\nulldelimiterspace} {\bar \tau }} $ {{\Delta \bar \tau } \mathord{\left/ {\vphantom {{\Delta \bar \tau } {\bar \tau }}} \right. \kern-\nulldelimiterspace} {\bar \tau }} is relative statistical error $ \bar \tau $ \bar \tau . Inequality appears to be a consequence of nucleation homogeneity and stability used at its deduction and taken in the theory as initial and determinant assumption. Calculations with the use of experimental data for the boundaries of the attainable superheating show that inequality is not satisfied. Thus, experimental data can not be considered a proof of the theory fundamentals.     

Criterion of homogeneous boiling-up of superheated liquids

It is difficult to eliminate the effect of vessel walls and impurities in practical studies of boiling-up of strongly superheated liquids. Therefore, some doubts are always cast upon validity of experiments and their agreement with the classical theory of homogeneous stationary nucleation, impairing the verification of theoretical considerations. This paper reports main results of the theory of homogeneous nucleation and presents formulas for calculating the work of formation of a critical nucleus by an incline of the accessible superheating boundary on isobars and isotherms. Matching of experimental and theoretical values of the work of formation was considered as the homogeneous boiling-up criterion. Calculations by isobars and isotherms were made for some liquids. The theoretical values of the work of formation of a critical nucleus were 1.23–4.5 times higher than the corresponding empirical values for all the liquids, i.e., they were much higher than the calculation error. Thus, boiling-up of the studied liquids was not homogeneous and, hence, it did not correspond to the classical theory of nucleation. The work was financially supported by the President of the Russian Federation (No. NSh-4429.2006.8) and the Russian Foundation for Basic Research (Grant No. 07-08-00575-a).     

过热液氦均匀核化速率的确定

预测不同压力下过热液氦的均匀核化速率是十分重要的,它与液氦的极限过热度密切相关。文中通过回顾动力学理论、分子聚集理论、涨落理论等研究液体均匀核化的方法,对过热液氦的均匀核化速率进行了计算,并且对各种方法进行了比较与分析。结果表明,用能量涨落理论来计算过热液氦的均匀核化速率是一种比较合理的方法。     

Pre-nucleation relaxation phenomenon in electric field induced nucleation in superheated liquids

Pre-nucleation relaxation phenomenon in electric field induced nucleation in liquids has been observed at subcritical fields. The relaxation times τ in the processes of the application of electric field and induced nucleation have been measured. τ is found to be function of the degree of superheat of the liquid.     

Classical nucleation theory with a tolman correction

The effect of the Tolman correction for the surface tension of small droplets on the classical Becker-Doering theory of nucleation is studied near the critical temperature T_c. Also a generalization of the kinetic prefactor is studied together with this correction. No qualitative change in the very small slope of the curve of the reduced supercooling as a function of (1–T)/T _c at constant nucleation rates was found.The Center for Polymer Studies is supported in part by grants from ARO, ONR, and NSF.     

Specifics of nucleation in superheated water and supersaturated vapor

This work is dedicated to the experimental studying of the nucleation kinetics in superheated water and supersaturated water vapor. A percolation model for the liquid water structure that explains a number of anomalous thermophysical properties of water and water vapor in the metastable region is proposed.     

Transient time in homogeneous nucleation

The problem of the transient time in nucleation is studied. The size-dependent transient time at a constant temperature is defined and the approximate analytical solution is found and compared with the exact numerical solution for the model Li₂O.2 SiO₂ melt. It is shown that the analytical solution for the size-dependent transient time is in agreement with the numerical result.     

Nucleation in superheated argon,krypton and xenon liquids

The superheating of condensed noble gases (argon, krypton, xenon) was investigated by the techniques of continuous heating of liquid specimen in a glass capillary. Experiments covered the pressure range 1–35 bar at the nucleation rates ≈10⁵ cm^-3 s^-1. The superheating data obtained here were compared with the results of calculations based on the Volmer-Becker-Döring-Zeldovich-Frenkel homogeneous nucleation theory. A good agreement between theory and experiment as well as the thermodynamic similarity of the studied substances with respect to the fluctuation nucleation was found.     

On the validity of the capillarity approximation in the rate theory of homogeneous nucleation

An Einstein model is used to calculate the internal vibrational free energy of approximately spherical fcc crystallites as a function of crystallite size at T/θ = 1. It is found that the free energy per surface atom does not become convergent until a size of about 3 × 10⁷ atoms is reached. The excess free energy at convergence is used to define the macroscopic surface tension for use in the capillarity approximation. The internal free energy of microcrystallites containing of the order of 100 atoms is fortuitously well described by the capillarity approximation. A good estimate of the total free energy of the microcrystallite (nucleus) is obtained from the capillarity approximation only by adding the contributions from free translation and rotation and the replacement partition function.     

Characteristics of acoustic emissions during nucleation of superheated droplets

Superheated droplet nucleation and subsequent bubble oscillation produces an acoustic pressure pulse that contains valuable information about the nucleation process. Spectral analysis of the pressure pulse indicates excitation of different modes of bubble oscillations in the nucleation process. In the present study it is observed that gamma induced droplet nucleation excites higher modal oscillations and also emits higher intensity acoustic emission compared to that of spontaneous nucleations.     

Activated instability of homogeneous bubble nucleation and growth

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."     

Extended (n/v)-Stillinger cluster for use in the theory of homogeneous nucleation

In this paper we develop a theory for an extended version of the (n/v)-Stillinger cluster that has been used in nucleation theory, where n means the number of particles constituting the cluster characterized by the volume v. The "extended cluster" incorporates some of the surrounding supersaturated vapor. This cluster, although requiring more extensive simulation than the original (n/v)-Stillinger cluster, is almost devoid of approximation. It maintains the non-ad-hoc nature of the original (n/v)-Stillinger cluster implicitly. The theory of the cluster is also applicable to clusters which avoid redundancy by some other means than the so-called "connectivity requirement." Simulation of the extended cluster is now being implemented and will be used in the theory of the homogeneous nucleation rate.     

The experimental verification of the absolute space-time theory—I

The fundamental postulate of our theory is the constancy of light velocity only with respect to absolute space. This postulate was proved right by our recently performed ‘coupled-mirrors’ experiment (Marinov, 1974). In the present paper it is shown that the so-called (by us) Newtonian and Einsteinian time synchronisations lead respectively to the Galilean and Lorentz transformations. Both types of synchronisation can be practically realised, hence both corresponding transformations describe the physical reality at low as well as at high velocities of the material points. The conception that the Einstein time dilation is an absolute phenomenon and the Lorentz length contraction a fiction is defended.     

Breakdown of the superheated Meissner state and spontaneous vortex nucleation in type II superconductors

The theory of local stability of the superheated Meissner state presented in an earlier paper is supplemented by an investigation of global stability in two dimensions. We conclude that flux penetration cannot be delayed beyond the fieldH _s1 where local instability sets in. Various new two-dimensional Ginzburg-Landau solutions, obtained numerically, are discussed. These include the lowest saddle point separating the Meissner from the normal and vortex state and a solution resembling the “nascent vortex state” whose existence was postulated recently by Walton and Rosenblum. Using these solutions the process of spontaneous vortex nucleation is discussed.     

Experimental determination of superheated liquids boiling-up expectancy time probabilities distribution

Results of statistical measurement of n-pentane and n-hexane boiling-up expectancy time near the boundary of attainable superheating are presented. Experiments were carried out in glass capillaries with various volumes of superheated liquid. Several samples with the volume from 100 to 200 measurements of life time for preset metastable state have been obtained (p, T = const). Their histograms contain small empty initial section, maximum and long “tail” in the area of large times. Non-monotonous dependence of probability distribution density on time proves non-stationary character of the random process resulting in the production of supercritical embryo. Two simple approximations of non-stationary nucleation flow well describing experimental data have been considered. For exponential distribution, the probabilities of experimentally found peculiarities of boiling-up expectancy time distribution density have been evaluated; they prove incompatibility of this distribution with the experimental one.     

非视线紫外光大气传输模型的建立及验证

基于蒙特卡罗方法建立了非视线紫外光传输模型。利用此模型模拟了不同传输距离、不同发射和接收仰角等多种传输条件下的传输情况,并在同等条件下进行了相关实验。结果表明,在相同条件下,信号强度模拟曲线与实验曲线的变化趋势相同且吻合较好,但具有一定的误差。进一步分析指出,模型中大气散射系数、吸收系数、分子散射比、传输测试距离等参数的误差影响了模拟结果的准确,以及模拟与实验曲线的吻合程度。     

可膨胀过热水系统多气核演化过程与临界过热度分析

使用分子动力学方法,研究过热水系统均质沸腾核化过程.采用Langevin 动力学方法控制体积可变系统的温度与压力,更好地模拟了沸腾实际物理过程.得到了液相系统体积连续膨胀、分子间距逐渐增大,最终稳定在汽相的现象学规律.当过热温度较高时,亚稳态液相系统可能在局部形成不同大小的近球形区域：气核,这些气核是不稳定的,处于不断演化之中.通过分析分子所受引力与斥力的共同作用,得到了气核形成与消亡以及多个气核融合的机理.比较了模拟结果与经典沸腾理论的差异,提出了气核生长是比气泡生长更为微观过程的认识.通过研究不同过热 关键词： 过热水系统 分子动力学 气核 临界过热度     

Stages of homogeneous nucleation in solid isotopic helium mixtures

We have made pressure and NMR measurements during the evolution of phase separation in solid helium isotopic mixtures. Our observations indicate clearly all three stages of the homogeneous nucleation-growth process: (1) creation of nucleation sites; (2) growth of the new-phase component at these nucleation sites; and (3) coarsening: the dissolution of subcritical droplets with the consequent further late-stage growth of the supercritical droplets. The time exponent for the coarsening, a=1/3, is consistent with the conserved order parameter Lifshitz-Slezov evaporation-condensation mechanism.