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.     

Experimental investigation of the collapse of laser-generated cavitation bubbles near a solid boundary

The oscillation of a laser-generated single cavitation bubble near a solid boundary is investigated by a fiber-optic diagnostic technique based on optical beam deflection (OBD). The maximum bubble radii and collapse time for each oscillation cycle are determined from a sequence of bubble oscillations. Furthermore, by combining the revised Rayleigh theory, the prolongation factor κ at different dimensionless parameter γ (γ=L/R_max, where R_max is the maximum bubble radius and L is the distance of a cavity inception point from a boundary) is obtained. In addition, the prolongation factor of the collapse time versus laser energy is also derived, which are valuable in the fields of hydraulic cavitation, laser lithotripsy and laser ophthalmology.     

Interconnection between dynamics of liquid boiling-up and heat transfer crisis for nonstationary heat release

This paper deals with investigation results on crisis phenomena for nonstationary heat release under the conditions of free convection and in falling liquid films. It is shown that the character of the crisis development and the critical heat flux for nonstationary heat release significantly depend on the characteristics determining the temperature head of liquid boiling-up. According to experimental data with an arbitrary temporal function of heating, the character of the dependence between the critical heat flux and the heat release increasing rate is significantly effected by ready nucleation sites. It is found that a change in the nonstationary critical heat flux in the range of high times between impulses for periodic heat release is connected with deactivation of ready nucleation sites on the heat-releasing surface. According to new experimental results, in the studied range of irrigation degree alteration (Re_in = 30–1660), parameters characterizing decay of the falling liquid film with stepped heat release (the distribution of the time of boiling-up expectation along the liquid film, the velocities of movable boundaries in the boiling-up and drying fronts, the intensity of liquid ejection from the heat-releasing surface) complexly depend on the Reynolds number, wave characteristics, and heat flux density. The text was submitted by the authors in English.     

A scaling equation of state near the critical point and the stability boundary of a liquid

A new scaling equation of state is proposed to describe the equilibrium thermodynamic properties of liquids near the critical point. In distinction from the existing scaling equations, which are parametric, the new equation is nonparametric and is expressed directly in terms of the physical quantities (pressure, temperature, and so on). It creates a number of advantages for the traditional representation and data processing. The equation gives rise to a binodal, spinodal, and a curve of thermal capacity divergence (pseudospinodal). The equation is expressed in terms of reduced variables (the ratio of the deviation of a thermodynamic variable from its critical value to the critical value) and contains 3 system-dependent adjustable constants. With the help of this equation, we conducted an approximation of the experimental PVT data in the critical region of ⁴He, C₂H₄, and H₂O with a pressure error of 0.4% and carried out a calculation of the C _v ⁴He thermal capacity with no more than 4% error using a three-system constant determined from the PVT data.     

Experimental study of boiling-up kinetics and superheat limit for n-hexane on solid powder-like structures

The experimental setup is described and results are presented for measuring average boiling-up lag time for superheated n-hexane mixed with solid structures (activated coal, cellulose, silica gel) as function of temperature under atmospheric pressure. The “aging” of the cell with the filler was carried out before measurements: this was about 600–1000 boiling events. We developed a new method for analysing of “aging” procedure: comparison of average flux (frequency) of boiling-up events (processing of experimental data) and the frequency of nucleation obtained from exponential model. By the end of aging of the cell with silica gel the average empirical flux reduces by factor of four relative to the “exponential” value. But for activated coal and cellulose the difference in these fluxes is about 20 %. In all experiments, the event flux was nonstationary. For n-hexane in tested systems, the margin of superheating was T _n/T _cr ≅ 0.873–0.875, although it was T _n/T _cr ≅ ≅ 0.883 for n-pentane in systems filled by nickel powder (sintered porous nickel with grains of 1.5 or 5.0 micron size) and in the presence of a smooth copper plate. The average time of boiling-up lag in n-hexane at low normalized temperatures was also smaller than for n-pentane. For all systems, the lag time is almost the same for the temperature range T _n/T _cr ≅ 0.860–0.874 (plateau). Thus, a smaller amount of superheated liquid or its division into smaller liquid elements does not result in longer liquid lifetime for superheat liquid and the maximal superheat temperature, as one could expect from the classical theory of homogeneous nucleation. Research was supported by the RF Presidential Foundation (NS-905.2003.2) and Russian Foundation for Basic Research (Grant No. 04-02-16285).     

光学玻璃光学均匀性高精度测量技术

高质量的透射光学系统对光学材料的光学均匀性要求非常高 ,材料局部折射率 10 -6 量级的变化就可能破坏整个系统的性能。详细介绍了三种用于测量光学玻璃光学均匀性的干涉法 ,研制了一台高精度光学玻璃材料光学均匀性测量仪。实验结果表明 :40mm左右厚的光学玻璃材料的光学均匀性检测精度可达 1× 10 -6 。     

Geometry of the vapor phase in explosive near-wall boiling-up

Methods for calculating the geometric characteristics of the vapor phase in explosive wall boiling-up processes on a metal wall are analyzed. A monotonic growth of superheat in the liquid above the equilibrium evaporation temperature is specified. We show that the choice of the model for bubble interaction has a profound influence on the geometric characteristics which define the value of the heat flux. Computer simulation was employed to obtain the dependence of dry area on time in two interaction models. We have found that, for a model with instantaneous bubble coalescence, the dry area can be evaluated by the Kolmogorov formula using a correction factor for the most probable triple interaction. An approximation of the distribution length of wetting line over the lifetime of wetting-line segments is obtained. The possibility of using the obtained data for calculation of rapid condensation is analyzed.     

Experimental evidence for fast heterogeneous collective structural relaxation in a supercooled liquid near the glass transition

We have extended the exploration of microscopic dynamics of supercooled liquids to small wave numbers Q corresponding to the scale of intermediate range order, by developing a new experimental approach for precise data correction for multiple scattering noise in inelastic coherent neutron scattering. Our results in supercooled Ca0.4K0.6(NO3)(1.4) reveal the first direct experimental evidence, after a decade of controversy, that the so-called picosecond process around the glass transition corresponds to a predicted first, faster stage of the structural relaxation. In addition, they show that this process takes the spatial form of fast heterogeneous collective flow of correlated groups of atoms.     

Melting mechanisms at the limit of superheating

The atomic-scale details during melting of a surface-free Lennard-Jones crystal were monitored using molecular dynamics simulations. Melting occurs when the superheated crystal spontaneously generates a sufficiently large number of spatially correlated destabilized particles that simultaneously satisfy the Lindemann and Born instability criteria. The accumulation and coalescence of these internal local lattice instabilities constitute the primary mechanism for homogeneous melt nucleation inside the crystal, in lieu of surface nucleation for equilibrium melting. The vibrational and elastic lattice instability criteria as well as the homogeneous nucleation theory all coincide in determining the superheating limit.     

Quantum properties near the instability boundary in optomechanical system

The properties of the system near the instability boundary are very sensitive to external disturbances, which is important for amplifying some physical effects or improving the sensing accuracy. In this paper, the quantum properties near the instability boundary in a simple optomechanical system have been studied by numerical simulation. Calculations show that the transitional region connecting the Gaussian states and the ring states when crossing the boundary is sometimes different from the region centered on the boundary line, but it is more essential. The change of the mechanical Wigner function in the transitional region directly reflects its bifurcation behavior in classical dynamics. Besides, quantum properties, such as mechanical second-order coherence function and optomechanical entanglement, can be used to judge the corresponding bifurcation types and estimate the parameter width and position of the transitional region. The non-Gaussian transitional states exhibit strong entanglement robustness, and the transitional region as a boundary ribbon can be expected to replace the original classical instability boundary line in future applications.     

Structure of liquid solutions near the critical point

Specific features of the structure of the critical state of binary liquid solutions leading to an anomalous behavior of the Rayleigh line due to a dramatic increase in concentration and density fluctuations are considered. It is shown that an experimental treatment must deal with two fluctuation regions near the critical point of solvent vaporization. In the first region, one can achieve a sufficient degree of accuracy by using theories like self-consistent field theory. In the second region, which is closer to the critical point than the first region, scaling theory of second-order phase transitions may be applied. It is found that the anomalous behavior of the Rayleigh line associated with kinetic coefficients is determined by the equilibrium thermodynamic properties and by the radius of fluctuation correlation (r_c). A general theory is developed for calculating thermodynamic potentials, especially the chemical potential and its concentration derivative in the fluctuation region. The results of these calculations are compared with the experimental data briefly described in the paper. Translated fromZhurnal Struktumoi Khimii, Vol. 39, No. 4, pp. 655–668, July–August, 1998.     

Finite-size scaling of critical cumulants near the ferromagnetic phase boundary

We employ the recently proposed scaling theory for first-order transitions to derive a detailed prediction for the large-argument behaviour of the critical-point scaling function of the reduced fourth order cumulant $\text{g}{}_{\mathrm{L}}\text{≡}\text{<s}{}^4\text{>}\text{<s}{}^2\text{>}{}^2\text{?3}$ correct up to a term exponentially small in L/ξ(T).     

Generation of vorticity near the boundary in planar Navier-Stokes flows

We construct the solutions of the planar Navier-Stokes flow for a viscous incompressible fluid in the half-plane, by means of a boundary layer equation describing the production of vorticity on the boundary. Regularity properties are also discussed.Research partially supported by Ministero della Pubblica Istruzione and CNR-GNFM