Transient processes in falling films of liquid under conditions of unsteady-state heat release

Results are given of experimental investigation of the dynamics of development of heat transfer and critical phenomena in falling wavy films of nitrogen under conditions of unsteady-state heat release from the surface of a thin-walled heater. The experiments involve the investigation of transient modes with formation of dry spots and development of dryout in the case of stepwise and quasi-steady laws of heat release. It is demonstrated that the disintegration of laminar-wavy film of liquid in the case of low heat flux in critical modes under conditions of stepwise increase involves the emergence of metastable regular structures with jets of liquid and large-scale non-wetted zones between them. The generalization of experimental data is used to demonstrate that the value of characteristic transverse dimension between jets of liquid is more than twice the respective values obtained under conditions of steady-state heat release with boundary condition T _heater ～ const. In the case of high heat flux, the vigorous boiling of liquid leads to a rapid ejection of liquid in the form of droplets and to complete drying (almost simultaneously) of the entire heat-emitting surface. Experimental data are obtained on the times of expectation of boiling of liquid, of development of regular structures, and of drying of the heat-emitting surface as functions of heat flux in the range of variation of Reynolds number Re_in = 90–1690. It follows from analysis of experimental data that, in calculating the time of expectation of boiling of liquid in the case of stepwise heat release in the investigated range of variation of heat flux, one must take into account the development of intense evaporation from the free surface of laminar-wavy film.     

New method of simulation of volume condensation of supersaturated vapor

A method of direct numerical solution of kinetic equation for the droplet size distribution function is suggested for the investigation of the process of volume condensation of supersaturated vapor. Use is made of analogy with the corresponding method of solution of kinetic Boltzmann equation. An advantage of the suggested approach is the absence of limitations on the Knudsen number. The method is tested using the example of simulation of the behavior of vapor under conditions of rapid development of the state of supersaturation in a vapor-gas mixture as a result of adiabatic expansion. The results are compared in a wide range of Knudsen number with the results obtained using the moments method in a version of a set of moments equations. Investigation is performed of the effect of the droplet size dependence of saturation pressure on the dynamics of the process of condensation relaxation of supersaturated vapor.     

结冰分裂导线舞动振幅分析

针对结冰分裂导线舞动问题,从功能的角度提出了一种舞动振幅的分析方法。导出了舞动振幅经历一个周期增量的表达式。所导出的舞动振幅增量的表达式说明了作用在结冰分裂导线上的气动力的各项在舞动振幅不同阶段的作用。得到的结论是:当舞动的振幅较小时,气动力中常数项与线性项的功是气动力总功中的主要部分;当舞动的振幅为中等时,气动力中常数项与线性项的功与非线性项的功在气动力总功中的比例相近;当舞动的振幅为较大时,气动力中非线性项的功在气动力总功中的比例大于常数项与线性项的功在气动力总功中的比例。     

A method for analytical monitoring of surface deposits on jackets of fuel elements of reactors with water heat carrier

A method of postreactor analytical monitoring of elemental composition of deposits on jackets of fuel elements from zirconium alloys based on chemical removal and subsequent quantitative analysis of deposited elements using inductively coupled plasma atomic emission spectroscopy (ICP-AES) is described. The choice of the method of chemical removal of deposits from jackets of fuel elements is substantiated; data on the composition of solution of chemical reagents and temperature-time regime of the procedure are presented. Devices for nondestructively obtaining detailed and precise information on element distribution in deposits along the fuel element height by means of a small length of the analyzed segment and the capability of sequential segment analysis along the whole fuel element length are developed. Advantages of ICP-AES application for analysis of elemental composition of deposits with allowance for the specific features of studies of irradiated reactor materials are considered. A method of quantitative analysis of deposits is developed, its metrological aspects are considered, and results of determination of some elements of deposits on jackets of fuel elements of the RBMK-1000 of the Leningrad Nuclear Power Plant are given.     

Development of the theories of strength in the mechanics of materials

We present a brief survey of the history of development of the mechanical theories of strength of materials, their advantages, and drawbacks. A physically reliable and experimentally justified criterion of the equivalence of quasihomogeneous materials is established. The structure of the criterion is determined according to the results of analysis of the equation of the limiting surface whose shape satisfies the necessary and sufficient requirements imposed by the principal regularities and postulates of the mechanics of deformed body. The corresponding equation contains invariants used to control shear and tensile fracture. The degrees of responsibility of each of these mechanisms are put in correspondence with the parameter of plasticity of the material appearing in the equation in the form of a weight coefficient determined according to the results of testing by tension and compression. The condition of limiting state of materials with inhomogeneous structure is established by introducing in the criterion the influence function taking into account the statistical aspects of strength of materials in connection with the presence of “weak places” (defects). The analysis of the structure of the influence function is reduced to the solution of the problem of probability theory of repeated sampling of a given volume.     

The inclusion of the effect of the evaporation coefficient on the rate of variation of droplet radius

The paper deals with the investigation of the effect of the evaporation (condensation) coefficient of droplet substance on the rate of unsteady variation of the radius of a spherical aerosol droplet in the cases of direct and indirect inclusion of this coefficient. It is found in both cases that the effect of evaporation coefficient is most significant at the initial instant of unsteady-state process of evaporation and of condensation growth of the droplet. At this instant, the size of spherical droplet has hardly any impact on the rate of variation of its radius. As the unsteady-state process continues, the effect of the evaporation coefficient on the rate of variation of the droplet radius depends significantly on the droplet size. The larger the droplet under consideration, the lower the effect of the evaporation coefficient on the rate of variation of its radius. The rates of variation, calculated for the same values of the evaporation coefficient but for different ways of inclusion of this coefficient, differ less for larger aerosol droplets. These methods of inclusion of the evaporation coefficient are considered for the process of slow evaporation of a droplet.     

一种用射影线束族生成曲线的方法

以两射影对应线束对应真线交点的轨迹是二阶曲线为基础，研究了射影线束族的形成原理，讨论了射影线束与线束族，射影线束族与线束族对应直线交点所构成的平面曲线及其性质，同时利用计算机绘制了部分曲线。     

Deformation of Rodlike Elements of Composite Materials Subjected to Uniform Compression

On the basis of generalization of the results of investigation of the operation of rodlike elements of composite materials, we make a conclusion that the influence of various factors on the deformability of these elements is studied incompletely. The comparison of the stress-strain states for different models of concrete and reinforced-concrete elements makes it possible to describe the effect of longitudinal reinforcement (coefficient of reinforcement, strength and deformation characteristics) on the critical level of strains in the cross section. According to the results of our investigations, we give recommendations concerning the evaluation of the critical value of the coefficient of reinforcement above which one may observe the effect of reinforcement on the deformability of the analyzed sections. It is shown that the compression strength of the brittle base of the composite with inhomogeneous structure decreases as a result of the fracture processes. It is also demonstrated that the existing procedure used for the evaluation of the indicated decrease in strength requires significant improvement. The problem of evaluation of the ultimate value of the coefficient of reinforcement is also analyzed.     

红木文化创意产品及其开发设计原则

目的探究红木文化创意产品相关理论及开发设计原则。方法从文化创意产品的概念和红木的属性分析,提出红木文化创意产品的定义;通过对传统红木文化产品和现代红木文化创意产品的分类比对,分析出现代红木文化创意产品的新增产品种类。在红木文化创意产品定义和分类的基础上,提出红木文化创意产品的特征和红木文化创意产品开发设计原则。结论红木文化创意产品开发设计原则是对文化创意产品设计理论体系的补充,并将促进红木文化的继承和红木产品的创新。     

Special Features in the Realization of Film Boiling on Wire Heaters. Distilled Water

The existence of a region of self-oscillatory instability of heat transfer is revealed under conditions of film boiling of water subcooled to the saturation temperature. In the case of short heaters, whose length is commensurable with the Taylor instability wavelength, the process is regular. For heaters of the same length, the form of oscillations and their characteristics are fully reproducible. An increase in the heater length results in the emergence of spatially distributed oscillations. It is found that an increase in subcooling on the interface between the modes of boiling is accompanied by the formation of a structure consisting of a system of single domains of continuously decreasing size. The formation of this structure causes a significant change in the temperature distribution in the zone adjoining that of nucleate boiling, which considerably reduces the film stability. A single domain of the film mode of boiling was stable at any temperature of the liquid. The singularities of realization of minimal-size domains of the film mode of boiling under conditions of stabilization of the integral mean temperature of the heater are investigated. It is found that the minimal zone of the film mode of boiling is a system of three elementary domains.     

Application of Fracture Mechanics for Guaranteeing the Reliability of Arctic Large-Scale Welded Metal Structures

Reliability control of constructions for development of the Arctic shelf requires both a well-grounded determination of criteria of crack resistance of applied materials from the viewpoint of fracture mechanics and development of methods for calculating the cyclic resource of welded blocks of constructions. Realization of practical decisions in each of these directions is hampered by the insufficient development of a number of theoretical aspects of fracture mechanics. We consider ways of overcoming these difficulties.     

Approximation of the solution of inverse problem of scattering of electromagnetic waves on plane dielectrics

We propose a method for the determination of the material parameters of dielectric coatings according to the measured values of scattered electromagnetic fields which enables us to introduce an efficient procedure of processing of the data of measurements in the methods of nondestructive testing. As a specific feature of the proposed method for the solution of the formulated inverse problem, we can mention the possibility of reconstruction of piecewise continuous profiles of dielectric permittivity for laminated materials. The procedure of reconstruction is based on the method of integral equations. The solution of the problem is obtained approximately. The measured values of the coefficient of reflection of plane electromagnetic waves are extrapolated to the high-frequency region, which enables us to guarantee higher accuracy of reconstruction of the functions of dielectric permittivity for the analyzed structures.     

Variational method for the solution of the problems of tomography of the stressed state of solids

We study the problem of reconstruction of the stressed state of piecewise-homogenous solids on the basis of the data of measuring of the effects of interaction of external physical fields with the stress field. The general mathematical model includes three main elements: a model of stressed state, the data of nondestructive testing obtained by one or several methods, and a model of interaction of the sounding radiation with the stress field. Within the framework of this model, the problem of reconstruction of the stressed state is reduced to the problem of minimization of a quadratic functional taking into account both the experimental data obtained by different physical methods and the conditions imposed on the surface of the body and the interfaces of its components of different nature. This approach enables one to perform the numerical realization of both direct and inverse problems on the basis of a single algorithm. We establish the analytic structure of the beam integrals of the stress field determined according to the results of polarization-optical measurements. On this basis, we apply the proposed method to the solution of problems of integral photoelasticity and present an example of the applicability of our method to the investigation of the stress concentration near the interface of bodies of different nature. Pidstryhach Institute of Applied Problems in Mechanics and Mathematics, Ukrainian Academy of Sciences, L'viv. Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 35, No. 5, pp. 23–32, September–October, 1999.     

On the Problem of Improvement of the Damping Ability of Rotor Blades of Contemporary Gas-Turbine Engines

We present the results of experimental investigations of the influence of structural and technological factors on the damping ability of lock joints of compressor blades carried out at the Pisarenko Institute of Problems of Strength of the National Academy of Sciences of Ukraine, study the possibility of using dampers mounted in shroud joints of turbine blades, and formulate some recommendations concerning the possibility of im proving the damping ability of rotor blades of contemporary gas-turbine engines.     

Methods of Physical Simulation of Electrochemical Processes at the Tip of a Crack

We analyze stresses and the degree of plastic deformation at the contours of cracks of two types, namely, a sharp crack and a crack with slip lines. We show that at the tip of a crack of the second type, at the contour of the bottom–walls of the crack galvanic couple, there appear two symmetric microgalvanic couples at the slip lines. Microinhomogeneities of a metal (grain boundaries, nonmetallic inclusions, etc.) are submicrogalvanic couples whose activity increases due to inhomogeneity of microplastic deformations of their vicinities. We distinguished the mechanisms of corrosion-cyclic fracture and corrosion-static cracking. Under cyclic loading, breaking of grains occurs and grain boundaries and nonmetallic inclusions fail, which levels the influence of currents of submicrogalvanic couples on the growth rate of a crack. Under static loading, micro- and submicrogalvanic couples are permanently operating, the cold work of the surfaces of the metal of the walls of the crack is lower than that under cyclic loading, while the difference of potentials and the current of the bottom–walls of the crack galvanic couple are greater than those under cyclic loading. This explains both the phenomenon of branching and the higher growth rate of a crack of corrosion-static cracking with time. In addition to the electrode potential and pH of the medium, we propose to consider the following parameters as defining factors of the growth of a crack: currents of a galvanic couple, micro-, and submicrogalvanic couples and the time of repassivation of freshly formed metal surfaces appearing in the process of the growth of a crack. According to analysis of the literature data, these parameters cannot be experimentally determined. For this reason, we propose to use methods of simulation to investigate distributions of the potentials and currents of corrosion at the tip of a crack. We propose certain structures of physical and mechanoelectrochemical models of a crack and methods for measurement of distributions of the current density and the electrode potential at their surfaces.     

The shock-wave mechanism of spontaneous ignition of hydrogen under conditions of sudden efflux from reservoir at high pressure

Analysis is made of the conditions of spontaneous ignition of hydrogen as a result of emergence of a starting shock wave in air before an expanding cold flow of gas. The rise of temperature behind the shock wave causes ignition of the mixture of combustible gas with air, which forms on the contact surface. The condition for spontaneous ignition is the sufficient time of residence of mixture at high temperature for mixing and ignition. The calculations of spontaneous ignition of hydrogen jet are based on a model which takes into account the gasdynamic transport of viscous gas, the kinetics of oxidation of hydrogen, multicomponent diffusion, and thermal conductivity. The range of pressures is determined in a reservoir, during whose depressurization the shock wave forming in air exhibits intensity sufficient for igniting the hydrogen-air mixture behind the front of propagating jet of compressed hydrogen. Results of analysis are given of the dependence of conditions of ignition on the pressure of hydrogen in the reservoir, on the size of the outlet opening, and on the initial temperature of hydrogen and air.     

陈钢国家标准化管理委员会主任

Cheng Gang, Researcher and Doctor of Engineering in Solid Mechanics of Tsinghua University Dr. Chen once served successively as Deputy Director and Chief Engineer of the Boiler Pressure Container Inspection Center of the State Bureau of Quality Technical Supervision, Secretary of the Party Committee and Chief Engineering of China Special Equipment Inspection and Research Institute of AQSIQ, Vice Administrator, Chief Engineer and Member of the Leading Party Group of SAC, and Director-General of Bureau of Safety Supervision of Special Equipment of AQSIQ.     

Mechanics and physics of quasibrittle fracture of polycrystalline metals under the conditions of stress concentration. Part I. Experimental results

In the present work, which consists of three parts, we make an attempt to formulate the fundamental ideas of the theory of quasibrittle fracture of polycrystalline metals and structural alloys on the macroscopic and microscopic levels. Within the framework of the usual approach, we consider physical aspects of the problem of analysis of the elementary acts of fracture of the crystal lattice and regularities of macroscopic fracture under conditions of stress concentration in connection with the problem of structural integrity. We propose simple and convenient practical criteria of quasibrittle fracture under conditions of stress concentration and formulate physically substantiated concepts of the ductility of metals. In the first part of the work, we present the results of the experimental investigation of the fracture of specimens with stress concentrators of various geometries and fatigue cracks, establish the regularities of changes in the local characteristics of fracture, and analyze the principal factors affecting the value of the critical cleavage stress σ_f. Institute of Physics of Metals, National Academy of Sciences of Ukraine, Kiev, Ukraine. Translated from Problemy Prochnosti, No. 4, pp. 5–16, July–August, 1997.     

CONVERSION OF SHORT FATIGUE CRACKS INTO A LONG CRACK

This paper presents a method for the statistical processing of results of initiation and propagation of short fatigue cracks. The distribution of the lengths of these cracks followed a Weibull distribution function. The value of the size parameter of this distribution grows with the number of cycles, but the value of the shape parameter declines as the number of cycles increases. A study of the modal value of fatigue crack lengths as a function of the number of cycles yielded a statistical criterion defining the conversion of the short fatigue crack initiation and propagation stage into the long fatigue crack propagation stage. One condition for this conversion is a zero magnitude of the first derivative of the modal value of fatigue crack lengths by the number of cycles. When the dependence of the Weibull distribution shape parameter and size parameter upon the number of cycles was inserted in this condition, solution of the resultant expression revealed the critical number of cycles that is necessary for the formation of a long fatigue crack.     

On the mechanism of action of inhibitors of hydrogenation in the process of electrodeposition of metals

We develop a new approach to the investigation of the effect of inhibitors of hydrogenation of the base in the process of electrodeposition of metals. We established the relationship between the structure of molecules of the inhibitor, their ability to interact with atomic hydrogen, their adsorption properties, the contents of various forms of hydrogen in steel, and physicomechanical parameters of the latter. On the basis of the results of quantum-chemical computations of electron parameters of molecules, we demonstrate the possibility of prediction of the efficiency of inhibitors of hydrogenation and regularities of changes in the strength and plastic properties of steel. Dnepropetrovsk State University, Dnepropetrovsk. Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 32, No. 6, pp. 7–17, November–December, 1996.