Acoustic waves in two-fraction bubble liquid with phase transformations

The propagation of acoustic waves in two-fraction mixtures of liquid with vapor-gas and gas bubbles of different sizes and compositions with phase transformations has been studied. A system of the differential equations of the motion of the mixture is presented, and the dispersion relation is deduced. Two local maxima in the frequency dependence of the attenuation coefficient for the case of the two-fraction mixture of water with vapor-gas bubbles of air and helium bubbles are revealed. The evolution of the weak pulsed perturbations of the pressure in this mixture was calculated numerically. It was established that the substitution of part of the vapor-gas bubbles in the monodisperse bubble mixture with phase transitions for inert gas bubbles can lead to both a decrease and an increase in the attenuation coefficient in the low-frequency region depending on the sort of gas.     

Acoustic disturbances in a mixture of liquid with vapor-gas bubbles

Results are given of theoretical study into the propagation of acoustic disturbances in mixtures of liquid with vapor-gas bubbles in view of interphase diffusion mass transfer. A unified general dispersion relation is obtained, which defines the propagation of harmonic disturbances in two-phase mixtures of liquid with bubbles of vapor and gas in the plane, spherical, and cylindrical cases. Numerical calculations are performed of the evolution of weak pulse disturbances of pressure of different geometries in liquids with vapor-gas bubbles at different values of parameters of the medium. It is demonstrated that the velocity of propagation of waves significantly decreases with increasing initial concentration of vapor in vapor-gas bubbles, and the wave damping significantly increases. In so doing, the effect of vapor content on the dynamics of acoustic disturbances significantly increases with the initial volume content of bubbles. The nonmonotonic dependence of damping of pulse disturbance of pressure on the initial radius of bubbles in liquid with vapor-gas bubbles in the presence of phase transformations is demonstrated.     

Numerical modeling of the aerodynamics, heat exchange, and combustion of a polydisperse ensemble of coke-ash particles in ascending axisymmetric two-phase flow

A two-dimensional stationary model of motion, heat and mass exchange, and chemical reaction of polydisperse coke and ash particles in ascending gas-suspension flow has been constructed with allowance for the turbulent and pseudoturbulent mechanisms of transfer in the dispersed phase. The system of equations that describes motion and heat transfer in the solid phase has been closed at the level of the equations for the second moments of velocity and temperature pulsations, whereas the momentum equations of the carrying medium have been closed using the equation for turbulent gas energy, which allows for the influence of the particles and heterogeneous reactions.     

Dynamics of acoustic waves in porous media saturated with gas-vapor mixture

Wave processes in wet porous media saturated with gas-vapor mixture have been studied with allowance for interphase interaction forces and heat and mass exchange between the skeleton of the porous medium and the gas-vapor mixture. Dispersion relations have been obtained for a porous medium saturated with gas-vapor mixture, vapor, or gas.     

Application of particle tracking velocimetry for studying the dispersion of particles in a turbulent gas flow

A method for the determination of the dispersion of solid particles in a turbulent gas flow has been presented. This method is based on recording the particle trajectories with a high-speed video camera on separate regions of a flow, located at various distances from a point source of particles, and the subsequent processing of the frames. This method has been used to study the dispersion of solid particles under the conditions of turbulence in a horizontal channel with a rectangular cross section of 200 × 400 mm for a measuring region length of 2 m. Turbulence of the gas flow was generated by means of a grid with square meshes of the size of 16 mm. The average velocity of the gas flow in the measuring region was 5.1 m/s. The dispersion of 36-, 56- and 128-micron glass particles of spherical shape was studied in a region 450 mm long from the point source of particles. It has been shown that the dispersion of these particles in the direction of the action of the gravity force is larger than their dispersion in the perpendicular direction to the gravity force. The results of this study have shown that an increase in the size of particles leads to a decrease in the dispersion at small flight times of the particles (short-time dispersion).     

Acoustic instability in a two-phase mixture with temperature relaxation of particles

Theoretical calculation of acoustic instability in a two-phase mixture with temperature relaxation of particles is performed. Particles are assumed to be spherical and monodisperse, while their mass fraction does not exceed 50%. The formula for calculation of the acoustic oscillation frequency and increment, as well as the approximate formula for oscillation-amplitude calculation, are derived in this work. The heat exchange between the particles and the gas mixture is taken into consideration explicitly in these formulas.     

Frequency Thresholds in the Energy Transmission Across Kapitza Interfaces

When heat is conducted from a solid into liquid helium, a thermal boundary resistance occurs across the interface. This effect, known as Kapitza resistance, has been described with limited success by the acoustic impedance theory. An energy exchange mechanism is proposed in this investigation which is distinct from that of the acoustic impedance theory. The resulting model is successful in predicting the existence of frequency thresholds in the energy transmission across Kapitza interfaces. These frequency thresholds were derived from an analysis of the interaction between helium atoms from the coupling fluid and adsorbed particles which are bound to the solid surface by the Van Der Waals potential of the interface. The predicted ratio of the onset frequencies for a solid surface coupled to ³ He and ⁴ He gas was found to be approximately equal to the square root of the mass ratio. This result is in good agreement with experimental observations.     

The propagation of linear waves in humid,gas-saturated media

The process of propagation of acoustic waves in humid, gas-saturated porous media is investigated in a two-velocity approximation. A dispersion relation is derived, which includes interphase interaction forces and heat transfer between the skeleton of porous medium, liquid, and gas. The effect of heat transfer between the phases on the propagation of the “fast” and “slow” waves is included by means of heat equation     

Sound conversion phenomena at the free surface of liquid helium. I. Calculation of the coefficients of reflection,transmission, and transformation of sound waves incident on the liquid-vapor interface of helium

On the basis of a set of boundary conditions describing quite generally mass and energy transport processes across the free surface of helium II, the acoustic coefficients of reflection, transmission, and transformation of first sound, second sound, and the sound wave propagating in the vapor are calculated in the case of perpendicular incidence of sound waves against the liquid-vapor phase boundary. Considering rigorously the influences of the Onsager surface coefficients, the isobaric thermal expansion coefficients, and the thermal conductivities of the liquid and the vapor, we derive sets of equations from which the acoustic coefficients are determined numerically. For estimations, simple explicit formulas of the acoustic coefficients are given. It is shown that the evaporation and energy transport processes occurring at the free surface of helium II due to the incidence of sound waves may be connected with appreciable energy dissipation. The surface absorption coefficients of first, second, and gas sound waves are deduced.     

Entrainment of Heterogeneous Particles from Gas-Fluidized Bed

The entrainment of heterogeneous particles in a gas-fluidized bed for particle mixtures of categories A and B according to the Geldart classification was conducted in this study. The experiments were carried out in an acrylic column of 0.092 m diameter. The distributors were perforated plates of up to 5.9% free area fraction. Measurements of pressure gradients were made using 24 pressure taps. Glass beads with particle diameters from 60 to 400 μm were used. The mixtures were described using the Rosin-Rammler-Bennet granulometric distribution model. The transport disengaging height (TDH) heights were obtained using the Geldart methodology. A 2⁵ experimental design was applied relating the dispersion index, mean diameter, solid mass, superficial gas velocity, and free area fraction of the distributor to obtain the TDH heights. Slugging and transition for turbulence regimes characterized the behaviors of fluidized beds. The results showed that TDH heights for heterogeneous particles were dependent on the solid mass and superficial gas velocity.     

The theory of the growth of vapor bubbles in a metastable liquid

The growth of a single bubble and a system of vapor bubbles in the initial state in thermal and mechanical equilibrium with a liquid has been considered. Linear and nonlinear solutions have been derived, and the effects of the radial inertia, viscosity of the liquid, interphase heat and mass exchange, and the conditions of the tightness of bubbles on the development of the process have been studied on their basis.     

Bed expansion ratio of mono-sized and binary mixtures in fluidized,spouted, and spout-fluid beds

Studies on bed expansion ratio were carried out in fluidized, spouted, and spout-fluid beds. A single column has been used to compare the characteristics of fluidized, spouted, and spout-fluid beds. Experiments were carried out using air and glass beads under fluidized, spouted, and spout-fluid bed conditions separately to study the effect of gas velocity, bed mass, and particle size on bed expansion ratio. Glass beads of different sizes (0.75, 1.2, 1.7, and 3.075?mm) have been used as solid bed material. Bed expansion ratio was determined for mono-size particles and binary mixtures (different diameter ratios and composition). It was found that the bed expansion ratio decreases with increase in bed mass for only spouting condition and spout-fluidization conditions. The bed expansion ratio increases with increase in bed mass for only fluidization condition.     

Dispersion of optical and acoustic phonons in diamond and germanium crystals

The dispersion laws of the optical and acoustic branches in diamond-like crystals have been derived using idealized models of crystal lattices. Two types of analytical expressions have been proposed, whose parameters can be derived from inelastic neutron scattering experiments and the properties of acoustic waves. The calculation results are in satisfactory agreement with experimental data for the crystallographic directions [100], [110], and [111]. The group velocities of optical and acoustic phonons have been determined, and expressions for the effective mass of optical phonons have been derived.     

高温高固气质量比条件下旋风预热器换热管压降的研究

为了掌握旋风预热器换热管压降随温度、风速和固气质量比的变化规律,在各种不同条件下,对旋风预热器换热管压降进行测试。结果表明:在气流速度固定不变的情况下,当固气质量比z≤1时,随着温度的升高,压降先增大后减小,在200℃附近出现高点;当固气质量比z≥1.5时,随着温度的升高,压降逐渐减小,在600℃附近趋于平缓,之后随着温度的升高略有增大。压降总是随着风速的提高而增大,随着固气质量比的增加而增大。     

Effect of disperse phase on instability in systems with combustion

The dynamics of weak perturbations with finite amplitude in a two-phase homogeneous medium (gas with suspended solid particles) featuring a nonequilibrium chemical reaction has been studied. Using an asymptotic approach, a weakly nonlinear model of the evolution of one-dimensional perturbations is developed that takes into account the kinetic wave interactions and dissipative properties including the interphase exchange of heat and momentum. Conditions for the loss of stability of the homogeneous state of the system are analyzed. Numerical solutions of the evolution equation are obtained in the form of established self-sustained oscillations. The stabilizing effect of the inert disperse phase is described.     

Hybridization of backward acoustic waves in piezoelectric plates

The phenomenon of hybridization of the backward acoustic waves propagating in a piezoelectric crystal plate has been studied. In an electrically free plate (in particular, of potassium niobate) with a crystal orientation for which a sagittal plane is the symmetry plane, the dispersion curves of backward acoustic waves exhibit points of intersection and hybridization is absent. However, for a small change in the direction of wave propagation, the dispersion curves exhibit “repulsion” and the waves become coupled. The degree of hybridization is quantitatively evaluated in terms of the hybridization coefficient, which is defined as the ratio of the total mutual energy density and the total energy density of the interacting waves. It is demonstrated that the extent of repulsion of the dispersion curves for the interacting waves is determined by the dependence of the hybridization coefficient on the product of the plate thickness and the wave frequency.     

Wave Motion of Solid Particles in a Pulsed Gas Flow

The effect of lowfrequency pulsations of gas on the motion of solid particles has been studied on the basis of numerical solution of equations of the dynamics of a monodisperse gas suspension with account for interphase forces of hydrodynamic drag, virtual masses, and forces due to nonstationary effects around particles. It is found that at certain parameters gas pulsations lead to enhancement of interphase heat transfer. The dependences of the time of particle residence in a pneumochannel on the frequency of gas pulsations have been obtained.     

Spherical and cylindrical waves in vapor-gas mixtures with polydisperse particles and drops

Propagation of plane, spherical, and cylindrical waves in vapor-gas mixtures with polydisperse particles and droplets, where one of the fractions is involved in phase transformations, was studied. A disperse correlation was obtained, and disperse curves were computed. The influence of polydispersity of particles and droplets on dispersion and dissipation of small perturbations was analyzed.     

Heat and mass transfer in the heterogeneous system matrix-inclusions under pulse electron-beam processing

A mathematical model of pulse electron-beam processing of a heterogeneous material with allowance for the fact that each phase (particles and the matrix) possess its own properties and thus is characterized by its own concentration and temperature has been proposed. The processes of transfer of heat and mass in particles and the matrix and exchange processes between the phases have been taken into account. An example of a partial problem enabling one to calculate the coefficients of heat and mass exchange between the phases as functions of the temperature and the particle size has been given. The influence of the character of the external heat flux on the temperature and concentration fields in particles and the matrix has been illustrated. __________ Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 81, No. 1, pp. 147–156, January–February, 2008.