Breakup of a droplet at high velocity impacting a solid surface

We have studied the collision between a droplet of different liquids with high impact energy and a solid plate with varied surface roughness, which is characterized by a dimensionless Weber number (We, defined as the impact inertia of the droplet normalized by its surface force) extending up to 12,000 for water. To make such collision, a technique was developed to generate a single droplet with speed up to 42 m/s, which was initially driven by upstream air flow through a nozzle and accelerated to nearly the same velocity of the high-speed flow downstream. Via a high-speed photographing system, the various splashing mechanisms were investigated and a specific prompt splash on a smooth plate was found at sufficiently high We, which was different somehow from the conventionally defined one that was generally believed to occur only on a rough surface. The radius when multiple secondary droplets were shed out of the rim of the expanding lamella was found to scale almost invariantly with We at large values, whereas the coupled effect of liquid viscosity might affect the ultimate value.     

Hollow droplets impacting onto a solid surface

The impact process of spherical hollow droplets impinging onto a solid surface has been experimentally studied. Formation of a counter-jet in a wide range of Reynolds and Weber numbers was revealed, this jet being similar to a Worthington jet. For characterizing the regime of liquid flow in the hollow droplet, we propose using the Euler number. Theoretically, the problem was treated using a simple model of axisymmetric liquid flow. The obtained results proved to be consistent with experimental data.     

Coalescence of two droplets impacting a solid surface

Coalescence of a falling droplet with a stationary sessile droplet is studied experimentally. High-speed video images are presented to show coalescence dynamics, shape evolution and contact line movement. Emphasis is put on spread length, which is the length of two coalesced droplets along their original centers. Experimental results have shown that the spread length can be larger or smaller than the ideal spread length, which is the spread diameter of individual droplet plus the center-to-center distance between the two droplets. Three different coalescence mechanisms based on comparing the maximum and the minimum spread lengths to the ideal spread length are identified. Correlations for the maximum and the minimum spread lengths are developed, which can be combined with the coalescence domains to determine the deposition conditions for forming continuous or discontinuous lines.     

Attachment of solid elongated particles on the surface of a stationary gas bubble

Froth flotation is a separation process which plays a major role in the mining industry. It is essentially employed to recover a vast array of different valuable commodities such as rare earth minerals essential to the manufacture of high-tech products. Owing to its simplicity, the process is also widely used for the de-inking of recycled paper fibres and for the removal of pollutants from waste water. The flotation process essentially relies on the attachment of solid particles on the surface of gas bubbles immersed in water. The present study seeks to investigate the effect of the particle shape on the attachment mechanism. Using an in-house optical micro-bubble sensor the approach, the sliding and the adhesion of micron milled glass fibres on the surface of a stationary air bubble immersed in stagnant water is thoroughly investigated. The translational and rotational velocities were measured for fibres of various aspect ratios. The results are compared with a theoretical model and with experimental data obtained with spherical glass beads. It is found that the fibre orientation during the sliding motion largely depends on the collision area. Upon collision near the upstream pole of the gas bubble the major axis of the fibre aligns with the local bubble surface (tangential fibre alignment). If collision occurs at least 30° further downstream only head of the fibre is in contact with the gas–liquid interface (radial fibre alignment).     

A study on the fragmentation of space debris particles at high-speed collision

A mathematical model was previously proposed by the first author to evaluate the number of fragments and their mass distribution at high-speed collision of two space debris particles and to determine their velocities after collision. The constants used in this model are assumed to be temperature-independent. In this paper it is shown that the consideration of temperature effects due to high-speed collision of particles leads to the formation of smaller fragments and to a significant increase of their total number.     

Dependence of the stagnation temperature of a jet of gas containing solid particles on the concentration of particles and their velocity

This article gives the results of experiments on the measurement of the stagnation temperature of a two-phase jet, issuing from a nozzle. The experiments were made using a mixture of air and aluminum oxide (particle diameter 50) with a ratio of the mass flow rate of the solid phase to the mass flow rate of the gas equal to 0.3–2.5, and at initial temperatures of the mixture of 150–450°C. It follows from the results of the experiments that the stagnation temperature of a two-phase flow considerably exceeds the temperature of the mixture at the inlet of the nozzle.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 4, pp. 175–176, July–August, 1970.     

The distribution of particles in a shock-induced boundary layer of a dusty gas over a solid surface

The laminar boundary layer behind a constant-speed shock wave moving through a dusty gas along a solid surface is studied. The Saffman lift force acting on a spherical particle in a gas boundary layer is taken into account. A method for calculating the density profile of dispersed phase near the wall is proposed and some numerical results are given. It is shown that behind the shock wave, there exists a curved thin layer where the density of particles is many times higher than the original one. This dust collection effect may be of essential importance to the problem of dust explosion in industry.     

Impact of a drop on a solid surface

A numerical solution is obtained to the unsteady-state problem of a direct collision between a liquid drop of cylindrical form and a rigid surface. It is shown that unsteady-state interaction between shock waves inside the drop leads to the development of broad zones of cavitation, promoting the dispersion of the drop.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 5, pp. 151–155, September–October, 1977.The authors thank L. F. Shaikhatarova for making the calculations.     

Fluidization of a bed of solid particles

As is known, fluidization of a bed of solid particles by liquid or gas filtration takes place for certain critical values of the parameters of the filtration regime. The determination of these critical values and the nature of the transition is of interest in connection with the development of fluidization technology in many branches of industry, and also in connection with certain other questions, among which we note the problem of the suspension of a sand plug in an oil well.The two-dimensional fluidization problem has been examined previously [1] as the problem of the limiting equilibrium of a medium which cannot withstand arbitrarily small tensile stresses. This model describes well the behavior of many types of bulk media encountered in practice. However, many cases lie beyond the limits of this model because of the presence of bonding forces between the particles. Bonding may be due to the adhesive forces which arise during the fluidization of fine powders [2, 3], and/or to magnetic and electrostatic forces [3, 4]. Another example is the agglomeration of particles during gas fluidization when small amounts of liquid are injected [5]; still another is the case in which sand particles are surrounded by thin films of oil when a sand plug is suspended in an oil well.In the present paper an extension of the results obtained in [1] is used to examine fluidization of a bed with account taken of the bonding forces between the particles. The two- and three-dimensional problems are studied.     

Some critical uniaxial experiments for viscoplasticity at room temperature

An austenitic AISI Type 304 stainless steel, a ferritic A533B pressure vessel steel and a Ti-7Al-2Cb-1Ta alloy were tested using a servocontrolled MTS axial-torsion testing machine. Tests involved changes in strain rate between 10^?8 and 10^?3 s^?1 and intermittent creep periods of less than 1200 s duration.The tests show that inelastic work is not a suitable repository for modeling strain (work)-hardening and the Bauschinger effect is found to be rate dependent. Upon an increase in stress level, creep rate can decrease. This anomaly can be reproduced by a theory of viscoplasticity based on overstress previously proposed by the first author and his co-workers.     

A moment model for phonon transport at room temperature

Heat transfer in solids is modeled by deriving the macroscopic equations for phonon transport from the phonon-Boltzmann equation. In these equations, the Callaway model with frequency-dependent relaxation time is considered to describe the Resistive and Normal processes in the phonon interactions. Also, the Brillouin zone is considered to be a sphere, and its diameter depends on the temperature of the system. A simple model to describe phonon interaction with crystal boundary is employed to obtain macroscopic boundary conditions, where the reflection kernel is the superposition of diffusive reflection, specular reflection and isotropic scattering. Macroscopic moments are defined using a polynomial of the frequency and wave vector of phonons. As an example, a system of moment equations, consisting of three directional and seven frequency moments, i.e., 63 moments in total, is used to study one-dimensional heat transfer, as well as Poiseuille flow of phonons. Our results show the importance of frequency dependency in relaxation times and macroscopic moments to predict rarefaction effects. Good agreement with data reported in the literature is obtained.     

常温下JBO-9021高能钝感炸药直径效应实验

通过光电联合测试方法,测量了常温下直径为10、15和30mm 高能钝感炸药柱JBO-9021炸药的定态爆速和波形,根据拟合的爆轰波阵面形状,分析了波阵面法向速度Dn与当地曲率 之间的关系。研究结果表明,JBO-9021炸药的定态爆速随药柱直径的增大而增大,JBO-9021(w(HMX)=15%)相对JB-9014炸药(w(TATB)=95%),爆轰波形更平坦,爆轰波非理想传播行为得到一定改进。     

Analysis of non-Fourier heat conduction in a solid sphere under arbitrary surface temperature change

In this paper, the non-Fourier heat conduction in a solid sphere under arbitrary surface thermal disturbances is solved analytically. Four cases including sudden, simple harmonic periodic, triangular and pulse surface temperature changes are investigated step-by-step. The analytical solutions are obtained using the separation of variables method and Duhamel’s principle along with the Fourier series representation of an arbitrary periodic function and the Fourier integral representation of an arbitrary non-periodic function. Using these analytical solutions, the temperature profiles of the solid sphere are analyzed, and the differences in the temperature response between the “hyperbolic” and “parabolic” are discussed. These solutions can be applicable to all kinds of non-Fourier heat conduction analyses for arbitrary boundary conditions occurred in technology. And as application examples, particular attention is devoted to the cases of triangular surface temperature change and pulse surface temperature change. The examples presented in this paper can be used as benchmark problems for future numerical method validations.     

Probe diagnosis of a flow of particles desorbed from the surface of a solid by a low-density plasma jet

Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, No. 5, pp. 144–150, September–October, 1993.