Dipole Electromagnetic Radiation by a Charged Drop Oscillating in a Uniform Electrostatic Field

The intensity of electromagnetic radiation generated by a charged drop oscillating in a uniform electrostatic field is studied within the framework of analytical calculations retaining the terms of the second order of smallness with respect to the ratio of the droplet oscillation amplitude to the droplet radius. It is found that the charge induced in the drop surface oscillations generates a dipole radiation detected in the first-order calculations and a self-charge detected with allowance for the second-order terms only. It is shown that the order of the magnitude of the total intensity of radiation generated by a cloud can be determined from small-droplet radiation. Among two radiation sources, namely, the radiation generated by small droplets oscillating at low modes and the radiation generated by hydrometeors oscillating at high modes, the first plays a dominant role.     

Radiation of electromagneticwaves by a spheroidal charged drop oscillating in a uniform electrostatic field

The dispersion relation is derived for a spheroidal charged drop oscillating in a uniform electrostatic field and radiating electromagnetic waves in the first and second orders with respect to the dimensionless oscillation amplitude and the steady-state deformation, respectively. For an individual drop and a model cloud the intensity of the electromagnetic radiation and the frequency bandwidth are estimated as functions of the drop dimensions and charge and the external electric field strength.     

Transfer of energy from an evaporating drop in a vapor medium

The article considers the temperature distribution around an evaporating drop in a vapor medium. The transfer of energy is effected by molecular thermal conductivity, convection, and radiation. The mean length of the free flight path of the radiation considerably exceeds the characteristic distance at which the temperature changes. The times required for relaxation of the temperature to a steady-state value are determined, as well as the characteristic distances at which the temperature distribution changes.Translated from Zhurnal Prikladnoi Mekhaniki i Tekhnicheskoi Fiziki, No. 1, pp. 74–78, January–February, 1972.The authors thank V. G. Levich for his evaluation of the results obtained.     

Heat Transfer Study of the Hencken Burner Flame

The Hencken burner flame is often used in combustion laser diagnostics as a calibration flame because of its near adiabatic condition. For a fast burning H₂ flame, it can tolerate high flow rate and the flame is indeed near adiabatic; however, for a slow burning CH₄ flame, the flow rate is not always high enough to maintain near adiabatic conditions. The heat transfer of the H₂ and CH₄ Hencken burner flames are studied numerically and experimentally. Three heat loss mechanisms are analyzed: the burner surface radiation, the hot gas radiation, and the convection heat transfer between the main flow and the co-flow. The surface radiation produces negligible temperature drop while the gas radiation and the convection heat loss contribute significant temperature drop. Reducing the co-flow rate can decrease the convection heat loss slightly. The temperature drop caused by the heat loss is inversely proportional to the main flow rate. Increasing the burner size and running the flame premixed mode can increase the flow rate and reduce the temperature deviation from the adiabatic equilibrium value. Based on the heat loss and temperature drop analysis, suggestions are given to maintain the flame at near adiabatic conditions.     

Nonlinear Capillary Oscillations of a Volumetrically Charged Dielectric Drop

For the axisymmetric capillary oscillations of a charged dielectric fluid drop an expression describing the shape of the generating surface of the drop as a function of time is obtained in the quadratic approximation in the amplitude of an arbitrary initial deformation of its spherical equilibrium shape. It is shown that in contrast to a perfectly conducting charged drop there is no displacement of the drop charge center during oscillation and, hence, such a drop cannot be a source of dipole electromagnetic radiation like a conducting drop in the quadratic approximation.     

Effect of interface deformability on thermocapillary motion of a drop in a tube

The effect of an externally imposed axial temperature gradient on the mobility and deformation of a drop in an otherwise stagnant liquid within an insulated cylindrical tube is investigated. In the absence of bulk transport of momentum and energy, the boundary integral technique is used to obtain the flow and temperature fields inside and outside the deformable drop. The steady drop shapes and the corresponding migration velocities are examined over a wide range of the dimensionless parameters. The steady drop shape is nearly spherical for dimensionless drop sizes <0.5, but becomes slightly elongated in the axial direction for drop sizes comparable to tube diameter. The adverse effect of drop deformation on the effective temperature gradient driving the motion is slightly more pronounced than its favorable effect of reducing drag, thereby leading to a slight reduction in drop mobility with increasing drop deformation. Increasing the viscosity ratio reduces drop deformation and leads to a slight enhancement in the relative mobility (with respect to free thermocapillary motion) of confined drops. When the drop fluid has a lower thermal conductivity than the exterior phase, the presence of the thermally-insulating wall increases the thermal driving force for drop motion (compared to that for the same drop in unbounded domain) by causing more pronounced bending of the isotherms toward the drop. However, the favorable thermal effect of the confining wall is overwhelmed by its retarding hydrodynamic effect, causing the confined drop to always move slower than its unbounded counterpart regardless of the value of the thermal conductivity ratio.     

Estimation of the diameter–charge distribution in polydisperse electrically charged sprays of electrically insulating liquids

The majority of scientific and industrial electrical spray applications make use of sprays that contain a range of drop diameters. Indirect evidence suggests the mean drop diameter and the mean drop charge level are usually correlated. In addition, within each drop diameter class there is every reason to suspect a distribution of charge levels exist for a particular drop diameter class. This paper presents an experimental method that uses the joint PDF of drop velocity and diameter, obtained from phase Doppler anemometry measurements, and directly obtained spatially resolved distributions of the mass and charge flux to obtain a drop diameter and charge frequency distribution. The method is demonstrated using several data-sets obtained from experimental measurements of steady poly-disperse sprays of an electrically insulating liquid produced with the charge injection technique. The space charge repulsion in the spray plume produces a hollow cone spray structure. In addition an approximate self-similarity is observed, with the maximum radial mass and charge flow occurring at r/d ~ 200. The charge flux profile is slightly offset from the mass flux profile, and this gives direct evidence that the spray specific charge increases from approximately 20% of the bulk mean spray specific charge on the spray axis to approximately 200% of the bulk mean specific charge in the periphery of the spray. The results from the drop charge estimation model suggest a complex picture of the correlation between drop charge and drop diameter, with spray specific charge, injection velocity and orifice diameter all contributing to the shape of the drop diameter–charge distribution. Mean drop charge as a function of the Rayleigh limit is approximately 0.2, and is invariant with drop diameter and also across the spray cases tested.     

双流体雾化液滴荷电特性分析

本文通过理论分析,提出了双流体荷电雾化过程中,增大电场强度或减小液滴粒径均能提高荷电效果的论点。针对不同的电极布置情况建立了数值模拟模型,计算结果表明,双流体喷嘴接地时,喷嘴与环状电极之间的电场强度比喷嘴不接地时大很多。通过实验,验证了电场强度、液滴粒径等参数对荷电效果的影响规律,在环状电极荷电情况下,双流体喷嘴接地时,液体荷质比高于双流体喷嘴不接地时的荷质比;电场强度增大,荷质比增加;液滴粒径越小,荷质比越大;在一定的电导率范围内,电导率越大,荷质比越小。实际喷雾中,运动液滴发生二次破碎的临界荷电量小于Rayleigh极限。     

Drop and Bubble Deformation in an Electric Field

A steady problem of drop (bubble) shape in a uniform electric field is considered when the drop and the surrounding medium are immiscible. The electric-charge transport includes both the ohmic current across the interphase boundary and convective transport over the interface. If there is no convective transport, the drop (bubble) may be transformed into either an elongated or a flattened spheroid. Under these conditions, the sign of the deformation remains unchanged for arbitrary values of the problem parameters. Convective charge transport along the surface initiates additional motion in both the drop and the surrounding medium. However, with increase in the convective-transport intensity the deformed drops display different behavior. The compression of a flattened drop slows and, under certain conditions, compression is replaced by extension. However, an elongated spheroid cannot be transformed into a flattened spheroid. The calculations were performed under the assumption that the drop is convex. It was found that, for both an elongated and a flattened drop, the maximum ratio of the major and minor spheroid axes is 2:1. In experiments with oils, the possibility of both a decrease in the drop compression rate and deformation sign reversal was demonstrated.     

Attenuation of forced weak plane pressure waves in a gas with radiative heat transfer

This paper considers the effect of radiative heat transfer on the propagation of forced plane harmonic pressure waves of small amplitude in an infinite emitting-absorbing inviscid nonconducting gas. The radiative pressure and radiative energy are neglected. The purpose of this paper is: a) to construct a theory based on the exact directional distribution of the total (frequency-integrated) specific intensity and to use this theory to calculate the parameters of the wave motion, b) to compare the exact theory with results obtained on the basis of the direction-averaged equation of radiative transfer [1] so as to estimate the errors introduced by various directional approximations and to demonstrate the importance of the anisotropy of radiation in radiation gasdynamics.In the linear theories of Stokes, Rayleigh, Kirchhoff, and Langevin the problem of wave attenuation is separated into special cases, in each of which only one single process is considered. This separation is admissible when to the first approximation the effects of the different dissipation mechanisms (viscosity, thermal conductivity, radiation, etc.) are additive. When only one factor is considered the problem becomes much simpler and the results are more amenable to physical interpretation, and these results can then be used in the solution of the complete problem.