Critical volume and chain activation of boiling sites in emulsions with low-boiling dispersed phase

A study is made of the features characteristic of boiling of emulsions with low-boiling dispersed phase compared to the boiling temperature of dispersion medium. The question of boiling sites and their chain activation is considered. Formulas are suggested for the calculation of the critical volume of emulsion; it is demonstrated that vigorous nucleate boiling of emulsion is observed only when the volume of superheated emulsion in the thermal boundary layer exceeds the critical volume.     

Boiling characteristics of emulsions with a low-boiling dispersed phase and surfactants

Results of measurement of heat-transfer coefficients are reported for the case of boiling of a dispersed phase of a water— PèS-5 emulsion on the surface of electrically heated thin platinum wires. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 70, No. 2, pp. 184–186, March–April, 1997.     

Results of experimental investigation of heat transfer with emulsions with low-boiling disperse phase

The results are given of a theoretical investigation of heat transfer from thin wires to emulsions in which the disperse phase is low-boiling compared to the dispersion medium. A special feature of heat transfer to such emulsions is observed in the mode of nucleate boiling, when only the droplets of the disperse phase of emulsion are boiling. The transition from the convective mode of heat transfer to nucleate boiling requires high values of temperature gradient ΔT = T _W ? T ₀ at which the temperature of the heat-transfer surface T _W is higher than the temperature T _S of saturated vapors of the disperse phase by 100 °C and more. Here, T ₀ is the temperature of the heat-transfer agent away from the heat-transfer surface. Note that, for pure liquids and solutions, the value of delay of the beginning of boiling ΔT _i = T _W ? T _S as a rule does not exceed 1–5 °C. Another feature of heat transfer to the emulsions being treated is a wide temperature range of the mode of nucleate boiling (over 100 °C); the upper limit of this temperature range is defined by the temperature of transition to film boiling of the dispersion medium of the emulsion being investigated that has already boiled by this instant of time. The value of delay of the beginning of boiling is affected significantly by additions of surfactants and adsorbents.     

Mechanisms of boiling of an emulsion with a low-boiling disperse phase in a turbulent flow of a homogeneous emulsion

A theoretical analysis of the time delay in the boiling of overheated drops in a turbulent flow of a homogeneous emulsion with a low-boiling disperse phase has been performed. Model relations determining the influence of the fluctuations of the velocity of a turbulent flow of an overheated emulsion on the formation of critical vapor bubbles in the disperse-phase drops have been derived. The initiation of formation of stable centers of nucleation of the vapor phase in an overheated emulsion by the factors determining the deformation and fragmentation of drops in it has been considered. The results obtained were compared with the corresponding experimental data.     

Dependence of the beginning of chain activation of boiling sites on superheating of droplets in the dispersed phase of the emulsion

The features characteristic of boiling of emulsions with a low-boiling dispersed phase are studied. The phenomenon of chain boiling up of droplets of the dispersed phase is considered. The dependence of the moment of emergence of chain activation of boiling sites and the subsequent chain boiling up of droplets of the dispersed phase on the temperature of the surface being heated (cooled) is obtained.     

Coalescence of coarsely dispersed concentrated emulsions with turbulent agitation

The coalescence of drops, larger than microscale vortices, induced by velocity pulsations in concentrated emulsions is examined based on the theory of locally isotropic turbulence.Notation n number of drops per unit volume of emulsion - t time - ₀ and L micro- and macroscales of turbulence - _e, _c, and _d densities of the emulsion, the continuous, and the disperse phases, respectively - interphase tension - W concentration of the dispersed phase - D_T diameter of the agitating turbine - N rate of rotation of the turbine - D and H diameter and height of the mixing volume - d₃₂ averaged volume-surface diameter of the drops - d_m maximum size of drops that are stable with respect to fragmentation - f(W) concentration dependence - ¯v and ¯v(W) averaged magnitudes of the pulsation velocity in finely dispersed and coarsely dispersed emulsions - ¯gq and rates of collisions and coalescence of drops - t_c and _c time and rate of circulation - Re_M Reynolds number of mixer - _e effective viscosity of the emulsion - K_v constant describing the efficiency of collisions drops induced by velocity pulsations - F_v(W) and F_g(W) functional relations between the rate of coalescence and concentration of drops in the inertial and gradient regimes Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 42, No. 1, pp. 27–33, January, 1982.     

Effect of the concentration and size of droplets of the dispersed phase of an emulsion on the character of heat exchange in a boiling emulsion

Heat transfer from thin platinum wires to emulsions with a low-boiling dispersed phase has been studied experimentally. The appearance, growth, and separation of vapor bubbles at boiling on horizontal and vertical heated surfaces were demonstrated. The dependence of the delay of the beginning of boiling on the concentration of the emulsion and the size of droplets of the dispersed phase were considered.     

Characteristic curve of helium pool boiling

The results of an experimental investigation on helium pool boiling over a wide range of temperature differences covering nucleate, transition, and film regions are presented. Heating surfaces under investigation were made of different materials and were processed with various degrees of roughness. Helium boiling curve on stainless steel has an anomalous character: heat flux in the transition region increases when temperature difference rises and there is no nucleate boiling zone on the surface with the lowest degree of roughness. A comparative analysis of the results presented with available data is also carried out.     

Special features of boiling of a slightly subcooled liquid

Slightly subcooled boiling is characterized by the fact that vapor bubbles that form at active sites on the heater surface grow continuously and, having attained a maximum size, separate and float. The frequency of bubble separation, which determines the rate of heat transfer, depends on the degree of subcooling of the boiling liquid. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 71, No. 6, pp. 993–995, November–December, 1998.     

Dielectrophoresis of reverse phase emulsions

Reverse miniemulsions, emulsions of droplets of size 200 nm-1 microm of a polar liquid dispersed in an apolar continuous liquid phase, exhibit strong electrokinetic responses in low-frequency electric fields. The electrokinetic behaviour of a reverse miniemulsion, previously developed for use as electronic paper, has been investigated under static and flow conditions, in uniform and non-uniform electric fields. Results reveal that when using frequencies lower than 10 Hz strong aggregation of the droplets occurs. In uniform electric fields, under static conditions, droplets reversibly aggregate into honeycomb-like or irregular aggregates. Under flow conditions, droplets aggregate into approximately equidistant streams. In non-uniform electric fields the droplets reversibly aggregate in high-field regions, and can be guided along regions of high field strength in a flow. The potential of the technique for the formation of structured materials is discussed.     

Transport in compounds containing a dispersed second phase

The introduction of a dispersion of small (≤ 1 micron), insoluble particles in a matrix alters the transport properties of the matrix. Solid electrolytes exhibit marked enhancement in ionic conductivity without an increase in electronic conductivity. Recent data and available models are discussed for electronic conductors and for ionic conductors (solid electrolytes).     

Internal relaxation in phase interaction in a dispersed system

Corrections have been made to the relaxation times for heat and mass transfer between phases in dispersed systems, which incorporate the thermal conduction and diffusion within the particles.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 37, No. 4, pp. 609–612, October, 1979.     

Thermodynamics of the migration of a liquid phase in a three-phase dispersed system with one dissolving solid phase

An expression describing a change in the Gibbs potential in a liquid phase migration in a three-phase dispersed system with one dissolving solid phase has been derived. The conditions have been defined, at which the structure formation is possible either without a change in the initial skeleton structure of a refractory phase, or due to a total or partial deconsolidation of the skeleton structure.     

Turbulent pipe flow of concentrated emulsions with a nonequilibrium disperse phase

Quantitative data are obtained in velocity pulsation damping and the amount by which particle coalescence exceeds the turbulence microscale is calculated for the pipe flow of concentrated emulsions.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 42, No. 3, pp. 366–372, March, 1982.     

The microstructure and fracture properties of MgO crystals containing a dispersed phase

MgO crystals containing up to 40% by volume of magnesioferrite and up to 2% by volume of iron and nickel were produced by a diffusion technique followed by appropriate heat treatments. Magnesioferrite precipitate did not significantly change the effective surface energy of a crack as measured by the double cantilever beam technique. Iron and nickel precipitate was produced in the form of platelets lying on {100}_MgO planes whose orientation relationships were [001]_MgO ∥[001]_Fe, [110]MgO ∥[100]_Fe with a spread of +10°, approximately, and [001]_MgO ∥[001]_Ni, [010]_MgO ∥[010]_Ni with negligible spread. Despite the crystallographic orientation relationships, the metal-MgO interface appeared to be very weak; the reasons for this are discussed. The effect of the metal precipitate on crack propagation was to markedly increase the density of cleavage steps. For a volume fraction of precipitate of 0.02, this led to a small increase in the effective surface energy, on the order of 1 Jm⁻².     

A procedure for calculating the characteristics of a dispersed phase in a mist flow on rewetting

The mechanisms involved in the formation of a range of droplets over a nonwetted region in a reflooded preliminarily heated channel are considered. A scheme is suggested for determining the droplet size.Moscow Power Engineering Institute, Moscow. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 65, No. 2, pp. 159–163, August, 1993.     

Exchange of heat in a reverse gas flow with a nonmoving dispersed solid phase

We have arrived at an analytical solution to the problem of convective heat exchange in a reverse gas flow with a disperse solid phase exhibiting high thermal conductivity.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 60, No. 3, pp. 439–441, March, 1991.