AerothermoopticsL'aerothermooptiqueAerothermooptikAэpoтepмooптикa

On the example of thermal gas lenses (TGL) a survey is presented of principles and methods of aerothermooptics. The relationship is established between optical and thermohydrodynamic parameters of TGL with regard for free convection. Velocity and temperature fields are determined in TGL, including those rotating around their axes. The analytical expressions are obtained for aberration coefficients in the eikonal expansion up to the fourth-order wave aberrations. Rotation of TGL is known to be an effective means of free convection suppression and symmetrization of optical characteristics. Perspectives are discussed of the further development of aerothermooptics.     

Intrinsic scales in thermohydrogasdynamicsEchelles intrinseques en hydrothermodynamique des gazEigenmasstäbe der thermo-hydro-gasdynamicСобственные масштаы в термохидрогазодинамике

Intrinsic scales and similarity criteria are considered as characteristics of local interactions in flows of homogeneous and inhomogeneous mixtures. Thereby in the analysis of similarity an important class of values is separated whose elements have been used previously, as a rule, at an intuitive level.     

Terminologie et unitesTerminology and unitsTerminologie und einheitenTepминoлoгия и eдиницы измepeния

Terminology and units raise and will always raise problems. We have chosen some examples for which more precise definitions would seem useful.     

Developed boiling heat transferTransfert thermique pour une ebullition developpeeWärmeübertragung beim ausgebildeten blasensiedenТеплообмен при развитом кипении01

In conformity with the heat transfer model considered, the developed boiling temperature conditions of the heating surface are mainly governed by the processes which are responsible for multipe star-ups of the different mechanisms of heat release. The analysis of the model yields a universal correlation for the developed boiling heat transfer on surfaces of known microgeometry and on commercial heating surfaces for all classes of heat transfer agents (water, organic liquids, cooling and cryogenic agents and liquid metals).     

Electrochemical performance of sealed NiMH batteries using nanocrystalline TiNi-type hydride electrodes

Mechanical alloying (MA) process was used to synthesize nanocrystalline TiNi-type hydrogen storage materials. The electrochemical behavior of these compounds in conditions of their performance in sealed rechargeable nickel–metal hydride batteries are presented and compared with those of Ni–Cd battery. The cells were constructed by the pressing negative and positive electrodes, polyamide separator and KOH (ρ=1.20 g cm⁻³) as electrolyte solution. The effects of the chemical composition of the nanocrystalline TiNi-type alloy with alkaline solutions were investigated. It was found that the respective replacement of nickel in TiNi by Fe or by Zr improved not only the discharge capacity, but also the cycle life of these electrodes. The results show that the sealed battery using the nanocrystalline TiNi_0.75Fe_0.25 alloy has a capacity about two times that with of TiNi.     

Counter-current mass transferTransfert massique a contre-courantStoffaustausch im gegenstromПpoтивoтoчный мaccoпepeнoc

A simple model for a counter-current mass transfer device is analysed asymptotically in certain parameter regimes. By using some recent results about eigenfunction expansions, explicit formulae are found for the efficiency of the device in terms of numbers of theoretical plates.     

Film condensation of mercuryCondensation en film du mercureFilmkondensation von quecksilberплэнoчнaя кoндэнcaция pTyTи

Measurements of vapour-to-surface temperature difference and heat flux for film condensation of mercury on a vertical plane square (side 40mm) nickel-plated copper surface are reported. Thermocouples, accurately located and spaced through the copper condensing block served to measure, by extrapolation, the temperature at the copper-nickel interface and from the temperature gradient, the heat flux. Special care was taken to ensure that the results were not vitiated by the presence in the vapour of non-condensing gases. The results have higher relative precision than other recent heat-transfer measurements for condensation of metals since the present observations were made under conditions (metal used, vapour temperature and condensation rate) for which the vapour-to-surface temperature difference was larger than in the earlier work. The observed vapour-to-surface temperature differences are substantially greater than those given by the Nusselt theory of film condensation. By attributing the excess temperature drop to the vapour-liquid interface, the results are compared with theoretical expressions for interphase matter transfer. As in other recent work, values for the correction factor (or apparent “condensation coefficient”) varied from near unity down to about 0.6. The precision of the present results is such as to reveal a dependence of the correction factor on the condensation rate as well as on the vapour pressure. It was found that both could be satisfactorily correlated by a single dimensionless variable.     

Heterodiffusion and polyrelaxationHeterodiffusion et polyrelaxationHeterodiffusion und polyrelaxationГeтepoдиффyзия и пoлиpeлaкcaция

In a mixture of the main medium with a dispersed filler, the coefficients of mass or energy diffusion of which differ substantially, the exchange by a diffusing substance occurs during the course of the whole process. The averaging of diffusion coefficients for a heterogeneous mixture such as this is impossible. The diffusing substance transport is described by an equation of polyrelaxational type with an infinite spectrum of relaxation times. Three types of polyrelaxational media have been found in which the phase velocity of propagation of high-frequency vibrations increases infinitely, has a constant value or approaches zero with an increase in the angular frequency, i.e. quenching of such oscillations takes place.     

Dropwise condensation theoryTheorie de la condensation en gouttesEine theorie für tropfenkondensationTeopия кAпeльнoи кoндeнcAции

Improved theoretical results for heat transfer through individual drops and for the mean distribution of drop sizes are used as a basis for assessing the validity of the basic assumption of dropwise condensation theory [1] i.e. that the mean heat flux can be found from steady calculation of the heat transfer through individual drops and a steady distribution of drop sizes.     

Performance of a Five-Phase Induction Machine With Optimized Air Gap Field Under Open Loop $V$/$f$ Control

The paper assesses the steady-state performance of a five-phase induction machine fed by a modified open loop constant volt/hertz ($V$/$f$) control method, which imposes a trapezoidal induction waveform in the air gap under varying load conditions. The trapezoidal air gap induction is achieved through the imposition of an appropriate combination of the third harmonic and fundamental stator voltages. This harmonic combination is determined from the steady-state model using a mathematical optimization procedure, which allows to obtain the optimal weighting factors for each harmonic component. The optimized reference voltages lead to a trapezoidal air gap induction, which allows a better iron utilization and higher output torque for the same rms stator current when compared to sinusoidal air gap induction. The resulting air gap induction is obtained from the induced voltage of a full pitch search coil placed in the air gap. The proposed control scheme was successfully simulated and implemented on a five-phase prototype machine running under different load conditions. Experimental and simulations results show an increase in the torque/ampere relationship for loads above $hbox{50}%$ when compared to the conventional $V$/$f$ method using only the fundamental current and air gap induction. A comparison between the simulation and experimental curves presents a very good agreement that confirms and validates the parameters and model used.      

Infrared flame radiationRayonnement infrarouge des flammesInfrarot-flammenstrahlungИнфpaкpacнoe излyчeниe плaмeни

Gaseous and particulate absorption for a non-homogeneous medium is considered both analytically and experimentally. A simple peak partial pressure and peak temperature scaling method applicable to combustion zones is successfully employed for non-homogeneous intensity calculations. Experimentally, natural convection controlled diffusion flame radiation is investigated. Spectral measurements of the radiance and transmittance are reported for polystyrene, Delrin, and Plexiglas fuels. The homogeneous gray model is shown to predict the experimental results reasonably well, yet is useful only when experimental data exist. The homogeneous nongray approximation is found to be inapplicable to highly non-homogeneous pathlengths. Non-homogeneous nongray calculations are shown to be accurate and with the peak partial pressure and peak temperature scaling method, simple calculations are possible from fundamental properties of the flames.     

The coating of fibresLe revetement des fibresDie beschichtung von fasernHaнeceниe пoкpытии нa вoлoкнa

An experimental investigation is reported of the coating of a fibre with a liquid in which a significant part of the coating is due to freezing. Numerical methods are outlined by means of which the coated thickness is calculated by solution of the relevant Stefan's problem and the addition of viscous terms. For the system studied (biphenyl on copper) freezing accounted for between 34 and 100% of the coating, depending upon time of immersion of the fibre in the liquid and the fibre velocity. The ratio of coating thicknesses as between two different substrate radii was in good agreement with predicted values. The prediction of individual thicknesses differed from observed values by up to 20%, the agreement being poorer for higher fibre speeds.     

The two-phase turbulent jetLe jet turbulent diphasiqueDer zweiphasige turbulente strahlдвyxфaзнaя тypбyлeнтнaя cтpyя

Turbulent two-phase axisymmetric jets, in which the volume fraction of the secondary phase is much less than unity, are considered. Emphasis is placed on cases in which the mass fraction of particles is of order unity. The available experimental measurements are examined and it is found that physical arguments and dimensional analysis lead to good correlations of the mean fluid velocity and particle mass flux fields in terms of the initial loading of particles. The jet may be simply described with reference to the momentum transfer between the phases. Two main regions exist: a near field in which essentially no momentum has been transferred between the phases, and a far field in which sensibly all the momentum resides in the fluid phase. Exponential and power law functions of the ratio of the mass density of the particles to that of the suspending fluid at the jet orifice are found to correlate much of the data with the corresponding single phase jet. A relationship for the virtual origins of the far field in terms of the integral invariants of the flow is derived and supported by the measurements.     

Analysis of binary film boilingAnalyse de l'ebullition en film binaireUntersuchung des filmsiedens binärer gemischeAнaлиз кипeния Бинapнoй плeнки

Binary film boiling has been analyzed on the basis of the conservation laws and other principles. It has been shown that the liquid-vapor interface temperature depends on diffusion phenomena within the liquid mixture. The omission of the diffusion processes in an analysis might lead to erroneous heat-transfer results.     

Numerical computations of wall-jet flowsCalcul numerique des jets parietauxNumerische berechnung von wandstrahlströmungenЧиcлeнныe pacЧeTы пpиcTeнныч cTpyй

Turbulent wall-jets on conical surfaces represent a practically useful situation and an important test for theoretical methods used for predicting turbulent transport. Experimental data on the velocity fields and the maximum concentration of a tracer gas have been obtained for turbulent wall-jets formed on conical surfaces of various angles. It is shown that the correct prediction of the data by a mixing-length hypothesis requires the mixing-length constant to be changed for each cone angle, A set of two-equation models of turbulence is then employed which solves two additional differential equations for the local properties of turbulence. These models correctly predict all the experimental data without the need for the adjustment of constants.     

Convection mixte en milieu poreuxMixed convection in porous mediaMischkonvektion in porösen medienКoнвeкция б пopиcтoй cpeдe

For conception of nuclear reactors of thermal insulation purposes a theoretical study and a experimental investigation were conducted to determine the flow interaction between free and forced convection in porous media.The equations describing the model are presented and a numerical computer code is developed. The analytical results are in good agreement with the experiments. The exploitation of the code show the governing parameters.     

Convection in a porous layerConvection dans une couche poreuseKonvektion in einer porösen schichtКoнвeкция в пopиcтoм цooe

Steady convective motions inside a rectangular cavity filled with a porous material are examined in the large Rayleigh number limit for flows driven by a horizontal temperature gradient. The boundary-layer structure on the side walls is determined using an integral relations approach. This method leads to results for the core mass flux, for the core-temperature gradient and for the heat-transfer characteristics which are in excellent agreement with numerical solutions of the boundary-layer equations.     

An investigation of a mixed convection in a shape channel moving with a reciprocating motion

This study focuses on utilizing numerical calculation to investigate the heat transfer mechanisms in a shape reciprocating channel system comprised of a horizontal channel at the bottom and vertical channels on both left and right sides. The issue is considered one kind of moving boundary problems and the finite element and Arbitrary Lagrangian–Eulerian (ALE) kinematic methods can be applied to this study. Due to the high temperature at the bottom surface of the horizontal channel and the direction of inlet cooling fluids in the same direction of the gravity, the heat transfer mechanisms induced by the mixed convection flow become extremely complex. The results show that thermal layers near the heat surface are disturbed drastically and the effect of reciprocating motion upon the heat transfer mechanisms strongly depends on a relationship between Reynolds and Grashof numbers.     

The aerosyphon: An exploratory studyL'aerosyphon: Une etude exploratoireDer kohlensauresyphon: Eine grundlegende studieЭкcпepимeнтaлянoe иccлeдobaниe aэpocифoнa

The paper is an experimental investigation of the aerated-thermosyphon, or aerosyphon. The work combines a visual flow study with a series of heat-transfer experiments in an attempt to understand the modus operandi of the device and explore its unusual heat-transfer characteristics.