Linear effects of the energy transfer in gases

The authors discuss the linear effects of energy transfer in a gas that can attain a steady state and the linear similarity theory based on geometric transformations preserving the distance between points.Notation L _ii ,L _ij phenomenological coefficients - x _i thermodynamic forces - I _q specific heat flux - U ^* transfer energy - T temperature - T ^* reduced temperature - thermal conductivity of the local-equilibrium gas - _* reduced thermal conductivity - k Boltzmann constant - , parameters of the intermolecular interaction potential - m molecular weight Institute of Applied Physics of the Academy of Sciences of Belarus, Academic Scientific Complex A. V. Luikov Heat and Mass Transfer Institute of the Academy of Sciences of Belarus, Minsk, Belarus. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 68, No. 5, pp. 793–798, September–October, 1995.     

A note on the similarity solutions for free convection on a vertical plate

Summary The similarity solutions for free convection on a vertical plate when the (non-dimensional) plate temperature is x and when the (non-dimensional) surface heat flux is –x are considered. Solutions valid for 1 and 1 are obtained. Further, for the first problem it is shown that there is a value ₀, dependent on the Prandtl number, such that solutions of the similarity equations are possible only for >₀, and for the second problem that solutions are possible only for >–1 (for all Prandtl numbers). In both cases the solutions becomes singular as ₀ and as –1, and the natures of these singularities are discussed.     

Condensation rate and coefficients of refraction and reflection of vacuum cryocondensates of water vapors on a metallic mirror

Specific features of heat transfer are investigated at the gas—solid interface at low temperatures for the case of water vapor condensation.Notation wavelength, nm - n_red reduced refractive index - angle of incidence, deg - r thickness, m - p pressure, mm Hg - T temperature, K - R_red reduced reflection coefficient - U_red reduced condensation rate Kazakh State University, Alma-Ata. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 63, No. 4, pp. 457–461, October, 1992.     

Free convective flow on a vertical plate with a constant heat flux in the presence of one or more steps

We carried out an experimental investigation of free convective heat transfer on a vertical plate subjected to a constant heat flux in the presence of one or several rectangular steps. Temperature fields were investigated with the help of a Mach-Zehnder interferometer. During the experiment the Rayleigh number changed from zero to Ra=2.8·10³. The flow was observed by the method of track visualization by means of a laser knife. Durectly behind a step we observed a circulating free convective flow having the shape of two oppositely rotating vortices.Academic Scientific Complex A. V. Luikov Heat and Mass Transfer Institute of the Academy of Sciences of Belarus, Minsk, Belarus. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 67, Nos. 3–4, pp. 190–196, September–October, 1994.     

Heat transfer for forced flow of a two-phase mixture in a pipe

An experimental investigation of heat transfer for flow of a two-phase water-ice mixture in a pipe is performed. A model of heat transfer is proposed, and the obtained experimental data are generalized.Academic Scientific Complex A. V. Luikov Institute of Heat and Mass Transfer of the Academy of Sciences Belarus, Minsk. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 64, No. 5, pp. 554–557, May, 1993.     

Stagnation flow and heat transfer in a zonal magnetic field

Summary The problem stated in the title is studied for small values of the diffusivity ratio and the magnetic force coefficient , the magnetic field being of internal origin. Uniformly valid expansions are derived for the velocity and magnetic fields in the fluid. It is found that as 1, the viscous layer is brought to rest and the current in the layer is uniform and normal to the wall.The heat transfer is next calculated at a uniformly heated wall on the assumption of small temperature variations. It is deduced that when log(^–1) approaches a certain value depending on the wall temperature etc., the thermal boundary layer separates at the stagnation point and, if dissipation is neglected, along the whole wall.     

Heat exchange between a fluidized bed and small-sized bodies

On the basis of the two-zone model, a procedure is developed for calculating the complex heat exchange of a probe of small dimensions (comparable with the diameter of the bed particles). The procedure takes into account the influence of the fluidizing agent pressure.Academic Scientific Complex A. V. Luikov Heat and Mass Transfer Institute of the Academy of Sciences of Belarus, Minsk. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 67, Nos. 5–6, pp. 428–432, November–December, 1994.     

Kinetics of nucleation and halt-in-growth processes in a thin layer

The methods of determining the kinetic exponents in the equation, dX/dVex = (1 – X)2–, used for nucleation and halt-in-growth processes where X is the transformed fraction, Vex the KJMA extended volume fraction which is related to time t, and is the overlap factor which accounts for the overlap between a crystallite and a phantom crystallite, are presented. The applications of the Kolmogorov–Johnson–Mehl–Avrami plot ( = 1) and the Austin–Rickett plot ( = 0) to this process are inappropriate, because the overlap factor is 0 < < 1. The impingement exponent 2- and the time exponent are determined from the linear relation of In {[(1 – X) – 1 – 1]/(1 – )} versus In t. From the value of , the crystal shape and growth dimension can be estimated by referring to the mathematical value of . The methods of evaluating the activation energy, Q, are presented using the Arrhenius relation. The value of Q is not directly related to the overlap factor however, appears as a constant term in the expression for Q.     

Thermal diffusivity of inhomogeneous systems

The possibility of analyzing the nonsteady temperature fields of inhomogeneous systems using the quasi-homogeneous-body model is investigated.Notation t, t_I, t_i temperature of quasi-homogeneous body inhomogeneous system, and i-th component of system - a, , c thermal diffusivity and conductivity and volume specific heat of quasi-homogeneous body - a_{i i}, c_i same quantities for the i-th component - q heat flux - S, V system surface and volume - x, y coordinates - macrodimension of system - dimensionless temperature Fo=a/² - Bi=/ Fourier and Biot numbers - N number of plates - =h/ ratio of micro- and macrodimensions - _V, volumeaveraged and mean-square error of dimensionless-temperature determination - time - m_i i-th component concentration Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 39, No. 1, pp. 126–133, July, 1980.     

On the theory of external heat transfer in a fluidization bed

The fundamental equations of the packet theory are transformed and critically analyzed, whereupon the concepts pertaining to the mechanism of external heat transfer in a fluid ization bed are further refined on the basis of new test data.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 25, No. 4, pp. 589–593, October, 1973.     

Temperature effects on the properties of Ge thin films

The effects of substrate temperature (T_s) on the properties of vacuum evaporated p-type Ge thin films have been investigated for 25s<400°C. Increase in the substrate temperature improves the crystallinity and increases the grain size resulting a gradual change from amorphous to polycrystalline structure which was attained above a substrate temperature of 225°C. Low resistive (1×10^–2 ohm-cm) and high mobility (280 cm²/V·s) films were obtained at T_s=400°C. It has been observed that the conduction mechanism in polycrystalline films was dominated successively by hopping, tunneling and thermionic emission as the sample temperature was increased from 40 to 400 K. In amorphous samples, conduction was described in terms of different hopping mechanisms.     

Phase Transitions in Solid Oxygen as Thermometric Fixed Points

For more than thirty years behaviour of phase transitions in solid oxygen has been the subject of an interest to thermometry because oxygen is one of few substances having three phase transitions in the low temperature range. The triple point of oxygen is the primary fixed point of the International Temperature Scale of 1990 and – and – phase transitions are recommended as secondary fixed points. In this paper heat capacity of oxygen in the region of the – transition is investigated. The heat capacity peak, which has the total width of about 50 mK, has been observed to be composed, in reality, of two sharper peaks separeted by 20 mK. Some preliminary results of the – transition investigation are also reported.     

One Method of Determination of the Effective Absorption Coefficient in Pulsed Laser Irradiation of Metals

An experimentaltheoretical method of determination of the absorption coefficients in laser treatment of metals has been proposed based on the solution of the boundaryvalue axisymmetric problem of heat conduction for a halfspace and metallographic measurements of the dimensions of the thermalhardening zone.     

Study of Broadband Long-Focus Optics for Synchrotron Infrared Diagnosis of Low-Energy Electron Beams

A special optical device for measuring the geometry and current parameters in electron rings by synchrotron infrared radiation is designed, fabricated, and studied. The optical elements of the device are made of an optical ceramic and operate at 1–8 m. The study results are presented.     

Thermal efficiency of manifold-heat-pipe heat exchangers

The thermal efficiency of manifold-heat-pipe heat exchangers is considered. A method for predicting the efficiency and an analysis of effects of various factors of the actual process are presented.Academic Scientific Complex A. V. Luikov Heat and Mass Transfer Institute of the Academy of Sciences of Belarus, Minsk. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 66, No. 2, pp. 173–178, February, 1994.     

Focusing of shock waves on reflection from concave curvilinear surfaces

Results from a comparative analysis of experimental and numerical simulation of the processes of reflection of plane shock waves from concave axisymmetric and two-dimensional surfaces are presented.Academic Scientific Complex The A. V. Luikov Heat and Mass Transfer Institute, Academy of Sciences of Belarus, Minsk. Scientific-Industrial Company Prostor, Moscow Region, Krasnoarmeisk. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 65, No. 5, pp. 548–552, November, 1993.     

Differential-flow-induced instability in a cubic autocatalator system

The formation of spatio-temporal stable patterns is considered for a reaction-diffusion-convection system based upon the cubic autocatalator, A + 2B 3B, B C, with the reactant A being replenished by the slow decay of some precursor P via the simple step P A. The reaction is considered in a differential-flow reactor in the form of a ring. It is assumed that the reactant A is immobilised within the reactor and the autocatalyst B is allowed to flow through the reactor with a constant velocity as well as being able to diffuse. The linear stability of the spatially uniform steady state (a, b) = (µ^–1, µ), where a and b are the dimensionless concentrations of the reactant A and autocatalyst B, and µ is a parameter reflecting the initial concentration of the precursor P, is discussed first. It is shown that a necessary condition for the bifurcation of this steady state to stable, spatially non-uniform, flow-generated patterns is that the flow parameter > _c(µ, ) where _c(µ,) is a (strictly positive) critical value of and is the dimensionless diffusion coefficient of the species B and also reflects the size of the system. Values of _c at which these bifurcations occur are derived in terms of µ and . Further information about the nature of the bifurcating branches (close to their bifurcation points) is obtained from a weakly nonlinear analysis. This reveals that both supercritical and subcritical Hopf bifurcations are possible. The bifurcating branches are then followed numerically by means of a path-following method, with the parameter as a bifurcation parameter, for representatives values of µ and . It is found that multiple stable patterns can exist and that it is also possible that any of these can lose stability through secondary Hopf bifurcations. This typically gives rise to spatio-temporal quasiperiodic transients through which the system is ultimately attracted to one of the remaining available stable patterns.     

Application of a differential-difference method to the solution of a one-dimensional nonstationary two-layer heat conduction problem with a moving boundary

We apply a differential-difference method to obtain an approximate solution of a nonstationary heat conduction problem with a moving boundary for a medium consisting of an unbounded plate (0xl) and a halfspace (l, 相似文献   

Mixing Rules for van der Waals-Type Equations of State Based on Activity-Coefficient Models

A new approach for incorporation of the excess free energy from an activity coefficient model (ACM) into an equation of state (EOS) has been proposed. The approach is based on a concept that any ACM is valid at a low but finite value of compressibility factor. This condition allows us to analyze the infinite pressure approximation in a general way. It is shown that the infinite pressure approach neglects the contribution of the repulsive term of the EOS to the excess free energy of a mixture. This, in turn, introduces inconsistency which results in the difference in the calculated excess free energy of the EOS and the base ACM. The new approach defines parameter a of the EOS as an implicit function of compositions and temperature, thus requiring an iterative procedure using the infinite pressure limit as a starting point. The new approach can be modified to provide the correct composition dependence of a mixture second virial coefficient. Applicability of the new method has been tested for binary systems under vapor–liquid and liquid–liquid equilibrium conditions.     

Compressibility measurements of β- and β″ -alumina

The compressibilities of the a- and c-axes for sodium - and -aluminas were determined up to 10 GPa from the pressure dependence of powder X-ray diffraction measured at room temperature using synchrotron radiation as an X-ray source. Powders of sodium - and -aluminas which were prepared from grinding synthesized single crystals were used as the specimens for X-ray diffraction. The compressibilities of - and -aluminas are 1.5 ± 0.2 ×10^–12 and 1.7 ± 0.2 × 10^–12 Pa^–1 for the a-axis and 2.9 ± 0.2x10^–12 and 1.6 ± 0.2 ×10^–12 Pa^–1 for the c-axis, respectively. For the c-axis, the compressibility of -alumina is larger than that of -alumina. This experimental fact is explained by the different stacking of oxygen layers and the different content in sodium ion between - and -aluminas.