Unsteady mixed-convection boundary layer flow along a symmetric wedge with variable surface temperature

Laminar two-dimensional unsteady mixed-convection boundary-layer flow of a viscous incompressible fluid past a sharp wedge has been studied. The governing boundary layer equations are transformed into a non-dimensional form and the resulting nonlinear system of partial differential equations is reduced to local non-similarity boundary layer equations, which are solved analytically for small time. Perturbation solutions are also obtained for small and large dimensionless time, τ. Solutions of the governing equations for all time are obtained employing the implicit finite difference method. Here we have focused our attention on the evolution of skin-friction coefficient (C_f) and local Nusselt number (Nu) (heat transfer rate), fluid velocity and fluid temperature with the effects of different governing parameters such as different time, τ, the exponent, m (=0.2, 0.4, 0.6, 0.8, 1.0), mixed convection parameter, λ (= 0.0, 0.5, 1.0) for fluids having Prandtl number, Pr = 0.1, 0.7, and 7.0.     

Surface-friction coefficient in turbulent flow at a boundary layer

Using Thompson two-parameter velocity profiles equations defining the dependence of the surface-friction coefficient on the integral characteristics of the boundary layer are obtained.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol.46, No. 1, pp. 51–56, January, 1984.     

Influence of the plasma of a high-frequency barrier discharge on the structure of the dynamic boundary layer on a flat surface

Methods of obtaining a surface high-frequency barrier discharge have been analyzed. The results of investigation of the influence of this discharge on the characteristics of the dynamic boundary layer on a flat surface have been given. __________ Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 81, No. 1, pp. 55–61, January–February, 2008.     

Viscous-fluid flow in a thin layer on the side surface of a rotating braking-upper-end cylinder

An analytical solution is obtained to the hydrodynamic problem on circulating viscous-fluid flow in a thin layer on the side surface of a rotating braking-end cylinder. Calculated data are in satisfactory agreement with the experimental findings and with the numerical integration of the equations of motion.Moscow Engineering Physics Institute. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 62, No. 6, pp. 814–840, June, 1992.     

Density and capacitance profiles and edge effects in a two-dimensional charge layer on a dielectric surface

The density and capacitance profiles and edge effects in a two-dimensional (2D) layer of electrons held on a liquid helium surface between two horizontal plates of a parallel-plate capacitor are studied by solving Laplace's equation on a computer. An effective length for experimental cells is defined to take into account nonuniform charge density and capacitance near the edges of the cells. The profiles and edge effects are studied as a function of charge density on the helium surface, helium depth inside the cell, repelling voltages on guard electrodes around the capacitor plates, and the frequency of excitation. The results should be useful in designing cells for experiments and better analyzing the results of measurements.     

Dissociated gas flow in the boundary layer along bodies of revolution of a porous contour

This paper studies the ideally dissociated gas flow in the so-called frozen boundary layer on bodies of revolution. The contour of the body of revolution is porous. The governing boundary layer equations are brought to a generalized form. The obtained equations are numerically solved using the finite differences method. Based on the obtained solutions, distributions of physical quantities in the boundary layer are presented in the form of diagrams. Conclusions on behaviour of these quantities are also made.     

Thermocapillary flow in a liquid layer at minimum in surface tension

Summary In the present paper a class of similarity solutions for the two-dimensional Navier-Stokes and energy equations describing thermocapillary flows in a liquid layer of constant width and infinite extent is presented. The layer is bounded by a horizontal rigid plate from one side and opened to the ambient gas from the other one. The physical properties of the liquid are assumed to be constant except the surface tension which varies as a quadratic function with temperature. It is supposed that a constant temperature gradient exists along either the liquid free surface (case I) or the rigid boundary (case II).In both cases, by means of a similarity transformation, the equations of motion and energy are reduced to a system of three ordinary differential equations, one for the velocity and two for the temperature. The equation for the velocity can be solved separately from the other equations and its solution, found numerically, exists only for the Marangoni number less than a certain finite value. The solution of the whole system depends also on the Prandtl number. The solution of one of the temperature equations is presented in an analytical form and the other equation is solved numerically. Asymptotic formulas of the functions are also obtained for small and large Marangoni numbers. Flow pattern and temperature fields are presented. One convective roll exists in every semi-infinite layer. Fluid velocities at different points of the free surface are evaluated for an aqueous solution of n-heptanol and compared with those measured in the experiments.     

Mixed convection boundary layer flow on a vertical surface in a saturated porous medium

Summary The flow of a uniform stream past an impermeable vertical surface embedded in a saturated porous medium and which is supplying heat to the porous medium at a constant rate is considered. The cases when the flow and the buoyancy forces are in the same direction and when they are in opposite direction are discussed. In the former case, the flow develops from mainly forced convection near the leading edge to mainly free convection far downstream. Series solutions are derived in both cases and a numerical solution of the equations is used to describe the flow in the intermediate region. In the latter case, the numerical solution indicates that the flow separates downstream of the leading edge and the nature of the solution near this separation point is discussed.     

Influence of body shape on the spatial boundary layer characteristics on a permeable surface

Results are presented of computations of the flow of a homogeneous gas in the spatial laminar boundary layer on blunt bodies of different shape with a permeable surface around which are flows at angles of attack and slip.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 53, No. 3, pp. 365–373, September, 1987.     

Pressure distribution along the surface of combined bodies streamlined by a hypersonic flow

The pressure distribution on the surface of a body with an external contour comprising various combinations of conical regions and a blunt spherical leading edge has been experimentally studied and theoretically interpreted for variable hypersonic streamlining conditions. It is established that the pressure gradient, the degree of turbulence of the air flow, and the breaks of the body contour are, in addition to the Reynolds number, important factors determining the pattern of streamlining.     

Local and integral turbulent boundary layer characteristics on a convex surface in diffusor flow

A semiempirical method is proposed for computing the local and integral characteristics of the turbulent boundary layer on a convex surface under conditions of a positive longitudinal pressure gradient. By using the method proposed, graphical dependences are obtained that characterize the influence of curvature on the form-parameter, the thickness of the momentum loss, the thickness of the viscous sublayer, and the relative flow coefficient.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 58, No. 6, pp. 916–920, June, 1990.     

Effect of deformation on electrochemical properties of the double layer and surface charge of metals

Electrochemical measurements on plastically deformed metals revealed the previously predicted [1] deformation-induced shifts toward positive surface charge values and clarified the character of the intensification of the electrochemical heterogeneity of deformed metal surfaces (localization of activated anodes as a result of mechanochemical phenomena). The deformation-induced increase in the differential capacitance of the double layer is attributable to an increase in the intensity of physical (electrostatic) adsorption of SO ₄ ^2– and HSO ₄ ^– HSO ₄ ^– anions on a positively charged surface in sulfuric acid solutions. A necessary (but not always sufficient) condition of the effectiveness of cation-active inhibitors of corrosion of plastically deformed metals is their stable chemisorption at potentials in the range of deformation-induced changes in the surface charge (of the order of tenths of a volt on the -scale).     

Influence of the nature of polyaniline-based hole-injecting layer on polymer light emitting diode performances

We have studied the use of water and solvent-based polyaniline (PANI) dispersions as a transparent hole-injecting layer in polymer light emitting diodes (PLEDs). We have investigated the effects of the pH, the conductivity, the work function and the nature of the solvent and the dopant on the hole-injection properties. The water-dispersed PANI at a low pH (pH 1.8) showed an efficiency similar to that of PEDOT-based devices due to its high HOMO level and high conductivity. For the solvent-based PANI dispersions, the influence of the nature of the solvent and the dopant on the crystallinity, the conductivity of the PANIs and on the performances of the light emitting devices is discussed.     

Giant magnetoresistance increase in a hard–soft spin valve structure with the growth of a semiconductor layer

Magnetic and transport properties of a hard–soft spin valve structures have been investigated. A first series of sandwiches composed of an artificial antiferromagnetic (AAF) Co/Ru/Co sandwich decoupled from a soft Fe/Co buffer layer as follows: Fe_{50 Å}/Co_{5 Å}/Cu_{30 Å}/Co_{30 Å}/Ru_{5 Å}/Co_{30 Å}/Cu_{20 Å}/Cr_{20 Å} has been prepared. This sandwich presents a giant magnetoresistance (GMR) of 1.7% and an exchange coupling strength of approximately −1.73 erg/cm². Afterwards, we have grown a second series of sandwiches in which the Cu/Cr capping layer has been replaced by a 15-Å thin semiconductor layer of ZnS, covered by a soft ferromagnetic layer of Co_{5 Å}/Fe_{50 Å}. Surprisingly, the giant magnetoresistance for the last sandwiches has been increased by a factor of 2, up to 4%. To explain this non-expected result, we have performed atomic force microscope imaging at the semiconductor layer surface. The results show that the semiconductor layer is not homogeneous and contains a non-negligible density of pin-holes, that are responsible of a direct magnetic coupling between the upper 30 Å Co layer of the AAF and the Co 5 Å/Fe 50 Å bilayer. This coupling induces a strong asymmetry between the magnetic layers of the AAF and consequently an enhancement of the GMR.     

Influence of surface charge on ingress of chloride ion in hardened pastes

The amount of free chloride content in concrete is one of major factors in initiating the corrosion process. The material and environmental factors play a key role in diffusing the chloride ion through the cover concrete to reinforcement. Thus, the electrochemical study is indispensable to understand the mechanism of chloride ingress into concrete. Determination of surface charge and its influence on diffusion of chloride ion into cement matrix of concrete are researched for Ordinary Portland Cement (OPC) paste and cement paste containing Ground Granulated Blastfurnace Slag (GGBS). Different kinds of experiments such as measurement of membrane potential, determination of porosity and pore size distribution, determination of pore solution concentration, and steady state diffusion coefficient of chloride and sodium ions are employed to understand the mechanism of chloride ingress. The obtained results show that the positive surface charge on the pore walls of hardened paste regardless of GGBS’s presents. The surface charge of hardened paste mainly depends on pore solution concentration and cement composition. The physiochemical characteristics of the pores are affecting on transporting ions through it. Hardened paste has greater resistance to diffusing sodium ions than chloride ions. Moreover, there is a strong interaction between transport of chloride ion and surface charge in matured hardened paste.     

Coherent charge oscillation in a semiconductor double quantum dot

The time evolution of a pulse-excited charge qubit in a semiconductor double quantum dot is investigated. All-electrical initialization and coherent gate control of the system are achieved, and coherent charge oscillation is observed through the transport measurements. The oscillation frequency and decoherence time T/sub 2/ are estimated by fitting the transport data with a simple model. Possible decoherence mechanisms in a charge qubit system are pointed out and discussed in detail.