Excitation of Narrow‐Band Pulsations in a Short Portion of Transition from the Smaller Diameter of a Pipe to a Larger Diameter and Possibilities of Preventing Them

By using models of the portions of the circuit of main gascompressor stations, data on the frequencies of narrowband pressure pulsations have been obtained; these data demonstrate the jet character of flow in divergent channels with angles of opening on one side of 12°47 and 23°50. It has been shown that narrowband acoustic disturbances are generated in the internal flow with largescale hydrodynamic structures. Intense narrowband pulsations are prevented by a grid of internal divergent channels in the transition portion with small angles of opening in canals and in excitation of certain disturbances upstream of a short divergent channel.     

Influence of Multiple‐Scattering Processes on the Laser Probing of Biological Tissues

Theoretical aspects of multiplescattering processes in laser probing of biological tissues have been considered. The method of digital dynamic specklephotography has been described. The results of experimental studies of the nearsurface blood flow and stressedstrained states in a pinstructure–toothroot model are presented.     

Modern Problems of Intensification of Heat Exchange in Channels

The current achievements in the field of intensification of heat exchange in tube heatexchange apparatus are considered. Requirements for highefficiency heattransfer surfaces have been formulated. Problems of intensification of heat exchange in bundles of finned tubes and in heatexchange apparatus under conditions of condensation and boiling of heattransfer agents and under scaling conditions have been investigated. Highefficiency designs of heatexchange apparatus are presented.     

Two‐Dimensional Calculation of the Parameters of a Steam‐Air Mixture in a Film‐Type Heat and Mass Exchanger

A mathematical model for twodimensional calculation of the temperature and density of the steam in a steamair mixture which rises between two water films flowing down adiabatic shields has been proposed. The parameters of the films have been calculated in a onedimensional approximation. The results of calculating the parameters of air according to the onedimensional and twodimensional models of the processes of heat and mass transfer have been compared. The range of applicability of the former to a filmtype heat and mass exchanger has been determined.     

Calculations of the Passage of Gamma‐Quanta through a Polymer Radiation‐Protective Composite

We have investigated the radiationprotective characteristics of a thermoplastic polystyrene composite material filled with a highdispersion modified lead oxide as well as the dependences of the energy (flux) buildup and transmission factors and albedos on the energy and protectiveshield thickness. Calculations of the integral characteristics of the radiationprotective properties of materials have been done.     

Influence of the Viscosity of Filled Epoxy Resins on Their Spreading on a Horizontal Surface

The rheological properties of ÉD20epoxyresinbased compositions filled (10–50 vol.%) with quartz sand, quartz flour, or their mixture have been investigated on Reotest2 and RV8 rotational viscosimeters. The relative viscosity of the filled compositions increased with their free volume according to the exponential equation with an exponent of 2.6. The compositions began to show an anomaly of viscosity in flowing for a content of the filler of more than 40 vol.%; the yield stress appeared for 50 vol.%. The rate of spreading of the compositions on a horizontal surface decreased with increase in the composition viscosity according to the exponential equation with an exponent of 1/8, which is similar to that calculated theoretically. The experiments conducted allowed calculation of the formula of epoxybased, selfleveling pouring floors.     

Characteristics of the Porous Structure of Carbonized Glass‐Reinforced Plastics

The results of experimental investigations of the porous structure of four glassreinforced plastics after the interaction of them with hightemperature flows have been presented. The dependences of the accessible porosity on the thermalaction time have been obtained. The values of the initial porosity of the glassreinforced plastics have been determined. The values of the effective radii of micro and macropores at different times of hightemperature heating of the glassreinforced plastics have been calculated.     

Widening the Scope of Working of Solid‐State Nd‐Glass Lasers

With the example of the serial model of a pulsed Ndglass laser, it is shown that the use of an unstable resonator with a semireflecting homogeneous exit mirror makes it possible to significantly decrease the laserbeam divergence and increase the uniformity of the radiationintensity distribution in the near zone. We were the first to obtain a laserbeam quality of (40–50) mm·mrad for technological glass lasers and to attain a depth of fusing of of 6.3 mm for steel (aspect ratio 10) for an energy of 23 J. The obtained uniformity of the radiationintensity distribution was estimated at the level of ±10%. The beamquality level attained for the Ndglass laser beam allows us to recommend it for both realization of deepfusion regimes and laser hardening without the use of external integrating optical elements.     

Acoustic Excitation of Noncircular Turbulent Jets

Results of experimental investigation of turbulent mixing in jets flowing out of nozzles with different cross sections in the case of low and highfrequency acoustic excitation of the jets are presented. The influence of the shape of the cross section of a nozzle on the acousticexcitation sensitivity of a jet flowing out of it is analyzed.     

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.     

Identification of Heat‐Exchange Processes in a Supersonic Spatial Flow Past Aircraft

Direct and inverse problems of heat exchange in a supersonic spatial flow past the front part of an aircraft in the form of a spherically blunted nose cone have been solved numerically. The prospects of using highheatconductivity materials and the blowing of the gascoolant for lowering the temperature on the surface of an aerodynamic body have been shown. A comparison of the solutions of the direct and inverse problems in one, two, and threedimensional formulations for various materials of the sheath has been made. The error in recovering the heat flow by the thinwalled method has been estimated.     

Investigation of the Process of Hardening of Diglycidyl Ether Bisphenol a by Phosphate Binders

The interaction between diglycidyl ether bisphenol A and conventional and waterdeficient phosphate binders has been investigated. The data of chemical analysis, IR spectroscopy, and differentialthermal analysis point to the formation of a spatially crosslinked epoxy polymer under the influence of the phosphate binders. It has been shown that conventional binders can be used as hightemperature hardeners of epoxy oligomers. When waterdeficient binders are used, the formation of a threedimensional polymer structure is observed at room temperature.     

Investigation of Sonoluminescence Amplification under the Interaction of Ultrasonic Fields Widely Differing in Frequency

The laws of sonoluminescence generation under the interaction of ultrasonic fields widely differing in frequency have been investigated. It is shown that nonadditive amplification of the sonoluminescence is observed not only under the simultaneous action of the fields on a liquid, but also in a highfrequency field after preliminary insonification of the liquid by a lowfrequency field. The phenomenon of a longduration aftereffect of the lowfrequency field on the cavitation generated by the highfrequency field has been revealed. On the basis of the obtained results the conclusion has been drawn that the main mechanism of increasing the cavitation activity in the interacting fields is the generation of new cavitation nuclei as a result of the collapse of bubbles excited by the lowfrequency field.     

Surface Heat Treatment of Facing and Other Materials with Concentrated Solar Energy

Surface treatment of building materials, ornamental ceramics, covercoat enamels, blastfurnace and openhearth slags, and natural stones of the basalt type has been carried out with the use of solar furnaces and their simulators for the purpose of obtaining protectivedecorative vitreous and glazed coatings. The specific energy consumption and the optimum heat fluxes necessary to obtain highquality coatings have been determined. The results of searching investigations testify to the fact that renewable environmentally safe concentrated solar energy can be utilized in industry and the national economy for surface heat treatment of different materials by melting them in the air.     

Analysis of Heat Stresses of the Parts of the Cylinder–Piston Group with Heat‐Protective Coatings in an Internal‐Combustion Engine

The process of heat exchange in the cylinder of an internalcombustion engine has been investigated and the heat stresses of the working surfaces of the piston and the cylinder head have been analyzed. A method for calculating the heat resistance, the strength, and the thickness of heatprotective coatings has been developed. Results of thermalcycle testing of a piston with heatresistant coatings, the properties of which were calculated by the method proposed, are presented.     

Numerical Modeling of Turbulent Flow inside a Wind‐Driven Plant with Allowance for the Forces on the Impeller

The operating efficiency of a winddriven plant based on a confuserdiffuser accelerator is evaluated within the framework of the multiblock approach to solution of steadystate Reynolds equations closed with the use of a twoparameter dissipative turbulence model.     

Investigation of the Serviceability of the Heat Shield of the Orbital Aircraft “Buran” under the Conditions of Radiant Heating on Solar Plants

We have investigated the serviceability of the heatinsulating tiles of the orbital aircraft Buran under radiant heating on an SGU7 solar plant with a mirror concentrator 5 m in diameter. Cycles of aerodynamic heating with a duration of 20 min were simulated. For the total number of cycles for different materials from 20 to 85, the efficiency and serviceability of TZMKtype materials with different coats have been corroborated. The results obtained agree with the test data obtained on gasdynamic (power consumption 1 MW) and radiation (250 kW) test beds, which enables such tests to be recommended for use at preliminary stages in powersaving and ecologically harmless solar furnaces.     

Numerical Calculation of the Flow Regimes of a Fluid Partially Filling a Horizontal Rotating Heat‐Exchange Cylinder

Consideration is given to a numerical determination of a twodimensional unsteady viscous flow with the free surface in a stationarily rotating horizontal cylinder in which heatexchange processes are carried out. The markerandcell method in a polar coordinate system is used. The features of modeling of the walllayer regime and the circulating flow regime that occur in rapid and slow rotation of the cylinder, respectively, are discussed. Based on the given results of numerical calculations, the influence of the Reynolds number on the character of flow is analyzed.     

On the Limiting Form of the Equation of Anisotropic Heat Conduction in a Rod

The paper considers the problem of the asymptotically substantiated reduction of the threedimensional, in coordinates, equation describing the process of heat propagation in an anisotropic material to a onedimensional equation. As a heattransfer region, a cylindrical rod of an arbitrary cross section was taken. It is assumed that the matrix of thermal diffusivity coefficients depends on the spatial coordinates. In the constructed equivalent heatconduction equation, a certain effective heattransfer coefficient is represented and formulas for its calculation have been obtained. Examples of the calculation have been considered.     

Bypass Laminar‐Turbulent Transition in a Thermal Boundary Layer

We present results of four series of experimental investigations of the bypass laminarturbulent transition (BLTT) initiated by actions of different nature (higher than usual degree of turbulence of the external flow, closed laminar separation at the leading edge, and their combination) on a flat surface in gradientfree flow. Our findings have supported the idea that strongly disturbed flows have a tendency toward the formation of an upper thermal bypass laminarturbulent transition whose heattransfer coefficient changes monotonically because of the formation of a pseudolaminar boundary layer before it. The influence of the scale of turbulence on the position of a bypass laminarturbulent transition and the intensification of the transfer processes in the boundary layers formed before and after the bypass laminarturbulent transition has been evaluated. We have developed a complex method for diagnostics of a bypass laminarturbulent transition, which allows one to establish the fact of formation of the bypass laminarturbulent transition and determine its starting and end points.