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.     

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.     

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.     

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.     

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.     

Modeling of Natural Thermogravitational Convection in Horizontal Channels with an Irregularly Shaped Cross Section

Results of a numerical investigation of the natural thermogravitational convection of air in horizontal channels with a shaped cross section are presented. Twodimensional unsteady equations of convection in the Boussinesq approximation, which are written in the velocity vortex–current function–excess temperature variables, are employed as a mathematical model. In investigating, the range of Rayleigh numbers was bounded above by the value 10⁶, which corresponds to the range of applicability of the Boussinesq approximation to air in the problem posed. The boundaryvalue problem was solved numerically by the finiteelement method of Galerkin (weak formulation). The distinctive features of the temperature and flow fields were revealed on the basis of calculations and the intensity of heat exchange was evaluated.     

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.     

Modeling of Heat and Mass Transfer in Systems of Radiation‐Evaporation Thermal Protection

Results of theoretical and experimental studies of models of different systems of radiationevaporation thermal protection are presented; the overalldimensionweight parameters of these systems and of systems of passive radiation thermal protection are compared.     

Solution of Mixed Contact Problems in the Theory of Nonstationary Heat Conduction by the Method of Summation‐Integral Equations

The laws governing the development of spatial nonstationary temperature fields in a bounded cylinder and a halfspace where one of the end surfaces of the cylinder touches the surface of the halfspace in a circular region are determined. A solution of a mixed axisymmetric nonstationary problem of heat conduction is obtained in the region of Laplace transforms. In solution of this problem, there appear summationintegral equations with the parameter of the integral Laplace transform (Lparameter) and the parameter of the finite integral Hankel transform (Hparameter).     

Calculation of a Temperature Error by the Conjugate Equation

A temperature error depending on the error of initial information can be calculated by the conjugate problem. On estimation of the error at one time and coordinatelocal point the expenditures of the computation time and computer memory are double the expenditures for calculation of the heatconduction equation. The conjugatetemperature field obtained in this case allows calculation of the effect of the error of any parameter of the problem (initial conditions, boundary conditions, coefficients). In the linear case, the conjugatetemperature field depends on the position of the point under estimation; in the nonlinear case, it additionally depends on the temperature field. The approach considered can be applied to calculation of the error of a wide class of temperature functionals.     

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.     

Investigation of the Processes in Torches for High‐Speed Gas‐Plasma Spraying of Powder Materials with the Use of the Flow‐Rate Method of Action on the Flow

The comparative characteristic of torches with geometric and flowrate methods of control of the characteristics of a twophase flow are given. Based on the mathematical model proposed, the advantage of the flowrate method is shown by calculation. By using particular examples, the estimates of the optimum values are given for the relation of the flow rates in feeding units and for the length of the heating portion for torches with a flowrate method of control of the twophase flow.     

Numerical Analysis of the Jet‐Vortex Pattern of Flow in a Rectangular Trench

Numerical simulation of the vortex structure of threedimensional laminar flow in a rectangular trench of square cross section has been carried out on the basis of the finitevolume solution of steadystate Navier–Stokes equations.     

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.     

Numerical Analysis of the Effect of Viscosity on the Vortex Dynamics in Laminar Separated Flow Past a Dimple on a Plane with Allowance for Its Asymmetry

Based on numerical solution of the Navier–Stokes threedimensional stationary equations by a factorized finitevolume method, the influence of physical viscosity on selforganizing jetvortex structures in a dimple on a plane immersed in a laminar flow is analyzed with allowance for the asymmetry of the dimple shape.     

Influence of the Mass Transfer of Water in Cartilaginous Tissue on the Temperature Field Induced by Laser Radiation

A study is made of the influence of the mass transfer of water on the temperature field occurring in cartilaginous tissue under the action of laser pulses. Two different mechanism of mass transfer of water in cartilaginous tissue (moleculardiffusion mechanism and laminar flow) have been considered in solving heat and masstransfer equations. The calculations have shown that the maximum temperature is attained inside the sample because of the evaporation of water from the biologicaltissue surface. The influence of different parameters of laser radiation and mass transfer of water on the surface temperature, on the maximum value of the temperature, on the position of the temperature maximum, and on the characteristic time at which the diffusionlimited relaxation of stresses in the cartilaginous tissue occurs has been analyzed.     

Self‐Organization and Dynamic Chaos in Chemical‐Technology and Heat‐Exchange Devices: Problems and Tasks

Nonlinear phenomena in thermophysical and chemicaltechnology processes are considered in the context of nonlinearity, instability, nonuniqueness, nonstationarity, and irreversibility. The perturbation frequency (phase)toamplitude ratio is the governing parameter of the nonlinear interaction of perturbations that are described by the proposed general nonlinear parabolic equation. The nonlinearity of this ratio characterizes turbulence, while its linearity characterizes selforganization. It is shown that chaotic conditions can be selforganized under the action of white noise, which favors the system getting into the domain of attraction of a stable node. The mechanism of the occurrence of turbulence is substantiated.     

Theoretical and Experimental Study of Oscillating Heat Pipes with Few Turns

A theoretical model of fewturn heat pipes is suggested. The equation for boiling liquid flow in a capillary of the pipe, which allows for the pressure difference of saturated vapor and for gravity and viscosity forces, is written. The parameters at which selfoscillations of the liquid occur have been estimated. It is shown that the period of selfoscillations is determined by the characteristic time of heat exchange between the liquid in the capillary and the surrounding medium. The time of selfoscillations obtained theoretically is in good agreement with the experimental one.     

Computational‐Experimental Approach to Prediction of Mass‐Transfer Processes in Metallic Coatings of Gas‐Turbine Blades and Their Service Life

A computationalexperimental approach to analysis of longtime processes of mass transfer of aluminum in metallic MCrAlY coatings of gasturbine blades and to prediction of their service life is proposed. The approach is based on the mathematical model describing the oxidation and diffusion processes in the coating and in the alloy of a blade, the parameters of which are identified by the data of shorttime experiments. The results of theoretical and experimental determination of the aluminumconcentration distributions in the coating and in the basic alloy of a gasturbine blade and the results of prediction of the service life of the coating are presented. It is shown that this approach allows one to perform analysis of longtime processes of masstransfer in metallic coatings of gasturbine blades and predict their service life with a high degree of accuracy.     

Rheology of Liquid‐Crystalline Polymeric Systems

Based on the Zubarev method of nonequilibrium distribution functions, a statisticalmechanical theory of the rheological properties of liquidcrystalline polymers has been constructed. The distinctive features of the media in question in the case of shear flow have been described using this theory.