Home – Home – Jornals – Thermophysics and Aeromechanics 2010 number 2

In the second part of review, we have considered the problems related to momentum and heat transfer in nanofluids. Results on hydrodynamic friction, forced and free convection in the laminar and turbulent flows are analysed; heat transfer at boiling is considered. The available models describing heat transfer intensification and suppression in nanofluids are studied. It is shown that for some problems on convective heat transfer there is a contradiction in data of different authors; possible reasons for this contradiction are analysed

Experimental heat-transfer data for a small-diameter hot wire have been obtained and generalized in a wide range of Reynolds numbers typical of hot-wire anemometry. The experiments were carried out using an IRVIS-TA5 digital hot-wire anemometer and standard critical nozzles used for regulating the flow in the test section of the Eiffel chamber in which the hot-wire sensor was installed. Approaches to carrying out hot-wire anemometric measurements without a labor-consuming calibration procedure for the hot-wire sensor are substantiated.

Time dependences of temperature distributions in a thin metal wall were studied experimentally under two conditions of convective heat transfer in a tank model. In the first case, the vertical working wall was heated from within due to a convective heat flux from the opposite wall heated monotonously, and it was cooled due to heat transfer to the ambient medium. Dependence of the temperature field on a thin wall at the stage of convective flow development was retraced with the help of the thermographic camera and thermocouple sensors. In the second case, the tank wall was heated uniformly by IR radiation from the outside, and nonstationary convective flow and volumetric liquid heating were formed inside. Time dependence of temperature distribution over the wall height is studied. It is shown that the flow structure and convective heat transfer in a fuel layer with free boundary are subjected not only to the buoyancy force, but also to the thermocapillary effect. The local features of the flow affect temperature distribution in a thin wall.

The dynamics of phase fronts in a hydrothermal solution filtering through the fluid-conductor pores upwards to the earth surface was investigated on the basis of the model of volcanogenic orthomagmatic fluid systems. The problem was solved with regard for the rise and gradual extinction of the source of a fluid related to the crystallization of water-saturated basite magma in a shallow intrusion chamber. The influence of the porosity and permeability of supra-intrusion rocks as well as the heat-exchange conditions at their boundaries on the evolution of the orthomagmatic fluid system was investigated.

Density of low-temperature eutectic in magnesium−lead system (83.06 at. % Pb) has been measured by gamma-raying of the samples with narrow beam from cesium-137 isotope over the temperature range 293−1000 K of solid and liquid states. Approximation density dependences have been obtained and data of this work and other authors have been compared. Reference tables of temperature dependences of the alloy thermal properties have been compiled for the entire range of measurements and their errors estimated. It is shown that differences in the values of volumetric changes obtained during melting and crystallization are bound with the metastable β′-phase formation.

The process of heating a moving medium by an electromagnetic radiation in high-frequency range is considered in the presence of heat exchange with the ambient medium in the approximation of a thermally thin layer. The existence of temperature profiles in the form of auto-waves is established. The analytic and numerical solutions are compared.

The one-phase Stefan problem was simulated numerically in a layer of semitransparent medium with different emissivity factors at the right moving boundary. The effect of optic properties of irradiated surface on formation of temperature fields and radiation flux densities was demonstrated.

The dynamics of planar one-dimensional shock waves applied to the available experimental data for the water−Freon system is studied on the basis of the theoretical model of the bubbly liquid refined with regard for a possible hydrate formation. A scheme is proposed for considering the fragmentation of bubbles in the shock wave, which is one of the main factors of the intensification of the hydrate formation process with the growth of the shock wave amplitude.

The unobvious effect of the limiting wetting angle on heat transfer intensity at boiling is shown. The purposeful experiments allow us to develop the mathematical model, which describes properly the results of experiments on determination of the role of limiting wetting angle: sometimes this role is obvious, sometimes it is ambiguous.

Experiments are performed to study the possibility of decreasing the net drag of a flat plate with the use of streamwise-oriented vertical elements mounted normal to the surface in an incompressible equilibrium turbulent boundary layer. The Reynolds number based on the boundary-layer momentum thickness in the section where the vertical elements are placed is 820. It is demonstrated that vertical large eddy breakup elements with the geometry used do not reduce the drag of a flat plate in the major part of the range of Reynolds numbers Re_{х examined. It is only at extremely low values of Reх that a certain gain in the net drag is reached, as compared with the value for a non-modified flow.}

In the present study, we examined, both experimentally and theoretically, the influence of surface permeability on the stability and laminar-turbulent transition of supersonic boundary layer at free-stream Mach number М_∞ = 2. A satisfactory agreement was obtained between the data calculated by the linear theory of stability and the data obtained in experiments with natural disturbances performed on models with different porous inserts.

Flow of two high-lift devices is studied on the basis of the solution to two-dimensional Reynolds equations with the Spalart - Allmaras one-equation turbulence model. Computation results are compared with the experiment under the conditions of airfoil flow in the low-speed wind tunnel with open test section. It is shown that such approach is the most correct for this comparison.

Presented below are the results of tests of turbine vanes with vertical rotation axis aimed at determination of their aerodynamic characteristics. Three types of vanes with the profiles in the form of semicylinder, semiellipse, and semiellipse with stabilizing plane have been tested. The last type of vane has been tested with stationary and rotary stabilizing planes.

The dependence of the flow patterns around two prism bodies with square cross sections on the distance between them has been studied. The specific structures arising around two bluff bodies have been obtained and divided into four main types. The thermoanemometer probing in aerodynamic wake of the same two bodies has been performed and resulted in the presented dependence of Strouhal numbers on the relative distance between the investigated prisms.