Home – Home – Jornals – Advanced Search

Experimental data on heat transfer in turbulent separation region behind obstacle in a broad frequency range of superimposed free-stream pulsations are reported. The heat-transfer coefficient was determined by solving an inverse non-stationary heat conduction problem based on experimentally measured wall transient temperature. Substantial heat-transfer intensification in the separation region of the pulsating flow was

Results of simulation study of evolution of solitary intensive second-sound waves spreading in superfluid helium are presented. Quantitative description was carried out on the basis of equations of hydrodynamics of superfluid turbulence (HST). HST equations with second-order accuracy (relative parameter deviation from equilibrium) were written for the cases of planar, cylindrical, and spherical geometries. The system of equations was solved using the disruption decay technique. Calculations were carried out for the temperature of undisturbed helium Т_{0 = 1.4 K. Simulation results were compared with experimental data.}

The model system of ordinary differential equations [1, 2] governing the behavior of a non-uniformly heated fluid in a tilted cavity is used for studying the stability of steady regimes of thermal convection at arbitrary (not small) tilting of the rectangular cavity. The bifurcation curve is constructed, which separates the region of parameters (the Rayleigh number ⎯ the cavity tilting angle) into two regions ⎯ the internal and external ones. In the external region, the system has one stable steady solution, and in the internal region, it has three steady solutions. One of them is always unstable in a monotone way, and two others may be both stable and unstable. The neutral curves are constructed, which determine the boundaries of the incipience of the oscillatory and monotone instabilities.

The reaction of the film interface to low-amplitude waviness of the wall was studied. A linearized version of the problem described by the Orr ⎯ Sommerfeld equation was considered; the solution was sought by asymptotic expansion in small parameter 1/Re, and usual spectral problem concerning stability to perturbations of exp[iα(x−ct)] type was solved. According to calculations, for some specially chosen wave numbers α the drift and dispersion effects balance each other, providing zero resulting velocity c_{R = 0. If we assume that a rigid wall is corrugated with the same α, we can say that stationary waves caused by the wavy wall are in resonance with intrinsic perturbations of the second kind.}

The results of theoretical and experimental studies of heat exchange at condensation of motionless steam on a vertical tube placed in a granular layer with different wetting angle are presented. Theoretical dependencies are obtained for the estimate of heat-exchange intensity, which account for the condensate slip on the surfaces of grains, and their satisfactory agreement with experimental data of the authors is shown.

The effect of liquid subcooling below the saturation temperature on the third heat transfer crisis was studied experimentally at pool boiling. Experimental data on the threshold values of superheating and heat fluxes, above which the evaporation front and third heat transfer crisis for acetone at subcooling from 0.3 to 10 K are formed, were shown. Formation of evaporation fronts is the necessary, but not sufficient condition for the third heat transfer crisis at subcooling. It was found that formation of a stable vapor film after propagation of condensation fronts over the heater surface is possible at heat fluxes considerably lower than the first critical one.

A thermal conductivity model is proposed for an orthogonally reinforced fiber medium with dispersed hardening of the bonding agent. On its basis, the problem of the design of a composite with a given set of effective thermophysical properties is solved as well as the solutions are derived for some inverse problems of the diagnostics of thermophysical properties of phase materials and the reinforcement structure of a fiber composite from known effective thermophysical characteristics.

Thermal conductivity of ozone-safe liquid refrigerant R507 was studied by the method of high-frequency thermal waves within the temperature range of 297.95 … 332.55 K and pressures from the saturation line up to 3.7 MPa. The estimated errors of temperature, pressure, and thermal conductivity measurements are 0.1 K, 3 kPa, and 1.5 %, correspondingly. Thermal conductivity of liquid R507 was calculated on the saturation line. Approximation dependences for thermal conductivity were derived for the whole range of studied temperatures and pressures and on the saturation line.

The properties of thermal radiation of the axisymmetric systems formed by an absorbing medium are analysed. Analysis of absorption and propagation abilities of the systems with an impermeable boundary on the basis of integral radiation equations is suggested together with absorption, transmission, and reflection abilities of the systems with a boundary permeable for radiation.

The peculiarities of cooling of stationary working hot and cold cathodes are under consideration. Scientific premises of the advisability of the tube electrodes arc-spot scanning are presented. The classification of the scanning methods is given. The assumption has been made that the phenomena of auto-electron emission of electrons in vacuum discharge tubes and in arc chambers of plasmatorches under the pressure equal or above atmospheric are somehow similar. The optimum scanning frequency and achievable values of the end-face tube cathode life-time have been estimated. Owing to the magnetic scanning, the area of the electrode surface, which is swept by the arc spot, increases one order or more, resulting in better cooling and reduced specific erosion. The continuous electrode lifetime becomes several orders longer than it is during the work without scanning.