P. P. Khramtsov

Experimental study of free-convective flow on a vertical plate with a constant heat flux in the presence of one or more steps

Abstract Free-convective heat transfer on a vertical plate with a constant heat flux in the presence of one or more regular steps on a plate was studied experimentally. Temperature fields were investigated by a Mach-Zehnder interferometer. The structure of free-convective flows on a plate was studied by the method of tracking visualization using a laser knife. A circulation free-convective flow, having the shape of two oppositely rotating vortices, was observed directly behind a step. During the experiment the Rayleigh number varied from zero to Ra = 2.8 × 103. The maximum Rayleigh number attained had a value Ra ∼ 2 × 104. The free-convective flow rate grew with Ra; however, qualitative changes in the structure of flow and of a temperature field were not observed in this case. The flow was visualized at different distances between the steps. As the width of the spacing between the steps increased, the vortices, arising in the separation zone, became more extended downstream. With the ratio of the step height to the spacing width equal to 1:3 and greater, a stagnation zone appeared near the first upstream step. A vortex flow between the steps enhanced heat transfer between the plate and environment.

Free-convective heat transfer on a vertical surface with heat-flux discontinuity

Abstract The character of free-convective flow near a vertical plate with a heat-flux jump on the surface is studied experimentally. Two cases of plate spatial orientation are investigated. The temperature field is measured and the velocity field is visualized in the free-convective flow near a surface. For the case of a higher heat flux from the lower portion of the plate, a change is noted in the character of the temperature profile in a boundary layer in the plate upper portion as compared with the constant heat flux surface. The shift of a temperature local maximum in a boundary layer to some distance from the surface into the flux depth is revealed. For the case of a large density of heat liberation at the initial stage of free-convective flow formation, the appearance of a two-dimensional vortex, originating from the interaction of the heated air flow with motionless cooler air in the upper portion of the plate, is found.

Some aspects of free-convective heat transfer in eddy flow through a horizontal tube

Abstract Experimental investigation of unsteady-state free convection in a horizontal cylindrical channel is carried out for the case of non-uniform distribution of heat flux along a channel at a constant temperature on the wall. The averaged temperature field in a gas was investigated on a Mach-Zender interferometer. Hydrodynamic structures were investigated by the smoke visualization technique. Heat fluxes were calculated on the basis of thermocouple measurements. In the case of non-uniform heat flux on the channel wall, the existence of longitudinal large scale hydrodynamic structures has been noted. Longitudinal and lateral Rayleigh numbers varied from 0 to 4 × 109 and from 0.8 × 104to 1.2 × 105, respectively. Investigations were carried out with air, carbon dioxide and helium flows.

Free convective flow on a vertical plate with a constant heat flux in the presence of one or more steps

We carried out an experimental investigation of free convective heat transfer on a vertical plate subjected to a constant heat flux in the presence of one or several rectangular steps. Temperature fields were investigated with the help of a Mach-Zehnder interferometer. During the experiment the Rayleigh number changed from zero to Ra=2.8·103. The flow was observed by the method of track visualization by means of a laser knife. Durectly behind a step we observed a circulating free convective flow having the shape of two oppositely rotating vortices.

Relaxation phenomena in nonstationary evaporation of liquid

Based on the phenomenological theory — the thermodynamics of irreversible processes — an analysis of a nonstationary process of liquid evaporation is carried out. It is shown that a sharp change in the heat‐flux magnitude causes the occurrence of processes of oscillating relaxation of vapor generation in the system.

Stable vortex structures in axisymmetric convective torch during oscillating combustion

A structure of a convective torch of axisymmetric flame in combustion of a propane-air mixture was studied experimentally under the conditions of velocity perturbations on the nozzle section. The flow was visualized by a Mach-Zehnder interferometer and also using stroboscopic photography of the flame proper luminescence. Mean temperature distribution in a torch was studied using a Chromel-Alumel thermocouple. The obtained data show the presence of torroidal coherent vortex structures moving downstream that substantially enhance combustion processes and heat transfer in a torch.

Unsteady free-convection heat transfer during vortex flow in a horizontal tube

We conducted a theoretical and experimental investigation of the hydrodynamic structure and unsteady free-convection heat transfer in a round horizontal tube under different conditions of the second kind. During the experiment the Grashof number varied from Gr=1.54·105 to Gr=7.9·105. Using the interferometric method we investigated the distribution of the temperature field for different structures of free-convection flow in the tube.

Heat transfer by natural convection and hydrodynamics on a vertical plate with a discontinuity in the heat flux

It is observed that the temperature distribution in the boundary layer changes qualitatively and the heat transfer in the upper part of a plate intensifies substantially in comparison with a surface with a continuous heat flux. For the case of substantial heat flux density in the initial stage of formation of a free convective flow a two-dimensional vortex is found to appear.

Two-stage light-gas magnetoplasma accelerator for hypervelocity impact simulation

The development of macroparticles acceleration methods for high-speed impact simulation in a laboratory is an actual problem due to increasing of space flights duration and necessity of providing adequate spacecraft protection against micrometeoroid and space debris impacts. This paper presents results of experimental study of a two-stage light- gas magnetoplasma launcher for acceleration of a macroparticle, in which a coaxial plasma accelerator creates a shock wave in a high-pressure channel filled with light gas. Graphite and steel spheres with diameter of 2.5-4 mm were used as a projectile and were accelerated to the speed of 0.8-4.8 km/s. A launching of particle occurred in vacuum. For projectile velocity control the speed measuring method was developed. The error of this metod does not exceed 5%. The process of projectile flight from the barrel and the process of a particle collision with a target were registered by use of high-speed camera. The results of projectile collision with elements of meteoroid shielding are presented. In order to increase the projectile velocity, the high-pressure channel should be filled with hydrogen. However, we used helium in our experiments for safety reasons. Therefore, we can expect that the range of mass and velocity of the accelerated particles can be extended by use of hydrogen as an accelerating gas.

Modification of the composite multi-layer oxide ceramic coating on meteoroid shielding element by compression plasma flow

The aim of this work is investigation of the influence of high-energy plasma impact on composite multi-layer coating (NiAl as a sublayer and Al2O3 as a top coat) on meteoroid shielding element. In order to reach this goal qausi-stationary plasma accelerator with impulse gas feeding was used. Experiments were conducted with use of helium and hydrogen gas mixture and nitrogen as plasma forming substance. Plasma accelerator generates plasma jet with electron temperature ≈ 150 kK and electron density (2.5-4) × 1016 cm-3. Visual examination, photography and spectral measurements were made through special vacuum chamber optical windows.