ИСТИНА

The main ways to improve the efficiency of power equipment are associated with an increase in the maximum temperature of the working fluid in the cycles of power plants. However, its value is limited by the strength of materials and the efficiency of cooling systems of the most heat-stressed elements of power plants. In connection with the growth of thermal stress level in the elements of the design of power plants and engines, there is a growing interest in the use of transpiration, screen, ablation and evaporative cooling methods. From the standpoint of thermal physics the most promissing cooling method is transpiration or porous cooling. In this case, the coolant flows through an extremely branched network of internal microchannels, intensively cooling down the wall. Porous cooling has the highest theoretical efficiency, which is characterized by the difference of the coolant temperature at the outlet of the permeable wall to the temperature of its outer surface. Due to technological and operational difficulties, as well as uncertainties in theoretical aspects, these cooling methods have so far limited application, but they are the most promising for use in cooling systems of gas turbine blades, combustion chambers, afterburner nozzles and rocket engines. To study the fundamentals of transpiration cooling, an experimental stand based on supersonic aerodynamic facility was created in the Institute of mechanics of Lomonosov Moscow State University. In the experiment the technique for acquisition of the heat-insulated (adiabatic) wall temperature is realized. This temperature corresponds to the moment when the heat flux through the wall is zero and represents a determining temperature for heat flux calculation in a high-speed flow. The urgent task is to establish the effect of critical injection, characterized by the displacement of the boundary layer from the wall. To determine adiabatic wall temperature, several experiments are carried out with different heat fluxes by means of changing the injection temperature. Then a graph of the dependence of the heat flux on the difference between the stagnation temperature and the wall temperature is plotted. The coordinate axes are chosen in such a way that the experimental points form a straight line, and its slope angle characterizes the heat transfer coefficient at a given blowing intensity. The intersection point of the interpolating curve with the abscissa axis makes it possible to determine adiabatic wall temperature.