Vol 28, No 4 (2019)

The shape of the liquid-liquid coexistence line in the phase diagram of a lithium-sodium system is determined using the gamma-ray attenuation technique. The measured coordinates of the critical point of the coexistence curve (critical temperature T_C = 576.8 ± 1.0 K; critical composition X_C= 35.9 ± 0.4 at. % Na) are in good agreement with the data in the literature. The critical exponent β for the coexistence curve is 0.34 ± 0.004 in the range 1 · 10⁻³ < (T_C—T)/T_C < 5 · 10⁻². Mutual diffusion in a Li-=Na melt of near-critical composition is studied at temperatures of 583 to 998 K using the same technique. The behaviour of the interdiffusion coefficient is found not to obey the Arrhenius law at temperatures below 700 K. Darken’s relation is used to estimate the temperature dependence of the long-wave limit S_CC(0) of the Bhatia-Thornton concentration-concentration correlation function.

The paper presents the results of experimental study on characteristics of non-boiling multi-jet water cooling. Experimental data on the characteristics of droplet jets including the distribution of droplets sizes and their velocity, as well as liquid irrigation patterns on a transparent heating surface, were obtained using high-speed visualization. The surface temperature field of the thin-film ITO heater was measured using IR thermography. The usage of synchronized techniques revealed the relationship between the irrigation dynamics and the temperature field of the heating surface. Moreover, IR thermography made it possible to determine both the distribution of local heat transfer rate in various areas of the impact surface and the integral heat transfer during multi-jet cooling. In particular, the dependence of the integral heat transfer rate on the distance between the spray source and the heater was revealed and it was shown that there is an optimal configuration of liquid irrigation pattern at which the maximum heat transfer coefficient is observed.

Gas turbines (GTs) are thermal machines used to transform the energy released in combustion with a hydrocarbon into mechanical power, in order to drive a machine or generate thrust in aircraft. The critical issue in the GT design are the parts exposed to extreme mechanical and thermal conditions, e.g., the first row of turbine blades. The GT thermal efficiency is limited by the maximum temperature the blade materials can withstand without softening or creeping. Currently, the maximum operating temperature is above the softening point of the blade material thanks to techniques of ceramic coatings of low thermal conductivity, called Thermal Barrier Coating (TBC), and techniques of blade cooling. The internal cooling of blades involves conduits inside them for air that comes from a bleed in an intermediate compressor stage. The air bleeding is around 3 to 5% of the main GT flow. This air and the heat flow that it receives are not used to generate power, so it is necessary to optimize the cooling techniques in order to control the temperature using the least amount of air and minimum heat flux evacuated, for holding the GT overall efficiency high. The present work studies the internal cooling of Elemental Gas Turbine Blade (EGTB) with a fixed thickness of the TBC and the optimization of the conduit shape and position over a cross section in 2D. The optimization is carried out by exhaustive searching method based on the Constructal Theory. The optimization of the position, size, and aspect ratio of EGTBs was done for two types of standard elliptical conduits of different geometries, uniformly distributed. Two different objective functions are analyzed: minimum maximum temperature on the metal and maximum heat evacuation efficiency. The outcome of this work establishes that the use of elliptical conduits of aspect ratio 2:5 leads to improvement in the thermal performance of cooled blades. As compared with circular conduits of the same area, elliptical conduits allow transfer of a greater amount of heat; with a correct design, they enable a lower maximum temperature on the metal. Besides, the constructal designs obtained in this study for the minimum maximum relative temperature \(\tilde{T}_{\rm{max}}\) or maximum heat evacuation efficiency ξ were not identical.

It is experimentally shown that diverging nozzles with a cone angle of 12^o -14° and a length of 10-15 mm provide the finest atomization of metastable superheated liquid with a submicron droplet fraction at a level of 65-70%.

The results of this study can be implemented in many fields of the industry where dryers and silica sand are used. The application of the temperature relations can improve the revenue by increasing the quality of drying material. For further study, it is recommended to apply various temperatures on different types of materials while defining the effect of evacuation pipe on drying material is advised.