A. Guelailia1, A. Khorsi2, S.A. Slimane1, A.M. Boudjemai1, A. Smahat1, P. Kumar3 1Centre of Satellite Development, Oran, Algeria 2University of Sciences and Technology Mohamed Boudiaf, Oran, Algeria 3Birla Institute of Technology, Mesra, India
Keywords: computational fluid dynamics, heat and mass transfer, turbulence, film cooling
The present paper aims to investigate the effect of longitudinal curvature on film cooling performance through a single row of cylindrical holes. Four different longitudinal curvature cases are considered by changing the curvature heights. Detailed film effectiveness distributions are presented for several blowing ratios. The ANSYS CFX has been used for this computational simulation. The turbulence is approximated by a shear stress transport (SST) model. The numerical results are compared with experimental data.
Temperature distribution was measured during the development of natural convection in a vertical rectangular cavity 364 mm high, 185 mm wide and 40 mm deep, filled with a lead-bismuth melt and with the temperature difference maintained on its vertical sidewalls. The initial temperature difference was set by changing the electric power supplied to the heated wall, and, accordingly, by changing the heat removed from the opposite wall. The measurements were carried out in a quasi-stationary regime of free convection, when the flow parameters and temperature distributions over the cavity cross-section were constant for several hours. As a result of the performed measurements, the temperature profiles along the width and depth of the rectangular cavity were obtained.
The processes of heat transfer in air and liquid plate-finned heat exchangers of a thermoelectric cooling system are considered. The flow modes in interfin channels are analyzed, and the local heat-transfer coefficients are determined. From the numerical solution of the two-dimensional thermal-conduction problem, the dependences of the thermal resistances of the heat exchangers on their geometric parameters are obtained. The influence of thermal resistances on the cooling capacity and on the coefficient of performance of the thermoelectric cooling system is determined. Optimization of heat exchangers in terms of fin thickness and interfin spacing has been performed.
A numerical method of inductive drag reduction by means of improving the aerodynamic performance of the tip elements of lifting systems is presented. The method allows one to optimize the distribution of the intensity of free vortices at the wing tips in the Trefftz plane for a prescribed lift force and unchanged base wing geometry. Optimization calculations of various lift systems are performed, including the STR-40DT short-range airplane developed at the Chaplygin Siberian Scientific Research Institute of Aviation (SibNIA). Good agreement of the numerical and experimental results is noted.
Heat transfer and critical heat flux on flat rectangular (16´24 mm) heat-releasing surfaces (HS) made of aluminum alloy D16 and modified by microarc oxidation (MAO) were investigated. Two types of coatings made using different electrolytes were studied: KOH and phosphates. Coatings had good adhesion to the HS and high dielectric strength. The thickness of coatings was 20 and 7 µm, respectively. The studies were carried out using freon R21 under conditions of natural convection with horizontal orientation of the HS. For comparison, measurements were carried out on identical working sections without a modifying coating: the first section was polished; the second one was ground with a roughness of 20 μm. It was shown that the heat transfer intensity on the modified HS was not lower than on the HS polished with a roughness of 20 μm, and it was almost twice as high as that on the polished HS. The values of the critical heat flux on the studied surfaces were almost the same. The use of these types of coating provides electrical insulation of the heat-releasing element without compromising the efficiency of heat removal.
The paper presents the calculated spectral densities of radiation energy fluxes and the emissivity factors of combustion products from model liquid and solid propellant rocket engines for the conditions of the combustion chamber, nozzle, initial and main sections of the plume. The influence of temperature non-equilibrium between gas and particle flows on the spectral and integral emission characteristics of combustion products is investigated. The calculated results of this work are compared with experimental and computed data of other authors. Particular attention is focused on the nature and level of emission at different locations of outflowing combustion products. The results of the work may be used to choose a section of the spectrum when determining the temperature of combustion products by pyrometric methods.
A.A. Morozov
Kutateladze Institute of Thermophysics SB RAS, Novosibirsk, Russia
Keywords: gas expansion dynamics, pulsed laser ablation, direct Monte Carlo statistical simulation, Gaussian beam, flat-top beam
In laser ablation, the nonuniform distribution of energy across the laser beam leads to a nonuniform heating and evaporation of the material from the irradiated surface. The influence of nonuniform temperature and that of the nonuniform flux of evaporated material from the surface on the laser-plume expansion dynamics during the nanosecond laser ablation in vacuum were studied. It was assumed that the surface temperature depended linearly on the laser radiation energy. Direct Monte Carlo simulation of pulsed gas expansion for a flat-top laser beam and for a Gaussian beam has been carried out under the assumption of no absorption of laser radiation in the plume. For the flat-top beam, the surface temperature proved to be areally uniform over the entire irradiation spot, whereas for the Gaussian beam, the temperature varied along the spot radius. It is shown that for both beams, the final distributions of particles in the plume are almost identical. However, in the case of the Gaussian beam the plume moves a little faster in comparison with the flat-top beam, which circumstance leads to an increased kinetic energy of particles passing through the time-of-flight detector by 2-4 %.
M.A. Vasyutin, E.V. Danilova, N.D. Kuzmichev
Ogarev Mordovia State University, Saransk, Russia
Keywords: heat transfer, inhomogeneous heat equation, boundary value problem, beryllium copper, NbN film
The process of heat transfer in NbN film while applying a pulse of current is considered using the 2D inhomogeneous heat equation. The boundary value problem is solved for a longitudinal cross-section in the film; the heat transfer problem is solved for a system “contacts-film-substrate-thermostat”. The temperature evolution for the film cross-section since the pulse start till the temperature relaxation is visualized. The maximum film heating is evaluated. It was shown that the contact material (beryllium cooper BeCu) ensures the effective heat drainage from a superconductive film existing in the resistance mode while passing a high density current through the film. The developed simulation method and the material for the contacts can be used for other types of metallic or semiconductor films.
Analytical formulas are derived for describing the direct pyrolysis of methane in a bubble column loaded with a catalyst molt. This math can be implemented in research or commercial computer codes aimed to multiparametric optimization of the metal bath (with consideration of its cost and catalytic performance), setup dimensions and productivity. These analytical expressions can be used also for validation of numerical codes.
On May 27, 2022, Academician of the Russian Academy of Sciences Dmitry M. Markovich, a well-known scientist, scientific administrator, Director of the Institute of Thermophysics SB RAS, Chief Academic Secretary of the SB RAS, member of the Presidium of the Russian Academy of Sciences, celebrated his 60th anniversary.
