Home – Home – Jornals – Advanced Search

Dynamic characteristics of an ohmic heater intended for heating the working-gas flow in hot-shot wind tunnels have been experimentally studied. The experiments were per-formed on a specially designed test facility. Experimental data on the dynamic characteristics of the heater were obtained.

A mathematical model was developed for conjugate heat transfer in a heterogeneous system "solid body – gas-liquid medium" with account for vapor generation at the surface of hot metal cylinder with cooling by a longitudinal water flow. Results are presented for numerical parametric calculations for influence of thermophysical and hydrodynamic characteristics on the pattern of vapor generation at the cooled cylinder surface.

This paper presents experimental results of investigation of high-intensity cooling of high-temperature metal heater by subcooled ethanol flow. The experiments have proved the presence of self-excited pressure pulsations with amplitude of 1.15 MPa, arising in ethanol. Expanding real signals of the sensors by the Hilbert–Huang trans-form has resulted in the intrinsic mode functions. Analysis of these functions and the high-speed video shooting results allows identifying the basic frequencies and me-chanisms of pressure oscillations. Comparison of the results with the data of film cooling and bubble boiling on the cooled heater has shown that maximum values of non-stationary heat-transfer coefficients for the self-excited oscillations and for the bubble boiling are the same.

Dynamics of a cavitation bubble is considered at its strong expansion and sub-sequent compression. The bubble is formed by merging of two identical spherical cavitation microcavities in the pressure antinode of the intensive ultrasonic standing wave in the half-wave phase with negative pressure. Deformations of bubble and deformations of radially converging shock waves occurring therein at bubble compression are studied depending on the size of microcavities forming the bubble. It is found that compression of the medium in the bubble by the converging shock wave is kept close to the spherical one only in the case, when the radius of merging microcavities is 1800 times smaller than the radius of the bubble formed by merging at the time of its maximal expansion.

The paper presents the experimental results for velocity and tempertaure disibutions of the condensed phase in a plasma jet from the plasmatorch PNK-50 (design from ITAM SB RAS, Novosibirsk). The plasma jet is used at different operational modes for thermal spraying of nickel alloy powder PR-NKh16SR3. The measurements for aver-age velocity (230–280 m/s) and temperature (2290–2410 K) of sprayed particles were matched to data on microhard-ness (630–710 HV) and porosity (1.7–13.5 %) of samples. Results were transferred into coating properties maps plot-ted in coordinates "arc current vs. torch offset" and "particle velocity vs. particle temperature". Experiments demons-trated the change in parameters of condensed phase in the jet after performimg of maintenance job for the plasma-torch. We propose the method for adjusting the operational parameters of thermal spraying equipment using optical methods of control for particle velocity and particle temperature. The exemplary apparatus function of the plasmatorch was plotted; an approach is proposed for optimization and transfer of spraying technology of coatings with specified properties between equipment from different manufacturers, different class and power.

The present study investigated fluid flow and natural convection heat transfer in an enclosure embedded with isothermal cylinder. The purpose was to simulate the three-dimensional natural convection by thermal lattice Boltzmann method based on the D3Q19 model. The effects of suspended nanoparticles on the fluid flow and heat transfer analysis have been investigated for different parameters such as particle vo-lume fraction, particle diameters, and geometry aspect ratio. It is seen that flow beha-viors and the average rate of heat transfer in terms of the Nusselt number (Nu) are ef-fectively changed with different controlling parameters such as particle volume fraction (5 % ≤ φ ≤ 10 %), particle diameter (d_p = 10 nm to 30 nm) and aspect ratio (0.5 ≤ AR ≤ 2) with fixed Rayleigh number, Ra = 105. The present results give a good approximation for choosing an effective parameter to design a thermal system.

The paper deals with justification of the formula for the latent heat of phase transition of the first kind, taking into account superheating and subcooling of the formed two-phase system, in application to the solution of Stefan problem in semitransparent ma-terials.

The influence of mixed convection boundary layer flow of a viscoelastic fluid over an isothermal horizontal circular cylinder has been analyzed. The boundary layer equa-tions governing the problem are reduced to dimensionless nonlinear partial differential equations and then solved numerically using Keller-box method. Skin friction coeffi-cient and Nusselt number are emphasized specifically. These quantities are displayed against curvature parameter. Effects of mixed convection parameter and radiation-conduction parameter on skin friction coefficient and Nusselt number are illustrated through graphs and table. The boundary layer separation points along the surface of cylinder are also calculated with/without radiation, and a comparison is shown. The presence of radiation helps to reduce the skin friction coefficient in opposing flow case and enhances it for assisting flow case. The increase in value of radiation-conduction parameter helps increase the value of skin friction coefficient and Nusselt number for viscoelastic fluids. The boundary layer separation delays due to thermal radiation.

The results of mathematical modeling of the thermal state of combustion chambers with regenerative cooling for ramjet engines of promising flying vehicles are presented. The cooling of combustion chambers by the gasification products of a combined charge of the energy-intensive material is considered, where the polyethylene is used as a stuff, and the HMX-based compounds are used as the active substance. The flow rates of the cooling eneregy-intensive material are determined, which provide acceptable levels of temperatures of combustion chambers at various modes of engines operation are determined.