Thermophysics and Aeromechanics最新文献

In endoreversible cycles, irreversibility is considered only between the systems and their surroundings. In this paper, the modelling of heat interaction with a solar regenerative Brayton cycle is studied with regard to various fidelities based on the first and second laws of thermodynamics. The effect of linearity and nonlinearity related to both convective and radiative heat interactions with the hot and cold reservoirs as well as radiation losses of the solar Brayton cycle have been studied, which is complementary to similar attempts for Carnot cycle. Total efficiencies are compared between various implemented models. The effect of temperature of six critical sections of the whole engine on the collector efficiency, cycle thermal efficiency and the system total efficiency has been studied. Besides, a comparison is done for a real example to show the importance of considering the nonlinearities for calculating thermal efficiency of a closed-loop Brayton cycle at different hot source temperatures, as well. These would help a more efficient analysis of the emerging power cycles that can accelerate progress toward low-carbon power production.

A nonisobaric supersonic jet of vibrationally excited carbon dioxide exhausting from converging axisymmetric nozzles with the diameter ranging in a wide interval (from 0.03 to 114 mm) is studied experimentally and numerically. Numerical simulations are performed within the framework of the two-temperature approach with the use of the Landau–Teller relaxation equation for each vibrational mode of carbon dioxide molecules. The simulations reveal that the vibrational nonequilibrium of molecules affects the gas-dynamic structure of the jets in the temperature range of 300–900 K, and this effect is verified experimentally. Vibrational excitation of molecules in the experiment is ensured by means of gas heating. The effect of vibrational nonequilibrium is manifested as a reduction of the amplitude of the static pressure in wave structure cells and as a reduction of the longitudinal size and number of wave structure cells as compared to the case of an equilibrium supersonic flow. It is shown that the maximum effect of nonequilibrium is observed in jets exhausting from the nozzle with a diameter of ≅ 3 mm.

In the present paper, a computational study of the influence of solar and thermal radiation on the formation of wind and temperature conditions in urban environment is carried out using the example of an urban area of Krasnoyarsk in winter. For calculations, a developed microscale mathematical model of urban atmosphere was used. The calculation results showed that the presence of radiation in the daytime leads to an increase of temperature and average speed of wind, as well as to the formation of an unsteady wind regime in urban environment.

The effect of barodiffusion on the dynamics of gas bubble growth in a highly viscous, gas-saturated magmatic melt undergoing rapid decompression is studied. A mathematical model of the process, which represents a joint dynamic and diffusion problem, is proposed. It is shown that as the bubble grows, a diffusive boundary layer is formed around it, leading to the appearance of a large viscosity gradient in the melt and, as a consequence, to a large pressure gradient. A semi-analytical solution of the problem based on the existence of a quasi-stationary state for the bubble growth process is found. It is shown that the effect of barodiffusion is significant at the initial and transient stages of the process. Its influence decreases with time and disappears completely at the stage of diffusion.

Nonlinear waves in a rectilinear rivulet flowing down a vertical plate are investigated on the basis of the developed semi-analytical model. The characteristics of nonlinear quasi-two-dimensional steady-state traveling waves are obtained numerically. Another wave family (the family of double-humped waves), branching off from the first family by doubling the spatial period, is found for small values of the wave number. It is shown that steady-state traveling waves do not exist in a certain narrow range of the excitation frequency, but a pulsating wave mode is realized.

The present work deals with the design optimization of different vehicle configurations for planetary entry. Choosing the aerothermodynamic characteristics of heat flux and drag as the objective function we have analyzed and simulated the effects of atmospheric resistance on planetary entry vehicles in the rarefied atmosphere. We have utilized the SPARTA (Stochastic PArallel Rarefied-gas Time-accurate Analyzer) DSMC simulator for our simulation. The optimization is carried out with the help of MATLAB optimization module. We have simulated the descent of the existing design of planetary entry vehicles and compared the aero-thermal characteristics of each entry vehicle. The present work demonstrates two of the planetary atmospheric conditions, the first one is Earth, and the later one is Mars. The vehicle geometry is then optimized according to the planetary atmospheric conditions. This work ultimately provides insight into how the effects of geometrical parameters play a pivotal role in the aerothermal loads of planetary entry vehicles.

The results of an experimental study of the thermal expansion of gallium garnets Gd₃Ga₅O₁₂, Gd_3.04Sc_1.8Ga_3.16O₁₂, and Ca₃Nb_1.5Ga_3.5O₁₂ in a wide temperature range (293.15–1473 K) are presented. A noticeable effect of niobium in the structure of gallium garnets on the thermal expansion coefficient has been found. The temperature dependences of the volumetric properties have been obtained.

The flow of liquid over the corrugated sheets of regular packings largely determines the processes of heat and mass transfer in distillation columns. An important role in the distribution of liquid over the structured packing sheets is played not only by the characteristics of packing surface microtexture, but also by the drip point location in the liquid distributor relative to the sheets in the structured packing plugs. It has been established that even a slight displacement of the drip point relative to the channels of a regular packing can lead to noticeable redistribution of liquid over the packing sheets. Knowledge of the detailed structure of the flow in the distillation column allows better understanding of the physical nature of the mechanisms that control the flow. It is shown experimentally that the negative impact of the uncertainty associated with the drip point position on the liquid distribution under a layer of a structured packing can be reduced using liquid redistributors in the form of inclined plates with horizontal microtexture.

Here we present the results of thermodynamic and kinetic calculations as well as experimental studies of plasma processing of rubber powder of recycled tires, demonstrating the promise of using the plasma-chemical technology for gasification of this powder with the production of energy gas. The results of experiment and calculations were compared and showed good agreement.

The problem of laminar mixed convection is considered in a flat vertical channel with upward and downward flow and liquid heating, i.e., for the cases of coincidence of the directions of free and forced convection, as well as their opposite directions. The system of equations of motion, continuity, and energy is solved by the finite difference method. Data on the profiles of the longitudinal velocity, temperature, and Nusselt numbers at the upward and downward flows are obtained. An explanation is given for the peculiarities of these values under the influence of buoyancy force. All components of the hydraulic resistance coefficient for the upward and downward flows are analyzed. The influence of the Prandtl number and the velocity profile at the channel input on the hydrodynamic and thermal characteristics of the flow is considered.