查看更多>>摘要：From the viewpoint of thermodynamics at a finite time, the limiting possibilities of mechanical separation systems are considered. Lower limits of energy expenditure are obtained for separation systems with a given performance. It is shown that these expenditures do not tend to zero, when one of the components of the mixture being separated tends to a unit concentration. The estimates obtained are used to analyze multistage separation systems with recycles and, in particular, isotope separation systems. For each systems, relationships between the flows, contact surfaces, and the stage number are found, which follow from the conditions of minimum dissipation under the assumption of the constancy of the enrichment factor. A condition of the optimality of the order of separation of multicomponent mixtures in mechanical systems has been obtained.
查看更多>>摘要：A thermodynamic analysis has been performed for the operation of piston machines using ideal and real gases as a working body in direct and inverse Carnot cycles. An interrelationship has been established between the fugacity coefficient of the working body (real gas) and the efficiency of a piston thermal machine. Calculating formulas have been obtained for identifying the dependence of the efficiency of such machines on the characteristics of their working body. Verification has been conducted for the proposed method of thermodynamic potentials and the relations obtained on its basis connecting the actual efficiency of a thermal machine with the fugacity coefficient of its working body.
查看更多>>摘要：A mathematical model has been constructed and investigated by numerical methods for unsteady gasless combustion of a binary mixture under the conditions of thermocapillary flow of the melt of one of the components. Various unsteady regimes have been identified for the propagation of a synthesis wave depending on mass concentrations of components and the initial porosity of the mixture. An investigation has been made into the process of forming the macrostructure of synthesis products in a self-sustained oscillating regime of combustion. A possibility in principle has been shown for combustion of mixtures with excess of a low-melting component at a higher rate than in combustion of a mixture of a stoichiometric composition.
Gimaltdinov, I. K.Bayanov, I. M.Stolpovskii, M. V.Chiglintseva, A. S....
8页
查看更多>>摘要：A mathematical model of confined combustion of a gas hydrate has been presented that assumes full evaporation of water on the "hydrate-gas" boundary. In accordance with this assumption, the processes of diffusion of the gas through a liquid layer and the formation of a foam structure are excluded from the theoretical model, which leads to its significant simplification. The influence of the transfer coefficient on the temperature and concentration fields of the components of the gas mixture, and also their action on the intensity of decomposition of the gas hydrate have been analyzed based on numerical calculations. It has been established that both the intensity of combustion of methane and the intensity of decomposition of the gas hydrate grow with increase in the values of transfer coefficients. Here, the speed of decomposition of the gas hydrate decreases with time. It has been shown that in the case of confined combustion a burnout regime is likely to occur, with the hydrate decomposition occurring due to the heat stored in the gas mixture.
查看更多>>摘要：Recent studies reveal that an internal coolant crossflow plays an important role in the flow field and film cooling performance in the near-hole region. In the present paper a single array of cylindrical holes with crescent-shaped blocks downstream is considered. The cooling performance under the quiescent coolant plenum conditions with a perpendicular coolant crossflow are studied numerically at the blowing ratios 0.5-2.5. The height-to-diameter ratio of the crescent-shaped block varies from 0.25 to 1.0 with an interval of 0.25. Based on the numerical results, it may be deduced that a perpendicular crossflow induces an asymmetric pair of in-hole vortices and a biased coolant coverage on the surface downstream of the hole exit. However, the bias direction depends on the value of the blowing ratio. Compared with the quiescent plenum case, the perpendicular crossflow reduces the cooling performance, and the benefits result from the crescent-shaped block downstream.
查看更多>>摘要：Consideration has been given to laminar flow of a liquid with constant properties in a channel on whose surface the temperature or density of the heatflux vary with time by a periodic law. An analytical solution to the problem of convective heat transfer in general form has been obtained, using which it has been established that heat transfer ceases to depend on the axial coordinate away from the inlet of the heated portion. Relations have been found to calculate stabilized heat transfer. It has been shown that at a high frequency of the process, a nonstationary stabilized heat-transfer coefficient varies noticeably over the period, however, its stabilization with time occurs as the frequency is reduced. Data on fully stabilized heat transfer have been given for various shapes of the channel, flow regimes, and boundary conditions.
Bykov, L. V.Ezhov, A. D.Martynyuk, L. A.Afanas'ev, D. B....
11页
查看更多>>摘要：A heat calculation is presented for a centrifugal compressor impeller of a small-size composite gas turbine engine. Consideration has been given to the existing approaches to designing centrifugal compressor impellers. A description has been given of the methods of numerical simulation of the thermal state of a polysegment impeller of a composite centrifugal compressor under the action of a thermal load Temperature distribution has been obtained f or each individual element of the design and the assembly on the whole. We have determined the value of the required consumption of cooling air to ensure a standard operation of the compressor in which the values of local temperatures on the product do not exceed permissible temperatures of operation. Conclusions have been drawn on the possibility of using polymer composite materials in heavily loaded components of advanced aircraft engines.
查看更多>>摘要：A mathematical model is formulated, and a finite-difference method and computer programs have been developed that allow effective computer simulation of the process of thermal breakdown of contact films. The system of equations includes the Stefan problem, the equations of electric transfer and of a switched circuit. The axial symmetry of the boundary-value problem conditions is assumed. A finite-difference method in a spherical coordinate system is used for the solution. During the development of the process, the radius of the conducting bridge made of a molten material changes by several orders of magnitude. An effective solution of this problem is the use of a "moving" grid by corresponding replacing the variables. The results of the work can be applied in the practice of research and design of electrical apparatuses and other electrotechnical devices.
查看更多>>摘要：A theoretical investigation of the radial temperature distributions in the upward and downward flows of fluid in the borehole of a production well has been performed. The radial differences between the temperatures at the axis and wall of such a well in the cases of water and oil in it were determined.
查看更多>>摘要：The generalized nonlocal thermoelastic model in the context of Eringen's nonlocal elasticity is applied to investigate the magnetothermoelastic interactions in a rod of finite length placed in a magnetic field with a moving source. With the use of the Laplace transform and numerical Laplace inversion techniques, the governing equations are solved, and the solutions in the time domain are obtained numerically. The distributions of the nonlocal thermal stress, temperature, and the displacement in the rod are obtained and presented graphically. The effects of the rotational speed and the speed of the moving heat source, nonlocal parameter, and the applied magnetic field intensity on the considered variables are discussed in detail.
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Springer Nature