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  • Mathematical modeling of non - stationary cooling 3d-printed multilayer objects

    Temperature regimes of heating and cooling in three-dimensional printing are the most significant part of the technological solution in the production of products in any industry: from printing parts for aviation and rocket engineering to the construction of buildings or the manufacture of prosthetic human bones. The paper considers a simple and reliable method for obtaining calculated values of non-stationary temperatures and heat fluxes during layer-by-layer printing of products with various thermophysical properties and imperfect contact between layers, which does not require special software shells and large machine resources for calculations.

    Keywords: non-stationary heat transfer, multilayer printing of products, additive manufacturing, 3D printing of products, heating and cooling of multilayer products, layer-by-layer deposition, optimization of the temperature regime of printing products

  • Heat transfer in boundary layers on radiating surfaces with gradient flow

    Numerical solution to the problem of heat transfer in boundary layers transparent Strip on the walls, exposed on the opposite side of the radiant-convective heating. Study of influence of mode parameters on heat transfer process of tasks carried out in the case of the gradient flow and included the most typical variants of transportation processes. The purpose of the real work is studying of processes of transfer at non-linear boundary conditions, obtaining approximate and analytical decisions non-linear warm and a mass transfer, establishment of communication between regime parameters and physical interpretation of results of a research. Also some conjugate problems of heat exchange in the presence of radiation are studied. The analysis received decisions is carried out. The executed research allowed to establish that existence of a transversal overflow of heat in a wall and also the radiation of a surface have significant effect on the nature of distribution of the surface temperatures.

    Keywords: boundary layer, convection, radiation, gradient flow, conjugate heat transfer

  • Boundary layers on the walls, exposed on the opposite side to the heating by convection and radiation at the same time

    Numerical solution of the problem of heat transfer in the boundary layers of transparent gas wall, exposed on the opposite side of radiant-convective heating. The energy dissipation due to viscosity is negligible, the wall is thermally thin, and the physical properties of the medium do not depend on temperature. The aim of this work - finding the local heat transfer coefficients (Nusselt number) needed for the analysis of heat exchangers. When solving the problem of nonlinear transfer functions linearizing method is used, based on which numerical scheme for computer calculations was constructed. The intensity of the local heat transfer in the boundary layer is determined by the number Kx = Nux / Nux0, where the value Nusselt numbers refer to the conditions under consideration of the problem of heat exchange (Nux) and constant surface temperature (Nux0). From a physical point of view, non-dimensional parameter Kx is a measure of the intensity of heat transfer in the boundary layer on a nonisothermal surface compared to heat transfer when the wall temperature everywhere the same. The analysis of this research showed that in radiative-convective heating number Kx on the front edge of the plate takes the largest value of Kx ≈ 1,37 corresponding to a constant heat flux on the wall. It is also shown that the relative temperature of the incoming flow has a significant impact on the value of Kx. The effect of this setting is especially evident in the processes when dominated by the effect of radiation and related to the nonlinearity of the transfer processes. The analysis revealed the influence of basic parameters of heat transfer on the development of transport processes in the boundary layer by heating radiation and convection simultaneously.

    Keywords: Boundary layer, convection, radiation, radiation-convection heating, high temperature gas invironment, linearizing function

  • The effect of decrease gas load consumers on optimally pressure of gas supply source

    The hydraulic test of perfect dead-end gas network with gas supply source and one consumer is performed by two ways: 1) natural experiment 2) the modelling of system in the specific programmatic sphere. Comparative analysis of natural experiment with the software simulation is performed. The effect of decrease gas load of consumers on optimally pressure of gas supply source is studied. The impact of the selective method of the calculation on the optimal huidraulic mode choice of the network function is analysed. The grafic relations are formed. The coefficient of optimum pressure is calculated and that makes it possible to determine the most adequate pressure of gas as it leaves the gas supply source on the basis of the pressure requirements in gas-based units.

    Keywords: Gas supplying, the reliability of gas distribution system, natural experiment, the software simulation

  • Problems of transition to the closed systems of a heat supply

    Discusses the problems of transition from open to closed systems of connection of consumers to the heat network. On the basis of fundamental analysis of the advantages and disadvantages of the various connection schemes of buildings comparison of energy efficiency and reliability of open and closed systems of a heat supply. Basic conditions guaranteeing the possibility of the device of the closed heating systems in buildings, присоединненных to thermal networks on the open circuit. Shows the need for reconstruction of water supply systems and power supply of the building when it transferred from open to closed scheme accession to the heat network.

    Keywords: heat supply, district heating, closed heat supply scheme, open circuit heat supply, individual heating unit, reliability of heat supply, energy efficiency.