PSI - Issue 36

Anatolii Pavlenko et al. / Procedia Structural Integrity 36 (2022) 3–9 Anatolii Pavlenko, Andrii Cheilytko, Serhii Ilin, et al. / Structural Integrity Procedia 00 (2021) 000 – 000

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1. to analyze the existing methods of creating predicted porous insulation structures; 2. determine the heat flow through closed porous structures; 3. determine the thermal permeability of the porous material, showing the distribution of the porosity of the material per pore in the heat pipe; 4. to analyze the influence of pores in the material on thermal conductive properties; 5. to obtain an equation describing the transfer of thermal energy in open porous constructions. 3. Results of research Porous materials include virtually any solid material used in construction and energy conservation: lightweight and cellular concrete, foam glass, brick, expanded polystyrene products, perlite products, etc. Also porous constructions include disperse materials (expanded clay and hydrosilicates) and materials having a capillary-porous structure (glass, mineral wool). With such an abundance and variety of materials relating to porous materials, there is an even greater number of theories and criteria that describe certain processes. It is worth noting that porosity, as an indicator of change in the effective coefficient of thermal conductivity of porous material, is not a generalized indicator. With the same porosity, the effective thermal conductivity of one material may differ more than twice. This is due to the different geometric sizes of pores and their different numbers. Also, for ducted open pores, it is necessary to consider the change in the effective coefficient of thermal conductivity of the material from the thermal conditions of operation (temperature gradient on the material). The effective thermal conductivity of the porous materials will be greatly influenced by the convective fluxes inside the pores. For taking into account its influence during the passage of heat flux through the porous structure, a study of the convective component of the effective coefficient of thermal conductivity of electrically conductive thermal protection structures was carried out. For models have been developed that take into account the full effective coefficient of thermal conductivity, taking into account the convective and radiation components. According to the obtained data, the difference between the convective component of the effective coefficient of thermal conductivity between the corridor and the chess arrangement of channels and in pores up to 2 mm in size is practically absent. Data studies have made it possible to find a rational algorithm for constructing complex complex models for calculating the effective thermal conductivity of porous materials. As the diameter of the spherical pore decreases in the insulating material, the movement of the air current lines in the pore changes to a spiral, and the velocity of convective air flows in the pore decreases. Spiral movement current lines are explained by the self-organization of a convective cell, similar to a Benard cell. The maximum value is the heat flux in the highly porous thermal insulation material gets on the front the surface of the spherical pore and becomes larger than the heat flux itself material. Increase in thermal flow is explained by the fact that the heat flux is influenced by convection it unfolds from the poles and partly goes in the opposite direction. There is summed up by the heat flux that goes to the front of the pore. The porous structure in these materials significantly influences their thermal conductivity. Determination of the dependence of the thermal conductivity coefficient of the porous thermal insulation material on the temperature is a necessary condition for the independence of the factors of the experimental design method to find the regression equation of the effective thermal conductivity coefficient. For the energy saving of both industrial enterprises and residential buildings, it is necessary to determine the thermal resistance of the enclosure structure. In this case, the largest problem will be large-porous materials and structures with voids, in which due to the uneven distribution of pores and convective air flows in porous channels, additional heat transfer will occur. Therefore, determining the effective coefficient of thermal conductivity of porous structures, ie such coefficient of thermal conductivity, which includes all methods of transferring thermal energy in porous material, is a separate empirical problem. We propose to solve this problem by analytical and empirical method. For porous thermal insulation material or structural elements of buildings, structures or power equipment, the transfer of thermal energy through the porous structure will be characterized by an effective thermal conductivity factor or thermal resistance. The heat flux through the porous structure can be divided into many heat fluxes whose lateral boundaries are formed by the projection of the lateral pore surface with a diameter. Let us call a single such heat flux a heat tube in a porous material. It is proved that the decrease in the coefficient of thermal conductivity of