The article presents a model for the formation of a thermodiffusion layer on steels. Thermodiffusion coatings on 45 steel and HVG steel were obtained by a chemical-thermal method in a powder mixture. Studies of layered X-ray diffraction phase and microrentgenospectral analysis of the studied coatings have been carried out. on steel. The obtained results of X-ray diffraction and microrentgenospectral analysis of diffusion coatings confirm the correctness of the model of formation of the diffusion layer and the theoretical prerequisites outlined. The results of the study can be used in the preparation of mixtures for thermal diffusion saturation.

Keywords: diffusion layer, diffusion chrome plating, diffusion coating

When choosing an intensification method, the assessment of thermal-hydraulic efficiency is an important criterion. In this paper, the thermal-hydraulic efficiency of the pulsating method of heat transfer intensification was assessed as applied to an in-line tube bundle. The thermohydraulic efficiency was estimated by comparing the ratio of the increase in the Nusselt number to the increase in the coefficient of friction factor in a pulsating flow compared to a stationary flow. The coefficient of friction factor was determined by numerical simulation in AnsysFluent. The results of a numerical study showed that an increase in the product of the pulsation amplitude and the Strouhal number leads to a decrease in the thermal-hydraulic efficiency at all values of the Reynolds number, while the thermal-hydraulic efficiency is higher at the minimum values of the Reynolds number.

Keywords: Reynolds analogy factor, flow pulsation, heat transfer enhancement, thermal hydraulic efficiency.

Insulating materials are widely used in the petrochemical, energy and other industries. Thermal insulation materials play an important role in the energy saving of district heating systems and in the construction sector. In this work, the influence of the wetting and drying cycle on the thermal conductivity and density of the heat-insulating material is determined by the experimental method. The thermal conductivity of the insulating material was determined by the protected hot plate method. It has been established that after four cycles of wetting and drying, the thermal conductivity and density of the heat-insulating material increase up to 2 and 2.5 times, respectively.

Keywords: thermal conductivity of heat-insulating materials, density of heat-insulating materials, dampening of heat-insulating materials

The accuracy of the calculation and the required computer time significantly depend on the choice of the turbulence model. This paper analyzes three turbulence models SST, k-w SST, and RNG k-e EWT with enhancement wall treatment applied to an in-line tube bundle. The distribution of heat transfer over the beam depth is determined. Velocity profiles in cross sections along the depth of the tube bundle are obtained. As a result of numerical studies, it was shown that the agreement with the experimental data for the SST, k-w SST, and RNG k-e EWT models was 75, 32 and 10%, respectively.

Keywords: turbulence modeling, tube bundles, heat transfer, mathematical modeling

In this work, the effective thermal conductivity of porous materials is studied by a numerical method. A technique for designing an insulating material with specified geometric characteristics is proposed, which makes it possible to predict the thermal conductivity of porous insulation with sufficient accuracy. The design of foamed porous heat-insulating materials was based on the 3D Voronoi tessellation. The effective thermal conductivity of porous media was determined for twenty structures with different geometric characteristics. The thermophysical properties of the material corresponded to melamine. To verify the numerical solution, the effective thermal conductivity of the melamine sponge was determined experimentally. One regular structure and three irregular structures were compared with each other. The porosity of the insulating structures ranged from 0.722 to 0.987, the fiber diameter ranged from 0.0489 mm to 0.1259 mm. A theoretical solution is proposed for determining the effective thermal conductivity of regular structures. The technique proposed in the work can be used to design heat-insulating materials based on additive technologies, with specified heat-insulating and structural properties.

Keywords: effective thermal conductivity, porous structure, porous insulating material, 3D Voronoi tessellation

The paper presents an experimental study of the effect of flow pulsations on heat transfer in bundle of pipes. The regularities of heat exchange in bundle of pipes under the pulsation regime of the flow are obtained experimentally. The maximum intensification of heat exchange was 3.23 times.

Keywords: heat transfer, pulsation flow, corridor tube bundle, intensification heat transfer, shell-and-tube heat exchanger

Porous media can be used as heat transfer intensifiers in the petrochemical, refrigeration, food, energy, and other industries. In this paper, heat transfer in a porous medium with a pulsating flow is studied numerically. The simulation was carried out in the AnsysFluent software product. The porous medium was represented as a two-dimensional channel with square tubes. The working medium was air and water. The heat transfer and hydraulic resistance of a porous medium in a pulsating flow are determined for different porosity and fiber diameter depending on the Reynolds number, Prandtl number, frequency and amplitude of pulsations. It is shown that with an increase in the intensity of pulsations, an increase in heat transfer occurs. Heat transfer intensification essentially depends on regime and geometrical parameters. Several empirical correlation are proposed for calculating heat transfer and the degree of heat transfer intensification for symmetric and asymmetric flow pulsations. The thermal-hydraulic efficiency is determined for the same Reynolds numbers and powers for pumping the heat carrier in a porous medium with symmetric and asymmetric flow pulsations.

Keywords: heat transfer, pulsation flow, porous media, mathematical modeling, thermal-hydraulic efficiency