In this paper, heat transfer in a staggered tube bundle under steady and pulsating flow conditions is analyzed using numerical simulation. The numerical study was conducted for tube bundles with 5, 10, and 15 longitudinal rows. The Reynolds number Re and the Prandtl number Pr were 3400 and 3 respectively. Flow pulsations were characterized by both symmetrical and asymmetrical reciprocating flow. The effect of pulsations was estimated using the product of the relative dimensionless pulsation amplitude and the Strouhal number A/DSh, which corresponded to values of 0.1, 0.25, and 0.4. The numerical study was conducted using Ansys Fluent. The flow hydrodynamics in the tube bundle was described using the Reynolds-averaged unsteady Navier-Stokes equations. Based on the results of numerical simulation, it was found that the effect of pulsations on heat transfer in the tube bundle varies depending on the number of longitudinal rows. It is shown that an increase in the number of rows leads to a decrease in the Nusselt number ratio in a pulsating flow compared to a steady flow. It is established that the thermal-hydraulic efficiency increases with an increase in the number of rows. It is shown that asymmetric pulsations are more effective than symmetric ones for intensifying heat transfer when taking into account energy costs

Keywords: heat transfer intensification, staggered tube bundle, heat transfer, numerical simulation, flow pulsations

This paper discusses the influence of the turbulence model selection in predicting heat transfer in tube bundles in two- and three-dimensional settings. Numerical studies were performed for in-line and staggered tube bundles using Ansys Fluent software with three RANS turbulence models (k-ω SST, RSM EWT, and RNG k-ε) and a laminar solver. The tube lengths l in three dimensions were 0.5D and 3D, with a fixed tube diameter D. The Reynolds number Re ranged from 100 to 2900. The results showed that the turbulence model selection affects the qualitative flow pattern in tube bundles, with two-dimensional structures predominating in the flow regardless of the turbulence model selection. Therefore, the tube length has virtually no effect on the ability to predict heat transfer intensity. It is shown that when using the laminar solver, the effect of the bundle tube length can be significant depending on Re and the bundle layout. Good agreement with experimental data is obtained for the RSM EWT and RNG k-ε EWT models. For a staggered bundle, when choosing the k-ω SST model, satisfactory agreement with experimental data is observed, while the heat transfer of the in-line bundle is significantly underestimated. The use of the laminar solver in a steady-state formulation is justified for a pronounced laminar flow, at Re < 1000 with a further increase in Re, it is necessary to use a unsteady formulation with sufficient time and mesh resolution.

Keywords: convective heat transfer, in-line tube bundle, staggered tube bundle, computational simulation, turbulence modeling

The work is devoted to the study of the temperature distribution and equivalent voltage on the surface of a thermal radiation receiver during experimental and computational series. The experiments showed a qualitative and quantitative coincidence of the temperature data obtained by thermal imaging with the results of numerical modeling. The average error was 0.5℃, with a maximum deviation of 1.5℃ at individual points, which is due to edge effects and thermal insulation features. The computational model reproduces the main characteristics of the temperature field, including the effect of shielding, using a relatively low density of the computational grid. As part of the verification of the numerical model, the analysis of grid convergence was carried out, as well as the control of residuals and control of solution parameters were performed.

Keywords: heat exchanger, numerical and analytical calculation, convective and radiant heat transfer, efficiency improvement, outgoing flue gas, heat recovery, gas-liquid heat exchanger, numerical modeling, mathematical model, ANSYS Workbench software

A two-dimensional coefficient inverse problem of thermal conductivity for a finite functionally graded cylinder is investigated. The thermal conductivity coefficient is considered to be variable along the radial and axial coordinates. The direct problem of finding the temperature distribution at different moments of time with known boundary conditions and the thermal conductivity coefficient is formulated in a weak statement and solved in the FreeFem++ finite element package. The influence of various two-dimensional power laws of the thermal conductivity coefficient on additional information (the temperature of the outer surface of the cylinder) is investigated. A projection-iteration scheme is constructed to solve the inverse problem. The thermal conductivity coefficient is presented as the sum of the initial approximation and the correction function specified as an expansion in a system of polynomials. At each stage of the iteration process, the expansion coefficients are calculated from the solution of the system of algebraic equations obtained by discretizing the operator equation of the first kind. The results of computational experiments on restoring various two-dimensional laws of change in the thermal conductivity coefficient are presented.

Keywords: functionally graded cylinder, finite element package FreeFem++, identification, thermal conductivity coefficient, inverse problem, iterative-projection approach, operator equation

Radiative cooling is an innovative and highly promising passive cooling technology that allows surfaces to dissipate heat via infrared radiation directly into the cold outer space. Unlike traditional cooling methods that require an external energy source, radiative cooling operates autonomously, offering a sustainable and energy-efficient alternative for temperature control. This natural process has attracted considerable attention in recent years due to its potential to mitigate the growing energy demands associated with air conditioning and refrigeration, which contribute significantly to global energy consumption and environmental degradation.

Keywords: radiation cooling, temperature, atmospheric window, air conditioning, energy efficiency, passive cooling, calcium carbonate, barium sulfide, boron nitride, titanium dioxide

Using numerical modeling, a study of heat transfer and hydrodynamics in plate heat exchangers with corrugated fins was carried out, while the height of the corrugation profile varied from 2 to 4 mm. The influence of profile height on heat flow and pressure drop was studied. It was revealed that an increase in the profile height leads to an increase in heat flow up to 34.05% and pressure drop up to 54.54%.

Keywords: corrugated heat exchanger, cooling system, microelectronics, profile height, heat flow, pressure drop, heat transfer, hydrodynamics, calculation, numerical modeling

Using numerical modeling, we performed studies of the influence of the angle of inclination of the plates of the regenerative heat exchanger element on the heating time and pressure drop. The studies were conducted for models of heat exchange elements with lengths of 6 and 20 mm. Depending on the length of the element, the angle of inclination of the plates was: 10°, 20°, 30°, 40° (at L=6 mm) and 3°, 6°, 9°, 12° (at L=20 mm). At the boundary of the calculation area, the air flow velocity and temperature were established, namely 1 and 3 m/s, and 303 and 973 K. The research results demonstrated that increasing the angle of inclination of the plates helped reduce the heating time of the regenerator by 38.56-49.1%, depending on the length of the heat exchange element, the speed and temperature of the air flow.

Keywords: heat recovery, honeycomb heat exchanger, numerical modeling, calculation, heating time, pressure drop, heat exchanger geometry, angle of plate, air flow velocity, air flow temperature

This article considers the problem of determining the temperature field near a heat-loaded source in the form of a dipole field. Solving this problem will make it possible to identify general patterns of distribution of the temperature field as one moves away from the source. This will make it possible to ensure the normal functioning of powerful electronic components by ensuring the required intensity of heat flux removal, mainly in close proximity to a heat-loaded source, that is, in the zone of maximum heat flux density.

Keywords: numerical methods, energy saving, heat engineering, thermal conditions of equipment, heat-loaded source, near zone, numerical modeling, temperature field, thermal processes, finite element method

The paper analyzes the thermal regime of a highly functional on-board control unit in an AMg6 aluminum alloy case and compares the obtained data with the thermal regime of a unit with a highly efficient heat sink made of composite materials. The calculation of the thermal field of the block was carried out using CAD tools based on the finite element method with a thermal application in order to assess its performance under given boundary conditions. Based on a comparative analysis of various heat-removing materials of the basic supporting structure, the least heat-stressed system was chosen.

Keywords: thermal regime, highly efficient heat removal, composite materials, on-board equipment, oxygen system, finite element method, mathematical model, computer-aided design system, electrical radio product, printed circuit board

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