Effect of Irradiation with Low-Energy He2+ Ions on Degradation of Structural, Strength and Heat-Conducting Properties of BeO Ceramics

The paper is devoted to the study of radiation-induced damage kinetics in beryllium oxide ceramics under irradiation with low-energy helium ions with fluences of 1015–1018 ion/cm2. It was revealed that at irradiation fluences above 1017 ion/cm2, a decrease in radiation-induced damage formation and accumulation rate is observed, which indicates the saturation effect. At the same time, the main mechanisms of structural changes caused by irradiation at these fluences are amorphization processes and dislocation density increase, while at fluences of 1015–1016 ion/cm2, the main mechanisms of structural changes are due to the reorientation of crystallites and a change in texture, with a small contribution of crystal lattice distorting factors. It was discovered that the radiation-induced damage accumulation as well as an implanted helium concentration increase leads to the surface layer destruction, which is expressed in the ceramic surface hardness and wear resistance deterioration. It was determined that with irradiation fluences of 1015–1016 ion/cm2, the decrease in thermal conductivity is minimal and is within the measurement error, while an increase in the irradiation fluence above 1017 ion/cm2 leads to an increase in heat losses by more than 10%.

Calculation of temperature waves in kurums

The article indicates the relevance of the study of heat transfer processes in kurums. Boundary value problems of vertical temperature change in kurums and in the underlying rock base are solved, when the temperature on the surface of kurums changes according to a given periodic law, which simulates daily and seasonal temperature fluctuations. The cases when the rock base is a heat-conducting medium and permafrost are considered. Some regularities of temperature propagation along the depth are revealed.

Thermal resistance of building envelopes with heat-conducting elements in summer period

The analysis of the current methods and techniques of solving the problem of heat resistance of building envelopes with heat-conducting elements shows the solution of a onedimensional problem of heat resistance. One of the possible methods for determining the temperature fluctuation amplitude on the inner surface of the building envelopes with heatconducting elements is the modeling of non-stationary temperature conditions in the computer program. However, this solution causes great difficulties, as it transfers the specified calculation from engineering to scientific and cannot be recommended for practical application. The second method of solving this problem is the application of the convergence coefficient, which can be obtained empirically. The selection of the convergence coefficient allows for the influence of the heat-conducting elements on the weighted average surface temperature depending on the envelope configuration.The structural analysis of the building envelopes and their impact on the averaged amplitude of oscillations on the inner surface are conducted. The arrangement of heat-conducting elements at the outer edge is characterized by a negligible influence of the vibration amplitude on the averaged amplitude over the structural surface. The arrangement of heat-conducting elements greatly affects the heat-conducting elements. According to the comparative analysis, the convergence coefficient is preferable in harmonics of the average temperature fluctuations on the inner surface.

Application Analysis of Medium Temperature Solar Refrigeration System in Civil Buildings

The lithium bromide absorption refrigeration system with medium temperature solar collector as driving heat source was built, and the refrigeration performance of the system was tested and analyzed. The medium-temperature solar collector adopts all-glass vacuum solar collector tube with heat-conducting oil as medium, and the inside of the vacuum tube is composed of heat-conducting medium flow channel on the sunny side and aluminum silicate insulation cotton on the backlight side. Through test and analysis, the medium temperature solar collector of the system can provide stable heat source, and the maximum temperature of solar heating can reach above 150°C in sunny weather and about 80°C in cloudy days. The generator driving heat of the system is stable and efficient. The driving heat of lithium bromide absorption refrigerator is higher than 200 MJ/h, and can reach 300 MJ/h in some periods. The COP of the system can be kept above 0.6 during stable operation, but when the driving temperature of the generator is higher than 80°C, the COP of the system basically does not increase with the increase of the driving temperature.

Analysis on the Improvement of Thermal Performance of Phase Change Material Ba (OH)2·8H2O

Benefitting from the characteristics of a high latent heat capacity and stable phase change behavior, phase change materials have widely received concerns in the field of thermodynamic management. Ba(OH)2·8H2O is an ideal phase change material (PCM) in the mid-to-low temperature range, but its large-scale application is still limited by severe supercooling during the nucleation process. In this paper, the experimental analysis and comparison are performed via an Edisonian approach, where Ba(OH)2·8H2O is adopted as an original substrate; BaCO3, CaCl2, NaCl, KH2PO4, and NaOH are selected as nucleating agents; and graphite is used as a heat-conducting agent. The results show that Ba(OH)2·8H2O containing 1.2% BaCO3 and 0.2% graphite powder has the best performance. Compared with pure Ba(OH)2·8H2O, the supercooling degree is reduced to less than 1 °C, the phase change latent heat duration is extended, and the thermal conductivity is significantly improved. Therefore, this study not only provides a reference for the application of Ba(OH)2·8H2O, but can also be used as a guidance for other material modifications.

Stationary solutions in thermodynamics of stochastically forced fluids

We study the full Navier–Stokes–Fourier system governing the motion of a general viscous, heat-conducting, and compressible fluid subject to stochastic perturbation. The system is supplemented with non-homogeneous Neumann boundary conditions for the temperature and hence energetically open. We show that, in contrast with the energetically closed system, there exists a stationary solution. Our approach is based on new global-in-time estimates which rely on the non-homogeneous boundary conditions combined with estimates for the pressure.