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The Cantor alloy (equiatomic CrMnFeCoNi) is a high-entropy alloy with unique physical properties and radiation resistance. To model its response to intense laser pulses, the parameters of the electronic ensemble are required. In this work, the electronic heat capacity, thermal conductivity, and electron-phonon coupling strength at elevated electronic temperatures are evaluated using a combined approach that incorporates tight-binding molecular dynamics and the Boltzmann equation. The damage threshold fluence is estimated for a wide range of photon energies, from XUV to hard X-rays. It is found that at the electronic temperatures ~ 24,000 K (absorbed dose ~ 6 eV/atom), the Cantor alloy experiences nonthermal melting due to modification of the interatomic potential induced by electronic excitation, even without the increase of the atomic temperature. This effect must be included in reliable models of CrMnFeCoNi ablation under ultrafast laser irradiation.

In heat transfer, fins are commonly used to enhance the heat transfer rate from surfaces and are widely applicable in heat exchangers and thermal energy storage systems. The material used for fins typically has a high heat conductivity. While the study of temperature-dependent heat conductivity for fins is already available, an insufficient mathematical description is observed in the case of size-dependent heat conductivity and convective heat transfer. In the current work, a heat transfer study is presented to estimate the temperature field in a moving fin that accounts for size-dependent heat conductivity and internal heat generation that depends on temperature under periodic boundary conditions. To observe the temperature field, we have developed a hybrid numerical method based on Taylor–Galerkin and Legendre wavelets. The stability analysis of the developed method is discussed in detail. Our numerical method shows excellent agreement with the analytical solution obtained in a special case. The impact of problem parameters is extensively discussed. This study shows that fin temperature decreases periodically with a space-dependent heat conductivity. In addition, for a problem which accounts for constant heat conductivity and movable fin, have greater temperature response, and standard problem which accounts for constant heat conductivity have weaker temperature response while it is between them for a problem that includes size-dependent heat conductivity and moving fin. It is shown that fin efficiency can be improved by lowering the value of the Knudsen number. Moreover, fin problem with fixed thermal conductivity offer greater efficiency in comparison with size-dependent thermal conductivity.

The study of convective heat transfer in differently shaped fins with radiation, internal heat generation and variable thermal conductivity was considered. The energy equation of the model was converted into the dimensionless form by adopting the proper variables, which was later solved using the differential transformation method. The impact of the parameters on the thermal performance, efficiency and heat transfer of the fins was analyzed graphically and also by performing thermal analysis on the fins. It was noticed that there was a significant effect on the thermal performance of the fins with different shapes, and also the heat transfer rate of the fin increased for improved values of the internal heat generation and radiation parameters. The exponential profile showed better results than other profiles, and the results obtained were supported by thermal analysis using ANSYS software.

The paper solves the parameters identification problem in a nonlinear heat equation with homogenization functions as the bases, which are constructed from the boundary data of the temperature in the 2D and 3D space-time domains. To satisfy the over-specified Neumann boundary condition, a linear equations system is derived and then used to determine the expansion coefficients of the solution. Then, after back substituting the solution and collocating points to satisfy the governing equations, the space-time-dependent and temperature-dependent heat conductivity functions in 2D and 3D nonlinear heat equations are identified by solving other linear systems. The novel methods do not need iteration and solving nonlinear equations, since the unknown heat conductivities are retrieved from the solutions of linear systems. The solutions and the heat conductivity functions recovered are quite accurate in the entire space-time domain. We find that even for the inverse problems of nonlinear heat equations, the homogenization functions method is easily used to recover 2D and 3D space-time-dependent and temperature-dependent heat conductivity functions. It is interesting that the present paper makes a significant contribution to the engineering and science in the field of inverse problems of heat conductivity, merely solving linear equations and without employing iteration and solving nonlinear equations to solve nonlinear inverse problems.

— The article considers a study of the possibility to increase the boiling critical heat flux q cr through the use of surfaces consisting of areas with different heat conductivity. The results of experiments on studying pool boiling heat transfer for saturated dielectric fluid methoxynonafluorobutane (Novec 7100) on bimetallic surfaces are presented. The studies were carried out for bimetallic samples and also for samples made of copper and grade 08Kh18N10T stainless steel in the pressure range 0.1–0.4 MPa. A description of the experimental setup and the procedures used is given. The boiling curves for each sample in the entire presented range of fluid pressures with a step of 0.1 MPa are obtained, and the tables of critical heat-flux values are given. The effect that the liquid pressure has on the relative increase of q cr for bimetallic samples is shown. The values of q cr obtained on all samples are compared with one another, and the increase of q cr on bimetallic surfaces by up to 20% is shown. The previously performed studies are briefly reviewed, and the experimental data obtained by other researchers on boiling heat transfer on surfaces with modulated heat conductivity and for boiling of Novec 7100 fluid are presented, including that on samples with a modified heat-transfer surface. The obtained results are compared with rather few data of other researchers. The temperature field in a bimetallic sample is numerically simulated, and the temperature distribution over the heat-transfer surface is presented. The growth of q cr is due to nonisothermal properties of the heat-transfer surface, which causes the boiling to become regularized.

This study analyzes the thermal performance of a specially designed heat pipe heat exchanger (HPHE) containing distinct evaporator and condenser sections and utilizes two convective heat transfer media—deionized (DI) water and silver nanofluids. Low-grade industrial waste heat at 50–60 °C is the primary heat source. The HPHE employs a stainless steel mesh wick and copper fins to promote efficient evaporation and condensation heat transfer (background). The goal was to assess and compare the HPHE's performance in recovering this waste heat using DI water and silver nanofluids as the working fluids (purpose). A custom-built experimental setup allowed careful control and systematic variation of operating parameters, including thermal load (70-90W), and hot and cold fluid mass flow rates (0.2–0.6 kg⋅min −1 and 0.1–0.3 kg⋅min −1 ). The nanofluid was synthesized robustly, demonstrating remarkable uniformity and stability. The working fluids' heat exchange rates and efficiencies were analyzed and compared based on calculated thermal resistance, overall heat transfer coefficient (U), and effectiveness (ε) values (methods). The nanofluid reduced thermal resistance by 10–15% and improved U and ε by over 60% compared to DI water. A maximum effectiveness of 39.25% proved the HPHE's exceptional waste heat recovery capacity using nanofluids (results). Heat transfer performance escalated with higher thermal loads yet required optimal mass flow rates to balance turbulence and exposure time. The modified HPHE with silver nanofluids shows immense potential for harnessing industrial waste heat through substantially intensified heat exchange rates and thermal efficiency.

Power transmission covering long-distances has shifted from overhead high voltage cables to underground power cable systems due to numerous failures under severe weather conditions and electromagnetic pollution. The underground power cable systems are limited by the melting point of the insulator around the conductor, which depends on the surrounding soils’ heat transfer capacity or the thermal conductivity. In the past, numerical and theoretical studies have been conducted based on the mechanistic heat and mass transfer model. However, limited experimental evidence has been provided. Therefore, in this study, we performed a series of experiments for static and cyclic thermal loads with a cylindrical heater embedded in the sand. The results suggest thermal charging of the surrounding dry sand and natural convection within the wet sand. A comparison of heat transfer for dry, unsaturated and fully saturated sand is presented with graphs and colour maps which provide valuable information and insight of heat and mass transfer around an underground power cable. Furthermore, the measurements of thermal conductivity against density, moisture and temperature are presented showing positive nonlinear dependence.

The heat transfer coefficients and thermal conductivity of glass coatings on heat exchange tubes were investigated. A formula is obtained for determining the maximum thermal conductivity of a glass coating. It was found that during long-time operation of a heat exchanger the heat transfer coefficient of the glass coating on the pipe is independent of the cleanliness of the glass surface from the time of operation. However, in brass or copper pipes, over time the heat transfer coefficient drops sharply due to the formation of a strong layer of scale and corrosion products. A formula is obtained for calculating the maximum value of the heat transfer coefficient of glass coatings on pipes.

We give new statements and solutions to the problems of optimization of a variable heat conductivity coefficient for an inhomogeneous pipe and a flat wall under mixed boundary conditions. The cost functionals and constraints are either the average or maximal temperature while the constraints are either the condition of constancy of the integral heat conductivity coefficient or a priori information about the change of the heat conductivity coefficient in a given range. To solve the problems for a pipe, we use the two optimization methods: the variational approach basing on the conjugate functions and an extended Lagrange functional as well as the Pontryagin’s maximum principle. To solve the optimization problem for a flat wall under the assumption of weak material inhomogeneity, we apply the method of expansion in a small physical parameter. The fourth problem under consideration is the optimization of the variable heat conductivity coefficient of an inhomogeneous flat wall under boundary conditions of the first kind. We find a solution to this singular optimization problem among broken extremals. Considering particular examples, we compare the values of minimized functionals for bodies with a constant heat conductivity coefficient and the optimal variable coefficient. We also estimate the gain of using optimization.

We are concerned with the Cauchy problem to the three-dimensional full compressible Navier–Stokes equations with zero heat conductivity. Under the condition that the initial energy is small enough, global existence of strong solutions is established. Especially, the initial density is allowed to have large oscillations. The key to estimate the pointwise lower and upper bounds of the density lies in the handling of the energy conservation equation and the boundedness of the L r –norm of the gradient of the pressure.