Heat Conductivity Coefficient Research Articles

İki Boyutlu Anizotropik Plakanın Isı İletim Analizi

The heat conduction of a two dimensional anisotropic plate with non-homogeneous general boundary conditions is solved by using ANSYS Fluent in the cartesian coordinate system. It is assumed that the thermal conductivity and heat generation of the material arbitrarily change in the direction of the two space variables. Under these conditions, a variable coefficient differential equation is obtained. Analytical solutions of such equations cannot be obtained except for some simple material functions. The variable coefficient differential equation, which includes the heat conduction coefficient and volumetric heat generation depending on the two space variables and non-homogeneous boundary conditions, is handled numerically by ANSYS Fluent user-defined function (UDF). The accuracy of the numerical method is demonstrated by comparing analytical and numerical solutions using simple material functions.

Study of the heat conductivity coefficient of heat carriers and working media in a wide range of state parameters

Study of the heat conductivity coefficient of heat carriers and working media in a wide range of state parameters

INFLUENCE OF FILLER QUALITY ON CONCRETE THERMAL CONDUCTIVITY

Studies on the effect of grain composition on the thermal conductivity of lightweight concrete, it was shown that the mineral composition of filler (aggregates) substantially reflects the thermal conductivity and density of concrete. The grains of the component have a slightly higher effect on the thermal conductivity than the material itself. The proof of this position is that the thermal conductivity of bulk materials is always slightly lower than cellular materials of the same average density. In an absolutely dry porous body, heat transfer can occur not only through thermal conductivity but also through the solid skeleton of the body, located in the air pores, but also by convection and radiation between the pore walls. With a pore diameter of less than 1 mm, convective heat transfer is practically zero, and the coefficient of radiant heat conductivity can be neglected only when the pore diameter is less than 0.5 mm. Therefore, with the same porosity, the thermal conductivity coefficient will be the greater, the larger the pores of the material. Therefore, the creation of a finely porous structure of lightweight concrete and the use of finely porous aggregates contributes to the production of concrete with reduced thermal conductivity. The proof can be the results of experiments and the curves presented. An increase in the pore size on the surface of the grains of the aggregates leads to an increase in intergranular voids of the mixtures. As a result of mineralogical-petrographic studies of artificial porous aggregates, it was established that aluminosilicate phases with a disordered structure — clay amorphized with firing and acidic glasses — predominate in expanded clay, agloporite, and expanded perlite. Slag is characterized by a predominance of crystalline phases - low-basic calcium silicates than calcium and magnesium aluminosilicates. The glassy phase is present only in the form of an impurity of 15 - 20%. When analyzing the experimental data, we came to the conclusion that the thermal conductivity of expanded clay increases with increasing density. However, at the same density, expanded clay of different batches of the same plant and especially of different plants, differ in the values of the coefficient of thermal conductivity.

POLYMERS AND PLASTIC USE FOR THE HEAT-EXCHANGE EQUIPMENT (REVIEW)

The possibility of use of the heat-exchangers in whole or in part manufactured with use of polymers and plastics is considered. Despite obvious, at first sight, inexpediency of use of polymeric materials in the heat-exchange equipment (low coefficient of heat conductivity, and also low, in comparison with metals, the strength properties of the majority of the most widespread polymers), «polymeric» heat-exchangers find application in various areas of the industry more and more surely. Classification of heat-exchange apparatuses which constructive elements are executed with use of polymeric materials is proposed. The following signs are the basis for classification: polymer type, a type of polymer meric material, type of the heat-exchange apparatus (a form of heat-exchange elements), reliance on polymeric materials in apparatuses, motion freedom of polymeric heat-exchange elements, level of assembly of a design, and also diameter of tubular elements. Critical analysis the most characteristic designs developed by domestic and foreign designers and inventors is carried out. Ref. 21, Fig. 13.

Analysis of empirical correlations of thermophysical properties of water suspensions of aluminum oxide nanoparticles

Here, we consider the empirical relationships presented earlier in the literature that describe the thermophysical properties of H2O + Al2O3 nanofluids, such as viscosity and heat conductivity coefficients. The main parameters affecting these properties of nanofluid are considered to be the volume fraction of particles ϕ, fluid temperature T, and particle size dp. The suitability of approximation formulas for calculating the viscosity and heat conductivity coefficients is determined by comparing the data calculated by these formulas with the experimental results. The behavior of the analytical curves of thermophysical coefficients is analyzed in the following ranges of influencing parameters: 0 < ϕ ≤ 0.1, 280 K ≤ T ≤ 360 K, 1 nm ≤ dp ≤ 100 nm. Estimates of the degree of dependence of calculation results on the values of these parameters are given. Conclusions on the qualitative and quantitative reliability of the correlation formulas proposed in the literature, as well as on the limits of their applicability in the ranges of variation of the influencing parameters are drawn.

Collision cross sections and nonequilibrium viscosity coefficients of N2 and O2 based on molecular dynamics

This study examines the collision dynamics of atom–atom, atom–molecule, and molecule–molecule interactions for O–O, N–N, O2–O, N2–N, O2–N, N2–O, O2–O2, N2–N2, and N2–O2 systems under thermal nonequilibrium conditions. Investigations are conducted from a molecular perspective using accurate O4, N4, and N2O2 ab initio potential energy surfaces and by performing Molecular Dynamics (MD) simulations. The scattering angle and collision cross sections for these systems are determined, forming the basis for better collision simulations. For molecular interactions, the effect of the vibrational energy on the collision cross section is shown to be significant, which in turn has a profound effect on nonequilibrium flows. In contrast, the effect of the rotational energy of the molecule is shown to have a negligible effect on the cross section. These MD-based cross sections provide a theoretically sound alternative to the existing collision models, which only consider the relative translational energy. The collision cross sections reported herein are used to calculate various transport properties, such as the viscosity coefficient, heat conductivity, and diffusion coefficients. The effect of internal energy on the collision cross sections reflects the dependence of these transport properties on the nonequilibrium degree. The Chapman–Enskog formulation is modified to calculate the transport properties as a function of the trans-rotational and vibrational temperatures, resulting in a two-temperature nonequilibrium model. The reported work is important for studying highly nonequilibrium flows, particularly hypersonic re-entry flows, using either particle methods or techniques based on the conservation laws.

Smart Home Innovative Heat Test Analysis for Heat Storage and Conductivity Coefficients

This paper aims at presenting an innovative methodological approach to identify the heat storage and heat conductivity coefficients of a smart house. For this purpose, an experimental room is selected and heated to a high degree and then left for cooling, during which the reduction in the room temperature is measured with time. The time–temperature record provides the basis for determining the heat storage and heat conductivity coefficients through an objective standard curve matching procedure as the main context. These coefficients help to calculate the heat performance of a single room and, accordingly, the whole building, depending on its surrounding environment, construction material, volume and meteorological conditions. The proposed methodology depends on the one-dimensional heat flow event assuming that the construction material is homogeneous and isotropic and that the heat scatters uniformly in the room. The novelty in the paper is the standard curve for time–temperature decrease record evaluation, which can be used in a smart building planning procedure for decisions on heat storage and transfer.

Kapitza resistance in basic chain models with isolated defects

We explore numerically the boundary Kapitza resistance in one-dimensional chain models with isotopic and/or coupling defects for variety of the inter-particle potentials. In linear models, the Kapitza resistance is well-defined and size-independent (contrary to the bulk heat conduction coefficient), but depends on the parameters of thermostats used in the simulation. For β-FPU model one also encounters the dependence on the thermostats; in addition, the simulated boundary resistance strongly depends on the total system size. Finally, in the models characterized by convergent bulk heat conductivity (chain of rotators, Frenkel-Kontorova model) the boundary resistance is thermostat- and size-independent. In linear chains, the Kapitza resistance is temperature-independent; thus, its temperature dependence allows one to judge on significance of the nonlinear interactions in the phonon scattering processes at the interface.

Homogenization of a non-homogeneous heat conducting fluid

We consider a non–homogeneous incompressible and heat conducting fluid confined to a 3D domain perforated by tiny holes. The ratio of the diameter of the holes and their mutual distance is critical, the former being equal to ε 3 , the latter proportional to ε, where ε is a small parameter. We identify the asymptotic limit for ε → 0, in which the momentum equation contains a friction term of Brinkman type determined uniquely by the viscosity and geometric properties of the perforation. Besides the inhomogeneity of the fluid, we allow the viscosity and the heat conductivity coefficient to depend on the temperature, where the latter is determined via the Fourier law with homogenized (oscillatory) heat conductivity coefficient that is different for the fluid and the solid holes. To the best of our knowledge, this is the first result in the critical case for the inhomogenous heat–conducting fluid.

FINDING THE TEMPERATURE CONDUCTIVITY COEFFICIENT FROM THE SOLUTION OF THE DIRECT PROBLEM OF HEAT CONDUCTIVITY FOR A SEMI-LIMITED SOLID

The article concerns methods and formulas for the calculation of the coefficient of thermal conductivity of solid bodies using the known solutions of direct thermal conductivity tasks. The solution to the inverse problem of heat conductivity is based on the quite complicated methods including both hyperbolic functions and finite-difference methods. Under certain experimental conditions, the task is simplified at the regular thermal modes of 1, 2, or 3 types. Thus final formulas are simplified to algebraic equations. The simplification of the inverse problem of heat conductivity to algebraic equations is possible using other approaches. These methods are based on the analysis of the reference points, zero values of temperature distribution function, function inflection points, and its first and second derivatives. Here, we present formulas for the calculations of the temperature field on the assumption of the direct task solution for the half-bounded bar under the pulsed heating followed the re-definition of the boundary conditions. The regular thermal mode of the third family is name the mode at which the harmonic heating is set (repetitive) in time. At the set harmonic mode the law of fluctuation in the temperature of all points of body is known in time. The article describes three methods in which solutions are reduced to simple algebraic formulas when using the specified points on heating thermograms of test examples. These solutions allow algebraic deriving of simple relations for inverse problems of determination of thermophysical characteristics of solid bodies. The calculation formulas are given for the determination of the heat conductivity coefficient determination by three methods: by amplitude of temperature wave, a period of vibrations is a relative coefficient of heat exchange; by the change of phase of temperature wave; by a wave-length. The second method uses the values of two coordinates of the test sample in two different points where the equal temperature is reached at different points in time. The final solution of the equation is logarithmic. The analysis of known methods and techniques shows that experimental methods are oriented on the technical implementation and based on facilities of available equipment and instruments. Existing experimental techniques are based on specific constructions of measuring facilities. Simultaneously, there are well-studied methods of solution of thermal conductivity standard tasks set out in fundamental issues. The theoretical methods come from axioms, equations, and theoretical postulates, and they give the solution of inverse tasks of thermal conductivity. This work uses the solutions of direct tasks presented in the monograph by A. V. Lykov “The theory of heat conductivity”. These solutions have a good theoretical background and experts' credit. The boundary conditions of the problem are next: the half-bounded thin bar is given. The side surface of the bar has a thermal insulation. At the initial moment, the harmonic heat source acts on the bar in its section at some distance from its end. Heat exchange occurs between the environment and the end of the bar according to Newton's law. The initial (relative) temperature of the bar is accepted equal to zero. The heat exchange between the free end face of the bar and the environment is gone according to Newton's law.

Formation of Temperature Cracks of Concrete in High-Rise Buildings and the Corresponding Measures

AbstractA lot of heat will generate in mass concrete after pouring to form temperature cracks, which will reduce structural stiffness. This paper briefly introduces the principle of solid heat conduction and the cause of temperature crack formation and then used COMSOL software to simulate and analyze the mass concrete. The results showed that the simulation model had enough reliability to analyze the temperature change; the internal and external temperature of concrete rose first and then decreased; the formation of temperature crack was related to the internal and external temperature difference; the internal and external temperature difference was inversely proportional to the heat conductivity coefficient of concrete and directly proportional to the pouring temperature. Then, according to the analysis results, two measures were put forward to prevent temperature cracks in mass concrete: selecting concrete materials with high thermal conductivity, i.e., selecting coarse aggregate and fine aggregate with larger heat conductivity coefficient and reducing concrete pouring temperature, i.e., selecting cement with lower hydration heat, paying attention to temperature reduction in the process of concrete stirring, and reducing the amount of cement.

Global stability of rarefaction waves for a viscous radiative and reactive gas with temperature-dependent viscosity

We study the nonlinear stability of rarefaction waves to the Cauchy problem of a one-dimensional viscous radiative and reactive gas when the viscosity and heat conductivity coefficients depend on both density and absolute temperature. Our main idea is to use the smallness of the strength of the rarefaction waves to control the possible growth of its solutions induced by the nonlinearity of the system and the interactions of rarefaction waves from different families. The proof is based on some detailed analysis on uniform positive lower and upper bounds of the specific volume and the absolute temperature.

Thermal Stressed States of the Bodies of Revolution made of Functionally Graded Materials

We propose a method for the determination of the thermal stressed state of elastic bodies of revolution made of functionally graded materials. The formulation of the mathematical problem contains a thermal loading. A numerical algorithm for the solution of the corresponding problem is developed and realized for the problems of heat conduction and thermoelasticity. The thermoelastic state of a hollow cylinder is computed for a given mode of heating and different heat-conduction coefficients, elasticity moduli, specific heat capacities, and linear coefficients of thermal expansion. These results enable us to plot the graphic dependences of the thermal stressed state of a hollow cylinder.

Numerical simulation of an anisotropic heat transfer in magnetized neutron stars with 3D basic operators method

We have solved numerically a three dimensional boundary-value problem for a heat transfer equation in a magnetized neutron star crust with an updated tensorial heat conductivity coefficient. The temperature distribution in a neutron star crust in presence of a magnetic field was simulated. To calculate the surface temperature distribution, we have constructed a local one-dimensional plane-parallel model of a magnetized outer envelope of the neutron star and used it as an outer boundary condition for 3D problem to find a self-consistent solution.This problem was solved with our extension of a basic (support) operators numerical method on a tetrahedral mesh. The idea of operator approach consists of inclusion the boundary conditions into difference form of the solving problem and its formulation as one operator equation. The finite difference operators are constructed in the way to fulfill corresponding relations between continuous operators (for example, div(curl)=0, div is conjugated to -grad so div(grad) is self-conjugated etc.). Such approach allows to obtain completely conservative implicit finite difference schemes. Efficient iterative methods can be used to find the solution because constructed matrixes have good properties, such as symmetry and positive definiteness.

Reverse Task of Heat Conductivity for the Semilimited Bar

The article concerns methods and formulas for the calculation of the coefficient of thermal conductivity of solid bodies using the known solutions of direct thermal conductivity tasks. The solution to the inverse problem of heat conductivity is based on the quite complicated methods including both hyperbolic functions and finite-difference methods. Under certain experimental conditions, the task is simplified at the regular thermal modes of 1, 2, or 3 types. Thus final formulas are simplified to algebraic equations.&#x0D; The simplification of the inverse problem of heat conductivity to algebraic equations is possible using other approaches. These me­thods are based on the analysis of the reference points, zero values of temperature distribution function, function inflection points, and its first and second derivatives. Here, we present formulas for the calculations of the temperature field on the assumption of the direct task solution for the half-bounded bar under the pulsed heating followed the re-definition of the boundary conditions.&#x0D; The article describes two methods in which solutions are reduced to simple algebraic formulas when using the specified points on hea­ting thermograms of test examples. These solutions allow algebraic deriving of simple relations for inverse problems of determination of thermophysical characteristics of solid bodies. The calculation formulas are given for the determination of the heat conductivity coefficient determination by two methods: by value of temperature, coordinate, and two moments at which this temperature is reached.&#x0D; The second method uses the values of two coordinates of the test sample in two different points where the equal temperature is reached at different points in time. The final solution of the equation is logarithmic. The analysis of known methods and techniques shows that experimental methods are oriented on the technical implementation and based on facilities of available equipment and instruments.&#x0D; Existing experimental techniques are based on specific constructions of measuring facilities. Simultaneously, there are well-studied methods of solution of thermal conductivity standard tasks set out in fundamental issues. The theoretical methods come from axioms, equations, and theoretical postulates, and they give the solution of inverse tasks of thermal conductivity. This work uses the solutions of direct tasks presented in the monograph by A.V.Lykov “The theory of heat conductivity”. These solutions have a good theoretical background and experts’ credit.&#x0D; The boundary conditions of the problem are next: the half-bounded thin bar is given. The side surface of the bar has a thermal insulation. At the initial moment, the instant heat source acts on the bar in its section at some distance from its end. Heat exchange occurs between the environment and the end of the bar according to Newton’s law. The initial (relative) temperature of the bar is accepted equal to zero. The heat exchange between the free end face of the bar and the environment is gone according to Newton’s law.

Global large solutions to the planar magnetohydrodynamics equations with constant heat conductivity

This paper is concerned with global existence of large solutions to the initial-boundary value problem of the planar magnetohydrodynamic compressible flow. Under the assumptions that viscosity and heat conductivity coefficients are constants, magnetic diffusion is a function of the specific volume, we obtain the global existence of strong solutions. Some new methods are developed to deal with the complex interaction between the hydrodynamic and magnetodynamics effects.

ИНТЕЛЛЕКТУАЛЬНАЯ ИНФОРМАЦИОННО-ИЗМЕРИТЕЛЬНАЯ СИСТЕМА ТЕПЛОФИЗИЧЕСКИХ СВОЙСТВ ТЕПЛОИЗОЛЯЦИОННЫХ ПОКРЫТИЙ МАГИСТРАЛЬНЫХ ТРУБОПРОВОДОВ

Актуальность. В магистральных трубопроводах для транспортировки, а также в резервуарах для хранения нефти и газа применяются теплозащитные покрытия из различных материалов. Теплозащита данных объектов неизбежно интенсивно подвергается воздействию различных климатических факторов, а в некоторых случаях механическим воздействиям, что приводит к деградации ее свойств. Разработка интеллектуальной информационно-измерительной системы с реконфигурируемой структурой для оперативного контроля состояния теплоизоляционных материалов, позволяющей расширить функциональные возможности существующих аналогичных систем и обеспечить требуемую точность измерений, является важной и актуальной. Цель: повысить точность определения коэффициента теплопроводности различных теплозащитных покрытий магистральных трубопроводов и резервуаров при их производстве и эксплуатации для предотвращения ухудшения свойств теплоизоляции под воздействием внешних влияющих факторов. Объекты: теплозащитные покрытия магистральных трубопроводов и резервуаров, используемых при транспортировке и хранении нефти и газа. Методы. Методологическую основу при решении поставленных задач проектирования интеллектуальной информационно-измерительной системы теплофизических свойств материалов составляют: теория измерительных систем, методы искусственного интеллекта, байесовский подход. Результаты. Разработана концептуальная модель проектирования интеллектуальной информационно-измерительной системы теплофизических свойств теплоизоляционных покрытий магистральных трубопроводов для транспортировки нефти и газа и резервуаров при хранении. В рамках концептуальной модели разработана методика определения измерительной ситуации в процессе теплофизических измерений на основе предварительной идентификации свойств исследуемого материала с использованием байесовского подхода к обработке выходных сигналов первичных измерительных преобразователей и структурных компонентов измерительного канала системы. Разработана модель процесса реконфигурирования и соответствующая структура интеллектуальной информационно-измерительной системы теплофизических свойств теплоизоляционных покрытий с целью повышения точности определения коэффициента теплопроводности теплоизоляционных материалов. Относительная погрешность измерения коэффициента теплопроводности с применением предложенной системы составляет не более 5 %.

Shock wave structure in a non-ideal gas under temperature and density-dependent viscosity and heat conduction

The structure of a shock wave is investigated using the continuum hypothesis for steady one-dimensional flow of a viscous non-ideal gas under heat conduction. The coefficients of viscosity and heat conductivity are assumed to be directly proportional to a power of the temperature and density of the gas. The simplified van der Waals equation of state for the non-ideal gas has been assumed in this work. Qualitative analysis of shock wave structure has been done in terms of singularity analysis, isoclines, and integral curves. The exact and numerical solutions of shock structure equations are obtained under the quantitative analysis. The validation of solution is established by comparing the results in the literature (Iannelli in Int J Numer Methods Fluids 72(2):157–176, 2013). The variation of normalized gas velocity, viscous stress, heat flux, and shock thickness have been investigated across shock transition zone with the non-idealness of the gas, temperature, and density exponents in the viscosity and heat conductivity of the gas and initial Mach number. It is found that gas velocity decreases significantly with the increase in non-idealness parameter, temperature, and density exponent in the viscosity of the gas. Shock wave thickness decreases with the increase in the non-idealness of the gas under constant viscosity and heat conductivity but increase under variable gas properties. The thickness of a shock wave decreases with the increase in the temperature exponent and increases with the increase in the density exponent.

On a simplified compressible Navier-Stokes equations with temperature-dependent viscosity

We consider a simplified compressible Navier-Stokes equations with cylindrical symmetry when viscosity coefficient λ and heat conductivity coefficient κ depend on temperature. We obtain global existence of strong solution and vanishing shear viscosity limit to the initial-boundary value problem in Eulerian coordinates. The analysis for the global existence is based on the assumption that μ=const.>0,1c˜θm≤λ(θ)≤c˜(1+θm),κ(θ)=θq, for m∈(0,1],q≥m. For the part of vanishing shear viscosity limit, we require in addition that 1c˜(1+θm)≤λ(θ)≤c˜(1+θm). In the paper, the acceleration effect in one direction is neglected, however, we do not need any smallness assumption for the initial data.

Optimisation of Cutting Tool and Cutting Parameters in Face Milling of Custom 450 through the Taguchi Method

Stainless steels with unique corrosion resistance are used in applications with a wide range of fields, especially in the medical, food, and chemical sectors, to maritime and nuclear power plants. The low heat conduction coefficient and the high mechanical properties make the workability of stainless steel materials difficult and cause these materials to be in the class of hard-to-process materials. In this study, suitable cutting tools and cutting parameters were determined by the Taguchi method taking surface roughness and cutting tool wear into milling of Custom 450 martensitic stainless steel. Four different carbide cutting tools, with 40, 80, 120, and 160 m/min cutting speeds and 0.05, 0.1, 0.15, and 0.2 mm/rev feed rates, were selected as cutting parameters for the experiments. Surface roughness values and cutting tool wear amount were determined as a result of the empirical studies. ANOVA was performed to determine the significance levels of the cutting parameters on the measured values. According to ANOVA, while the most effective cutting parameter on surface roughness was the feed rate (% 50.38), the cutting speed (% 81.15) for tool wear was calculated.