Heat Conduction In Materials Research Articles

A Thermo-electric Apparatus for Thermal Diffusivity and Thermal Conductivity Measurements

In this study, a one-dimensional heat transfer measurement device is developed based on the mathematical theory of the Angstrom method. To conform to the mathematical assumption, it is required that the device precisely controls the heat source to generate sinusoidal temperature signal. A thermo-electric module is used as the heat source for the measurement platform. This module is connected to a computer for program control, such that the temperature can be controlled quickly, precisely, and dynamically. In this study, five common heat-conducting materials are tested to verify the proposed one-dimensional heat transfer measurement device. By substituting the experimental results into the mathematical model of the Angstrom method, the thermal diffusion and thermal conductivity of the test material is calculated. The experimental results are compared with the physical properties of the materials, and the accuracy error is extremely low. This study confirmed that the Angstrom method theory applied thermal diffusivity and thermal conductivity measurement, which can be realized by thermo-electric temperature control technology.

COMSOL Simulation of Heat Distribution in Perovskite Solar Cells: Coupled Optical–Electrical–Thermal 3-D Analysis

The heat dissipation has been rarely investigated in solar cells although it has a significant impact on their performance and reliability. For the first time, an extended three-dimensional (3-D) simulation of heat distribution in perovskite solar cells is presented here. We use COMSOL Multiphysics to investigate the temperature distribution in conventional perovskite solar cells through a coupled optical–electrical–thermal modules. Wave optics module, semiconductor module, and heat transfer in solid module are coupled in COMSOL Multiphysics package to perform the simulation in 3-D wizard. The electrical behavior, optical absorption, and heat conduction or convection are considered to gain insight into heat dissipation across the cell. The simulation results suggest that the heat produced in the cell is best dissipated from the metallic contact where the PbI $_2$ defect forms because of oxidation or decomposition of the perovskite layer at moisture exposure. The generated heat varies significantly from the front FTO contact to bottom metallic electrode. The more heat dissipation and accumulation is observed at the junction and electrode sides too. In our simulations, we consider the Joule heating, nonradiative recombination heating, and heat flux in every layer of the cell and calculate the carrier's concentration, electric field distribution, Joule heating, Shockley–Read–Hall heating, total heat flux, and temperature distribution across the solar cell structure. The simulations reveal that the metallic contact must be selected as a highly heat conductive material in order to accelerate the heat dissipation on the bottom of the cell and to enhance the cell reliability against temperature increase under normal operation.

Use of Nanoparticles of a Finely Dispersed Silicon Carbide Obtained in an Electrothermal Boiling Bed as a Structural Modifier of Thermoplastic Polymers

Porous powders of a finely dispersed silicon carbide obtained as a result of the carbothermal reduction of silica in an electrothermal boiling-bed reactor were investigated. It was established that such a powder comprises silicon-carbide nanoparticles of size ~50–70 nm and filametry formations of these nanoparticles with an aspect ratio of ~5–15. It is shown that the silicon-carbide nanoparticles introduced in a thermoplastic polymer interact with its matrix and, in so doing, change the polymer structure, with the result that a composite material is formed. Such thermoplastic polymer composites possess enhanced physical, mechanical thermal, and thermophysical properties. New heat-conducting polymer composite materials having a high wear resistance and good antifriction properties have been developed. These materials can be used in machine building as protective coatings, members, and units of facilities operating in the regime of abrasive wear, in power and electrical engineering, and in microelectronics where there is a need for heat-conducting thermoplastic polymer materials.

Electrical and Heat Conduction Properties of Polymerization-Filled Composites Based on Ultra-High-Molecular-Weight Polyethylene and Nano- and Micron-Sized Aluminum Particles

The electrical and heat conduction properties of polymerization-filled composites based on ultra-high-molecular-weight polyethylene and differently proportioned mixtures of aluminum micro- and nanoparticles coated with oxide layers of various thicknesses have been studied. The composite composition optimal for producing heat-conductive dielectric materials for heat sinks in electronics has been determined. By analyzing the frequency and concentration dependences of the electrical conductivity of the studied composites and the concentration dependences of their thermal conductivity, conclusions were drawn on the charge-transfer mechanisms and the structure of the clusters of the filler.

Designing a system of liquid cooling for industrial microwave installations

The paper considers the issue on ensuring a thermal regime of the magnetron's anode unit by replacing an air-cooling system with the system of liquid cooling. It has been argued that a liquid cooling system is most suitable for magnetrons, for which currently an air-cooling system is implied, although they are not designed for a continuous operation in the structure of industrial microwave installations. Arranging the system of liquid cooling would makes it possible for a magnetron to work over long time without overheating and under favorable conditions, which rule out a possibility to clog the heat exchange surface with particles and dust, as well as the occurrence of overheating of the anode unit's surface. The basic element of the proposed system for liquid cooling is a cooling jacket, which represents an annular channel made from a heat-conducting material. Cooling jacket is mounted directly on the anode unit; in this case, a compression ratio of surfaces and the thickness of an air gap must ensure a minimum total thermal resistance. In order to determine heat transfer coefficients, an empirical dependence was established, which reflects the fact that when cooling the anode units the rational regimes are the viscous and transitional motion modes. The basic thermal characteristics of the cooling process have been defined, which include a coefficient of heat transfer, change in a heat-carrier temperature, the maximally permissible temperature at inlet. Calculations were carried out for two types of heat-carriers: water and a 54 % aqueous solution of ethylene glycol. A circuit for the system of liquid cooling has been proposed, which implies cooling from 1 to 6 magnetrons. Applying a given circuitry and choosing the rational estimated modes make it possible to solve the task on improving production efficiency, as well as reliability of microwave equipment.

Decay rates of Saint-Venant type for functionally graded heat-conducting materials

This paper investigates decay rates for the spatial behaviour of solutions for functionally graded heat-conducting materials. From a mathematical point of view, we obtain a new inequality of Poincaré type. This new result allows us to give new decay rates for functionally graded materials when the inhomogeneity depends on the radial variable and the axial variable of the cylinder. The case when the cross-section is increasing is also considered. Besides, we propose to obtain estimates for the case of mixtures. Some pictures illustrate our estimates.

Determination of distribution of heat-conducting material concentration in protective layer of thermal protection system panel

Paper presents the problem of heating the damaged insulation of an orbiter. Changes of the insulation?s thermal properties, made by adding conductive material of high value of specific heat in a form of a dope to the protective layer, were examined. An iterative algorithm determining a variable of dope concentration in the material was developed. Insulating material LI900 was used for calculations. Determination of distribution of conductive material concentration was made for materials which, after verification, demonstrated the most beneficial effect on protective properties of the modified insulation layer. Change of properties was to enable time extension of the LI900 insulation tile heating up to the maximal temperature and, additionally, to lowering this temperature.

Modeling and Experimental Studies of Thermophysical Properties of Gradient and Combined Materials

In this paper we describe the approach of effective modification the substrate elements contributing to expansion of operating conditions of electronic devices. A method of local laser surfacing of heat-conducting materials on the surface of metal housings and substrates of radio-electronic products for obtaining the heat-transfer structures was used. The proposed method helps to reduce a thermal load on structural elements exposed to strong heating. The proposed approach is effective in cases where the usage of hinged heat sink elements or radiators are complicated by the design features or operating conditions of the device. In the work the materials and equipment used, the results of metallographic studies of the obtained structures and calculations of the thermal load of the electronic device are presented. The graphic material demonstrating an effectiveness of the approach of obtaining the heat-sinkregions for removing excess heat from the heated components of the device formed on the external metallic housing constructions ispresented.

The comparison of a numerical and empirical calculation of thermal transmittance of ventilated facade with different heat-conductive connections

The energy efficient buildings are priority these days. The building energy efficiency requirements are increasing and thicker thermal insulation layer is used for building envelopes in order to achieve these high requirements. Ventilated facades are often used for the construction of public buildings, whose thermal insulating layers are crossed with connections made from various materials. Previously, steel and aluminium connections were used, whose influence on the heat transfer through the construction was high. When increasing the thickness of thermal insulation, the amount of connections should be increased, therefore the heat transfer will increase even more and such connections are no longer suitable for energy efficient buildings. Looking for less heat-conductive materials for connections, it has been observed that different calculation methods give different results of heat transfer, depending on characteristics of materials for thermal insulation and connections. In order to find out the reasons for these differences, calculations of ventilated walls with various connections were carried out. The heat transfer through the wall with connections crossing thermal insulating layer could be calculated in two ways. The first way is simpler and was often used earlier - this is the calculation of the heat transfer coefficient increase depending on type and geometry of connection using the formulas presented in the standards. A more precise calculation method is the calculation of the heat transfer coefficient of wall with connections using two - dimensional and three - dimensional heat transfer modelling computer software (heat flow analyses). The use of these two calculations methods shows the differences of results of the heat transfer through ventilated walls. For both calculations, the fragments of ventilated walls with connections made from aluminium alloy (λ - 160 W/(m∙K)), zinc coated steel (λ - 50 W/(m∙K)), stainless steel (λ - 17 W/(m∙K)) and glass fiber reinforced plastic (λ – 0,23 W/(m∙K)) were created. Calculations have shown that the heat transfer coefficient calculated for walls with zinc coated and stainless steel connections using different methods varies by 29 %, for walls with glass fiber reinforced plastic connections – by 0,4 %, and for walls with aluminium alloy connections - by 130 %. The main aim of this paper is the investigation of reasons of different calculations results according to numerical and empirical calculations methods. When the causes of discrepancies are found, empirical formulas can be corrected. DOI: http://dx.doi.org/10.5755/j01.sace.23.2.21204

Vibration analysis of functionally graded plates using the eight-unknown higher order shear deformation theory in thermal environments

This paper deals with free vibration of functionally graded material plates using eight-unknown higher order shear deformation theory in thermal environments. The theory is based on full twelve-unknown higher order shear deformation theory, simultaneously satisfies zero transverse shear stress at the top and bottom surfaces of the FG plate. Heat conduction and temperature-dependent material properties are both taken into account. The temperature field considered is assumed to be a uniform distribution over the plate surface and varied in the thickness direction only. Material properties are assumed to be temperature-dependent, and graded in the thickness direction according to a simple power law distribution in terms of the volume power laws of the constituents. Equations of motion are derived from Hamilton's principle. The accuracy of present analytical solution is confirmed by comparing the present results with those available in existing literature. The effects of the temperature field, volume fraction index of functionally graded material, side-to-thickness ratio on free vibration responses of the functionally graded plates are investigated.

The Study of the Properties of Heat-conducting Composite Materials

The Study of the Properties of Heat-conducting Composite Materials

Free vibration analysis of functionally graded doubly curved shell panels resting on elastic foundation in thermal environment

The purpose of the paper is to develop an analytical investigation on free vibration of a simply supported functionally graded (FG) doubly curved shell panels resting on elastic foundation in thermal environment. Heat conduction and temperature-dependent material properties are both taken into account. The temperature field considered is assumed to be a uniform distribution over the shell surface and varied in the thickness direction only. Material properties are assumed to be temperature dependent and graded in the thickness direction according to a simple power law distribution in terms of the volume fractions of the constituents. Based on the first-order shear deformation theory and applying the Hamilton’s principle, governing equations of motion are derived. The results of the study are compared with the available published literature. The numerical results obtained reveal that the material volume fraction index, geometrical parameters and temperature change have significant effects on natural frequencies of the FG doubly curved shell panels.

Energy-Efficient Compact Heat Exchangers Made of Porous Heat-Conducting Materials

After successful increase of levels of thermal resistances of building enclosing structures, expenses of heat on ventilation of rooms in many cases reached similar magnitudes of indicators of heating in a cold season. Therefore, the development of new efficient heat exchangersheat exchangers of small size is of particular importance. It is possible now to create highperformance thin (of a few centimeters) heat exchangers of such high-porous heat-conducting materials as copper, aluminum, etc. Highly porous materials include porous-permeable structures having an open porosity (with a total pore surface area of more than 50 % in relation to a smooth surface). One of the main conditions for the qualitative use of such high-porous thermal conductive materials is the rapid removal of condensate outside the heat exchange zone without a significant increase in filtration resistance. Thermal calculation of such heat exchangers is based on the criteria of Fourier (Fu) and Predvoditelev (Рd). Various ways of using high-porous heat-conducting materials in the design of heat exchangers are considered. The method of production of the heat exchanger based on the application of porous-permeable material in the channels of the heat exchange part of recuperative devices is presented; the difference of the method is that the heat exchange part is performed of two or more parallel heat exchange plates with spacing between them. It has been found that a significant increase in the energy efficiency of heat exchangers of this type is possible due to the application of even small discontinuities of the heat-conducting layers of high-porous materials so to use the specific features of increased heat exchange of the initial sections with the flowing fluid. One of the main advantages of using air-to-air heat exchangers made of foamed high-heat-conducting material in the climatic conditions of Belarus is freezing resistance.

Development of a PVDF Pressure Gauge for Blast Loading Measurement

We investigate the development of a sensor for dynamic pressure measurement. The sensor relies on a Bauer shock gauge of 25-μm thin Polyvinylidene fluoride (PVDF) film [AIP Conf. Proc 706:1121–1124, [21]. These gauges unfortunately require some skills to be integrated in an acquisition chain and the obtained results are strongly “experiment dependent.” In the presented work, the classical Bauer gauge has been adapted: the reproducible PVDF film is poled at high voltage, in electrical symmetrical response and reproducibility. The sensitive area is a 3 × 3 mm square. The gauge has been electrically shielded and overlaid with a heat conductive material. A 5-m long coaxial wire connects the gauge to a charge amplifier, allowing its connection to a deported oscilloscope. The output electrical charge of the PVDF gauge has been correlated with the pressure measured by calibrated PCB® sensors. Measured pressures are validated by an analytical approach and numerical simulations of the flow in the shock tube. A calibration curve can be deduced for pressures below 10 bar, values which are often met in blast loading situations. This customizable sensor is hence suitable and easy to use to measure the blast-reflected pressure on a flat material.

Methodological Errors of Defining the Thermophysical Characteristics of Materials Using the Laser Pulse Method at High Temperatures

Methodological errors of defining the thermophysical characteristics of construction materials have been evaluated. Methodological errors are caused by heat exchange of a sample with the environment in conditions corresponding to execution of the laser pulse method at high temperatures. Analysis was done of the effect on methodological errors of heat exchange (as a result of natural convection) with the environment. It has been shown that the laser pulse method can be used to determine thermal diffusivity and thermal capacity of highly heat-conductive wire materials (metals and alloys) at temperatures to 1173 K.

Determination of distribution of heat-conducting material concentration in protective layer of TPS panel

Paper presents the problem of heating the damaged insulation of an orbiter. Changes of the insulation’s thermal properties, made by adding conductive material of high value of specific heat in a form of a dope to the protective layer, were examined. The analysis was made using insulating material LI900 and beryllium dope. In the paper was investigated the effect of the dopant’s share on the temperature distribution on the aluminum surface. This influence was depended on the size of the damage, defined by parameter D, as well as a constant percentage volume fraction.

Evaporation-condensation cooling systems for electronic equipment

The paper shows that heat pipes with metal-fibrous capillary structures and evaporation-condensation cooling system based on heat pipes are highly efficient means of providing optimal thermal conditions for different electronic instruments and devices. Such cooling system combining the functions of effective heating conduit (equivalent heat conductivity is much higher than the heat conductivity of the best heat-conducting materials) and effective radiator with the possibility of passive heat dissipation is characterized by a high heat transport ability, low thermal resistance, relatively small size and weight, reliable performance at different orientation in space under exposure to mass forces action. The paper presents examples of developed designs and investigations of heat pipes and evaporation-condensation systems with metal-fibrous capillary structures aimed at cooling the different heat generating items of electronic equipment. In this case, special types and designs of systems are discussed. These systems operate under different conditions of heat removal to absorbing medium and feature both a high heat transport ability and specific dielectric properties. In addition, the thermotechnical characteristics of proposed cooling systems are also presented.

Rayleigh–Bènard convection in the generalized Oberbeck–Boussinesq system

The original Oberbeck–Boussinesq (OB) equations which are the coupled two dimensional Navier–Stokes(NS) and heat conduction equations have been investigated by E.N. Lorenz half a century ago with Fourier series and opened the way to the paradigm of chaos. In our former study—Chaos, Solitons and Fractals 78, 249 (2015)—we presented fully analytic solutions for the velocity, pressure and temperature fields with the aim of the self-similar Ansatz and gave a possible explanation of the Rayleigh–Bènard convection cells. Now we generalize the Oberbeck–Boussinesq hydrodynamical system, going beyond the first order Boussinesq approximation and consider a non-linear temperature coupling. We investigate more general, power law dependent fluid viscosity or heat conduction material equations as well. Our analytic results obtained via the self-similar Ansatz may attract the interest of various fields like meteorology, oceanography or climate studies.

Nonisothermal Flow Around a Circular Cylinder with a Permeable Layer at Moderate Reynolds Numbers

Results of a numerical investigation of a separation nonisothermal flow of an incompressible viscous fluid around a circular cylinder covered with a permeable porous layer at moderate Reynolds numbers are presented. This flow was defined with the use of Navier–Stokes and energy equations, and the filtration flow in the porous layer was determined by the Forchheimer law. The dependence of the hydrodynamical drag of the indicated cylinder and the length of the vortex region in the flow around it on the Reynolds and Darcy numbers was determined. An analysis of the heat transfer from cylindrical bodies covered with permeable layers of a highly heat-conducting material or a heat-insulating material has been performed.

Thermo-mechanical properties of carbon nanotubes and applications in thermal management

Thanks to their very high thermal conductivity, high Young’s modulus and unique tensile strength, carbon nanotubes (CNTs) have become one of the most suitable nano additives for heat conductive materials. In this work, we present results obtained for the synthesis of heat conductive materials containing CNT based thermal greases, nanoliquids and lubricating oils. These synthesized heat conductive materials were applied to thermal management for high power electronic devices (CPUs, LEDs) and internal combustion engines. The simulation and experimental results on thermal greases for an Intel Pentium IV processor showed that the thermal conductivity of greases increases 1.4 times and the saturation temperature of the CPU decreased by 5 °C by using thermal grease containing 2 wt% CNTs. Nanoliquids containing CNT based distilled water/ethylene glycol were successfully applied in heat dissipation for an Intel Core i5 processor and a 450 W floodlight LED. The experimental results showed that the saturation temperature of the Intel Core i5 processor and the 450 W floodlight LED decreased by about 6 °C and 3.5 °C, respectively, when using nanoliquids containing 1 g l−1 of CNTs. The CNTs were also effectively utilized additive materials for the synthesis of lubricating oils to improve the thermal conductivity, heat dissipation efficiency and performance efficiency of engines. The experimental results show that the thermal conductivity of lubricating oils increased by 12.5%, the engine saved 15% fuel consumption, and the longevity of the lubricating oil increased up to 20 000 km by using 0.1% vol. CNTs in the lubricating oils. All above results have confirmed the tremendous application potential of heat conductive materials containing CNTs in thermal management for high power electronic devices, internal combustion engines and other high power apparatus.