Thermal Conductivity Of Alumina Research Articles

Advancing energy recovery ventilators with phase change materials for cooling load reduction and heat exchange efficiency improvement

Efforts to reduce building energy emissions and achieve net-zero carbon scenarios globally have increasingly focused the building sector on improving energy efficiency. Heating, ventilation, and air conditioning (HVAC) systems play a vital role in providing comfortable indoor environments but significantly contribute to energy consumption and greenhouse gas emissions. Energy recovery ventilators are efficient active systems that prevent unnecessary indoor heat loss and gain, regardless of outdoor climate, making them excellent technologies for achieving zero energy. In a hot and humid summer climate, such as in Korea, it is crucial to enhance the efficiency of energy recovery ventilators and reduce cooling energy consumption. A Green HVAC design aimed at reducing the energy consumption of active systems to near zero was proposed by applying phase change material-based modules with high heat storage performance to energy recovery ventilators. The phase change material module is stabilized with high thermal conductivity aluminum packing and is configured as a mesh-type structure to amplify heat exchange efficiency with air. Compared to the energy recovery ventilator, the application of the module demonstrated a reduction in supply air temperature by an average of 2.6 °C in high-temperature outdoor. During the effective operating period, a continuous indoor intake temperature reduction effect was observed, and the sensible heat exchange efficiency showed a 21.32 % improvement with the module using n-octadecane. Phase change material modules that can enhance ventilation and improve energy efficiency in high-temperature environments can be proposed as a technology to achieve Green HVAC.

Limiting the lattice oxygen impurities to obtain high thermal conductivity aluminum nitride ceramics

Currently, the lattice oxygen is the key factor affecting the thermal conductivity of AlN ceramics. In this paper, three methods are proposed to limit lattice oxygen, namely reducing the original powder oxygen content, changing the debinding atmosphere, and extending the sintering time. The results show that the low powder oxygen content and protective debinding atmosphere alter the carbon and oxygen content, and further promote the formation of the Y4Al2O9 (YAM) phase. The generated YAM phase can effectively reduce the lattice oxygen in terms of thermodynamics. Prolonged high temperatures can provide kinetic conditions to reduce the lattice oxygen to 0.0343 wt%. In addition, morphological changes of the phase at the grain edges and their influence on the mechanical properties were noted. Finally, AlN ceramics with a thermal conductivity of 220 W m−1 K−1 and a flexural strength of 340 MPa were obtained. This study can provide a valuable reference for the industrial production of AlN ceramics.

Experimental Study on Interface Thermal Resistance of Heat Dissipation Channel in Low-Temperature Detector

Abstract To achieve a good heat dissipation effect in the heat dissipation channel of the low-temperature detector, it is necessary to study the thermal conductivity performance of GD414C and indium foil between detector and thermal conductive aluminum block. Based on the experimental principle and referring to the ASTM D-5470 testing method, a set of interface thermal resistance experimental testing equipment is designed. The experiment comparatively studies the relationship between the temperature difference between detector and thermal conductive aluminum block (TCAB) under different power and thermal conductive fillers. The experimental results show that when GD414C is filled between detector and thermal conductive aluminum block, the total thermal resistance is 0.728 ℃/W. When 0.1-mm-thick indium foil is filled, the total thermal resistance is 0.235 ℃/W. When 0.2-mm-thick indium foil is filled, the total thermal resistance is 0.123 ℃/W. Therefore, 0.2-mm-thick indium foil should be selected as the thermal conductive filler.

Fabrication of High Thermal Conductivity Aluminum Nitride Ceramics via Digital Light Processing 3D Printing.

The sintering of high-performance ceramics with complex shapes at low temperatures has a significant impact on the future application of ceramics. A joint process of digital light processing (DLP) 3D printing technology and a nitrogen-gas pressure-assisted sintering method were proposed to fabricate AlN ceramics in the present work. Printing parameters, including exposure energy and time, were optimized for the shaping of green bodies. The effects of sintering temperature, as well as nitrogen pressure, on the microstructure, density, and thermal conductivity of AlN ceramics were systematically discussed. A high thermal conductivity of 168 W·m-1·K-1 was achieved by sintering and holding at a significantly reduced temperature of 1720 °C with the assistance of a 0.6 MPa nitrogen-gas pressure. Further, a large-sized AlN ceramic plate and a heat sink with an internal mini-channel structure were designed and successfully fabricated by using the optimized printing and sintering parameters proposed in this study. The heat transfer performance of the ceramic heat sink was evaluated by infrared thermal imaging, showing excellent cooling abilities, which provides new opportunities for the development of ceramic heat dissipation modules with complex geometries and superior thermal management properties.

First-Principles Investigation of Point Defects on the Thermal Conductivity and Mechanical Properties of Aluminum at Room Temperature

The effects of point defects on the mechanical and thermal conductivity of aluminum at room temperature have been investigated based on the first-principles calculations combined with the Boltzmann equation and the Debye model. The calculated results showed the equilibrium lattice constants a0 of all REAl are larger than that of Al, and the defective formation energy Ef of all REAl is lower than that of VAl. Both a0 and Ef increase from Sc to La and then decrease linearly to Lu. The effects of solute atoms on the mechanical properties of the Al matrix were further calculated, and compared with Al, it is found that the REAl defects decrease the elastic constant Cij, Cauchy pressure C12–C44, bulk modulus B, shear modulus G, Young’s modulus E, B/G and Poisson’s ratio ν of Al, except for C44 of REAl (RE = La-Nd). With the increase of atomic number, the C11 and E of Al-containing REAl decrease from Sc to La and then slowly increase to Lu, whereas C12, C44, B, and G have little change. Meanwhile, the values of C12–C44 and B/G of Al-containing REAl increase from Sc to Ce, and it slightly change after Ce, while ν is nearly unchanged. All defects containing Al present nonuniform and ductility. Finally, the effects of rare earth (RE) atoms on the thermal conductivity (TC) of Al alloys have been investigated based on the first-principles calculations. The reduction of TC of Al alloys by RE solute atoms REAl is much greater than that by the L12 Al3RE phase with the same concentration of RE, which is in good agreement with the experiments. With the RE atomic number increasing, the total TC κ of the Al-RE solid solution decreases from Sc to La firstly and then increases linearly to Lu. Moreover, the decrement of TC Δκ of the Al matrix by early REAl (RE = La-Sm) is larger than that by VAl, while the later REAl (RE = Gd-Lu) shows the opposite influence.

Effect of alloying elements on thermal conductivity of aluminum

Effect of alloying elements on thermal conductivity of aluminum

Exceptionally Enhanced Thermal Conductivity of Aluminum Driven by Extreme Pressures: A First-Principles Study.

Extreme pressure conditions reveal fundamental insights into the physical properties of elemental metals that are otherwise not evident under ambient conditions. Herein, we use the density functional perturbation theory to demonstrate that the change in thermal conductivity as a result of large hydrostatic pressures at room temperature for aluminum is the largest of any known material. More specifically, in comparison to ambient conditions, we find that the change in thermal conductivity for aluminum is greater than the relative changes in thermal conductivities of diamond and cubic boron nitride combined, which are two of the most thermally conductive bulk materials known to date. We attribute this to the relatively larger increase in mean free paths and lifetimes of electrons in aluminum as a result of weaker electron-phonon coupling at higher pressures. Our work reveals direct insights into the exceptional electronic transport properties of pressurized aluminum and advances a broad paradigm for understanding thermal transport in metals under extreme pressure.

Effects of solid solution, grain size and porosity on the thermal conductivity of aluminum- and boron-added porous silicon carbide ceramics with in-situ grain growth

The effects of solid solution, grain size and porosity on the thermal conductivity of aluminum (Al)- and boron (B)-added porous SiC ceramics with in-situ grain growth were investigated. Al-added porous SiC ceramics showed higher porosity, higher solubility of Al in SiC lattice, and lower thermal conductivity with the range of 8.5 – 18.2 W/m⋅K. The higher solubility of Al in SiC lattice was considered as the reason of their low thermal conductivity. B-added porous SiC ceramics have lower porosity, lower solubility of B in SiC lattice, and higher thermal conductivity with the range of 30.6 – 79.0 W/m⋅K. The high thermal conductivity of B-added porous SiC ceramics would result from the low solubility of B in SiC lattice and the low porosity. The effect of grain size was found to increase the phonon mean free path for B-added SiC ceramics.

Highly efficient solar distiller integrated with photothermal membrane, superhydrophilic glass, and superhydrophobic heat sink

Solar steam generation and re-condensing into water is an effective way to lighten water scarcity caused by unreasonable waste of water. In this report, superhydrophobic, high thermal conductive aluminum and superhydrophilic glass was applied as condensing system and anti-fogging unit to ensure highly efficient process of drinkable water collection. The nanowire array of copper sulfide with nanorod array architecture guarantees strong solar absorption, which was used as photothermal conversion membrane to evaporate water. The efficiency of photothermal conversion to steam generation reached up to 81% under 1 sun illumination. Etching and surface modification was applied on high thermal conductive aluminum and glass to obtain a superhydrophobic and superhydrophilic surface nature. These three synergies of nanorod array architecture, anti-fogging glass and high-efficiency condensing system made the solar distiller a highly water collection efficiency up to 66%.

Impact of Window Frames on Annual Energy Consumption of Residential Buildings and Its Contribution to CO2 Emission Reductions at the City Scale

Windows are among building components that have the strongest effect on thermal load. They play a significant role in heat loss in buildings because they usually have a largely higher thermal conductance than other components of the building envelope. Although many studies have highlighted the relevance of heat transfer through frames and aimed to improve their thermal performance, poorly insulated aluminum frames (thermal conductivity of aluminum is 160 W/m·K, while that of polyvinyl chloride [PVC] is 0.17 W/m·K) are still in use in Japan. Therefore, the U-values of different window frames were calculated, and annual thermal loads were calculated according to the window configurations, including the frame, glazing, and cavity. We focused on standard residential buildings in Japan with a total floor area of 120.6 m2 (two-story building), and the number of newly built houses and the application rate of window configurations in 2019 were surveyed to estimate the CO2 emissions by regions. CO2 emissions were reduced by approximately 3.98–6.58% with the application of PVC frames. Furthermore, CO2 emissions were converted into the amount of CO2 gas absorbed by cedar trees, which cover nearly 18% of the total land area of Japan. In conclusion, analogous to the amount of CO2 gas absorbed by cedar trees, the absorption effect was equivalent to 327,743–564,416 cedar trees. Changing the window frame material can facilitate a significant energy-saving effect as a considerable amount of energy is saved, especially at a city scale.

Type and Properties of High Thermal Conductivity Aluminum Alloys for Die Casting

Type and Properties of High Thermal Conductivity Aluminum Alloys for Die Casting

Investigation of Heat Flux Propagation in Heat-Conducting Oxide Substrates with Different Heat Conductivity by the Linear Heat Source Method

Introduction. For controlled thermal management of power electronics devices, an important task is to increase the efficiency of heat removal from active components. Aim. To introduce a new approach to placing a linear contact-type heat source on the surface of thin samples in order to study the features of propagation of heat fluxes in oxide substrates from materials with different thermal conductivities. Methods and materials. The paper presents the results of studies of the propagation of heat fluxes in oxide substrates with different thermal conductivity (glassceramic and aluminum oxide ceramic - polycor). To generate the heat flux, a linear heat source was used, for which an electrically conductive carbon fiber was applied. Results. Thermograms and temperature distribution profiles were obtained at different periods of heating time on the surface of the substrate with a heating element and on its reverse side. It was shown that the placement of the linear heat source, implemented using an electrically conductive carbon filament, on the surface of the studied samples and time monitoring of thermograms from two opposite surfaces of the samples allowed to obtain data for evaluating the thermal properties of oxide substrates. The distribution of the heat flux in a homogeneous material near the generation point had the form of a cone of a heat pipe with a base on the surface with a heat source. The thermal cone for an aluminum oxide ceramic substrate had a larger angle of inclination than that in the case of glassceramic. Conclusion. The results obtained allowed to propose a method for reduction of thermal resistance of a heatconducting substrate by creating conditions for increasing the area of heat-conducting section.

Thermal Conductivity of Al2O3 and CeO2 Nanoparticles and Their Hybrid Based Water Nanofluids: An Experimental Study

In many heat exchange systems, there is a demand to improve the thermal conductivity of the working fluids to make those fluids more efficient, and this can be done by dispersing solid nanomaterials into conventional liquids. In the present work, the thermal conductivity of alumina, ceria, and their hybrid with ratio (50:50) by volume-based deionized water nanofluids was experimentally measured. The nanofluids were prepared by two-step method with a range of dilute volume concentration (0.01-0.5 % Vol.), and measured at various temperatures (35, 40, 45, and 50 ºC). The experimental data for basefluid and nanofluids were verified with theoretical and experimental models, and the results have shown good agreement within the accuracy of the thermal conductivity tester. The results demonstrated that the higher thermal conductivity enhancement percentages for Al2O3, CeO2, and their hybrid nanofluids were (5.3 %, 3.3 %, and 8.8 %) at volume concentration (0.5 % Vol.) and temperature (50 ºC) compared to deionized water, respectively. Moreover, a correlation was proposed for the thermal conductivity enhancement ratio of the hybrid nanofluid and showed good accuracy with measured experimental data.

Phase mixture modeling of the grain size dependence of Young’s modulus and thermal conductivity of alumina and zirconia ceramics

The grain size dependence of Young’s modulus and thermal conductivity of alumina and zirconia ceramics is predicted via phase mixture modeling, using both analytical and numerical approaches. Using typical values for the thickness and properties of the grain boundaries, the equivalent volume fraction of “grain boundary phase” is calculated for a given grain shape. Based on this volume fraction estimate and a rough estimate of the grain boundary properties, the effective properties of the polycrystalline materials are calculated and compared in terms of volume-equivalent sphere diameters. For grains of cubic and tetrakaidecahedral shape excellent agreement is found between numerical calculations and analytical predictions based on the lower Hashin-Shtrikman bound. The grain size dependence is extremely weak for Young’s modulus, but can be more significant for thermal conductivity, especially when the intrinsic conductivity of the material is high. The predictions are compared to literature data.

First-principles determination of the ultrahigh electrical and thermal conductivity in free-electron metals via pressure tuning the electron-phonon coupling factor

Responses of materials at high pressures can reveal fundamental insights into properties of condensed matter that are otherwise masked under ambient conditions. Using first-principles calculations to determine the electron-phonon interactions of free-electron metals at high pressures, we show that the electrical and thermal transport properties of aluminum, gold, and silver can be significantly enhanced with the application of high pressures. This is partly attributed to the decrease in electron-phonon coupling with increasing pressures. At elevated temperatures, under these high-pressure conditions, the thermal conductivity of aluminum is amongst the highest of any known material, surpassing the thermal conductivity of diamond at ambient pressure. Moreover, through calculation of the spectrally resolved electron-phonon coupling parameter at high pressures, we show an increased contribution to electron-phonon coupling from high-frequency longitudinal phonon modes scattering with electrons in aluminum. Using the same analysis with gold and silver, we show that low frequency acoustic phonon scattering with electrons is increased at high pressures. This work provides valuable insights into the electron-phonon scattering processes occurring under high pressures, which gives rise to new regimes of electrical and thermal transport properties in metals.

A wide-range modeling approach for the thermal conductivity and dielectric function of solid and liquid aluminum

This study aims at providing a simple method to obtain the electronic thermal conductivity of aluminum over a wide range of temperatures and densities in the crystalline solid as well as the disordered liquid phase. All calculations are based on first order perturbation theory and the pseudo-potential theory without resorting to ab-initio simulations. Wherever possible, the results are compared to experimental data or quantum molecular dynamics simulations. In addition a straightforward approach is demonstrated to estimate the complex permittivity from the Drude model.

Flame propagation in nano-aluminum–water (nAl–H2O) mixtures: The role of thermal interface resistance

A detailed numerical analysis of flame propagation in nano-aluminum–water (nAl–H2O) mixture is performed. Emphasis is placed on investigating the role of particle thermal conductivity in the prediction of the burning properties of the mixture. Flame structure and burning characteristics are obtained by solving the energy equation using finite difference discretization and the Gauss–Seidel iteration method. Particle thermal conductivity is modeled using the temperature-dependent thermal conductivities of the aluminum core and oxide layer, as well as their interface resistance. The effective thermal conductivity of the mixture is modeled as a function of temperature, spatial coordinate, and local mixture composition, by means of the unified Maxwell–Eucken–Bruggeman model, accounting for random particle distribution and inter-particle interaction. Results indicate that the combined thermal resistance offered by the oxide layer and the interface constitute 95% of the total resistance of the particle. The calculated particle-size dependent linear burning rates show good agreement with experimental data, with only 5% error. Error in burning rate prediction increases, however, to 20% when interface resistance is excluded from the particle thermal conductivity model. It was also observed that burning rate varies as the inverse of particle size. Finally, an analysis of the sensitivity of burning rate to the individual components of the particle thermal conductivity model is also performed. Results suggest a 30% decrease in burning rate for two orders of magnitude reduction in both interface conductance and oxide thermal conductivity. The burning rate drops by only 15%, however, for a similar reduction in aluminum thermal conductivity. A heat conduction perspective on flame propagation in nanocomposites is presented, identifying the highest and the lowest conductive pathways for energy transport.

Nanosecond laser pulses for aluminum and copper drilling

Nd:YAG laser pulses of 9 nanosecond pulse duration and operating wavelength at 1.06 μm, were utilized to drill high thermal conductivity and high reflectivity aluminum and copper foils. The results showed a dependence of drilled holes characteristics on laser power density and the number of laser pulses used. Drilled depth of 74 ϻm was obtained in aluminum at 11.036×108 W/cm2 of laser power density. Due to its higher melting point, copper required higher laser power density and/or larger number of laser pulses to melt, and a maximum depth of 25 μm was reached at 13.46×108 W/cm2 using single laser pulse.

Effects of Different Backing Materials of Hybrid Rapid Tooling on the Demolding Time in the Hot Embossing Process

Fresnel lenses are becoming more and more important because they are widely used as optical elements for concentrating solar power. Micro-hot embossing is a promising approach to fabricate Fresnel lenses. Precision optical elements must be more quickly and cheaply introduced to the market due to the pressure of global competition. The thermal conductivity of Aluminum (Al)-filled epoxy resins is lower than that of conventional mold steel materials. This work demonstrates a technique for fabricating hybrid rapid tooling with different backing materials to investigate the demolding efficiency in the hot embossing process. It was found that the Al was strongly recommend as backing material for fabricating hybrid rapid tooling due to cost, demolding time efficiency and dimensional accuracy of the embossed parts. Demolding efficiencies for the hot embossing mold with backing materials of copper, aluminum and steel about 78 %, 68 % and 50 % can be enhanced compared to that of the conventional rapid tooling. The replication rate exceeding 96 % in the hot embossing mold manufacturing process can be reached. The transcription rate exceeding 93 % in the hot embossing process can be obtained.DOI: http://dx.doi.org/10.5755/j01.ms.24.3.13897

Numerical modeling for alumina nanofluid magnetohydrodynamic convective heat transfer in a permeable medium using Darcy law

CVFEM is employed in this article to model alumina nanofluid magnetohydrodynamic flow through a permeable enclosure. Influences of Hartmann number, buoyancy, radiation parameters on nanofluid treatment were displayed. Viscosity and thermal conductivity of alumina are predicted considering Brownian motion and shape factor impacts. Results are displayed that Lorentz forces boosts the conduction mechanism. Nuave enhances with reduce of Ha. Augmenting radiation parameter makes thermal boundary layer to be thinner.