Papers by Keyword: Thermal Resistivity

Abstract: This paper presents a comprehensive examination of foamed concrete and its use in contemporary building technology. Due to its lightweight and porous properties, foamed concrete provides notable advantages such as improved thermal insulation, soundproofing, and decreased structural load. The assessment documents progress in foamed concrete technology, encompassing enhancements in mix composition, resilience, and environmentally sustainable manufacturing techniques. Notwithstanding its benefits, the presence of problems such as variable quality control, absence of standardized testing, and long-term performance problems is emphasized. The analysis also examines the many uses of the material, ranging from structural elements to non-structural filler, and its contribution to sustainable building methods. The paper suggests future research paths that highlight the need of conducting further study on performance optimization and expanding the range of application scenarios. By effectively tackling these obstacles and capitalizing on continuous technical progress, foamed concrete has the capacity to greatly influence modern building methods, providing a range of environmental and economic advantages.

Abstract: Understanding the thermal properties of a construction material is necessarily to evaluate its heat transfer resistance that has a major contribution to the energy-efficiency required to achieve sustainable structure. Thermal properties are evaluated through three main parameters namely: thermal conductivity, thermal resistivity and thermal transmittance. The aforementioned parameters are commonly referred as K-value, R-value, and U-value respectively. Recent regulations by Dubai municipality enforced to use sustainable concrete in construction. This is by replacing cement with supplementary cementitious materials (SCMs), such as grand granulated blast furnace slag (GGBS) and fly ash. The use of grand granulated blast furnace slag (GGBS) at relatively high percentage replacement became a typical practice in ready-mixed concrete industry in Dubai. As such, it is essential to characterize the thermal properties of this sustainable concrete. The current paper investigates the thermal properties of sustainable concrete mixtures incorporating supplementary cementitious materials, air entrainment additives, polypropylene and hybrid synthetic fiber. K-value, R-value and U-value are evaluated in accordance with ASTM C518. Additionally, hardened density of all investigated mixtures are measured. The results show that the foamed concrete has better heat transfer resistance than that for the non-air entrained mixture.

Abstract: This paper reports work done which seeks to enhance the insulating property of locally mined clays with application to the building and insulation of medium temperature furnaces. Mixtures of locally mined clays with kaolin obtained from Teleku bokasso in the Western Region of Ghana were made. Samples were mixed in different ratios to form composite bodies in the form of bricks of dimensions 7mm×7mm×7mm cast at constant pressure and sintering temperature of 1000 °C. The clays used were characterized in terms of their particle size and chemical composition. The thermal resistivity, water absorption, weight loss, shrinkage, porosity and strength of samples were determined. The results showed that for all samples studied, an increase in Teleku bokasso clay enhanced the insulating properties of the samples from an average of 0.24% for samples containing 20% Teleku bokasso to approximately 2% for samples containing 60% of Teleku bokasso. Mixtures of Teleku bokasso with Afari clay were on the average 1% more thermally resistant than those of Mfensi. Sample A3 (with 40% Teleku bokasso with Afari) is recommended for the building of local furnaces because it had its strength more than doubled (105%) and was by 2% more resistant to heat than M3 (40% Teleku bokasso with Mfensi). All samples showed low weight loss levels, low water absorption, good linear shrinkage and compressive strength.

Abstract: In this study, we analyzed the effect of microstructure and oxygen content on the thermal conductivity of dense AlN ceramics by Slack’s plot, which plots the oxygen content estimated from the lattice parameter c versus the thermal resistivity, which is inverse of the thermal conductivity. The analyses were carried out for the AlN ceramics sintered with oxide additives such as Y2O3, Y2O3-Al2O3, or Y2O3-CaO-B. The data of AlN ceramics sintered with Y2O3 or Y2O3-CaO-B located on the plot of the relation between oxygen content in AlN lattice and thermal resistivity of AlN presented by Slack (Slack’s line) or Harris et al (Harris’s line), respectively. In contrast, the data of the sample sintered with Y2O3-Al2O3, which contains excess grain boundary phases, located above the Harris’s line. These results suggest that the thermal conductivities of AlN ceramics are influenced by not only the oxygen contents in the AlN lattices but also the contents of grain boundary phases.

Abstract: In this paper we compare the thermal behavior of identical SiC Schottky diodes mounted in i) a standard TO220 package (TO220) with non-isolated backside applying standard soft solder and diffusion solder die attach with ii) a so called FULLPAK TO220 package (TO220FP, only diffusion soldering). Depending on the solder technique the heat transport from the junction area of the SiC Schottky diode to the heat sink or to the package backside is improved for the diodes mounted via diffusion solder. For small chips this holds even for TO220FP in comparison to TO220 with standard solder. Simulations of the vertical temperature distribution after electrically heating with a half sine wave for 10ms up to 190W show a decrease of the maximal junction temperature of the SiC Schottky diode from TJ=260 °C to TJ=180 °C if the diffusion solder is used independent from the package type.

Abstract: The LED chips, packages and related materials have been already key issue on electronic applications and substitution of conventional lights. It is easily expected that the development trend of LED products is nearly the same as that of electronic products with higher performance, higher integration, lower energy and lower cost. And then we also prospect that the dissipated heat from LED chip is to be big problem for a reliability of products, as likely that electronic packages contain heat sink or heat spreader for controlling heat dissipation. In fact, the heat from an LED package with 1~3W LED chip shows a nearly 60~150°C, which affects thermal damage related to performance, joint failure, crack, etc. The thermal via was fabricated with 16 segments of via sizes ranged 0.2~1.2mm and via pitches ranged 0.5~3mm using 1~3W LED, respectively. The thermal resistivity was analyzed by the thermal transient tester with the variation of via sizes and pitches, which was also compared with the temperature difference of the top and bottom side of LED package. As a results, we convincingly proved the relationships between the design of thermal via and the heat dissipation of LED module, which were directly applicable to LED industry.

Abstract: Light emitting diode (LED) has been largely used in industry of consumer electronics such as cell-phones, PDAs, and computers. Since all light sources convert electric power into radiant energy and heat, LED also does the same with an increase of its power. Generally, it only converts 15~25% of electric power into visible light; the rest of the power, 75~85%, is converted into heat. This excess heat should be conducted away from the LED die to circuit boards or heat sinks since heat affects directly performance of the LED. The piled heat in LED products brings color shift and reduces light output very rapidly. Furthermore, the lifecycle of LED products shorten if the heat problem continues. In order to prevent LED products from these negative effects, effective thermal resistance paths need to be achieved so that LED products let the heat conduct from the LED to the outside such as printed circuit board. In this research, optimization studies on thermal-via is to be performed. The 1W and 3W LED assembled printed circuit board with 16 different via designs is set up to measure its temperature for 4 hours in a real time. It was obtained by this work that the optimized thermal via was very effective to dissipate the heat from the LED.