Papers by Keyword: Thermal Resistance

Abstract: Geopolymer is an alkali-activated aluminosilicate material that combine ceramic-like thermal performance with low thermal conductivity, high-temperature resistance, while remaining castable and structurally adaptable. It is synthesized from calcined kaolin (metakaolin) and fly ash, which react with alkaline solutions to form strong covalent bonds through geopolymerization. This material offers a viable alternative to conventional refractories and imported ceramic products.In this study, a geopolymer material was developed for welding applications and utilized as a weld backing strip for gas metal arc welding (GMAW) of ASTM A36 carbon steel. Weld backing strips are essential for achieving full penetration and consistent root quality in large-scale steel fabrication, particularly in structural, shipbuilding, and heavy industrial construction. The geopolymer binder consisted of 35 wt% metakaolin, 15 wt% fly ash, and a 1:1 ratio of 10 M NaOH and sodium silicate solution. To enhance thermal resistance, river sand, fine glass powder, or recycled SAW flux was incorporated as an external solid phase. Geopolymer specimens were thermally cured and fired at 500 °C to eliminate moisture and organic. Moreover, it was heated to 900 °C to simulate welding heat exposure. Microstructural, mineralogical, and functional group transformations were evaluated using XRD, SEM, and FTIR, while mechanical strength, thermal conductivity, and density were also assessed. The results indicated that glass-enhanced geopolymer exhibited the lowest thermal conductivity (0.89 W/m·K) and highest compressive strength retention after firing, owing to its partial crystallinity and preserved amorphous phase. Flux-based composites showed extensive ceramic phase formation, while sand-based composites retained high thermal conductivity and suffered severe strength loss. Welding trials confirmed that geopolymer backings effectively supported root bead formation with no cracking.

Abstract: A heat sink is a cooling device that transfers the dissipated heat away from electronics to the surroundings. The testing method presented in the paper applies the nonequilibrium thermodynamic analysis of heat sink cooling curves. Here, the heat sink temperature time course is measured by using a thermal imager. The used thermal imager Flir T-640 takes single shots with recording of images. The proposed method validation test was performed on a selected heat sink. By analyzing the heat sink cooling curves, it is possible to obtain courses of the heat power and the heat sink surface to ambient thermal resistance. The presented testing method also enables a thermal analysis to distinguish between the convective and radiative components of heat transfer.

Abstract: In this study, we developed alkali-activated geopolymer cement (GP) using finely powdered granite waste (GW), blast furnace slag (BFS), and nano-silica (NS). NaOH and Na₂Si₂O₃ (1:1) were used as an alkaline activator to activate the GP mix and promote the alkali-activation reactions. The mechanical properties of various GP mixes were analyzed to evaluate the durability of the resulting GP when subjected to firing at temperatures up to 750°C and the destructive effects of gamma-ray irradiation. The study revealed that blending up to 30% granite powder to the GP formulation led to faster setting due to the excess soluble Si ions sourced from the granite powder which accelerated the alkali-activation reactions and increased the stiffness of the pastes. Additionally, blending the GP mix by 10 % GW improved the compression resistance by 7 to 10 % during the later curing ages. Besides, these blended mixes have thermal stability behaviors against firing up to 750°C and irradiation by gamma rays. This is related to the thermal stability and heat storage capability of GW. Amelioration of BFS/GW mix by up to 2% NS greatly improves the compression resistance at all the stages of the alkali-activation process. Furthermore, the mixes reinforced by NS exhibited better durability in the two types of deterioration studied. This is attributed to the thermal stability of GW and the filling and/or catalytic actions of the dispersed nanoparticles through GP matrix. These factors strengthen the geopolymer network, enabling it to withstand the deteriorating effects of these harsh environments.

Abstract: Understanding heat transfer phenomena is crucial in high-power amplifiers to keep components within safe operating temperatures. This article investigates the GaN Power Amplifier (PA) thermal analysis for the optimum design of the heatsink. GaN PAs are roughly separated into junction, package, and heat sink layers to calculate the junction’s transient thermal response. It has been proven that allowing individual components to operate at temperatures over their maximum rated junction temperatures significantly reduces the system's operational reliability as a whole. This analysis investigates two different heat sinks for the optimum case temperature (T_case) for these different PAs. These PAs are operating S-band (2-3.4 GHz) and C-Ku-band (5-18 GHz) with drain efficiency of 60-65% and 9-22%, respectively. The design analysis of the heat sink for optimal performance is explored in this work.

Abstract: The article is devoted to the problem of reducing energy consumption in the production of building materials and the operation of buildings by replacing the traditional wall material with more efficient material such as lightweight concrete based on the porous filler of glass granulate (foamed glass granulate concrete) and mineral wool mats, as well as the analysis of the thermal stability of enclosing structures with non-stationary heat flow. Much attention is paid not only to the energy efficiency of systems providing microclimate but also to the efficiency of capital construction, since the development of market relations in the economy has led to a significant increase in the prices for all types of energy carriers. The right shape tuff has been applied in Armenia for the wall material, obtained by sawing mechanically from a rock mass, which in modern construction becomes ineffective, as the thermal technical requirements for building envelopes have become tougher. During the mining of the rock, huge amount of wastes have been accumulated that have valuable properties and can serve as raw materials for obtaining building materials according to energy-saving schemes because of their activity. The issue of disposal of these wastes, which are of great importance both from an economic and environmental point of view, is considered. Given that building materials, products and structures account for 50÷60% of construction costs, the choice of energy-efficient, environmentally friendly building materials will significantly reduce construction costs and lower operating costs. Clinker-free binders have been developed on the basis of cement-free concrete of cellular and conjoint structure using the inherent activity of the rock and by means of energy-saving technologies. In these article thermal technical requirements for enclosing construction in some developed countries and the classification of buildings in terms of energy saving are considered. The ways to improve the energy efficiency of buildings in Armenia are considered taking into account the duration of the heating season with the thermal resistance required ranges from 1.8 to 4.6 (m^2oC) /W. In the view of the peculiarities of climatic conditions in Armenia it is not possible to limit only by indicators of thermal resistance, it is necessary to take into account the heat absorption, thermal stability and thermal inertia of materials. Based on the calculations found that in the structure of construction the lowest fluctuation in temperature takes place with mineral wool mat A_τ=0.167°C, and the largest - concrete on foam glass granulate A_τ=0.381 °C, in addition, a change in the temperature of the outside air does not immediately affect the change in temperature on the inner surface of the structures, since there is a time deviation between a concrete on foam-glass granulate which is 7.16 hours and mats on mineral wool - 8.44 hours.

Abstract: The present paper deals with the determination of the mechanical and physical properties of the heavyweight concrete formulation used in the shielding construction of the reactor casing power plant. The recipe includes the use of baryte and cast-iron crumbs as fillers for the preparation of heavyweight concrete. The binder paste was obtained using CEM I 42.5 R with w/c ratio = 0.44 and a lignosulfonate-based plasticizer prepared according to the used Ralentol plasticizer's standard requirements, which is currently no more produced. The result of the concrete slump according to the S -cone was S1 (1 cm slump). The bulk density of fresh and hardened concrete was over 4000 kg m^-3. The compressive strength at 28 days exceeds 80 N mm^-2 and the flexural strength is 4 N mm^-2. The modulus of elasticity is 40 GN m^-2. The shrinkage of concrete is 0.52 ‰. The weight loss due to shrinkage rises to almost 1.3 %. The thermal properties of the heavyweight concrete are as follows: the thermal conductivity λ is 2.2 W m^-1 K^-1; the thermal resistance R for thickness d = 1 m is 0.44 m² K W^-1; volume heat capacity c_ρ rises to almost 2 J m^-3 K^-1 and thermal diffusivity a 10^-6 drops to 1,15 m² s^-1.

Abstract: New halogen-containing oligoethers based on 1,1-hydroxy-2,2-di (4-hydroxyphenyl) ethylene and 1,1-dichloro-2,2-di (4-hydroxyphenyl) ethylene of various degrees of condensation were synthesized by the method of high-temperature polycondensation. Features are investigated and optimal conditions of synthesis of new oligoethers are defined. On the basis of polysulfone compositions with various maintenance of oligoethers are prepared. With usage of the modern methods of researches, it is shown that new composites surpass industrial polysulfone in the main physical and chemical and production characteristics.

Abstract: At present, the existing thermal interface materials (TIMs) cannot meet the heat dissipation requirements of some high-power density electronic devices. In this study, Bi-based low melting point alloy was made into a thermal conductive sheet to reduce the interface thermal resistance. The thermal conductivity of a thermal conductive sheet was found to be 37.83 W/(m·K), 10 times higher than Dow Corning 5021 thermal grease. In addition, the surface morphology of the Bi-based alloy thermal conductive sheet was changed in this experiment, which was divided into textured and planer type, and the measured interface thermal resistance values lower than Dow Corning 5021 thermal grease by approximately 30% and 27%, respectively. The results prove this Bi-based alloy thermal conductive sheets have the ideal heat dissipation performance and their wide application prospects in high-power density electronic devices.

Abstract: In the article research results are presented, which aim to provide evaluation of thermal protection properties of volume textile materials. However, as a result of experts wearing it has been revealed that by their operational performance their characteristicsare quite high to such materials: Holofiber, Tinsulate, Arctic, etc. At the present time to research thermal protection properties of sewing materials methods are used that can be divided into 2 groups: Methods based on the principle of steady heat mode and Methods based on the principle of unsteady (regular) mode. New device has been developed which allows to simplify both the schematic diagram and the methodological approach to experimental evaluation of thermal protection properties of volume textile materials. The corresponding experimental research were held based on the developed bicalorimeter. Study results allowed to establish heat insulation material «ArcticP» possesses the highest thermal resistance.It is located with its metallized coating facing outside. High values of thermal protection properties of this material are explained by availability of metallized coating from outer side which ensures partial heat reflection.. The research was made in Don State Technical University within the framework of State Assignment of the Ministry of education and science of Russia under the project 11.9194.2017/БЧ.

Abstract: Bulk moulding compounds (BMCs) are composite materials of thermosetting polymer matrix reinforced by short glass fibers. BMCs have known as the alternative of the traditional materials thanks to their optimal properties such as lightweight, durability, corrosion under certain environment, formable, high electrical resistance... The previous study mentioned the process of manufacturing composite materials BMCs from unsaturated polyester resin reinforced with short glass fiber and CaCO₃ filler by Z axis mixer and applying in the circuit breaker bottom, [1, 2]. To improve the thermal resistance of BMCs under high temperature condition in the industry, in this research, alumina filler was added to investigate the influence of alumina with the different content of 15wt.% and 20wt.% on the mechanical, thermal and electrical properties of BMCs. Specimens manufactured with and without alumina filler content were compared. The results show clearly that adding alumina could improve the thermal properties whereas this might decrease the tensile strength of BMCs. The experimental results also indicated the influence of mass fraction of alumina filler content on properties of BMCs.