Papers by Keyword: Thermal Conductivity (TC)

Abstract: In this paper, the aluminum nitride (AlN) was fabricated by pressureless sintering with YF3 and various silicon compounds as the sintering aids. The phase, microstructure, density and thermal conductivity were characterized by XRD, SEM and laser thermal diffusivity method. The sample densities were detected varied from 3.17 to 3.30g/cm3 and room-temperature thermal conductivity varied from 196 to 233 W/m·K. Samples sintered with YF3 additives have the highest thermal conductivity. The sintering aids with SiO2, Si3N4 and SiC would decrease the density and the thermal conductivity obviously, and also change the fracture mode from the intergranular to transgranular , which is a key for the toughness of the AlN substrate.

Abstract: Porous silicon nitride (Si₃N₄) ceramics green were prepared by sol-gel and freeze drying processing. Al₂O₃ and MgO were selected as sintering additives. Porous Si₃N₄ ceramics were sintered at 1200~1300 °C. The porosity of porous Si₃N₄ ceramics reached 60~80%, the pore size of porous Si₃N₄ ceramics dried by freeze drying is less than 5μm. Two kinds of pores were formed, including open pores with pore size of 1~5μm and closed pores pore size with the nanometer level. The compression strength of porous Si₃N₄ ceramics was 15~25MPa. Thermal conductivity of porous Si₃N₄ ceramics was 0.08-0.1 W/m·K.

Abstract: The heat conductivity, specific heat and bulk density are the basic material parameters and thus indispensable. There are numbers of methods used for measurement of heat conductivity. However, the non-stationary (transient pulse method) measurements methods are preferred for description of heat conductivity moisture dependence. This article discusses on the establishment dependence of heat conductivity on water content for selected porous building materials by using non stationary measurement methods. Dependence of the thermal conductivity on the water content is necessary for coupled heat, air and moisture (HAM) simulation in building construction.

Abstract: Increasing demand for new progressive construction materials requires development of modern environmentally friendly materials with excellent end-use properties and reasonable price. One of the main objectives of material research in building industry is using renewable resources of raw materials of industrial waste for development of new construction materials. Current trend of thermal insulation of building constructions results in development of environmentally friendly insulation materials based on renewable material resources from agriculture and stock farming, which could became alternative for current common use insulation materials in the future. Paper describes results of research and development of materials based on natural fibres.

Abstract: The comprehensive survey on the thermal conductive cement concrete consists of graphite is obtained in this paper. The effects of graphite on mechanical properties and thermal properties were investigated to determine the optimum materials design. Additionally, scanning electron microscopy (SEM) was used to elucidate micrographs of the fracture graphite modified cement concrete. Result indicated that graphite could greatly improve the thermal conductivity properties of cement concrete, but degrade the related compressive strength simultaneously. When the graphite content is 15%, the increment of the thermal conductivity was 50% while the reduction of the compressive strength was almost 90%. Furthermore, SEM images illustrated that the reason for the degradation of mechanical strength maybe depend on the flake structure of graphite.

Abstract: Based on three-dimensional models of key components, a thermoelastic finite element model of disc brake is established. The results of stress field and temperature distribution are acquired considering the relationship of heat convection coefficient and wheel angular velocity. The effect of heat convection coefficient fluctuation and disc material conductivity fluctuation on the model output is analyzed. The simulation results shows that disc temperature is not sensitive to heat convection coefficient, but sensitive to thermal conductivity. And this model mentioned in this paper is of great significant for building a temperature finite element model with engineering accuracy.

Abstract: The rock soil thermal conductivity is the most important design parameter for the ground source heat pump system. Based on the equation applied for the heat transfer between the geothermal heat exchanger and its surrounding rock soil, a quasi-three dimensional heat conduction model showing the heat transfer inside the borehole of the U-tube was established to determine the thermal conductivity of the deep-layer rock soil. The results obtained show that the average thermal conductivity got through calculation and actual determination in a tube-embedding region of the ground source heat pump engineering were 1.895 and 1.955W/(m·°C), respectively. The soil layer, which has a great thermal conductivity and a strong integrated heat transfer capability, is suitable for the use of the ground source heat pump system with the tubes embedded underground. The soil layer, with a body temperature of 19 °C and a higher initial temperature, is suitable for the heat extraction from underground in winter. The deviation between the calculation and the determination of the average thermal conductivity in the abovementioned region was 0.06, which could meet the required precision, indicating that the results from the calculation could be used for design.

Abstract: The paper introduced a new-style vitrified micro bubbles aerated concrete block. By adding a certain amount of vitrified micro bubbles to general aerated concrete, the compressive and breaking strength can reach the B05 self-insulation standard. And the thermal conductivity of single new-style aerated concrete wall can realize the target of energy saving. It is proved that vitrified micro bubbles aerated concrete is a new wall material with the functions of containment, energy saving, sound insulation and self-supporting.

Abstract: The sludge, dredging silt and other materials prepared by mixing the ceramic, studying the effects of different sludge ratio, sintering temperature, the amount of excess sludge moisture content on ceramic, pile density, ignition loss rate. Produced ceramic concrete specimens tested by experiment and standard ceramic concrete specimens concrete specimen strength and thermal conductivity. Test specimen obtained ceramic concrete compressive strength of 13.57MPa, mixing concrete block compressive strength of 13.96MPa; gravel concrete specimens of thermal conductivity 0.394, ceramic concrete specimens thermal conductivity of 0.387. The results show that adding the ceramic concrete, ceramic concrete strength of certain decline, but the performance is enhanced thermal insulation, thermal insulation properties can greatly enhance it.

Abstract: This study experimentally investigated effect of thermal conductivity on the combustioncharacteristics of gaseous fuel inside a meso-scale combustor. Combustion characteristics that wereobserved in this research include flame visualization and flammability limit. Quartz glass, stainlesssteel and copper tubes with inner diameters of 3.5 mm were used as combustors. Stainless steel wiremesh was inserted inside meso-scale combustor as a flame holder. Liquid petroleum gas (LPG),which is common fuel use by Indonesian people, was used as a gaseous fuel. A stable blue flame wasestablished inside meso-scale combustor at the downstream of wire mesh for all combustor withdifferent thermal conductivity. Furthermore, flame color is blue for combustion of fuel lean orstoichiometric mixture, and blue-green for combustion of fuel rich mixture. Meso-scale combustorwith the highest thermal conductivity has the narrowest flame cross section area, especially at lowerreactant velocity. Vice versa, this combustor has the widest flammability limit, mainly at the higherreactant velocity.