Papers by Keyword: Thermal Conductivity (TC)

Abstract: In this work, pure ZnS and Mn doped ZnS nanoparticles are synthesized by simple chemical precipitation method. The structure of pure zinc sulphide and Mn doped zinc sulphide sample are analyzed by X-ray diffraction technique. The morphological structure of zinc sulphide and Mn²⁺ doped zinc sulphide nanoparticles are studied using scanning electron microscope (SEM). The average particle sizes of pure ZnS nanoparticles are determined to be from 29 nm to 44 nm and Mn doped ZnS nanoparticles are determined to be from 99 nm to 135 nm. The optical properties of pure and Mn doped ZnS nanoparticles have been investigated by photoluminescence (PL) spectroscopy. The emission spectrum of Mn²⁺ doped with ZnS particles of the present study shows blue shift of the yellow-orange emission peak at 590 nm. Nanofluids are prepared for six different concentrations by dispersing pure and Mn²⁺ doped ZnS nanoparticles in de-ionized water. Thermal conductivity studies are carried out for both nanofluid systems and the results are discussed.

Abstract: The purpose of this study is to evaluate the performances of Super Sulfated Cement (SSC) foams, focusing on structural, thermal and mechanical characteristics. The studied set of SSC foam samples is obtained with the same slurry. The chosen foaming method allows an interesting density variation: from 489 kg/m³ to 1793 kg/m³. Thanks to a CCD camera, the visual study of foam pore structure reveals two kinds of bubbles distribution and associated connectivity. This may partially explain the obtained thermal and mechanical behavior. Results show that SSC foams with low density (< 550 kg/m³) are usable as thermal insulator for non-loadbearing walls. Mean density SSC foams (550 kg/m³ < - < 640 kg/m³) can be used as slight-loadbearing and thermal insulating products in housing and SSC foams with high density (640 kg/m³ < - < 1200 kg/m³) as loadbearing products staying within lightweight class.

Abstract: In modern science and engineering nanofluids are playing a vital role in the application of heat transfer devices due to their effective properties. Addition of nanoparticles in the fluid can alter thermophysical properties of the nanofluid. Experimental and theoretical studies are essential to understand the change in fluid dynamics aspects of the fluid by the addition of nanoparticles. This paper presents a brief review on the viscous and thermal transport effects of nanofluids. The main emphasis is on the comparison of previous theoretical and experimental studies for thermophysical properties of nanofluids. These properties include density, viscosity, thermal conductivity and specific heat capacity of nanofluids.

Abstract: Polydimethylsiloxane (PDMS) has widely appeared in different electronic and medical applications. The knowledge of the thermal properties of PDMS and especially its thermal conductivity is required while processing PDMS to design a particular device. In this paper measurement of the thermal conductivity of PDMS using the three omega method is presented at different temperatures. The three omega method has been chosen because of its ease of use and accuracy. It requires the fabrication of metallic lines which act as heaters and thermometers on the surface of the material under test. A different procedure is introduced in this paper through which the metallic lines are embedded in the surface of PDMS. Experimental results are then compared to Cahill's approximate solution and to the results obtained by numerical simulations using a finite element method.

Abstract: The presented work is aimed at determining thermal diffusivity, thermal conductivity and heat capacity coefficients of silica quartz bentonite foundry sand. The values of the above thermo-physical properties were determined for temperature range of about 30 - 450 °C using the Casting measuring method [1-. The results obtained during the examinations presented in the paper can be useful when formulating boundary conditions in numerical models of heat and mass transfer in the system: casting mould ambient. The Casting method allows preserving real conditions during the experiment, i.e. contact of the mass with liquid metal and solidifying casting, and the obtained results are in a good agreement with the mean values available in literature. From the obtained results it follows that examinations should be also focused on thermo-physical properties vs. mass density dependency.

Abstract: The mill scale (MS) waste is produced in steel industry during the milling process from the rapid oxidization of the hot iron products, and is mainly consisted of iron oxides (>95%). The aim of this work is to evaluate the utilization of MS (known in Greece as “kalamina”) as an admixture in clay bricks manufacturing by applying extrusion and sintering processes. For that purpose, specimens were formed from various clay/MS mixtures (up to 9 wt% MS) and then fired at different temperatures (up to 1100°C). Shrinkage and weight loss upon firing as well as density, porosity, bending strength and thermal conductivity of sintered specimens were determined and studied as a function of the % MS content and the firing temperature for optimization. The experimental results show that the incorporation of MS in clay bricks production is feasible, as an efficient secondary resource, thus turning waste from one industry into useful feedstock for another one. Specifically, the mechanical performance and thermal conductivity are not significantly affected with increasing the mineral admixture percentage and the sintering temperature.

Abstract: The porous mullite ceramics doped with such metal oxides as ZrO₂, WO₃ and MgO in quantity of 5 wt% were prepared by slip casting method. The mullite phase was the main and dominant phase of ZrO₂-, WO₃- and MgO-doped samples, which were sintered at the temperatures of 1650°C, 1500°C, respectively. The ZrO₂, WO₃ and MgO had the positive effect on the increase of porosity and decrease of thermal conductivity of porous mullite ceramics and the degree of this effect was in the order of ZrO₂<MgO<WO₃.

Abstract: This paper presents investigations of thermal conductivity, tensile strength and compressive stress at 10% deformation of effective thermal insulation composites made from hemp shives and sapropel. Images of hemp shives and hemp composite microstructure obtained by scaning electron microscope (SEM) are analised. The paper presents properties of composite from seven compositions. Composite forming mixture contains different amount of sapropel as well as paper production wastes (PPW) obtained in paper processing industry.

Abstract: Natural fibres from flax and hemp are used as raw materials for efficient thermal insulation. In current work, tests were carried out using chopped and combed long flax fibres as well as chopped and combed long hemp fibres. Investigations have shown that thermal conductivity of natural fibres depends on their preparation method (combing, chopping) and materials density.

Abstract: Highly dense AlN/CNT composite ceramics with 1-10% volume fractions of CNT were fabricated by spark plasma sintered (SPS) at 1400°C-1700°C. The results indicated that origination diameter of AlN had a great effect on microstructure and thermal conductivity. In details, for the system with AlN origination diameter of nanosized, the tubular structure of CNT has not been destructed, but when micro-sized AlN powder was adopted, the structure of CNT showed unstable at high temperature. Even though the degradation with incorporation of CNT into AlN, thermal conductivity of sintered AlN/CNT composites ceramics was evidently improved by adjusting content of additive Y₂O₃ and the sintering process. Both the real part and imaginary part of the composites of Ka-Band (26.540.0 GHz) increase with the increase of CNT content, in which the increase of imaginary part is more than that of real part, resulting in an increase of loss factor. The AlN/ CNT thermal conductivity composites with appropriate CNT content and sintering temperature possess good dielectric dissipation and thermal conductivity.