Sumit Sharma; Pramod Kumar; Ajay Kumar Diwakar
Abstract
Nowadays there is a requirement of material that has high thermal conductivity as well as suitable electric insulating properties. Such materials are required in industries where thermal management is desirable but electrical conductivity is not required, such as substrates for electronic components ...
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Nowadays there is a requirement of material that has high thermal conductivity as well as suitable electric insulating properties. Such materials are required in industries where thermal management is desirable but electrical conductivity is not required, such as substrates for electronic components and solar panels. In this study, the multi-scale modeling of epoxy (bisphenol-A) reinforced alumina composite has been performed using BIOVIA Materials Studio and Abaqus. Modeling has been done for varying volume fraction (Vf) of alumina. The properties predicted are the thermal conductivity and Young’s modulus. Heat transfer analysis has been done using Abaqus/Explicit. It was found that the thermal conductivity first increased till Vf = 20% and then decreased. When the concentration of alumina was increased further after Vf = 20%, the orientation of alumina particles changed from being in-plane to random, resulting in a fall in the values of thermal conductivity. In the silicon/insulator plate system, there was found to be an accumulation of heat resulting in a decrease in temperature on the bottom surface of the insulator plate. Thus, more time was taken for the heat to conduct through this system. Whereas, when the heat was transferred through the system of silicon/composite plate, no accumulation of heat in the system was observed.
R. Alajmi; B.F. Yousif; F.M. Alajmi; A. Shalwan
Abstract
In this study, the potential of utilizing natural fibres in construction substances is studied such as the compression strength and heat conductivity. Gypsum walls are reinforcement using sisal fibres for the industrial and construction applications. The sisal fibre has been washed by fresh water and ...
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In this study, the potential of utilizing natural fibres in construction substances is studied such as the compression strength and heat conductivity. Gypsum walls are reinforcement using sisal fibres for the industrial and construction applications. The sisal fibre has been washed by fresh water and treated with concentration of NaOH (6%), to achieve a real interfacial adhesion between the gypsum and sisal fibres. To survey the impact of different volume fractions of glass and sisal fibres on the conductivity of gypsum, a newly designed heat conductivity test setup was developed. Also, compressive test was carried out for the selected materials. The scanning electron microscopy (SEM) is using to figure out the failure mechanisms by examining the samples after compressive test. The test outcomes detected that the addition of fibres to the gypsum matrix enhances the compressive strength and led to minify brittleness. The optimum fibre content for sisal fibre-gypsum composite and glass fibre-gypsum composite are at 25 vol. and 30 vol. %, respectively. The pure gypsum samples have achieved the highest value of thermal conductivity among other composite samples in thermal conductivity test. The thermal conductivity of the composites reduce with the increase of fibre volume fraction for both glass and sisal addition of the fibres. Due to porous nature of sisal fibre-gypsum composites, as the presence of air voids work as traps and impeded the heat transfer, sisal fibre-gypsum composites performs better than glass fibre-gypsum composites as an insulation material.
Alena Sicakova; Viola Hospodarova; Nadezda Stevulova; Vojtech Vaclavik; Tomas Dvorsky
Abstract
In this paper, the experimental work providing the testing of cement mixture containing two types of cellulosic fibers, namely fibers from bleached wood pulp and recycled waste paper fibers, is given. Fibers are described by selected characteristics such as length, density, and pH. They were applied ...
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In this paper, the experimental work providing the testing of cement mixture containing two types of cellulosic fibers, namely fibers from bleached wood pulp and recycled waste paper fibers, is given. Fibers are described by selected characteristics such as length, density, and pH. They were applied as additive to the cement composite/plaster while they were dosed in different amounts: 0.2 %, 0.3 % and 0.5 % of the weight of both the filler and binder. Mixtures without fibers were prepared as reference samples. Density, water absorption, thermal conductivity, flexural and compressive strength were studied following by analyses of differences between resulting values. The observed differences in the physical, mechanical and thermal properties were found to be influenced by the properties (such as type, amount and other characteristics) of cellulosic fibers.
Ehsan Rezaei; Jafarsadegh Moghaddas
Abstract
Silica aerogels have interesting physical properties such as hydrophobicity and low thermal conductivity are advantageous for a wide variety of actual applications, such as super thermal insulators. Poor mechanical properties prevented to use silica aerogel directly. In this study, nano silica aerogel ...
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Silica aerogels have interesting physical properties such as hydrophobicity and low thermal conductivity are advantageous for a wide variety of actual applications, such as super thermal insulators. Poor mechanical properties prevented to use silica aerogel directly. In this study, nano silica aerogel and its composite with cotton were synthesized using a water glass precursor by ambient pressure drying method .To modify silica aerogel use trimethyl chlorosilane (TMCS) diluted in n-hexane (1:5 volume ratio). By adding TMCS, –OR groups in silica aerogel structure replaced –OH and silica aerogel became hydrophobic. Thermal conductivity and hydrophobicity of synthesized samples were measured by needle probe method and contact angle meter respectively. Pure silica aerogel contact angel is 166 o and it shows silica aerogel is super hydrophobic. Silica aerogel added to cotton structure in 20 %, 40 %, 60 % and 80 % wt. Silica aerogel particles attached cotton fibers and changed hydrophobicity properties. Contact angels of composites are 115°, 120°, 128° and 129° respectively. Cotton is hydrophilic and its ability to absorb moisture causes decreasing contact angel in composites. Silica aerogel and cotton thermal conductivities are 0.0134 Wm-1K-1and 0.0308 Wm-1K-1respectively. Having low thermal conductivity, pure silica aerogel is known as super thermal. Thermal conductivity of composites was measured 0.0251, 0.0227, 0.0216 and 0.0171 Wm-1K-1 respectively. By increasing silica aerogel ratio, thermal conductivity decreased. In silica aerogel- cotton composite improved structural strength and the thermal conductivity and hydrophobicity were acceptable.
Maria C. Basso; Xinjun Li; Vanessa Fierro; Antonio Pizzi; Samuele Giovando; Alain Celzard
Abstract
New, green and cheap rigid foams presenting outstanding performances for thermal insulation are described. Such ultra-lightweight cellular materials are mainly based on renewable chemicals: tannin and furfuryl alcohol, are very easy to produce and have thermal conductivity as low as 38 mW/m/K. Compared ...
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New, green and cheap rigid foams presenting outstanding performances for thermal insulation are described. Such ultra-lightweight cellular materials are mainly based on renewable chemicals: tannin and furfuryl alcohol, are very easy to produce and have thermal conductivity as low as 38 mW/m/K. Compared to previously reported tannin-based foams, these new materials are much “greener” and present improved resistance to compression and to water. Especially the formaldehyde, formerly used as cross-linking agent of tannins but known as a volatile and harmful chemical, could be successfully removed from the formulation. The as-obtained, 2nd generation, tannin-based foams are totally stable and have an expected interest for thermal insulation of buildings.
P.B. Thakor; Y.A. Sonvane; P.N. Gajjar; A.R. Jani
Abstract
The electronic transport properties like electrical resistivity (ρ), thermoelectric power (Q) and thermal conductivity (σ) of liquid lanthanides are calculated through Ziman’s formulism. To describe electron-ion interaction we have used our newly constructed parameter free model potential ...
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The electronic transport properties like electrical resistivity (ρ), thermoelectric power (Q) and thermal conductivity (σ) of liquid lanthanides are calculated through Ziman’s formulism. To describe electron-ion interaction we have used our newly constructed parameter free model potential alongwith Percus Yevick hard sphere (PYHS) reference system. To see the influence of exchange and correlation effect on the electronic transport properties, we have used five different local field correction functions like Hartree (H), Sarkar et al. (S), Taylor (T), Ichimaru Utsumi (IU) and Farid et al. (F). The obtained results have found good in agreement with available experimental data as well as other theoretical data. Lastly, we conclude that our newly constructed model potential is capable to explain the electronic transport properties of liquid lanthanides.
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