229,511 research outputs found

    Remarkable thermal conductivity enhancement in Ag‚ÄĒdecorated graphene nanocomposites based nanofluid by laser liquid solid interaction in ethylene glycol

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    We report on the synthesis and enhanced thermal conductivity of stable Ag-decorated 2-D graphene nanocomposite in ethylene glycol based nanofluid by laser liquid solid interaction. A surfactant free nanofluid of Ag nanoparticles anchored onto the 2-D graphene sheets were synthesized using a two-step laser liquid solid interaction approach. In order to understand a pulsed Nd:YAG laser at the fundamental frequency (őĽ‚ÄČ=‚ÄČ1,064 nm) to ablate Ag and graphite composite target submerged in ethylene glycol (EG) to form AgNPs decorated 2-D GNs-EG based nanofluid. From a heat transfer point of view, it was observed that the thermal conductivity of this stable Ag-graphene/EG is significantly enhanced by a factor of about 32.3%; this is highest reported value for a graphene based nanofluid

    The thermal conductivity of the masonry of handmade brick Cultural Heritage with respect to density and humidity

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    This work was carried out with funding from the Ministry of Economy and Competitiveness of Spain and the European Regional Development Fund (ERDF) for the project entitled: ‚ÄúProposal evaluation of the humidity that rises by capillarity in the masonry walls of the historical heritage through non-destructive testing‚ÄĚ BIA2015-68449 ( MINECO / FEDER, EU ) at the ETS Construction Laboratory of Architecture of the University of Valladolid, in which researchers from the Universities of Valladolid, Salamanca and Granada have participated.It is very common that the energy refurbishment of buildings of Cultural Heritage is undertaken without considering that their materials and the methods of construction are different from those of modern buildings. Therefore, when seeking the most efficient and effective solutions from an energy point of view, the first step is to understand the thermal characteristics of the materials with which these buildings were constructed. Likewise, as part of this heritage, the fact that many such buildings were constructed using uncoated bricks and with rich voluminous ornamentation or murals must be taken into consideration. This prevents the use of normal construction solutions which consist of attaching a layer of insulating material to the interior or exterior. In addition, the rich surface ornamentation of the walls is not conducive to carrying out tests in situ, so other procedures are needed to determine the thermal behaviour of the facade and thus be able to determine the most appropriate processes for their conservation. To this end, various heat flow tests have been carried out on brick masonry specimens that have characteristics similar to those of the walls of such buildings. This allows an abacus of the approximate thermal conductivity of such brick masonry to be produced with respect to the density of the brick and the moisture content of the wall. The values ‚Äč‚Äčof this abacus will serve as a reference to guide the energy refurbishment work to be performed on these buildings.European CommissionMinisterio de Econom√≠a y CompetitividadEuropean Regional Development Fund BIA2015-6844

    Thermal conductivity enhancement of laser induced graphene foam upon P3HT infiltration

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    Significant research has been dedicated to the exploration of high¬†thermal conductivity¬†polymer¬†composite materials¬†with¬†conductive¬†filler particles for use in heat transfer applications. However, poor particle dispersibility and interfacial phonon scattering have limited the effective¬†composite¬†thermal conductivity.¬†Three-dimensional¬†foams¬†with high ligament¬†thermal conductivity¬†offer a potential solution to the two aforementioned problems but are traditionally fabricated through expensive and/or complex manufacturing methods. Here, laser induced¬†graphene¬†foams,¬†fabricated through a simple and cost effective laser ablation method, are infiltrated with poly(3-hexylthiophene) in a step-wise fashion to demonstrate the impact of¬†polymer¬†on the¬†thermal conductivity¬†of the¬†composite¬†system. Surprisingly, the addition of¬†polymer¬†results in a drastic (250%) improvement in¬†material¬†thermal conductivity,¬†enhancing the¬†graphene¬†foam's¬†thermal conductivity¬†from 0.68‚ÄČW/m-K to 1.72‚ÄČW/m-K for the fully infiltrated¬†composite material.¬†Graphene¬†foam¬†density measurements and theoretical¬†models¬†are utilized to estimate the effective ribbon¬†thermal conductivity¬†as a function of¬†polymer¬†filling. Here, it is proposed that the¬†polymer¬†solution acts as a binding¬†material,¬†which draws¬†graphene¬†ligaments together through elastocapillary coalescence and bonds these ligaments upon drying, resulting in greatly reduced contact resistance within the¬†foam¬†and an effective¬†thermal conductivity¬†improvement greater than what would be expected from the addition of¬†polymer¬†alone

    Thermal conductivity probe

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    Low-mass probe accurately measures the thermal conductivity of polyurethane foam /and other thermal insulating materials/ while exposed to either hydrogen of helium permeation in temperature ranges from ambient to cryogenic. The thermal conductivity of a specimen is determined from an experimentally determined increase in temperature

    A Universal Gauge for Thermal Conductivity of Silicon Nanowires With Different Cross Sectional Geometries

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    By using molecular dynamics simulations, we study thermal conductivity of silicon nanowires (SiNWs) with different cross sectional geometries. It is found that thermal conductivity decreases monotonically with the increase of surface-to-volume ratio (SVR). More interestingly, a simple universal linear dependence of thermal conductivity on SVR is observed for SiNWs with modest cross sectional area (larger than 20 nm^2), regardless of the cross sectional geometry. As a result, among different shaped SiNWs with the same cross sectional area, the one with triangular cross section has the lowest thermal conductivity. Our study provides not only a universal gauge for thermal conductivity among different cross sectional geometries, but also a designing guidance to tune thermal conductivity by geometry.Comment: 22 pages, 6 figure
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