Terms Of Thermal Conductivity Research Articles

Lightweight alkali-activated materials and ordinary Portland cement composites using recycled polyvinyl chloride and waste glass aggregates to fully replace natural sand

Polyvinyl chloride plastic (PVC) and glass waste have proven to be significant environmental concerns considering their restricted reuse and complicated recycling procedures. Glass and PVC waste materials form a substantial portion of total solid wastes that negatively influence the environment. This study aims to fully replace natural sand with recycled PVC and waste glass aggregates in alkali-activated materials (AAMs). A comprehensive testing programme was employed to investigate the effect of 100 % aggregate replacement on the composites’ mechanical performance, water absorption, impact resistance, thermal conductivity, resistance to harsh environments, and microstructural changes. Results revealed that AAMs containing recycled PVC and glass aggregates outperformed their ordinary Portland cement (OPC)-based composite counterparts in terms of mechanical properties, energy absorption, thermal conductivity, and carbon footprint estimation. Although mixtures containing recycled aggregates cannot be deemed for load-bearing applications, these composites exhibited a promising capacity to be used in insulating applications. AAMs containing 100 vol-% PVC aggregates with flexural and compressive strengths of 9 and 11 MPa, respectively, registered the highest energy absorption of about 6 J, three times higher than the AAM control sample, and the lowest thermal conductivity of about 0.5 W/mK, with about 80 % reduction of thermal conductivity compared to the AAM control sample. With the full replacement of PVC and glass aggregates, the most significant decrease in the carbon footprint is achieved for AAM (−352.25 kg CO2-eq) and OPC (−353.94 kg CO2-eq), respectively.

Influence of Pozzolans and Hemp Shives on the Properties of Non-Autoclaved Foamed Concrete.

In this study, new foam concretes incorporating hemp shives without the use of autoclaving have been developed and studied. Several protocols and parameters were investigated. Firstly, the influence of the addition of pozzolanic additives on the resulting density, mechanical behaviour and thermal conductivity was examined. Secondly, the effects of the incorporation of hemp shives at 5, 10 and 15 vol% on the previous three properties in such concretes were investigated. Moreover, economic cost and CO2 emissions were estimated to outline an optimized formulation of non-autoclaved biobased foam concretes. First, the target characteristics in terms of compressive strength (minimum of 2 MPa), thermal conductivity (less than 0.2 Wm-1K-1) and density (800 kg/m3) were achieved. It was noted that pozzolanic additions slightly improved the mechanical and thermal strength of non-autoclaved foamed concrete, while the addition of hemp shives improved the thermal strength but had an unfavourable effect on the mechanical strength. Moreover, both reduced the CO2 emissions.

3D printing for heat transfer: characterisation of additive manufactured copper

Recent technological advancements now allow for copper to be 3D printed, opening the doors for this technology to take a greater part in heat transfer applications. In this study, copper samples were additively manufactured through a print-debind-sinter process and thermally characterised in terms of thermal conductivity and specific heat capacity, and mechanically characterised in terms of Vickers hardness. The microstructure porosity levels appeared to control the thermal properties measured, with the thermal conductivity, while the specific heat was unaffected, while the heat treatment effect caused by the sintering process appeared to control the Vickers hardness measured.

A bibliometric analysis on graphene nanoplatelet for Sustainable material

• This paper performs a bibliometric analysis on the publications of Graphene nanoplatelet (GNP) as listed on Scopus database with Harzing’s Publish or Perish and VOSviewer. • The patterns of GNP publications such as years, document types, source and subject types, countries, co-authorships, keywords and citation metrics are presented in this paper. • This paper has been conferred with the Best Paper Award in the Second Global Conference on Recent Advancements in Sustainable Materials (GC-RASM 2022). Graphene nanoplatelet (GNP) has become the focus of researchers in industry and the academics. The adoption of GNP has been widely proposed in medicine, electronics, chemistry and construction over the years. Therefore, this paper performs a bibliometric analysis on the 1942 publications of GNP as listed on Scopus database from 2013 to 2022 with Harzing’s Publish or Perish and VOSviewer. Publication growth has been steady since 2017 with most of the papers published as articles and in journals. Most publications are listed under materials science, engineering and chemistry. China, United States and India have the most contributions on GNP literature while South Korea has the highest citations per paper and citations per cited paper. From the keyword analysis, researchers are still interested in understanding GNP in terms of mechanical properties, thermal conductivity, functionalization, heat transfer, tensile strength and viscosity. This paper also presents the co-authorships, top source titles, popular publications and citation metrics. GNP materials are expected to increase in the coming years due to its practicality. Future studies can be performed on other carbon-based derivatives to understand their roles in various industries.

Experimental Characterisation of Different Ecological Substrates for Use in Green Roof Systems

Green roofs are made up of several components, including those belonging to the waterproofing and drainage layers, substrate, and vegetation. Of these, the substrate is undoubtedly one of the most important layers of a green roof, contributing not only to the healthy growth of vegetation but also to the water retention capacity and thermal behaviour of the whole solution. Although green roofs are widely recognized as sustainable solutions, it is possible to further improve their environmental performance by developing more ecological substrates that contain industrial by-products. Bearing this objective in mind, sixteen newly developed substrates were characterized in terms of thermal conductivity, specific heat, emissivity, water vapour transmission, hygroscopic sorption, and water retention/drainage capacity. These properties are extremely relevant when solving heat and mass transfer problems as well as for water management prediction. Two reference substrates were also studied for comparison purposes. The results showed that the new ecological substrates have properties that make them comparable to conventional substrates already available on the market. Additionally, the results showed that temperature, moisture content, and density play an important role in the behaviour of substrates of this kind and have a significant influence on many of the studied properties.

Sheath-core structured Ca-alginate/PVA aerogel fibers via directed freezing wet-spinning

Biomass-based aerogel fibers have attracted increasing attention due to their renewable nature. However, their disadvantages, such as low mechanical strength, poor long-range order, and easy combustion, are still significant challenges. Herein, a directed freezing-assisted forced stretching strategy is developed to fabricate sheath-core structured Ca-alginate/polyvinyl alcohol (Ca-A/PVA) aerogel fibers with Long-range-ordered pores. The Ca-A/PVA aerogel fibers (3:2 m/m) exhibit the best comprehensive mechanical properties in terms of low thermal conductivity of 0.0524 W·m−1·K−1, a density of 0.1614 g·cm−3, a porosity of 89.9 %, a tensile strength of 8.72 MPa, a tensile modulus of 249.7 MPa, a toughness of 1.98 MJ∙m−3, and a self-extinguishing time from the fire of <1.2 s. The Ca-A/PVA fabrics showed a maximum absolute temperature difference of 11.4 °C at −20 °C and 14.0 °C at 60 °C compared to the plate temperature. The presented strategy is generalizable to other alginate-based aerogel fibers (e.g., alginate/guar gum).

Parametric Investigation of Closed Loop Pulsating Heat Pipe with Cerium Oxide Nanofluid

In this study, a closed-loop pulsating heat pipe experimental investigation was done with 1% wt concentration of cerium oxide/EG-water (60-40) nanofluid. The unsteady state measurement was done to determine the effect of heat input, filling ratio and evacuation pressure on the thermal performance of the closed-loop pulsating heat pipe. The thermal performance is assessed in terms of temperature variation, thermal resistance and effective thermal conductivity of the pulsating heat pipe. The most appropriate behaviour is observed at 0.0799 bar evacuation pressure with 50% FR. The lowermost thermal resistance of 0.116598K/W was observed at 0.0799 bar evacuation pressure and 50% FR. The effective thermal conductivity value was observed as 5078.34 W/mK at 50% FR, 0.0799 bar for 80W heat input which is 12 to 13 times better than pure copper. The pulsation action inside the pulsating heat pipe is verified with the power spectral density analysis. This study supports the better performance of the heat pipe at 50% FR with a lower evacuation pressure of 0.0799 bar.

Heat Transfer in an Inclined Rectangular Cavity Filled with Hybrid Nanofluid Attached to a Vertical Heated Wall Integrated with PCM: An Experimental Study

In this paper, natural convective heat transfer in a rectangular cavity filled with (50% CuO-50% Al2O3)/water hybrid nanofluids connected to a wall containing a phase change material (PCM) has been experimentally investigated. The vertical walls were heated at varying temperatures while the horizontal walls were kept adiabatic. The considered parameters were the concentration of hybrid nanomaterial (Φ = 0.03, 0.05), the cavity inclination angle (θ = 0°, 30°, 45°), and the temperature difference between the hot and cold sides (∆T = 10, 15, 20 °C). The results have been validated and agree well with previously published papers. Furthermore, the main results stated that when the nanomaterial concentration increased, the heat transfer rate by free convection also increased. By increasing the natural convection flows via high temperature, symmetrical vortexes may appear near the heated wall. It also found that the PCM can potentially reduce the temperature of the hot side by up to 22% due to its high absorbability and heat storage. Furthermore, the inclusion of hybrid nanofluids in addition to the PCM enhanced its efficiency in heat storage and, therefore, its capacity to cool the hot side. Moreover, the influence of the inclination cavity enhanced the heat transfer, where θ = 30° was the optimal angle in terms of thermal conductivity.

Thermal conductivity prediction of pure refrigerants and mixtures based on entropy-scaling concept

The residual entropy scaling (RES) concept builds up connection between the transport properties and thermodynamic equation of state directly. However, the low-density divergence issue of the reduced dimensionless thermal conductivity might not be fixed properly through current literature models. This study proposes a new RES model coupled with the original perturbed-chain statistical associating fluid theory (PC-SAFT) equation of state (EoS) for the thermal conductivities of 11 typical refrigerants (including hydrocarbons, hydrofluorocarbons, hydrofluoroolefins and carbon dioxide) and their multicomponent mixtures. Model parameters are adjusted to saturated vapor and liquid data obtained from REFPROP. The combination of a modified reference thermal conductivity term as an extension of the original work by Rosenfeld et al. and the new formulation of the reduced term could provide reasonable predictive results for the investigated pure and mixture systems with AAD% of 3.95% and 5.76%, respectively. As expected, quasi-linear behaviors in both dilute and dense fluid regions could be observed for the refrigerant systems under study. The extended corresponding states (ECS) and the other two RES approaches reported in the literatures are used as reliable tools for assessing the predictive capability of the proposed model. However, the critical enhancement of thermal conductivity and the correction of the reference EoS especially near the critical point will be the priority in the future.

Mechanical properties and flow characteristics of dolomite-based porous supports for catalysts using different pore-forming agents

Three kinds of pore-forming agents (corn flour, starch, and biochar) were selected to prepare dolomite-based porous ceramic catalyst carriers with good mechanical properties. Pore-forming agents occupy space within preformed agglomerates, such that after the pyrolysis and sintering have been completed there are spaces within the resulting ceramic material. Porous ceramic samples prepared with biochar exhibited high apparent porosity and water absorption. By contrast, the apparent porosity of the porous ceramic samples prepared with starch as the pore-forming agent was low. When the ratio of the dolomite to quartz sand in the ceramic aggregate was changed from 4:6 to 3:7, the change of the apparent porosity of the porous ceramic samples made with starch as a pore-forming agent was very small, with high bulk density and compressive strength. Compared with corn flour and biochar, starch was less suitable as a pore-forming agent for porous ceramics. The apparent porosity and water absorption of the porous ceramics prepared with biochar as a pore-forming agent decreased slightly. But its bulk density and thermal conductivity were increased. This is mainly attributable to the fact that biochar is lighter, but it performs well in terms of mechanical strength and thermal conductivity.

Bark based porous materials obtained with a simple mechanical foaming procedure

Tree bark is a by-product of the wood industry and has currently only little use as raw material. In this study, spruce bark disintegrated into three different types of particles was used to obtain porous structures with a wide range of properties. The manufacturing process includes a simple mechanical foaming method, using bark particles, a common wood adhesive, a surfactant and water. Physical and mechanical characterization of the materials was carried out in terms of density, thermal conductivity, water uptake, compression resistance and microscopy observation. All materials produced presented a heterogeneous open porous structure. Thermal conductivity values range between 0.075 and 0.125 W m-1 K-1, while the density values range between 100 and 650 kg/m3. Water uptake percentage varies between groups but is stabilized after 24 h of immersion, and in some cases, the water uptake reaches up to 450%. Regarding the mechanical properties, they vary greatly showing a tendency of decreasing when adding higher amounts of surfactant.

Thermal and Dielectric Properties of 3D Printed Parts Based on Polylactic Acid Filled with Carbon Nanostructures

AbstractPolylactic acid (PLA) containing 12 wt% of nanofillers, such as multi‐walled carbon nanotubes (MWCNTs), graphene nanoplates (GNPs), is considered to obtain a non‐conventional filament suitable for additive manufacturing (AM) process with enhanced thermal and electrical properties. In details, three‐dimensional (3D) printed specimens obtained by means of fused deposition modeling (FDM) are experimentally characterized in terms of thermal conductivity and relative permittivity. The results are interpreted on the basis of the different features of the fillers and their interaction with the PLA, as evidenced by a morphological analysis. It is found better thermal transport by using two‐dimensional (2D) shape nanoparticles (GNPs) with an improvement of about 260% respect to the unfilled polymer most likely due to its favorable arrangement and the lower thermal boundary resistance between the two phases, matrix, and fillers. Differently, mono‐dimensional filler like MWCNTs is to be preferred in order to obtain higher value for the relative permittivity, due to the enhancement of the interfacial polarization and the presence of functionalized groups. It is found a value of 5.35 × 103 much greater than that of 3.7 measured for pure PLA. Given the good combined thermal and dielectric properties, such materials are promising candidates for packaging applications with electromagnetic (EM) shielding capability.

Tuned physical characteristics of PbSe binary compound: a DFT study

Physical features of transition metal (TM) doped lead selenide, Pb1-xCrxSe, Pb1-xCoxSe and Pb1-xNixSe (x=0% and 25%) have been investigated by ab-inito method. The exchange correlation energy is computed by generalized gradient approximation (GGA). A direct band gap (Eg) of 0.35 eV has been observed for PbSe. The analysis of spin-resolved electronic band structure (BS) and density of states (DOS) reveal the half-metallic ferromagnetic (HMF) character of doped compounds. In addition, the calculated magnetic moments (μB) of Pb1-xCrxSe, Pb1-xCoxSe and Pb1-xNixSe compounds are found to arise due to doped transition metals and confirmed by 3D spin-polaized iso-surface density plots. The optical features including optical conductivity (), absorption coefficient, extinction coefficient k, refractivity R, dielectric function and refractive index n() have been calculated to envisage the optical response of given materials. Further, the BoltzTrap code has been implemented to probe the thermoelectric characteristics in term of power factor (PF), Seebeck coefficient (S), thermal and electrical conductivity. The outcomes of calculations divulge that Pb1-xXxSe (X=Cr, Co, Ni) would be suitable candidates for both optoelectronics and thermoelectric applications.

Fluctuation-driven thermal transport in graphene double-layers at charge neutrality

We develop a theory of fluctuation-driven phenomena in thermal transport in graphene double-layers. We work in the regime of electron hydrodynamics and focus on the double charge neutrality point. Although at the neutrality point charge transport is decoupled from the hydrodynamic flow, thermal fluctuations of electron density cause both drag and heat transfer between the layers. The thermal transport in the bilayer system is governed by these two phenomena. We express the drag friction coefficient and the interlayer thermal conductivity in terms of the interlayer distance and the intrinsic conductivity of the electron liquid. We then obtain the thermal conductance matrix and determine the spatial dependence of the hydrodynamic velocity and temperature in the system. For shorter system the thermal drag resistance is determined by drag. In longer systems the situation of perfect thermal drag is realized, in which the hydrodynamic velocities in both layers become equal in the interior of the systems. Estimates are given for the monolayer and bilayer graphene devices. The predictions of our theory can be tested by the high-resolution thermal imaging and Johnson-Nyquist nonlocal noise thermometry.

Performance Evaluation of Plate Heat Exchanger Using CuO-DI Water Nanofluid

Abstract Experimental and numerical investigations have been carried out for performance evaluation of plate heat exchanger (PHE) using CuO-DI water nanofluid at different volume concentrations of (ϕ = 0, 0.005, 0.01, 0.03, 0.05, and 0.07) for the Reynolds number, Re = 71–1350, Prandtl number, Pr = 3.18–13.7, and at fixed inlet temperatures of hot and cold fluids Thi = 60 °C and Tci = 20 °C, respectively. The two main influential thermo-physical properties of the nanofluid, namely, dynamic viscosity and thermal conductivity obtained for various volume fractions at different temperatures, are further utilized for performance analysis of the PHEs. The thermo-hydraulic performance of PHE is evaluated based on the J.F. factor. According to experimental and simulated results, volume concentration, ϕ = 0.03 is found to be the optimum concentration of nanofluids. The individual correlations for Nusselt number, friction factor, dynamic viscosity, and thermal conductivity in terms of nanofluid volume fraction are proposed based on the experimental results.

Surface Coating of Needle-Punched Nonwovens with Meltblown Nonwovens to Improve Acoustic Properties

Unlike the term sound insulation, which means reducing the penetration of noise into other areas, sound absorption means reducing the reflection and energy of the sound on the surface. It has become a highly noticed issue in recent years because the noise in our daily life is increasing day by day, and it causes some health and comfort disorders. In many areas, textiles have been used for acoustics control and noise absorption purposes. The purpose of this work is to determine the most effective media for sound absorption performance and its relation to thermal conductivity from needle-punched nonwoven, meltblown nonwoven and hybrid forms in different arrangements of these fabrics. To provide comparable samples, both needle-punched nonwoven and meltblown nonwoven samples were produced from 100% Polypropylene fibres. According to sound absorption tests, the hybrid-structured sample having a composition similar to the needle-punched nonwoven sample placed at the bottom of our study, while the meltblown nonwoven sample placed as a face layer outperformed the rest of the samples in terms of sound absorption and thermal conductivity. ‘Meltblown only’ samples had remarkably higher sound absorption efficiency than most of the samples, while the ‘needle-punched nonwoven only’ sample had the lowest sound absorption efficiency in all frequencies.

An optimization case study to design additively manufacturable porous heat sinks based on triply periodic minimal surface (TPMS) lattices

Cellular materials have been widely used in thermal management applications such as heat sinks (HSs) for electronic devices. The topology optimization technique has recently gained interest in designing the topology of HSs with optimized thermal performance. Triply periodic minimal surface (TPMS) based structures offer unique opportunities for tailoring the design and performance of HSs, but their potential has not been explored in customizing additively manufactured porous optimized HSs. Therefore, research is needed to analyze the thermal performance, such as thermal conductivity, within optimized HSs customized with TPMS structures. In this study, the thermal HSs were designed using the topology optimization technique and two unique mapping approaches; namely, averaging and gradient methods, were proposed to transform porous cellular structures to gyroid-based HSs. Unit-cell homogenization approach was used to determine the effective thermal conductivity of gyroid-sheet and gyroid-solid structures. Effect of heat transfer area on thermal transport of optimized topologies was also investigated. Computational analysis was performed to analyze and compare the thermal transport in the optimized porous and gyroid mapped HSs. Moreover, mapped structure's ability to dissipate heat was examined by calculating the maximum temperatures when applying an external heat source. Mapped gyroid-sheet structure obtained through gradient method demonstrated the effectiveness of the proposed mapping approach in terms of effective thermal conductivity. The findings of the research provide valuable guidance for customizing the topology and predicting the performance of TPMS based heat sinks in terms of pure heat conduction analysis.

Implicit Solar Coronal Magnetohydrodynamic (MHD) Modeling with a Low-dissipation Hybridized AUSM-HLL Riemann Solver

In this paper, we develop a 3D implicit single-fluid magnetohydrodynamic (MHD) model to simulate the steady-state solar corona with a wide range of Mach numbers and low plasma β. We employ a low-dissipation advection upstream splitting method (AUSM) to calculate the convective flux in the regions of low Mach numbers for a high resolution, and hybridize the AUSM with Harten-Lax-van Leer Riemann solver in the regions of high Mach numbers to improve the solver’s robustness. The inner boundary condition of no backflow is implemented by numerical flux. A reconstruction method based on the divergence-free radial basis function is adopted to enhance the divergence-free constraint of magnetic field. Also, an anisotropic thermal conduction term is considered; the positivity-preserving reconstruction method is used to prevent the presence of negative thermal pressure and plasma density, and the implicit lower-upper symmetric Gauss Seidel method is implemented for a better convergence rate. After establishing the implicit solar wind MHD model, we employ it to simulate steady-state solar coronal structures in Carrington rotations 2177 and 2212. The simulations demonstrate that the MHD model’s computational efficiency is desirable, and the modeled results are basically in agreement with the solar coronal observations and the mapped in situ measurements from the OMNI archive. Consequently, this implicit MHD model is promising to simulate a complex plasma environment with high-intensity magnetic field and wide-ranging Mach numbers.

First-principles calculations to investigate structural, elastic, electronic, and thermoelectric properties of monolayer and bulk beryllium chalcogenides

A detailed first-principles investigation on the structural, vibrational, elastic, electronic, and thermoelectric properties of the family of beryllium chalcogenides (BeX; X = O, S, Se, Te) in hexagonal monolayer (h-BeX) and bulk (zinc blende; zb-BeX) phases are studied in this work. The stabilities of the compounds are assessed by phonon dispersion analysis and elastic properties. The band structure and partial density of states predicts the nature and understanding of the electronic properties of the considered BeX compounds. The effective mass, mobility and relaxation time for carriers are also predicted for both the BeX phases. The thermoelectric properties are evaluated for a wide temperature range of 50–800 K in terms of thermal conductivity (κ), electrical conductivity (σ), Seebeck coefficient (S) and figure of merit (ZT). The considered BeX materials shows outstanding thermoelectrical promises. The present findings will undoubtedly aid experimentalists in prospective synthesis and future thermoelectric power applications of the recognized BeX compounds.

DFT and experimental investigations on CdTe1-xSex for thermoelectric and optoelectronic applications

The optical and electronic characteristics of CdTe-based semiconductors play an important role in modern optoelectronic devices. In the current study, pure and Se doped CdTe compositions were theoretically investigated through density functional theory within the framework of Wien2k code using a modified Becke–Johnson technique. Experimentally CdTe1−xSex (x = 0, 3.125 %, 6.25 %, and 12.5 %) uniform and evenly distributed thin films were successfully deposited through a chemically derived sol-gel-based spin coating technique. The morphological, electronic, thermoelectric, and optical properties were studied through comparative simulations and experimental investigations. Ab-initio and experimental results reveal the similarities and correlation among the findings. The experimental energy band gap was found to reduce from 1.84 eV for pure CdTe to 1.55 eV by incorporation of Se in the pristine CdTe structure. The thermoelectric response in terms of electrical conductivity, Seebeck coefficient, thermal conductivity, and specific heat was recorded and a significant variation was observed. The optical parameters show an enhanced trend in the visible regime with the incorporation of Se content in structure. Absorption coefficient and real epsilon were shown to a sharp increase with increment of Se content. The outcomes of this work are considered that Se containing CdTe composition are promising candidates for enhanced thermoelectric and optoelectronic applications.