Solid Conductivity Research Articles

Combined Method of Separation of Variables. 3. Nonstationary Heat Conduction in Solids with the First-Kind Boundary Condition

Combined Method of Separation of Variables. 3. Nonstationary Heat Conduction in Solids with the First-Kind Boundary Condition

A study on physicochemical parameters of fish pond effluents: A case study of Umudibia fish farm

This study investigated the physicochemical characteristics of fish pond effluents. Four (4) effluent samples were collected at two-day intervals from a fish pond located at Umudiba Nekede, Owerri, and analyzed to ascertain their characteristics. The physiochemical parameters assessed are the temperature, biochemical oxygen demand, chemical oxygen demand, total dissolved solids, turbidity, ammonia, total hardness, alkalinity, pH, and electrical conductivity. The result revealed the following ranges for the physicochemical characteristics: temperature (23.0 to 25.9°C), pH (6.24 to 3.1), total alkalinity (43.1 to 50.4mg/l), total dissolved solid (27.9 to 95.2 mg/l), total hardness (19.7 to 21.5mg/l), turbidity (12 to 170 NTU), and electrical conductivity (137.6 to 144.3 μmhos/cm). The result of the study indicated that the effluents from the fish pond could constitute a threat to the ecology of the aquatic water bodies if not properly treated before discharge.

Melamine-formaldehyde rigid foams – Manufacturing and their thermal insulation properties

The manufacturing of novel melamine-formaldehyde rigid foam material, by blowing the melamine-formaldehyde (MF) resin emulsion with pentane and further catalytic and thermal curing, is presented in this work. The process of foaming is described in terms of particular process parameters, which are; the proportions of blowing, curing, emulsifying agents. The examination of the foam, by SEM images, shows that the foam pore sizes are in the range from 150 to 250 µm. The thermal characterization of the obtained foams, is described in terms of thermal conductivity contributions of solid, gas and radiation conduction to total thermal conductivity at atmospheric and vacuum condition. The foam with densities from 50 to 80 kg/m3achieve thermal conductivity at an atmospheric pressure of 33–34 mW/(m × K), while in a vacuum of 6–7 mW/(m × K). Compared to other organic polymer foams, MF foams have superior fire resistance and chemical stability. The innovation of MF rigid foams presented here, compared to other well-known MF flexible foam, is in their rigid structure, combined with low density and thermal conductivity, which makes this particular foam potentially useful in the manufacture of vacuum insulation panels (VIP).

Cattaneo-LTNE Effects on the Stability of Brinkman Convection in an Anisotropic Porous Layer

The stability of Brinkman local thermal nonequilibrium anisotropic porous convection under the impact of Cattaneo law of heat conduction in solid is investigated. In the analysis, anisotropies in permeability and thermal (solid and fluid phases) conductivities are highlighted. Condition for stationary onset and oscillatory onset is obtained by carrying out linear instability analysis. A novel result is that the instability occurs through oscillatory mode against the stationary convection perceived in the absence of Cattaneo effect. The relative magnitudes of governing parameters on the initiation of oscillatory instability are delineated in detail. The thermal and mechanical anisotropies inflict stabilizing and destabilizing effects on the onset, respectively. The influence of mechanical anisotropy, thermal anisotropy of fluid, thermal relaxation time parameters and the Darcy number is to broaden the size of convection cells whereas thermal anisotropy of the solid and the Darcy-Prandtl number demonstrate a mixed behaviour. A first order amplitude equation is derived separately for steady and overstable modes by performing a weak nonlinear stability analysis using a modified multiscale method. Depending on the values of governing parameters, it is seen that the stationary mode bifurcates subcritically and supercritically, while the oscillatory mode always bifurcates supercritically.

Solar distillation of impure water from four different water sources under the southwestern Nigerian climate

Abstract. The enormous problems caused by the scarcity of potable water and the transmission of waterborne diseases such as cholera, dracunculiasis, hepatitis, typhoid and filariasis in some parts of Nigeria have created a public health concern. Every day thousands of lives are lost due to contact with waterborne diseases. The insufficient medical resources available in developing countries are deployed towards the treatment of waterborne diseases that can easily be avoided if potable water can be made available. This study seeks to investigate the purification of four different water samples (namely water from flowing rivers, freshly dug well or groundwater, rainwater from the rooftops and heavily polluted dirty water) consumed by the people in the local community using a solar desalination method. A single basin solar still was constructed, and experimental studies were carried out to determine the influence of solar insolation and temperature variations on the yield of the distillate for both the passive and active solar stills tested. The quality of the distillate was tested by measuring the total dissolved solid (TDS) and electrical conductivity (EC) and later comparing it to the World Health Organization (WHO) standard for drinkable water. The values obtained after desalination fall within the acceptable/tolerable range for TDS and EC, in accordance with the WHO standard for drinkable water. This analysis provides an indigenous distillation method to enhance the production of drinkable water at a low cost.

Combined Heat Transfer Mechanisms in the Porous Char Layer Formed from the Intumescent Coatings under Fire

This study examines the combined heat transfer by thermal conduction, natural convection and surface radiation in the porous char layer that is formed from the intumescent coating under fire. The results show that some factors, such as the Rayleigh number, conductivity ratio, emissivity, radiation–conduction number, void fraction and heating mode have a certain effect on the total heat transfer. In addition, the natural convection of the air in the cavity always inhibits surface radiation among the solid walls and thermal conduction, and the character of the total heat transfer is the competition result of the three heat transfer mechanisms.

Intrinsically Low Lattice Thermal Conductivity in Natural Superlattice (Bi2)m(Bi2Te3)n Thermoelectric Materials

Understanding the origin of intrinsic lattice thermal conductivity in crystalline solids is critical to research fields ranging from thermoelectric materials to thermal barrier coatings. This work ...

Predicting effective thermal conductivity in sands using an artificial neural network with multiscale microstructural parameters

Accurate and efficient prediction of thermal conductivity of sands is challenging due to the variations in particle size, shape, connectivity and mineral compositions, and external conditions. Artificial Neural Networks (ANN) models have been used to predict the effective thermal conductivity but they have not considered variables related to particle connectivity. This work uses computed tomography (CT) scanned images of four dry sands and network analysis to redress this significant shortcoming. Here sands are represented as networks of nodes (grains) and edges (interparticle contacts or/and small gaps between neighbouring particles) to extract network features that characterise interparticle connectivity. A network feature – weighted coordination number (WCN) capturing both particle connectivity and contact area – was found to be a good predictor of effective thermal conductivity in dry materials. Roundness, sphericity, solid particle thermal conductivity and porosity are other input parameters rigorously selected for an ANN model that predicts well the effective thermal conductivity of sands.

Unsteady Coupled Heat Transfer Simulation of Unsteady numerical simulation of slot flow in anti-heating tile

An unsteady coupled heat transfer solver is developed in the study. The coupled solver, solving the partial differential equations for fluid flow and thermal conduction in the solid, is employed to predict the unsteady heat and transfer in the anti-heating tile. The influence of gap depth on the fluid flow and solid thermal conduction is studied. The results show that the flow field distribution between the different gap depths is similar, otherwise reducing the gap depth is conducive to reducing the thermal load in the bottom plate.

Understanding the Selective Deposition of Li Metal on Nonuniform Electrode Surfaces Using Atomic Force Microscopy

The use of lithium metal in secondary batteries has been impeded by its tendency to form dendrites: branching conductive structures of metal that can lead to capacity loss and, ultimately, internal shorts in the battery. Patterned electrodes, in addition to artificially increasing the current density of cells by increasing the surface area available for reaction, also generate a nonuniform electric field in the vicinity of the electrode surface. This nonuniform electric field, though rapidly screened by the electrolyte, can promote inhomogeneous deposition and Solid Electrolyte Interphase formation. As the consequence of these effects is not theoretically apparent since Solid Electrolyte Interphase volume and conductivity changes can, in principle, offset variations in local current density, we have performed experiments to examine the deposition of Li on nonuniform electrode surfaces using Atomic Force Microscopy. We measure the local variations in topography, SEI thickness, and composition, and discuss their implications for the formation of dendrites in Li metal.

Improving the surface morphology and crystallite size of isonicotinohydrazide based binuclear Cr(III), Zn(II) and Sn(IV) complexes after irradiation with γ-rays

In this work, binuclear Cr(III), Zn(II) and Sn(IV) complexes with: (Z)-N'-(4-methoxybenzylidene)isonicotinohydrazide (L) have been prepared and well assigned and then exposed to gamma ray irradiation with dose up to 100 kGy using Indian 60Co γ-ray cell type GE-4000 A. The structural properties of the synthesized compounds and the structural modifications of the irradiated samples were studied by analytical, magnetic, molar conductance measurements, different spectral (FT-IR, 1H NMR, UV–Vis), powder XRD and thermogravimetry (TG) techniques. The data show that all complexes are dinuclear, Cr(III) complex supposed in distorted teteragonal geometry and Zn(II) complex supposed in distorted square planar geometry have the formula [Cr2L(OH)4]Cl2(1) and [Zn2LCl2(H2O)2]Cl2.3H2O (2), respectively and Sn(IV) has distorted octahedral geometry and the formula is Sn2LCl2(OH)4(H2O)2]Cl2.H2O(3), no geometry change was detected upon irradiation. The XRD of both non-irradiated and irradiated complexes indicate that they are in a nanometer range. A reduction in average crystallite size was observed for irradiated Cr(III) complex. Scanning electron microscopy (SEM) micrographs of [Cr2L(OH)4]Cl2 complex (1) show improving of its crystallinity after γ-irradiation. Further, the solid electrical conductivity of [Zn2LCl2(H2O)2]Cl2.3H2O complex (2) before and after γ-irradiation has been investigated, both samples behaved like insulator. The antimicrobial screening for all metal complexes before and after γ-irradiation was achieved against pathogenic bacteria Staphylococcus aureus as Gram +ve bacteria, Escherichia coli as Gram -ve bacteria and Candida albicans as fungal strain. The results pointed that the metal complexes have moderate antimicrobial activity compared to the standards and in some cases γ-irradiation enhances antimicrobial activity.

Mode localization and suppressed heat transport in amorphous alloys

Glasses usually represent the lower limit for the thermal conductivity of solids, but a fundamental understanding of lattice heat transport in amorphous materials can provide design rules to beat such a limit. Here we investigate the role of mass disorder in glasses by studying amorphous silicon-germanium alloy (a-Si$_{1-x}$Ge$_x$) over the full range of atomic concentration from $x=0$ to $x=1$, using molecular dynamics and the quasi-harmonic Green-Kubo lattice dynamics formalism. We find that the thermal conductivity of a-Si$_{1-x}$Ge$_x$ as a function of $x$ exhibits a smoother U-shape than in crystalline mass-disordered alloys. The main contribution to the initial drop of thermal conductivity at low Ge concentration stems from the localization of otherwise extended modes that make up the lowest 8\% of the population by frequency. Contributions from intermediate frequency modes are decreased more gradually with increasing Ge to reach a broad minimum thermal conductivity between concentrations of Ge from $x=0.25$ to $0.75$.

Dependence of Heat Transport in Solids on Length-Scale, Pressure, and Temperature: Implications for Mechanisms and Thermodynamics.

Accurate laser-flash measurements of thermal diffusivity (D) of diverse bulk solids at moderate temperature (T), with thickness L of ~0.03 to 10 mm, reveal that D(T) = D∞(T)[1 − exp(−bL)]. When L is several mm, D∞(T) = FT−G + HT, where F is constant, G is ~1 or 0, and H (for insulators) is ~0.001. The attenuation parameter b = 6.19D∞−0.477 at 298 K for electrical insulators, elements, and alloys. Dimensional analysis confirms that D → 0 as L → 0, which is consistent with heat diffusion, requiring a medium. Thermal conductivity (κ) behaves similarly, being proportional to D. Attenuation describing heat conduction signifies that light is the diffusing entity in solids. A radiative transfer model with 1 free parameter that represents a simplified absorption coefficient describes the complex form for κ(T) of solids, including its strong peak at cryogenic temperatures. Three parameters describe κ with a secondary peak and/or a high-T increase. The strong length dependence and experimental difficulties in diamond anvil studies have yielded problematic transport properties. Reliable low-pressure data on diverse thick samples reveal a new thermodynamic formula for specific heat (∂ln(cP)/∂P = −linear compressibility), which leads to ∂ln(κ)/∂P = linear compressibility + ∂lnα/∂P, where α is thermal expansivity. These formulae support that heat conduction in solids equals diffusion of light down the thermal gradient, since changing P alters the space occupied by matter, but not by light.

Discrimination of Malaysian stingless bee honey from different entomological origins based on physicochemical properties and volatile compound profiles using chemometrics and machine learning

Identification of honey origin based on specific chemical markers is important for honey authentication. This study is aimed to differentiate Malaysian stingless bee honey from different entomological origins (Heterotrigona bakeri, Geniotrigona thoracica and Tetrigona binghami) based on physicochemical properties (pH, moisture content, ash, total soluble solid and electrical conductivity) and volatile compound profiles. The discrimination pattern of 75 honey samples was observed using Principal Component Analysis (PCA), Hierarchical Clustering Analysis (HCA), Partial Least Square-Discriminant Analysis (PLS-DA), and Support Vector Machine (SVM). The profiles of H. bakeri and G. thoracica honey were close to each other, but clearly separated from T. binghami honey, consistent with their phylogenetic relationship. T. binghami honey is marked by significantly higher electrical conductivity, moisture and ash content, and high abundance of 2,6,6-trimethyl-1-cyclohexene-1-carboxaldehyde, 2,6,6-trimethyl-1-cyclohexene-1-acetaldehyde and ethyl 2-(5-methyl-5-vinyltetrahydrofuran-2-yl)propan-2-yl carbonate. Copaene was proposed as chemical marker for G. thoracica honey. The potential of different parameters that aid in honey authentication was highlighted.

Thermal conductivity and extinction coefficient of opacified expanded perlite for vacuum super insulation up to 1073 K

A vacuum super insulation for temperatures up to 1073 K has been developed using an opacified powder mixture with high-density (ρ= 180 kg m−3) expanded perlite as base material. To analyze radiative transfer, the mass-specific extinction coefficient e of expanded perlite and various opacifiers (SiC, B4C, FeTiO3, TiO2) has been determined by FTIR spectrometry. For reduction of radiative transfer, a SiC powder with mean grain diameter of 2 μm–4 μm and bulk density of 870 kg m−3 has been identified as most suitable opacifier, also under economic aspects. Subsequently, six homogeneous powder mixtures with weight fraction w of SiC between 0% and 60% have been prepared. In order to determine the optimum w, guarded hot plate (GHP) measurements under high vacuum conditions (p < 0.1 hPa) and at 673 K mean temperature have been performed on these mixtures, yielding a minimum effective thermal conductivity of λe = 13∙10−3 W m−1 K−1 for w = 40% and ρ = 263 kg m−3. This mean temperature corresponds to an insulation application with 950 K hot-side and ambient temperature cold-side. For the optimum mixture with w = 40%, e has likewise been determined with FTIR spectrometry. Furthermore, λe has been measured with the GHP method also at mean temperatures between 373 K and 873 K, where excellent values between 4∙10−3 W m−1 K−1 and 20∙10−3 W m−1 K−1 have been obtained. For the evaluation of these measurements, two different methods have been applied in order to separate radiative thermal conductivity λr and solid thermal conductivity λs: first the common plot of λe versus T3, and second an improved method, which includes the temperature dependencies of e and λs. Expanded perlite, opacified with SiC, has proven as a highly efficient and economic vacuum super insulation material for industrial applications up to 1073 K.

The influence of inner material with different average thermal conductivity on the performance of whole insulation system for liquid hydrogen on orbit storage

At present, several composite insulation systems were proposed that can be used for passive insulation systems, including foam-variable density multilayer insulation (VDMLI), aerogel-VDMLI and hollow glass microspheres (HGMs)-VDMLI. The passive insulation systems with different inner material (IM) showed different performances. However, the relationship between the average thermal conductivity of IM and the insulation performance of the whole system has rarely been investigated. It is of great significance for efficient configuration and matching of the passive insulation system. In this paper, a series of average thermal conductivity of IM were assumed to predict the insulation performance of the whole system at 20 K–300 K and high vacuum. In order to further illustrate the relationship between IM and MLI/VDMLI, the foam was replaced by the HGMs as 5 mm a unit forming a series of HGMs-foam-MLI/VDMLI insulation systems. The performance of the systems was investigated. After the foam was completely replaced by the HGMs, the performance of MLI and VDMLI systems was improved 33% and 13%, respectively. Moreover, each mode of heat transfer including solid conduction, radiation, and gas conduction for foam-MLI/VDMLI and HGMs-MLI/VDMLI insulation systems were calculated and analyzed.

Room-temperature fast zinc-ion conduction in molecule-flexible solids

Understanding solid-state zinc-ion conduction will not only be academically interesting but also benefit the development of energy-dense devices. However, zinc ions in conventional ceramic and polymer hosts are only mobile at high temperatures, and intriguing questions remain regarding the correlation between ionic local environment and conductivity performance. Here, we demonstrate a room-temperature fast zinc-ion conduction in solids with a high degree of molecular flexibility and elucidate the subtle trade-off between molecular-scale interactions and ion transport properties. Importantly, a determining role of the strong cation-anion pairing in suppressing zinc-ion mobility has been experimentally uncovered. When removed, the upper limit of ionic conductivity can be extended to the order of 10−4 S/cm, exceeding those of previous solid (solvent-free) zinc-ion conductors. Concomitant with the reversible plating/stripping of zinc (over 700 h), the successful creation of solid-state zinc-ion batteries confirms the practical applicability of the resultant conductors.

Light-Responsive Proton Conductor: Record High Gain of Proton Conductivity Achieved by Photoinduced Electron-Transfer Strategy

Light-Responsive Proton Conductor: Record High Gain of Proton Conductivity Achieved by Photoinduced Electron-Transfer Strategy

Effects of solid particle thermal conductivity on heat storage performance of heat storage bed

The thermal properties of particles are important parameters that directly affect the heat storage performance of the solid particle heat storage bed. This paper reports the effects of solid particle thermal conductivity on heat storage performance of heat storage bed. A three-dimensional steady-state heat transfer model of heat storage bed with a single vacancy was established using ANSYS 19.0. The effects of thermal conductivity of particles were studied. With the increase in thermal conductivity of particles, the effect of the vacancy on heat storage particle bed heat transfer performance increases, the affected area size increases, so the heat storage and release performance of heat storage bed decreases. With the increase of thermal conductivity of particles from 0.5 W/ (m·K) to 50 W/ (m·K), the size of the affected region increased from 0.61 times of particle size to 1.82 times of particle size in the direction perpendicular to the heat transfer, and the size of the affected region increased from 1.61 times of particle size to 3.91 times of particle size in upstream of the direction parallel to the heat transfer. At the same time, the size of the affected region increased from 1.69 times of particle size to 3.93 times of particle size in downstream of the direction parallel to the heat transfer. It can provide a basis for improving the thermal resistance theory.

Lattice Thermal Conductivity of Transition Metal Carbides: Evidence of a Strong Electron-Phonon Interaction Above Room Temperature

Strong electron-phonon interaction, can not only control charge carrier mobility, but also impact heat transport by reducing lattice thermal conductivity. In this work, we reveal by experiments a strong electron-phonon interaction in group IV and V transition metal carbides, which results in anomalous weak temperature dependence of lattice thermal conductivity from 300 K up to 773 K. This contrasts with the common belief that electron-phonon interaction would be only important for lattice heat transport at very low temperatures. The other important finding is that strong electron-phonon interaction can notably suppress lattice thermal transport and its temperature dependence provided that free charge carrier density is large enough, whereas Fermi surface nesting may not be necessary. This work provides new perspective on electron-phonon interaction and its consequence on lattice thermal conduction in solids, and it suggests a new avenue to modulate heat transfer above room temperature.