Little is known on the effect of opacifiers in perlite core vacuum insulation panels at lower temperatures in the range of 10–70 °C, which are important for applications like refrigerators, transport ...boxes, buildings, and domestic hot water storage tanks. This paper shows that the effect of opacifier on perlite core Vacuum Insulation Panels (VIPs) is radically different than that on fumed silica VIPs. Identifying an optimum proportion of opacifiers for perlite core VIPs is not a trivial task because of a concomitant rise in solid conductivity as the radiative conductivity decreases. Further, the effect of opacifiers on temperature dependent thermal conductivity of VIPs has been resolved. Opacifiers in perlite are shown to yield clear benefits by reducing the overall thermal conductivity for insulation exposed to ≥70 °C. This was not the case for ≤20 °C. Several VIPs were manufactured using a low-density expanded perlite and 3 different proportions of 4 opacifiers i.e., carbon black, graphite and two variants of silicon carbide (SiC I, SiC II). These VIPs were tested at various combinations of sealing pressure and four different average temperatures i.e., 10 °C, 20 °C, 40 °C and 70 °C. A novel methodology has been developed to derive the evacuated thermal conductivity of perlite core VIPs by curve fitting technique, in order to eliminate the effect of gaseous conduction. The results were also compared with fumed silica core vacuum insulation panels with different proportions of carbon black as opacifier. Among the opacifiers tested (carbon black, graphite, SiC I and SiC II) in this research, Silicon carbide I with a mean particle size of 20 μm was found out to be the best opacifier, with one of its composite resulting in a 50% lower thermal conductivity at 70 °C in comparison to pristine perlite core VIPs.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
The electric conductivity is one the most routinely inspected characteristics of aqueous media, being employed in monitoring drinking water quality and determining thermodynamic properties of ...electrolytes. In this work, we utilize fused deposition modelling 3D printing (3DP) to manufacture a platform composed of supporting cells and sensing electrodes for electric conductivity measurements of aqueous solutions. For the first time, the electric conductivity of liquid electrolytes is sensed by 3DP electrodes, employing a direct electrode/electrolyte contact. Conductivity measurements performed in the presented 3DP platform are controlled by an electronic circuitry developed employing a programmable system on chip prototyping kit. The entire conductometric setup was validated employing commercial conductance standards as well as in-lab prepared aqueous solutions of potassium chloride and formic and acetic acid as representatives of strong and weak electrolytes. Conductivity measurements enabled the correct determination of limiting molar conductivity (for potassium chloride) and dissociation constants (for the two weak acids). Finally, the functionality of the presented platform was confirmed by measuring conductivity of various bottled water samples. Results obtained in this work pave the wave for further development and applications of conductometers based on 3DP electrodes and cells.
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•FDM was successfully used for the manufacture of 3D printed cell and electrodes for direct conductivity sensing of aqueous solutions.•An inexpensive programmable system on chip prototyping kit was used to devise and construct the readout electronics.•The platform was used to determine the dissociation constant of weak acids.•The platform was employed to determine conductivity of bottled water samples.
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This study presents material characterization in the D band using a balanced-type circular disk resonator (BCDR) with waveguide interfaces. In the developed BCDR, ultrafine and brittle coaxial lines ...are covered by waveguide interfaces, which alleviates the robustness issues that occur when increasing the measurement frequency of conventional BCDRs with coaxial-line interfaces. The BCDR provides broadband complex permittivity and conductivity measurements of low-loss substrate materials over the entire D band, owing to the mode-selective behavior of the resonator. Moreover, a modified modal analysis is derived to improve the accuracy of determining the permittivity from the measured resonant frequency based on the full-wave circuit analysis. A comparison between the analytical results and those of numerical simulations shows that the proposed analysis provides accurate calculations, even in cases with high-dielectric or thick samples, which typically cause inaccuracies in the conventional analysis. The developed BCDR and modified analysis are experimentally demonstrated by measuring the complex permittivity of three dielectric samples and the conductivity of two copper foil samples in the D band.
•The AC conductivity observed in WO3 nanostructures shows a strong dependence on the frequency and temperature.•The CBH model is more applicable in explaining the conduction mechanism of WO3 ...nanostructures.•The temperature dependence of WO3 nanostructures follows the Arrhenius rule. The activation energy for WO3 is 0.055 eV.•The high imaginary part of the dielectric constant can be agreed by using Koop’s model.•The WO3 nanostructures are used for electrochromic device fabrication.
The electrical conductivity and dielectric properties of WO3 nanostructures were measured by impedance spectroscopy using 50 Hz–5 MHz frequency in steps of 100 Hz and 303–383 K temperature. The dielectric behavior is analyzed using real and imaginary parts of dielectric constant (ε′), dielectric loss (ε″), loss factor (tan δ), electric modulus (M′ and M″) and impedance (Z′ and Z″) and complex impedance analysis. The electrical conductivity remained originate towards a function of frequency and temperature. The frequency exponent ‘s′ is found to decrease from 0.89 to 0.35 with an increase of temperature which infers the correlated barrier hopping mechanism (CBH) that exists in WO3 nanostructures. The Cole-Cole plot explains the complex impedance for different temperatures.
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•New laboratory unsaturated hydraulic conductivity data for green roof substrates.•New runoff and internal moisture flux data from laboratory detention tests.•Detention modelling requires robust ...estimations of K(ϴ) at higher moisture contents.•The Durner-Mualem K(ϴ) model is not suitable for green roof substrates.•An exponential model for K(ϴ) is proposed based on ϴ at Ks and ϴ at 0.1 cm/min.
Characterising the unsaturated hydraulic conductivity of a green roof substrate is essential for accurately modelling runoff detention in response to rainfall events. In this paper, the unsaturated hydraulic conductivities for four representative green roof substrates were determined in an infiltration column using steady state and transient techniques. The conventional Durner-Mualem Hydraulic Conductivity Function (HCF) model, for which parameters were calibrated based on the measured Soil Water Release Curve (SWRC) data, was shown to provide a poor fit to the experimental data. A new three-segment HCF was, therefore, proposed to fit measured unsaturated hydraulic conductivity data. Detention tests were carried out on 100 mm and 200 mm deep substrates using four simulated storm events. The runoff and moisture content data collected during the detention tests was used to validate the HCFs using the Richards Equation. The new three-segment HCF resulted in simulated runoff and moisture content profiles that closely matched the measured data (with mean Rt2 = 0.754 for modelled runoff), in contrast to predictions made using the conventional Durner-Mualem model (with mean Rt2 = 0.409 for modelled runoff). It was also demonstrated that further simplification of the HCF to a function defined by moisture content at just two points – the saturated hydraulic conductivity and at an unsaturated hydraulic conductivity of 0.1 cm/min – provides a model that is fit-for-purpose for green roof runoff estimation (with mean Rt2 = 0.629 for modelled runoff).
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
In this paper we report the thermal conductivity for commercial battery components. Materials were obtained from several electrode- and separator manufacturers, and some were extracted from ...commercial batteries. We measured with and without electrolyte solvent and at different compaction pressures. The experimentally obtained values are used in a thermal model and corresponding internal temperature profiles are shown. The thermal conductivity of dry separator materials was found to range from 0.07±0.01 to 0.18±0.02WK−1m−1. Dry electrode (active) materials ranged from 0.13±0.02 to 0.61±0.02WK−1m−1. Adding the electrolyte solvent increased the thermal conductivity of electrode (active) materials by at least a factor of 2.
•Thermal conductivity for Li-ion battery components are reported.•Values are for different anodes, cathodes and separators.•Values are with and without electrolyte and at different compaction pressures.•We report corresponding internal temperature gradients for batteries in operation.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
Pore-scale modeling developed over the past decades has become a powerful method to evaluate the effective transport properties of porous electrodes. Experimental verification for such a method is ...crucial to confirm the method's validity. In this study, experimental data of gas diffusion layer (GDL) are compared with results of pore-scale modeling. GDL microstructures are scanned and reconstructed by X-ray computed tomography. Explicit dynamic simulations based on the finite element method are performed on these reconstructed models to reveal the 3D displacement of the microstructure during compression. Over the deformed models, the effective diffusivity, thermal and electrical conductivities are then computed using a pore-scale model code. It is found that, as the compression ratio increases to 30%, the fiber displacement increases obviously with significant anisotropy, and the fibers gradually squeeze into nearby pores located in the adjacent layers inside GDL. The effective diffusivity and permeability decrease by about 15% and 35% respectively. The conductivity increases by 100% and 20% in the through-plane and in-plane direction respectively. Compared with the empirical model, the pore-scale models are in better agreement with the experiments. The validated methods can support microstructure optimization and transport properties improvement for different types of porous electrodes.
•GDL reconstruction under various compression ratios is conducted.•3D deformation of GDL is investigated experimentally and numerically.•Effect of compression on anisotropic transport properties for GDL is studied.•Pore-scale modeling is validated by experimental data.
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This work is focused on the structural and morphological investigations of polyaniline and poly(
-anisidine) polymers generated in a direct current glow discharge plasma, in the vapors of the ...monomers, without a buffer gas, using an oblique angle-positioned substrate configuration. By atomic force microscopy and scanning electron microscopy we identified the formation of worm-like interlinked structures on the surface of the polyaniline layers, the layers being compact in the bulk. The poly(
-anisidine) layers are flat with no kind of structures on their surfaces. By Fourier transform infrared spectroscopy we identified the main IR bands characteristic of polyaniline and poly(
-anisidine), confirming that the polyaniline chemical structure is in the emeraldine form. The IR band from 1070 cm
was attributed to the emeraldine salt form of polyaniline as an indication of its doping with H⁺. The appearance of the IR band at 1155 cm
also indicates the conducting protonated of polyaniline. The X-ray diffraction revealed the formation of crystalline domains embedded in an amorphous matrix within the polyaniline layers. The interchain separation length of 3.59 Å is also an indicator of the conductive character of the polymers. The X-ray diffraction pattern of poly(
-anisidine) highlights the semi-crystalline nature of the layers. The electrical conductivities of polyaniline and poly(
-anisidine) layers and their dependence with temperature are also investigated.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
A detailed procedure is presented for the implementation and evaluation, by Nano-Flash Method, of thermal conductivity of nanofluids with water as base fluid and at different volume concentrations of ...Al2O3. The main advantages of this measurement technique are short measurement times, easy sample preparation and high accuracy. The ultra-sonication technique was employed for preparing the mixture and results showed that the stability and thermal conductivity enhancements of Al2O3–H2O nanofluids are highly dependent on sonication time and the energy supplied to the fluid for its preparation. An estimation of the optimal supplied energy and time for sonication was suggested, while temperature and volumetric concentration effects on thermal conductivity are evaluated by measurements. An enhancement of thermal conductivity with respect to temperature and volumetric concentration is found, as expected. Comparisons with data from literature confirmed the validity and the suitability of the nanoflash technique applied to thermal conductivity evaluation.
•Evaluation of thermal conductivity of nanofluids by Nano-Flash Method is presented.•Nano-flash technique is a fast and accurate method for measuring thermal conductivity of nanofluids.•An estimation of the optimal supplied energy and time for sonication is suggested.•Stability and thermal conductivity of nanofluids depend on sonication time and energy supplied for fluid preparation.•Thermal conductivity improves for low volumetric concentrations (<0.2%) and high temperatures (>50 °C).
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•Investigation was examined between CnTAC and ethyl orange (ETO) by spectrophotometric method.•By calculating the Gibbs free energy (ΔG°), the affinity of ETO to micelles was determined.•Cmc values ...for pure CnTAC solutions determined were consistent with reported values.•Strength of this binding was found to be dependent on the alkyl chain length of CnTAC.
This research presents the application of electrical conductivity measurements to ascertain the critical micelle concentration (CMC) values for N-alkyltrimethylammonium chloride surfactants (CnTAC; with alkyl chain lengths of n = 12, 14, 16, and 18). Complementary spectrophotometric analysis was conducted to probe the interactions between CnTAC series and Ethyl Orange (ETO), an anionic dye. Applying the Benesi-Hildebrand and Scott equations, we evaluated the binding constant (Kb) of the cationic micelles’ interaction with ETO, which in turn facilitated calculations of Gibb’s free energy (ΔG°) changes. These calculations provided insight into the binding affinity of ETO to the micelles. Our findings suggest that the interaction between ETO and CnTAC is contingent on the surfactant concentration, with higher concentrations leading to a disassociation of the ETO-CnTAC complex and a reduction in ETO adsorption. Notably, the alkyl chain length within CnTAC molecules critically affects various properties, including ΔG°, CMC, and other thermodynamic parameters that determine the surfactant’s energetic behavior. The study underscores the importance of the alkyl chain length in dictating the interaction dynamics and properties of CnTAC surfactants. A trend was observed where longer alkyl chains lead to increased Kb values and reductions in both CMC and ΔG°, enhancing dye solubilization and interaction spontaneity. The affinity sequence of ETO to the micelles, influenced by alkyl chain length, was found to be C12TAC < C14TAC < C16TAC < C18TAC.
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