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Showing papers in "Journal of Thermal Analysis and Calorimetry in 2014"


Journal ArticleDOI
TL;DR: In this paper, the results of experiments on the thermal conductivity of MgO/ethylene glycol (EG) nanofluids in a temperature range of 25-55°C and volume concentrations up to 5% are presented.
Abstract: The application of nanofluids in energy systems is developing day by day. Before using a nanofluid in an energy system, it is necessary to measure the properties of nanofluids. In this paper, first the results of experiments on the thermal conductivity of MgO/ethylene glycol (EG) nanofluids in a temperature range of 25–55 °C and volume concentrations up to 5 % are presented. Different sizes of MgO nanoparticles are selected to disperse in EG, including 20, 40, 50, and 60 nm. Based on the results, an empirical correlation is presented as a function of temperature, volume fraction, and nanoparticle size. Next, the model of thermal conductivity enhancement in terms of volume fraction, particle size, and temperature was developed via neural network based on the measured data. It is observed that neural network can be used as a powerful tool to predict the thermal conductivity of nanofluids.

211 citations


Journal ArticleDOI
TL;DR: In this paper, the authors measured the thermal conductivity of very narrow Al2O3 nanoparticles with the size of 5nm suspended in water in a temperature range between 26 and 55°C.
Abstract: A considerable number of studies can be found on the thermal conductivity of nanofluids in which Al2O3 nanoparticles are used as additives. In the present study, the aim is to measure the thermal conductivity of very narrow Al2O3 nanoparticles with the size of 5 nm suspended in water. The thermal conductivity of nanofluids with concentrations up to 5 % is measured in a temperature range between 26 and 55 °C. Using the experimental data, a correlation is presented as a function of the temperature and volume fraction of nanoparticles. Finally, a sensitivity analysis is performed to assess the sensitivity of thermal conductivity of nanofluids to increase the particle loading at different temperatures. The sensitivity analysis reveals that at a given concentration, the sensitivity of thermal conductivity to particle loading increases when the temperature increases.

184 citations


Journal ArticleDOI
Guangming Liu1, Minggao Ouyang1, Languang Lu1, Jianqiu Li1, Xuebing Han1 
TL;DR: In this article, a series of experiments based on a power-type lithium manganese oxide/graphite battery was implemented under different conditions and the parameters for Joule heat and reaction heat were determined, and the estimated temperature variation showed good correspondence with experimental results under different currents and aging conditions.
Abstract: Operating temperature of lithium-ion battery is an important factor influencing the performance of electric vehicles. During charging and discharging process, battery temperature varies due to internal heat generation, calling for analysis of battery heat generation rate. The generated heat consists of Joule heat and reaction heat, and both are affected by various factors, including temperature, battery aging effect, state of charge (SOC), and operation current. In this article, a series of experiments based on a power-type lithium manganese oxide/graphite battery was implemented under different conditions. The parameters for Joule heat and reaction heat are determined, and the Joule heat, reaction heat as well as total heat generation rate is detailed and analyzed considering the influence of temperature, aging, SOC, and current. In order to validate the accuracy of heat generation rate, a lumped battery heat transfer model is applied to calculate the temperature variation, and the estimated temperature variation shows good correspondence with experimental results under different currents and aging conditions. Due to its simplicity, the temperature variation estimation method is suitable for real time applications.

153 citations


Journal ArticleDOI
TL;DR: In this paper, the apparent activation energy needed to break the bonds of hemicelluloses and cellulose of rice husk and elephant grass during the thermal conversion was evaluated according to the kinetics models of Flynn and Wall and Model Free Kinetics developed by Vyazovkin.
Abstract: A comparative evaluation of different biomasses allows the choice that presents the best potential as fuel for energy production. The knowledge of the thermal and kinetics parameters of the biomass in the process of thermal conversion is fundamental as their chemical and physical characterization. Various methodologies have been developed for the determination of kinetic parameters as apparent activation energy and reaction order from the thermogravimetric analysis. In this work, the apparent activation energy needed to break the bonds of hemicelluloses and cellulose of rice husk and elephant grass during the thermal conversion was evaluated according to the kinetics models of Flynn and Wall and Model Free Kinetics developed by Vyazovkin. The biomass elephant grass and rice husk were characterized for moisture, ash and volatile matter by ASTM E871, ASTM E1755, ASTM E872, respectively, and fixed carbon by difference. The percentage of carbon, hydrogen, nitrogen, and oxygen were determined by ultimate analysis. The elephant grass showed to be more suitable for production of bio-oil through pyrolysis due to the higher percentage of volatile, less ash content and less energy required to break the bonds of hemicellulose and cellulose than rice husk in the thermal conversion process.

138 citations


Journal ArticleDOI
TL;DR: In this paper, the authors discuss some basic concepts of chip calorimetry in general and study the influence of additives and molecular modifications on the structural formation at technically relevant cooling rates.
Abstract: The structural formation of polymers during processing significantly influences the mechanical properties and the temperature stability of polymer products. The analysis of structural formation by conventional thermal analysis techniques is limited because of the relatively low scanning rates. Thus, reorganization during heating changes the initial structure, and the applicable cooling rates are not representative for the applied cooling rates during production, i.e., crystallization at high supercooling cannot be investigated. To overcome these limitations, chip calorimeters with very high scanning rates have been developed. The fast scanning Flash DSC 1 based on MEMS chip-sensors allows for scanning rates up to 40,000 K s−1. In this paper, we discuss some basic concepts of chip calorimetry in general. We then study the influence of additives and molecular modifications on the structural formation at technically relevant cooling rates. This information is crucial to adapt polymer formulation and processing conditions to specific product requirements.

132 citations


Journal ArticleDOI
TL;DR: In this article, internal curing with superabsorbent polymers (SAP) is a method for promoting hydration of cement and limiting self-desiccation, shrinkage and cracking in high performance concrete with low water-to-binder ratio.
Abstract: Internal curing with superabsorbent polymers (SAP) is a method for promoting hydration of cement and limiting self-desiccation, shrinkage and cracking in high-performance, and ultra high-performance concrete with low water-to-binder ratio SAP are introduced in the dry state during mixing and form water-filled inclusions by absorbing pore solution The absorbed solution is later released to the cement paste during hydration of the cement In this paper, cement pastes with low water-to-binder ratios incorporating superplasticizer and different dosages of SAP and corresponding additional water were prepared Reference cement pastes without SAP but with the same amount of water and superplasticizer were also mixed Isothermal calorimetry was used to measure hydration heat flow Water entrainment by means of SAP increased the degree of hydration at later hydration times in a manner similar to increasing the water-to-binder ratio Addition of SAP also delayed the main calorimetric hydration peak compared to the reference pastes, however, in a less prominent manner than the increase in water-to-cement ratio

127 citations


Journal ArticleDOI
TL;DR: In this article, a thermogravimetric (TG) analysis from room temperature to 873 K with a heating rate of 5 −40 K min−1 in an inert atmosphere was performed.
Abstract: Co-pyrolysis behaviors of plastics–biomass blends were investigated using a thermogravimetric (TG) analysis from room temperature to 873 K with a heating rate of 5–40 K min−1 in an inert atmosphere. The selected biomass sample was sawdust of pine wood (WS). Polyvinyl chloride (PVC), low-density polyethylene (LDPE), high-density polyethylene (HDPE), and polypropylene (PP) were selected as plastic samples. The difference of mass loss between experimental and theoretical ones (calculated as arithmetic sums of those from each separated component) was used as a criterion of synergetic effect. The experimental results indicated that a significant synergetic effect existed during the high-temperature region of plastics and WS co-pyrolysis process, specially, the dehydrochlorination reaction of PVC and the degradation of hemicellulose and cellulose in the WS during the co-pyrolysis process showed synergetic effect, as well as the reaction of plastics (LDPE, HDPE, and PP) and WS. Based on the TG data with different heating rates, the kinetics parameters, especially activation energy, were calculated using the Friedman method. The activation energy of plastics, WS, and their blends were from 92.8 to 359.5 kJ mol−1. The activation energy of the PVC–WS blends was at a range of 180.2–254.5 kJ mol−1 in the second stages. The activation energies range of LDPE–WS, HDPE–WS, and PP–WS blends were 164.5–229.6, 213.2–234.3, and 198.4–263.6 kJ mol−1, respectively.

124 citations


Journal ArticleDOI
TL;DR: In this paper, a form-stable composite phase change material (PCM) through vacuum impregnation method was prepared as a novel formstable composite PCM, which was dispersed by surfactant and then, was absorbed into the porous structure of the expanded graphite (EG).
Abstract: In this study, CaCl2·6H2O/expanded graphite (EG) composite was prepared as a novel form-stable composite phase change material (PCM) through vacuum impregnation method. CaCl2·6H2O used as the PCM was dispersed by surfactant and then, was absorbed into the porous structure of the EG. The surfactant was used to enhance the bonding energy between CaCl2·6H2O and EG, which fulfilled the composites with good sealing performance and limited the leakage of the inside CaCl2·6H2O. Differential scanning calorimetry and thermal gravimetric analysis show that all the composite PCMs possess good thermal energy storage behavior and thermal stability. Thermal conductivity measurement displays that the conductivities of the samples have been significantly improved due to the highly thermal conductive EG. The thermal conductivity of the sample including 50 mass% CaCl2·6H2O (8.796 W m−1 K−1) is 14 times as that of pure CaCl2·6H2O (0.596 W m−1 K−1). Therefore, the obtained composite PCMs are promising for thermal energy storage applications.

112 citations


Journal ArticleDOI
TL;DR: In this article, the authors measured thermal diffusivity and specific heat capacity for four rock types (granite, granodiorite, gabbro, and garnet amphibolite) from room temperature to 1,173 K using laser-flash technique and heat flux differential scanning calorimetry.
Abstract: The thermo-physical properties for four rock types (granite, granodiorite, gabbro, and garnet amphibolite) from room temperature to 1,173 K were investigated. Thermal diffusivity and specific heat capacity were measured using the laser-flash technique and heat flux differential scanning calorimetry, respectively. Combined with the density data, rock thermal conductivities were calculated. Rock thermal diffusivity and conductivity decrease as the temperature increases and approach a constant value at high temperatures. At room temperature, the measured thermal conductivity is consistently near or lower than the calculated conductivity using the mineral series model, which suggests that real thermal conduction is more complicated than is depicted in the model. Therefore, in situ measurement remains the best method for accurately obtaining thermal conductivity for rocks.

112 citations


Journal ArticleDOI
TL;DR: In this paper, the effect of oxidized multi-walled carbon nanotubes on transformer oil thermophysical properties was experimentally investigated, and the maximum amount of carbon nanotsubes was chosen up to 0.01% to assure the maximum purity of transformer oil.
Abstract: Power transformers play a key role in power and electrical industries and thus boosting their efficiency is necessary. In this study, the effect of oxidized multi-walled carbon nanotubes on transformer oil thermophysical properties was experimentally investigated. The maximum amount of carbon nanotubes was chosen up to 0.01 mass% to assure the maximum purity of transformer oil. Heat transfer characteristics of transformer oil and nanofluids in two cases of free and forced convection were studied. Breakdown voltage, flash point, pour point, density, electrical and thermal conductivities, viscosity and shear stress, as eight important quality parameters, were determined. According to the experimental results, the Breakdown voltage decreased through concentration increasing. Electrical conductivity is not changed considerable with increasing concentration and temperature. Thermal conductivity of nanofluids and transformer oil changed with increasing temperature and concentration. Furthermore, at all concentrations and temperatures, the viscosity of the nanofluids was lower than that of transformer oil.

108 citations


Journal ArticleDOI
TL;DR: In this paper, a binary (−)-linalool/β-cyclodextrin (β-CD) system was characterized by differential scanning calorimetry, thermogravimetric analysis, FT-IR spectroscopy and scanning electron microscopy.
Abstract: (−)-Linalool is a monoterpene alcohol which is present in the essential oils of several aromatic plants. Recent studies suggest that (−)-linalool has antimicrobial, anti-inflammatory, anticancer, antioxidant, and antinociceptive properties in different animal models. The aim of this study was to prepare and characterize inclusion complexes of (−)-linalool with β-cyclodextrin (β-CD). Equimolar binary (−)-linalool/β-CD systems were prepared by physical mixture, paste (PM), and slurry methods (SC) and characterized by differential scanning calorimetry, thermogravimetric analysis, FT-IR spectroscopy, X-ray diffractometry, Karl Fisher titration, and scanning electron microscopy. Thermal characterization indicates the occurrence of complexation, mainly in paste complexes, which is present in the interval from 140 to 280 °C a gradual mass loss (4.6 %), probably related to (−)-linalool loss. FT-IR spectra showed changes that may be related to the formation of intermolecular hydrogen bonds between (−)-linalool and β-CD. The new solid-phase formed using the PM and SC methods, had a crystal structure which was different from the original morphology of β-CD.

Journal ArticleDOI
TL;DR: In this paper, three cassava starch samples were exposed to microwave radiation for periods of 5, 10 or 15 min. The temperature of each sample was measured immediately after each exposure time and the temperature of the samples was around 135°C.
Abstract: Three samples of native or untreated cassava starch were exposed to microwave radiation for periods of 5, 10 or 15 min. The temperature of each sample was measured immediately after each exposure time and the temperature of the samples was around 135 °C. The samples were cooled to room temperature and maintained in a desiccator with anhydrous calcium chloride. All the samples were analysed by thermogravimetry-derivative thermogravimetry, differential scanning calorimetry (DSC), rapid viscoamylographic analysis (RVA), X-ray diffraction powder patterns, non-contact atomic force microscopy and colour characteristics by reflectance spectrophotometry. The thermal behaviour, gelatinisation temperatures, enthalpy and pasting properties were determined. Relative to the time of microwave exposure, the peak viscosity and gelatinisation (RVA and DSC) increased slightly after 5 min, and, after 10 and 15 min, it decreased considerably. The degree of relative crystallinity (%) decreased, while the average roughness increased. The reflectance spectrophotometry showed that microwave action occured quickly and progressively, causing colour changes (mainly with trends to yellow) and very small differences to the starch samples that were heated at controlled temperature in a conventional oven.

Journal ArticleDOI
TL;DR: In this article, the authors investigated the kinetics and mechanism of co-pyrolysis of cellulose and polypropylene (PP) in a thermogravimetric analyzer at various heating rates from 5 to 180 Kmin−1.
Abstract: The present research work focuses on understanding the kinetics and mechanism of co-pyrolysis of cellulose, a major constituent of biomass, and polypropylene (PP) that is abundantly present in waste plastics. Co-pyrolysis of cellulose and PP of different compositions, viz., 100:0, 80:20, 60:40, 40:60, 20:80, and 0:100 (mass%/mass%), was carried out in a thermogravimetric analyzer at various heating rates from 5 to 180 K min−1. The kinetics of slow to medium heating rate pyrolysis was analyzed using first Kissinger and Kissinger–Akahira–Sunose techniques. Cellulose and PP decomposition occurred in two distinct temperature regimes, viz., 575–650 and 675–775 K, respectively. However, apparent activation energies of thermal decomposition of the mixtures clearly indicated the presence of interaction between cellulose and PP. The presence of cellulose in the mixture decreased the apparent activation energy of PP decomposition from 210 to 120 kJ mol−1, while the presence of PP did not affect the apparent activation energy of cellulose decomposition (E a = 158 ± 3 kJ mol−1). A significant decrease in apparent activation energy was observed in the conversion regime corresponding to the completion of cellulose pyrolysis and beginning of PP pyrolysis. Differential scanning calorimetry data clearly showed the shift of exothermic char formation to higher temperatures with PP incorporation in the mixture. The presence of PP also resulted in reduction of final char content. Based on the above analyses, a new interaction step that involves a bimolecular reaction of activated PP with volatiles from cellulose pyrolysis to form interaction products and char is proposed, and the rate limiting steps for char formation are clearly identified.

Journal ArticleDOI
TL;DR: In this paper, several effects on the properties of epoxy asphalts have been investigated in detail, and it was shown that the addition of asphalt contents showed no significant effect on the curing reaction and the glass transition temperature.
Abstract: Epoxy-modified asphalts (epoxy asphalts) have been widely used in the pavements of orthotropic steel bridge deck. In this paper, several effects on the properties of epoxy asphalts have been investigated in detail. First, the addition of asphalts showed no significant effects on the curing reaction and the glass transition temperature of epoxy resin. Second, the damping properties of epoxy asphalts were increased with the addition of asphalt contents. Furthermore, mechanical results showed that the stress at yield, stress at break, and tensile modulus of epoxy asphalts decreased with the increase of asphalt contents, whereas the strain at break increased with the increasing asphalt contents. The morphology of phase separation for epoxy asphalts was also observed.

Journal ArticleDOI
TL;DR: The use of soybean protein isolates (SPI) and corn starch (CS) for the manufacturing of textured protein by thermo-mechanical means requires a characterization of their thermal properties as discussed by the authors.
Abstract: The use of soybean protein isolates (SPI) and corn starch (CS) for the manufacturing of textured protein by thermo-mechanical means requires a characterization of their thermal properties. SPI and CS mixtures were examined at starch mass fractions from 0 (pure SPI) to 100 (pure CS). The blends were determined by means of differential scanning calorimetry, with water content of 30, 50, and 70 % and heating rate of 5 and 10 °C min−1 over 20 to 130 °C. The results obtained showed that protein in the blend increased the onset (To) and peak (Tp) temperatures of the starch gelatinization, while starch in the blend decreased the ΔH and ΔT1/2 of the protein. To, Tp, and ΔT1/2 of SPI and CS decreased significantly with the increase of water content. Tp and ΔT1/2 of SPI and CS had a marked increase with an increase of heating rate from 5 to 10 °C min−1. These results suggested that there was no chemical reaction between SPI and CS when they were heated from 20 to 130 °C. SPI in the blend restricted the CS gelatinization, while the presence of CS protected the SPI from denaturation. The increasing water content did promote thermal transition of the mixture. Higher heating rate leads to higher transition temperature.

Journal ArticleDOI
TL;DR: In this paper, the authors studied the heat generation rate of a 25-Ah lithium-ion battery through estimating each term of the Bernardi model and compared with the result from the calorimetric method.
Abstract: The heat generation rate of a large-format 25 Ah lithium-ion battery is studied through estimating each term of the Bernardi model. The term for the reversible heat is estimated from the entropy coefficient and compared with the result from the calorimetric method. The term for the irreversible heat is estimated from the intermittent current method, the V–I characteristics method and a newly developed energy method. Using the obtained heat generation rates, the average cell temperature rise under 1C charge/discharge is calculated and validated against the results measured in an accelerating rate calorimeter (ARC). It is found that the intermittent current method with an appropriate interval and the V–I characteristics method using a pouch cell yield close agreement, while the energy method is less accurate. A number of techniques are found to be effective in circumventing the difficulties encountered in estimating the heat generation rate for large-format lithium-ion batteries. A pouch cell, using the same electrode as the 25 Ah cell but with much reduced capacity (288 mAh), is employed to avoid the significant temperature rise in the V–I characteristics method. The first-order inertial system is utilized to correct the delay in the surface temperature rise relative to the internal heat generation. Twelve thermocouples are used to account for the temperature distribution.

Journal ArticleDOI
TL;DR: In this article, the effect of photoinitiators on the thermal stability of poly(methyl methacrylate) films was studied by thermogravimetric analysis, and it was found that the effect depended on the chemical structure of organic compound modifying the polymer.
Abstract: Films of poly (methyl methacrylate) (PMMA) were prepared by the addition of photoinitiator to the polymer. The influence of five organic photoinitiators on thermal stability of poly(methyl methacrylate) was studied by thermogravimetric analysis. Next, the PMMA films doped with these photoinitiators were UV irradiated and investigated in terms of changes in their thermal stability. It was found that the photoinitiators had accelerated thermal degradation of non-irradiated PMMA films due to the action of free radicals coming from the additives’ thermolysis. For UV-irradiated specimens, the effect of photoinitiator on PMMA thermal stability depended on the chemical structure of organic compound modifying the polymer. In general, thermal stability of irradiated samples was higher in the presence of additives. Thermal destruction of modified PMMA can be explained by the formation of resonance structures in aromatic photoinitiators and consumption of energy in dissipation processes.

Journal ArticleDOI
TL;DR: The nonahydrate of iron(III) nitrate shows no phase transitions in the range of −40 to 0 ǫC as discussed by the authors, which is a different mechanism than those described for other trivalent elements.
Abstract: The nonahydrate of iron(III) nitrate shows no phase transitions in the range of −40 to 0 °C. Both hexahydrate Fe(NO3)3·6H2O and nonahydrate Fe(NO3)3·9H2O have practically the same thermal behavior. Thermal decomposition of iron nitrate is a complex process which has a different mechanism than those described for other trivalent elements. Thermolysis begins with the successive condensation of 4 mol of the initial monomer accompanied by the loss of 4 mol of nitric acid. At higher temperature, hydrolytic processes continue with the gradual elimination of nitric acid from resulting tetramer and dimeric iron oxyhydroxide Fe4O4(OH)4 is formed. After complete dehydration, oxyhydroxide is destroyed leaving behind 2 mol of Fe2O3. The molecular mechanics method provides a helpful insight into the structural arrangement of intermediate compounds.

Journal ArticleDOI
TL;DR: In this paper, the influence of fineness on the cementitious properties of steel slags and the properties of cement containing steel slag with different finenesses were investigated. And the results showed that increasing the fineness can significantly enhance the early as well as the late cementitious property of steel.
Abstract: In this paper, the influence of fineness on the cementitious properties of steel slag and the properties of cement containing steel slag with different finenesses were investigated. The results show that increasing the fineness can significantly enhance the early as well as the late cementitious properties of steel slag. However, the early hydrations of cement and steel slag tend to hinder each other especially in the case of large steel slag replacement and high fineness of steel slag. Therefore, increasing fineness of steel slag cannot improve the early cementitious properties of the cement containing steel slag. At 28 days, the hydrations of steel slag and cement tend to promote each other. Increasing the fineness of steel slag enhances the late cementitious properties of the cement containing steel slag significantly.

Journal ArticleDOI
TL;DR: In this article, the effects of heat-moisture treatment (HMT) on starch were studied using the following techniques: thermogravimetry, differential scanning calorimetry (DSC), rapid viscoamylographic analysis (RVA), reflectance photocolorimetric, atomic force microscopy (NC-AFM) and X-ray diffractometry (XRD).
Abstract: Organic foods and crops are produced throughout the world under strict controls on growing conditions, so that synthetic chemicals, irradiation or genetic modifications are avoided. Organic starch is extracted following the same rules. Heat–moisture treatment (HMT) on starch is a physical method considered to be natural: it consists of heating starch at a temperature above its gelatinisation point with insufficient moisture (<35 %) to cause gelatinisation. Samples of organic cassava starch (with 12.8 % moisture) were dried in an oven with forced air circulation at 50 °C for 48 h and, immediately, distilled water was added to each sample until it reached the ratios of 10, 20, and 30 %, respectively. The samples were transferred into 100 mL pressure flasks, sealed tightly with a cap, and maintained in an autoclave for 60 min at 120 °C. The flasks were opened and the samples were kept in a desiccator containing anhydrous calcium chloride up to constant mass. The effects of HMT were studied using the following techniques: thermogravimetry and derivative thermogravimetry (TG/DTG), differential scanning calorimetry (DSC), rapid viscoamylographic analysis (RVA), reflectance photocolorimetry, atomic force microscopy (NC-AFM) and X-ray diffractometry (XRD). Rheological properties such as the pasting temperature (RVA) and the peak temperature (DSC) increased, while gelatinisation enthalpy ∆H (DSC) decreased. The average diameters of the granules showed no significant changes, while the degree of relative crystallinity decreased.

Journal ArticleDOI
TL;DR: In this article, the thermal degradation of HAuCl4·3H2O starts immediately after melting at 75°C and takes place in three steps in the temperature range of 75-320°C with total mass loss of 49.4 and 49.7% in artificial air and Ar atmospheres, respectively.
Abstract: Thermal decomposition of HAuCl4·3H2O and AgNO3, as precursors for Au and Ag nanoparticles, respectively, was monitored by coupled TG–DTA with TG/EGA–FTIR and EGA–MS techniques in a flowing 80 %Ar + 20 %O2 and Ar atmospheres in the temperature range of 30–600 °C. The intermediate and final products of thermal decomposition were analysed by ex situ XRD and FTIR techniques. The thermal degradation of HAuCl4·3H2O starts immediately after melting at 75 °C and takes place in three steps in the temperature range of 75–320 °C with total mass loss of 49.4 and 49.7 % in artificial air and Ar atmospheres, respectively. EGA by MS and FTIR revealed a simultaneous release of H2O and HCl in the temperature range of 75–235 °C. EGA by MS revealed a release of Cl2 at around 225 °C and in the interval of 250–320 °C. According to the XRD analysis, the main solid product in the end of the first decomposition step at 190 °C is AuCl3; in the end of the second decomposition step at 240 °C is AuCl and the final product at 320 °C is Au. The thermal decomposition of AgNO3 takes place in a single step in the temperature range of 360–515 °C with a total mass loss of 39.0 and 37.8 % in flowing artificial air and Ar atmospheres, respectively. According to EGA–MS and EGA–FTIR the main evolved gases are NO2, NO and O2. The final product of the thermal decomposition at 600 °C is Ag irrespective of the atmosphere.

Journal ArticleDOI
TL;DR: In this article, the performance of solar dryers and thin-layer drying characteristics of garlic cloves in a developed system was evaluated with thermodynamic analysis, which offers an alternative approach to evaluate the performance.
Abstract: This investigation deals with thermodynamic analysis, which offers an alternative approach to evaluate the performance of solar dryers and thin-layer drying characteristics of garlic cloves in a developed system. The garlic cloves were dried from a moisture content of 55.5 % (w.b.) to 6.5 % (w.b.) for 8 h. The drying data obtained were fitted to five different drying kinetics models. Of these, the model suggested by Midilli et al. [28] had the best fit with the drying behavior of garlic cloves. The energy efficiency without and with recirculation of the air exiting the drying chamber during the study varied from 43.06 to 83.73 %, and 3.98 to 14.95 %, respectively, while the exergy efficiency corresponding to the energy efficiency of the drying process ranged from 5.01 to 55.30 % and 67.06 to 88.24 %, respectively.

Journal ArticleDOI
TL;DR: In this article, the tensile modulus and strength of polyamide-6/carbon fiber composites were investigated, and it was found that the CF plays a role as nucleating agent in PA6 matrix and the α-form crystalline structure was favorable in the PA6/CF composites, as confirmed from X-ray diffraction analysis.
Abstract: Polyamide-6 (PA6)/carbon fiber (CF) composites were prepared by melt-extrusion via continuous fiber fed during extruding. The mechanical, thermal properties, and crystallization behavior of PA6/CF composites were investigated. It was found that the tensile modulus and strength of the composites were increased with the addition of CF, while their elongations at break were decreased. Scanning electron microscopy observation on the fracture surfaces showed the fine dispersion of CF and strong interfacial adhesion between fibers and matrix. Dynamic mechanical analysis results showed that the storage modulus of PA6/CF composites was improved with the addition of CF. Non-isothermal crystallization analysis showed that the CF plays a role as nucleating agent in PA6 matrix, and the α-form crystalline structure was favorable in the PA6/CF composites, as confirmed from the X-ray diffraction analysis. A trans-crystallization layer around CF could be observed by polarizing optical microscopy, which proved the nucleation effect of carbon fiber surface on the crystallization of PA6. The thermal stability of PA6/CF composites was also enhanced.

Journal ArticleDOI
TL;DR: In this paper, the modified transient plane source method implemented in the C-Therm Technologies TCi Analyzer provides an easy way to accurately measure the thermal conductivity and distinguish this form of heat transfer in negating the impact of convection.
Abstract: Heat transfer fluids are often a critical performance component in industrial processes and system design. Fluids are used in heat dissipation to maintain stable operating temperatures in a variety of applications, such as diesel engines, chemical production, asphalt storage, and high-power electric transformers. A wide range of fluids specific to various applications are available, thus a reliable and accurate thermal conductivity characterization is extremely important. Thermal conductivity analysis of heat transfer fluids with traditional methods is time-consuming and error-prone due to the impact of convection. Convection often distorts effective thermal conductivity measurement as an additional source of heat transfer. The modified transient plane source method implemented in the C-Therm Technologies TCi Analyzer provides an easy way to accurately measure the thermal conductivity and distinguish this form of heat transfer in negating the impact of convection by (a) employing the shortest test time in commercially available sensors (0.8 s), (b) offering a minimal sample volume requirement (1.25 mL), and (c) employing a low-energy power flux to the specimen under test (approximately 2,600 W m−2). This work presents thermal conductivity results generated on three types of heat transfer fluids over a wide temperature range and discusses the significance of the data in relevance to the application.

Journal ArticleDOI
TL;DR: In this article, the hydration kinetic of PCM-mortars was investigated using the semi-adiabatic Langavant test and the numerical Diffuse Element Method was used for the computation of the heat flux.
Abstract: The Phase Change Materials are considered an attractive way to reduce energy consumption thanks to their heat storage capacity. Their incorporation in the construction materials allows the energy to be an integral part of the building structure. Even though PCMs have shown their reliability from a thermal point of view, some drawbacks linked to their use were emphasized such as the loss of the compressive strength of the PCM-material. This paper attempts to provide an explanation by the investigation of the hydration kinetic of PCM-mortars. The semi-adiabatic Langavant test was adapted to this case. The numerical Diffuse Element Method was used for the computation of the heat flux which is a compulsory step for the determination of the hydration degree. The results showed a lower heat released by the PCM mortars compared to a control mortar as well as a delay in the hydration progress with the addition of PCMs.

Journal ArticleDOI
TL;DR: It is shown that the integral isoconversional methods are mathematically incorrect if the activation energy depends on conversion, and non-sensical snake-like shape of the conversion versus time curves is observed when the kinetic results are extrapolated to lower temperatures.
Abstract: Kinetic parameters resulting from the application of isoconversional methods mostly depend on the degree of conversion. This paper shows that the integral isoconversional methods are mathematically incorrect if the activation energy depends on conversion. In this case, the incorrectness resides in improper separation of variables in the general rate equation. As a consequence, non-sensical snake-like shape of the conversion versus time curves is observed when the kinetic results are extrapolated to lower temperatures.

Journal ArticleDOI
TL;DR: The structure and morphology of ammonium metatungstate (AMT), (NH4)6[H2W12O40]⋅4H2O, and its thermal decomposition in air and nitrogen atmospheres were investigated by SEM, FTIR, XRD, and TG/DTA-MS.
Abstract: The structure and morphology of ammonium metatungstate (AMT), (NH4)6[H2W12O40]⋅4H2O, and its thermal decomposition in air and nitrogen atmospheres were investigated by SEM, FTIR, XRD, and TG/DTA-MS. The cell parameters of the AMT sample were determined and refined with a full profile fit. The thermal decomposition of AMT involved several steps in inert atmosphere: (i) release of crystal water between 25 and 200 °C resulting in dehydrated AMT, (ii) formation of an amorphous phase between 200 and 380 °C, (iii) from which hexagonal WO3 formed between 380 and 500 °C, and (iv) which then transformed into the more stable m-WO3 between 500 and 600 °C. As a difference in air, the as-formed NH3 ignited with an exothermic heat effect, and nitrous oxides formed as combustion products. The thermal behavior of AMT was similar to ammonium paratungstate (APT), (NH4)10[H2W12O42]⋅4H2O, the only main difference being the lack of dry NH3 evolution between 170 and 240 °C in the case of AMT.

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TL;DR: In this article, the authors investigated the thermal decomposition of various commercially produced hydrated magnesium carbonates (HMCs) classified as light and heavy, highlight their differences, and provide an insight into their compositions in accordance with the results obtained from thermal analysis and microstructure studies.
Abstract: Upon heating, hydrated magnesium carbonates (HMCs) undergo a continuous sequence of decomposition reactions. This study aims to investigate the thermal decomposition of various commercially produced HMCs classified as light and heavy, highlight their differences, and provide an insight into their compositions in accordance with the results obtained from thermal analysis and microstructure studies. An understanding of the chemical compositions and microstructures, and a better knowledge of the reactions that take place during the decomposition of HMCs were achieved through the use of SEM, XRD, and TG/differential thermal analysis (DTA). The quantification of their CO2 contents was provided by TG and dissolving the samples in HCl acid. Results show that variations exist within the microstructure and decomposition patterns of the two groups of HMCs, which do not exactly fit into the fixed stoichiometry of the known HMCs in the MgO–CO2–H2O system. The occurrence of an exothermic DTA peak was only observed for the heavy HMCs, which was attributed to their high CO2 contents and the relatively delayed decomposition pattern.

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TL;DR: In this paper, the authors presented the methods for the calculation of chemical exergies of coal, heavy fuel oil and natural gas that are used as fuel in conventional thermal power plants.
Abstract: This paper presents the methods for the calculation of chemical exergies of coal, heavy fuel oil and natural gas that are used as fuel in conventional thermal power plants. Calculations have shown that the chemical composition of the fuel greatly influences the value of its chemical exergy. In case of coal in which carbon and hydrogen are not combined together, an increase in both carbon and hydrogen contents increases its chemical exergy value. In case of heavy fuel oils, hydrogen–carbon ratio is the most influencing parameter in the chemical exergy value. An increase in hydrogen–carbon ratio in the fuel tends to increase its chemical exergy. In case of natural gases, a decrease in lighter hydrocarbon gas contents and an increase in heavier hydrocarbon gas contents tend to increase the chemical exergy value of the fuel. High moisture and/or ash contents also tend to lower the value of the chemical exergy.

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TL;DR: In this paper, the activation energy of experimental Jurassic coals at the ignition temperatures was calculated by Ozawa method based on the non-isothermal and differential heating rates, ranging from 80 to 105kJ/mol−1, which was lower than that of the eastern permo-carboniferous samples.
Abstract: Thermal analysis of seven Jurassic coal samples from North Shaanxi in West China and three permo-carboniferous coal samples from East China was studied to identify ignition temperatures in the process of the oxidation and spontaneous combustion. The experiments were carried out under non-isothermal heating conditions up to 700 °C at the heating rates of 5, 10, 15, and 20 °C min−1 in an air atmosphere. Through the FTIR spectrometer experiments, the absorbance peaks of functional groups of coal samples were analyzed at the ignition temperatures, pre-ignition of the 10 °C, post-ignition of the 10 °C at the heating rate of 10 °C min−1. By the differential spectrum method, the changes of functional groups were discussed with the aim to determine characteristics and reactivity of the ignition temperature around. The results showed that ignition temperatures of experimental coal samples increased with the rising heating rates, and ignition temperatures of Jurassic coals were lower than that of the permo-carboniferous coal samples at the same heating rate. Apparent activation energy of experimental Jurassic coals at the ignition temperatures was calculated by Ozawa method based on the non-isothermal and differential heating rates, ranging from 80 to 105 kJ mol−1, which were lower than that of the eastern permo-carboniferous samples. On the basis of Pearson correlation coefficient method which can signify the degree of correlations ranging from −1 to 1, the correlation analyses were conducted between activation energy and functional groups variation within 10 °C before and after ignition temperature. It was concluded that the key functional groups of Jurassic coals in the oxidation and ignition reaction were methyl and alkyl ether within 10 °C before ignition temperature, and carboxyl and carbonyl within 10 °C after ignition temperature.