Calorimetric measurements of sodium chloride dihydrate NaCl·2H2O (mineral name hydrohalite) were carried out with using DSC. Heat capacity from 190 to 250 K was measured and found to increase from 109 to 137 J mol?1 K?1. The enthalpy of formation of hydrohalite from solid ice and halite at 273.15 K was derived from the thermal effect of melting/decomposition in DSC measurements and found to be close to ??1.8 kJ mol?1. The same DSC results show clearly that the upper temperature limit for the existence of hydrohalite is several degrees greater than the current value of 273.15 K accepted for the peritectic decomposition of hydrohalite. The phase diagram of the NaCl–H2O system needs correction.
相似文献In this study, energy and entropy analysis of a residential-type direct absorption solar collector using hybrid Fe3O4/SiO2 nanofluid is evaluated experimentally. The hybrid nanofluid samples are prepared in the different volume ratios of Fe3O4/SiO2 (25:75, 50:50 and 75:25) and different volume fractions (500 ppm, 1000 ppm and 2000 ppm). The appropriate nanofluid samples for using as the working fluid of the collector are chosen based on the results of stability and optical properties of nanofluid. Then, outdoor thermal performance of collector is investigated using the experimental setup based on EN12975-2. Measurement of nanofluid optical properties using the spectrophotometry method shows that the extinction coefficient of 2000 ppm hybrid Fe3O4/SiO2 nanofluid is on average 10 cm?1 higher than that of the base fluid. Results of energy analysis display that the collector efficiency is increased by mass flow rate and volume fraction of nanofluid asymptotically. The asymptotic value is about 83% for 2000 ppm hybrid Fe3O4/SiO2 nanofluid. The findings indicate that the variation of exergy efficiency of a direct absorption solar collector with the volume fraction and mass flow rate is similar to energy efficiency. The enhancement of exergy efficiency is 66.4% for mass flow rates of 0.0225 kg s?1 by increasing the volume fraction from 0 to 2000 ppm. It is also observed that dimensionless entropy generation number is decreased by nanofluid volume fraction and by mass flow rate. The lowest entropy generation number is obtained in the mass flow rate of 0.0225 kg s?1 and the volume fraction of 2000 ppm. The variation of Bejan number by volume fraction shows that the contribution of pressure drop in entropy generation is insignificant.
相似文献An experimental investigation on the feasibility and relevance of the tri fuel blends of ethanol and dibutyl ether with diesel was studied to replace pure diesel. The solubility of the ethanol and dibutyl ether with a percentage of 25% and 75% resulted with no phase separation, found miscible and stable with diesel at any percentage. However, the properties such as densities and refractive index experimentally verified for different blend ratios. A density of test samples with various compositions was tested. High precise equipment is engaged to analyze the density, speed of sound, refractive index for various fuel compositions. The temperature ranges between 298 K and 343 K show a greater impact on variation in the fuel properties. Density, speed of sound, refractive indices measured as a function of the temperature with an accuracy of?±?0.001 and?±?0.0001. Further, the validation of experimental method has been tested using Lorentz–Lorenz (L–L) analysis with a deviation of 0.4%. The uncertainty for fluid velocity is?±?0.3 m s?1, and the experimental estimated excess molar volume uncertainty is 2?×?10?3 cm3 mol?1. The substantiation of intermolecular interactions between the liquids is found to be significant in both experimental and prediction analysis of each sample. The exergy destruction specifies with 46% which includes the air flow and chemical heat energy transfer losses.
相似文献Two procyanidin B2 conformers were identified in a relative abundance ratio of approximately 3:1 at 298 K by 1H NMR experiments in acetonitrile. The conformational interchange reactions between these two conformers are 1st order in both reactions, with ?G? for forward and reverse of 57.12?±?5.62 and 54.56?±?5.48 kJ mol?1, respectively. The experimentally obtained standard thermodynamic energies for this reaction are ΔH0rxn (3.67?±?0.22 kJ mol?1), ΔS0rxn (4.05?±?1.57 kJ mol?1 K?1), and ΔH0rxn (2.96?±?0.33 kJ.mol?1). Conformational search results at the DFT (PBE, PBE-D2, and B3LYP with 6-311++g**) level of theory yielded four novel conformations, named fully compact (FC), partially compact (PC), partially extended (PE), and fully extended (FE). Although the FC conformer is electronically the most stable of the four as a result of extensive intramolecular non-covalent interactions, the PC and FE conformers are thermodynamically favored in a 5:1 ratio (B3LYP), with the FC and PE conformers present in negligible amounts at equilibrium. The DFT computed standard reaction energies using the B3LYP functional for the PCmajor to FEminor conformational interchange reaction compare exceptionally well with experimental data at 298 K: ?G0rxn (3.86 kJ mol?1), ΔH0rxn (5.34 kJ mol?1), and ?S0rxn (4.97 kJ mol?1 K?1). It was found that inclusion of solvation energies is crucial to obtain accurate thermodynamic energies. The secondary equilibria found in chromatographic separations are predicted to be highly dependent on solvent polarity and temperature. Similar conformational diversity and hierarchies should exist for all non-rigid procyanidin oligomers and the unique chromatographic behavior of these compounds may be a result of conformational interchange.
相似文献Hydrophobically modified silica aerogel nanoparticles (H-SiANp) were used for in situ polymerization of methyl methacrylate by reverse atom transfer radical polymerization to synthesize well-defined PMMA nanocomposites. Inherent characteristics of the prepared H-SiANp were evaluated by nitrogen adsorption/desorption isotherms, SEM, and TEM. Conversion and molecular weight determinations were carried out using GC and SEC, respectively. Addition of 3 mass% of the H-SiANp leads to decrement of conversion from 92 to 74%. Molecular weight of poly (methyl methacrylate) chains also decreases from 19,737 to 15,662 g mol?1 by addition of only 3 mass% H-SiANp; however, PDI values increase from 1.36 to 1.82. Linear increase of ln(M0/M) with time for all the samples shows that polymerization proceeds in a living manner. In addition, suitable agreement between theoretical and experimental molecular weight in combination with low PDI values can appropriately demonstrate the living nature of the polymerization. TG results indicate that by increasing H-SiANp content, improvements in thermal stability of the nanocomposites were obtained. DSC results show a decrease in glass transition temperature from 87.4 to 80.9 °C by addition of 3 mass% H-SiANp.
相似文献In this paper, it was suggested the use of green corn husk, which is a biomass from agro-industry, as an alternative source of energy through its pyrolysis. Green corn husk characterization was done through immediate and elemental analysis of its components: cellulose, hemicelluloses, and lignin. It was also measured its higher calorific value. The pyrolysis study of green corn husk was done by the isoconversion and the Master plots method. Thermogravimetric plots were obtained at heating rates of 5, 10, 15, and 20 °C min?1. The pyrolysis kinetics parameters were studied through the Flynn–Wall–Ozawa (FWO), Kissinger, and Friedman models. The Master plots method was used to determine the pyrolysis reaction order. The results of the reaction energy activation were found to be in the range 105.21–157.46 kJ mol?1 by the FWO method, 150.50 kJ mol?1 by the Kissinger method, and ranged 120.66–163.81 kJ mol?1 by the Friedman method. The Master plots method showed a three-way-transport diffusional kinetics for the biomass de-volatilization process. The higher calorific value found for green corn husk was 16.14 MJ kg?1. The simulation showed correlation between the experimental data and the proposed model for conversion values up to 0.8.
相似文献A new nitrogen-rich energetic salt of bis-1-methylimidazole 1H,1′H-5,5′-bistetrazole-1,1′-diolate salt, (1-M)2BTO, was synthesized and characterized (FT-IR, 1H NMR, 13C NMR, elemental analysis, and X-ray single-crystal diffraction). Results indicated that (1-M)2BTO crystallizes in the triclinic space group P-1. The thermal decomposition behavior of (1-M)2BTO was determined by differential scanning calorimetry (DSC) and thermogravimetric tandem infrared spectroscopy. The decomposition peak temperature of (1-M)2BTO was 530 K, which suggested that the salt is strong heat resistance. The apparent activation energies were 130.56 kJ mol?1 (Kissinger’s method) and 132.50 kJ mol?1 (Ozawa’s method), respectively. The enthalpy of formation for the salt was calculated as 917.3 kJ mol?1. The detonation velocity and detonation pressure of (1-M)2BTO were 7448 m s?1 and 20.7 GPa, respectively, using the Kamlet-Jacobs equation. Furthermore, the sensitivity test results showed that its impact sensitivity is greater than 50 J and friction sensitivity is 180 N, indicating that it has a lower sensitivity.
相似文献Magnetic graphene oxide/lanthanum phosphate nanocomposite (MGO@LaP) was synthesized and used as an efficient adsorbent for magnetic dispersive microsolid-phase extraction (MD-µ-SPE) of pesticides before gas chromatography–electron capture detector (GC–ECD) analysis. The adsorbent was thoroughly characterized with scanning electron microscopy, vibrating sample magnetometer, energy-dispersive X-ray spectroscopy, and Fourier transform infrared spectroscopy. Optimized extraction conditions were investigated concerning extraction time, adsorbent amount, sample pH, and salt amount as well as desorption conditions (type and volume of desorption solvent and desorption time). Under the optimal conditions, the method demonstrated good linearity (3–1500 µg L?1) with satisfactory determination coefficients of >?0.997 and low detection limits for both chlorpyrifos (0.67 µg L?1) and hexaconazole (0.89 µg L?1). Finally, the method showed high analyte relative recoveries in the range of 78–120% for the determination of the selected pesticides in water and fruit juice samples.
相似文献Pyrolysis is a commonly used method for the recovery of used lubricating oil (ULO), which should be kinetically improved by a catalyst, due to its high level of energy consumption. In this research, the catalytic effects of carbon nanotube (CNT) and graphene nanoplatelets on the pyrolysis of ULO were studied through thermogravimetric analysis. First, the kinetic parameters of ULO pyrolysis including activation energy were calculated to be 170.12 and 167.01 kJ mol?1 by FWO and KAS methods, respectively. Then, the catalytic effects of CNT and graphene nanoplatelets on pyrolysis kinetics were studied. While CNT had a negligible effect on the pyrolysis process, graphene nanoplatelets significantly reduced the temperature of maximum conversion during pyrolysis from 400 to 350 °C, due to high thermal conductivity and homogenous heat transfer in the pyrolysis process. On the other hand, graphene nanoplatelets maximized the rate of conversion of highly volatile components at lower temperatures (<?100 °C), which was mainly due to the high affinity of these components toward graphene nanoplatelets and also the effect of nanoplatelets’ edges which have free tails and can bond with other molecules. Moreover, graphene nanoplatelets decreased the activation energy of the conversion to 154.48 and 152.13 kJ mol?1 by FWO and KAS methods, respectively.
相似文献In this work, the bioenergy potential of green microalgae Scenedesmus acuminatus was evaluated through the psychochemical characteristics and kinetic study of pyrolysis, where the results indicate a good candidate for application in the thermochemical process due to its low moisture and ash content and high calorific value. Its thermal behavior under a heating rate of 10 °C min?1 and inert atmosphere shows that decomposition occurs in two stages. Stage I (125–309 °C) involves the pyrolysis of carbohydrates and protein and stage II (309–501 °C) the pyrolysis of lipids. The Starink isoconversional method showed a better application for simulation curves, compared with methods of FWO and KAS. The average values of activated energy were 107.1 and 132.6 kJ mol?1 for stages I and II, respectively, which indicates that pyrolysis occurs more easily in stage I than in stage II. The conversion rate curves show that the calculated kinetic parameters are satisfactory for the evaluation of the thermochemical systems.
相似文献Octamethylenedicarboxylic dibenzoylhydrazide (TMC-300) was used as a nucleating agent for isotactic polypropylene (iPP) for the first time. The Avrami method and the Caze method were used to analyze the isothermal and non-isothermal crystallization kinetics of iPP incorporated with TMC-300, respectively. During isothermal crystallization, the half crystallization time at 130 °C reduces from 130 s of virgin iPP to 44 s after addition of TMC-300, which reflects that TMC-300 increased the crystallization rate of iPP obviously. The crystallization activation energy decreases from 382.5 kJ mol?1 of virgin iPP to 275.3 kJ mol?1 of iPP/TMC-300. During non-isothermal crystallization, the crystallization peak temperature of iPP nucleated with TMC-300 was increased by 5.1 °C when compared to that of virgin iPP at the cooling rate of 20 °C min?1, and both the reduction of half crystallization time and the increase in peak crystallization temperature also justified that the addition of TMC-300 accelerated the crystallization of iPP.
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