Papers by Keyword: Thermodynamic

Abstract: Based on the phase diagrams analysis, the activity model of Fe-C-B ternary system was established with the ion and molecule coexistence theory. The activities of Fe, C, B, Fe3C, FeB, FeB2 and B4C in melt were calculated by analyzing the model. We have researched the thermodynamic condition of boron oxide reducing with carbothermic method and analyzed the effects of CO partial pressure, B2O3 content and slag type for the lowest smelting temperature. In normal pressure, the carbon content is high in melt, so it needs 2000°C for decarbonizing and chrome remaining. When CO partial pressure is 0.1 kPa and CaO content is less 60%, the lowest temperature of smelting ferro boron could be below 1600°C.

Abstract: Mckibben pneumatic muscle actuators (PMA) have many advantages such as high power-mass ratio and low price, but their strong nonlinear characteristics makes modeling and controlling very hard, which limits their applications. This paper presents the modeling of PMA and methods to enhance their dynamic performances. Considering the incorporated models of fast-switching valves and PMAs, the entire system model is modified in some aspects and the dominant model parameters are determined through experimental results to estimate the dynamic characteristics precisely. Simulation and proper experiments reveal that the dynamic performance of PMA can be improved through filling the PMA with materials of high thermal conductivity. The slow time-varying disturbance caused by the temperature variation of inner gas can be reduced much, which lowers the difficulty of controlling.

Abstract: The ground state geometrical of cyclic sulfur molecules S8 has been studied with RHF/6-311G* of ab initio methods. Gibbs free energy of CO, SO2, S8 and CO2 from 300 to 1673K has been calculated using ab initio method. Besides, the reaction free enthalpies were calculated. The results show that resultants of reaction of CO and SO2 are S8 and CO2 below 1451K and the reaction is spontaneous.Fe2O3 in glass can is reduced into FeO whose redox number is negative. The Gibbs free energy of FeO is smaller than that of FeS while chemical stability of FeO is higher than that of FeS. Structures of cycle sulfur are versatile. Bond energy of S8, S12 and S18 is broken, which need high energy. When small sulfur ring molecules be formed, the chemical and heat stability of S8 are improved.

Abstract: In the present work at the first time the hydrogen interaction with Ce₆Ni_1.67Si₃ at pressure up to 45 atm and temperature 51_˚C has been investigated by means of the calorimetric method. The ΔHabs. – C dependence (ΔHabs. –the partial molar enthalpy of the reaction of the hydrogen interaction with IMC, C – hydrogen concentration, C=H/IMC) was obtained.

Abstract: Amongst the Metal Matrix Composites (MMCs), Al-Si-Mg alloy/ SiCp MMCs are very attractive for their properties. But, the formation of brittle interfacial reaction product, Aluminium carbide has been one of the major concerns when these materials are processed by liquid phase methods. The extent of Aluminium carbide formation depends on various processing parameters such as temperature, wt% of SiCp, particle size of SiCp and chemical composition of the matrix alloy especially Silicon (Si) content. According to recent studies, various difficulties in finding the process parameters to get desirable properties of Al alloy/ SiCp MMCs as desired by the industries. Thus, in the present study thermodynamic & structural estimates in Al alloy/ SiCp MMCs under various process conditions, composition, microstructures were performed. The relatively low cost liquid stir casting technique is used in the production of Al alloy/ SiCp MMCs with varying Silicon content (0–7%) in the alloy matrix using process temperature 710°C. Aluminium carbide layer formation on SiCp surface, Critical Si content for Aluminium carbide separation from SiCp surface, eutectic Si formation, existence of near-dislocation segregation regions after formation of Aluminium carbide on SiCp surface and the equilibrium amount of Si to suppress Aluminium carbide formation were investigated using Transmission electron microscopy (TEM). The separation of Aluminium carbide from SiCp surface was observed after 3% Si. The equilibrium Si content of 7% was found to suppress the formation of Aluminium carbide with thermodynamic model and its significance has been assessed.

Abstract: The absorption heat pump was studied with finite time thermodynamics. A four reservoirs model of absorption heat pump which is treated as an irreversible Carnot heat pump driven by an irreversible Carnot heat engine was established considering the heat resistance and the irreversibility of the internal cycle. A generalized optimization relationship between the main parameters and the corresponding conditions were derived. It is show that, two internal irreversibility parameters, the heat engine cycle and the heat pump cycle has different effects on system performance, and the reduction of the friction, heat loss, and internal dissipations of the equivalent heat pump cycle are more important than its reduction of heat engine cycle.

Abstract: The thermodynamic properties of YCu intermetallics with B2 structure are investigated with molecular dynamics. The thermodynamic properties at various temperatures, such as lattice parameter, cohesive energy, enthalpy of formation, elastic constants, heat capacity, vibrational entropy and vibrational free energy are computed. The present calculated results show good agreements with available experimental and previous calculated data. The calculated elastic constants suggested that YCu compound has a mostly ductile behavior. This prediction match well with experimental findings. At high temperature, the heat capacity tends to a constant with obeys the classical equipartition law. At 300K, the heat capacity of YCu is 23.80J mol-1 K-1. The calculated coefficient of thermal volume expansion α increases sharply at T<20K. When T<300K α gradually approaches a linear increase with enhanced temperature and the propensity of increment becomes moderate. At T=300K, the value of α is 5.88×10-5K-1. And those data enrich thermodynamic data-base for YCu compound.

Abstract: Ethylenediamine-modified chitosan magnetic nano-adsorbent (EMCN) was prepared and used for the sorption of methyl orange(MO). The kinetics of the sorption fitted well with the pseudo-second-order kinetics model. The activation energy of sorption (Ea) was determined to be 16.47 kJ.mol-1. Adsorption isotherms showed that the sorption process was consistent with both Langmuir and Freundlich isotherm, and the thermodynamic parameters were calculated and indicated that the sorption process was spontaneous and exothermic. The saturated sorption capacity is 247.66, 227.58, 214.19 mg.g-1 at 5°C, 25°C, 45°C(pH=5.6),respectively.

Abstract: The geometric shape of a crystal can be simulated via a thermodynamic model using breaking bond energy calculations. When this model was applied to the case of the KDP crystal, a thermodynamic description of the KDP crystal growth was successfully developed, which was consistent with experimental observations. Additionally, the effect of surface chemistry on the morphology of the KDP crystal was also investigated using the model based on the surface energy of the KDP crystal. These results confirm that bond making and breaking strongly influence the thermodynamic morphology of the KDP crystal during the crystallization.

Abstract: Through immersion precipitation phase inversion, poly(vinyldiene fluoride) (PVDF) membranes applied in ultrafiltration were prepared. The influences of four solvents on the phase separation of PVDF casting solutions and membrane structure were discussed by mechanism of skin-sublayer two steps precipitation. The results showed that the delayed solid-liquid demixing occurred in the skin layer under the control of the thermodynamics of casting solutions, and the dense skin layer formed with spherical or dendritic crystals. The phase separation behaviors of the sublayers were controlled by the kinetic diffusion (DW-S/DS-W).