DEPENDENCE OF THE MULTIPLICITY FEATURES OF AN ISOTHERMAL CATALYTIC REACTION ON EXTERNAL AND INTERNAL TRANSPORT RESISTANCES

A mathematical model (Robin) which accounts for both internal and external transport resistances is used to determine the multiplicity features of a porous catalytic pellet in which an isothermal Langmuir-Hinshelwood reaction occurs. At most three solutions exist for a slab, but an arbitrarily large number of solutions can be found for an infinite cylinder or a spherical pellet. The maximal number of solutions for any finite external mass transfer resistance is bounded between that existing for a model which ignores the external mass transfer resistance and one which ignores intra-particle concentration gradients. The approximate shape of the cross section of the bifurcation set and of the uniqueness boundary of the Robin model can be estimated from the knowledge of the multiplicity features of three simplified (lumped, Dirichlet and Neumann) models, each containing one less parameter.     

Measurement of excess enthalpies using a high-pressure flow microcalorimeter and determination of binary interaction parameters for thermodynamic models

While an equation of state (EOS) plays a critical role in estimating thermodynamic properties, employing it in the determination of binary interaction parameters is extremely important. In general, these parameters can be determined from phase equilibrium data. However, data collection from experiments is a time-consuming and tedious process. In this study, after measuring the excess enthalpies of binary systems containing CO₂ by high-pressure flow isothermal microcalorimetry (IMC), we determined the EOS binary interaction parameters, specifically, the Peng-Robinson EOS binary interaction parameters. These binary interaction parameters obtained by IMC were compared with those obtained by vapor-liquid equilibrium (VLE) experiments. Hence, high-pressure flow IMC appears to be an effective method for the determination of interaction parameters that are used in the estimation of thermodynamic properties. Further, the Flory-Huggins interaction parameters of a binary mixture CO₂ containing with various mole compositions were also estimated by employing high-pressure IMC.     

LDPE及LDPE/TiO_2纳米复合材料的熔限及等温结晶研究

采用熔融共混法制备了LDPE／TiO2纳米复合材料,以膨胀计对LDPE及LDPE／TiO2复合材料的熔点、熔限及等温结晶进行了研究。结果表明：膨胀计可用于LDPE及LDPE／TiO2纳米复合材料熔点及熔限的测试：与LDPE相比,LDPE／TiO2复合体系的半结晶期及AVrami指数较小,表明TiO2粒子对LDPE的结晶具有明显的异相成核作用;而Avrrdmi指数为非整数,且Avrami作图直线的最后部分与实验点的偏离,则表明LDPE及LDPE／TiO2纳米复合材料的等温结晶过程比Avrami方程要复杂得多。     

00Cr25Ni7Mo3WuCuN双相不锈钢超塑性成形

采用自行设计制造的恒温热拉伸装置,对双相不锈钢的超塑性能进行系统的研究,确定了双相不锈钢的超塑成形工艺参数。利用气胀成形的方法进行双相不锈钢的超塑成形试验,经过一道次成形出两种形状比较复杂的制品。试验表明该双相不锈钢材料具有良好的超塑成形性能。     

Kinetics of quality changes of pumpkin (Curcurbita maxima L.) stored under isothermal and non-isothermal frozen conditions

The effects of freezing process and frozen storage at isothermal (−7, −15 and −25 °C) and non-isothermal (accelerated life testing with step-stress methodology; temperature range from −30 to −5 °C) conditions on pumpkin quality were investigated. Storage temperature conditions were selected to embrace the limits practiced in the cold chain. Quality changes, such as texture, colour CIE Lab and vitamin C (ascorbic acid) content, were evaluated for both frozen storage regimes. The freezing process (that included a pre-blanching step) and subsequent frozen storage had significant impacts on all quality parameters analysed.A fractional conversion kinetic model was adequate in colour, texture and vitamin C data fits. The storage temperature effect was successfully described by the Arrhenius law.This study shows that non-isothermal frozen storage has a marked effect on pumpkin quality.     

Spark plasma sintering of UO2 nanopowders: Pressure,heating rate and current effects

We analysed with different methods the densification of UO₂ nanopowders in SPS under constant heating rate (CHR) and isothermal sintering conditions. The apparent activation energy of densification in SPS (75 kJ/mol with CHR method) is significantly smaller than in conventional sintering. It is shown that this is likely not an effect of the applied current. We also observed a threshold stress at 64 MPa for the transition from pressure-insensitive sintering (stress exponent n≈0) to pressure-assisted sintering, suggesting that the contribution of the capillary stresses in such nanopowders is comparable with the typical stress applied in SPS.     

An isothermal oxidation behaviour of atmospheric plasma and high-velocity oxy-fuel sprayed nickel based coating

This paper describes the isothermal oxidation behaviour of NiCrBSiFe coatings on SS 316 L deposited by the atmospheric plasma (APS) and high-velocity oxy-fuel (HVOF) processes. As-sprayed coatings were oxidised isothermally in the air at 900 °C temperature for 1000 h. The thermogravimetric analysis was performed to measure the oxidation rate. The coating and oxide scale characterisation was carried out using SEM, EDAX, XRD, porosity analysis, and nanoindentation. The HVOF sprayed NiCrBSiFe coating shows better oxidation resistance than the APS coating, due to high density, less porosity, and formation of more protective oxide scale.     

A new hybrid solar photovoltaic/ phosphoric acid fuel cell and energy storage system; Energy and Exergy performance

Present work investigates the performance of a combined solar photovoltaic (PV) and Pumped-Hydro and Compressed-Air energy storage system to overcome the challenges of using solar energy systems. This energy system, which is one of the newest hybrid systems, is able to generate electricity and store energy. To examine the solar PV performance the climatic conditions of Shiraz (in Iran) and Abu Dhabi (in UAE) are considered. The results revealed that, the required pump work, which must be supplied by PV system, is equal to 2.85 and 2.62 MJ/m³ for isothermal and isentropic processes, respectively. Furthermore, the total system efficiency is equal to 76.5%. In addition, the total exergy destruction of hybrid system for isentropic process is 8.91% less than that isothermal process. In addition, instead of the solar PV system, a phosphoric acid fuel cell is coupled to the storage system and the results are compared with the main system.     

On the dependence of interfacial resistance on contact materials between cathode and interconnect in solid oxide fuel cells

The dependence of interfacial contact resistance (ICR) on contact materials between cathode and interconnect is systematically studied under both isothermal oxidation and thermal cycling conditions. Three kinds of cathode current-collecting layer (CCCL) are used, (La,Sr) (Co,Fe)O₃ (LSCF), LSCF+10%Ag, and Ag, and tested in a SUS430/CCCL/SUS430 sandwich structure to simulate the actual operation of the solid oxide fuel cells (SOFCs). Experimental results show that the ICR of LSCF+10%Ag exhibits the smallest value, in comparison with the specimens with LSCF and Ag paste, as well as the sample without a CCCL. For LSCF+10%Ag contact, the ICR increases from 0.0069 mΩ cm² to 3.74 mΩ cm² under an isothermal condition for 150 h, then increases from 3.74 mΩ cm² to 10.79 mΩ cm² after 15 thermal cycles. This work provides information for the understanding of possible mechanisms of performance degradation of SOFCs.     

Influence of External Interface Normal Stress on the Growth of Cu-Sn IMC During Aging

A U-shape clamp was designed to apply stress perpendicular to the interface of Cu/Sn/Cu solder joints, and its influence on the growth behavior of Cu-Sn intermetallic compound (IMC) during thermal aging at 150 °C was investigated. The results show that compared with the sample at general stress-free state, the growth rate of IMC under compression is faster, while that under tension is slower. Moreover, the interface between IMC and Sn is smoother under compressive stress, and the corresponding IMC grains are smaller and more uniform than that under tensile stress. According to the growth kinetic analysis, the growth of IMC under general, compressive and tensile states is all controlled by the combination of grain boundary diffusion and volume diffusion with a similar growth exponent (n ≈ 0.4). However, external stress can affect the Ostwald ripening process of grain growth, causing a change of grain size and grain boundary density in the IMC layer. As a result, the IMC growth behavior at the interface of the solder joint will be affected by the applied external normal stress.