Heterogeneous modeling for fixed-bed Fischer–Tropsch synthesis: Reactor model and its applications

A comprehensive one-dimensional heterogeneous reactor model is developed to simulate the performance of fixed-bed Fischer–Tropsch reactors for hydrocarbon production. The detailed mechanistic kinetics is combined into the reactor model along with considering the fact that the catalyst pores are filled with liquid wax under realistic conditions. The equilibrium between the gases in the bulk and the wax in the catalyst pores is correlated by using a modified SRK equation of state (MSRK EOS). The model is solved by using Gear method to integrate the reactor model with the embedded pellet model discretized by orthogonal collocation on finite elements. The validity of the reactor model is tested against the measured data from different-scale demonstration processes. Satisfactory agreements between model predictions and experiment results are obtained. Detailed numerical simulations are performed to investigate the effect of major process parameters on the reaction behavior of fixed-bed FTS systems with recycle operation.     

A new model for nanofluid conductivity based on the effects of clustering due to Brownian motion

Conductivity values of nanofluids calculated with the model proposed by Nan et al. 1 consistently underestimate the corresponding measured values for 20 sets of experimental data from 12 published studies; thus the conclusion of the recent International Nanofluid Property Benchmark Exercise 2 which stated that it is not necessary to resort to other theories (e.g., Brownian motion, liquid layering, and aggregation) for the interpretation of the INPBE database cannot be generalized. In view of this situation, a new model which takes into account clustering and micro‐convection is proposed and compared with experimental data for five nanofluids (with different particle sizes and a range of particle concentrations) as well as two previously published models. The maximum difference between the predictions of the proposed model and the measured values is 6.7% of the latter. © 2011 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley Online Library ( wileyonlinelibrary.com/journal/htj ). DOI 10.1002/htj.20350     

Reconstruction of Temperature Distribution in the Combustion Region of a Non-Gray Medium

Two-dimensional temperature distribution in the combustion region of a radiant furnace with non-gray gaseous products is reconstructed in an inverse manner. The discrete ordinate method is used to solve the radiative transfer equation, and the non-gray behavior of gaseous medium is modeled by the spectral line weighted sum of gray gas model. Conjugate gradient method is employed for the inverse analysis. The domain of interest is divided into two regions: the unknown- and known-temperature zones. The temperature distribution in the unknown-temperature zone, near the flame, is recovered in an inverse manner by the measurement of heat fluxes over the opposite walls in the direction of flame diffusion. Effects of the size of unknown-temperature zone, variable concentrations, and measurement errors in temperature reconstruction are discussed.     

Diffusion in FSW Joints by Inserting the Metallic Foils

The aims of this investigation were to study diffusion phenomenon in friction stir welding （FSW） joints and its influence on the tensile strength of joints. To study diffusion in stir zone, various metallic foils were inserted between two pure aluminium plates. The thin foils of pure copper, pure zinc, brass and Cu-Zn-Ni alloy with the thickness of 250 μm were used as metallic foils. The transversal cross sections of welds were observed by optical microscopy and scanning electron microscopy （SEM） equipped with an energy dispersive X-ray spectroscopy （EDS） system. The spot analyses near the metallic foils indicated that diffusion occurs from foils into the aluminium plates during welding; consequently, the strength of stir zone increases even by 50%. Besides, the metallic foils could reveal the flow of metal after FSW process.     

Application of laminated and metalized films to prolong the shelf life of dried barberries

Barberry is a nutritional and therapeutic crop mostly dried and consumed in bulk. However, the lack of proper packaging leads to the decline of many of its valuable properties. The aim of this study was to investigate the effect of different packaging films on barberries properties during storage. 150 g of freshly dried barberries were kept for 6 months at 25 °C within different packaging materials: (i) low-density polyethylene (LDPE); two laminated layers film including LDPE and polyethylene terephthalate (PET) with a total thickness of (ii) 45 μm (LDPE/PET-45) and (iii) 60 μm (LDPE/PET-60); (iv) oriented polypropylene (OPP); (v) three laminated layers film of OPP (3OPP); (vi) three laminated layers film including LDPE, metalized PET and PET (LDPE/mPET/PET); and (vii) four laminated layers film including LDPE, PET, aluminum foil and PET (LDPE/PET/Al/PET). After six months, the least change in moisture content, the lowest loss of DPPH scavenging capacity (97.9%), the minimum overall color difference, and the least increase in acidity (39.3%) were related to barberries packaged in the LDPE/PET-45 film. This is while the lowest loss of ascorbic acid (99.8%) and anthocyanin (62.8%) contents and the minimum microbial deterioration were related to the LDPE/PET-60 film. On the other hand, the LDPE/PET/Al/PET film entailed the lowest barberry weight loss (0.67%) and the minimum increase in firmness (40.7%), while the 3OPP film providing the best preservation of phenolic compounds. In conclusion, it seems two laminated layers films composed of LDPE and PET are appropriate for the preservation of dried barberries during storage.     

Parents’ living conditions influence offspring fitness and competency

In this study, we used Callosobruchus maculatus as a model insect to assess the idea of whether or not environmental conditions experienced by parents subsequently moderate offspring fitness and competency. We observed that parents’ experiences (sex ratio of parents, restricted access to mates, and honey access) influenced their offspring’s features and did not significantly affect traits such as offspring sex ratio, larval duration, and longevity. However, not only offspring (F1) but also grand-offspring (F2) copulation behaviors, egg number, and hatching percentage were influenced by parents’ experiences. Hence, the offspring of parents living in unfavorable conditions had higher copulation success, higher male mating propensity, and a lower mating latency time in adulthood than the progeny of parents kept under natural or favorable conditions. Interestingly, the offspring of parents with favorable living conditions showed the least tendency to copulate immediately. Even grandparents’ experience could affect descendant behaviors and shorten copulation duration. Adjustments of the parents to their environment were inherited by offspring and grand-offspring to cope better with challenging circumstances and might make the organism more competent. Therefore, the parents’ living conditions have a remarkable impact on how their progeny behave in different situations.     

Conjugate heat transfer of laminar mixed convection of a nanofluid through an inclined tube with circumferentially non-uniform heating

Laminar mixed convection of a nanofluid consisting of water and Al₂O₃ in an inclined tube with heating at the top half surface of a copper tube has been studied numerically. The bottom half of the tube wall is assumed to be adiabatic (presenting a tube of a solar collector). Heat conduction mechanism through the tube wall is considered. Three-dimensional governing equations with using two-phase mixture model have been solved to investigate hydrodynamic and thermal behaviours of the nanofluid over wide range of nanoparticle volume fractions. For a given nanoparticle mean diameter the effects of nanoparticle volume fractions on the hydrodynamics and thermal parameters are presented and discussed at different Richardson numbers and different tube inclinations. Significant augmentation on the heat transfer coefficient as well as on the wall shear stress is seen.     

Enhanced visible light photocatalytic activity of Zn2SnO4 via sulfur anion-doping

Sulfur anion doped Zn₂SnO₄ was prepared by calcining the mixture of thiourea and spinel Zn₂SnO₄ at 300 °C under argon atmosphere and characterized by XRD, XPS and DRS. It was found that S^2? was incorporated interstitially into the bulk phase of Zn₂SnO₄. After the doping of S^2?, the band gap of Zn₂SnO₄ was sharply decreased to 2.7 eV compared with that of undoped Zn₂SnO₄ (~ 3.6 eV). The photocatalytic activity of S-doped Zn₂SnO₄ was enhanced for photodegradation of Rhodamine B (RhB) in aqueous solution under visible light irradiation.