Estimation of instantaneous local heat transfer coefficient in spark-ignition engines

Optimizing heat transfer for internal combustion engines requires application of advanced development tools. In addition to experimental method, numerical 3D-CFD calculations are needed in order to obtain an insight into the complex phenomenas in-cylinder processes. In this context, fluid flow and heat transfer inside a four-valve engine cylinder is modeled and effects of changing engine speed on dimensionless parameters, instantaneous local Nusselt number and Reynolds number near the surface of combustion chamber are studied. Based on the numerical simulation new correlations for instantaneous local heat transfer on the combustion chamber of SI engines are derived. Results for several engine speeds are compared for total heat transfer coefficient of the cylinder engine with available correlation proposed by experimental measurements and a close agreement is observed. It is found that the local value of heat transfer coefficient varies considerably in different parts of the cylinder, but it has equivalent trend with crank angle position.     

Erratum to: Biasing Effect on Modifying of the Tokamak Plasma Horizontal Displacement

In this contribution we presented the first biasing experiments performed on the IR-T1 tokamak. For this purpose, a movable biasing system was designed, constructed, and installed, and then the positive voltage applied to an electrode inserted inside the tokamak limiter and the plasma current and also the plasma horizontal displacement in the absence and presence of the biased electrode based on the multipole moments and magnetic probes techniques were measured. Measurements result has shown a modification of plasma confinement by decreasing the plasma displacement.     

Coke deposition mechanism on the pores of a commercial Pt-Re/γ-Al2O3 naphtha reforming catalyst

Coke deposition mechanism on a commercial Pt-Re/γ-Al₂O₃ naphtha reforming catalyst was studied. A used catalyst that was in industrial reforming operation for 28 months, as well as the fresh catalyst of the unit were characterized using XRD, XRF, and nitrogen adsorption/desorption analyses. Carbon and sulfur contents of the fresh and the used catalysts were determined using Leco combustion analyzer. The pore size distributions (PSD) of the fresh and the used reforming catalysts were determined using BJH and Comparison Plot methods. The Comparison Plot method produced the most reasonable PSDs for the catalysts. Through comparison of the PSDs of the fresh and the used catalysts, it was revealed that coke deposited on both micropores and mesopores of the catalyst at a constant thickness of 1.0 nm. The constant coke thickness on the catalyst pore walls in the naphtha reforming process (temp. ∼ 500 °C) implies that coke deposition reaction is the slow controlling step in comparison to the fast mass transfer rate of coke ingredients into the pores. The bulk density of the deposited coke on the used catalyst was calculated as 0.966 g/cm³.     

Murine CD4 T-cell response to Helicobacter infection: TH1 cells enhance gastritis and TH2 cells reduce bacterial load

BACKGROUND & AIMS: Previous findings suggest that TH1 cellular immune responses contribute to Helicobacter-associated gastritis. To further investigate this issue, interleukin 4 gene targeted mice were infected with Helicobacter felis, and a series of adoptive transfer experiments was performed to evaluate the role of both TH1 and TH2 cells. METHODS: Antigen-specific spleen cells from immunized/challenged or nonimmunized/infected mice or CD4+ T-cell lines were transferred adoptively into naive recipients before live bacterial challenge. RESULTS: Transfer of cells from both groups of donors as well as TH1 or TH2 cell lines exacerbated gastric inflammation in the recipients. No effect on bacterial load was observed in recipients of bulk spleen cells from infected mice or recipients of TH1 cell lines. In contrast, when either a TH2 cell line or bulk cells from immunized challenged mice were transferred adoptively, recipients showed a dramatic reduction in bacterial load. Increased numbers of bacteria were also noted in interleukin 4-deficient mice. CONCLUSIONS: These data suggest a differential contribution of TH1 and TH2 cell-mediated immune responses in Helicobacter infection: one associated with the pathogenesis of disease (TH1 phenotype) and the other associated with protection from or control of infection (TH2 phenotype).     

Thin-layer template-free polycrystalline mordenite membranes on cylindrical mullite supports

Continuous nanoporous mordenite membranes were reproducibly fabricated on tubular microporous mullite supports. The ceramic supports were prepared during calcination of kaolin clay, followed by a leaching post-treatment. A template-free seeded hydrothermal synthesis in a brass autoclave was used to prepare the zeolite membranes. The membranes and the powder crystals collected from the bottom of the autoclave were characterized with XRD, SEM and EDAX. PV properties of the membranes were assessed using dehydration of different ethanol–water mixtures. XRD patterns showed that mordenite was the only zeolitic material present in the membrane. SEM examination of the membrane revealed that thickness of the mordenite crystals filling the voids as a dense thin-layer among the mullite support was 5–10 μm. The continuous top-layer of the membrane was formed by many large and oriented crystals. EDAX analysis showed a Si to Al ratio of 6 for the mordenite powder. The polycrystalline membranes were found to be selective for dehydration of different ethanol/water mixtures. It was concluded that selective adsorption of water on the zeolite pores, small intercrystalline defects and a pinhole-free structure of the membrane layer leaded to high water selectivity of the mordenite membranes studied.     

Asymmetric cellulose acetate dialysis membranes: Synthesis,characterization, and performance

Cellulose acetate (CA) is highly comparable to other synthetic polymer materials and is effective in the hemodialysis process. In this work, asymmetric CA membranes were synthesized with the phase‐inversion method. CA with a molecular weight of 52,000, poly(ethylene glycol) (PEG) with a molecular weight of 400, and 1‐methyl‐2‐pyrrolidone (NMP) were used as the polymer, additive, and solvent, respectively. The effects of the CA and PEG concentrations and coagulation bath temperature (CBT) on the morphology, pure water permeability (PWP), insulin/human serum albumin (HSA) transmission, and finally thermal and chemical stability of the prepared membranes were determined and investigated. In general, increasing the PEG concentration and CBT and reducing the CA concentration resulted in increased PWP and insulin/HSA transmission. Also, these variations facilitated the formation of macrovoids in the membrane sublayer. On the other hand, increasing the PEG and CA concentrations and reducing CBT resulted in increased thermal and chemical stability of the prepared membranes. Also, ratios of 15.5/10/74.5 and 17.5/10/72.5 (w/w) for the CA/PEG/NMP casting solutions and their immersion into coagulation baths with CBTs of 0 and 25°C, respectively, resulted in the preparation of membranes that had not only optimum sieving properties and higher PWP but also thermal and chemical stability better than that of conventional CA hemodialysis membranes. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Characterization of poly(lactic acid) multifilament yarns. I. The structure and thermal behavior

The structure and thermal behavior of poly(lactic acid) (PLA) multifilament yarns were studied by complementary techniques of differential scanning calorimetry (DSC), Fourier transform infrared (FTIR) spectroscopy, and wide angle X‐ray diffraction (WAXD). As for PLA filaments, notable differences in the WAXD patterns, DSC curves, and FTIR spectra were observed. The combination of the WAXD and FTIR results showed that PLA samples with different crystallinity contain α‐form crystal structure. The FTIR spectra of the filaments were analyzed to study their crystallinity and crystal structure. The total crystallinity of the PLA filaments was obtained from the percent area loss of the skeletal amorphous band at 955 cm^?1. Crystalline fraction from FTIR and DSC were comparable with each other. The C?O stretching region, which is sensitive to crystallization and dipole–dipole interactions, was evaluated to provide information about chain conformers and crystallinity of the samples. Depending on the processing conditions, double melting peaks were observed in the DSC curves of the samples. This exhibited the structural reorganization of the crystal phase during heating affected by heating and cooling rate. In the DSC curves of the nearly amorphous multifilament yarn, the exothermic peak observed right above the glass transition temperature (T_g) indicated two relaxed and deformed amorphous regions. However, the multifilament yarn with higher crystallinity showed just endothermic melting peak after its glass transition. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Effect of applied voltage on surface and volume charge density of the jet in electrospinning of polyacrylonitrile solutions

To investigate the effect of applied voltage on jet charge density, one must investigate its effect on the jet electric current and flow rate. However, there are some difficulties in measuring the jet flow rate. Here, the electrospinning jet flow rate is calculated by applying a new method and the effects of applied voltage and feed rate on jet charge density are investigated. The jet flow rate was independent of the feed rate and increased on increasing the applied voltage. By defining an experimental equation for dependence of jet flow rate on jet current, a relation between jet volume charge density and jet current could be defined. By measuring the electrospun fiber diameter, surface charge density of the jet could be estimated. On increasing the voltage, the jet volume charge density decreased whereas the jet surface charge density remained unchanged. POLYM. ENG. SCI., 2010. © 2010 Society of Plastics Engineers