Bubble columns for condensation at high concentrations of noncondensable gas: Heat‐transfer model and experiments

Carrier gas based thermodynamic cycles are common in water desalination applications. These cycles often require condensation of water vapor out of the carrier gas stream. As the carrier gas is most likely a noncondensable gas present in very high concentrations (60–95%), a large additional resistance to heat transfer is present. It is proposed to reduce the aforementioned thermal resistance by condensing the vapor–gas mixture in a column of cold liquid rather than on a cold surface using a bubble column heat exchanger. A theoretical predictive model for estimating the heat‐transfer rates and new experimental data to validate this model are described. The model is purely physics based without the need for any adjustable parameters, and it is shown to predict heat rates within 0 to ?20% of the experimental values. The experiments demonstrate that heat‐transfer rates in the proposed device are up to an order magnitude higher than those achieved in existing state‐of‐the‐art dehumidifiers. © 2012 American Institute of Chemical Engineers AIChE J, 59: 1780–1790, 2013     

The stability of direct carbon fuel cells with molten Sb and Sb–Bi alloy anodes

The long‐term stability of direct carbon fuel cells, based on solid oxide fuel cells with molten Sb and Sb–Bi anodes, was examined for operation with activated charcoal, rice starch, and bio‐oil fuels at 973 K. With intermittent stirring of the fuel–metal anode interface, the anode performance was stable, and reasonable power densities (～250 mW/cm²) were achieved for periods up to 250 h. With Sc‐stabilized zirconia, severe thinning of the electrolyte occurred in regions of high current flow. No electrolyte thinning was observed with yttria‐stabilized zirconia as the electrolyte operating at the same current densities. © 2012 American Institute of Chemical Engineers AIChE J, 59: 3342–3348, 2013     

From Overcrowded Polycyclic Aromatic Enes to Semifullerenes

Abstract

Overcrowded polycyclic aromatic enes (1), e.g., bi-9H-fluoren-9-ylidene (2) and bi-4H-cyclopenta[def]-phenanthren-4-ylidene (3) are potential starting materials for the preparation of bowl-shaped fragments of fullerenes. Semiempirical MNDO-PM3 calculations of C₂₆ H_n and C₃₀ H_n (n = 12,14,16) species 2–14 are used to analyze energetic and steric effects on the dehydrocyclization and isomerization reactions of these molecules. the out-of-plane bending and pyramidalization in these species are ascribed to intramolecular overcrowding in the fjord and cove regions and to strain introduced by C5 rings in the PAH skeleton. Oxidative photocyclization reactions on Z-2,2′-bridged derivatives of 2 and 3 are briefly outlined.     

选用合适的阀门

阀门选用不当,给工业界每年都造成了数百万美元的损失。不合适的阀门会导致阀门失灵,从而造成系统流体泄漏、产品偏离规格、停工检修费用、工作场所不安全以及对环境的危害。     

Polyethylene multiwalled carbon nanotube composites

Polyethylene (PE) multiwalled carbon nanotubes (MWCNTs) with weight fractions ranging from 0.1 to 10 wt% were prepared by melt blending using a mini-twin screw extruder. The morphology and degree of dispersion of the MWCNTs in the PE matrix at different length scales was investigated using scanning electron microscopy (SEM), transmission electron microscopy (TEM), atomic force microscopy (AFM) and wide-angle X-ray diffraction (WAXD). Both individual and agglomerations of MWCNTs were evident. An up-shift of 17 cm⁻¹ for the G band and the evolution of a shoulder to this peak were obtained in the Raman spectra of the nanocomposites, probably due to compressive forces exerted on the MWCNTs by PE chains and indicating intercalation of PE into the MWCNT bundles. The electrical conductivity and linear viscoelastic behaviour of these nanocomposites were investigated. A percolation threshold of about 7.5 wt% was obtained and the electrical conductivity of PE was increased significantly, by 16 orders of magnitude, from 10⁻²⁰ to 10⁻⁴ S/cm. The storage modulus (G′) versus frequency curves approached a plateau above the percolation threshold with the formation of an interconnected nanotube structure, indicative of ‘pseudo-solid-like’ behaviour. The ultimate tensile strength and elongation at break of the nanocomposites decreased with addition of MWCNTs. The diminution of mechanical properties of the nanocomposites, though concomitant with a significant increase in electrical conductivity, implies the mechanism for mechanical reinforcement for PE/MWCNT composites is filler-matrix interfacial interactions and not filler percolation. The temperature of crystallisation (T_c) and fraction of PE that was crystalline (F_c) were modified by incorporating MWCNTs. The thermal decomposition temperature of PE was enhanced by 20 K on addition of 10 wt% MWCNT.     

Synthesis and cryogenic properties of polyimide-silica hybrid films by sol-gel process

Polyimide-silica hybrid films were prepared from tetraethoxysilane (TEOS) and polyamic acid (PAA) via sol-gel process in the solution of N,N-dimethylacetamide (DMAc). The cryogenic mechanical and electrical properties of polyimide-silica hybrid films were studied taking into account the effects of silica content. The results indicated that the cryogenic modulus increased with the increase of silica content while the tensile strength and failure strain had a maximum value at proper silica contents. Moreover, the tensile strength and modulus of the hybrid films at cryogenic temperature (77 K) were obviously higher than those at room temperature, while the failure strain of the hybrid films was much lower at cryogenic temperature (77 K) than that at room temperature. The mean electrical breakdown strength of the hybrid films was shown to range from 151 to 225 kV/mm at cryogenic temperature (77 K).