Condensation heat transfer on tubes in actual flue gas (Parametric study for condensation behavior)

In order to improve boiler efficiency, latent heat recovery from the flue gas is a very important concept. Condensation heat transfer on horizontal tubes was investigated experimentally by using flue gas from a natural gas boiler. The parametric studies concerning the effects of tube stages, gas velocities, SO₂ in the flue gas, and Teflon‐lined tubes were conducted at a wide range of tube surface temperature. The heat transfer was enhanced at the second stage due to the wake turbulence of the first stage. No significant decrease of the condensation in the second stage due to the condensate falling from the first stage could be observed. Even at the high gas velocity condition, the condensation pattern was similar to that observed in previous low gas velocity experiments. The effect of SO₂ in the flue gas on the condensation behavior could not be observed. The heat and mass transfer behaviors on stainless‐steel and Teflon‐lined surfaces were well predicted with the analogy correlation. The above results suggested that the heat and mass transfer were dominated by the convection and diffusion process on the gas side. © 2003 Wiley Periodicals, Inc. Heat Trans Asian Res, 32(2): 153–166, 2003; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.10079     

COMPARISON OF SCOURS IN FRONT OF VERTICAL BREAKWATERS DUE TO REGULAR AND IRREGULAR WAVES

1 .　ＩＮＴＲＯＤＵＣＴＩＯＮＴｈｅｓｃｏｕｒｓｏｆｓａｎｄｂｅｄｉｎｆｒｏｎｔｏｆｖｅｒｔｉｃａｌｂｒｅａｋｗａｔｅｒｓｕｎｄｅｒｔｈｅａｃｔｉｏｎｏｆｒｅｇｕｌａｒｓｔａｎｄ ｉｎｇｗａｖｅｓｗｅｒｅｉｎｖｅｓｔｉｇａｔｅｄａｎｄｓｏｍｅｇｏｏｄｒｅｓｕｌｔｓｗｅｒｅｏｂｔａｉｎｅｄ ,ｉｎｃｌｕｄｉｎｇｓｃｏｕｒｉｎｇｐａｔ ｔｅｒｎｓ ,ｓｃｏｕｒｉｎｇｍｅｃｈａｎｉｓｍｓ ,ｃｒｉｔｅｒｉａｆｏｒｄｉｓｔｉｎｇｕｉｓｈｉｎｇｓｃｏｕｒｉｎｇ ｐａｔｔｅｒｎｓ ,ｐｒｅｄｉｃｔｉｏｎｏｆｓｃｏｕｒｉ…     

Growth of untwinned Bi2Sr2Ca n−1Cu n O2n+4+δ thin films on Nd : YAlO3 substrates

Thin film growth of Bi₂Sr₂Ca _n?1Cu _n O_2n+4+δ by molecular beam epitaxy is performed on Nd : YAlO₃ (001) substrates. It was revealed that the orthorhombicity of the Nd:YAlO₃ substrate is quite effective to the growth of untwinned Bi₂Sr₂Ca _n?1Cu _n O_2n+4+δ thin films. In all phases withn=1～3, the incommensurate structural modulation lies parallel to the Nd : YAlO₃ [100] direction, and this relation holds even in the case of superlattices. The origin of the epitaxial relation is discussed from the viewpoint of the lattice misfit. The orthorhombicity of the substrate competes with the step edges on a vicinally polished substrate for determining the in-plane growth direction. The rotation of the modulation direction was observed when the off angles are varied.     

Effect of nanoscale curvature of single-walled carbon nanotubes on adsorption of polycyclic aromatic hydrocarbons

Liquid-phase adsorption of tetracene and phenanthrene on a single-walled carbon nanotube (SWCNT) was examined. Tetracene adsorption was more than six times greater than that of phenanthrene. X-ray photoelectron spectroscopic examination clearly showed that tetracene and phenanthrene molecules efficiently coated the SWCNT external surfaces. The remarkable difference between the adsorption amounts of tetracene and phenanthrene was caused by the nanoscale curvature effect of the tube surface, resulting in a difference in the amount of contact between the molecule and the tube surface. The adsorption of tetracene and phenanthrene caused a significant higher frequency shift in the radial breathing mode (RBM) of the Raman band of the SWCNT, indicating an intensive pi-pi interaction between these polycyclic aromatic hydrocarbons and the external SWCNT surface.     

Crystal growth and structure refinement of monoclinic Li2TiO3

Colorless platelet crystals of monoclinic Li₂TiO₃ with a maximum size of 5.0 mm × 5.0 mm × 0.5 mm were successfully grown by a flux method at 1373 K using a LiBO₂-Li₂O system flux. The stoichiometric chemical composition of Li₂TiO₃ was determined by the SEM-EDX, ICP-AES and density measurement using the single crystal samples. The thermal conductivity of the Li₂TiO₃ single crystals was evaluated using hot-disk method. A single-crystal X-ray diffraction study confirmed the monoclinic Li₂SnO₃-type structure, space group C2/c and the lattice parameters of a = 5.0623(5) Å, b = 8.7876(9) Å, c = 9.7533(15) Å, β = 100.212(11)°, and V = 427.01(9) Å³. The crystal structure was refined to the conventional values of R = 2.4% and wR=3.3% for 2187 independent observed reflections. The cationic arrangement of (LiTi₂) layers in Li₂TiO₃ was precisely revealed by the structure analysis.     

Atomic force microscopy observation of Bi2Sr2CaCu2O8+δ thin films prepared by molecular beam epitaxy

We observed the surface structures of 1200 Å-thick c-axis oriented Bi₂Sr₂CaCu₂O₈₊ thin films, which we intend to use for the base electrode of a planar type Josephson junction. The films were prepared by molecular beam epitaxy on the Nd:YAlO₃(001)substrates at a growth rate of 20 Å/min.Atomic force microscopy observation revealed that the surface of the films prepared at a substrate temperature of 780 °Cand an ozone pressure of 2.3 × 10^–3 Pahas island-like structures. Their shape is like a stack of cylindrical plates and the diameter of the island is typically 250 nm.Most of the steps have a height of 15 16 Å,which corresponds to the primitive-cell thickness of Bi₂Sr₂CaCu₂O8+.We discuss the result in comparison with that observed in Bi₂Sr₂Ca₂Cu₃O₁₀₊ films grown by metal organic chemical vapor deposition and YBa₂Cu₃O_7– films by sputtering. The occurrence of the structure with several steps is attributed to the insufficient supply of elements. The roughness less than 100 Åis favorable for the fabrication of junctions with thin barriers.     

WAVE TRANSMISSION AND REFIECTION DUE TO A THIN VERTICAL BARRIER

1 .　ＩＮＴＲＯＤＵＣＴＩＯＮＡｔｒａｉｎｏｆｓｕｒｆａｃｅｗａｔｅｒｗａｖｅｓｉｎｃｉｄｅｎｔｆｒｏｍｉｎｆｉｎｉｔｙｏｎａｎｏｂｓｔａｃｌｅｐｒｅｓｅｎｔｉｎｗａｔｅｒ ,ｅｘｐｅｒｉｅｎｃｅｓｔｒａｎｓｍｉｓｓｉｏｎａｎｄｒｅｆｌｅｃｔｉｏｎｂｙａｎｄｏｖｅｒｏｒｂｅｌｏｗｔｈｅｏｂｓｔａｃｌｅ.Ｔｈｅｏｂｓｔａｃｌｅｍａｙｂｅｉｎｔｈｅｆｏｒｍｏｆａｒｉｇｉｄｔｈｉｎｖｅｒｔｉｃａｌｂａｒｒｉｅｒ .Ｔｈｅｒｉｇｉｄｔｈｉｎｂａｒｒｉｅｒｄｅｓｃｅｎｄｉｎｇｆｒｏｍｔｈｅｗａｔｅｒｓｕｒｆａｃ…     

The use of graphite oxide to produce mesoporous carbon supporting Pt, Ru, or Pd nanoparticles

Mesoporous carbon having platinum, ruthenium or palladium nanoparticles on exfoliated graphene sheets were produced from graphite oxide (GO) and metal complexes. The Pt included carbon was made by heating of the intercalation compound including tetraammineplatinum (II) chloride monohydrate. Samples having Ru or Pd are producible by heating in nitrogen gas atmosphere using hexaammineruthenium (III) chloride or tetraamminepalladium (II) chloride monohydrate instead of Pt complex. The particle sizes of platinum, ruthenium, and palladium were, respectively, 1-3, 1-2, and 3-7 nm. The platinum- or palladium-containing sample showed catalytic activity for oxygen reduction.     

Nano-phase structures and mechanical properties of epoxy/acryl triblock copolymer alloys

Phase structures and mechanical properties of epoxy/acryl triblock copolymer alloys using several curing agents were studied. PMMA-b-PnBA-b-PMMA triblock copolymers synthesized by living anionic polymerization were applied as the toughening modifiers for the epoxy resins. An aromatic amine, an acid anhydride and an anionic polymerization catalyst as curing agents resulted in macro-phase separation in the epoxy/triblock copolymer blends during the cure process. However, a phenol novolac as the curing agent created nano-phase structures in the epoxy blends. The size of the spherical phases or cylindrical phases was about 40 nm in diameter, and the main component in the nano-phases was the PnBA of the triblock copolymer. The fracture toughness of the epoxy/triblock copolymer alloys with the nano-cylindrical phases reached 2530 J/m². The fracture toughness was more than twenty fold relative to the unmodified epoxy resin, and was equivalent to the toughness of polycarbonates.     

A computer simulation and experimental study of the difference between krypton adsorption on a graphite surface and in a graphitic hexagonal pore

Adsorption isotherms and isosteric heats have been studied experimentally and by computer simulation for the krypton-graphitic hexagonal pore and krypton–graphite planar surface systems in the 60–109 K temperature range. The existence of a 2D transition in the sub-monolayer film on the basal plane of graphite that is observed experimentally is confirmed by the computer simulation results, but this transition is not observed in graphitic hexagonal pores because the onset of adsorption occurs at the junctions of adjacent pore walls, and the mechanism of surface adsorption is the spreading of adsorbate from the junction towards the basal planes until the first layer is completed. This is followed by molecular layering of higher layers, and then by capillary condensation when the empty core is small enough.