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Tube Wall (tube + wall)
Selected AbstractsThe heat transfer heterogeneities of bends in flow boiling of hairpin tubesHEAT TRANSFER - ASIAN RESEARCH (FORMERLY HEAT TRANSFER-JAPANESE RESEARCH), Issue 8 2009Meng Meng Abstract A series of visual experiments were conducted for liquid, vapor two-phase flow in hairpin tubes, and it was observed that most of the nucleation sites were located at the outer tube wall of the bend. From the simulation, it was concluded that the uneven velocity distribution in the bend induced the heat transfer heterogeneity. Furthermore, the nucleation of both the inner and outer tube wall of the bend and the wall temperature distribution were discussed to understand the physical phenomena. © 2009 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/htj.20269 [source] Thermal radiation effects of a high-temperature developing laminar flow in a tubeHEAT TRANSFER - ASIAN RESEARCH (FORMERLY HEAT TRANSFER-JAPANESE RESEARCH), Issue 5 2004Xin-Lin Xia Abstract The thermal radiation effects of a high-temperature developing laminar flow in a tube are investigated numerically. The two-dimensional steady flow and heat transfer are considered for an absorbing-emitting gray medium, whose density is dependent on the temperature. The governing equations of the coupled process are simultaneously solved by the discrete ordinate method combined with the control volume method. For a moderate optical thickness, the velocity distribution, the temperature distribution, and the radial heat flux distribution in the medium as well as the heat flux distribution on the tube wall are presented and discussed. The results show that the thermal radiation effects of a high-temperature medium are significant under a moderate optical thickness. The flow and convective heat transfer are weakened, and the development of temperature distribution is accelerated noticeably. © 2004 Wiley Periodicals, Inc. Heat Trans Asian Res, 33(5): 299,306, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/htj.20018 [source] Measuring velocity distributions of viscous fluids using positron emission particle tracking (PEPT)AICHE JOURNAL, Issue 7 2004S. Bakalis Abstract Positron emission particle tracking (PEPT) can be used to trace the path of a radioactive particle within opaque fluids in pilot-scale equipment; the method can track particles through several centimeters of metal. PEPT has been successfully used to follow isokinetic tracers in viscous fluids and thus to measure velocity distributions under both isothermal and nonisothermal conditions in pipe flow. The accuracy of the method decreased as the measured velocities increased; the faster the particle traveled, the less accurate its detection. For velocities of up to 0.5 m/s the accuracy of the method was acceptable. Agreement between experimentally measured and theoretical velocity distributions was very good, for a range of fluids and process conditions. As tracer particles are used, there were problems ensuring that all parts of the measurement volume were sampled. This is possible to overcome to an extent by adjusting particle size; 600-,m tracers did not pass within 1 mm from the tube wall, whereas 240-,m particles passed much closer to the boundaries of the flow. © 2004 American Institute of Chemical Engineers AIChE J, 50: 1606,1613, 2004 [source] Raman scattering from double-walled carbon nanotubesJOURNAL OF RAMAN SPECTROSCOPY, Issue 2 2008H. Kuzmany Abstract Raman scattering from double-walled carbon nanotubes is reported with particular emphasis on the response from the radial breathing mode (RBM) of the inner-shell tubes. The unexpected large number of very narrow lines observed is explained by the growth of one and the same inner tube type in different outer tubes in a highly shielded environment. The response of the RBM and of the G-line is used to analyze the transition from peapods to double-walled carbon nanotubes. During the transformation process the Raman response disappears for a short time, indicating the existence of some Raman dark matter. By preparing the starting peapods from heterofullerenes such as (C59N)2 or 13C-substituted fullerenes, hetero-nanotubes can be grown where nitrogen or the 13C atoms are incorporated into the inner tube wall. Copyright © 2007 John Wiley & Sons, Ltd. [source] Mesophase Separation of Diblock Copolymer Confined in a Cylindrical Tube Studied by Dissipative Particle DynamicsMACROMOLECULAR THEORY AND SIMULATIONS, Issue 9 2006Jian Feng Abstract Summary: The morphologies of diblock copolymers confined in a cylindrical tube have been investigated by the dissipative particle dynamics (DPD) method. Results indicate that the morphology depends on the volume ratio of the immiscible blocks, the diameter of the cylindrical tube and the interactions between the blocks and between the confinement wall and blocks. For symmetric diblock copolymers, when the tube wall is uniform toward the two blocks, perpendicular lamellae or a stacked disk morphology are generally formed except when the diameter of the cylindrical tube is very small; in that case, a special bi-helix morphology forms because of the entropy effect. When the tube wall is non-uniform, as the diameter of the tube increases, perpendicular lamellae are first formed, then changing to parallel lamellae and, finally, back to perpendicular lamellae again. An intermediate morphology characterizing the transition between perpendicular and parallel lamellae is observed. If the non-uniformity of the wall is further enhanced, only parallel lamellae can be found. In the case of asymmetric diblock copolymers, more complex morphologies can be obtained. Multi-cylindrical micro-domains and a multilayer helical phase as well as other complex pictures are observed. Generally, the morphologies obtained could find their counterparts from experiments or Monte Carlo simulations; however, differences do exist, especially in some cases of asymmetric diblock copolymers. Bi-helix and stacked disks morphologies of A5B5 diblock copolymer confined in two different neutral nanocylinders. [source] Modeling of the Wall Effect in Packed Bed AdsorptionCHEMICAL ENGINEERING & TECHNOLOGY (CET), Issue 11 2004W. Kwapinski Abstract A model developed for catalytic packed bed reactors and consistently accounting for the influence of the tube wall on porosity, flow and transport phenomena is used in order to simulate the operation of packed bed adsorbers. By comparison of simulation results with reduced versions of the model the influence of the wall on the adsorber performance is worked out and found to be major at low ratios between tube and particle diameter. The interaction between maldistribution, thermal effects and intraparticle resistances in such adsorber tubes is discussed. [source] Aligned Carbon Nanotubes with Ferromagnetic BehaviorADVANCED MATERIALS, Issue 4 2010Eleni C. Vermisoglou Magnetic carbon nanotube (CNT) arrays are grown by in situ encapsulation of ferromagnetic iron carbide nanoparticles within the tube walls (see figure). The resulting structures, combining the inherently unique characteristics of aligned and open-ended CNTs with the fact that magnetic functionality is provided from "inside the walls", are promising functional units in highly efficient flow systems, for example, as parallel magnetic nanoreactors and in biological separations. [source] | |||||||||||||