Intensification of convective heat exchange in channels with a porous high-thermal-conductivity filler. Heat exchange with local thermal equilibrium inside the permeable matrix

Results are presented from analytical and experimental studies of intensification of convective heat exchange in a channel with a porous high-thermal-conductivity filler in the case of moderate external heating.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 47, No. 1, pp. 13–24, July, 1984.     

Excitation of a quasi-plane shear wave by a surface acoustic source producing normal stresses

The generation of elastic volume waves by a source which is widely used in acoustic flaw detection is considered. This source produces normal stresses at the boundary of an elastic solid. The source is large compared to the wavelength of the waves that are launched. The possibility of exciting a shear wave with a plane front in the near zone is established, and an estimate of its intensity is made. Pis’ma Zh. Tekh. Fiz. 23, 91–94 (December 12, 1997)     

Extreme-length carbon nanofilaments with single-walled nanotube cores grown by pyrolysis of methane or acetylene

We describe a process of catalytic hydrocarbon pyrolysis which yields a new class of carbon nanotubes/nanofilaments (NT/NFs). It is characterized by high temperature (1000-1050 °C), and higher concentrations of gaseous species normally active in coke formation. Usually coke growth quickly encapsulates a catalyst particle in such environments, which in turn blocks further NT/NF growth. In our case the NT/NF lengths can reach 3-5 mm at a virtually constant filament diameter of 50-130 nm. HRTEM studies revealed a novel filament structure consisting of a SWNT core 2-4.5 nm in diameter covered by an outer shell of disordered carbon with a soot-like structure. The growing tip of a NT/NF is conical without any visible evidence of a catalyst particle at its end. The growth rate of the observed NT/NFs reaches 5-10 μm/s, far exceeding that of common catalytically grown NTs and filaments. Variation of the catalyst metal (iron, nickel, cobalt) and in the feedstock gas (acetylene, methane) did not result in any significant changes in the NT/NFs structure. These features all point to a non-catalytic growth mechanism of NT/NFs. The process described here can be a basis for development of a technology for production of very long carbon NTs with the aspect ratio as high as several tens of thousands.