Electro-spinning of highly-aligned polyacrylonitrile nano-fibres with continuous spooling

This paper reports on a new configuration for producing highly-aligned electro-spun fibres that can be produced on a static substrate or one where it is hauled off and spooled continuously to enable the production of continuous lengths. The fixture consists of a Vee-shaped polytetrafluorethylene shield at 60° with a 1 cm wide integral rectangular base that is mounted on a copper disk with a 10 cm diameter. Specified concentrations of polyacrylonitrile in dimethyl sulfoxide were electro-spun on to a strip of cellulose paper. In the static setup, approximately 91% of the fibres were deposited to within 3°. When the spooling rig was used, a tape of the cellulose paper was hauled off at 0.07 mm/min, 78% of the fibres were aligned to within 3°. Simulations of the conventional and Vee-shield electro-spinning setups were undertaken and they provided corroboration for the experimental observations with regard to the mechanism responsible for fibre alignment. The feasibility of using this technique to produce 0°/− 45°/+ 45° stacked layers of aligned fibre preform is demonstrated.

Nucleate and Transition Boiling in Inclined Narrow Spaces

The purpose of this work is to describe nucleate and transition boiling occurring in an inclined narrow space (0° ≤ φ ≤ 35°) between a heated upward-facing copper disk and an unheated surface for saturated n-pentane. The distance between the heated surface and the confinement plate is enclosed between 200 μm ≤ s ≤ 90 mm. The heat flux and the wall temperature are determined by mean of an inverse heat conduction method. The instantaneous volume fraction of the vapour phase within the confined space is measured using capacitive sensors. The influence of the confinement and the inclination angle on the boiling curves and the flow patterns are analysed. The evolution of void fraction with the heat flux increase, the reduction of the gap size and the inclination of the heated surface are determined. Boiling becomes unsteady for given heat flux and inclination angle ranges. The boiling cycles are characterized by periodic liquid feeding and two-phase structure expulsion from the confined space. The cycle’s frequency increase with the heat flux and the inclination angle increase is analyzed. The conditions of unsteady boiling apparition are summarized in unsteady boiling pattern maps.

Wear Properties of Metal-Impregnated Carbon Fiber-Reinforced Carbon Composite Sliding Against a Copper Plate Under an Electric Current

The metal-impregnated carbon fiber-reinforced carbon composite (C/C composite) is expected to be a candidate material for pantograph contact strips of high-speed electric railway vehicles, because its mechanical strength for flexure and impact is much higher than that of the conventional metal-impregnated carbon. The authors have investigated the wear properties of copper-titanium-alloy impregnated C/C composite sliding against a copper disk under an electric current and frequent arc discharges. The tested C/C composite was prepared by press molding and baking of laminated carbon fiber woven sheets. There exists anisotropy in the physical properties originated from the orientation of carbon fiber woven sheets lamination. The C/C composite was slid in two directions, in parallel with or perpendicular to the sheet layer. The test results show that the wear rate in sliding in the parallel direction exceeds that in the perpendicular direction, especially in the cases where the material is subjected to higher current density and more frequent arc discharges.