Development of an apparatus for obtaining molecular beams in the energy range from 2 to 200 eV

The formation and detection of molecular beams obtained by charge exchange from a low-energy ion source is discussed. Dispersion in energy of the ion source was measured and problems concerning detection of neutral beams were studied. Various methods were used, specifically secondary electron emissivity of a metallic surface and ionization of a gas target with a low ionization voltage. The intensities of neutral beams as low as 10 eV are measured by a tubular electron multiplier and a lock-in amplifier

Bubble formation at a flexible orifice with liquid cross-flow

In waste water treatment, biological processes for denitrification and nitrification are performed using oxidation ditches. In these reactors, the mixing and the aeration functions are dissociated: a bubble cloud is generated from flexible membrane spargers and is subjected to a horizontal liquid flow. The objective of this paper is to study the effects of the liquid crossflow on the bubble formation at a single flexible orifice in water. The several forces acting on the forming bubble have been modelled in order to understand the dynamics of the bubble growth and detachment. The bubble detachment is controlled by the drag force due to the liquid motion and not by the buoyancy force. The experimental analysis of the bubble growth has shown that, under liquid cross-flow conditions, the bubbles move downstream and are flattened during their growth (position of the bubble centre of gravity, bubble inclination angle). The bubbles spread over the orifice surface, and the advancing and the receding bubble angles were measured. The detached bubbles have significantly smaller sizes and higher frequencies when compared to bubble formation under quiescent liquid conditions