Investigations on increasing safe gas volumetric flow rate through a water trap flame arrester

In the process industries, safety problems may arise when combustible gases are transported through pipes. Therefore, it is necessary to prevent propagation of flame fronts into or through systems, in order to avoid undesired explosions and flashbacks into the production plant. Safety devices which are used in such cases are the flame arresters, e.g. water trap flame arresters. There is a maximum gas flow rate through a water trap flame arrester below which a flashback is unlikely to occur. Based on investigations of the explosion behaviour of bubbles in suspensions of glass spheres, experiments were carried out in a water trap flame arrester of industrial demensions. It is shown that the safe gas volumetric flow rate through a water trap flame arrester can be increased by up to 30% for H₂/air mixtures when glass spheres are added to the liquid in the flame arrester.     

Open a Window to the Cognitive Work Process! Pointillist Analysis of Man–Machine Interaction

Technological progress keeps on changing our lives and our work. We can only improve this mutual influence between human and technology if we understand the impact of technology on the work process, and if we are also able to share this understanding with other people in the design process. Quantitative assessment methods like workload offer at least a keyhole to the work process, but only additional concepts like situation awareness or usability in an appropriate combination with qualitative aspects can open this keyhole into a wider window. The pointillist approach uses a powerful metaphor, borrowed from the arts, to combine quantitative with qualitative aspects systematically. Based on this approach, a tool for human factors analysis was built and used to analyse the interaction between a pilot and an assistant system in a simulator. Three examples illustrate the possible interplay between quantitative and qualitative aspects of the approach.     

THE EFFECT OF SOLUTES ON BUBBLE SIZE IN AIR-WATER DISPERSIONS

Bubble size distributions in a bubble column of 200 mm diameter were measured by means of a photoelectric probe. The gas-liquid dispersion was generated by distributing air with a porous plate into aqueous solutions of electrolytes and of organic compounds (alcohols, glycols, ketones, carboxylic acids, saccharose, carboxymethyl-cellulose, detergents). For all these solutes there exists a rather narrow concentration range in which the change from quick coalescence in pure water to coalescence suppression takes place. Though rough relationships between concentrations for coalescence suppression and molecular properties can be found (ionic strength for electrolytes, number of carbon atoms in a homologous series of organic compounds), exact equations based on a theory of coalescence cannot be given.

The bubble size distributions obtained in the experiments have also been used to show the impact of coalescence phenomena on gas-liquid mass transfer. For this purpose, surface areas were calculated from measured gas hold-up and mean bubble diameters (Sauter diameters). A comparison of these data with the trends for volumetric mass transfer coefficients reported in the literature for n-alcohols (C₁-C₂i) showed good agreement, despite the fact that the mass transfer data had been obtained in a quite different gas-liquid contacting device (stirred vessel).