Adrian Melling

Tracer particles and seeding for particle image velocimetry

The size specifications for suitable tracer particles for particle image velocimetry (PIV), particularly with respect to their flow tracking capability, are discussed and quantified for several examples. A review of a wide variety of tracer materials used in recent PIV experiments in liquids and gases indicates that appropriately sized particles have normally been used. With emphasis on gas flows, methods of generating seeding particles and for introducing the particles into the flow are described and their advantages are discussed.

High precision trace humidity measurements with a fibre-coupled diode laser absorption spectrometer at atmospheric pressure

Laser absorption spectroscopy offers the potential for fast and precise trace moisture detection in gases at atmospheric pressure with a small cross sensitivity towards other molecules. We report on the development and calibration of a fibre-coupled tunable diode laser absorption spectrometer operating in the 1 - 100 ppm humidity range. The spectrometer was tested at three European humidity standards laboratories. The performance of the spectrometer was characterized by monitoring constant water vapour concentrations over several hours, yielding a good long-term stability, reproducibility and accuracy. The standard deviations of the measured water vapour concentrations for values above 5 ppm were below ±2%. Comparisons of the instrument with chilled mirror hygrometers demonstrated its fast response time. The dependences of the signal upon the flow rate and temperature are discussed.

Experimental investigation of the water vapour concentration near phase boundaries with evaporation

We report on the development of a prototype diode laser absorption spectrometer suitable for measurements of water vapour concentration with high spatial and temporal resolution. The theoretical and experimental factors influencing the design of the instrument are discussed. A spatial resolution of 0.2 mm perpendicular to the line of sight suits the instrument particularly for measuring one-dimensional concentration profiles in the vicinity of planar liquid–vapour phase boundaries. As an example, the instrument was applied to the determination of the diffusive evaporation flux at a horizontal water–air interface. For mass transfer at a curved surface, as in a water droplet, the output of the spectrometer represents a convolution of the concentration distribution with the radiation intensity distribution integrated along the laser beam. The applicability of the spectrometer to droplet evaporation is demonstrated with humidity profiles measured near phase boundaries of acoustically levitated water droplets using an approximate mathematical approach to derive the parameters of the concentration field at the phase boundary. The rapid response of the instrument allows such measurements at approximately constant droplet radius. The measurements demonstrate the potential for detailed investigations of diffusion and evaporation phenomena.

Spektrometer für experimentelle Untersuchungen der Wasserdampfdiffusion in Gasen (Spectrometer for Experimental Investigation of Water Vapour Diffusion in Gases)

Diffusionsprozesse spielen in vielen verfahrenstechnischen Bereichen eine wichtige Rolle, allerdings stehen geeignete Messverfahren zur lokalen Konzentrationsbestimmung nur in beschränktem Umfang zur Verfügung. Ein Diodenlaser-Absorptionsspektrometer wurde entwickelt, welches entlang dem kurzen, kollimierten Messstrahl integrierte Wasserdampf-Konzentrationsmessungen mit einer lateralen Auflösung von 200μm ermöglicht. Es wurden Konzentrationsprofile in teilweise mit Wasser gefüllten Standardküvetten vermessen und daraus der Stoffstrom berechnet. Weiterhin werden Messungen der Feuchteprofile ober- und unterhalb einer Polymerfolie vorgestellt, welche die direkte Bestimmung der Permeabilität der Folie erlauben.

Continuous Engineering Education through Short Courses: Problems and Opportunities in Germany

Engineering education at German universities is currently faced with requirements for shortening the course of studies without compromising the quality of education, provision of postgraduate education and continuous learning for engineers in industry, and adaptation to the educational systems in other countries of Europe. This paper considers the factors which have led to the German university education system in its present form, and then proposes solutions to reshape this system for engineering courses. First, a pre-university year is suggested as a replacement for the present final year of secondary schooling. Second, a programme of short courses is proposed for practising engineers to update their education. Finally, it is recommended that successful participation in a short course programme with participating universities across Europe could lead to the award of the degree of European Graduate Engineer.