Analysis of low Reynolds number flow around a heated circular cylinder

The objective of this study is to investigate the forced convection from and the flow around a heated cylinder. Experimental and computational results are presented for laminar flow around a heated circular cylinder with a diameter of 10 mm. The experiments were carried out using Particle Image Velocimetry (PIV) in a wind tunnel, and numerical simulations using an in-house code and a commercial software package, FLUENT. This paper pre-sents comparisons for vorticity and temperature contours in the wake of the cylinder. Experimental and computa-tional results are compared with those available in the literature for heated and unheated cylinders. An equation is suggested for a temperature-dependent coefficient defining a reference temperature to be used in place of the con-stant used in other studies. An attempt is also made to correct differences between average cylinder surface tem-perature and measured interior temperature of the cylinder

Modeling the BCF of persistent organic pollutants

The uptake of persistent organic pollutants (POPs) from soil by plants allows the development of phytoremediation protocols to rehabilitate contaminated areas. In this study theoretical descriptors have been employed as independent variables for developing quantitative structure-activity relationship (QSAR) models for predicting the bioconcentration factors (BCFs) of POPs in different plants. A quantitative estimation has been given on the molecular properties of POPs in terms of theoretical molecular descriptors that are relevant to the uptake from soil and pharmacokinetic behavior in plants. The study resulted in statistically significant linear regression models developed for the BCF values of 20 polychlorinated dibenzo-p-dioxins/dibenzofurans and 14 polyhalogenated biphenyls in two zucchini varieties based on retrospective data. The parameters have been selected from a set of 1660 DRAGON, 150 VolSurf and 11 Quantum Chemical descriptors. The best regression model (Eq. 1), employing VolSurf, DRAGON GETAWAY and quantum chemical descriptors, displayed the following highly significant statistical parameters: n=27, R2=0.940, SE=0.155, F=392.1, q2=0.922; external validation set: n=7, R2=0.739, q2=0.47, SE=0.338, F=14.2 It is suggested that the QSAR models proposed might contribute to the development of workable soil remediation strategies

Droplet Collisions and Interaction with the Turbulent Flow within a Two-Phase Wind Tunnel

Experiments in wind tunnels concerning meteorological issues are not very frequent in the literature. However, such experiments might be essential, for instance for a careful investigation of droplet-droplet interactions in turbulent flows. This issue is crucial for many configurations, in particular to understand warm rain initiation. It is clearly impossible to completely reproduce cloud turbulence within a wind tunnel due to the enormous length scales involved. Nevertheless, it is not necessary to recover the whole spectrum in order to quantify droplet interactions. It is sufficient for this purpose to account correctly for the relevant properties only. In the present paper, these properties and a methodology for setting those in a two-phase wind tunnel are first described. In particular, droplet size and number density, velocities, turbulent kinetic energy, k, and its dissipation rate, ɛ, are suitably reproduced, as demonstrated by non-intrusive measurement techniques. A complete experimental characterization of the air and droplet properties is freely available in a database accessible at http://www.ovgu.de/isut/lss/metstroem. Finally, quantifications of droplet collision rates and comparisons with theoretical predictions are presented, showing that measured collision rates are higher, typically by a factor of 2 to 5. These results demonstrate that model modifications are needed to estimate correctly droplet collision probabilities in turbulent flow

Gas flow measurements by 3D Particle Tracking Velocimetry using coloured tracer particles

This work describes an original approach for 3D Particle Tracking Velocimetry (3D PTV), applicable also for gaseous flows and based on tracer particles of different colours. On the images acquired by several cameras, tracer particles are handled by colour recognition and 3D localisation. Then, the PTV tracking algorithm rebuilds the trajectories of the tracer particles using a criterion of Minimum Acceleration. Theoretical and numerical calculations are first presented to demonstrate that the employed coloured tracer particles follow in a suitable manner the considered gas flows. The test cases analysed comprise low Reynolds number flows involving a variety of interesting features, in particular boundary layer separation, continuous acceleration and recirculations. The experimental setup and the 3D PTV procedure are then described. All results are analysed in a quantitative manner and demonstrate the performance of the developed measurement strategy in gas flows

Improved 3-D Particle Tracking Velocimetry with colored particles

This work describes an original approach for 3D Particle Tracking Velocimetry (3D PTV), applicable also for gaseous flows and based on tracer particles of different colours. On the images acquired by several cameras, tracer particles are handled by colour recognition and 3D localisation. Then, the PTV tracking algorithm rebuilds the trajectories of the tracer particles using a criterion of Minimum Acceleration. Theoretical and numerical calculations are first presented to demonstrate that the employed coloured tracer particles follow in a suitable manner the considered gas flows. The test cases analysed comprise low Reynolds number flows involving a variety of interesting features, in particular boundary layer separation, continuous acceleration and recirculations. The experimental setup and the 3D PTV procedure are then described. All results are analysed in a quantitative manner and demonstrate the performance of the developed measurement strategy in gas flows