Decay of swirl in turbulet pipe flows

vi+143hlm.;24c

An experimental and numerical study of turbulent swirling pipe flows

Both experimental and numerical studies have been performed aimed at the description of the decay of swirl in turbulent pipe flows. Emphasis is put on the effect of the initial velocity distribution on the rate of decay. The experiments show that, even far downstream of the swirl generator, the decay of the integral amount of angular momentum depends on the initial velocity distribution. This suggests that the description of the decay in terms of the widely suggested single exponential, function, is not sufficient. The calculations are based on (i) a standard k – e model and (ii) models based on an algebraic transport model for the turbulent stresses. It appears that in a weakly swirling pipe flow, second-order models reduce to simple modifications of the standard k – e model. While the standard k – e model predicts a decay largely insensitive to the initial velocity distribution, the modified versions of the k – e model, the ASM and the RSM, predict a strong sensitivity to the initial velocity distribution. Nevertheless, the standard k – e model seems to predict the rate of decay of the swirl better than the second-order models. It is concluded that the corrections for the streamline curvature introduced by the second-order closures, largely overestimate the effect of rotation on the radial exchange of angular momentum

Real-time MALDI for TOF MS analysis of biological aerosols and contaminated paper dust with the BioSparQ™ detector

A bioaerosol detector based upon single particle MALDI TOF MS, BiosparQ™, is described. The functioning of the system is illustrated by an example for a civil and a military context. In the civil context a particulate paper sample, spiked with Bacillus atropheus spores, is successfully analysed. The paper sample is a representative sample for dust collected at post sorting machines. In a military context a demonstrator of the system is evaluated in a bio-aerosol test chamber. In the chamber the detector is exposed to the type of challenges as can be expected in realistic field trials. The result show the single particle approach offers the possibility to detect biological agents in a complex biological background

Response of burner-stabilized flat flames to acoustic perturbations

The response of burner-stabilized flat flames to acoustic velocity perturbations is studied numerically and analytically. The numerical setup involves the set of one-dimensional transport equations for the low-Mach number reacting flow using a simple and a more complex reaction mechanism. The physical background of the phenomena observed numerically is explained by a simple analytical model. The model uncouples the unsteady transport equations into two parts: the first part describes the flame motion through the G-equation and the second flamelet part describes the inner flame structure and mass burning rate of the flame. The G-equation can be solved exactly in the case of a quasi-steady flame structure. The mass burning rate is assumed to be directly related to the flame temperature. Relations for the fluctuating heat release and heat loss to the burner are derived, from which the coupling between the velocity fluctuations at both sides of the flame is found. Comparison of the numerical and analytical results with earlier work of McIntosh and with primary experimental results on a lean methane/air flame shows the validity of the models. The origin of the differences encountered is discussed. The resulting transfer function for the velocity perturbation can be applied to the acoustic stability analysis of combustion systems. The most interesting application is the acoustic behaviour of central heating boilers

Vlammen als akoestische versterkers : een probleem voor toestelfabrikanten?

no abstract

Kinetic modeling of powder charcoal haemoperfusion

The aim of this study was to achieve more understanding of the mass transfer characteristics of the filmadsorber haemoperfusion device. First, a structural model with mathematical description of the different diffusion steps was developed. Exact quantification appeared very difficult, resulting in insufficient fit of predicted and measured concentration curves. Moreover, the mathematics turned out simple, since the concentration courses could be described with one exponential power. Therefore, a formal model was developed, assuming linear isotherms and adsorption, proportional to the average concentration in the column. With this model predicted in-vitro inlet and outlet concentrations could be fitted to the measured data accurately. A relation between both models is given under the condition of high intraparticle mass transfer, which is allowed in case of powder adsorbents. It can be concluded that structural models do not yield predictive tools for optimization of device geometry. A formal model with two constants determining device performance enables device optimization with the help of some in-vitro experiments