Tracer experimental setup

The aim of dispersion models is the prediction of atmospheric dilution of pollutants in order to prevent or avoid nuisance. Established dispersion models, designed for the large scale of industrial air pollution have to be modified to the small scale of agricultural pollutions. An experimental setup is described to measure atmospheric dilution of tracer gas under agricultural conditions. The experimental results deliver the data base to identify the parameters of the models, For undisturbed airflow modified Gaussian models are applicable. For the consideration of obstacles more sophisticated models are necessary,... 

The next problem is to find the functional relationship between the variance of the tracer curve and the dispersion coefficient. This is done by solving the partial differential equation for the concentration, with the dispersion coefficient as a parameter, and finding the variance of this theoretical expression for the boundary conditions corresponding to any given experimental setup. The dispersion coefficient for the system can then be calculated from the above function and the experimentally found variance. 

Figure 35 Schematic of positron-emitting tracer imaging system (PETIS) and an example of experimental setup.

Figure 1 is a schematic diagram of the experimental setup. The test section is a horizontal rectangular channel 40 mm in height (H), 160 mm in width (W), and 6,000 mm in length (L). The rectangular channel is completely constructed of transparent acrylic resin, as shown in Figure 2. Tap water and air are used as the gas and liquid phases, respectively. Water is circulated by a 2.2 kW pump fed by a water reservoir 4.2 m away. Air bubbles are injected into the horizontal channel from the upper inner surface of the channel. An array of capillary needles produces bubbles 10-100 mm in length. Before the air and water are mixed, their volumetric flow rates are measured. After leaving the horizontal channel, the gas-liquid mixture is dumped into a tank that acts as a bubble remover when the liquid phase is recirculated it is free of bubbles. At the end of the horizontal channel tracer particles are added to the water to act as ultrasound reflectors. The mean particle diameter is 200 pm and the particle density is 1020 kg/m3. These tracer particles are assumed to...

Various modifications are reported with respect to the experimental setup (single pass or recirculated intestinal perfusion) as well as the site of blood collection, e.g. mesenteric vessels for estimation of the intestinal absorption rate (DeGraw RT, Anderson BD 2004). vs. peripheral veins for estimation of systemic availability of the candidate compound. This method is widely used for investigation of intestinal absorption of nutrients by using radioactive tracers (e.g. cholesterol, glucose) and their interference with the candidate compound (Arts et al. 2004). In addition the secretion of the candidate compound into the intestine can be studied by peripheral administration of the compound into a peripheral vein and subsequent determination of the appearance of the candidate compound in the intestinal perfusate (Merino et al. 2003 Berggren et al. 2004). Also variations are reported using chronically isolated intestinal loops in rats (Poelma et al. 1992). 

Riigge K., Bjerg P. L., Pedersen J. K., Mosbaek H., and Christensen T. H. (1999a) An anaerobic held injection experiment in a landhll leachate plume (Grindsted, Denmark) 1. Site description, experimental setup, tracer movement and fate of aromatic and chlorinated aliphatic compounds. Water Resour. Res. 35, 1231-1246. 

The RTD can be determined experimentally and is typically used in chemical reactor engineering for the determination of the reactor behaviour. It uses the injection of a tracer as an excitation of the reactor in steady state operation. At the outlet of the reactor the transient response of the tracer concentration is measured. This method has been used for the experimental investigation of furnaces by various authors [4-8]. The authors cited used for their investigations simplified experimental setups or did not have to consider the dynamics of the measurement system. 

Chemical reactions that attain equilibrium within the confines of the experimental setup do not affect the degree of mixing as long as they do not change the physical properties of the medium or the fluid rather they change only the velocity at which the tracer moves through the porous medium. However, reactions that are kineticaUy controUed, and do not reach equilibrium in the temporal or spatial confines of the experiment, do affect the concentration distribution and cannot be readily separated from mechanical mixing. 

The experimental setup to capture real-time images of the two-fluid mixing is similar to that used for p-PlV (Fig. 4). It also consists of an inverted microscope, but a continuous light source such as Hg arc lamp is used. The microscope filter cube, color filter assembly, is selected for the specific dye to be used as tracer. Fluorescein is the most common and inexpensive fluorescent dye with the absorption maxima of 490 nm and the emission maxima of 513 nm. For fluorescein, a FITC filter cube must be used. The standard FITC filter set from Chroma Technology consists of a 480 nm bandpass exciter filter, a 505 nm dichroic beam splitter, and a 535 nm bandpass emission filter. For another popular fluorophore, rhodomine 6G (absorption maxima of 530 run and emission maxima of 566 nm), a TRITC filter cube must be used. The standard TRITC filter set from Chroma Technology consists of a 540 run bandpass exciter filter, a 565 nm dichroic beam splitter, and a 605 nm bandpass emission filter. Higher quality filters... 

Morell et al. (1985) as well as Hellmann et al. (1991) reported on such technical-scale experiments using an experimental setup which is schematically shown in Fig. 6.6. From a high-pressure vessel, water at 310 °C, 10 MPa and doped with an appropriate tracer is supplied to a IS mm diameter orifice simulating the break in the transducer line, from where it expands into a SOm vessel initially kept at ambient temperature (which in the course of the experiment increased to about 100 °C) and pressure this volume roughly corresponds to that of a transducer compartment. The steam produced in the flash evaporation process is carried off... 

Fig. 4. Experimental setup for measurement of (a) drag reduction and (b) tracer particle trajectories (c) profiles of turbulent intensity in the longitudinal direction A, Water O, polymer injection (water phase) , poisoner injection (polymer thread) , premixed...

Prior to experiments with SHE, systematic studies with homologues at the tracer scale have to be carried out to select the experimental conditions (solvent extraction, ion exchanger, aqueous media,. ..). On line experiments with short lived isotopes of homologues are also necessary to improve the setup, e.g. to evaluate the eventual impact of edge effects (sorption,. ..). Furthermore, on line experiments involving SHE may preferably be performed with homologues since it is the only way to ensure strictly identical experimental conditions for all present elements. 

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