Agricultural Engineering Research - English edition

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Chemosensor Systems and Odour Measurement - Current Developments in Electronic Olfactometry
(2001) Boeker, Peter
Chemosensor measuring systems termed “electronic noses” have been introduced which, very generally speaking, imitate the biological sense of smell. Even though these systems cannot primarily analyze odour char- acteristics, but rather compositions of gas mixtures, they are also used for “electronic olfactometry”. In this contribution, the background and the problems of their use and application for odour measurement are discussed. The methods which have been employed so far do not provide meaningful results. In addition, perspectives and research goals for future development are Described.
Reduction of the Measuring Gas Dew Point - Concentration Changes and Washing Out of Noxious Gases and Odorous Compounds
(2001) Boeker, Peter
Gas cooling devices are used as a means of conditioning humid measur- ing gas flows. In these devices, the dew point is lowered. This causes the surplus quantity of water to condense. Two resulting effects influence the concentration of noxious gases and odorous compounds. The condensa- tion part of the humidity reduces the total gas flow. Therefore, the con- centrations of the other gas components rise. Water-soluble components, however, cause additional washing-out due to absorption in the conden- sate. The concentration of these components diminishes. Both effects are influenced by the degree of dew point reduction and the temperature in the cooler. At low temperatures, gas solubility and the quantity of con- densing water increase. Therefore, the largest washing out effect occurs here. In the case of odorous compounds, the washing-out effect must be taken into special consideration. In order to pass the mucous membrane which covers the olfactory receptors in the nose, odorous molecules must be water-soluble. Depending upon the degree of water solubility, different concentration shifts occur. The resulting odour impression may therefore alter significantly due to the change in relative composition. The alter- native dilution of the measuring gas with dry air for dew point reduction results in a considerable reduction of the concentrations. In this contribution, the fundamental procedures and methods for the calculation of these effects are presented.
The Modelling of Odour Dispersion with Time-Resolved Models
(2000) Boeker, Peter; Wallenfang, Oliver; Koster, Frank; Croce, Roberto; Diekmann, Bernd; Griebel, Michael; Schulze Lammers, Peter
In connection with the methods used so far, this contribution describes a new approach for the modelling of odour dispersion. Using the aid of example cases, the methodology of odour prognosis with different approaches is explained, and their advantages and dis- advantages as well as their limitations are discussed. Particular attention is given to close-range dispersion from odour emis- sion sources with low source heights and a complex fluidic environment. Typical examples of such cases are agricultural sources or biological processing plants (composting, sewage treatment plants). The new dispersion model is a further development of the NaSt3D model with two variants of improved dispersion modelling, an advection- diffusion approach (Euler model) and a Lagrange-particle model. This model is able to conduct time-resolved calculations of flows and disper- sion and hence allows the question of concentration fluctuation, which is important for odour phenomena, to be integrated into the model. The parallelizing of the computer code enables terrain- and source configu- rations which have been too complex thus far to be calculated in a fine division of the calculation grid. At present, computer clusters and high- performance computers can be used for this purpose in anticipation of the fast further development of efficient personal computers. The consistently analytical approach avoids empirical model supple- ments with adaptation parameters, such as the otherwise necessary mo- dels of exceeding probability, and can thus be calibrated on a physical basis.
Tracer Measurements for the Validation of Odour Dispersion Models
(2001) Boeker, Peter; Wittkowski, Martin; Wallenfang, Oliver; Koster, Frank; Griebel, Michael; Diekmann, Bernd; Schulze Lammers, Peter
Dispersion models are computer-based numerical models which are spe- cially developed for the prognosis of the dispersion behaviour of sub- stances in natural wind flows. They integrate different theoretical sub- models from fluid, gas, and particle dynamics. Since efficient modelling requires simplifications and additional assumptions, the simulation re- sults provided by these models must be compared with real-world data in order to prove the validity of the model. This is called validation. Odour perception at the input location is determined by the fluctuations of local immission concentration. Odour perception begins only when the threshold value is exceeded. Therefore, the determination of values in ex- cess of the threshold level requires that, in addition to the mean input value, its fluctuation be known. Due to the turbulence of natural wind flows, odorants are diluted to a varying degree during transmission. Mo- reover, changing wind directions lead to a shift in the main direction of propagation, which causes the odour plume to meander. The new NaSt3D model was examined as an example of the validation of odour dispersion models. For this reason, field measurements were taken in or- der to determine odour propagation. A mobile tracer measurement technique with simultaneous recording of the meteorological data, the measuring positions, and the tracer concentration allowed measurements with high temporal and spatial resolution to be carried out. Comparisons of model calculations and measurements showed a high degree of consi- stency and proved the applicability of the NaSt3D model for detailed odour dispersion simulation.

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