Quantifizierung des Luftvolumenstromes in frei gelüfteten Rinderställen mit Hilfe der Kompartimentalisierungsmethode zur Bestimmung umweltrelevanter Emissionsmassenströme

Air flow calculation in natural ventilated dairy stables with the method of compartmentalisation to determine emission mass flows of important environmental gases

by Gunnar Brehme
Doctoral thesis
Date of Examination:2000-11-23
Date of issue:2001-01-10
Advisor:Dr.-Ing. Karl-Heinz Krause
Referee:Prof. Dr. Herman van den Weghe
Referee:Prof. Dr. Axel Munack
Persistent Address: http://dx.doi.org/10.53846/goediss-1709

 

 

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Abstract

English

The assessment of airflow volume becomes increasingly important in estimating the environmental impact of airborne stable emissions. In contrast to mechanically ventilated stables the amount of air exchange is irregular in open stables and depends on the natural variables windspeed and wind direction. Statistics on the emission mass flow of natural ventilated stables are not available. An etablished method for the calculation of airflow is based on the measurement of the decay of radioactively marked tracer particles (Krypton 85) in the stable atmosphere at different points. In general the decay behavior can be judged by the air change rate and further by the air flow. The main disadvantage of this method is that the airflow is calculated by averaging the average air change rate of the measured values. But this only holds true if the averaged air change rate is averaged over equal time periods. A condition that is not garanteed. In addition this method assumes that the wind direction is constant during the whole measuring time - a condition that is not valid in practice. To overcome these disadvantages a new calculation method is designed to improve the quality of the results of air flow determination. By dividing the open stable into different compartments it is possible to develop a set of equations describing the complete mass flow. An equation is derived for each virtual compartment in relation to its neighboring compartments. The equations of all compartments are taken for one period of time comprise one time step. The air change between the compartments and the surrounding is described by transfer coefficients. In addition for each time step a local flow pattern is generated for the interior of the stable. The flow pattern chart changes during each time step according to the wind velocities and wind direction.
Keywords: compartment; natural ventilation; air flow calculation and simulation
 
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