Measurements and modelling of tracer gas distribution in a naturally ventilated greenhouse for pesticide dispersion determination

Abstract

In this study numerical and experimental results concerning the dispersion of a tracer gas (N2O) inside an experimental greenhouse with a tomato crop were presented and analyzed. The proposed simulation concerns a greenhouse block located in the University of Thessaly near Volos, the continental area of eastern Greece. The tracer gas was injected into the greenhouse, and after its homogenization, vents were opened and simultaneously wind velocity, wind direction and gas concentration were recorded. Air samples were continuously taken at six points in the greenhouse and in two positions outside the greenhouse using a multiple inlet infrared gas analyser. In the numerical model, calculations were made for several combinations of wind speed and direction. In first set, used to validate the numerical model, experimental values were used for the boundary conditions. The final solution for every case was obtained, firstly by a convergent solution under steady - state conditions and secondly by an unsteady one, where at time zero the volume of the experimental greenhouse was considered to contain a new mixture of 'air' and 'N2O'. Good overall agreement was found between the experimental and simulated data. The simulation results provided useful information about the emission of N 2O around the experimental greenhouse and are a first step towards the determination of the behaviour of pesticides around greenhouses.