ISHS Acta Horticulturae 718: III International Symposium on Models for Plant Growth, Environmental Control and Farm Management in Protected Cultivation (HortiModel 2006)
MATHEMATICAL MODELLING OF THE CLIMATE INSIDE A GLASSHOUSE DURING DAYTIME INCLUDING RADIATIVE AND CONVECTIVE HEAT TRANSFERS |
| Authors: | S.A. Ould Khaoua, P.E. Bournet, G. Chassériaux |
| Keywords: | CFD, Bi-band radiative model, sky and solar radiation, inside climate heterogeneity, airflow |
| Abstract:
A two dimensional CFD model was developed to investigate the airflow and temperature patterns inside a compartmentalised multi-span glasshouse during summer daytime, by combining convective and radiative heat transfers. The CFD software solved the Navier-Stokes equations with the Boussinesq assumption and a k ε closure. Solar (i.e. short wavelength [0-3 µm]) and thermal (i.e. long wavelength ]3-100 µm]) radiative fluxes were included in the model through the resolution of the radiative transfer equation. The optical characteristics of the cover glass were set by distinguishing short and long wavelength radiation and its thickness was meshed in order to monitor its temperature. The accuracy of this device was firstly validated against experimental data. Yet, good agreement was found between calculated temperatures and measured ones. The model was then used to study the consequence of radiation modelling on the temperature and heat flux at roof surfaces and also on the distributed climate inside the greenhouse. For a solar radiation of 740 W m-2, a sky temperature of 15°C and a low wind of 1.26 m s-1, the roof absorbed solar radiation and was therefore warmer (19 to 20 K) than the outside air temperature, as predicted by the bi-band CFD model. The heat transfer coefficient of the roof of the west compartment directly exposed to the wind was about 30% higher than that of the leeward roof. The simulations highlight that convective heat transfer was about 0.4 times less than the radiative one at outer roof surface and about 0.8 times less than at inner roof surface. The airflow patterns and temperature distribution inside the greenhouse were expected to be significantly influenced by temperature gradient situated near the cover surfaces and the floor. Thus, when the buoyancy effect constitutes the main driving force of the flow, temperatures homogenise at the same level, i.e. at plant canopy height. | |
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