Transfer of Momentum and Energy in and above Infinite Screenhouses

摘要

The trend in recent years towards ever larger greenhouses restricts ventilation by reducing the efficacy of the wall vents. The roof, therefore, becomes the only effective route for the transfer of momentum, heat and water vapour between the greenhouse and the atmosphere. In this study the limiting case of an infinite flat-roof screenhouse is analysed in terms of the mixing length methodology, assuming a one-dimensional quasi-adiabatic shear flow. A simple energy balance is used to partition net radiation into sensible and latent heat fluxes. The vertical energy fluxes are calculated with the same adiabatic turbulent transfer coefficient as momentum. The resulting temperature and humidity profiles in and above the screenhouse depend on atmospheric conditions, and on screen and crop properties. Realistic responses to changes in these conditions and properties are obtained. The mixing-length results may be used as benchmarks for solutions obtained by computational fluid dynamics, often used for ventilation studies.