A method for studying natural ventilation by thermal effects in a tunnel greenhouse using laboratory-scale models

A laboratory method for the physical simulation of natural ventilation by t hermal effects in greenhouses is presented. Scale models of a tunnel greenh ouse were constructed and immersed in a water tank. A solution of salty wat er and black dye was injected to produce density differences that simulated the buoyancy flux due to the heating of the greenhouse air. Flow was visua lized using a video camera and images were processed in order to relate pix el intensities and density increments. Scaling laws allowed the calculation of the temperature increments associated with relative density increments for each experiment. Experiments with Reynolds numbers Re ranging from 101 to 1350 were carried out in order to estimate the minimum Re necessary to neglect Viscosity effe cts. For the type of greenhouse under study, this minimum value of Re was d etermined to be close to 900. The increments of temperature obtained from laboratory experiments were abo ut 25% lower than those obtained by the theoretical model developed by Bruc e. The method could be a useful tool for testing ventilation arrangements i n greenhouse structures and for comparing results with those obtained by ca lculation based on models. (C) 1999 Silsoe Research Institute.