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

摘要

A laboratory method for the physical simulation of natural ventilation by thermal effects in greenhouses is presented. Scale models of a tunnel greenhouse were constructed and immersed in a water tank. A solution of salty water and black dye wasinjected to produce density differences that simulated the buoyancy flux due to the heating of the greenhouse air. Flow was visualized using a video camera and images were processed in order to relate pixel 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 effects. For the type of greenhouse under study, this minimum value of Re was determined to be close to 900.The increments of temperature obtained from laboratory experiments were about 25% lower than those obtained by the theoretical model developed by Bruce. The method could be a useful tool for testing ventilation arrangements in greenhouse structures andfor comparing results with those obtained by calculation based on models.