An Experimental Investigation Of Displacement Natural Ventilation Driven By Buoyancy

In large workshops where natural displacement ventilation is adopted, a good many of plumes are released from equipment. Interacts among rising plumes can influence the height of the interface. In addition heat transfer through the wall and solar radiation play a very important role in temperature field and heat eliminated by the natural ventilation. The thesis aimed at studying natural ventilation in a large single-zone building effect by heat source, plumes, heat transfer through the walls and solar radiation using scaled-down model experiment. The experiments were performed using salt-bath scaled model and air-buoyant model technique. The ratio between model and prototype was analyzed based on similarity theory.Natural ventilation in a imaginary building whose walls are adiabatic was studied using salt-bath scaled model experiment. In this experiment, temperature difference in the prototype building was modeled by density difference of brine and fresh-water in the scaled model. The height of the interface could be seen and the temperature (density) profile could be measured using conduct meter. The movement and interacting of the plume could be observed by adding pigment in the brine. The effect of vent, heat source, and plumes could be studied using the salt-bath model.Natural ventilation in a large building which has heat transfer through the walls was studied using the second experiment——the air-buoyant model. During the experiment, one sidewall and canopy were uniformly"heated", corresponding to a uniformly distributed solar radiation incidence. Air-flow rate was measured using tracer gas technique. The influence factors of natural ventilation such as solar radiation, vent area and heat source were studied. System identification method was introduced in order to minimize error caused by fluctuate of the ambient temperature.The result of the experiment shows that when the heat source in the building is fixed, the height of the interface is clear and temperature grads are large at the interface. The steady interface within the space depends on the effective area of vent, the height of the space and the entrainment caused by the...