Flow Visualization of Airflow Through a Rectangular Duct With Combined Heat and Mass Transfer

Radiant ceiling panels have been shown to provide good thermal comfort for occupants and reduce energy consumption in large buildings. A disadvantage of radiant panels however, is the inability to alter the relative humidity (RH) of a space, which can also lead to occupant discomfort. A new panel is being developed which will transfer both heat and moisture to a room, to moderate space temperature and RH simultaneously. In order to determine how this panel performs, a test panel has been created and tested in an experimental facility. The panel is situated in the top of a rectangular duct. The surface of the panel is made of a porous membrane, which allows moisture to transfer between the air and the panel. Air passes through the duct and underneath the panel, at low Reynolds numbers (Re). As heat and moisture are transferred between the panel and the air, temperature and concentration gradients form in the duct. If these gradients become large, free convection will occur. Depending on which type of convection is dominant, free or forced, the air will flow in different patterns. In order to understand the performance of the panel, flow visualization is used to determine how the airflow is affected by temperature and concentration gradients. Test conditions include heating, cooling, humidification and dehumidification.