Wind tunnel, Operating envelope, Capacity limit, Low temperature testing, Psychrometric analysis
A wind tunnel conditions the air flow for testing equipment, such as heat exchangers, over a wide range of conditions. In this paper, a procedure to develop the operating envelope for the tested equipment in a wind tunnel is presented. The temperature and humidity of the air that requires conditioning is controlled and maintained by the combination of cooling coil (or evaporator), heating elements, and a steam injection system. Therefore, the capacity of the components to be tested inside the wind tunnel is limited by the combined capacity of the cooling coil, heaters, and the steam injection system. For cooling coils or evaporators, an analysis is performed for different sensible heat ratios (SHR), inlet temperatures, and humidity. A similar analysis is performed for sensible heating coils or condensers where the SHR is 1. Â For a cooling coil or evaporator of a capacity of more than 3 tons, the condition of air inside the wind tunnel can be controlled by heating elements and steam injection system. Low capacity cooling and sensible heating equipment may require operation of the cooling coil, heating elements, and steam injection depending on the required temperature and humidity in the tunnel. The psychrometric and thermodynamic analysis for determining the operating envelope is performed for both heating and cooling equipment using ACHP (Bell , 2010). Heat transfer between the wind tunnel and its surroundings is calculated using a simplified heat transfer model adopted from literature (Cremaschi & Lee, 2008).