Intake and Exhaust Fans
Intake and exhaust fans are used to model the flow of air into or out of a system. In Discovery, two-dimensional intake fans are inlets that allow air to flow into the system and exhaust fans are modeled as outlets that allow air to flow out of the system.
Fan Curves
When modeling fans, fan curves are used to select the appropriate size and type of fan for a particular application. A fan curve, which is usually supplied by the fan manufacturer, is a graph that represents the relationship between volumetric flow rate and the pressure rise across the fan (static pressure). Fan curves are also used to determine the fan pressure rise (also known as the operating point of a fan) based on the computed volumetric flow rate. The operating point represents the fan pressure rise and volumetric flow rate where the fan is in stable equilibrium with the system.
The figure below shows a curve for a common tube-axial fan. The total volumetric flow rate, Q, is plotted against the fan static pressure, pfs.
The accuracy of the fan flow rate used by Discovery is directly related to the accuracy with which the fan static pressure is computed. This, in turn, depends on how accurately pressure losses in the entire system are modeled. Therefore, care should be taken to model all features of the system that contribute to the overall nature of the pressure distribution in the system.