| An experimental investigation was performed on a building ventilation fan with an installed aerodynamic shroud. The fan system used for this study was characterized by its high volume flow rate, low pressure rise and downstream conical diffuser. A new definition of efficiency is presented that differs than the currently accepted industry standard. Arguments are presented to support this definition, and its use not only in this type of fan, but also other turbomachinery applications. An energy balance is derived that includes this definition of efficiency and the specific loss mechanisms of turbomachinery. This formulation clearly shows how the efficiency can be increased by reducing these loss mechanisms.; Integral measurements of pressure rise vs. flow rate and efficiency are presented for a number of different configurations, blade designs, diffusers and aerodynamic shroud conditions. These data show that the aerodynamic shroud is able to increase the flow rate by over 35% while simultaneously increasing the efficiency by over 15%. Furthermore, it is shown that the choice of blade design is critical to these improvements and that a larger diffuser cone can be used. Particle Image Velocimetry (PIV) measurements are presented to show how the aerodynamic shroud affects the flow field downstream of the fan. These data show that the aerodynamic shroud is able to reduce specific loss mechanisms that were identified in the energy balance and also create a more uniform exit profile at the exit of the diffuser cone. Finally, a new fan system is proposed that incorporates the modifications that were made and proven successful in this study. |
