Centrifugal fans are mechanical devices capable of displacing large volumes of air/gas in industrial processes. The air entering into the fan passes through a pair of impellers where it gains kinetic energy, increases its speed and gets displaced radially, changing the direction typically by 90°. These fans are well suited for industrial processes and pollution control systems because of their operational excellence. The operational performance of a centrifugal fan depends on several factors including fan type, size, and capacity. But there are also few other components that specifically alter the efficiency and performance of a centrifugal fan system.
Inlet and Outlet Duct Arrangements
While the selection of the fan is critical for any industrial process to meet the requirements of air flow rate and system pressure, the fan installation type also plays an important role in its performance. Typically, centrifugal fans have four types of ducting arrangements, free inlet & free outlet, free inlet & ducted outlet, ducted inlet & free outlet and ducted inlet and ducted outlet. In addition to these ducting arrangements, the duct size, a number of bends and the length of the duct will also affect the performance of a fan.
Motors in centrifugal fans have a tremendous impact on energy usage and performance. Motors that operate at voltages less than 10% of the recommended value offer optimum performance and energy savings. Since the ventilation and air movement requirements often vary significantly in industrial processes, motors with multiple speeds can be installed with the ability to adjust the fan speed as needed. Motors that maintain operating conditions under rated electrical supply and equip with proper lubrication offer higher performance and efficiency.
Air Flow Control Devices
Airflow control devices such as dampers & louvers, inlet and outlet vanes attached at the inlet and outlet of the fan will affect airflow pattern and influence the fan performance. These devices control the air flow at the inlet by admitting only required amount of air and impose a resistance to the air stream at the outlet. If the air flow is not properly channelized though the fan system then there will be inefficiency in fan operation with lower performance.
The shaft design of the centrifugal fans have three types of drive mechanisms such as direct, belt driven and variable speed. These mechanisms often influence the energy efficiency and performance of a fan systems. Fans with belt drives are widely used in industrial applications because they allow flexibility in changing fan speed. Belt systems that have proper alignment and tension offer higher performance when compared to improperly installed and maintained belts. Improper belt tension may lead to inefficient power transmission and belt failures resulting in premature motor failures.
Centrifugal fan performance also depends on other air moving devices like filters and heat exchangers which are used in industrial processes to regulate the temperatures or remove the unwanted particulate or gases.