By AMCA InternAtIonAl’s IndustrIAl ProCess/Power GenerAtIon MArket GrouP selection of Fans T for Industrial Process and Power Generation Applications Before discussing the aerodynamic principles associated with fans, it is important to understand the definition of a fan. A fan is a device that converts rotational mechanical energy to move a continuous volume of gas while increasing the pressure of the gas. A fan has at least one inlet and one outlet. his is the first in a series of articles by AMCA’s Industrial Process/Power Generation Group on various aspects of fan performance and design that are significant to fan applications in the Industrial Process and Power Generation Markets. When starting the selection process, one must determine if the fan will have appurtenances that affect aerodynamic performance. This determination is normally established by defining the inlet and outlet boundaries or planes for the fan. The primary purpose of purchasing a fan for such applications is to obtain a machine to provide the motive force for moving air or gas within the system. The cost of the fan is often relatively small compared to the cost of annual operation, or the value of the end product or service provided by the facility. Making sure that the fan is properly selected to meet the needs of the process using the least amount of energy and providing the greatest reliability is of utmost importance. This article reviews major concepts related to fan performance definitions and selection criteria that are important to ensuring that the fan chosen is appropriate for the application. The next step is to consider aerodynamic parameters associated with fans. The first of these is pressure, which is force per unit area. Pressure can be described in several ways: Absolute Pressure is the value of pressure when the datum is absolute zero; it is always positive. Barometric Pressure is the Absolute Pressure exerted by the atmosphere; it also is always positive. Gauge Pressure is the value of pressure when the datum is barometric pressure at the measurement point; it can be positive or negative. Figure 1: Interpretation of fan pressures for rating purposes. Image courtesy of AMCA International. INLET DUCT FAN FAN MFR. CUSTOMER FAN INLET FAN OUTLET CUSTOMER OUTLET DUCT t2 Pv1 Pv Pt P s2 Ps 0 + P Pv + 1 Ps 1 Pv1 2 ∆Ps Pt1 AMBIENT 0 ATMOSPHERIC PRESSURE For fan applications, there are some very specific definitions concerning pressure. Fan 1. ENTRANCE LOSS 2. ACCELERATION ENERGY 6 Fa l l 2 0 1 3 There are three types of pressure we are concerned about with fan applications: Static Pressure, Velocity Pressure, and Total Pressure. Static Pressure is the pressure that exists by virtue of compression and density only; it can be positive or negative. Velocity Pressure is the pressure that exists by virtue of motion and density only; it can only be positive. Total Pressure is the sum of static and velocity pressure at a measurement point, and therefore defines the total energy at a given point; it can be positive or negative. a m c a I n t e r nat I o na l inmotion w w w. a m c a . o r ghttp://WWW.AMCA.ORG