These fan laws hold true only when all fan component dimensions are scaled by the impeller diameter ratio. These three laws are used to correlate the flow ( Q ), pressure developed ( P ), and power required ( H ) with the rotational speed ( N ), fan impeller diameter ( D ), and density ( å ) of the gas. The performance characteristics of fans follow relationships known as the affinity laws. For more information, see the resource guide in the expanded version of this article on our web site: Fan affinity laws Detailed data are found in the various textbooks, application guides, handbooks, manuals, and reports available from manufacturers and associations. Axial fans are further classified as vaneaxial, tubeaxial, and propeller.įigure 2 shows exploded views of each of the two major fan types. When space is a concern, axial fans are often preferred. w.g.) while handling large airflow rates. Axial fans are used to generate lower pressures (less than 12-in.
The backward curved and the airfoil fans have the highest efficiencies among centrifugal fans.Īxial fans move the air parallel to the axis of rotation. Centrifugal fans are further classified on the basis of impeller design geometry: backward curved, airfoil, radial, and forward curved. They are used to generate higher pressures at lower airflow rates. Centrifugal fans have an intake at the center and force the air radially outward, perpendicular to the axis of rotation. w.g.) are referred to as compressors.įans are classified into two major design categories: centrifugal and axial. Turbomachines producing pressures greater than 15-psig (416-in. at a relatively low airflow is referred to as a blower or a pressure blower. A fan that produces pressures above 30-in. More detailed information on fans and blowers is available from any of a number of sources including manufacturers and trade associations.įans are turbomachines that provide the means to move air through a system. Understanding the principles of fan system operation helps the user in determining performance, selecting the optimum device, and keeping the fan system well maintained. In these situations, air is often contaminated in some way. Process ventilation typically involves controlled or contained movement of air from one point to another.
Applications include dilution ventilation, makeup air, and cooling of personnel and equipment. General ventilation typically involves the movement of uncontained air. They are found in an infinite number of components and used in a variety of systems from heating, ventilating, and air conditioning to industrial processes (Fig. Fans are used throughout the industrial plant.
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