Fan degradation in airstreams that have corrosive

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Fan Degradation. In airstreams that have corrosive gases or abrasive particles, fan blade degradation can present a threat to reliable operation. As fan blades degrade, the airflow over the surfaces becomes disrupted and the fan imparts energy less efficiently to the airstream. Certain blade types are particularly susceptible to erosion because of the angle of attack with the airstream. In applications where higher-than-expected blade degradation has occurred, different fan types or fan materials should be considered. Many fan manufacturers have developed materials and coatings that solve this problem. System Problems Poor system performance can be caused by several factors, including improper system design and component selection, incorrect installation practices, and inadequate maintenance. Improper system design usually means the system is configured so that it has high system effect factors (SEFs) that result in high operating costs, system leakage, and noisy system operation. Poor component selection includes oversizing fans or using ineffective or wasteful flow control devices. Improper installation practices include on-site modifications to the duct system that result in high SEFs, improper fan rotational speed selection, and incorrect fan rotation. Inadequate maintenance often means a lack of bearing lubrication and fan cleaning. Contaminant accumulation on fan blades, duct surfaces, and in filters results in decreased system efficiency and inadequate airflow. High Operating Costs. Many fan systems are designed to support the highest expected operating loads. Because systems are frequently not re-adjusted during periods of low demand, fans often generate higher-than-necessary airflows and incur
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A Sourcebook for Industry 31 4–Common Fan System Problems higher-than-necessary operating costs. Awareness of the costs of inefficient system operation can lead to efforts that reduce these costs and increase system reliability. An important part of evaluating whether operating costs can be significantly reduced is to measure the amount of variability in delivery requirements and determine operating con- figurations that meet—but do not exceed—these requirements. Fouling. The accumulation of contaminants in parts of a system can disrupt airflow profiles and create high-pressure drops. Finned heat exchangers and filters are particularly susceptible to contaminant accumulation that can severely impair airflow. In heat exchangers, fouling interferes with heat transfer, which can compound an airflow problem by requiring more airflow to compensate for the reduction in heat exchanger effectiveness. Consequently, fouling can have a compounding impact on energy use. Another aspect of fouling that can affect fan performance is interference with inlet-guide vane operation or blade-angle adjustment in variable- pitch fans. Inlet-guide vanes are used to change the load on a fan according to system airflow requirements, thus allowing lower energy consumption during periods of low demand.
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  • Summer '15
  • Electric motor, Fan, Fan Systems

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