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Fan Laws and System Curves - The
purpose of this Engineering Letter is to explain the basis and application of
the rules used to predict fan performance in a given system. With a basic
understanding of these rules, the performance of a fan can be quickly calculated
for various conditions.
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Increasing Fan Performance -
Industrial process and plant-ventilation systems often need more air than
originally designed. Increased production requirements, process changes, and
facility renovations are a few of the major reasons. Additionally, the lack of
adequate maintenance over time can negatively impact system airflows. This
letter discusses several procedures that can increase air flow.
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Pneumatic Conveying - A well
designed pneumatic conveying system is often a more practical and economical
method of transporting materials from one point to another than alternative
manual or mechanical systems. This Engineering Letter outlines some of the
fundamental principles of pneumatic conveying systems and explains various
special considerations for fan selection.
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Screw Machines - Screw machines
produce finished metal products from round stock. The stock is fed to the
machine automatically from a magazine-fed stock reel and held in position by
collets. Screw machines cycle automatically finishing a part each time the
machine indexes. Learn More...
System Calculation - A fan system
is any combination of ductwork, hoods, filters, louvers, collectors, etc., that
relies upon a fan to produce airflow. When the air moves past each of these
components, resistance is created which must be considered in system
calculations. It is also important to remember that fans are rated independently
of a system and that fan performance will vary depending upon the accuracy of
the system calculations. This Engineering Letter will explain some of the basic
fundamentals of system design and calculation.
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Fan Performance - The System
Effect - Fans are typically tested and rated in prescribed test configurations
defined by the Air Movement and Control Association. This is done to ensure
standardized procedures and ratings so that system designers can make realistic
choices among various manufacturers. Beyond the routine system resistance
calculations, the location of some of the common components and their proximity
to the fan inlet or outlet can create additional immeasurable losses commonly
called System Effect. These losses, if not eliminated or minimized, will
necessitate fan speed and horsepower increases to compensate for the performance
deficiencies. This Letter will outline some of the common causes for these
deficiencies and provide useful guidelines for more efficient and predictable
air-handling systems. Learn More...
Understanding Fan Performance Curves
- One of the most important documents customers request from fan manufacturers
is performance curves. In addition to graphically depicting the basic fan
performance data of CFM, RPM, and SP (on the static pressure curve) and BHP (on
the brake horsepower curve), these curves also illustrate the performance
characteristics of various fan types, like areas of instability, or the rate of
change between flow and pressure. With some basic knowledge of performance
curves, decisions can be made concerning fan selection, fan and system
alterations, or the advisability of using a fan in a modulating system, for
example.
Except for very large fans, performance curve
information is generated by connecting the fan to a laboratory test chamber.
Very specific test procedures are followed as prescribed in the Air Movement and
Control Association's Standard 210 to assure uniform and accurate readings. Data
points are collected at a given RPM while the flow is slowly modulated from full
close to full open. The information gathered is then used to develop computer
selection programs and published capacity tables for use by system designers
and end users. Learn
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