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In addition to the general construction material of the
fan Cheap MLB Jerseys China Free
Shipping , other considerations can be made to increase the limiting
temperature. One of the most critical components of the fan are the bearings. So
naturally if the bearings are kept out of the hot airstream they are less
susceptible to the effects of the high temperature, and therefore the air
temperature can be higher than the limiting temperature of the bearings. Inline
fans inherently have drive components in the airstream. In such cases, the unit
can sometimes be designed so that cooler outside air is drawn over the drive
components, providing some additional cooling. Incorporating this type of
external cooling is one of the main reasons GreenheckÕs medium pressure tube
axial inline fan (TBI) can be used for high temperature exhaust applications.
There are, however, some arrangements that donÕt allow for the incorporation and
benefits of external cooling. For instance, fans in arrangement 3 have the wheel
suspended in-between the two bearings. Consequently, one or both of the bearings
will always be located in the air stream. Similarly, direct drive fans are
limited by the maximum operating temperature of the motor, since the motor is
located directly in the hot air stream. That is why most often high temperature
exhaust fans are required to be belt driven units; typically the motor is the
temperature-limiting component of the unit when it is installed in the
airstream. Other than the installation location of the bearing within the fan
assembly, other critical points to consider include the type of lubrication in
the bearing Cheap MLB Jerseys China
Wholesale , as well as the construction of the bearing itself. There is a
seemingly endless list of lubricants available for most any application, but the
appropriate lubricant can add considerable life to bearing operation. In
addition, high temperature bearings can be constructed with inherent
construction modifications, such as a larger grease cavity to hold more
lubricant.

Another common variation to the standard fan design is the
addition of insulation. The bearing mounting plate, bearing cover and belt tube
are the most likely components to be insulated for a high temperature
application. Canada Blower automatically includes insulation for these
components on all fans specified with either HT Option III or HT Option
IV.

It is important to understand that emergency smoke exhaust fans are
designed to operate effectively for the temperature and time limits stated as
long as the power supply to the fan is not terminated. Since they are not
designed to sustain higher temperatures for continuous use, exposure to the
extreme high temperatures caused by a fire likely would destroy some or all
parts of the fan once the time design limit has elapsed, rendering it incapable
of future operation.

Fans that are built for continuous high temperature
ventilation have many of the same construction features and options as those
built for emergency smoke exhaust. For example, both are typically constructed
of higher temperature ferrous materials, have high temperature bearings, have
the motor and drive installed either out of the airstream or with some type of
additional cooling capabilities, and incorporate some heat shielding or
insulation. There are Cheap MLB
Jerseys Free Shipping , however, some distinct differences between the fan
designs for the two application categories. One of the most common applications
for which continuous duty high temperature exhaust fans are specified is
commercial kitchen ventilation.

Fans that are specified for continuous
operation at higher temperatures need to be carefully selected taking into
account air density corrections. Although a fan will move the same amount of air
at two different temperatures, the static pressure and horsepower requirements
can change drastically as the density of the air varies with changing
temperatures. For example, if a fan moves 3,000 CFM at 70 F it will also move
3,000 cfm at 500 F. However, since the hotter air weighs much less than the 70¼F
air, the fan will require less brake horsepower and will create less static
pressure.

There are also some accessories and construction options that
are incorporated into high temperature process fans to increase the limiting
temperature. For example, a heat slinger can be installed on the shaft between
the fan housing and the inboard bearing. A heat slinger is an aluminum disc that
absorbs and dissipates some of the heat conducted along the shaft before it
travels to the bearings. Many heat slingers incorporate fans that promote
additional inboard bearing cooling because it circulates air with every rotation
of the shaft.

Another common construction technique is the use of a heat
gap. A heat gap is a physical gap between the bearing support structure and the
hot fan housing. This separation slows the process of heat conduction to the
bearings and drive components through the housing and support structure. An
expansion bearing should be installed where the fan shaft is predicted to
conduct enough heat that it could expand to a length greater than that of the
structure to which it is secured. This allows for expansion of the shaft within
the bearing due to the higher temperatures.

High temperature applications
can be found in many different areas of the air movement and control industry.
It is important to remember that one high temperature fan design is not suited
to all applications.

Susan Terlitski
HVAC Ventilation
Engineer
Canada Blower
Co.
http:www.canadablowerairindex
http:www.canadablowerenclosuresindex
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