Chromalox Tubular Heaters Installation Guide
Tubular Heaters
Design & Installation
Guidelines
Components
Design Considerations
Sheath Material — For resisting corrosion
inherent in the process or environment and for
withstanding the sheath temperature required
— Standard sheath materials are INCOLOY
steel, copper and stainless steel (type 304).
Other types of stainless steel, MONEL
nium and INCONEL
Job Requirements — The calculation of
total heat requirements for an application is
outlined in Technical section. For assistance,
contact your Local Chromalox field sales
engineer who will be glad to contribute his
judgement, experience and knowledge in solving your heating problem.
After the specific heater size and rating has
been tentatively selected, the watt density
must be checked against the curves in Technical section.
If the heater selected has a watt density higher
than stipulated by the curve, consider these
alternatives:
1. Use more heaters of a lower watt density
to obtain the required kW capacity.
2. Reduce the kW capacity needed by
reducing heat losses and/or allowing for
a longer heat-up time.
Watt Densities — The watt density of the
element, or watts per square inch of element
heated area, should be low for heating asphalt,
molasses and other thick substances with low
heat transferability. It can be higher for heating
air, metals, liquids and other heat-conducting
materials. See curves in Technical section for
determining allowable watt densities.
When high operating temperatures are
needed, watt density must be limited in order
not to exceed the maximum sheath temperature. Watt density is given in the specifications
for each tubular heater.
In general, a viscous material with low thermal
conductivity requires a low watt density.
Higher watt densities can be used with thinner
liquids and with materials of high thermal
conductivity. Premature loss of the element
due to excessive temperature may result if the
material’s heat-take-away ability is low. Also,
the material may be charred, carbonized or its
chemical makeup altered by overheating.
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are available.
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Terminal Selection — Stocked tubulars are
shipped with standard terminals, see Terminal
Options in this section. Many other terminals
and terminal end seals are available made to
order.
CAUTION — Protect terminals from possible
contamination from surrounding atmospheres
such as oil fumes, chemical vapors from
other processes, moisture, weather, etc. MgO
insulation is hygroscopic.
Vacuums — Tubular heaters operate at higher
temperatures in a vacuum because there is
no air to take away the heat. Therefore, watt
densities are recommended to be 20 to 30%
lower. It is recommended terminals of the element be kept outside of the vacuum.
Code Compliance — Chromalox manufactures the highest quality heaters and controls
and, where applicable, in compliance with
such codes as the Canadian Standards
Association (CSA), Underwriters Laboratories
Inc. (UL) and Verification of Devices for
Europe Testing and Certification Institute
(VDE) and CE.
Installation Guidelines
Wiring — Must be in accordance with The
National Electrical Code (NEC). It is important
to use the correct wire gauge to carry the
amperage required. A wire not large enough
can overheat, become brittle and break. The
ambient temperature must also be considered
in choosing the correct type of wire and insulation. Make sure wiring to terminals is tight.
Keep terminals away from heat, if possible.
(For higher temperatures, contact your Local
Chromalox Sales office.)
Mounting Methods — Elements can be
supplied with threaded fittings for mounting
thru walls of tanks, ovens, etc. Compression
threaded fittings are also available for easy
field installation. Rings, clips, brackets and
washers can also be attached to elements for
mounting purposes.
Sheath Material
Copper 1 1 3/8 21/64 3-3/8 1-1/2 1±1/16 #10-32
Steel or INCOLOY
Copper, Steel or INCOLOY
1. See complete heater dimensions in table on product pages.
®
A B C D E F G
1 1 3/8 21/64 3-3/8 1-1/2 1±1/16 #10-32
®
1 1 1/2 15/32 3-7/16 2-1/2 13/16±1/16 #8-32
Easy Bending — To put heat where
it is needed, tubular elements can be bent to
fit most requirements. See following pages for
customer bending and factory bending details.
Bending should be done around a smooth
round object such as a piece of pipe. For minimum bending radii, see Bending Guidelines.
Triangular Cross-Section
These unique cross-sectioned elements are
specially designed for high element surface
temperature applications, and wherever
extreme rigidity is required.
Triangulation — A patented extra step by
Chromalox to increase insulation density and
maximize heat transfer and operating life. This
method of compaction increases uniformity of
resistance wire spacing to help eliminate hot
and cold spots. It also increases the rigidity of
the element, which is an advantage in some
applications.
The terminal ends of these elements are
re-rounded to facilitate the use of threaded
fittings or other mounting methods.
The heart shaped cross-section is recommended for certain heavy duty applications.
It has added structural strength, achieved
through die pressing, which resists deformation or sagging when installed in the flow of
high velocity air or thick oils and compounds,
or in high surface temperature air heating.
A
E
F
Heated Length
B
D
C
E
F
Terminal
Size
Terminal
Size
G
Insulation
Dimensions (In.)
G
A-6
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