Immersion Heat Exchanger Coils for Corrosive/Ultrapure Chemicals
Today, Immersion Coils for heating and cooling are available in a variety of shapes, materials,
designs and assemblies from various manufacturers. Polymer (Polyethylene, High Performance
fluoropolymer), common and exotic metal alloys, pancake coil shapes, racetrack coils, grid
structures, spaghetti tube U bends, welded and non-welded tube terminations, and tube ends
connected to a manifold are among the many options available. Less than fully informed
decisions lead to suboptimal or wrong choices (for example, based on purchase price only).
Such choices end up in faster than expected deteriorating performance or even catastrophic
failure.
Among materials, fluoropolymer coils have been around for 40+ years, and have secured a
unique position in a multitude of diverse industries that use heat exchangers for temperature
control of corrosive chemicals and ultrapure liquids.
What are Fluoropolymers?
Fluoropolymers are thermoplastics with fluorine as part of their chemical structure. Most
common plastics such as polyethylene and polypropylene have hydrogen in their structure. The
substitution of hydrogen with fluorine imparts some unique properties, such as chemical
inertness, high use temperature, flame resistance, low coefficient of friction, and “non-stick”
characteristic, among others.
FEP, PFA PVDF, PTFE are among the more popular polymers, in addition to some others such as
ETFE, PCTFE etc. The maximum use temperature, pressure rating, thermal conductivity, and
FLUOROTHERM flexibility are some of the properties that determine the best resin for use in a specific
application.
Why Fluoropolymers instead of metals for heat exchangers?
While metal heat exchangers (made of carbon and stainless steel, copper, aluminum), and now
low temperature plastic (polyethylene) are utilized in many commercial and household
products, air conditioners and space heating for example, where corrosion or contamination
may not be a serious concern, many industrial and specialty applications require the heating
and/or cooling of corrosive acids, alkalis, organics. Radiant floor heating is an exception, and
there is new interest in using fluoropolymers because of their long life – the low temperature
rated tubes turn brittle are not readily accessible for repair after installation.
Fluoropolymers are ideally suited for facilitating heat transfer in chemically aggressive
environments., common metal heat exchangers will not last very long when exposed to the
liquid or vapor.
The primary reasons dictating the choice of fluoropolymer heat exchangers are the following
• They are corrosion resistant, unlike their metal and other material counterparts
• They can handle reasonably high bath temperatures, up to about 310 F
• Steam at pressures up to 80 psi can be used as a heating medium
• Fluoropolymers are ultrapure materials, their innate chemical inertness makes them
unreactive to most chemicals, including organics.