When choosing a heat transfer fluid, there are many things
to consider to ensure optimum performance. There are four main categories of
heat transfer fluid:
- Water (including deionised water)
- Glycol/water combinations (ethylene glycol/water
or propylene glycol combination)
Water is one of the most efficient and highest quality
products available for heat transfer by theory, but freezes and boils,
providing a limited temperature range within which water alone can be used as a
heat transfer medium. Glycol and water combinations are able to offer very high
stability at higher temperatures and often require a lower start up temperature
than oils. Oils are often non-toxic, efficient, and cost-effective, performing
well at moderate to high temperatures. The benefits and drawbacks of each of
these heat transfer fluids will be discussed in a later section of this article.
PFPE, or Perfluoropolyether, is a type of fluorinated fluid
that can operate at both temperature extremes, with typical operating
temperatures ranging from -70ºC to 290ºC. PFPE is able to offer high thermal
stability, has good dielectric properties and is chemically inert, compatible
with metals, plastics and elastomers. However, PFPEs are expensive and have seeking
To select an efficient heat transfer fluid, you must first
know the minimum and maximum operating temperatures of your equipment. Fluid
with a lower operating temperature will offer protection from premature
degradation of your equipment when turning on. It is important to consider the
thermal stability, heat transfer efficiency, and expansion rate of heat
transfer fluids, and ensure that the fluid will meet the requirements of both
the process and chiller.
Several questions must be asked regarding the operating
conditions of the heat transfer fluid to ensure maximum compatibility.
- Is the fluid able to operate efficiently
throughout the entire process cycle, transitioning between temperatures
- What is the local climate?
- Will the chiller be located outside and so open
to the atmosphere?
- Is this a continuous process?
- Does this process require heat transfer fluids
with a food-grade rating?
To ensure that phase separation does not occur, it is
essential to consider fluid compatibility when replacing existing heat transfer
fluids. As it is incredibly challenging to completely drain fluid from a
system, any remnants of expired fluid that do not effectively mix with
replacement fluid could cause pump cavitation and unnecessary wear and tear on
other parts throughout the system. It is also important to ensure that there is
no contamination of heat transfer fluids during maintenance, as contaminants
are incompatible with most heat transfer fluids and will immediately degrade
their efficiency. When considering compatibility, it is also essential to
ensure that the heat transfer fluid is compatible with the construction
materials of your equipment to prevent leeching of particles into the fluid.
There are four crucial factors that should be compared when
choosing a heat transfer fluid:
- Heat transfer efficiency
- Temperature range
- Material compatibility
- Thermal stability
The heat transfer efficiency of a heat transfer fluid is
determined by several characteristics. An ideal heat transfer fluid will have:
- Low viscosity
- High density
- High thermal conductivity
- High specific heat capacity
With the right balance of these characteristics, a heat
transfer fluid will provide better heat transfer efficiency at a range of
operating temperatures and flow conditions.
Any impurities should be removed from the heat transfer
fluid to prevent fluid degradation and fouling on surfaces within the system.
This extends the life of heat transfer fluids and reduces the amount of
When comparing the thermal stability of heat transfer
fluids, it is important to remember that a product with higher thermal
stability will provide higher heat transfer efficiency for a longer period and
poses a lower risk of system damage or safety hazards when used in accordance
Consider how frequently heat transfer fluids need to be
replaced and whether a specialist waste removal service will be required to
safely dispose of expired fluids. Ensure that the cost of this has been
factored into the budget. It is also worth noting that although selecting a
heat transfer fluid with an extended temperature range will provide a safety
cushion, it can come at an enhanced cost, so discuss specific system
requirements with the supplier.
Take time to discuss the requirements of your chiller with
the manufacturer and take note of their heat transfer fluid recommendations.
Working with a heat transfer fluid supplier who can provide technical support
through the lifecycle of the product is beneficial, as fluid degradation will
In summary, choosing the right heat transfer fluid is
essential in protecting against accelerated degradation, machine failure,
increased maintenance, and decreased efficiency. Ensuring that fluids work in
synchronisation with the specifications of the chiller and that regular
preventative maintenance is undertaken will protect both the chiller and the
fluid from damage. Expert advice should be sought from the heat transfer fluid
supplier or chiller manufacturer to ensure that the right fluid is selected,
and a proper maintenance plan formed. This will ensure that the operation runs
with increased safety, efficiency, and reliability, with decreased downtime.