Paratherm NF® vs. Glycol Oleo Termicos
Paratherm NF® non-fouling, non-toxic heat transfer fluid has for years successfully replaced high-temperature glycol fluids in a broad range of applications. Here are some comparisons.
Although the highest temperature glycols are rated for service to 500°F, field reports indicate that fluid degradation has frequently occurred at 400°F and below. The NF fluid provides extended, trouble-free service in demanding applications to 600°F.
Hard Carbon Deposits
Hard carbon deposits baked onto heated surfaces result from severe fluid overheating. Overheating occurs when the fluid flows decrease, and its molecules linger too long in contact with overheated surfaces.
Overheating can be reduced or eliminated by maintaining good fluid flow and turbulence at the heated surfaces.
With a decrease in fluid flow, glycol fluids overheat and produce a fine sooty carbon (“coke”) that adheres, bakes on to, and builds up on heated surfaces.
Under similar severe overheat conditions, the NF fluid evolves carbon granules – granules that don’t adhere, that remain in suspension and that are easy to filter out.
Glycols are considered regulated waste in most states, and can be very costly to dispose. The NF non-toxic fluid can be safely combined with used or contaminated lube oils and sent to the local oil recycler (EPA, citation 57FR21524). Note: Some state and local regulations may differ from federal regulations.
High-temperature glycol heat transfer fluids can cost upwards of $15.00 per gallon in 55-gallon drums – and much more in smaller quantities. Cost of the NF fluid? One-half to two-thirds this.
Glycol fluids are naturally hygroscopic. They readily mix with water and absorb water vapor from the air. Allowed to stand in thermal systems and tooling, the fluid/water mixture almost always produces corrosion. The NF fluid is hydrophobic. It does not absorb water, and provides the same high degree of protection to metal surfaces as the finest lubricating oils.
When glycol fluids are heated, dissolved water will flash to steam. This significant volumetric expansion to vapor can cause pumps to cavitate, and may cause hot fluid to spurt from the system (similar to the geyser that occurs when you remove the radiator cap from a hot engine).
Water dissolved in the glycol fluid must be slowly vaporized off before the system can be brought much above 230°F. Water is immiscible with – and more dense than – the NF fluid. It will seek the system’s low points, where it can be easily and quickly drained off.
High-temperature glycols have among the highest flash and fire points of any heat transfer fluid. In fact, they are even higher than glycol’s maximum rated operating temperature.
In closed-loop heat transfer systems however, the autoignition* temperature – not flash and fire point – is the most critical.
Heat transfer fluids are routinely operated above their flash and fire points, but never above autoignition temperature. While they will burn under the right conditions, heat transfer fluids have for years proven exceptionally safe in a broad range of high-temperature applications. The NF fluid is so safe that it is used in demanding high-temperature die-casting service. It is widely specified by die casting machinery OEMs as well.
Although glycols are not generally considered extremely hazardous, more and more regulatory attention is being paid them. Aware of the potential hazards, system operators have begun to steer away from these fluids. Problems most commonly mentioned are disposal, cost, fumes (odor), skin dermatitis, and miscibility with water (effluent containing water/glycol can ultimately leach into the water table).
The NF fluid is safely and easily disposed by combining with used lube oils and sending to the local oil recycler. Environmentally, water-accommodated fractions of the NF fluid have passed Bioassay with Rainbow trout, Daphnia pulex and Mysidopsis bahia. No organisms died, and there were no observable ill effects.
Industries involved in the production of food, pharmaceuticals and many types of packaging prefer completely non-toxic fluids. In lower temperature applications for example, we often suggest a mixture of food grade propylene glycol and water. Propylene glycol is typically used to 275°F. The NF fluid is widely specified in higher temperature applications.
Mixing of Fluids
Because of the severe problems that may result, we strongly recommend that heat transfer fluids never be mixed. A typical example surfaced where automotive-grade ethylene glycol was mixed with a high-temperature glycol. Finding they were out of glycol heat transfer fluid, the plant found it expedient to send the maintenance person to the local automotive store. The antifreeze was cheap and readily available. It even performed satisfactorily — for a short time.
Unfortunately for this plant, all glycols aren’t the same. Even if they’re called glycol.
*Autoignition is the temperature at which the fluid will spontaneously ignite in the presence of air. See Paratherm technical data sheet, “Significance of Flash and Fire Points in Oleo Termicos.”
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