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What Is Thermal Degradation and How Is It Measured?

By Eastman |

Choosing the right heat transfer fluid is the first step to enhancing the efficiency of your applications and the performance of your equipment. The second is understanding how to keep that fluid performing at its maximum capacity – so you get the best results, every day.

If heat transfer fluids are heated to excessively high temperatures, they begin to thermally degrade into what are called low and high boilers. This occurs when carbon-carbon bonds in the fluid break and form new materials with new molecular weights.

Low boilers are created when the fluid degrades and smaller molecules are formed with lower molecular weights and lower boiling points. In contrast, other compounds may react with each other to form larger, heavier polymerized molecules called high boilers. Both low and high boilers can negatively impact your operation.

After thermal degradation, heat transfer fluids do not have the same heat transfer efficiency and thermal stability of the original fluid, causing unfavorable – potentially unsafe — conditions for your application. For low boilers, excessive heating causes reduced viscosity and increased volatility. These lighter molecules also reduce the fluid’s flash point and fire point. Left unchecked, low boilers can cause damage to equipment and require extra costs when they need to be replaced with new, fresh fluids.

On the other hand, high boilers can increase heat transfer fluid viscosity, which will affect the fluid's pumpability at low temperatures. Insoluble compounds can begin to form solids, which can foul the heat transfer surfaces. In this case, fouling of the heat transfer surfaces can be rapid and the system capability will diminish, ultimately resulting in increased costs due to downtime, repairs, clean-out and lost production.

Keeping a close eye on degrading fluids is crucial; however, it requires the proper tools. That’s why at Eastman, we lab and field test all our fluids at elevated temperatures to measure the rate of formation of these compounds. For each product, this is expressed as a percent degradation vs. time, which provides the basis for setting the maximum operating temperature recommended for each fluid.

We follow the ASTM D-6743/7213 standardized methods for measuring thermal stability of organic heat transfer fluids, which are similar to DIN 51528/51435 in Europe. These test methods thermally stress the fluids, and provide analysis of the degradation products formed by simulated distillation (chromatography). The output from these test methods is a quantitative assessment of low and high boiling thermal degradation products.Heat Transfer Fluids by Eastman

Eastman lab fluid testing and analysis is just one aspect of the TLC Total Lifecycle Care® program. We provide you with the tools (Therminol® fluid sample collection kits) and services you need to proactively monitor your fluid quality and plan ahead for fluid replacement before you ever experience a loss in system performance. Contact an Eastman Therminol fluid specialist to learn more.

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