There are many potential reasons at the root of why a heat transfer fluid may require replacement throughout its active service. For instance, heat transfer fluids can lose their effectiveness when they become contaminated with unwanted debris. When viscosity levels rise, fluids can also perform poorly at low temperatures and when the quantity of molecular weight degradation matter become too high, they can exceed the limit of solubility.
When heat transfer fluids age, they can increase energy costs at both the pump and the heater, requiring a change over. Additionally, heat transfer efficiency loss impacting through rates is another reason. Finally, accelerated thermal degradation of the heat transfer fluid in deteriorated condition will also need changing.
Over an extended period of use, substantial fluid contamination and overheating will negatively impact the quality of any heat transfer fluid system through deterioration; fluids must be changed before they impact the performance of a company’s operation.
What is the difference between oxidative and thermal degradation?
Overall, degradation is the key reason why heat transfer fluid requires replacing in systems. This process happens in two different ways, referred to as oxidative and thermal degradation.
When a heat transfer fluid is exposed to air, oxidation degradation can occur. Impacted heat transfer fluids become more viscous (thicker) and, as a result, are harder to pump. This is not the only effect, however. As viscosity increases, the heat transfer attributes of the fluid become less effective and there is a greater likelihood that unwanted coke residue will develop within the system. This sludge usually accumulates in low-flow parts of the system like fluid reservoirs, as well as expansion tanks. Finally, oxidation also makes heat transfer fluids more acidic.
At room temperature the extent of oxidation is barely noticeable, but as the operating temperature of the heat transfer fluid rises, the rate is exponential. As a result, thermal system operators employ solutions to mitigate oxidation like nitrogen blanketing.
Thermal degradation is not caused by contact with air, but when heat transfer fluid temperatures rise beyond its boiling point. As the fluid overheats, its molecules start to break down and separate releasing vapours and producing unwanted coke which starts to coat the system surfaces. If this is not remedied it can result in total shutdown for the heat transfer system.
When thermal degradation takes place at particularly high temperatures, it will not only break carbon–carbon bonds, but it will separate hydrogen and carbon atoms, with the formation of coke happening as a result. Coke will then begin to quickly foul the heat transfer system surfaces, causing the potential end of the entire operation.
In worst case scenarios, the fluid’s auto ignition temperatures, along with its flash and fire points, can be decreased to unsafe operating levels.
Why fluid analysis is the answer
As no heat transfer fluid manufacturer can deliver absolute guidelines on fluid change intervals, the onus rests on users to monitor their system closely. Operators are always advised to use a dedicated fluid analysis programme which is professionally recommended to keep track the health of the heat transfer fluids in use. Fluid analysis is commonly offered as a free service or for a minimal fee from specialist vendors.
The benefit of using a comprehensive fluid analysis is that it can provide an early warning system which proactively detects any changes within the heat transfer fluid. By taking this preventative approach of continual monitoring and making use of a fluid maker’s fluid analysis programme, companies are given time to implement any necessary system corrections. This means that not only is the fluid’s overall condition improved but fluid degradation can be inhibited. If heat transfer fluid requires changing, operators will be the first to know.
