Fluid Life Tests
While oxidation is the #1 reason that heat transfer fluids need to be replaced, it doesn’t always follow that using a fluid with an oxidation inhibitor will prevent oxidative sludging.
Oxidation inhibitors are chemical additives designed to prevent the sludge formation, acidification, and viscosity increases that result when air and hot heat-transfer-fluid molecules meet. These additives, which can prevent such viscosity-related symptoms as slow startups and even fluid solidification at room temperature, don’t last forever though. They are sacrificial in nature and are used up steadily as the fluid is exposed to air.
Figure 1 — Oxidation can influence fluid color and consistency; but darkened color doesn’t always indicate oxidative deterioration
The rate of inhibitor depletion is increased when there is greater exposure to air (by circulating the fluid in the expansion tank for example) and higher temperature (depletion rate doubles with every 10°C increase in temperature). So problems can hit hard when these additives are completely depleted leaving the fluid unprotected and ready to begin its new life as an uninhibited fluid. And sometimes, the problems that the additives have been holding off, such as the viscosity issues mentioned above, can crop up quickly and unexpectedly.
Does lab testing tell the whole story?
Answer in our next post. Read it here: Air and Heat Transfer Fluids Part 2