Air and Heat Transfer Fluids, Part 1

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.

7 fluid samples ranging from clear to nearly black in color

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

4 Responses to 'Air and Heat Transfer Fluids, Part 1'

  1. RANDY FRAZIER says:

    Mr. Jim I run and operate 3 asphalt plants here in columbus GA.and we use waste oil to fire/run our burners and they have jacketed lines,the temps on the jacketed lines range from 120-170 f degrees and our AC tanks have jacketed line and they run temps of 300-350f degrees. My problem is sludge and debree build-up and lines get cold causing slow or no production until we can get the line blew out or cleared. Do you have any suggestions with the products that your company carries. thanks lines are getting cold. looking at broucher right now

  2. joetinger joetinger says:

    1. an additive cleaner like the Paratherm LC System Cleaner will clean out the sludge in the jacketed lines. Run it until the lines are hot again and then change the oil.
    2. Changing to a fluid with an additive package that is supposed to prevent sludge won’t cure the problem, it’s just a Band-Aid that is only going to last so long. The cure is to figure out what is causing the sludge/debree etc. HINT: It involves the expansion tank. I’ll contact you offline to discuss further.

  3. Arsalan Ahmed says:

    Dear Sir:

    We have a problem with our oil. We have been using heat transfer Oil and in two years span of time the oil got oxidized badly. The oil company said that there is no problem with the oil. Now advise what could go wrong in our operation that impacted oil. We have oil boiler to heat our plate that used in our chip board manufacturing process.
    Waiting for your reponse.

  4. Andy Andrews says:

    If your oil supplier said there was no problem with the badly oxidized oil, we would suggest you have the oil analyzed by a third party. Contact us to find a laboratory in your region that will perform the proper testing for heat transfer fluids. Lube oil tests are not sufficient.

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