In this comparative study of two industry heat transfer fluids, we demonstrated the superior oxidative resistance of Relatherm HT-2 High Temperature Heat Transfer Fluid over a competitor product. This study was done under simulated oxidation conditions using the Rotary Pressure Vessel Oxidation Test (RPVOT)/ASTM-D2272. Samples of both thermal fluid products were pressurized with pure oxygen along with water and a copper catalyst in a pressure vessel. Oxidative resistance is measured in terms of oxygen pressure drop and induction time. Oxygen pressure drop has a direct correlation with oxidative stability of the thermal fluid samples. A quick pressure drop indicates a higher reactivity with oxygen, a lower oxidative resistance and a potentially short service life. Of the two heat transfer fluids, Relatherm HT-2 was found to have the least reactivity with oxygen, the most delayed oxygen pressure drop and the longest induction time. This indicates that Relatherm HT-2 outlasts and outperforms the competitor fluid by virtue of its Extended Life Additive Technology even under advanced oxidative conditions.

Figure 1.0 – Graphical Results of RPVOT / ASTM-D2272 Test Results


We collected 100ml/3-4 oz. of two heat transfer fluid products. A virgin sample of Relatherm HT-2 was drawn from the inventory of Relatherm Heat Transfer Fluids. A virgin sample of Sample A manufactured by a Pennsylvania-based heat transfer fluid manufacturer was also collected from an end-user. All the samples were transferred into clearly labeled glass beakers.


We utilized a test apparatus consisting of two pressurized vessels axially rotating at 100 rpm, at an angle of 30° from the horizontal, in baths maintained at 150°C/302OF. 50 grams of each heat transfer fluid sample, 5 g of distilled water, and a freshly polished copper coil are placed into separate glass liners, and inserted into the pressurized vessels. The vessels are initially pressurized to 600 kPa/87 psi at room temperature. The 150°C bath temperature caused the pressure in the vessels to increase to approximately 1241 kPa / 180 psi. As oxidation occurred, the pressure dropped and the induction times were recorded. The results were reported as the induction time which is the number of minutes it took each sample to reach 100 kPa/14.5 psi loss.


The Relatherm HT-2 sample was found to have an induction time of 2,455 minutes while Sample A was found to 58 minutes. We observed a rapid drop in the oxygen pressure of the vessel holding Sample A indicating rapid oxidation. The vessel holding the Relatherm HT-2 sample demonstrated very low reactivity with oxygen and a longer induction time. As shown in Figure 1a and 1b below, the copper coil immersed in Sample A accumulated a significantly higher mass of sludge. No considerable sludge deposit was found in the copper coil inserted in the Relatherm HT-2.

Figure 1a. Copper Coil in Sample A
Figure 1b. Copper Coil in Relatherm HT-2 Sample


Based on the results of the comparative RPVOT/ASTM-D2272 test conducted, Relatherm HT-2 High Temperature Heat Transfer Fluid has a much higher resistance to oxidation and longer service life than Sample A.