Application Considerations: Mobiltherm heat transfer oils should not be mixed with other oils since this may impair the excellent thermal and oxidation stability of the Mobiltherm oils, cause a change in other properties, and complicate the interpretation of analyses made to determine the oil's useful life. If the oils are used above their recommended maximum temperatures, vapor lock may result unless the system is designed to operate at the higher temperature by pressurising with an inert gas such as nitrogen. However, at higher temperatures, fluid life will be shortened because the rate of thermal degradation increases markedly as temperatures rise above the recommended limit. In well-designed systems the temperature of the oil film surrounding the heating element should be about 15ºC to 30ºC above the bulk oil temperature. If higher than this, the service life of the oil may be shortened and sludge and coke may be deposited which would interfere with the heat transfer rates. As with other mineral oils, Mobiltherm heat transfer oils should be used only in systems with forced circulation. Systems that depend on convection for circulation of the heat transfer medium do not provide a rapid enough flow to prevent local overheating and rapid deterioration of the oil. Further, these oils are not recommended for use in open systems where hot oil is exposed directly to the air. If they spray or escape from leakage points, hot Mobiltherm oils may spontaneously ignite.
Mobiltherm 603 and Mobiltherm 605 can be used in open and closed installations where the bulk oil temperature ranges are as outlined in the table below and where minimum shutdown temperatures are not below -7ºC.
- Bulk Oil Temperature Ranges for Mobiltherm 603: Closed Systems (-7 C to 285 C), Open Systems (-7 C to 150 C)
- Bulk Oil Temperature Ranges for Mobiltherm 605: Closed Systems (-7 C to 315 C), Open Systems (-7 C to 180 C)
- Closed, cold-oil sealed, indirect heating and cooling systems in all kinds of industrial processes operating at bulk oil temperatures up to the maximum temperatures quoted in the table above and at atmospheric pressure.
- Open systems provided the bulk temperatures do not exceed the maximum temperatures quoted in the table above.