Thermic Oil

High temperature heat transfer fluids are used in process applications where their optimum bulk fluid operating temperatures of 300°F to 750°F are safer and more efficient than steam, electrical, or direct fire heating methods. Selecting the proper heat transfer fluid for a new system while in the design phase or for possible process fluid improvements during an upcoming retrofit will assure sufficient and uniform BTU delivery (or removal). The properly selected heat transfer fluid will also minimize potential production loss and downtime due to required design changes, mechanical problems, or fluid failure.
The process of selecting the optimum heat transfer fluid should begin once the energy transfer required by the process and the planned/actual service ratings of the mechanical components of the heat transfer system have been calculated and thoroughly researched. Since there are of number companies specializing in heat transfer fluids and a wide range of fluid products available, the knowledge of this key element of the system's operating requirements can help to create a set of criteria that can be used to compare various fluids and allow rapid elimination of fluids that are not best suited for the application.
However, before comparing and contrasting various individual fluids, much time and effort in the selection process can be saved by comparing and contrasting the various chemistries of the fluids. Once a fluid chemistry is selected that best meets the performance properties and other criteria required by the application, the resultant list of potential fluids becomes significantly more manageable for more detailed apples-to-apples comparisons.

A heat transfer fluid's operating range is the temperature range between the pumpability point and the recommended maximum bulk fluid operating temperature. The pumpability point is roughly defined as the temperature where a fluid's viscosity reaches 2000 centipoise. At this point the fluid becomes too viscous for centrifugal pumps to maintain sufficient fluid flow. Although heat transfer fluids technically can be used at temperatures close to their pumpability points, many fluids (especially petroleum-based fluids) lose much of their heat transfer ability and efficiency when used close to their pumpability points.

A fluid's ability to withstand thermal cracking (thermal degradation) is the primary factor in setting its maximum bulk fluid operating temperature. This temperature is the maximum temperature the fluid manufacturer recommends the fluid can be used and still maintain an acceptable rate of degradation over time.

Typically, a good fit between a heat transfer fluid and an application happens when the required fluid temperature of the process falls right in the middle of the operating range of the heat transfer fluid. This "cushion" on either side of the operating temperature allows for good overall heat transfer efficiency and minimal fluid degradation.

As a general rule of thumb, the higher the maximum bulk fluid operating temperature, the more expensive the fluid. This is due to the fact that the chemistries required to achieve acceptable thermal stability and heat transfer efficiency at elevated temperatures gets more complex and expensive as the temperature increases. The two primary types of fluids used by the majority of high temperature applications are:

Aromatics: Also know as "synthetics". These consist of benzene-based chemistries and, depending on he specific type, have a bulk fluid operating range generally from -70°F to 750°F.

Petroleum-based: Also known as "hot oils". These consist of paraffinnic and/or naphthenic hydrocarbons. The bulk fluid operating range for these fluids are generally from -10°F to 600°F.