What Is Thermal Oil? Basic Guideline

What is thermal oil? These are the common questions that most people ask.

Actually, Thermal oils are a kind of medium used to carry thermal power in metalworking, process heating, and engine heating applications in a heat transfer system. Also, you can use these oils in different types of products, like circulating coolants, boiler & chiller fluids, anti-freeze, and refrigerants.

Besides this, it provides cooling within machinery, combustion engines, and process material. However, read on to learn what thermal oil is and more information.

What Is Thermal Oil?

Thermal oil is also known as heat transfer oil, HTF, or thermal fluid. Thermal oil can transfer heat from one heat source to another process because it’s also a heat transfer fluid. Additionally, this oil can do it from any exothermic process or combustion chamber.

The primary application is liquid-phase heat transfer. Also, it can control the process temperature to circulate a system. During working at high temperatures, this oil is subjected to corrosion.

Chemically, they are available in different forms:

  • Synthetic oils are aromatic compounds.
  • Petroleum-based oil, which is paraffin.
  • Synthetic glycol-based fluids.

You can find these oils in various specifications to suit different process needs. The maximum temperature range of currently available thermal oils is around 400 °C. You can use thermal oils in cryogenic applications down to -100 degrees Celsius.

Typically, thermal oil primarily can transfer heat from one place to another by any means capable of doing so. Hence, it can do it after preheating using burners, resistances, or other devices.

what is thermal oil

What Is Thermal Oil Used For?

Adequately, thermal oils are used in various applications and industries. Some thermal oil suits automotive, aerospace, marine, or military applications. Mainly, others are best for processing components, heat transfer applications, heating and cooling applications, etc. Unique heat transfer fluids can inhibit or prevent corrosion, oxidation, or microbial growth.

Biodegradable products break down into toxic chemicals when disclosed into the environment. Non-foaming properties are acquired through additives that break up entrained air. Heat transfer fluids are also rated for beverage, food, and pharmaceutical applications.

Examples of fluids used for high-temperature transfer include water glycol, mineral oil, propylene glycol in food, and synthetic fluids. Example names for such fluids include duratherm, dowtherm, and Mobiltherm.

Example Of Thermal Oil Applications:

  • Use as a heating jacket medium to maintain the hydrocarbons, viscosity of resins, and bitumen.
  • It also provides consistent laboratory-controlled temperatures to the pharmaceutical industry when handling high-value thin liquids.
  • Wood drying in kilns
  • Industrial heating in the food & textile industry
  • Cooking and maintaining cooking oil temperature can cause thermal decomposition due to burners.

What Are The properties of Thermal Oil?

Depending on the field of application, thermal oil contains various properties. Compared to steam and water, these oils’ advantages are that they are suitable as conductive media at temperatures above 200°C.

They can work as a heat transfer medium up to about 400°C. It is usually sufficient to use relatively inexpensive mineral oil in the temperature range up to a maximum of 300°C.

If the temperature exceeds this mark, it’s best to use synthetic oils. The reason is that they have high-temperature resistance, and you can use them for a long time.

Unlike water, heat transfer oil doesn’t need to be pressurized. For the system, this means lower load benefits. Other valuable properties of these oils are good thermal conductivity and resistance to oxidation.

Specific Heat Capacity of Thermal Oil

Thermal fluids are used as thermal energy storage media in several power technologies, from solar thermal heating to battery thermal management. Modern thermal fluids have a heat capacity of ∼50% that of water. And their viscosities are generally more than one order of magnitude.

The results show that the heat capacity of the proposed thermochemical liquid is considerably higher over a wide temperature range. In fact, its capacity is also higher than that of water between 60°C and 90°C.

The viscosity of a fluid is only three times that of water, and the operating temperature range is between −90°C and 135°C. Furthermore, a model was developed that allows the novel design of thermochemical thermal liquids with higher heat capacity.

Thermal Oil Boiling Point:

Thermal oil has a boiling point of 308°C (586°F). But a constant pressure of about 2 bar must be maintained in the liquid phase at high temperatures.

This product is non-corrosive to common heat transfer system materials of construction. And also it has a low odor and good handling properties.

Is Thermal Oil Flammable?

Thermal oil is a substance that can form flammable mists at high temperatures inducing fire and explosion hazards. Controlling the working temperature of thermal oil is crucial for the thermal oil heater’s safe operation. Though heat transfer fluid is a flammable substance, it has a high flash point of 249°F (120°C). The fire point of thermal oil is 255°F (124°C) and an autoignition temperature of 773°F.

Read Also Is Synthetic Oil Flammable?

Thermal Oil Price:

Price is crucial when you purchase a new thermal oil for your application. The cost will depend on your properties, so if the fluid is more extraordinary, its price will be higher.

You should select a cost-effective fluid for your facility without compromising the properties needed for the application. Generally, the mineral-based thermal oil price is around 3-4$ per liter, which can vary from brand to brand.

For Selecting the right one, Read Selection of Best Heat Transfer Oil

What Is a Thermal Oil Boiler?

You can use a thermal oil boiler instead of a traditional water and steam boiler. It is selected to acquire a high temperature at low operating pressure with oil as the heat-transfer medium.

According to the steam table for traditional water and steam boilers, high steam temperature equals high pressure. A non-pressurized hot oil boiler can achieve temperatures up to 300°C. In contrast, temperatures up to 400°C can be achieved with a pressurized hot oil boiler. A thermal boiler can produce heat in a furnace or Coal and transfer the heat to the application point by thermal oil.

Final Word:

In summary, Thermal oil is mainly a low-viscosity fluid that is slowly heated, cooled, and circulated. As mentioned above, thermal oils are subject to corrosion when operating at high temperatures. Thermal oil will fail prematurely as thermal oil forms new compounds and becomes more volatile.

It’s known as ‘thermal cracking,’ which lowers the fluid’s flash point. Some thermal oils can also burn when exposed to air. Overall, this is the article where we have described what is thermal oil and more information about this topic. We hope you know what thermal oil is. Thanks for reading this article.

Read Also: How To Increase The Service Lifetime Of Heat Transfer Oil?


Emon is Lubricants specialist who studied on Petroleum Engineering in UAE. He have more than 10 years experience on different kinds of lubrication including automobile troubleshooting.