Thermal heaters, also known as thermal fluid heaters, employ the use of a thermal liquid such as water, glycol, mineral oil, synthetic liquids or aromatics as the source of heat transfer. The medium for transferring heat is circulated within a closed loop system to supply heat to the end user. In many applications, mineral oil is primarily used as a heat transfer medium.

When it comes to selecting the best medium of heat transfer, a lot of factors are taken into account. For example if the application requires a higher temperature range of up to 330 degrees Centigrade, a synthetic liquid would be preferred because of its thermal stability at high temperatures. On the other hand, mineral oil experiences about six times the rate of degradation if exposed to higher temperatures.  In such situations, the life expectancy of the transfer medium is considered which is determined by the liquid’s thermal stability. However the life expectancy of the medium is not always affected by its thermal stability; there can be multiple operating problems that can influence the life expectancy as well. More than often, the hardware and mechanical issues dictate the duration of stay of the liquid medium in the system.

When the mechanical aspects are considered, mineral oils have the edge over synthetic fluids and when mineral oils are used as the medium for transferring heat, they are called ‘thermal oil heaters’. Some of the advantages of using mineral oils are:

• Mineral oils are inexpensive when compared to synthetic liquids, of which the initial cost is two to three times greater than the initial cost of mineral oil. There is loss of the thermal fluid during the maintenance of a thermal heater and it costs a lot to replace the fluid back into the system. Even if the cost of replacing the fluid is higher, the cost of replacing mineral oil will be much less than the costs associated with replacing a synthetic fluid.
• Once the mineral oil is used up, it can be mixed with fuel to be used in oil-fired boilers. Hence, the cost of disposing mineral oil is less and much easier than to that of synthetic fluids.
• There is much less odor associated with mineral oils than with synthetic liquids.
• If a spill occurs, it doesn’t require comprehensive reporting as compared to synthetic fluids.
• Mineral oils are benign as compared to synthetic liquids.
• Some synthetic fluids require higher atmospheric pressures to reach higher temperatures, whereas mineral oils can reach a high temperature of up to 300 degrees Centigrade without the need of increasing the pressure.
• Thermal oil systemsrequire little maintenance when compared to thermal heaters that use synthetic fluids.
• It is easy to determine the level of impurities present in mineral oil by looking at its color. The color basically shows the type of molecules contained within the oil. The oil with the least amount of impurities will be water white.

Mineral oil is favoured in certain thermal fluid heaters due to its ability to absorb large amounts of heat without changing state.