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Oil cooling is the process of removing heat from machinery and electrical components with oil as a transfer medium. The process typically involves circulating cool oil past the heat source, thereby allowing it to absorb thermal energy, and then circulating the hot oil to a cooling mechanism where it sheds the heat. Oil is an ideal liquid coolant medium because it has a higher boiling point than water. The oils in cooling applications are typically mineral varieties produced as byproducts in the petroleum refinement process.
Although oil is not often though of as a “cold” liquid, it makes an appropriate coolant medium nevertheless. It readily absorbs thermal energy and features a boiling point higher than water, thereby allowing it to be used for cooling components with temperatures in excess of 212° F (100° C). It is also an electrical insulator when free of moisture and impurities.
This form of cooling is typically an immersion process where heat sources operate within an oil bath. The process relies on the oil absorbing thermal energy from direct contact with the hot equipment. Once heated, the oil then circulates through convection or is pumped out of contact with the heat source to a radiator where it sheds the heat into water or the air. It then moves back to the heat source to repeat the cycle. This process is a good example of heat transfer cooling where thermal energy is moved or transferred from a high temperature source to a low temperature sink or absorber.
The oils used in oil cooling applications are typically mineral varieties although plant varieties are sometimes used. These oils are byproducts of petroleum refinement and are typically low to medium viscosity, colorless combinations of alkanes and cyclic paraffins. Several additives are included in cooling oils to enhance their performance including corona and arc suppressants, fire retardants, and corrosion inhibitors.
Electrical oil cooling applications include transformers, switchgear, and oil bath welding machines. Oil is also used to cool high performance electronic components; several experimental computers feature main boards and processors totally submerged in mineral oil. Mechanical oil cooling applications include machining operations such as cutting, milling, and turning where oil is used to lubricate and cool the tool tip. The lubricating oil in automobile engines also serves as a coolant, thereby absorbing heat from the combustion area and shedding it through a separate oil cooler or the reserve oil in the engine sump. Large industrial gearboxes and drive trains also utilize combined oil lubrication and cooling.