6. Thermal and flammability characteristics

6.1 Heat transfer properties

In many applications, in addition to its lubricating function, the oil must also perform a cooling function to dissipate heat and limit contact temperatures.

The thermal conductivities of mineral oils are 4 to 5 times lower than those of water. They decrease linearly with temperature, from 0.14 W/m · K at 0°C to 0.11 W/m · K at 400°C. At standard temperatures (20 to 60°C), the average value is 0.13 W/m · K. Those of conventional synthetic oils (esters, synthetic hydrocarbons such as polyalphaolefins (PAO), polyisobutenes (PIB) and dialkylbenzenes (DAB) are very close to those of mineral oils (0.12 to 0.17 W /m · K at 20°C), those of polyglycols are slightly higher (0.15 to 0.18 W /m · K), those of esterphosphates are around 0.13...