In power plants and heat exchangers, lubricants are used as test media, specifically, high-temperature heat carriers, heat-insulating materials, fuel mixtures, etc. (O’Connor and Boyd, 1969; Braithwaite, 1967; Franke, 1971; Zerbe, 1969; IFP, 1969; Hersey, 1966).

Organic petroleum oils are a mixture of hydrocarbons and their derivatives. Animal and plant oils are primarily used as additives to petroleum oils. Synthetic oils serve as petroleum oil substitutes at very low and high temperatures for cases of elevated fire danger, etc. The oil quality is improved by alloying additives such as antiwear and viscosity additives, set point additives (for lowering solidification temperature), detergents, anticorrosion additives, etc. At positive temperatures, oils serve as Newtonian fluids. Polymer thickening of oils produces a viscous anomaly.

Plastic lubricants consist of a homogeneous medium (oil) and a solid phase: fatty acid salts (soaps), solid hydrocarbons, silica gels, and bentonites with additives and solid additions (graphite, metal powders, etc.). Very long particles form a mobile structure that undergoes reversible destruction beyond the yield stress, and the lubricant flows as a rheologically complex nonlinear viscoplastic fluid (Shulman, 1975).

Oil lubricant-cooling liquids (LCL) alloyed with additives are used in metal processing as well as in heat exchangers and hydraulic systems. In aqueous LCLs, the emulsifying agent envelopes oil particles and prevents their coalescence. Emulsions may be weakly non- Newtonian and Newtonian fluids.

References appear at the end of Section 516.