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Heat Transfer Base Fluid Selection

The first and most basic requirement of an engine coolant is to transfer heat from the internal combustion engine to the radiator, where the fluid is cooled by means of airflow. The coolant may also need to provide protection against freezing and boiling, all year round.

The effectiveness of a coolant in relation to these requirements is predominantly determined by the base fluid. Commonly used base fluids are mixtures of monoethyleneglycol/water, monopropyleneglycol/water or simply water when the coolant is used in temperate climates.

Ethylene Glycol (EG) formulations are the most common antifreeze and coolant products providing year-round freezing, boiling and corrosion protection. Ethylene Glycol is preferred over Propylene Glycol (PG) not only because of its higher flash point, but also mainly because of its better thermal or heat transfer properties. In particular, EG has a lower viscosity (better fluidity) than PG, thereby assisting heat transfer.

In temperate climates where freeze protection is not required, formulated water-only systems remain the better heat exchange fluid even compared to any mixture of EG and water. With EG or PG systems, a compromise between the required freezing protection and heat exchange efficiency has to be made. As engine efficiency is increased, in part by increasing engine temperature, more heat must be rejected through the cooling system. Additional cooling can be provided through higher cooling system pressure and by allowing the coolant to circulate at a higher maximum temperature. The boiling point difference of a premixed 50% volume EG coolant versus water-only systems is only about 8°C.

The PrixMax OAT product range offers a comprehensive choice of heat transfer base fluids. The application, climatic conditions and target market should all be carefully considered before selection of the base fluid.