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The discussion of non-aqueous (aka anhydrous or waterless) engine coolants begins with the acknowledgment of the superiority of liquid-state water as a medium of heat transfer. Even when the water is cut 50 % with the addition of a freezing point depressant, the resulting heat capacity and thermal conductivity parameters dominate in comparison to those figures for any practical non-aqueous fluid. The challenge for water-based coolant, however, is keeping it in its liquid state at all times under the high heat density conditions of modern engines and their EGR coolers. As water-based coolants are operated close to their boiling points, water vapor from localized boiling is not always surrounded by liquid coolant cold enough to condense it. Consequences of vapor accumulation are discussed. Non-aqueous coolants have atmospheric boiling points that are far hotter than the temperatures at which they are used. Localized boiling can still produce vapor but it condenses immediately into colder surrounding liquid coolant, avoiding the accumulation and pocketing of vapor. Just as the users of water-based engine coolants need the assurance of ASTM Standards with regard to functionality and corrosion protection, so do users of non-aqueous coolants. Additionally, the opening up of the use of new chemical compositions for coolants, offered by non-aqueous possibilities, require that coolant candidates conform to viscosity, thermal conductivity, and flash point limits. This paper discusses the development of standards and specifications for non-aqueous coolants, including the use of existing tests that may be used without changes, the modification of existing tests (making them become new tests), and tests that are entirely new.
non-aqueous, waterless, anhydrous, engine coolant
Light, Jonathan Thomas
Chief Engineer, Evans Cooling Systems, Inc., Suffield, CT