Heat exchange characteristics of silicate and carboxylate-based coolants in air-cooled engine parts

Effective heat transfer is the most important duty of an engine coolant. The heat exchange characteristics of the cooling system are primarily defined by the physical properties of the coolant, the presence of coatings and air resistance. Good heat transfer properties result in lower local temperatures (reducing the risk of corrosion at heat rejecting surfaces) and allow for more efficient engine designs (less coolant is needed to achieve the same amount of heat transfer, therefore, smaller radiators, heater cores and coolant overflow bottles could be used). If a coating is present, it not only interferes with heat transfer by acting as an insulator, but it may also result in hot spots from the uneven heat distribution and induce localized corrosion. This paper will compare the heat exchange characteristics of silicate and carboxylate-based engine coolants by measuring the rate of heat transfer in a heater core exposed to an air current. The heat transfer rates are obtained experimentally. The experimental setup consists of a heater core, a coolant heater, a coolant pump, a thermostat and an air blower. The experiments were run at two different coolant flow rates (1 and 2 gpm) and one air speed (1.72 m/s). The study shows that there is a 7 - 8% improvement in heat transfer rate when using a light duty carboxylate-based coolant compared to a light duty silicate-based coolant. Theoretical calculations simulated what would be the predicted change in heat transfer with different thickness of deposits using programs written in FORTRAN and FLUENT.