The Effect of Radiator Size on Cooling Air Flow Requirements and Cooling Drag

The dischargeable heat output and the cooling drag of motor vehicles are largely determined by the radiator size and the cooling air mass flow rate. In the present work, the effect of varying the radiator size on the cooling air requirement and the cooling drag of a motor vehicle is investigated. The starting point is the assumption that the transferred cooling power remains constant when the radiator size is changed. Based on the physical principles of heat and momentum transfer, a simple mathematical representation of the relationship between the radiator size, cooling air demand, and cooling drag is developed for this case, enabling an overall representation in clear diagrams. The results are validated by an experimental example from the literature. In addition, the application of the new equations is demonstrated in a real vehicle project where the aerothermodynamic challenge was a reduction in radiator size. The developed equations and diagrams allow a quick overview of the relationships and dependencies and enable rapid estimation of the effects on cooling-air demand and drag resulting from a change in radiator size.