Cool air is then forced across the radiator’s core, by a fan and by using air produced by the motion of the vehicle, to absorb and remove the heat from the coolant. During the entire process two main forms of heat transfer occur: 1) convection due to the internal flow of fluid passing through non-circular tubes and 2) convection due to the external flow of air across the tube bank. Fig. 3 shows the single tube geometry and the internal fluid flow direction through the tubes.