A combinatorial method was used to determine the smallest size of the radiator that can satisfy the heat duty requirements under all driving conditions on the warmest day (taken as 42 ◦C in this study). It was found that a cross-flow radiator of plate-fin construction with 60 cm × 50 cm frontal area and 1mm high coolant passages that are 9mm apart can suffice.The fins on the air side of the radiator have 1mm pitch. The depth of the flow passages was determined from the calculated heat transfer area to be 5.4 cm for the high-temperature radiator and 4.5 cm for the low-temperature radiator for a 120kWe FCS. Fig. 9a presents the performance of the hightemperature radiator as a function of vehicle speed. It compares the required heat duty of the radiator and its maximum