Thermal Performance Analysis of a Cross-Flow Automotive Radiator under Variable Air and Coolant Flow

The study examines the thermal performance of a cross-flow automotive radiator typically used in internal combustion engine vehicles, where 8–30 kW of heat must be dissipated under varying operating conditions. Radiator cooling efficiency primarily depends on air velocity (1–6 m/s) and coolant flow rate (0.05–0.3 kg/s), with air-side management exerting the strongest influence. Experimental analysis showed a maximum coolant-side heat transfer rate of 26.25 kW, with Reynolds numbers between 16,650- 2,800 yielding a convective coefficient of 22.49 kW/m²K. On the air side, Reynolds numbers of 217–1,520 correspond to a heat transfer coefficient of 168 W/m²K and a peak heat flow of 23.8 kW. The overall heat transfer coefficient reached 167 W/m²K. Coolant temperatures decreased significantly along the radiator core, with low flow rates achieving large temperature drops (90°C to ~ 64.3°C), while higher flow rates enhanced total heat removal through increased turbulence. Variable air velocity from 1 m/s to 5 m/s markedly improved convective heat transfer, confirming the dominance of air-side effects. System-level analysis highlights that, since pump flow depends on engine speed, variable-speed fan control provides the primary means of adjusting heat rejection in real time, improving thermal efficiency and reducing energy consumption in modern automotive cooling systems.