Performance of a guided plate heat sink at high altitude

•Thermal/hydraulic performance of a fan driven heat sink is analyzed at sea level to 12,000 m.•Optimal design parameters for a parallel fin heat sink are determined under different operating conditions.•A guide plate enhances the thermal performance of the heat sink under all operating conditions.•Weight optimization is influenced more thermal performance at high altitude and low fan speed.•Optimization results at sea level are usually not suitable for high-altitude condition.