A fine surface roughness about 20micrometers on air-cooling heat exchanger fins, where steam vaporin the atmosphere condenses to dewdrops, improves wettability of fin surfaces and changes thedewdrops to a thin film of water. The water easily falls off the fin due to the force ofgravity, and the airside pressure loss decreases by 30% compared with that of smooth-surfacefins. Changing the smooth surface to the rough surface has no adverse effect on the heattransfer coefficient of louvered fins, which have many louvers parallel to the airflow. Newand high performance evaporators for automobiles have been developed using a combination ofrough-surface fins and louvered fins.