Extended surfaces or fins are employed in heat exchangers for effectively improving the overall heat transfer performance. This is especially imperative for air-cooled heat exchanger since the dominant thermal resistance is usually on the air side. The surfaces can be in the form of continuous surfaces (e.g. plain, wavy) or interrupted (louver, slit, offset, and the like). Several review articles by Wang[1–2] had reported the patents of enhanced surfaces relevant to the fin-and-tube heat exchangers. He reported that 90% out of the surveyed patents were related to the interrupted surfaces. However, the interrupted surfaces showed appreciable pressure drops in association with heat transfer performance. In this
connection, one of the recent designs is via introduction of the so-called vortex generator through which the heat transfer