Heat transfer enhancement of wavy fin-and-tube heat exchangers via innovative compound designs

The present study examines some novel improvements in association with the airside performance of wavy fin-and-tube heat exchangers. Effects of waffle height, adding slits on wavy fins and vortex generators on the thermal resistance of wavy fin-and-tube heat exchangers are investigated. Increasing waffle height, imposing slits on the wavy fin, or adding vortex generators can provide 6-10% reduction in thermal resistance subject to constraints of the same pumping power. Yet, the compound design including all these three features together is even more powerful to achieve a 16% reduction of thermal resistance. Increasing waffle height will decrease thermal resistance, but the accompanied pressure drop is even higher. Hence, it is highly recommended that the waffle height should be less than the fin pitch or at a corrugation angle being less than 15 degrees. Punching slits on the top of wavy fin surface can result in 6-7% decrease in thermal resistance. Effect of increasing the width of slits on heat transfer characteristics is negligible. Conversely, increasing the length of slits is much more effective. It can be seen from the results that slits with a length of 12 mm and a width of 1 mm yield 8-10% reduction in thermal resistance.