Experimental study on the pressure drop and heat transfer of two different tubes with plain-rectangle internal fins

Pressure drop and heat transfer characteristics of air in two tubes with internal longitudinal plain fins were investigated experimentally at constant wall heat flux. The tested tube has a double-pipe structure, with the inner blocked tube as an insertion. Two different fins, plain-rectangle fin and perforated plain-rectangle fin, are in the annulus and stretch its full width in a wavy manner. The friction factor and Nusselt number correlations in the fully developed region were obtained within the Reynolds number range from 400 to 4000. The comprehensive heat transfer characteristics of the tested tubes were evaluated using three criteria: identical mass flow, identical pumping power and identical pressure drop. The results show that perforated internal longitudinal finned tube provides more excellent comprehensive thermal performance than the other at the same geometrical parameter.