Experimental study on the pressure drop and heat transfer characteristics of tubes with internal wave-like longitudinal fins

Experiments were performed to determine the heat transfer and pressure drop characteristics in the entrance and fully developed regions of tubes with internal wave-like longitudinal fins. The test tube has a double-pipe struc ture, with the inner tube as an insertion. The wavelike fins are in the ann ulus and span its full width. Experiments were conducted for two cases: one with the inner tube blocked (no air flowing through it) and the other with the inner tube unblocked. The outer tube was electrically heated. Local an d average heat transfer coefficients and friction factors were measured. Th e friction factor and Nusselt number correlations in the fully developed re gion were obtained in the Reynolds number range of 9 x 10(2) to 3.5 x 10(3) . It has been found that the wave-like fins enhance heat transfer significa ntly with the blocked case being superior. In addition, the in-tube heat tr ansfer process is characterized by an earlier transition from laminar to tu rbulent flow and Reynolds number-dependent thermal entrance length.