Turbulent heat transfer, pressure drop and fin efficiency in annular regions with continuous longitudinal rectangular fins

Abstract

Abstract Experiments were performed to determine average heat transfer coefficients and friction factors for turbulent flow through annular ducts with continuous longitudinal rectangular fins. In addition, the fin efficiency was also determined by means of a numerical two-dimensional heat transfer analysis. The total number of fins attached to the inner wall of the annular region was 20. The measurements were made by using a double-pipe heat exchanger. The fluids were, air flowing in the annular section, and water through the inner tube. The average heat transfer coefficients were obtained from the experimental determination of the overall heat transfer coefficients of the heat exchanger. To attain fully developed conditions at the entrance and exit, the heat exchanger was built with additional lengths before and after the test section (30 hydraulic diameters). The double-pipe heat exchanger and fins were made of brass. Due to the high thermal conductivity of the brass and the small water temperature variation, the surface of the inner tube was practically isothermal. The external tube was well insulated and can be considered adiabatic. The results are presented in dimensionless forms, in terms of the average Nusselt number, friction factor and fin efficiency, as functions of the flow Reynolds number. A comparison of the present results with those for smooth sections (without fins) is also presented. The purpose of such comparison is to study the influence of the presence of the fins on the pressure drop and heat transfer rate.