Experimental measurements of heat transfer in an internally finned tube

Abstract

This paper reports new experimental data for turbulent fluid flow and heat transfer in a tube having internal fins. An experimental set-up was designed to study the heat transfer performance in the entrance region as well as in the fully-developed region. The tube and the fin assembly was cast from aluminum to avoid any thermal contact resistance. The length of the test section was 15.2 m. The inner diameter of the tube was 70 mm. The tube contained six equally spaced fins of height 15 mm. Air was used as the working fluid in all experiments. The Reynolds number based on hydraulic diameter ranged from 2.6×10 4 to 7.9×10 4. Heat was supplied from an electrical heating system providing an uniform heat flux around the tube periphery over the entire length of the test section. Results exhibited high pressure gradients and high heat transfer coefficients in the entrance region, approaching the fully developed values away from the entrance section. Nusselt numbers of the finned tube were compared with those for an unfinned (smooth) tube for both constant Reynolds number and constant pumping power.The enhancement of heat transfer rate due to integral fins was found to be very significant over the entire range of flow rates studied in this experiment. Heat transfer coefficient, based on inside diameter and nominal area of finned tube exceeded unfinned tube values by as much as 112%. When compared at constant pumping power, an improvement as high as 52% was observed for the overall heat transfer rate. The results of this study indicates that significant enhancement of heat transfer is possible by using internal fins without sacrificing any additional pumping power. The experimental results are expected to be very useful for the design of pipelines and heat exchanger tubes.