Experimental characterization of heat transfer enhancement in a circular tube fitted with Koflo Blade™ inline mixer

Abstract

This paper addresses the experimental study of heat transfer enhancement of laminar flow in a tube fitted with Koflo Blade™ inline mixer as the swirl-flow generator and under constant surface heat flux. Experiments were carried out with air as heat transfer fluid and two different types of the mixer having blades crossing angles of 90° and 120° The flow swirling in the mixer is mainly due to the centrifugal force induced by the angle between the blades, which is responsible for heat transfer augmentation. The results show that the mixer with 90° blades supplies Nusselt numbers higher than the 120° mixer but, likewise, results in higher pressure drop. The rate of heat transfer in the tube equipped with inserts was augmented up to 78% and 47% for 90°-blades and 120°-blades mixers, respectively. The enhancement in heat transfer was correlated with the Graetz number that supports the experimental data for both mixers by a deviation within ±10%. Furthermore, the tube fitted with a 120°-blades mixer yields higher thermal performance with a maximum value of 1.77. As well, the 120°-blades mixer provides thermal performance factors up to 17% greater than that for 90°-blades mixer for the same pumping power, which implies that heat transfer effects significantly dominate pressure drop effects.