Characterization of Heat Transfer by Overlapped-Quadruple Counter Tapes

Abstract

This paper deals with the influence of overlapped-quadruple twisted tape (OQT) and typical quadruple twisted tape (QT) on the enhancing heat transfer rate in a heat exchanger tube. The effects of tube orientation (co-tapes and counter tapes), tape arrangement (cross and parallel arrangements), and overlapped twist ratio (yo/y = 0.625, 0.75, and 0.875) were investigated. The experiments were performed in the turbulent flow regime (5000 ≤ Re ≤ 20,000) under uniform wall heat flux boundary condition, using air as the testing fluid. The experimental results indicates that all OQTs consistently yield higher Nusselt number and thermal performance than QTs. The tapes in cross arrangement show better heat transfer enhancement and thermal performance than the ones in parallel arrangement. Heat transfer, friction loss, and thermal performance increase with decreasing overlapped twist ratio. The maximum thermal enhancement factor (TEF) of 1.58 is achieved by the use of overlapped-quadruple counter tapes in cross arrangement (CC-OQTs) with yo/y = 0.625 at the lowest Reynolds number of 5000.