A Numerical Simulation of Heat Transfer Characteristic of Twisted Tube in an Annular Heat Exchanger

Abstract

AbstractHeat transfer performance of heat exchanger system play significant role toward energy conservation. In this research, numerical simulation using ANSYS was conducted to evaluate the performance of square twisted tube and oval twisted tube for heat transfer enhancement. A comparative models were developed to evaluate the geometry alternation on heat transfer coefficient and pressure drop. The analysis revealed that the square twisted tube heat exchanger has better performance and smaller friction factor compared to the oval twisted tube heat exchanger. Moreover, a computational fluid dynamics (CFD) simulation with a realizable k-ε was used to investigate the influence of twist pitch length on the heat transfer performance and pressure drop. The geometrical parameters include two different cross-section shapes and two different twist pitch lengths of the square twisted tube heat exchanger. The twist pitch lengths used in the investigation are 160 mm and 200 mm. The numerical results shown that the tube with the smallest pitch length offers a higher friction factor and Nusselt number. In addition, heat transfer mechanism of twisted tubes, velocity, streamlines, Nusselt number distribution, and temperature distribution are presented. Heat transfer enhancement of the square twisted tube heat exchanger is associated with the secondary flow production by the curved tube wall. In the oval and square twisted tubes, a secondary flow is formed which offers a longer flow path, hence an enhanced heat exchanger performance. It concluded that alternation of geometry on tube surface is potential to improve the overall performance with acceptable pressure drop.KeywordsHeat transferTwisted tubeCFDTwist pitchNusselt number