Abstract
The presence of curvature-induced secondary flow in helical pipe which create complex transport phenomena and higher transfer rate has attracted significant attention from both academic and industry. Flow behavior and transport processes in helical tube have been intensively investigated. Nevertheless, most studies were focused on the performance based on first law of thermodynamics with limited studies concerning the performance based on second law of thermodynamics. The objective of this study is to investigate the heat transfer performance of helical tube according to both first and second law. The heat transfer rate and entropy generation of helical tubes with various cross-sections, i.e. circular, ellipse and square, subjected to constant wall heat flux conditions are numerically evaluated by utilizing computational fluid dynamics (CFD) approach. Their performances are compared to those of straight tube with identical cross-section. The results indicate that helical tube provides higher heat transfer at the cost of higher pressure. Moreover, it was found that entropy generation in helical tubes is considerably lower as compared to that in straight tube. Among the studied cross-sections, square has the highest heat transfer albeit having the highest pressure drop and entropy generation for both straight and helical tubes.
Highlights
The complex transport processes occur in helical tube due to the presence of curvatureinduced secondary flow has attracted considerable attention from researcher worldwide
Characteristic of secondary flow in helical tube and other coiled tubes are primarily dictated by Dean Number, a dimensionless parameter which is defined as the ratio of the viscous force acting on a fluid flowing in a curved pipe to the centrifugal
Secondary flow can be clearly observed at the region near the outer wall
Summary
The complex transport processes occur in helical tube due to the presence of curvatureinduced secondary flow has attracted considerable attention from researcher worldwide. Initiated by the pioneer work of Dean [1,2] using Toroidal tube, a string of studies on helical tube have been carried out. Subsequent studies revealed that helical tube provides higher heat transfer at smaller footprints as compared to straight tube. Many industrial processes have adopted helical tubes to achieve higher performance. Driving by the need to continuously improve and intensify heat transfer process, a vast number of studies on the heat transfer performance of helical tubes have been conducted and reported
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