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Heat transfer enhancement by twisted tapes with alternate-axes and triangular, rectangular and trapezoidal wings
Authors:Khwanchit Wongcharee  Smith Eiamsa-ard
Affiliation:a Department of Chemical Engineering, Faculty of Engineering, Mahanakorn University of Technology, Bangkok 10530, Thailand
b Department of Mechanical Engineering, Faculty of Engineering, Mahanakorn University of Technology, Bangkok 10530, Thailand
Abstract:The effects of twisted tapes with alternate-axes and wings on heat transfer, flow friction and thermal performance characteristics in a round tube are investigated. The influence of wing shape including triangle, rectangle and trapezoid is also studied. The experiments are performed using twisted tape with three different wing-chord ratios (d/W) of 0.1, 0.2 and 0.3 and constant twist ratio (y/W) of 4.0. The alternate-axis is made by arranging each plane of twisted tape to 60 degree difference relative to the adjacent plane. The results show that both heat transfer rate and friction factor associated by all twisted tape are consistently higher than those without twisted tape. Under the similar operating conditions, Nusselt number, friction factor as well as thermal performance factor given by the tape with alternate-axes and trapezoidal wings are higher than those given by the others. It is also found that that Nusselt number, friction factor and thermal performance increase with increasing wing-chord ratio. The maximum thermal performance factor of 1.42 is found with the use of twisted tape with alternate-axes and trapezoidal wings at d/W = 0.3, where the heat transfer rate and friction factor, respectively increase to 2.84 and 8.02 times of those in the plain tube.
Keywords:T-A  twisted tape with alternate-axes  TT  typical twisted tape  T-Rec  twisted tape with rectangular wings and alternate-axes  T-Tra  twisted tape with trapezoidal wings and alternate-axes  T-Tri  twisted tape with triangular wings and alternate-axes
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