Turbulent Heat Transfer and Friction Factor in Circular Tube Fitted with Opposite/Parallel

Rectangular Wing Twisted-Tapes

V. Kongkaitpaiboon, K. Nanan and S. Eiamsa-ard

Department of Mechanical Engineering, Faculty of Engineering

Mahanakorn University of Technology, Bangkok 10530, Thailand

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Manuscript received September 3, 2010,

Revised September 15, 2010

 

 


ABSTRACT

The influences of rectangular wing twisted-tape inserts on heat transfer and friction factor behaviors in a heat exchanger tube are reported. The rectangular wing twisted tapes with a constant twist ratio (y/W), were arranged in two different forms: (1) opposite rectangular wing twisted-tape (OW-T) and (2) parallel rectangular wing twisted-tape (PW-T). The experiments were performed using water as a working fluid under a uniform wall heat flux condition, for the Reynolds number range between 5500 and 22,000. The plain tube and the tube with typical twisted tape (TT) were also tested at the same operating conditions, for comparison. The experimental results reveal that the heat transfer rate, friction factor and thermal performance factor of the OW-T and the PW-T are considerably higher than those of the TT. For the range examined the increases of mean Nusselt numbers in the tubes equipped with the OW-T, PW-T and TT, are, respectively, found to be 110%, 100% and 27.5% over the plain tube with no insert. The average thermal performance of the OW-T is higher than those of the TT and PW-T at 24.9% and 2.74%, respectively and the maximum thermal performance factors by the TT, PW-T and OW-T are 0.96, 1.36 and 1.4. In addition, the correlations of the Nusselt number, friction factor and thermal performance factor of the tubes with the OW-T and PW-T are also developed in terms of Reynolds number (Re) and Prandtl number (Pr).

 

 

Keywords: Turbulent flow, Heat transfer enhancement, Twisted tape, Thermal performance factor

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