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Thermal and swirl flow topologies in a twisted square duct with a multi-twisted tape installed
(2020-01-01)
Promthaisong, Pitak
;
Chuwattanakul, Varesa
;
Eiamsa-Ard, Smith
This paper presents 3D numerical investigation of the turbulent flow and heat transfer characteristics of a twisted square duct installed with multi-twisted tapes. Air was used as the working fluid with flow rates in terms of Reynolds numbers ranging from 3000 to 20,000. The effects of (1) multi-twisted tape width ratios (w/H) of 0.2 to 1.0 and (2) the number of channels (N = 2 and 4) on heat transfer and flow mechanisms were studied at constant twist ratio of y/D = 3.5. The numerical results showed that twisted square duct combined with twisted tape caused swirl flows which effectively promoted fluid mixing and provided heat transfer over those of both a straight smooth square duct and twisted square duct. Increasing w/H led to increases in both heat transfer and the friction factor. At a given multi-twisted tape width ratio (w/H), the heat transfer and friction factor with N = 4 were higher than those with N = 2, while thermal enhancement factor showed the opposite trend. A maximum thermal enhancement factor of 1.93 was obtained at tape width ratio of w/H = 1.0, channel number of N = 2 and Re = 3000.
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Thermal performance in circular tube with Co/counter-twisted tapes
(2014-01-01)
Chokphoemphun, Suriya
;
Hinthao, Chayodom
;
Eiamsa-Ard, Smith
;
Promvonge, Pongjet
;
Thianpong, Chinaruk
Thiswork presents an experimental study on enhanced heat transfer and pressure loss characteristics in a tube having a uniform heat-fluxed wall by using small double and triple co- and counter-twisted tapes at two twist ratios, y/w=4 and 4.5. The investigation has been conducted for Reynolds number from 5300-20,000. The experimental results of the heat transfer and pressure drop are proposed in terms of Nusselt number and friction factor, respectively.The experimental results reveal thatthe maximum TEF for the triple counter-twisted tapesat smaller twist ratio isabout 1.26. © (2014) Trans Tech Publications, Switzerland.
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Thermal characteristics in round tube fitted with serrated twisted tape
(2010-09-01)
Eiamsa-Ard, Smith
;
Promvonge, Pongjet
The article presents an investigation of the effect of twisted tape with serrated-edge insert on heat transfer and pressure loss behaviors in a constant heat-fluxed tube. In the experiments, the serrated twisted tape (STT) was inserted into the entire test tube with a constant twist ratio in order to generate a continuous swirling airflow. Two geometry parameters of the STT to be considered in the present work are the serration width ratio and the serration depth ratio. The measurements have been conducted for the airflow rate based on Reynolds numbers in the turbulent regime from 4000 to 20,000. The experimental results of the STT inserted tube are compared with those of the plain tube fitted with typical twisted tape (TT). The results show that the heat transfer rate in terms of Nusselt number, Nu increases with the rise in the depth ratio but decreases with raising the width ratio. The heat transfer rate is up to 72.2% and 27% relative to the plain tube and the TT inserted tube, respectively. The use of the STT leads to higher heat transfer rate and friction factor than that of the TT for all cases. The thermal performance factor of the STT tube under constant pumping power is evaluated and found to be above unity indicating that using the STT tube is advantageous over the TT tube or the plain tube. In addition, the empirical correlations developed by relating the serration width ratio, serration depth ratio and Reynolds number are determined. © 2010 Elsevier Ltd. All rights reserved.

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