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Heat transfer visualization of swirling impinging jets using nozzle with centrally hollow helical-tape
(2020-05-01)
Eiamsa-Ard, Smith
;
Kunnarak, Kengkla
;
Wongcharee, Khwanchit
;
Chuwattanakul, Varesa
The present research was conducted to determine the heat transfer visualization of swirling impinging jets (SIJs) induced by nozzle with centrally hollow helical-tape using a thermochromic liquid crystal (TLC) sheet. The effects of jet-to-plate spacing ratios (L/D= 2.0, 4.0, 6.0 and 8.0) and Reynolds numbers (10,000 Re 20,000) on the radial uniformity and intensity of convective heat transfer were investigated. The experimental results of SIJs were compared with those of conventional impinging jets (CIJs). The formation of swirl flow of swirling impinging jet (SIJs) helped in improving the uniformity of local heat transfer or Nusselt number (Nu) and also average Nusselt number, as compared to those of conventional impinging jets (CIJs). Furthermore, the average Nusselt number (Nu) increased as jet-to-plate spacing ratio (L/D) decreased while Reynolds number (Re) increased for both conventional impinging jets (CIJs) and swirling impinging jets (SIJs). The highest Nusselt number (Nu) of swirling impinging jet (SIJ) was obtained at the jet-to-plate spacing ratio (L/D) of 4.0 and Reynolds number (Re) of 20,000. The maximum Nusselt number (Nu) of swirling impinging jet (SIJ) was higher than that of conventional impinging jets (CIJs) at similar conditions by around 5.3%.
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Effect of geometrical parameters on turbulent flow and heat transfer behaviors in triple-start corrugated tubes
(2018-01-01)
Promthaisong, Pitak
;
Jedsadaratanachai, Withada
;
Eiamsa-Ard, Smith
Computational results of flow structure, pressure loss and heat transfer characteristics in triple-start corrugated tubes are reported. The influences of the depth ratio (DR = 0.02, 0.04, 0.06, 0.08, 0.1, 0.12, 0.14 and 0.16) and pitch ratio (PR = 0.5, 0.65, 0.75, 1.0, 1.5 and 2.0) were investigated in turbulent flow regime, Re = 5000 to 20,000. The computational results indicated that the triple-start corrugated tubes generate main swirl flow and helical swirl flow which helps to reduce the thermal boundary layer thickness and enhance the heat transfer rate. The flow and heat transfer become under fully developed periodic condition around x/D = 6.0. The friction factor monotonically increases with the rise of DR values and decrease PR values while maximum heat transfer rate is found at DR = 0.08 and PR = 0.75. Nusselt numbers and friction factors of triple-start corrugated tubes in the investigated range are found to be 0.8 to 2.31 and 1.0 to 17.14 times over those of the straight circular smooth tube, respectively. For the range studied, the triple-start corrugated tube with DR = 0.06 and PR = 0.75 offers the maximum thermal enhancement factor of 1.21 at Re = 5000.
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Thermal performance evaluation of micro-fin tube with twisted tape inserts
(2015-01-01)
Eiamsa-Ard, Smith
;
Kunlabud, Suttisak
;
Wongcharee, Khwanchit
;
Pimsarn, Monsak
;
Eiamsa-Ard, Petpices
The heat transfer coefficient and pressure drop characteristics of turbulent flow through micro-fin tubes fitted with twisted tape in co/counter-arrangement have been studied. In the experiments, water as the tested fluid is passed in a Reynolds number range of 7800 to 17,650. The results reveal that, the Nusselt numbers in the system with a micro-fin tube and twisted tape are considerably higher than those in the system without tape. Evidently, the tape with the smaller twist ratio gives higher heat transfer rate, friction factor as well as thermal performance factor than the one with larger twist ratio as a result of a larger contact surface area, and stronger turbulence intensity and thus better fluid mixing which leads to a thinner thermal boundary layer. The result reveals that for using the micro-fin tube with twisted tape, the increases in the mean Nusselt number and friction factor are, respectively, up to 181% and 3.86 times of the plain tube and the maximum thermal performance factor is 1.52. It is also obvious that the heat transfer and friction factor obtained from the micro-fin tube with twisted tape in counter-arrangement is higher than that from the micro-fin tube with twisted tape in co-arrangement.
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Heat transfer enhancement by helical screw tape coupled with rib turbulators
(2014-11-23)
Nanan, Kwanchai
;
Pimsarn, Monsak
;
Thianpong, Chinaruk
;
Eiamsa-Ard, Smith
The influence of helical screw tape coupled with rib turbulators (HST-R) on thermohydraulic characteristics in a circular tube has been experimentally investigated. The experiments were performed under constant heat flux condition for Reynolds number between 6,000 and 20,000. The rib-pitch ratio (p/D) was varied from 1.0 to 3.0 while rib-height ratio (e/W) was varied from 0.5 to 1.5. The experimental results revealed that heat transfer and friction factor increase with increasing rib-height ratio (e/W) and decreasing rib-pitch ratio (p/D). For the range examined, the HST-Rs with moderate rib-pitch ratio (p/D = 2) and the largest rib-height ratio (e/W = 1.5) gave the maximum thermal performance factor while HST possessed thermal performance factor around average value of those of the tubes with HSTRs. The developed empirical correlations for Nusselt number, friction factor and thermal performance factor gave the predictions within ±4.4%, ±13% and ±4.2%, respectively as compared to the experimental data.
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Turbulent heat transfer in a microfin tube with twisted tape insert
(2012-12-01)
Eiamsa-Ard, Smith
;
Kongkaitpaiboon, Vichan
;
Eiamsa-Ard, Petpices
;
Pimsarn, Monsak
The purpose of the present study is to investigate experimentally the heat transfer, turbulent flow friction and thermal performance factor characteristics in a microfin tube with a twisted tape insert. In the experiment, heat transfer augmentation is expected from both the turbulence of flow near the tube wall produced by fin surface and the swirling flow generated by the twisted tape. Effect of the twisted tape at different twist ratios of y/W = 3, 4 and 5 on the heat transfer enhancement characteristics is also reported. In the experimental set-up, cold water was passed through the uniform heat flux tube in a range of Reynolds number between 5000 and 17000. The experimental results obtained are compared with those from plain tubes. The results show that the thermal performance from using the microfin tube fitted with twisted tape is considerably higher than that from the microfin tube alone. The Nusselt numbers and friction factors are found to be, respectively, 3.0, 4.0 and 5.0 times over the microfin tube alone for the microfin tube combined with twisted tape. In addition, the results demonstrate that as the twist ratio (y/W) decreases, the twisted tape will give better heat transfer enhancement. The microfin tube combined with twisted tape provides higher thermal performance factor than those the microfin tube alone around 172%, 142% and 124%, respectively, for y/W = 3, 4 and 5. The results were correlated in the form of Nusselt number as a function of Reynolds number, Prandtl number and twist ratio.
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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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