Heat transfer performance of flag vortex generators in rectangular channels

Gallegos, Ralph Kristoffer B.; Sharma, Rajnish N.

doi:10.1016/j.ijthermalsci.2018.11.001

Cited by 29 publications

(6 citation statements)

References 155 publications

(542 reference statements)

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“…Also shown are corresponding values of the thermal effectiveness factor

η goodbreak= ((), {Nu}_{reed} / {Nu}_{reedless}) / {({\overset{W}{true}}_{italicreed} / {\overset{W}{true}}_{italicreedless})}^{1 / 3}

where we have recognized that at fixed Re , the mechanical power dissipation rate is proportional to the friction factor, so that

η

is identical to the quantity used by Shoele and Mittal [ 15 ] and Gallegos and Sharma. [ 25,26 ] For

L_{reed} / W = 2

and 2.5, we see that

{Nu}_{reed} / {Nu}_{reedless}

{\dot{W}}_{reed} / {\dot{W}}_{reedless}

, and

η

decrease downstream, as would be expected, based on the fact that the enhancement in these single‐reed cases is localized near the inlet. At each streamwise position, the values of these three quantities are higher for

L_{reed} / W = 2.5

than for

L_{reed} / W = 2

, as would be expected.…”

Section: Computationssupporting

confidence: 65%

Heat transfer enhancement in fin channels using aeroelastically fluttering reeds

Jha

Glezer

Park

et al. 2021

J Adv Manuf & Process

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Forced convection heat transfer in rectangular channels is enhanced by aeroelastically fluttering thin reeds extending over the channel span. The resulting small‐scale vortical motions substantially increase local heat transfer at the channel walls and mixing between the wall thermal boundary layers and the channel's core flow. Mechanisms associated with evolution of these small‐scale motions and their thermal effects are experimentally studied in a channel of width W, span 5W, and length 50W. Reed effects on heat transfer are characterized at Reynolds numbers (Re) of 2000, 7000, and 12,000 using embedded thermocouple arrays, and related to small‐scale motions by particle image velocimetry and hot‐wire anemometry. Reed‐induced small‐scale motions increase turbulent kinetic energy, increasing the global Nusselt number (by up to 145% at Re = 7000), with enhancement being sustained even when the base flow becomes fully turbulent (Re = 12,000). Enhancement is also demonstrated for fin arrays. Single‐reed computations show the effect of reed length on enhancement. Computations with two reeds, one downstream of the trailing edge of the other, predict heat transfer enhancement significantly greater than twice the single‐reed result, and point the way to use of a streamwise array of reeds in long channels. A techno‐economic analysis for an air‐cooled condenser suggests that fluttering reeds can be economically justified for a range of operating conditions.

show abstract

“…Also shown are corresponding values of the thermal effectiveness factor

η goodbreak= ((), {Nu}_{reed} / {Nu}_{reedless}) / {({\overset{W}{true}}_{italicreed} / {\overset{W}{true}}_{italicreedless})}^{1 / 3}

where we have recognized that at fixed Re , the mechanical power dissipation rate is proportional to the friction factor, so that

η

is identical to the quantity used by Shoele and Mittal [ 15 ] and Gallegos and Sharma. [ 25,26 ] For

L_{reed} / W = 2

and 2.5, we see that

{Nu}_{reed} / {Nu}_{reedless}

{\dot{W}}_{reed} / {\dot{W}}_{reedless}

, and

η

L_{reed} / W = 2.5

than for

L_{reed} / W = 2

, as would be expected.…”

Section: Computationssupporting

confidence: 65%

Heat transfer enhancement in fin channels using aeroelastically fluttering reeds

Jha

Glezer

Park

et al. 2021

J Adv Manuf & Process

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show abstract

“…This indicates that the degree of interaction is related to the strip width in this study. As the principle of using a flexible vortex generator to enhance heat transfer is the enhanced flow unsteadiness due to fluid-structure interactions [20,[33][34][35], stronger fluidstructure interactions induce better heat dissipation effect in non-fully-turbulent flow. A moderate strip width, which is 1 cm for the 1-4 flag in this study, provides the strongest interaction among all the studied cases, thus leads to the optimal heat dissipation effect.…”

Section: High-speed Camera Investigationmentioning

confidence: 99%

“…Later, a number of studies that employed fluid-structure interaction of flexible structures [14][15][16][17] coupled with heat convection have been published [18][19][20][21]. Shi et al [22] used a thin film behind a cylinder in a channel flow to study the effect of flutter-induced vortex on heat transfer in a numerical way.…”

mentioning

confidence: 99%

Experimental study on the thermal-hydraulic performance of a fluttering split flag in a channel flow

Zhong

Chan

et al. 2022

International Journal of Heat and Mass Transfer

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“…Numerical results showed that mixing is enhanced for larger flaps displacement, such that 99% improvement was seen in the rate of the mixing process. The performance of flag vortex generators in increasing heat transfer rate in convection duct flow was studied experimentally by Kristoffer et al [11]. In that study, the heat transfer characteristics of turbulent convection airflow under the presence of a flapping flag as a VG were investigated.…”

Section: Introductionmentioning

confidence: 99%

Enhancement in Rejected Heat from Heat Sinks Using High Flexible Winglets with Large Deformation and Low Blockage Effect

Nassab

2022

IJEE

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Heat transfer performance of flag vortex generators in rectangular channels

Cited by 29 publications

References 155 publications

Heat transfer enhancement in fin channels using aeroelastically fluttering reeds

Heat transfer enhancement in fin channels using aeroelastically fluttering reeds

Experimental study on the thermal-hydraulic performance of a fluttering split flag in a channel flow

Enhancement in Rejected Heat from Heat Sinks Using High Flexible Winglets with Large Deformation and Low Blockage Effect

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