A novel caudal-fin-inspired hourglass-shaped self-agitator for air-side heat transfer enhancement in plate-fin heat exchanger

Li, Kuojiang; Wang, Sheng; Ke, Zhaoqing; Chen, Chung‐Lung

doi:10.1016/j.enconman.2019.03.048

Cited by 22 publications

(6 citation statements)

References 21 publications

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“…Flapping mode Deflected mode Increasing flow velocity Fig. 1: Distinctive flap modes as airflow increases [10].…”

Section: Stretched-straight Modementioning

confidence: 99%

“…Although, the transition to the flapping mode occurred at a lower airflow, the friction coefficient was augmented 6 to 8-fold, while achieving only an 80% increase in the Nusselt number. Furthermore, Li et al [10] investigated hourglass-shaped agitators, different numbers and various pitches. They reported that an optimum distance between two consecutive flaps was 25 mm.…”

Section: Stretched-straight Modementioning

confidence: 99%

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A Biomimetic Approach to Improve Convective Heat Transfer Using Fluid-Induced Vibrations from Self-Excited Flaps

Najafpour¹,

Bahrami²

2023

World Congress on Momentum, Heat and Mass Transfer

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Bio-inspired flexible plates have shown promising results as a passive method to enhance convective heat transfer and mixing in flow. Flap fluttering is a self-excited phenomenon caused by the fluid-structure-interaction between the main flow and the flap. Among all the parameters, the direction of the flap relative to the incoming flow appears to be the key factor in determining the transition into the flapping mode. In this study, flaps made of a 50-micron thick polyester sheet were cut into rectangular shapes and placed at the centerline of the channels of a shrouded straight fin heatsink. Both hanging and vertical positions of the flap in the axial flow were investigated using a custom-built testbed in our lab. We measured the convective heat transfer rates and pressure drop in the heatsink for both arrangements. We observed that: i) the rectangular cantilevered flap is more unstable in the hanging flap configuration compared to the vertically installed flap, i.e., the transition to the fluttering mode occurs at a lower airflow velocity; ii) the critical flow velocity -the velocity at which the flap becomes unstable-is lower for the flap aspect ratio of 0.5. We attribute this behavior to the longer viscous boundary layer around the vertical case, which stabilizes the flap; iii) from a thermal performance point of view, the hanging configuration outperforms the vertical one with the same flap dimensions; iv) at a Reynolds number of 8,940, large amplitude vibrations and coherent fluttering in a hanging configuration render a superior thermal performance of 39 percent improvement in the Nusselt number compared to when bare channels are measured. On the contrary, at higher flowrates, the difference falls in the range of measurement uncertainty; and v) as for the pressure drop, unlike the hanging configuration, the vertical flap creates a higher pressure drop as it tends to block half the channel at the end of the trailing edge stroke. Furthermore, the presence of the flap holder adds to the pressure drop increase, which is eliminated in the hanging position and therefore, flaps could be connected to the shroud directly.

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“…Flapping mode Deflected mode Increasing flow velocity Fig. 1: Distinctive flap modes as airflow increases [10].…”

Section: Stretched-straight Modementioning

confidence: 99%

Section: Stretched-straight Modementioning

confidence: 99%

A Biomimetic Approach to Improve Convective Heat Transfer Using Fluid-Induced Vibrations from Self-Excited Flaps

Najafpour¹,

Bahrami²

2023

World Congress on Momentum, Heat and Mass Transfer

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“…For forced convection heat transfer from a circular cylinder with a flexible fin in laminar flow, Sun et al [25] showed that when the vortex shedding frequency approached the natural frequency of the fin, the FIV frequency locked on to the natural frequency and the fin exhibited large-amplitude vibration improving convection heat transfer. Also, self-agitators (airfoil-based [26] and caudalfin-inspired [27]) were used to generate vortices to enhance flow mixing and thus heat transfer performance in exchangers operating in laminar-transitional-turbulent regime. All the passive techniques although do not require any external power eventually lead to an increase in fluid pressure drop [28] as they use power from the system itself.…”

Section: General Audience Abstractmentioning

confidence: 99%

Characterization of heat transfer enhancement for an oscillating flat plate-fin

Rahman

Tafti

2020

International Journal of Heat and Mass Transfer

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“…Self-oscillating FVGs were recently introduced as a way for heat transfer and mixing enhancement where it was shown that installing the FVGs could enhance the thermal performance in a very effective way (Ali et al , 2016, 2017; Li et al , 2018a; Li et al , 2019).…”

Section: Introductionmentioning

confidence: 99%

Heat transfer enhancement using second mode self-oscillating structures

Ali

Shami

Badran

et al. 2019

HFF

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Purpose In this paper, self-sustained second mode oscillations of flexible vortex generator (FVG) are produced to enhance the heat transfer in two-dimensional laminar flow regime. The purpose of this study is to determine the critical Reynolds number at which FVG becomes more efficient than rigid vortex generators (RVGs). Design/methodology/approach Ten cases were studied with different Reynolds numbers varying from 200 to 2,000. The Nusselt number and friction coefficients of the FVG cases are compared to those of RVG and empty channel at the same Reynolds numbers. Findings For Reynolds numbers higher than 800, the FVG oscillates in the second mode causing a significant increase in the velocity gradients generating unsteady coherent flow structures. The highest performance was obtained at the maximum Reynolds number for which the global Nusselt number is improved by 35.3 and 41.4 per cent with respect to empty channel and rigid configuration, respectively. Moreover, the thermal enhancement factor corresponding to FVG is 72 per cent higher than that of RVG. Practical implications The results obtained here can help in the design of novel multifunctional heat exchangers/reactors by using flexible tabs and inserts instead of rigid ones. Originality/value The originality of this paper is the use of second mode oscillations of FVG to enhance heat transfer in laminar flow regime.

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A novel caudal-fin-inspired hourglass-shaped self-agitator for air-side heat transfer enhancement in plate-fin heat exchanger

Cited by 22 publications

References 21 publications

A Biomimetic Approach to Improve Convective Heat Transfer Using Fluid-Induced Vibrations from Self-Excited Flaps

A Biomimetic Approach to Improve Convective Heat Transfer Using Fluid-Induced Vibrations from Self-Excited Flaps

Characterization of heat transfer enhancement for an oscillating flat plate-fin

Heat transfer enhancement using second mode self-oscillating structures

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