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Research Papers: Forced Convection

Control of Laminar Pulsating Flow and Heat Transfer in Backward-Facing Step by Using a Square Obstacle

[+] Author and Article Information
Fatih Selimefendigil

Assistant Professor
Department of Mechanical Engineering,
Celal Bayar University,
Manisa 45140, Turkey
e-mail: fthsel@yahoo.com

Hakan F. Oztop

Professor
Department of Mechanical Engineering,
Technology Faculty, Firat University,
Elaz iğ 23119, Turkey
e-mail: hfoztop1@gmail.com

1Corresponding author.

Contributed by the Heat Transfer Division of ASME for publication in the JOURNAL OF HEAT TRANSFER. Manuscript received October 8, 2012; final manuscript received March 24, 2014; published online April 23, 2014. Assoc. Editor: Alfonso Ortega.

J. Heat Transfer 136(8), 081701 (Apr 23, 2014) (11 pages) Paper No: HT-12-1549; doi: 10.1115/1.4027344 History: Received October 08, 2012; Revised March 24, 2014

In the present study, laminar pulsating flow over a backward-facing step in the presence of a square obstacle placed behind the step is numerically studied to control the heat transfer and fluid flow. The working fluid is air with a Prandtl number of 0.71 and the Reynolds number is varied from 10 and 200. The study is performed for three different vertical positions of the square obstacle and different forcing frequencies at the inlet position. Navier–Stokes and energy equation for a 2D laminar flow are solved using a finite-volume-based commercial code. It is observed that by properly locating the square obstacle the length and intensity of the recirculation zone behind the step are considerably affected, and hence, it can be used as a passive control element for heat transfer augmentation. Enhancements in the maximum values of the Nusselt number of 228% and 197% are obtained for two different vertical locations of the obstacle. On the other hand, in the pulsating flow case at Reynolds number of 200, two locations of the square obstacle are effective for heat transfer enhancement with pulsation compared to the case without obstacle.

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References

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Figures

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Fig. 1

Geometry (not drawn to scale) with boundary conditions

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Fig. 2

Distribution of the mesh in the vicinity of the step and square obstacle

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Fig. 3

Variation of the local Nusselt number distribution along the bottom wall for different grid sizes

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Fig. 4

Space-averaged Nusselt number along the bottom wall at Re = 200, St = 1, b/H = 1.0 for different time step sizes

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Fig. 5

Streamlines for no-obstacle case and for square obstacle at various locations for Reynolds number of 10 (first box), 100 (second box), and 200 (third box)

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Fig. 6

Isotherms for no-obstacle case and for square obstacle at various locations for Reynolds number of 10 (first box), 100 (second box), and 200 (third box)

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Fig. 7

Effect of the obstacle and its position on the distribution of the local Nusselt number for Reynolds number of 10, 100, and 200

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Fig. 8

Variation of the maximum location of the Nusselt number (bottom) and maximum value of the Nusselt number (top) versus Reynolds number for different obstacle positions and for the case without obstacle

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Fig. 9

Variation of the length-averaged Nusselt number along the bottom wall downstream of the step versus Reynolds number for different obstacle positions and for the case without obstacle

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Fig. 10

Effect of the position of the obstacle on temporal variations of spatial-averaged Nusselt number when the steady state periodic oscillations are reached at Reynolds number of 10, 100, and 200 for Strouhal number of 0.1

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Fig. 11

Effect of the position of the obstacle on temporal variations of spatial-averaged Nusselt number when the steady state periodic oscillations are reached at Reynolds number of 10, 100, and 200 for Strouhal number of 2

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Fig. 12

Time evolution of the streamlines for no-obstacle case (first box) and for square obstacle at various locations denoted by P1, P2, and P3 at Reynolds number of 100 for three different time instances corresponding to minimum (-a), middle (-b-) and maximum(-c-) part of the cycle during an acceleration phase of a half period

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Fig. 13

Time evolution of the isotherms for no-obstacle case (first box) and for square obstacle at various locations denoted by P1, P2, and P3 at Reynolds number of 100 for three different time instances corresponding to minimum (-a), middle (-b-) and maximum (-c-) part of the cycle during an acceleration phase of a half period

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Fig. 14

Temporal evolution of the local Nusselt number for no-obstacle case and for square obstacle at various locations - position 1 (b/H = 0.5), position 2 (b/H = 1.0) and position 3 (b/H = 1.5) at Reynolds number of 100, Strouhal number of 0.5 for three different time instances corresponding to minimum (-a), middle (-b-) and maximum(-c-) part of the cycle during an acceleration phase of a half period

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Fig. 15

Variation of normalized Nusselt number (time- and spatial-averaged Nusselt number in pulsating flow divided by the average in steady flow) for no-obstacle case and for obstacle at different locations with Strouhal number at Reynolds number of 10, 100, and 200

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Fig. 16

Variation of heat transfer enhancement for pulsating flow in comparison to the steady state flow with obstacle at different locations and with no-obstacle case (HTEw,o), with Strouhal number at Reynolds number of 10, 100, and 200

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Fig. 17

Snapshots of the streamlines for the case without obstacle and for the case at obstacle position P3: b/H = 1.5 during the acceleration phase of a half of the pulsating cycle. Time reads from t1 (min) to t5 (max).

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