Research Papers

Laminar Convective Nanofluid Flow Over a Backward-Facing Step With an Elastic Bottom Wall

[+] Author and Article Information
Fatih Selimefendigil

Department of Mechanical Engineering,
Celal Bayar University,
Manisa 45140, Turkey
e-mail: fatih.selimefendigil@cbu.edu.tr

Hakan F. Öztop

Technology Faculty,
Department of Mechanical Engineering,
Fırat University,
Elaziğ 23119, Turkey
e-mail: hfoztop1@gmail.com

1Corresponding author.

Contributed by the Heat Transfer Division of ASME for publication in the JOURNAL OF THERMAL SCIENCE AND ENGINEERING APPLICATIONS. Manuscript received July 4, 2017; final manuscript received October 21, 2017; published online March 30, 2018. Assoc. Editor: Nesrin Ozalp.

J. Thermal Sci. Eng. Appl 10(4), 041003 (Mar 30, 2018) (7 pages) Paper No: TSEA-17-1229; doi: 10.1115/1.4038738 History: Received July 04, 2017; Revised October 21, 2017

In the present study, laminar forced convective nanofluid flow over a backward-facing step was numerically investigated. The bottom wall downstream of the step was flexible, and finite element method was used to solve the governing equations. The numerical simulation was performed for a range of Reynolds number (between 25 and 250), elastic modulus of the flexible wall (between 104 and 106), and solid particle volume fraction (between 0 and 0.035). It was observed that the flexibility of the bottom wall results in the variation of the fluid flow and heat transfer characteristics for the backward-facing step problem. As the value of Reynolds number and solid particle volume fraction enhances, local and average heat transfer rates increase. At the highest value of Reynolds number, heat transfer rate is higher for the case with the wall having lowest value of elastic modulus whereas the situation is reversed for other value of Reynolds number. Average Nusselt number reduces by about 9.21% and increases by about 6.1% for the flexible wall with the lowest elastic modulus as compared to a rigid bottom wall for Reynolds number of 25 and 250. Adding nano-additives to the base fluid results in higher heat transfer enhancements. Average heat transfer rates enhance by about 35.72% and 35.32% at the highest solid particle volume fraction as compared to nanofluid with solid volume fraction of 0.01 for the case with wall at the lowest and highest elastic modulus. A polynomial type correlation for the average Nusselt number along the flexible hot wall was proposed, which is dependent on the elastic modulus and solid particle volume fraction. The results of this study are useful for many thermal engineering problems where flow separation and reattachment coupled with heat transfer occur. Control of convective heat transfer for such configurations with wall flexibility and nanoparticle inclusion to the base fluid was aimed in this study to find the effects of various pertinent parameters for heat transfer enhancement.

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Grahic Jump Location
Fig. 1

Physical model with boundary conditions

Grahic Jump Location
Fig. 2

Effects of varying Reynolds number on the distribution of streamlines and isotherms (E = 104, ϕ = 0.02): (a) Re = 25, (b) Re = 100, (c) Re = 250, (d) Re = 25, (e) Re = 100, and (f) Re = 250

Grahic Jump Location
Fig. 3

Streamline and isotherm distributions for various elastic modulus of the flexible bottom wall (Re = 200, ϕ = 0.02): (a) E = 104, (b) E = 105, (c) E = 106, (d) E = 104, (e) E = 105, and (f) E = 106

Grahic Jump Location
Fig. 4

Distribution of local Nusselt number along the hot wall for different elastic modulus and Reynolds number (ϕ = 0.02): (a) E = 104, (b) E = 105, and (c) E = 106

Grahic Jump Location
Fig. 5

Average Nusselt number versus Reynolds number for various elastic modulus of flexible wall (ϕ = 0.02)

Grahic Jump Location
Fig. 6

Effects of solid particle volume fraction on the distribution of local Nusselt number for various elastic modulus of flexible wall (Re = 200): (a) E = 104, (b) E = 105, and (c) E = 106

Grahic Jump Location
Fig. 7

Average Nusselt number versus solid particle volume fraction for various elastic modulus of flexible wall (Re = 200)



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