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Energies 2018, 11(4), 919; https://doi.org/10.3390/en11040919

Numerical Simulation of Nanofluid Suspensions in a Geothermal Heat Exchanger

1
School of Mechanical Engineering, Nanjing University of Science and Technology, Nanjing 210094, China
2
School of Marine Science and Technology, Northwestern Polytechnical University, Xi’an 710072, China
3
U.S. Department of Energy, National Energy Technology Laboratory (NETL), Pittsburgh, PA 15236-0940, USA
4
Key Laboratory of Transient Physics, Nanjing University of Science & Technology, Nanjing 210094, China
*
Author to whom correspondence should be addressed.
Received: 28 February 2018 / Revised: 9 April 2018 / Accepted: 9 April 2018 / Published: 13 April 2018
(This article belongs to the Special Issue Mathematical and Computational Modeling in Geothermal Engineering)
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Abstract

It has been shown that using nanofluids as heat carrier fluids enhances the conductive and convective heat transfer of geothermal heat exchangers. In this paper, we study the stability of nanofluids in a geothermal exchanger by numerically simulating nanoparticle sedimentation during a shut-down process. The nanofluid suspension is modeled as a non-linear complex fluid; the nanoparticle migration is modeled by a particle flux model, which includes the effects of Brownian motion, gravity, turbulent eddy diffusivity, etc. The numerical results indicate that when the fluid is static, the nanoparticle accumulation appears to be near the bottom borehole after many hours of sedimentation. The accumulated particles can be removed by the fluid flow at a relatively high velocity. These observations indicate good suspension stability of the nanofluids, ensuring the operational reliability of the heat exchanger. The numerical results also indicate that a pulsed flow and optimized geometry of the bottom borehole can potentially improve the suspension stability of the nanofluids further. View Full-Text
Keywords: nanofluids; geothermal heat exchanger; suspension stability; pulsed flow; nanoparticle accumulation nanofluids; geothermal heat exchanger; suspension stability; pulsed flow; nanoparticle accumulation
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Sun, X.-H.; Yan, H.; Massoudi, M.; Chen, Z.-H.; Wu, W.-T. Numerical Simulation of Nanofluid Suspensions in a Geothermal Heat Exchanger. Energies 2018, 11, 919.

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