Title: The effect of external fluid flow direction on the rheological behaviour of nano-sized sand in hydrated slurry using molecular dynamics simulation

Authors: Milad Jahanbakhsh Ghahjaverestani; Mehdi Jamali Ghahderijani; Arash Karimipour; Davood Toghraie; Mohammad Mehdi Razzaghi

Addresses: Department of Mechanical Engineering, Na.C., Islamic Azad University, Najafabad, Iran; Aerospace and Energy Conversion Research Center, Na.C., Islamic Azad University, Najafabad, Iran ' Department of Mechanical Engineering, Na.C., Islamic Azad University, Najafabad, Iran; Aerospace and Energy Conversion Research Center, Na.C., Islamic Azad University, Najafabad, Iran ' Department of Mechanical Engineering, Na.C., Islamic Azad University, Najafabad, Iran; Aerospace and Energy Conversion Research Center, Na.C., Islamic Azad University, Najafabad, Iran ' Department of Mechanical Engineering, Kho.C., Islamic Azad University, Khomeinishahr, Iran ' Department of Mechanical Engineering, Na.C., Islamic Azad University, Najafabad, Iran; Aerospace and Energy Conversion Research Center, Na.C., Islamic Azad University, Najafabad, Iran

Abstract: This study presented molecular dynamics simulations to investigate the rheological and agglomeration behaviours of nano-sized sand in hydrated slurry under horizontal and vertical external flows. The simulations assessed how flow direction affected sand nanoparticle behaviour. A 10 ns simulation duration was sufficient to reach equilibrium, with temperature stabilising at 299.19 K and kinetic energy at 0.89 kcal/mol. Under Earth's gravity, flow direction was found to significantly influence structural evolution. Perpendicular external forces caused strong atomic fluctuations, especially in the central region, with a peak temperature of 350.96 K. In side regions, oil molecule agglomeration led to particle velocities of 0.00072 Å/fs. When gravitational and external forces were aligned, reduced particle attraction increased fluctuations and raised the average temperature to 388 K. This alignment enhanced particle mobility, reaching velocities of 0.000905 Å/fs, and shortened agglomeration time to 4.03 ns versus 4.19 ns under perpendicular forces. It also increased slurry viscosity to 1.29 mPa·s, compared to 1.16 mPa·s in the perpendicular case.

Keywords: rheological behaviour; agglomeration time; hydrated slurry; flow direction; molecular dynamics simulation.

DOI: 10.1504/PCFD.2026.153747

Progress in Computational Fluid Dynamics, An International Journal, 2026 Vol.26 No.3, pp.202 - 210

Received: 22 May 2025
Accepted: 02 Oct 2025
Published online: 22 May 2026 *

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