Investigating the Effect of Surface Roughness Size and Shape on the Nanofluid Behavior and Nanoparticles Aggregation in a Square Nanochannel by Molecular Dynamics Simulation

In this article, the effect of surface roughness size and shape on the Poiseuille flow of Ar–Cu nanofluid in a square copper nanochannel is investigated. To do this, hemispherical, cubic, semi-cylindrical roughness, shapes extended along the nanochannel length and width, and square protrusions extended along the nanochannel length and width are studied. The simulations are carried out using the molecular dynamics method and LAMMPS software. The results show that the roughness causes a change in the velocity and structure of nanofluid atoms in the nanochannel. For example, the hemispherical roughness with a height of 7.5Å$$7.5{\text{\AA}}$$ causes 24% decrease in the nanofluid velocity. Also, the results show that the effect of different shapes and sizes of roughness on the nanofluid behavior is different. For example, at the same height of roughness (7.5Å$$7.5{\text{\AA}}$$), the velocity difference created by different roughness shapes is around 0.208Åps$$0.208\frac{{\text{\AA}}}{ps}$$, which is around 13% of the nanofluid velocity in the smooth state. Additionally, it is found that the roughness makes the nanofluid velocity profile flatter in the central part of the nanochannel. Also, the results reveal that the shape and height of the roughness have an effect on the aggregation time of nanoparticles and on how they move in the nanofluid. Specifically, increasing the height of the roughness and decreasing the velocity of the nanofluid, decreases the accumulation time of nanoparticles.