Insight into the pressure-induced displacement mechanism for selecting efficient nanofluids in various capillaries

Designing fluids to regulate two-phase displacement has been of great interest because of their roles in groundwater remediation, oil recovery and water desalination. Currently, the displacement efficiency of fluids is observed to be dependent on the surface properties of capillaries and external pressure. Herein, pressure-induced displacement mechanisms in various capillaries are investigated by molecular dynamics simulations. Our results suggest that surface wettability and pressure are crucial to the displacement performance of fluids. Specifically, reducing the interfacial tension of fluids is beneficial to displacement efficiency in hydrophobic capillaries, while increasing the viscosity of fluids favors hydrophilic capillaries. Based on our proposed mechanisms and considering the capillaries' wettability, three types of nanofluids are designed to improve the displacement efficiency for different capillaries. Our results are significant for understanding fluid flow phenomena and provide an efficient way to design target fluids for numerous applications.