Transverse effect on liquid viscosity: A many-body dissipative particle dynamics simulation study

Abstract

Fluid viscosity plays an important role in multiphase flows, and the many-body dissipative particle dynamics (MDPD) method is an efficient means of simulating such flows at the mesoscopic scale. As the viscosity of the standard MDPD (S-MDPD) fluid cannot be efficiently adjusted, a transverse MDPD (T-MDPD) scheme is newly proposed to tune the viscosity of an MDPD fluid over a large range. With a lateral friction coefficient added to the S-MDPD form, the viscosity of the T-MDPD fluid is higher than that of an S-MDPD fluid, and the viscosity is about five times larger than that of an S-MDPD fluid with a friction coefficient of 40.5. In a T-MDPD fluid, the viscosity is much more sensitive to the new transverse friction coefficient, as it increases about five times higher when this coefficient increases from 4.5 to 40.5, while the viscosity only increases two times higher with the same variation of the original coefficient. By increasing the repulsive coefficient, the liquid particle number density, or the cutoff radius, the viscosity of the T-MDPD fluid is enhanced as well. Based on this extension of the MDPD scheme, a quantitative expression for the variation of the viscosity in the current T-MDPD fluid is derived. In future simulations of multiphase flows using an MDPD scheme, the transverse effect can be extended to effectively tune the viscosity, and this empirical expression will be useful to predict the viscosity of the T-MDPD fluid.

Two local slip modes at the liquid–liquid interface over liquid-infused surfaces

“…50 Recently, a new transverse MDPD (T-MDPD) scheme was proposed to tune the viscosity of a MDPD fluid over a wide range. 51 With a lateral friction coefficient added to the S-MDPD form, the three pairwise forces, namely, the conservative, dissipative, and random forces, are redefined as follows:…”

“…With a lateral friction coefficient added to the S-MDPD form, the viscosity of the T-MDPD fluid is much higher than that of a S-MDPD fluid, and it is sensitive to the transverse friction coefficient, as shown in literature. 51 While the particle number density of the working fluid and the lubricant fluid are set in the DPD units to q w ¼ 6:74 and q i ¼ 3:24, respectively, the viscosities of these two types of T-MDPD fluids are primarily adjusted by the friction coefficient. Then, the viscosity ratio between the working fluid and the lubricant fluid varies over a wide range, which exceeds the range for a classical SHS with air trapped in surface structures, as described in Sec.…”

“…II A) are the same for a pair of particles in current simulations. By applying the Poiseuille flow method, 51,56,57 the viscosities of these two types of T-MDPD fluids were obtained as l w ¼ 74:31 and l i ¼ 1:22 in the DPD units, which provides a maximum value of 60.77 for the viscosity ratio. Based on the Irving-Kirkwood equation, 58,59 the surface tension of the working fluid C ww is 12.76 in the DPD units.…”