Meso Scale Model Based on First Principles - Fluid Properties at Nano/Meso Scale: A Numerical Treatment - page 65

Meso Scale Model Based
on First Principles

Aim. The reader should understand how fluid modelling at the meso scale
can be undertaken by employing molecular physics models to characterize
bulk properties.

3.1 INTRODUCTION

The meso scale represents the range of scales in between the scales that can be
defined by the continuum laws (typically 10 − 6 m) and molecular physics (typ-

10 − 9 m). The behaviour of fluid at these scales is neither fully described
by the bulk continuum nor the molecular scale properties and physics. Contin-
uum simulations are unable to model molecular scale effects, which presents a
lower limit to the scale at which these approximations can be used. A molecular
scale fluid model can predict the behaviour of fluid by considering thousands of
molecular interactions, but provides no method of quantifying bulk effects, such
as viscosity or temperature and velocity gradients, throughout the flow field.
Continuum mechanics, however, can describe and quantify these bulk proper-
ties, but molecular scale effects are ignored. The onset of molecular behaviour
must be understood to recognize the point at which the continuum approxima-
tions fail.
The molecular dynamics simulations are able to predict the behaviour of the
fluid accurately, but in order to describe the flow quantitatively, the bulk character-
izing properties, such as pressure, temperature and velocity, need to be extracted.
Such properties arise from the molecular interactions intuatively modelled by the
molecular simulation, but are not quantified locally for at molecular scales they

ically