From Introduction to Computational Fluid Dynamics
A.1 Introduction
In the study of transport phenomena in moving fluids, the fundamental laws of motion (conservation of mass and Newton s second law) and energy (first law of thermodynamics) are applied to an elemental fluid. Two approaches are possible:

a particle approach or

a continuum approach.
In the particle approach, the fluid is assumed to consist of particles (molecules, atoms, etc.) and the laws are applied to study particle motion. Fluid motion is then described by the statistically averaged motion of a group of particles. For most applications arising in engineering and the environment, however, this approach is too cumbersome ^{[1]} because the significant dimensions of the flow are considerably bigger than the meanfreepath length between molecules. In the continuum approach, therefore, statistical averaging is assumed to have been already performed and the fundamental laws are applied to portions of fluid (or control volumes) that contain a large number of particles. The information lost in averaging must however be recovered. This is done by invoking some further auxiliary laws and by empirical specifications of transport properties such as viscosity , thermal conductivity k, and mass diffusivity D. The transport properties are typically determined from experiments. Notionally, the continuum approach is very attractive because one can now speak of temperature, pressure, or velocity at a point and relate them to what is measured by most practical instruments.
Guidance for deciding whether the particle or continuum approach is to be...
Products & Services
Topics of Interest
B.1 Structure of the Code The 1D conduction code is divided into two parts: a user part containing files COM1D.FOR and USER1D.FOR and a library part containing file LIB1D.FOR. The user part is...
2.1. Continuum and Transport Phenomena The motion of a fluid is studied on the basis of the fundamental principle of mechanics, namely the conservation laws of mass, momentum and energy. For a state...
Daniel J. Rader and Anthony S. Geller Sandia National Laboratories New Mexico, Albuquerque, NM, USA 3.1 Introduction This chapter reviews the theoretical models available to describe particle...
4 Integral and differential equations of motion In this section we derive the basic conservation equations for the flow within the surface layer. While it is clear that conservation equations for...
4.1 Kinetics of a Continuous Media In this section the laws of motion applicable to a continuous medium analogous to Newton s laws of motion in particle mechanics will be formulated. Newton s laws of...