# Introduction to transport phenomena

### From Thermal-FluidsPedia

## Continuum Flow Limitations

The transport phenomena are usually modeled in continuum states for most applications – the materials are assumed to be continuous and the fact that matter is made of atoms is ignored. When the characteristic dimension, *L*, is small compared to the molecular mean free path, λ, which is defined as average distance between collisions for a molecule, the traditional Navier-Stokes equation and the energy equation based on the continuum assumption have failed to provide accurate results. The continuum assumption also fails when the gas is at very low pressure (rarefied).

*See Main Article* Continuum flow limitations

## Momentum, Heat, and Mass Transfer

Transport phenomena include momentum transfer, heat transfer, and mass transfer, all of which are fundamental to an understanding of both single and multiphase systems. It is assumed that the reader has basic undergraduate-level knowledge of transport phenomena as applied to single-phase systems, as well as the associated thermodynamics, fluid mechanics, and heat transfer.

*See Main Article* Momentum, Heat, and Mass Transfer

## Introduction to Momentum Transfer

A fluid at rest can resist a normal force but not a shear force, while fluid in motion can also resist a shear force. The fluid continuously deforms under the action of shear force. A fluid’s resistance to shear or angular deformation is measured by viscosity, which can be thought of as the internal “stickiness” of the fluid. The force and the rate of strain (i.e., rate of deformation) produced by the force are related by a constitutive equation.

*See Main Article* Introduction to Momentum Transfer

## Introduction to Heat Transfer

*See Main Article* Introduction to Heat Transfer

## Introduction to Mass Transfer

*See Main Article* Introduction to Mass transfer

## Multiphase Systems and Phase Changes

*See Main Article* Multiphase Systems and Phase Changes

## Multiphase Systems and Phase Changes

*See Main Article* Multiphase Systems

## Transport Phenomena in Micro- and Nanoscales

*See Main Article* Transport Phenomena in Micro- and Nanoscales

## Dimensional Analysis

*See Main Article* Dimensional Analysis

## Scaling

*See Main Article* Scaling