1. 2.3 General molecular transport equation
For Momentum, Heat And Mass Transfer
Objectives
Gain brief understanding of the three transport phenomena.
Understand the general form of molecular transport equations
Recognize the analogy of the three laws of transport (Momentum, Heat and Mass) to the general form.
CHE315
2.3 General molecular transport equation
For Momentum, Heat And Mass Transfer

2. Rate of a transfer process = driving force / resistance
Demonstration Clip
All three of transport processes (Momentum, heat or mass) are characterized by the same general type of transport equation:
Rate of a transfer process = driving force / resistance
This states that a driving force is needed to overcome a resistance in order to transport a property.
CHE315
2.3 General molecular transport equation
For Momentum, Heat And Mass Transfer

3. For molecular transport or diffusion of a property, we can formalize by writing:
Ψz = - d (dG/dz)
z1 z2 G1 G2
Yz Flux
Concentration G
CHE315
2.3 General molecular transport equation
For Momentum, Heat And Mass Transfer

4. 2.3 General molecular transport equation
Property Flux
Property Concent.
Diffusivity
Direction
Transport Equation
General Form
Momentum
Heat
Mass
CHE315
2.3 General molecular transport equation
For Momentum, Heat And Mass Transfer

5. Property Concentration
Property Flux
Property Concentration
Diffusivity
Direction
Transport Equation
General Form YZ G d Z
Momentum
tzx
vxr n
Heat
qz/A
rcp a
Mass
Jzx CA
DAB
CHE315
2.3 General molecular transport equation
For Momentum, Heat And Mass Transfer

6. General property balance for unsteady state
(rate of property in) +
(rate of generation of property) =
(rate of property out) +
(rate of accumulation of property)
CHE315
2.3 General molecular transport equation
For Momentum, Heat And Mass Transfer