Heat Transfer about Introduction to Convection

Introduction to Convection
 

• Convection denotes energy transfer between a surface and a fluid moving over the surface.  
• The dominant contribution due to the bulk (or gross) motion of fluid particles.

• In this chapter we will 

        –Introduce the convection transfer equations 

        –Discuss the physical mechanisms underlying convection 

        –Discuss physical origins and introduce relevant dimensionless parameters that can help   

          us to perform convection transfer calculations in subsequent chapters.

 

*Note similarities between heat, mass and momentum transfer 

 

 

Heat Transfer Coefficient

Recall Newton’s law of cooling for heat transfer between a surface of arbitrary shape, area As and temperature Ts and a fluid:

 

Generally flow conditions will vary along the surface, so q” is a local heat flux and h a local convection coefficient. 

The total heat transfer rate is :

where,

 

 is the average heat transfer coefficient.

 

 

Mass Transfer Coefficient

 

Recall mass transfer between a surface of arbitrary shape, area As and molar concentration species A of CAs and a fluid flow with molar concentration species A of CA∞: 

 

Generally flow conditions will vary along the surface, so NA” is a local mass flux and hm is a local convection coefficient. 

The total mass transfer rate is

where,

is the average mass transfer coefficient.