Convection Heat Transfer

 

Convection heat transfer is the mode of energy transfer between a solid surface and the adjacent liquid or gas that is in motion, and it involves the combined effects of conduction and fluid motion.

 

 

 

The rate of heat transfer by convection, , is determined from Newton's law of cooling, expressed as

 

 

Where

= heat transfer rate, (W)

A

= heat transfer area, (m2)

h

= convective heat transfer coefficient, (W/(m2-K))

Ts

= surface temperature, (K)

Tf

= bulk fluid temperature away from the surface, (K)

 

The convective heat transfer coefficient is an experimentally determined parameter that depends upon the surface geometry, the nature of the fluid motion, the properties of the fluid, and the bulk fluid velocity. Ranges of the convective heat transfer coefficient are given below.

 

 

h W/(m2-K)

free convection of gases

2-25

free convection of liquids

50-100

forced convection of gases

25-250

forced convection of liquids

50-20,000

convection in boiling and condensation

2500-100,000

 


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