Convection
Convection
Convection ▣ Definition:between fluid in motion and a bounding surface when the two are at different temperatures ■ Natural Convection (water boiling):gravity- induced ■ Forced convection(disturbing,blowing, Breathing):pressure gradient Boiling and Condensation:Latent heat Exchange
Convection Definition: between fluid in motion and a bounding surface when the two are at different temperatures Natural Convection（water boiling）: gravityinduced Forced convection( disturbing, blowing, Breathing): pressure gradient Boiling and Condensation: Latent heat Exchange
Convective Transfer Coefficient ▣ Newton's Law of cooling g =h(T:-T) h=fn(flow condition,properties,surface geometry)
Convective Transfer Coefficient Newton’s Law of cooling ( ) '' = T − T∞ q h s h=fn( flow condition, properties, surface geometry)
Free stream T 6,x) Thermal boundary layer T+ Thermal Boundary Layer development on an isothermal flat plate Thickness T.-T T.-T. =0.99
Thermal Boundary Layer development on an isothermal flat plate δ t = 0.99 − − T T∞ T T s s Thickness
Convective Heat transfer Coefficient h= T、-T y=0 h= Empirical or Nusselt c N- Semi-empirical Number
0 0 ( ) ( ) = − − ∞ ∂ = ∂ − = − − ⋅ = ∞ y LyT T T T cf s y y T f cs s dd Lk T T k h Nu Nusselt Number f u c k N h L = Empirical or Semi-empirical Convective Heat transfer Coefficient