TD Transferts thermiques 2: convection naturelle

D S L2D2
Thaut
t= 0 Tbas > Thaut
β=−1
ρ(∂ρ/∂T )Pρ
β > 0
t= 0 β
d3Tbas
Thaut
L, D, g, ρ, β ∆T=Tbas −Thaut V
η
−→
∇V
σij ij σikkj
dt 
−→
∇V
×dt
η V D L
ν=η/ρ m2/s
V ν D
Gr
Gr =β g ∆T D3
ν2
Ra =β g ∆T D3
νa

Ra > 1000
Ra < 1000 D= 8 mm ∆T
β∆T
P r =ν
aa
D
P r
P r 1T
P r 1
T
q η ν D
∆Tfriction ην2
λD4
∆Tfriction
D1∆Tfriction
Ra D1∆T= 2 ∆Tfriction
∆T/∆Tfriction Ra
P r