thanks for replies.
SYMBOLS in roman characters:
h =heat transfer coefficient
Nu=Nusselt Number
k=thermal conductivity of the fluid
L=characteristic length
Ra=Rayleigh number=Gr*Pr
Gr=Grashof number
g=gravity
b=coefficient of expansion (1/T for ideal gas)
alpha=thermal diffusivity=k/( rho cp)...
Air convection between two (glass) plate for low vacuum, 0.1mbar to 100 mbar
For flat plate solar collection in cold weather half the heat is lost though the front glass.
Radiation losses are handled via selective coatings, low e glass etc. Radiation losses are more or less independent of...
