The space between the glass cover (on top) and the absorber plate (at the bottom) of a horizontal solar thermal water heater is
2 cm
high) and filled with air. The glass cover is at
25 ∘
C
and the absorber plate is at
65 ∘
C
. Estimate the heat transfer rate per unit area between the absorber and the cover due to natural convection and compare with pure conduction
(Nu L
=1)
. The relevant properties of air are:
c p
=1007 J⋅kg −1
⋅K −1
;μ=1.9×10 −5
Pa⋅s;k=0.027
W⋅m −1
⋅K −1
; and
R=287 J⋅kg −1
⋅K −1
.
