Radiation
Stefan-Boltzmann’s Law: q = oe1e2(T14-T24)
Where q = heat flux due to radiation (W/m )
A = Stefan-Boltzmann constant (= 5.673xl0"8 W/m2 K4)or (= 0.1713×10"* Btu/h. ftz R) e = surface emittance (-)
T = surface temperature (K)
R =l/hr |
The equation can be further written as:
Q = oe1e2(T13+T12T2 + TjT2 + T2 )(Tj — T2) When Ti ~ T2, the equation can be approximated as:
|
Tl |
|
T 2 |
Q = 4ae1e2T3(T1 -T2) = hr(T:-T2)
— T +T
Where T = ———
And the radiative heat transfer coefficient hr = 4ae, e2T3
Determine hr in a typical classroom at PSU.
O
Overall heat transfer coefficient h = hc + hr Overall film resistance R = 1/h = l/(hc + hr)
(See Table 5-2 for values)
Radiative heat transfer between two arbitrary surfaces is o(T,4-T24)
_ ————————————————
TOC o "1-5" h z 1 —Ј, 1 1-6,
—— — +——— +—— —
AjEi AjFj2 -^2^2
Posted in Fundamentals of Heating. Ventilating, and Air-Conditioning