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)

N

R>

R =l/hr

подпись: n r>
 
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

подпись:   tl

T 2

подпись: t 2Q = 4ae1e2T3(T1 -T2) = hr(T:-T2)

— T +T

Where T = ———

And the radiative heat transfer coefficient hr = 4ae, e2T3

Example 5.2

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


Добавить комментарий

Ваш e-mail не будет опубликован. Обязательные поля помечены *