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DESIGN AIDS

THERMAL RADIATION NOMOGRAM

Thermal-Radiation

Exchange by Nomogram

PAUL R. KRIKORIAN, Pembroke, Mass.

Heat exchange between two bodies by radi­
REF. LINE

ation can be calculated by the expression:

where:

Emissivity factor for gray bodies

Heat exchange. Btu/hr/ft2

Cold-body temperature, deg

Rankine

= Hot-body temperature, deg

Rankine

<Z>
(T Stephan -Boltzmann Constant
C Q
0.173 x o I

For an enclosed body that is small com­

pared with the enclosing body, such as a

piece of electronic equipment within a

room, Fe — ep the emissivity of the en­

closed body.

For an enclosed body that is large com­

r/ft2 pared with the enclosing body:

/h 1

tu L + X_j

B ^1 C2

TEMPERATURE. EXCHANGE, where:

= Emissivity of enclosed body

e2 = Emissivity of enclosing body

To use the nomogram; the emissivity
BODY HEAT factor, Fe, first must be calculated. For

total heat transfer, Q, in Btu/hr, multiply
COLD- 500 q by the area of the enclosed body.

Example: Determine the radiation ex­

change between a surface at 720F and a

surface at 240F with an emissivity factor

550
of 0.72.

4000
Solution: Connect Th = 720F to 7C =

240F. From the intersection of the

reference line, draw through Fe = 0.72

to q. Read q = 2125 Btu/hr/ft2.

600
4500

Reference:

Brown, A. and Marco, S., Introduction to Heat

Transfer, McGraw Hill, 3rd edition, 1958.

Paul R. Krikorian holds a degree '
5000
in Architectural Engineering

from Wentworth Inst, and a

BSME from Lowell Technologi­

cal Inst. Mr. Krikorian has

worked for the Hazeltine Corp,

5500 on underwater acoustics de­

vices and for the Raytheon Co.,
—
—
—
—
on underground antenna sys­
7000
6000
8000
9000
tems. He is self employed.
10,000
[END]
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