Page 240 - Mechanical Engineers' Handbook (Volume 4)

8 Heat Transfer 229

Figure 10 Diagrams of log-mean temperature difference (MTD). 1

temperatures in R are large and unwieldy, it is more convenient to express temperatures in
S, equivalent to ( F 460)/100. The constant N is then reduced to 0.1713.
With source and receiver temperatures identified as T and T in S, and with allowance
r
s
for emissivity and view factors, the complete equation becomes
Q/A 0.1713 em Fr(T T ) Btu/hr ft 2
4
4
s
r
at the receiving surface,
where em combined emissivity and absorptivity factors for source and receiving surfaces
Fr net radiation view factor for receiving surface
T and T source and receiving temperature in S
s
r