APPENDIX C

Step #1 Determine the heat loss per foot of line.

Q = 2? (Tst - Tout)/(ln(ro/ri )/kp + ln(rio /ro) /kin + 1/3r io)

Assumptions. This equation models an insulated pipe surrounded by air. The convective

resistance between the insulation and the outside of the pipe is assumed to be negligible. Also,

the convective heat transfer coefficient outside of the insulation is assumed to be 3 BTU/hr-ft2

deg. F.

Step #2 Determine the flow of condensate from the heat loss calculated in step #1.

m = Q/(hst - hcon)

Step #3 Multiply the flow rate per foot, calculated in step #2, by the total number of feet of steam

line that slopes toward the trap in question. The result is the minimum flow capacity of the trap.

where:

Q

= heat loss per foot of pipe; Btu/hr-ft

Tst

= temperature of steam; deg. F

Tout

= temperature of ambient conditions; deg. F

ro

= outside pipe radius; feet

ri

= inside pipe radius; feet

rio

= outside insulation radius; feet

kp

= thermal conductivity of pipe; Btu/hr-ft- deg. F; (26 Btu/hr-ft-deg. F for steel)

kin

= thermal conductivity of insulation; Btu/hr-ft- deg. F * (see table below)

m

= mass flow rate of condensate; lbm/hr-ft

hst

= enthalpy of saturated steam; Btu/lbm

hcon

= enthalpy of condensate; Btu/lbm

------------------------

Insulation Type

400 deg. F

300 deg. F

200 deg. F

Mineral Fiber

0.034

0.029

0.024

Calcium Silicate

0.042

0.038

0.035

C-1