Problem: Heat lose from insulated pipe.
A standart schedule 40 two-inch steel pipe (inside diameter 2,067 in and wall thickness 0,154 in) carrying a steam is lagged (i.e.insulated) with 2 in of 85 % magnesia covered in turn with 2 in of cork. Estimate the heat loss per hour per foot of pipe if the inner surface of the pipe is at 250 0F and the outer surface of cork is at 90 0F. The thermal conductivity of the substances concerned are.
Steel 26,1 Btu hr-1ft-1
85 % magnesia 0,04 Btu hr-1ft-1
cork 0,03 Btu hr-1ft-1
SOLUTION
Din = 2,067 in =0,17225 ft
x1 = 0,0154 in = 0,01283 ft
x2 = 2 in = 0,16667 ft
x3 = 2 in = 0,16667 ft
k1 = 2,61 Btu/hr ft 0F
k2 = 0,04 Btu/hr ft 0F
k3 = 0,03 Btu/hr ft 0F
Ta = 250 0F, Tb = 90 0F
Question : Q loss (Btu/hr ft)
Answer:
ro = 0,17225 ft / 2
= 0,08613 ft
r1 = r0 +x1
= (0,08613 +0,02813) ft
= 0,09896 ft
r2 = r1+x2
= (0,09896 ft + 0,16667) ft
= 0,26563 ft
r3 = r3 + x3
= (0,26563 ft + 0,16667) ft
= 0,4328 ft
ln r1/r0 = ln r1 – ln r0
=ln 0,09896 – ln 0,08613
=(-2,31304) – (-2,45189)
= 0,13885
ln r2/r1= ln r2 – ln r1
= ln 0,26563 – ln 0,09896
= (-1,32565)- (-2,31304)
= 0,98739
ln r3/r2= ln r3 – ln r2
= ln 0,4328 – ln 0,26563
= (-0,83748) – (-1,32565)
= 0,48817
Asumsi L= 1 ft
