Pipes and Cylinders - Conductive Heat Losses
Conductive heat losses through cylinder or pipe walls.
Uninsulated Cylinder or Pipe
Conductive heat loss through the wall of a cylinder or pipe can be expressed as
Q = 2 π L (ti - to) / [ln(ro / ri) / k] (1)
where
Q = heat transfer from cylinder or pipe (W, Btu/hr)
k = thermal conductivity of piping material (W/mK or W/m oC, Btu/(hr oF ft2/ft))
L = length of cylinder or pipe (m, ft)
π = pi = 3.14...
to = temperature outside pipe or cylinder (K or oC, oF)
ti = temperature inside pipe or cylinder (K or oC, oF)
ln = the natural logarithm
ro = cylinder or pipe outside radius (m, ft)
ri = cylinder or pipe inside radius (m, ft)
Insulated Cylinder or Pipe
Conductive heat loss through an insulated cylinder or pipe can be expressed as
Q = 2 π L (ti - to) / [(ln(ro / ri) / k) + (ln(rs / ro) / ks)] (2)
where
rs = outside radius of insulation (m, ft)
ks = thermal conductivity of insulation material (W/mK or W/m oC, Btu/(hr oF ft2/ft))
Equation 2 with inside convective heat resistance can be expressed as
Q = 2 π L (ti - to) / [1 / (hc ri ) + (ln(ro / ri) / k) + (ln(rs / ro) / ks)] (3)
where
hc = convective heat transfer coefficient (W/m2K)
