10J. Temperature Drop in Buried Lines Using Equation 10.55 or 10.56 Back to Main
This
page is used to determine two different things. Method "A" is used to calculate the required distance
for the temperature to be equal to the hydrate formation temperature. Method
"B" is used to calculate the outlet temperature for a specific pipe
length. The equation used in Method B’s
calculation is
(Equation
10.57)
Where: = temperature at
= temperature at
J = Joule-Thomson coefficient
= distance from initial point
= distance from initial point
= ground or water temperature
L =
a = dU / (mCp)
U = overall heat transfer coefficient
= gas sp gr (air = 1.00)
= heat capacity
To
calculate the temperature drop, the method of calculation must be decided.
Choose Required pipe length to reach hydrate formation temperature or Pipe
outlet temperature calculation by given length by clicking and shading the
circle provided for that selection.
Once
the method of calculation has been chosen, by clicking and shading the circle
provided for that selection, the Inlet gas temperature, Water or ground
temperature, Hydrate formation temperature, Pipe outside diameter, Gas flow
rate, Overall heat transfer coefficient, Gas relative density, Pipe length, and
Gas heat capacity of the gas must be entered into their entry spaces. To do so
use the mouse to click the curser in the entry spaces and input the data. Once
this has been done, select Run to
execute the solution.
Water
or ground temperature is not a constant quantity but depends on the air
temperature to some degree. At a burial
depth below the "frost line" the soil temperature generally will vary
from 2-16°C [35-60°F] seasonally. About the same temperature range will be encountered with burial
in water of 30 m [100ft] deep.
Pipe
outside diameter is the length from one outer edge of the pipe to another outer
edge of the pipe, on the exact opposite side.
Gas
flow rate is the flow rate of the gas that flows inside the pipe.
Overall
heat transfer coefficient (U) is the single number that represents all of the
resistances in series. In a buried
pipe, all of the following resistances to heat flow can occur:
1.
Film coefficient between fluid and pipe wall
2.
Inner pipe wall conductivity (tubing)
3.
Annular space between inside and outside pipe
4.
Pipe wall
5.
Pipe coating
6.
Insulation
7.
Concrete layer or bond
8.
Sand backfill
9.
Native soil near pipe at temperature above normal due to heat gain from
pipe
As
with heat exchanger, the most reliable values of "U" are found by
test.
Gas
relative density is the density of the gas divided by the density of air or the
molecular weight of the gas divided by the molecular weight of air at
atmospheric pressure.
(1.2)
Gas
heat capacity can be found from the slope of h Vs T plots at a given pressure or
for pure substances are readily available from many handbooks and similar
reference materials.