The gas pipe element is a pipe element with constant cross section (Figure
77) It is allowed to rotate about an axis at a constant rotational speed. In
that case the distance from the center point of the entrance and of
the exit
to the rotational axis have to be specified.
The friction parameter is determined as
![]() |
(13) |
for laminar flow (
Re) and
![]() |
(14) |
for turbulent flow. Here, is the diameter of the material grains at the surface of the pipe
and Re is the Reynolds number defined by
Re![]() |
(15) |
where is the liquid velocity and
is the kinematic viscosity.
A gas pipe is described
by the following parameters (to be specified in that order on
the line beneath the *FLUID SECTION,TYPE=GAS PIPE
ADIABATIC or *FLUID SECTION,TYPE=GAS PIPE
ISOTHERMAL card):
The default gas pipe is adiabatic, i.e. there is no heat exchange with the pipe. Alternatively, the user may specify that the pipe element is isothermal. This means that the static temperature does not change within the pipe. In that case the energy equation in one of the two corner nodes of the element is replaced by a isothermal condition.
The form factor is only used to modify the friction expression for
non-circular cross sections in the laminar
regime as follows:
![]() |
(16) |
Values for for several cross sections can be found in
[13]. For a square cross section its value is 0.88, for a rectangle
with a height to width ratio of 2 its value is 0.97.
Example files: gaspipe10, gaspipe8-cfd-massflow, gaspipe8-oil.