The gas pipe element is a pipe element with constant cross section (Figure 83) 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
for laminar flow ( Re) and
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
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:
Values for for several cross sections can be found in . 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.