### Branch, Split

Properties: adiabatic, not isentropic, directional, inlet based restrictor

In a split the flow from a gas pipe is split and redirected through two other pipes. So in principal three network elements of type GAS PIPE have one node in common in a split. The fluid elements of type BRANCH SPLIT represent the extra energy loss due to the splitting of the flow and have to be inserted in the outward branches of the split. This is represented schematically in Figure 102. The filled circles represent end nodes of the fluid elements, the others are the midside nodes. For a split to work properly the flow direction must be as indicated in Figure 102. If the solution of the equation system indicates that this is not the case appropriate measures must be taken. For instance, if the solution reveals that there are two inward flows and one outward flow, branch joint elements must be selected.

Several types of geometry are available.

A branch split of type GE [91], Figure 103, is quite general and allows arbitrary cross sections and angles (within reasonable limits). It is characterized by the following constants (to be specified in that order on the line beneath the *FLUID SECTION, TYPE=BRANCH SPLIT GE card):

• label of the gas pipe element defined as branch 0.
• label of the gas pipe element defined as branch 1.
• label of the gas pipe element defined as branch 2.
• cross section of branch 0.
• cross section of branch 1.
• cross section of branch 2.
• angle ().
• angle ().
• oil mass flow in branch 1 (only if the OIL parameter is used to define the kind of oil in the *FLUID SECTION card)
• oil mass flow in branch 2 (only if the OIL parameter is used to define the kind of oil in the *FLUID SECTION card)
• not used (internally: oil material number)

A branch split of type Idelchik1, Figure 104, can be used if the incoming branch is continued in a straight way and does not change its cross section [34]. It is characterized by the following constants (to be specified in that order on the line beneath the *FLUID SECTION, TYPE=BRANCH SPLIT IDELCHIK1 card):

• label of the gas pipe element defined as branch 0.
• label of the gas pipe element defined as branch 1.
• label of the gas pipe element defined as branch 2.
• cross section of branch 0.
• cross section of branch 0.
• cross section of branch 2.
• angle .
• angle ().
• hydraulic diameter of .
• hydraulic diameter of .
• oil mass flow in branch 1 (only if the OIL parameter is used to define the kind of oil in the *FLUID SECTION card)
• oil mass flow in branch 2 (only if the OIL parameter is used to define the kind of oil in the *FLUID SECTION card)
• -correction factor for branch 1 ( ). This allows to tune the value with experimental evidence (default is 1).
• -correction factor for branch 2 ( ). This allows to tune the value with experimental evidence (default is 1).
• not used (internally: oil material number)

A branch split of type Idelchik2, Figure 105, is used if the outward branches make an angle of with the incoming branch [34]. It is characterized by the following constants (to be specified in that order on the line beneath the *FLUID SECTION, TYPE=BRANCH SPLIT IDELCHIK2 card):

• label of the gas pipe element defined as branch 0.
• label of the gas pipe element defined as branch 1.
• label of the gas pipe element defined as branch 2.
• cross section of branch 0.
• cross section of branch 1.
• cross section of branch 2.
• angle .
• angle .
• oil mass flow in branch 1 (only if the OIL parameter is used to define the kind of oil in the *FLUID SECTION card)
• oil mass flow in branch 2 (only if the OIL parameter is used to define the kind of oil in the *FLUID SECTION card)
• -correction factor for branch 1 ( ). This allows to tune the value with experimental evidence (default is 1).
• -correction factor for branch 2 ( ). This allows to tune the value with experimental evidence (default is 1).
• not used (internally: oil material number)

By specifying the parameter LIQUID on the *FLUID SECTION card the loss is calculated for liquids. In the absence of this parameter, compressible losses are calculated.

Example files: branchsplit1, branchsplit2, branchsplit3.