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### Branch, Split

In a split the flow from a gas pipe is split and redirected through two other pipes. So in principal three fluid 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 60. 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 60. 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.

Figure 60: Element selection for a split

Several types of geometry are available.

A branch split of type GE [51], Figure 61, is quite general and allows arbitary 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 ().

Figure 61: Geometry of a split fluid section type GE

A branch split of type Idelchik1, Figure 62, can be used if the incoming branche is continued in a straight way and does not change its cross section [22]. 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 2.
- angle ().

Figure 62: Geometry of a split fluid section type Idelchik 1

A branch split of type Idelchik2, Figure 63, is used if the outward branches make an angle of with the incoming branch [22]. 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.

Figure 63: Geometry of a split fluid section type Idelchik 2

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