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### Branch, Joint

In a joint the flow from two gas pipes is united and redirected through a third pipe. So in principal three fluid elements of type GAS PIPE have one node in common in a joint. The fluid elements of type BRANCH JOINT represent the extra energy loss due to the merging of the flows and have to be inserted on the incoming branches of the joint. This is represented schematically in Figure 56. The filled circles represent end nodes of the fluid elements, the others are the midside nodes. For a joint to work properly the flow direction must be as indicated in Figure 56. 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 is one inward flow and two outward flows, branch split elements must be selected.

Figure 56: Element selection for a joint

Several types of geometry are available.

A branch joint of type GE [51], Figure 57, 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 JOINT 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 57: Geometry of a joint fluid section type GE

A branch joint of type Idelchik1, Figure 58, can be used if one of the incoming branches 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 JOINT 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 58: Geometry of a joint fluid section type Idelchik 1

A branch joint of type Idelchik2, Figure 59, can be used if one of the incoming branches is continued in a straight way but may 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 JOINT 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 ().

Figure 59: Geometry of a joint fluid section type Idelchik 2

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