Branch, Split

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 93. The filled circles represent corner 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 93. 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 93: Element selection for a split

Several types of geometry are available.

A branch split of type GE [69], Figure 94, 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 $A_0$ of branch 0.
• cross section $A_1$ of branch 1.
• cross section $A_2$ of branch 2.
• angle $\alpha_1$ ($^\circ$).
• angle $\alpha_2$ ($^\circ$).
• 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)

Figure 94: Geometry of a split fluid section type GE

A branch split of type Idelchik1, Figure 95, can be used if the incoming branch is continued in a straight way and does not change its cross section [31]. 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 $A_0$ of branch 0.
• cross section $A_1=A_0$ of branch 0.
• cross section $A_2$ of branch 2.
• angle $\alpha_1=0^\circ$.
• angle $\alpha_2$ ($^\circ$).
• hydraulic diameter ${D_h}_0$ of $A_0$.
• hydraulic diameter ${D_h}_2$ of $A_2$.
• 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)
• $\zeta$-correction factor $k_1$ for branch 1 ( $\zeta_{eff} = k_1\zeta$). This allows to tune the $\zeta$ value with experimental evidence (default is 1).
• $\zeta$-correction factor $k_2$ for branch 2 ( $\zeta_{eff} = k_2\zeta$). This allows to tune the $\zeta$ value with experimental evidence (default is 1).

Figure 95: Geometry of a split fluid section type Idelchik 1

A branch split of type Idelchik2, Figure 96, is used if the outward branches make an angle of $90 ^\circ$ with the incoming branch [31]. 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 $A_0$ of branch 0.
• cross section $A_1$ of branch 1.
• cross section $A_2$ of branch 2.
• angle $\alpha_1=90^\circ$.
• angle $\alpha_2=90^\circ$.
• 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)
• $\zeta$-correction factor $k_1$ for branch 1 ( $\zeta_{eff} = k_1\zeta$). This allows to tune the $\zeta$ value with experimental evidence (default is 1).
• $\zeta$-correction factor $k_2$ for branch 2 ( $\zeta_{eff} = k_2\zeta$). This allows to tune the $\zeta$ value with experimental evidence (default is 1).

Figure 96: Geometry of a split fluid section type Idelchik 2

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.