> For the complete documentation index, see [llms.txt](https://lbl-2.gitbook.io/tough4-user-manual/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://lbl-2.gitbook.io/tough4-user-manual/preparation-of-model-input/keywords-and-input-data/conne.md). # CONNE Keywork CONNE is used for define the connections of model mesh. It must be placed after the keyword ELEME. **CONNE** introduces information for the connections (interfaces) between elements. Record **CONNE.1** Free format for 8 parameters ELNE1, ELNE2, ISOT, D1, D2, AREAX, BETAX, SIGX Or Format (A3, I2, A3, I2, 4I5, 5E10.4) (for 5 five-character element name only). EL1, NE1, EL2, NE2, NSEQ, NAD1, NAD2, ISOT, D1, D2, AREAX, BETAX, SIGX *ELNE1* first element name. *ELNE2* second element name. *EL1*, *NE1* code name of the first element (for formatted input only). *EL2*, *NE2* code name of the second element (for formatted input only). *NSEQ* number of additional connections in the sequence (used for formatted input only). *NAD1* increment of the code number of the first element between two successive connections sequence (used for formatted input only). *NAD2* increment of the code number of the second element between two successive connections (used for formatted input only). *ISOT* set equal to 1, 2, or 3; specifies absolute permeability to be *PER(ISOT)* for the materials in elements (*ELNE1*) and (*ELNE2*), where *PER* is read in block ROCKS. This allows assignment of different permeabilities, e.g., in the horizontal and vertical direction. ISOT can be in negative or a number large than 3 for some specific purposes such as in wellbore simulation (see [Section 7/wellbore flow/subsection 2](/tough4-user-manual/process-modeling/wellbore-flow.md)) and [active fracture model](/tough4-user-manual/appendix/d-description-of-fractured-flow/active-fracture-modle.md). *D1* distance (m) from first element to interface. *D2* distance (m) from second element to interface. *AREAX* interface area (m2). *BETAX* cosine of the angle between the gravitational acceleration vector and the line between the two elements. *GF* × *BETAX* > 0 (<0) corresponds to first element being above (below) the second element. *SIGX* “radiant emittance” factor for radiative heat transfer, which for a perfectly “black” body is equal to 1. The rate of radiative heat transfer between the two grid blocks is $$G\_{rad}=SIGX\*\sigma\_0*AREAX*(T\_2^4-T\_1^4)$$ (8-1) where $$\sigma \_0=5.6687e^{-8}J/m^2K^4s$$ is the Stefan-Boltzmann constant, and $$T\_1$$and $$T\_2$$ are the absolute temperatures of the two grid blocks. *SIGX* may be entered as a negative number, in which case the absolute value will be used, and heat conduction at the connection will be suppressed. *SIGX* = 0 will result in no radiative heat transfer. Repeat record CONNE.1 for the number of connections desired. Record **CONNE.2** A blank record closes the CONNE data block. Alternatively, connection information may terminate on a record with ‘+++’ typed in the first three columns, followed by element cross-referencing information. This is the termination used when generating a MESH file with TOUGH4. **Used in**: All EOS modules **Example**: *CONNE* // this is for input in the main input file *A1001, A1002, 3\*0, 1, 0.150000E-05, 0.153200E+00, 0.188500E+03, 2\*0.0* In the free format MESH file, TOUGH4 does not allow including NSEQ, NAD1, and NAD2 in input line: *CONNE* *A1001, A1002, 1, 0.150000E-05, 0.153200E+00, 0.188500E+03, 2\*0.0*