The GF number for 1-D heat transfer has the form X- - B- - G-T-  where the dashes represent numbers. Designation X- -  is required, the rest is optional.
 

Number	Specifies
X - -	Types of boundary conditions, one digit for each boundary.  Boundary types are: 1=specified temp.; 2=specified flux; 3=specified convection; and, 0=semi-infinite (boundary far away).
B - -	Heat effect at boundaries, one digit for each boundary: 0=none; 1=steady; and, 2=linear-in-time,3=polynomial-in-time.
G -	Volume (internal) heat generation:  G0=none; G1=uniform; and, G2=linear, G3=polynomial.
T -	Initial condition (transient only):  T0=zero; T1=uniform; and, T2=linear, T3=polynomial.

Example:  X12B10G1

Designation X12B10G1 has three segments.  Segment X12 represents a body described by a Cartesian coordinate system with a type 1 boundary (specified temperature) at x=0, and type 2 boundary (specified flux) at x=L.  Segment B10 describes the boundaries further with a constant, non-zero temperature at x=0, and at x=L the boundary flux is zero (insulated boundary).  Segment G1 indicates uniform heat generation throughout the body. Because the "T" designation is missing, the heat transfer is (assumed to be) steady.

For more on the GF numbering system see Organization of the GF Library .