Temperature Dependent Conductors

The support straps are made of a glass epoxy material whose thermal conductivity varies greatly with temperature. Since we don't yet know what temperature the strap will be, it is best to use the SIV option. This option allows the user to define a single conductor having a temperature varying conductance. The conductance is supplied in a doublet array of conductance versus temperature that is entered in the ARRAY DATA block. The average temperature of the two adjoining nodes (ie. (TNA+TNB)/2. ) is used as the independent value for the interpolation. If the average temperature exceeds the data in the array then the last conductance (or the first) value in the array is used. The array data is not extrapolated. The format of a SIV node is shown below. SIV G#, N1, N2, A#, FAC $ (basic format) where:

G# conductor number, (Integer)
N1,N2 node pair connected by the conductor, (Integer)
A# doublet array number of conductance versus temperature, (Integer)
FAC floating point multiplying factor, (Floating Point)

SIV  4001,  1,  621, 1,  0.123E+01   $ STRAPS L=30 cm, AREA=36.8 sqcm cross-section

In our example conductor 4001 is used to connect nodes 1 and 621 together. Array number 1 is interpolated using the average temperature of nodes 1 and 621. That value is multiplied by 1.23 and is then used for the conductor. The conductor is evaluated every iteration in both the steady state and transient routines. Conductors 41, 42 and 43 represent part of the dewar support system.

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