Heat flow between groups through direct conductances

The heat flow between groups A and B via direct conductances is evaluated by summing the heat flow through all conductances connecting elements of group A and B directly.

This is expressed by the following equation:

QdirectBA is the total heat flow from B to A through direct conductances (radiative, conductive, thermal coupling, etc.), where one end of conductance lies in B, other in A.

GABk is the kth direct conductance between A and B.

TAi, TBj are the temperatures of the elements eAi and eBj, joined by the conductance GABk.