  The present paper is an attempt to demonstrate how the energy minimization
principle may be considered as a governing rule for the physical equilibrium
that determines the flow fields in tubes and networks. We previously
investigated this issue using a numerical stochastic method, specifically
simulated annealing, where we demonstrated the problem by some illuminating
examples and concluded that energy minimization principle can be a valid
hypothesis. The investigation in this paper is more general as it is based to a
certain extent on an analytical approach.
