A simple algebraic methodology for computing turbulent stresses and fluxes in arrays of heat exchanger elements is proposed. An effective Reynolds number is computed from the back-projection of the friction or heat transfer factor onto the low-Reynolds-number profile. This is then used to obtain the turbulent viscosity for fluid friction, or turbulent Prandtl number, for heat transfer. It is shown that under certain circumstances, the resulting mathematical expression is consistent with the Brinkman-Forchheimer modified form of Darcy's law and also with the Reynolds quadratic form for frictional/heat transfer resistance. The model is critically appraised in comparison to empirical data for compact and tube bank heat exchangers. The circumstances where it renders a good predictive measure are highlighted and discussed critically.