The Macro Model is quite suitable for thin rectangular heat exchanger cores, where the pass-to-pass is perpendicular to the primary flow direction and the auxiliary flow is uniform (so it can be treated as a 1D flow). Moreover, the mesh should be uniform and structured. However, many practical heat exchangers have a non-rectangular core and the auxiliary fluid, before reaching the core, may pass through arbitrary shaped inlet tanks, which make them highly non-uniform. It is quite possible that due to the complex shape of the core and or ease of meshing, the structured mesh may not be the obvious choice. These shortcomings of the macro model can be easily overcome by using the dual cell heat exchanger model. This model allows the solution of both the primary and auxiliary flow on separate co-located meshes and couples the two flows only through heat transfer at the heat exchanger core.