14.1.1 Restrictions

The following restrictions exist for the macro heat exchanger models:

• The core must be approximately rectangular in shape.

• The primary fluid streamwise direction (see this equation in the separate Theory Guide) must be aligned with one of the three orthogonal axes defined by the rectangular core.

• Flow acceleration effects are neglected in calculating the pressure loss coefficient.

• For the simple-effectiveness-model, the primary fluid capacity rate must be less than the auxiliary fluid capacity rate.

• Auxiliary fluid phase change cannot be modeled using the ntu-model.

• The macro-based method requires that an equal number of cells reside in each macro of equal size and shape.

• Coolant flow is assumed to be 1-D.

• The pass width has to be uniform.

• Accuracy is not guaranteed when the mesh is not structured or layered.

• Accuracy is not guaranteed when there is upstream diffusion of temperature at the inlet/outlet of the core.

• Non-conformal meshes cannot be attached to the inlet/outlet of the core. An extra layer has to be created to avoid it.