The rapid change of fluid properties strongly influences the CFD calculation.
The accuracy of calculation worsens if the mesh is coarse.
If the meshes are refined sufficiently, the mesh number might increase.
The mesh number is limited by the amount of computer resources.
For that reason, we cannot refine the mesh sufficiently if the computer resource is insufficient.
Another means to avoid the radical property change inside the heat exchanger is to reduce the temperature difference between the inlet and outlet.
The fluid property change can be presumed as constant when the temperature difference is sufficiently small. However, a small temperature difference means that only a part of a heat exchanger can be simulated.
To predict the performance of whole heat exchanger,a new method of integrating these local data will be needed.