A moving grid algorithm for a heat exchanger with phase changes Original Research Article

The numerical simulation of a chemical industry plant requires models for each unit operation. In flowsheeting, the whole system of resulting equations can be solved in an equation-oriented simulation package. We treat an important unit operation that requires a moving grid—the countercurrent heat exchanger where phase changes occur in the streams. The model is introduced, and two approaches to find a numerical solution for the moving phase changes are proposed—a static and a dynamic regridding algorithm based on the method of lines. The first approach, a splitting technique, results into a semi-explicit DAE of index 1 whereas the moving grid method yields a quasilinear DAE system. Examination and comparison show some advantages of the first method for our special problem where numerical simulation results are encouraging: phase changes are well tracked and the steady state for the desired pressure is finally reached.