This strategy acts on the terms ∂ρ/∂p and ∂ρ/∂h. The peak in the density derivative occurring after the transition from liquid to two-phase is truncated, as shown in the figure below. The maximum time derivative of the density is a model parameter and the maximum partial derivatives are calculated using the following equation:

This strategy conserves mass balance in each cell, except when a phase transition occurs. In this case, a fictitious creation or destruction of mass appears. **The error of this method on the simulation results and on the heat balances can be significant. It should therefore be used with care.**

This approach can be implemented at the Modelica level, i.e. it does not involve a modification of the equation of state.

# Reference

Sylvain Quoilin, Ian Bell, Adriano Desideri, and Vincent Lemort. *Methods to increase the robustness of finite-volume flow models in thermodynamic systems*. To be published in Energies, 2014.