Vapor Compression System Modelica Library for Aircraft ECS

This work presents a Modelica library aimed to simulate vapor compression systems at both steady and transient conditions. The simulation of these specific systems is particularly challenging from both the phenomena and the numerical resolution point of views. The main goal of the library is to provide, not only accuracy and robustness, but also very low computational time. It is worth mentioning that, although the baseline version of the library is currently operative, its development continues in order to improve or add new features.Most of the components developed for the library are simulated by means of look-up tables or efficiency curves for the sake of quickness. The main efforts were focused on two critical aspects of the system. On the one hand, heat exchanger models were developed based on a switching moving boundary approach in order to have a relatively high ratio between accuracy and resolution time. This method takes into account the distribution of phases along heat exchangers which is crucial for the accurate simulation of evaporators and condensers. The whole heat exchanger domain is divided in three zones, namely, sub-cooled, superheated and two-phase, and its computational time is lower than distributed models as only one control volume per zone is used. On the other hand, several aspects of the whole cycle resolution were tackled with meticulosity, namely, the management of refrigerant amount, the initialization procedure, the thermostatic control loop, the numerical issues at null mass flow rate, the convergence criteria, and other aspects related to the transient simulation. The results shown in this work are devoted to highlight the numerical robustness of the system and its components together with the low computational time required for simulations.Peer ReviewedPostprint (published version