Ejector Model for High Temperature Fuel Cell Hybrid Systems: Experimental Validation at Steady-State and Dynamic Conditions

The aim of this work is the experimental validation of a steady-state and transient ejector model for high temperature fuel cell hybrid system applications. This is a mandatory step in performing the steady state and the transient analysis of the whole plant to avoid critical situations and to develop the control system. The anodic recirculation test rig, developed at TPG-University of Genoa; and already used in previous works to validate the ejector design models (OD and computational fluid dynamics), was modified and used to perform tests at transient conditions with the aim of ejector transient model validation. This ejector model, based on a "lumped volume" technique, has been successfully validated against experimental data at steady-state and transient conditions using air or CO2 at room temperature and at 150 degrees C in the secondary duct inlet. Then, the ejector model was integrated with the models of the connecting pipes, and with the volume simulation tool, equipped with an outlet valve, in order to generate an anodic recirculation model. Also in this case, the theoretical results were successfully compared with the experimental data obtained with the test rig. The final part of the paper is devoted to the results obtained with square wave functions generated in the ejector primary pressure. To study the effects of possible fast pressure variations in the fuel line (ejector primary line), the test rig was equipped with a servo-controlled valve upstream of the ejector primary duct to generate different frequency pressure oscillations. The results calculated with the recirculation model at these conditions were successfully compared with the experimental data too.