Performance Assessment of Bladeless Micro-Expanders Using 3D Numerical Simulation

This paper summarizes the development of fully 3D Computational Fluid Dynamics (CFD) analysis for bladeless air micro expander for 200 W and 3 kW rated power. Modelling of nozzle along with rotor is done using structured mesh. This analysis, for the first time, demonstrates the interaction between nozzle and rotor using compressible flow density-based solver. The Shear Stress Transport (SST) turbulence model is employed to resolve wall effects on the rotor and to determine the shear stress accurately. The results illustrate the flow field inside stator and rotor along with complicated mixing zone between stator and rotor. The comparison of rotor-stator CFD simulation results is done with experiments to preliminary validate the model. The losses in the turbine are discussed with the help of experimental and numerical data

Validated ejector model for hybrid system applications

The aim of this work is the presentation of a new model for ejector performance calculation using a commercial tool. Due to the critical issues in recirculation performance, special attention is devoted to applications in hybrid systems based on high temperature fuel cells. The theoretical activity is supported by an experimental rig able to operate tests on ejectors at different operative conditions, with a layout similar to the fuel cell anodic recirculation. The model validation, operated considering experimental data obtained with this rig, is essential to evaluate the tool performance for design and off-design calculations. This aspect is particularly critical due to important limitations in the recirculation ratio (especially for the anodic side), to avoid unacceptable operative conditions in the fuel cells. The results presented in this work were obtained with this validated model for an ejector applied on the anodic side of a Solid Oxide Fuel Cell (SOFC). A parametric analysis was carried out to show the effects of several parameters on the recirculation performance. The fully independent analysis of the influence of different properties (carried out with a specifically validated model) is an important innovative result for the application of such ejectors on high temperature fuel cells

state of charge estimation of thermal storages for distributed generation systems

Abstract The aim of this work is the development of three different models to calculate the enthalpy content of a stratified water thermal storage tank from discrete temperature measurements. The difficulty related to enthalpy value evaluation comes from the discrete temperature measurement along the storage (often only 2 to 4 temperatures along the volume height are known): the actual temperature distribution between two subsequent probes is unknown. Three different models based on three different approaches were developed and compared, basing on experimental data. A first model calculates the enthalpy value considering the measured temperatures and the thermal power difference between generation and consumption. The second model uses a mathematical pre-defined temperature shape fitted considering real-time experimental data. The latter model is based on a 1-D physical approach using a multi-nodal method. All the models were validated against the experimental data obtained from the distributed generation laboratory installed in Savona, Italy

Turbocharged SOFC System: Emulation and Control in Cyber-Physical Mode

The objective of this work regards an SOFC system pressurized by a turbocharger and the related emulation tests for control system development. Due to the interest in coupling high efficiency operations with reasonable capital costs a turbocharged SOFC plant layout has been proposed. This is due to significant cost decrease (in comparison with microturbine-based SOFC hybrids) related to the application of a turbocharger based on large mass manufacturing process. Moreover, the system has been sized to work with biogas to operate with a renewable source. Due to the difficulties in studying the SOFC/turbocharger integration, especially for the dynamic and control aspects, the University of Genoa developed a devoted test rig where the fuel cell is emulated with a pressure vessel equipped with a burner (to have the same temperature range) and inert ceramic material (to have the same time-dependent response). The emulation tests presented in this work have been carried out to demonstrate the system feasibility in dynamic conditions and to assess the control system performance

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 (0D 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 \u201clumped volume\u201d technique, has been successfully validated against experimental data at steady-state and transient conditions using air or CO2 at room temperature and at 150\ub0C 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

Experimental Validation of an Unsteady Ejector Model for Hybrid Systems

The aim of this work is the experimental validation of a transient ejector model for hybrid system applications. This is a mandatory step in performing the transient analysis of the whole plant to avoid critical situations and to develop the control system. So, the anodic recirculation test rig already used in previous works to study the ejector design validating the steady-state 0-D and CFD models, was used in this work to perform tests at transient conditions and to validate the ejector transient model. An initial validation was carried out at steady-state conditions, then the ejector transient model was successfully compared with the experimental data, also under unsteady conditions. A second step was carried out to better investigate the whole anodic recirculation system. So, the validated ejector transient model was connected to the components necessary to simulate the pipes, the valves and the anodic volume. Also in this case, the calculated results were successfully compared with the experimental data obtained with the laboratory test rig. The final part of the paper is devoted to the results obtained at impulse conditions. In fact, this work investigates the effects on the anodic ejector and on the whole anodic circuit coming from fuel line impulses caused by possible unsteadiness conditions. The results obtained with impulses at different frequency values were successfully compared with the experimental data

Emulatore celle a combustibile: controllo dinamico temperature e pressione stack, monitoraggio remoto impianto ibrido con microturbina

Questo articolo presenta l'utilizzo di NI Compact FieldPoint e LabVlEW per il monitoraggio ed il controllo di un impianto emulatore di sistemi ibridi con microturbina a gas recuperata (Turbec T100) da 100 kW elettrici, accoppiata con un volume modulare di 4 m3 per l'emulazione di sisterni ibridi con cella a combustibile ad alta temperatura. L'impianto sperimentale, installato presso il laboratorio dell'Universit\ue0 di Genova, DIMSET-TPG, a Savona \ue8 il primo esempio in Europa ed il secondo al mondo del suo tipo, in quanto si propone di studiare sperimentalmente l'accoppiamento di una microturbina a gas con un volume modulare, al fine di verificare il funzionamento della macchina e del suo controllo in condizioni di forte off-design tipiche di tali sistemi ibridi e durante i transitori