12In this work, a three-dimensional PEM fuel cell model has been developed and is used to investigate the 13 effects of water flooding on cell performance parameters. The presence of liquid water in the cathode gas diffusion 14 layer (GDL) limits the flow of reactants to the cathode catalyst layer, thereby reducing the overall reaction rate and concentration of reactants/products and cell current densities. It is determined that the gas diffusion layer 23 permeability has little or no effect on the current densities due to the diffusion dominated nature of the gas flow. 24However, through the incorporation of percolation theory based effective diffusivity model; a marked reduction in 25 the cell performance is observed which closely resembles published experimental observations. This is a reasonable 26 approximation for effects of water flooding which has been inherently used for further parametric studies. 27

This paper reports a review of an environmentally clean and efficient source of energy such as solid oxide fuel cell hybrid systems. Due to climate concerns, most nations are seeking alternative means of generating energy from a clean, efficient and environmental-friendly method. However, this has proven a big hurdle for both academic and industry researchers over many years. Currently, practical and technically feasible solution can be obtained via an integration of a microturbine and a fuel cell (hybrid systems). Combining the two distinct systems in a hybrid arrangement the efficiency of the microturbine increases from 25-30% to the 60-65% range. Hence, this paper outlines an engineering power generation solution towards the acute global population growth, the growing need, environmental concerns, intelligent use of energy with attendant environmental and hybrid system layouts concerning arising problems and tentative proposed solutions. Furthermore, advantages of a solid oxide fuel cell hybrid systems with respect to the other technologies are identified and discussed rationally. Special attention is devoted to modelling with software and emulator rigs and system prototypes. The paper also reviews the limitations and the benefits of these hybrid systems in relationship with energy, environment and sustainable development. Few potential applications, as long-term potential actions for sustainable development, and the future of such devices are further discussed. KeywordsSolid oxide fuel cell; hybrid system; prototypes; modelling with software and emulator rigs; environmentally clean energy; high efficiency.

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Computational fluid dynamics (CFD) is applied to study the unsteady flow inside a pulsatile pump left ventricular assist device, in order to assess the sensitivity to a range of commonly used turbulence models. Levels of strain and wall shear stress are directly relevant to the evaluation of risk from haemolysis and thrombosis, and thus understanding the sensitivity to these turbulence models is important in the assessment of uncertainty in CFD predictions. The study focuses on a positive displacement or pulsatile pump, and the CFD model includes valves and moving pusher plate. An unstructured dynamic layering method was employed to capture this cyclic motion, and valves were simulated in their fully open position to mimic the natural scenario, with in/outflow triggered at control planes away from the valves. Six turbulence models have been used, comprising three relevant to the low Reynolds number nature of this flow and three more intended to investigate different transport effects. In the first group, we consider the shear stress transport (SST) [Formula: see text] model in both its standard and transition-sensitive forms, and the 'laminar' model in which no turbulence model is used. In the second group, we compare the one equation Spalart-Almaras model, the standard two equation [Formula: see text] and the full Reynolds stress model (RSM). Following evaluation of spatial and temporal resolution requirements, results are compared with available experimental data. The model was operated at a systolic duration of 40% of the pumping cycle and a pumping rate of 86 BPM (beats per minute). Contrary to reasonable preconception, the 'transition' model, calibrated to incorporate additional physical modelling specifically for these flow conditions, was not noticeably superior to the standard form of the model. Indeed, observations of turbulent viscosity ratio reveal that the transition model initiates a premature increase of turbulence in this flow, when compared with both experimental and higher order numerical results previously reported in the literature. Furthermore, the RSM is indicated to provide the most accurate prediction over much of the flow, due to its ability to more correctly account for three-dimensional effects. Finally, the clinical relevance of the results is reported along with a discussion on the impact of such modelling uncertainties.

A detailed computational fluid dynamics (CFD) study of transient, turbulent blood flow through a positive displacement left ventricular assist device is performed. Two common models for non-Newtonian blood flow are compared to the Newtonian model to investigate their impact on predicted levels of shear rate and wall shear stress. Given that both parameters are directly relevant to the evaluation of risk from thrombus and haemolysis, there is a need to assess the sensitivity to modelling non-Newtonian flow effects within a pulsatile turbulent flow, in order to identify levels of uncertainly in CFD. To capture the effects of turbulence, the elliptic blending Reynolds stress model is used in the present study, on account of superior performance of second moment closure schemes previously identified by the present authors. The CFD configuration includes two cyclically rotating valves and a moving pusher plate to periodically vary the chamber volume. An overset mesh algorithm is used for each instance of mesh motion, and a zero gap technique was employed to ensure full valve closure. The left ventricular assist device was operated at a pumping rate of 86 BPM (beats per minute) and a systolic duration of 40% of the pumping cycle, in line with existing experimental data to which comparisons are made. The sensitivity of the variable viscosity models is investigated in terms of mean flow field, levels of turbulence and global shear rate, and a non-dimensional index is used to directly evaluate the impact of non-Newtonian effects. The clinical relevance of the results is reported along with a discussion of modelling uncertainties, observing that the turbulent kinetic energy is generally predicted to be higher in non-Newtonian flow than that observed in Newtonian flow. Copyright © 2016 John Wiley & Sons, Ltd.

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To achieve active noise cancellation over a large area, it is often necessary to get a measure of the physical properties of the noise source to devise a counter measure. This, however, is not practical in many cases. A mathematical approach, the difference potential method, can provide an alternative solution for active shielding over a large area. In this approach, the cancellation of unwanted noise requires only measurements near the boundary surface but not at the source itself, and no other information is required. Moreover, the solution based on difference potentials applies to bounded domains in the presence of acoustic sources inside the domain to be shielded. This paper reports on the results of experimental validation for the methodology. It has been demonstrated that while preserving the wanted sound, the developed approach can cancel out the unwanted noise. The volumetric noise cancellation offered by the proposed methodology, along with leaving the wanted sound unchanged, is a unique feature compared with other techniques available in the literature. It can be most useful in the context of applications related to civil aviation, in particular, for eliminating the exterior noise inside the passenger compartments for both current and future generations of commercial aircraft.

This paper reports an entirely new simulation tool for a hybrid system emulator facility built by the Thermochemical Power Group (TPG) at the University of Genoa, Italy. This new software was developed with the following targets: realtime performance, good stability level and high calculation reliability. In details, to obtain real-time performance a new approach based on 0-D technique was chosen also for components usually analysed with 1-D or 2-D tools (e.g. the recuperator). These are essential key aspects to operate it in hardware-in-the-loop mode or to evaluate predictive results for long transient operations. This work was based on collaboration between the University of Manchester, UK and the University of Genoa, Italy.\ud The activity was carried out with a test rig composed of the following technology: a microturbine package able to produce up to 100 kWe and modified for external connections, external pipes designed for several purposes (by-pass, measurement or bleed), and a high temperature modular vessel necessary to emulate the dimension of an SOFC stack. The real-time transient model of this facility was developed inside the Matlab-Simulink environment with the following modelling approach: a library of components allows to reach a high level of flexibility and an user-friendly approach. This model includes the machine control system as an essential device to analyse further layouts (new components in the rig) and hardware-in-the-loop operations.\ud The experimental data collected in the laboratory by TPG were used to validate the simulation tool. The results calculated with the model were satisfactory compared with experimental data considering both steady-state and transient operations. The most important innovative aspects of this work are related to this wide validation range (not only small power steps, but the whole operative range was considered) obtaining real-time performance and considering microturbine conditions different from standard operations (additional pressure and temperature losses and unusual thermal capacitance). The modelling simplified approach used for such a complex system is an important innovative aspect, because usually the model reliability performance is obtained with more complex (and not real-time) tools. This work is based on an innovative modelling approach based on 0-D tools able to operate in real-time mode (as necessary for hardware-in-the-loop tests) with an accuracy level comparable with more complex and more time consuming software.\ud This validated tool is an important base for future calculations to study innovative hybrid system layouts. For instance, TPG is planning to analyse the option of increasing fuel cell pressure and performance with a booster system (e.g. a turbocharger)