HYDROSOFC

Design oriented flow distribution optimization of the solid oxide fuel cell stack operating under electric load

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 Obiettivo del progetto (Objective)

'Solid oxide fuel cells (SOFC) offer high electrical efficiency of power generation, multifuel operation and internal reforming capabilities among other benefits. However, flow maldistribution of gas reactants among cells of the fuel cell stack and uneven utilization of the active cell area is one of the reasons for the performance loss in the scale-up process or even a stack failure at high electric load, high fuel utilization conditions. Efficient and uniform supply of reactants and removal of products was previously studied using computational fluid dynamics (CFD) methods. These methods, although accurate, require significant computing power, computing time and offer limited optimization capabilities. The flow networks modeling approach offers accuracy sufficient for the engineering design together with the accelerated optimization capabilities. It shows accuracy sufficient for engineering design optimization. In the proposed model, design oriented mass and flow distribution model of the SOFC stack, stack manifolds and flow channels are simulated as a network of differential hydraulic resistances. In order to simulate hydraulic network operation under electric load conditions, differential model of the SOFC cell (DCM) will be implemented and combined with the hydraulic networks model. In the DCM model, principal geometrical parameters of the cell will be implemented (electrolyte/electrode thickness, electrode porosity) together electrochemical performance characteristics, including polarization characteristics. The modeling results will explain physical mechanisms of flow distribution in the SOFC stack. They will also allow optimization of combined manifold and flow channels geometry under both no-load and electric load operation.'

Introduzione (Teaser)

Fuel cells convert the chemical energy in fuels (hydrogen and hydrocarbons such as methane, butane, gasoline or diesel) into electrical energy to power devices. EU-funded researchers developed a simplified computational model simulating flow distribution within the fuel cell stack with the potential to enhance performance and efficiency and thus the widespread implementation of this clean, renewable form of energy.

Descrizione progetto (Article)

Over the past 50 years, fuel cells have been gaining interest as an alternative renewable form of energy to minimise dependence on fossil fuels while protecting the environment.

Particular focus has been on solid oxide fuel cells (SOFCs) because of their high-efficiency, low-cost, multi-fuel capacity and obvious environmental benefits. With no moving parts rendering them vibration-free, they even eliminate noise pollution.

However, uneven and inefficient distribution of reactant gas flows especially under high fuel utilisation conditions often result in decreased efficiency and performance loss.

European researchers with funding for the Hydrosofc project sought to apply simple flow network modelling techniques, computationally cheaper than complex computational fluid dynamics (CFD) methods, to investigate the most important factors affecting flow distribution and enable its reliable prediction. Such methods could provide the accuracy engineers require faster and with enhanced optimisation capabilities.

Scientists developed three different models to simulate a range of effects and their importance in flow distribution, including a semi-three-dimensional (3D) CFD model, a 2D analytical model and a 2D hydraulic model.

They determined that operation of the stack under electric load (high fuel utilisation) conditions increases maldistribution for U-flow manifold configurations (a U-turn of sorts) in which flow enters and leaves from the same end of the stack compared to Z-flow, characterised by flow entering on one end and leaving on the other end.

According to the models, maldistribution was determined by the ratio of pressure drop in the inlet and outlet manifolds of the model to the pressure drop in the fuel cell flow field. Experimental measurements confirmed computational results and supported the feasibility of the hydraulic model in calculating flow distribution in the fuel stack with the accuracy required for engineering design estimates.

Hydrosofc scientists have provided a simplified computational flow model capable of predicting maldistributions of flow critical to SOFC performance and overcoming one of the main stumbling blocks so far to widespread SOFC commercial exploitation.