Microstructure in SOFC: electrochemical simulations and experiments

Solid oxide fuel cells (SOFCs) are highly efficient and environmentally friendly power sources that convert chemical energy directly into electricity and heat, without the need for combustion. Despite their many benefits, the performance and durability of SOFCs heavily depend on the quality of their porous anode and cathode components. There are significant challenges with regard to their commercialization due to the potential failure and degradation of their anode and cathode components. Optimizing SOFC electrodes requires obtaining critical microstructure parameters and understanding their impact on the overall performance. This can be achieved through advanced tomography techniques and fully coupled Multiphysics simulations, which provide insights into the quality of the electrode and the complex electrochemical processes that occur within it. In this thesis, experiments were conducted to investigate different anode microstructure impacts on SOFC performance through electrochemical analysis. Besides, 2D microstructure tomography was obtained to construct real 3D volumes. Based on the tomography information, the porosity and tortuosity of the porous electrode were calculated and compared. Different tortuosity calculation methods were compared to obtain values used for Multiphysics simulations. A fully coupled Multiphysics model was constructed step by step. Firstly, the electrochemical kinetic models are compared based on the Butler-Volmer equations. Secondly, different diffusion models are compared with and without Knudsen diffusion. Based on the 3D Multiphysics CFD model, the microstructure parameters' impact on the SOFC performance was studied. Meanwhile, a SOFC model based on different sealant materials was constructed to investigate the overall thermal stress distribution. Thermal stress at an electrode/electrolyte interface was also modelled and analyzed. The results showed that the interface contact mode and the geometry size of the SOFC component significantly impacted the thermal stress distribution and its values.In summary, the experiment analysis findings emphasize optimizing the microstructure design to balance gas diffusion, charge transport, and electrochemical reactions. The fully coupled Multiphysics models can be used for further SOFC design, regarding internal transport processes and mechanical stability. In general, this thesis has made contributions to the field of SOFCs

Theoretical investigation of the thermal performance of a novel solar loop-heat-pipe façade-based heat pump water heating system

The aim of the paper was to present a dedicated theoretical investigation into the thermal performance of a novel solar loop-heat-pipe façade based heat pump water heating system. This involved thermo-fluid analyses, computer numerical model development, the model running up, modelling result analyses and conclusion. An energy balance network was established on each part and the whole range of the system to address the associated energy conversion and transfer processes. On basis of this, a computer numerical model was developed and run up to predict the thermal performance of such a system at different system configurations, layouts and operational conditions. It was suggested that the loop heat pipes could be filled with either water, R134a, R22 or R600a; of which R600a is the favourite working fluid owing to its relatively larger heat transfer capacity and positive pressure in operation. Variations in the system configuration, i.e., glazing covers, heat exchangers, would lead to identifiable differences in the thermal performance of the system, represented by the thermal efficiency and COP. Furthermore, impact of the external operational parameters, i.e., solar radiation and ambient air temperature, to the system's thermal performance was also investigated. The research was based on an innovative loop-heat-pipe façade and came up with useful results reflecting the thermal performance of the combined system between the façade and heat pump. This would help promote development and market penetration of such an innovative solar heating technology, and thus contribute to achieving the global targets in energy saving and carbon emission reduction

New unique existence criteria for higher-order nonlinear singular fractional differential equations

In this paper, a nonlinear three-point boundary value problem of higher-order singular fractional differential equations is discussed. By applying the properties of Green function and some fixed point theorems for sum-type operator on cone, some new criteria on the existence and uniqueness of solutions are obtained. Moreover, two iterative sequences are given for uniformly approximating the positive solution, which are important for practical application. At last, we give two examples to illustrate the main results

Patient-derived xenografts or organoids in the discovery of traditional and self-assembled drug for tumor immunotherapy

In addition to the rapid development of immune checkpoint inhibitors, there has also been a surge in the development of self-assembly immunotherapy drugs. Based on the immune target, traditional tumor immunotherapy drugs are classified into five categories, namely immune checkpoint inhibitors, direct immune modulators, adoptive cell therapy, oncolytic viruses, and cancer vaccines. Additionally, the emergence of self-assembled drugs with improved precision and environmental sensitivity offers a promising innovation approach to tumor immunotherapy. Despite rapid advances in tumor immunotherapy drug development, all candidate drugs require preclinical evaluation for safety and efficacy, and conventional evaluations are primarily conducted using two-dimensional cell lines and animal models, an approach that may be unsuitable for immunotherapy drugs. The patient-derived xenograft and organoids models, however, maintain the heterogeneity and immunity of the pathological tumor heterogeneity