1,720,981 research outputs found
Micropolar flow over a porous stretching sheet with strong suction or injection
No full textWe consider self-similar boundary layer flow of a micropolar fluid driven by a porous stretching sheet. For the limiting cases of large suction or injection, an order of magnitude analysis is used to obtain analytic results for the shear stress and the microrotation at the surface. Our analysis reveals how the wall shear stress is significantly affected by two of the parameters in the micropolar model and we indicate how our findings may be of use in technological applications involving micropolar flow
Modeling the stepped potential discharge of primary alkaline battery cathodes
No full textA novel model for the potentiostatic discharge of primary alkaline battery cathodes is presented. The model is used to simulate discharges resulting from the stepped potential electrochemical spectroscopy (SPECS) of primary alkaline battery cathodes cathodes, and the results are validated with experimental data. We show that a model based on a single (or mean) reaction framework can be used to simulate multi-reaction discharge behaviour and we develop a consistent functional modification to the kinetic equation of the model that allows for this to occur. The model is used to investigate the effects that the initial exchange current density, i00, and the diffusion coefficient for protons in electrolytic manganese dioxide (EMD), DH+, have on SPECS discharge. The behaviour observed is consistent with the idea that individual reduction reactions, within the multi-reaction, reduction behaviour of EMD, have distinct i00 and DH+ values
A least squares based finite volume method for the Cahn-Hilliard and Cahn-Hilliard-reaction equations
No full textA vertex-centred finite volume method (FVM) for the Cahn-Hilliard (CH) and recently proposed Cahn-Hilliard-reaction (CHR) equations is presented. Information at control volume faces is computed using a high-order least-squares approach based on Taylor series approximations. This least-squares problem explicitly includes the variational boundary condition (VBC) that ensures that the discrete equations satisfy all of the boundary conditions. We use this approach to solve the CH and CHR equations in one and two dimensions and show that our scheme satisfies the VBC to at least second order. For the CH equation we show evidence of conservative, gradient stable solutions, however for the CHR equation, strict gradient-stability is more challenging to achieve
A comparison of the Nernst-Planck and Maxwell-Stefan approaches to modelling multicomponent charge transport in electrolyte solutions
No full textAn understanding of charge transport in electrolytic solutions is of vital importance in the modelling and simulation of electrochemically and photoelectrochemically active porous media. To this end, we present two multicomponent charge transport models for an electrolyte system based on the generalized Maxwell-Stefan equations and the dilute solution Nernst-Planck equations. These transport models are used to develop two further models of a simple electrochemical cell consisting of ideally polarizable metal electrodes and a binary electrolyte. The results from the numerical solution of these Maxwell-Stefan and Nernst-Planck models are compared for a range of electrolyte concentrations and the applicability of each model approach is discussed
A mathematical model for the anodic half cell of a dye-sensitised solar cell
No full textWe present a mathematical model of the steady-state current produced by the anodic half cell of a dye-sensitised solar cell (DSC) under both illuminated and non-illuminated conditions. A one-dimensional transport model that describes the transport of charged species via\ud
migration and diffusion within the electrolyte filled pores and the porous semiconductor that constitutes the porous anode of the DSC is given. This model is coupled to an interfacial model, developed previously by the authors, that describes charge transfer across the semiconductor–dye–electrolyte interface by explicitly accounting for each reaction at the interface involving dye molecules, electrolyte species, and semiconductor electrons. An equivalent circuit extension to the anode model (in the form of a boundary condition) is developed in order to validate some of the simulation results of the anode model with experimental results obtained from a full DSC\ud
specifically commissioned for the study. Parameter values associated with the model are obtained from the literature or experimentally from the specifically commissioned cell. A comparison of the numerical simulation results with experimental results shows a favourable correspondence without the need to fit parameter values
Modelling of the evaporation of a droplet suspended in a binary atmosphere
No full textThe process of spray drying is applied in a number of contexts. One such application is the production of a synthetic rock used for storage of nuclear waste. To establish a framework for a model of the spray drying process for this application, we here develop a model describing evaporation from droplets of pure water, such that the model may be extended to account for the presence of colloid within the droplet. We develop a spherically-symmetric model and formulate continuum equations describing mass, momentum, and energy balance in both the liquid and gas phases from first principles. We establish appropriate boundary conditions at the surface of the droplet, including a generalised Clapeyron equation that accurately describes the temperature at the surface of the droplet. To account for experiment design, we introduce a simplified platinum ball and wire model into the system using a thin wire problem. The resulting system of equations is transformed in order to simplify a finite volume solution scheme. The results from numerical simulation are compared with data collected for validation, and the sensitivity of the model to variations in key parameters, and to the use of Clausius–Clapeyron and generalised Clapeyron equations, is investigated. Good agreement is found between the model and experimental data, despite the simplicity of the platinum phase model
The Modelling of Primary Alkaline Battery Cathodes: A Simplified Model for porous manganese oxide particle discharge
No full textA simplified model, to that produced previously by the authors, for the galvanostatic discharge of primary alkaline battery cathodes is presented. Laplace transform and perturbation methods are employed to obtain the leading order spatial and temporal behaviour of the porous cathode over two distinct size scales. It is shown that for a wide range of industrially relevant discharge conditions the time taken for KOH electrolyte to diffuse into a porous electrolytic manganese dioxide particle is fast compared with the cathodic discharge time and that ohmic losses within the graphite phase of the cathode can be considered to be negligible. Numerical solution of the simplified model equations is discussed and the results are validated against relevant experimental data
Modelling interfacial charge transfer in dye-sensitised solar cells
No full textA mathematical model of interfacial charge transfer within dye-sensitised solar cells (DSC) is presented for the semiconductor–dye–electrolyte interface. A general framework for the model equations of interfacial current is developed. The model accounts for the transfer of charge produced by reactions involving dye molecules, electrolyte species and adsorbed electrons at three semiconductor surface states. The model framework allows for identification of the required kinetic parameters necessary for solving the model equations. The general framework serves as a motivation for discussion on obtaining the required kinetic parameter values experimentally
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