The electrokinetic conversion of flow work to electricity using a glass microchannel array coated with nano-layers of gold that serve as electrodes on both its ends was studied and a maximum power output of 1 mW at an efficiency of 1.3% is reported. The establishment of such a high power generation capability in combination with a low pressure drop (26 kPa) makes this electrokinetic work conversion device more practical than those previously reported in literature.
An analytic multi-physics model for pouch-type lithium-ion (Li-ion) batteries is presented. Both electrical and thermal processes are considered in the model to resolve their interplay on heat generation and battery thermal behavior. Voltage response of a sample Liion battery during galvanostatic discharge processes is measured to obtain a concentration-independent polarization expression. By numerically solving the charge balance equation on positive and negative electrodes in conjugation with the polarization expression, it is shown that the transfer current between the electrodes remains approximately constant, in particular when depth-of-discharge is less than 90%. Based on this observation, the electrochemical performance of the battery is simplified, and by using the method of separation of variables a closed-form electrical model is proposed. Joule heating on each electrode, calculated from the electrical model, is used as a local heat source in a two-dimensional battery thermal model. The distributed thermal model is solved analytically with the method of integral transform. The analytical results are successfully validated through comparisons with experimental and numerical data. It is confirmed that ohmic heating in the electrodes contributes to a relatively small portion (8-18%) of the total heat generation; nonetheless, since this heat is highly localized it results in spatial non-uniformity in temperature.
A new two-dimensional model is proposed to describe the electrical conduction in current collectors of prismatic lithium-ion batteries, and to investigate the effects of tab design on voltage drop. Polarization expression for a large-scale lithium-ion cell is determined experimentally and implemented in a numerical analysis to show that reaction current remains approximately uniform when depth-of-discharge is less than 85%. Based on this observation, a compact analytical model is developed to determine bulk and constriction/spreading resistances in current collectors. Moreover, the model predictions are successfully validated through comparisons with experimental data. It is demonstrated that constriction/spreading resistance in current collectors of the considered battery is fairly small; about 10% of the total cell resistance but it is larger than the contribution of bulk resistance which is about 3%. The model confirms that constriction/spreading increase with: decrease in the aspect ratio of the current collector, decrease in the tab width, and increase in the tab eccentricity.
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