فهرست مطالب mehdi borji

Carbon deposition has a serious effect on the failure mechanism of solid oxide fuel cells. A comprehensive investigation based on a two-dimensional model of a solid oxide fuel cell with the detailed electrochemical model is presented to study the mechanism and effects of carbon deposition and unsteady state porosity variation.  Studies of this kind can be an aid to identify the SOFC optimal working conditions and provide an approximate fuel cell lifetime. It has been revealed that, due to carbon deposition, the porosity coefficient of the fuel cell decreases. Consequently, a reduction in the amount of fuel consumption along the fuel cell and the chemical and electrochemical reaction rates are resulted which can be clearly seen in the off-gases molar ratio. The percentage of output fuel changes in the timeframe is useful information for optimizing CHP systems including fuel cells. The percentage of the output water vapor, which usually increases compared to the input, decreases by 17% at the end of the working period. Also, unreacted methane in the output of the fuel cell increased by 12%; in other words, it is wasted. The other consequence of carbon deposition reduced electrochemical and chemical reaction rates and the reduction of temperature difference along the cell. The study shows that after 145 working days, the temperature difference along the cell varies from 117 °C for the starting time to 7 °C. Also, by reducing the current density, the cell output power density decreases by 72% after 145 working days.

The development of air pollution control strategies is a relatively complex process that has various aspects; there are also development plans in urban transportation networks, but this models are mainly unable to investigate the simultaneous effects of increasing and decreasing on air pollution. In this research, a dynamic system model has been created to investigate various parameters affecting air pollution compared to their long-term study over 20 years. The model is developed by creating economic, social, environmental and transportation sub-models and their simultaneous relationship to study public transport infrastructure development programs in urban air pollution and evaluates and compares the performance of public transportation and helps to adopt innovative policies for its future planning and management. To evaluate the developed model, the results of 14 criteria in 14 scenarios based on 3 general strategies were reviewed and three-dimensionalization methods were used to assess the policies. The results of the study led to the presentation of the proposed package of public transport policy, which shows that the quality improvement policy of the metro and BRT have been evaluated as the best policies among disposal and absorption policies. The novelty of this paper is the long-term review of various policies as well as all modes of transportation in the system dynamics model, the results of which can be the basis of urban transportation policy.

In the present study, heat transfer enhancement of a non-Newtonian nanofluid by different arrangements of double fins in a corrugated channel was numerically investigated. Finite volume method is used to solve governing equations of flow and energy with assumptions of 2D, steady-state, and single phase. The fluid flow is in the hydraulically laminar regime and the channel is under a constant heat flux. A set of case studies are conducted for a corrugated channel model to analyze the influence of the main contributing factors; Reynolds number, nanofluid volume fraction, the different fin configurations, on the flow field and the heat transfer characteristics as well. . Results indicate that using non-Newtonian fluid of water+0.5%CMC instead of water fluid leads to enhance heat transfer. The numerical results showed that implementing configuration D in a corrugated channel leads to heat transfer rate compared to other configurations. Besides, for configuration D, raising the Reynolds number from 200 to 1000 and the nanofluid volume fraction from 0.5% to 1.5% cause the mean Nusselt number and performance evaluation index to increase about 9.85% and 9.09%, respectively.

The main important roles of bipolar plates in solid oxide fuel cells are the uniform distribution of reactants to the reaction sites, the collection of current, and the separation of each cell from another. Therefore, the performance of a solid oxide fuel cell is highly dependent on air and fuel flow channel design. In order to investigate how the geometry of air and fuel flow channels affects performance, current, and power density, simulation results are discussed to evaluate the performance of two types of fuel cells with direct ducts and converging-diverging ducts. In this research, a three-dimensional model of an anode-supported hydrocarbon fueled solid oxide fuel cell is presented. The results show that the pressure difference between the converging diverging channels produces a transverse flow in the channels and ribs which is in favor of better distribution of the reactants in the fuel cell with the converging diverging channels. This transverse velocity causes a 6% increase in fuel consumption in the cell with converging diverging channels than the cell with direct channels at a voltage of 0.7V, but due to the reduction of the reaction area of this cell compared to the usual cell, the current density is 10% lower. At voltages above 0.55V, fuel cells with converging diverging channels have a higher fuel consumption than fuel cells with direct channels due to the presence of transverse flows.