Modeling and simulation of micro direct methanol Fuel Cells

Fuel cells have unique technological attributes: efficiency, absence of moving parts and low emissions. The Direct Methanol Fuel Cell (DMFC) has attracted much attention due to its potential applications as a power source for transportation and portable electronic devices. With the advance of micromachining technologies, miniaturization of power sources became one of the trends of evolution of research in this area. Based on the advantages of the scaling laws, miniaturization promises higher efficiency and performance of power generating devices, so, MicroDMFC is an emergent technology. Models play an important role in fuel cell development since they facilitate a better understanding of parameters affecting the performance of fuel cells. In this work, a steady state, one-dimensional model accounting for coupled heat and mass transfer, along with the electrochemical reactions occurring in a fuel cell, already developed and validated for DMFC in [1-3], is used to predict Micro DMFC performance. The model takes in account all relevant phenomena occurring in a DMFC. Polarization curves predicted by the model are compared with experimental data existing in literature and the model shows good agreement, mainly for lower current densities. The model is used to predict some important parameters to analyze fuel cell performance, such as water transport coefficient and leakage current density. This easily to implement simplified model is suitable for use in real-time MicroDMFC simulations

Impact of iron amendment on soil bacterial abundance and diversity

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Efeito de genótipo e ambiente sobre o percentual de grãos esverdeados de soja, em seis locais da região Sul de Mato Grosso do Sul, safra 2004/05.

Em grãos de soja, tem-se constatado diferentes níveis de esverdeamento entre cultivares e locais de semeadura da cultura. Com o objetivo de verificar os efeitos de genótipo e ambiente sobre a incidência de grãos esverdeados, foi conduzido o presente trabalho utilizando-se oito cultivares de soja (BRS 133, BRS 181, BRS 239, EMBRAPA 48, BRS 206, BRS 240, BRS 241 e CD 202) em seis ambientes de Mato Grosso do Sul, na safra 2004/2005bitstream/item/38718/1/BP200530.pdfDocumento on-line

Microfluidic paper-based analytical devices for the determination of salivary NOx

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Determination of nitrate and nitrite in human saliva with a specially designed microfluidic paper-based analytical device (μPAD)

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On-hand tool for ammonium and urea determination in saliva to monitor chronic kidney disease – design of a couple of microfluidic paper-based devices

In this work, two microfluidic paper-based analytical devices (μPADs) were developed for the quantification of urea and NHx in human saliva to aid in the diagnosis/monitoring of chronic kidney disease (CKD). The NHx determination was based on the conversion of ammonium to ammonia, followed by its diffusion through a hydrophobic membrane and then the color change of bromothymol blue (BTB) indicator. In the urea determination, prior to the ammonium conversion and BTB color change, the enzymatic conversion of urea into ammonium was produced, using urease. Several optimization studies were carried out to attain a quantification range of 0.10–5.0 mM with 0.032 mM limit of detection for the NHx μPAD, and a determination range of 0.16–5.0 mM with 0.049 mM limit of detection for the urea μPAD. The method accuracy was assessed, and the measurements obtained with NHx μPAD were compared with the ones obtained from an ammonia ion selective electrode; while the measurements of the urea μPAD were compared with the ones obtained from a commercially available kit. There were no statistically significant differences between methods, proving that both NHx and urea μPAD were effective on-hand tools for CKD monitoring in saliva. To evaluate their functionality as point-of-care devices, stability studies were also performed and revealed that both NHx and urea μPAD were stable when stored in a vacuum for 2 and 1 month, respectively. After the sample introduction, the NHx μPAD could be scanned within the first 2 h and the urea μPAD within 1 h.info:eu-repo/semantics/publishedVersio

Heat and mass transfer effects in direct methanol fuel cell: 1D model

Models play an important role in fuel cell development since they facilitate a better understanding of parameters affecting the performance of fuel cells and fuel cells systems. In this work, a steady state, one-dimensional model accounting for coupled heat and mass transfer, along with the electrochemical reactions occurring in the DMFC is presented. The model accounts for the kinetics of the multi-step methanol oxidation at the anode while the kinetics of the cathodic oxygen reduction is modelled using the Tafel equation. Two-phase flow effects are neglected. The anode and cathode flow channels are treated using the continuous stirred tank reactor (CSTR) approach. The cell voltage expression incorporates the anodic and cathodic overpotentials as well as the ohmic losses across the membrane. The mixed potential of the cathode due to methanol crossover is also included. The reactions in the catalyst layers are considered homogeneous. Pressure gradients across the layers are assumed as negligible. Methanol and water transport through the membrane is assumed to be due to the combined effect of the concentration gradient and electro-osmotic force. Mass transport in the diffusion layers and membrane is described using effective Fick models. Local equilibrium at interfaces is represented by partition functions. The methanol flux in the cathode catalyst layer is considered as well as methanol crossover. The transport of heat through the gas diffusion layers is assumed to be a conduction-dominated process. The thermal conductivity for all the materials is assumed to be constant. Heat generation is considered in the catalyst layers. The analytical solutions for concentration and temperature across the cell are compared with recently data existing in literature and with in-house obtained results, for a wide range of operating conditions. The model shows very good agreement. This easily implemented simplified model is suitable for use in real-time DMFC simulation