e. afshari

Heat management in the polymer membrane fuel cell is necessary to increase the rate of reactions, prevent the formation of hot spots, and prevent the membrane from drying out. In the polymer membrane fuel cell, in the polymer membrane fuel cell, there is a limitation in increasing and decreasing the temperature. The flow field affects the mass and heat transfer and consequently the current density, and the proper design of the flow field leads to the improvement of the fuel cell performance. Parallel flow channels with baffles can increase the transfer of reactants to the catalyst layer and reduces the maximum temperature, uniforms temperature distribution and improve battery performance. In this article, the numerical, three-dimensional and two-phase modeling of the fuel cell with channels along with baffles is discussed and its electrochemical and thermal performance is compared with the battery with simple parallel channels. The results show that the addition of the baffles improves the mass transfer from the channels to the gas diffusion layer and hence the reaction rate in the cell increases and leads to improved cell performance. Also, the presence of the baffles causes the maximum temperature of the fuel cell to decrease by more than 1 Kelvin and the temperature distribution becomes more uniform.

Humidification of polymer membrane fuel cell (PEMFC) reactant gases is necessary for keeping the membrane humidified. Planar membrane humidifiers are widely used for reactant gas humidification due to their proper performance, simple structure, and long life span. In this study performance of a planar membrane humidifier with symmetrical L-shaped obstacles in both channels is investigated numerically by ANSYS fluent and its performance is compared with a simple planar humidifier. The Effects of geometrical parameters are studied by 3D numerical modeling. Accordingly, two parameters of water recovery ratio (WRR) and dew point temperature at the dry channel outlet are considered the main performance criteria. Results show performance decreases with the increase of the gasses mass flow rates. Dry gas outlet temperature noticeably increases by the L-shaped obstacles insertion which indicates better heat transfer. The effect of four geometrical parameters of the obstacle consisting of obstacle length, height, the distance between the obstacles and the top and bottom of the channels, and their relative distance are investigated. Three values are considered for each geometrical variable, and the distance between the obstacles and the membrane exhibits more influence on the performance of the humidifier. The geometrical study improves the performance of the obstacles and raises the WRR and the dew point temperature by about 3% and 3.5 degrees, respectively.

In this paper for a given prescribed Ritz values that satisfy in the some special conditions, we find a symmetric nonnegative matrix, such that the given set be its Ritz values.

Doubling the number of chromosomes in a medicinal plant leads to variation in allelic composition and diversity of active enzymes in secondary metabolites biosynthesis route and can facilitate the process of secondary metabolism and increase secondary metabolite. This experiment was conducted in order to study the effect of colchicine and trifluralin on ploidy induction and cytogenetic characteristics of cells in the root meristem of fenugreek. Root tips were used for karyotypic studies. Seedlings were treated by colchicine solution at 0.25, 0.5 and 1 gl-1 concentrations and trifluralin solution 48% at 7.5, 15 and 22.5 μM concentrations for 12 and 24 h. The Video Analysis System was used for karyotype analysis. The basic chromosome number was X=8. Results showed that concentration of trifluralin and colchicine, treatments duration and interaction between them on the ploidy induction were statistically significant. The maximum ploidy induction was happened by seedling immersion in 22.5 μM trifluralin for 24 h and in 0.5 gl-1 colchicine for 12 h. Treatments affected the length of chromosomes and karyotypic formula. Result of analysis of variance based on completely randomized design (CRD) showed significant differences among the karyotype of control and treated samples for all karyotypic traits (p <0.01). Induced polyploidy affected by trifluralin was more than that of colchicines, although the concentrations of trifluralin were approximately 100 times lower than concentrations of colchicine. This indicates a greater ability of trifluralin in ploidy induction in this plant.