b. farhanieh

Using Fire Dynamic Simulator (FDS) software, this study investigates the effects of sprinklers, branches and blowing fan on fire in a 40-meter-long coal mine tunnel corridor. This study has shown that nozzles, despite reducing the visibility due to water evaporation, will reduce the temperature throughout the corridor and reduce the concentration of carbon dioxide by 15,000 ppm at the farthest point. A branch in a corridor and providing an evacuation route from the damaged area will increase the time for different parts of the mine to remain safe in terms of temperature and the concentration of harmful gases. On the other hand, if the branch is close to the fire, it will cause the fire to spread due to providing the required oxygen. The presence of a blowing fan for ventilation in the tunnel corridor, despite faster fire extinguishing and a 46% reduction in the average temperature on the fire source, will increase the concentration of carbon monoxide by 7.5 ppm at the farthest point. Also, the nozzles connected to the thermocouple, due to the lack of Time Response Index (RTI) compared to sprinklers, are more effective in fire controlling and will reduce the temperature on the fire source by 69%.

In the present study, the effect of the use of false-ceiling on fire-induced smoke flow characteristics in tunnels is investigated using a 3D developed computational fluid dynamics tool. The critical velocity, the minimum required tunnel ventilation velocity to stop the smoke flow from moving toward the tunnel inlet (toward the upstream of the fire source), and the maximum gas temperature beneath the ceiling are selected to evaluate the smoke flow control in presence of the false-ceiling. The hydraulic height of the cross-sectional geometry of the tunnel is used as the characteristic length in order to dimensional analyze and compare the nondimensional results. The results indicate that the use of the false-ceiling reduces the critical velocity and the smoke backlayering, while increases the maximum ceiling gas temperature. Reducing the critical velocity results in ventilation cost reduction (positive impact), while increasing the maximum gas temperature beneath the ceiling increases the risk of instrumental and life damages (negative impact). The detailed results and corresponding physical discussions are presented to clarify the reason for the significant differences between the results of the tunnels with and without false-ceiling.

High current density performance of polymer electrolyte fuel cell (PEM) is known to be limited by transport of reactant and products. In addition, at high current densities excessive amount of water is generated and condenses, filling the pores of electrode with liquid water, and hence limiting the reactant transport to active catalyst. This phenomenon known as flooding, is an important limiting factor of PEM performance. When some magnet particles are deposited in the catalyst layer of a cathode and magnetized, the cell performance has been improved compared with that of non-magnetized case. Numerical simulation to explain this phenomenon shows that the repulsive Kelvin force caused by the magnet particles manages the liquid water and gas flow in the porous electrode layer. In addition, the saturation level of liquid water (s) near the catalyst interface decreases with increasing the residual magnetic flux density of the magnet particles, and this method improves the cell performance by decreasing the value of s and making more pore space for oxygen gas that decreases the diffusion looses in cathode. At last we considered disadvantages of this method and calculated cell performance with a realistic sight.