Dissipative Particle Dynamics simulation hydrated Nafion EW 1200 as fuel cell membrane in nanoscopic scale

The microphase separation of hydrated perfluorinated sulfonic acid membrane Nafion was investigated using Dissipative Particle Dynamics (DPD). The nafion as a polymer was modelled by connecting coarse grained beads which corresponds to the hydrophobic backbone of polytetrafluoroethylene and perfluorinated side chains terminated by hydrophilic end particles of sulfonic acid groups [1, 2]. Each four water molecule coarse grained in a bead to obtain the same bead size as built in Nafion model. The morphology of hydrated Nafion is studied for branching density of 1144, an example of Nafion EW1200, water content of 10%, 20% and 30% and polymer molecular weight of 5720, 11440 and 17160. The results show water particles and hydrophilic particles of Nafion side chains spontaneously form aggregates and are embedded in the hydrophobic phase of Nafion backbone. The averaged water pore diameter and the averaged water clusters distance were found to rises with water volume fraction

UNCONSTRAINED MELTING AND SOLIDIFICATION INSIDE RECTANGULAR ENCLOSURE

The present study concerns with the numerical study of unconstrained solidification and melting of phase change material (PCM) inside a two dimensional open rectangular cavity. The Cavity is filled by RT-27 as phase change material and air. Numerical study is carried out for different cavity aspect ratios. Result indicates that the conduction heat transfer is dominant at initial time of melting process where the layer of liquid PCM near hot surface is so thin. Solid PCM sinks to bottom of cavity due to higher density in respect to liquid PCM. Melting rate does not experience significant change by increasing cavity aspect ratio. The time of full solidification is much more than melting. It is due to the absence of natural convection with respect to melting process. By increasing the cavity aspect ratio, the solidification rates enhances significantly and its total time therefore reduces.</p

Absorption and desorption of hydrogen in long metal hydride tank equipped with phase change material jacket

A numerical study was carried out to address the practical aspects of hydrogen absorption and desorption process in a long tubular LaNi metal hydride tank (MHT) integrated with Rubitherm phase change material (PCM) jacket for hydrogen supplying of PEM fuel cell. Different H supply pressures (p = 10, 15 and 20 bar), different discharge pressures (p = 1.5, 1.75 and 2 bar) and metal hydride bed porosities (0.4, 0.5 and 0.6) were rigorously analyzed to report their influences on transient and local temperature distributions across H-MHT system and PCM jacket. The time-dependent changes of hydrogen to metal (H/M) ratio and PCM melt fraction were also investigated until they reach equilibrium. It was found that system temperature, PCM melt fraction and H/M ratio reach steady state with different rates, such that systems with higher supply pressure in absorption, lower discharge pressure in desorption and higher bed porosity approach steady state faster. Up to the steady state, 64%, 79% and 91% of the initial volume of solid PCM liquefies in absorption and 67%, 83% and 95% of liquid PCM solidifies in desorption for bed porosities of 0.6, 0.5 and 0.4, respectively. The MHT is charged with hydrogen much faster under high supply pressures. Also, it is discharged much faster under lower discharge pressure. Inserting metal foam in the PCM jacket enhances the thermal conductivity, and significantly reduces the charging and discharging time