Influence Of Compression Pressure Research Articles

(Digital Presentation) Effect of Compression Pressure on Water Removal and Power Generation Performance of PEFC with Modified Electrode/Channel Structure

Water flooding in cathode electrodes of polymer electrolyte fuel cells (PEFCs) is a critical issue that must be solved for achieving high efficiency and high power density operations. To alleviate this problem, it is necessary to design the optimum electrode/channel structure for actively removing liquid water from the porous media to the flow channel. In the previous studies, Okuhata et al. [1] revealed that the introduction of penetration holes to gas diffusion electrodes (GDEs) effectively promotes the water discharge and improves the limiting current density. Nishida et al. [2] investigated the effect of channel hydrophilization on the water behavior in the cathode of an operating cell using the cross-sectional visualization technique. It was found that the hydrophilization of cathode channels encourages the water suction from the gas diffusion layer (GDL) to the channel and enhances the oxygen diffusibility to the catalyst layer (CL). Our research group has proposed a novel hybrid electrode/channel structure combining the electrode perforation and channel hydrophilization and has investigated its effect on the improvements of water drainage and cell performance. In this study, we directly visualized the liquid water distribution in the cathode GDL of a customized PEFC with the hybrid electrode/channel structure using X-ray imaging and evaluated the transient response of cell voltage under the constant-current operations. Furthermore, the influence of compression pressure on the water behavior in the perforated GDL and the performance characteristics of the customized cell was also examined.For the X-ray investigation, we fabricated a specialized miniature fuel cell with the effective electrode area of 2.88 cm2. The membrane electrode assembly (MEA) was sandwiched between two carbon separators with a single-serpentine flow field (number of channels: 7, channel width: 1.0 mm, depth: 1.0 mm, total length: 88.5 mm). Fig. 1 shows a schematic cross-sectional view on the cathode side of the experimental cell. Since the cathode GDL is irradiated with X-ray beam in the in-plane direction, the through-plane distributions of water can be observed in the GDL under the 4th channel and under the land between the 3rd and 4th channel. To promote the water discharge from the fine porous media, a penetration groove (width: 300 μm, length: 11 mm) was installed into the GDL, MPL and CL and positioned along the right sidewall of the 4th channel. The channel walls on the cathode side were coated with the silica-based hydrophilic solvent. The contact angle of water on the hydrophilized channel is 9.8o. In the hybrid electrode/channel structure, liquid water accumulated in the CL and MPL is firstly discharged into the large groove in the in-plane direction. Subsequently, water droplets gathered in the groove are grown up and attached to the hydrophilized channel walls. The droplets are spread out on the hydrophilic sidewalls and the liquid films are moved upward. Fig. 2 presents the distributions of water saturation in the perforated GDL of the customized cell assembled under two different compression pressures of 0.5 and 1.0 MPa. The current density was increased stepwise from 0.14 to 1.02 A/cm2 for 8 min under the room temperature and non-humidification condition. All images were captured at t=8 min after starting the operation. Dry hydrogen (stoichiometry: 1.5@2.0A/cm2) and oxygen (stoichiometry: 3.0@2.0A/cm2) were supplied to the anode and cathode in the counter-flow arrangement. It was found that the introduction of the hybrid structure effectively decreases the water saturation around the groove due to the in-plane water discharge. The reduction of saturation under the land is much less than under the channel because the strong mechanical compression crushes the pore structure under the land regions and suppresses the water transport. In addition, the low-saturation region of 28% or less around the groove is enlarged with a decrease in compression pressure. The low compression pressure maintains the relatively large porosities in diffusion media and facilitates the water removal.

(Digital Presentation) Effect of Compression Pressure on Water Removal and Power Generation Performance of PEFC with Modified Electrode/Channel Structure

To prevent the water flooding in polymer electrolyte fuel cells (PEFCs), it is essential to investigate the water transport in cathode diffusion media of operating cells and design the optimum electrode/channel structure for encouraging the water discharge. Our research group has proposed a hybrid structure with the electrode perforation and channel hydrophilization. This study directly visualized the water distribution in the cathode gas diffusion layer (GDL) of a customized PEFC using X-ray radiography and characterized the cell performance under the constant-current operations. Furthermore, the influence of compression pressure on the water behavior in the perforated GDL and the performance characteristics of the customized cell was examined. It was found that the modified electrode/channel structure enhances the water discharge from the diffusion media and effectively reduces the water saturation around the penetration groove. The excessive mechanical compression of the customized cell suppresses the water removal through the diffusion media.

The influence of compression pressure on thermal expansion, bulk density, and Young’s modulus of electroporcelain mixture up to 1100 °C

The production technology has a significant impact on physical and mechanical properties of ceramic materials. The common manufacturing processes are pressing, extrusion, or casting. Porcelain products are often formed by pressing, which increases their mechanical properties. Therefore, samples made from electroporcelain mixture for production of high-voltage insulators are studied using pressing with five different compression pressures from 70 MPa up to 110 MPa. Young’s modulus, thermal expansion, and bulk density are investigated during firing in temperature interval from 25 to 1100 °C. All measurements are carried out in the same temperature program with a heating rate of 5 °C min−1 in static air atmosphere. The influence of pressing and heating on Young’s modulus, thermal expansion, and bulk density of electroporcelain mixture is examined.

Microstructural modifications of polyethylene glycol powder binder in the processing of sintered alpha alumina under different conditions of preparation

In this study, amounts of polyethylene glycol (PEG) plasticizer which used in the forming and sintering α-alumina ceramics of the sample are optimized. PEG as a conventional binder is used for the preparation of alumina-based materials. The main aim of this work was to investigate the effect of different contents of PEG and sintering conditions on the critical quality of produced alumina including microstructure, porosity, compressibility, and mechanical properties. Also, the influence of compression pressure (from 3500 to 5000 bar) on the green density of the produced alumina pellets was evaluated while the binder contents are varied from 1 to 5 wt%. The analysis results showed that the addition of PEG to the alumina powder enhances the green density of the produced disks until a maximum value. Over the maximum point, the density did not further change with increasing PEG content. This high green density leads to a high sintered density of the alumina disks. The results show that the formulation containing more than 4 wt% of PEG causes both lower sintered and green density. The fabricated alumina pellets were then compared to those without additives in terms of mechanical strength, and it was indicated that the density of fabricated pellets enhanced by rising the compaction pressure greater than 3500 bar.

Hybrid magnetorheological elastomer: Influence of magnetic field and compression pressure on its electrical conductivity

Graphene nanoparticles are used to produce a hybrid electro-conductive magnetorheological elastomer (MRE-hybrid). We fabricate a magnetoresistive sensor based on the obtained MRE-hybrid. We measure the electrical resistance of the MRE-hybrid in a transverse magnetic field of intensity 0≤H (kA/m)≤65, and separately, the electrical resistance under the influence of a compression pressure p≤14.4kPa. From the obtained results we determine the variation of electrical conductivity with H, and respectively with p. We develop a theoretical model which explains the effects of H and p on electrical conductivity of MRE-hybrid. The obtained results are presented and discussed.

The influence of compression pressure on transport properties of polyaniline

The transport of charge carriers and the thermal diffusivity were studied on a set of polyaniline (emeraldine) samples that were compressed at various pressures, 50–1000 MPa. Marked correlations between the plots of compression pressure dependence of the electrical resistivity, the thermal diffusivity and the sample density were observed. This study has demonstrated that in order to obtain comparable data on samples prepared by compression of polymeric powders it is necessary to use sufficiently high pressure. In the case of polyaniline powder the pressure should be higher than 400 MPa. The values of the thermal diffusivity measured on polyaniline salt and its respective base indicate that charge carriers are not dominant in a heat-transport mechanism; only less than ten per cent of the thermal diffusion in pressed polyaniline samples can be eventually attributed to charge carriers.

Influence of Compression Pressure and Velocity on Tablet Sticking

A rotary tablet machine fitted with 8-mm diameter flat-faced punches was used to measure scraper pressure (SCR), a type of shear stress, to evaluate sticking behavior. The shear stress between the surfaces of the tablet and lower punch was determined using an SCR detection system. Mean surface roughness (R(a)) of tablets, measured by a scanning laser-microscope, was used to estimate the magnitude of sticking. Tablet tensile strength tended to increase with compression pressure at either of the tablet production velocities tested, which was consistent with previous reports. SCR decreased with increasing compression pressure for samples at all compression velocities, and showed a tendency to increase with binder concentration. SCR also tended to increase with compression velocity for samples at all compression pressures, suggesting that the frequency of tablet sticking increased as compression velocity increased. R(a) associated with sticking increased with SCR, indicating that the adhesive force between the particles of the tablet surface and the lower punch surface plays an important role in sticking.

Influence of compression pressure from the hand access device on hand microcirculation during hand-assisted laparoscopic surgery

Hand access devices in hand-assisted laparoscopic surgery depend on compression pressure to prevent air leakage. Surgeons frequently experience hand ache during surgery. This study aimed to test whether the pressure with such a device affects the microvascular function of the hand. Eight healthy volunteers participated in this experimental study. The hand access device, applied to the forearm, was inflated to 0, 8, 12, and 16 mmHg in a random order, and the microvascular activity of the skin of the hand dorsum was quantified using laser Doppler and iontophoresis of increasing doses of acetylcholine (endothelial-dependent vasodilator) and sodium nitroprusside (endothelial-independent vasodilator). The end point was skin erythrocyte flux ratio as a measure of microvascular skin activity. No significant differences in microvascular responses to iontophoresis of acetylcholine and sodium nitroprusside were found at the four doses used when the hand access device was inflated at different pressures. The peak values for the hand allocated to acetylcholine were 3.48 +/- 1.33, 3.42 +/- 2.33, 3.38 +/- 2.55, and 2.84 +/- 3.10 arbitrary units, and the peak values for the hand allocated to sodium nitroprusside were 2.79 +/- 1.60, 2.00 +/- 1.60, 2.30 +/- 1.50, and 2.40 +/- 1.62 arbitrary units at cuff pressures of 0, 8, 12, and 16 mmHg, respectively. The pressure in the hand access device up to 16 mmHg does not affect the hand cutaneous microcirculation.