The effect of wall roughness on the liquid removal in micro-channels related to a proton exchange membrane fuel cell(PEMFC)

In this paper, the effect of the wall roughness on the water behavior related to the PEMFCs gas channel is investigated by the two-phase flow simulation. And, the different wetting conditions of the wall surface are considered, i.e. hydrophilic surface and hydrophobic surface. The relative roughness height and the roughness element density as well as the roughness element type are also considered in the study. And the results show: (1) for hydrophilic surface, water behavior for smooth case is different from the roughness cases, due to the effect of roughness on the water slug morphology even for r/H = 0.2% roughness. (2) r/H = 0.2% is positive for water removal and will not lead to the high pressure drop for hydrophilic surface, (3) r/H = 5% is advantageous for water removal for hydrophilic surface but disadvantageous for hydrophobic case, and the pressure drop greatly increases for both cases, (4) for hydrophobic surface, roughness of r/H = 1% and r/H = 2% slow down the water removal speed, but will not affect the amount of the removable water, (5) there is nearly no effect for r/H = 0.2% for hydrophobic case, (6) for both conditions, the average pressure drop obviously increases when r/H ≥ 2%. (7) Increase of the roughness element can help water removal for hydrophilic case but no obvious function for hydrophobic surface. (8) The triangle roughness element is better than rectangle element with the same height.     

Area specific resistance of oxide scales grown on ferritic alloys for solid oxide fuel cell interconnects

Planar solid oxide fuel cells (SOFC) are considered to be power generators with high efficiency and low emission at small power units (1-200 kW_el). Many prototype systems are already successfully realized. For mass production the costs have to be reduced and the long-term stability has to be enhanced. Power losses <0.5%/1000 h is the target value for stacks in stationary SOFC-based power systems. To reach this goal, the factors influencing degradation have to be found and reduced. In this work the interaction between interconnect and different ceramic materials such as perovskites (La_0.8Sr_0.2(Mn_,Co)O₃, La_0.65Sr_0.3MnO₃, La_0.65Sr_0.3(Mn,Co)O₃) and spinels (Mn(Co,Fe)O₄, (Cu,Ni)Mn₂O₄) was investigated on the cathode (air) side of conventional ferritic interconnect materials (CroFer22APU, ITMLC, ZMG232L). The method to determine the value of the area specific resistance between interconnect and contact layer (R_#ICC) within a tolerance of 10% has been developed to provide reliable data for ASR values and their degradation.The R_#ICC-value increases with annealing time. The degree of this increase depends on used materials and their combination. The spinel contact layers form a thin dense ceramic layer at the beginning of the annealing process. This layer reduces the oxidation rate of the alloy. Because of this protection layer a thinner oxide scale grows and the ASR aging rate is much lower (0.4-0.9 mΩ cm²/1000 h). The comparison of the aging rates of different alloys with La_0.8Sr_0.2(Mn,Co)O₃ contact layer reveals remarkable differences: 3.1 mΩ cm²/1000 h for CroFer22APU, 10.9 mΩ cm²/1000 h for ITMLC and 21.2 mΩ cm²/1000 h for ZMG232L.The degradation in a stack has been determined from the R_#ICC-values and geometric factors. The impact of oxidation at the cathode side of interconnect is about one third of the total stack degradation. The method opens the possibility for comparing area specific resistances of special material combinations with high accuracy. By optimized material combinations the degradation in stacks can be reduced to <0.5%/1000 h.     

Integrated carbon composite bipolar plate for polymer–electrolyte membrane fuel cells

The electrical resistance of bipolar plates for polymer–electrolyte membrane fuel cells (PEMFCs) should be very low to conduct the electricity generated with minimum electrical loss. The resistance of a bipolar plate consists of the bulk material resistance and the interfacial contact resistance when two such plates are contacted to provide channels for fuel and air (oxygen) supplies.     

Influence of particle contact models on soil response of poorly graded sand during cavity expansion in discrete element simulation

The discrete element method (DEM) has been extensively adopted to investigate many complex geotechnical related problems due to its capability to incorporate the discontinuous nature of granular materials. In particular, when simulating large deformations or distortion of soil (e.g. cavity expansion), DEM can be very effective as other numerical solutions may experience convergence problems. Cavity expansion theory has widespread applications in geotechnical engineering, particularly to the problems concerning in situ testing, pile installation and so forth. In addition, the behaviour of geomaterials in a macro-level is utterly determined by microscopic properties, highlighting the importance of contact models. Despite the fact that there are numerous contact models proposed to mimic the realistic behaviour of granular materials, there are lack of studies on the effects of these contact models on the soil response. Hence, in this study, a series of three-dimensional numerical simulations with different contact constitutive models was conducted to simulate the response of sandy soils during cylindrical cavity expansion. In this numerical investigation, three contact models, i.e. linear contact model, rolling resistance contact model, and Hertz contact model, are considered. It should be noted that the former two models are linear based models, providing linearly elastic and frictional plasticity behaviours, whereas the latter one consists of nonlinear formulation based on an approximation of the theory of Mindlin and Deresiewicz. To examine the effects of these contact models, several cylindrical cavities were created and expanded gradually from an initial radius of 0.055 m to a final radius of 0.1 m. The numerical predictions confirm that the calibrated contact models produced similar results regarding the variations of cavity pressure, radial stress, deviatoric stress, volumetric strain, as well as the soil radial displacement. However, the linear contact model may result in inaccurate predictions when highly angular soil particles are involved. In addition, considering the excessive soil displacement induced by the pile installation (i.e. cavity expansion), a minimum distance of 11a (a is the cavity radius) is recommend for practicing engineers to avoid the potential damages to the existing piles and adjacent structures.     

基于遗传运算法QSPR模型预测润滑剂在铜箔表面的润湿能力

采用静态悬滴法研究了润滑剂中脂肪酸、醇类和酯类添加剂在压延铜箔表面的接触角和润湿行为。利用半经验的量子化学方法计算了这些化合物的一些结构参数对其接触角进行了研究。利用遗传运算(GFA)统计分析方法,通过分子折射率和几种结构参数研究了其定量结构-性质关系。结果表明计算的量子参数可用于预测润滑剂在压延铜箔表面的接触角和润湿能力。这些润滑剂的接触角是其粘度、界面张力和物理化学参数的函数。其中起到主要作用的参数中,分子的折射率、分子的折射率、分子的弹性、总分子质量、溶剂表面积、元素计数、总能量和偶极子最关键。值得注意的是,润滑剂在压延铜箔表面的研究使润湿理论能精确到微观尺度,这为预测润滑剂在压延铜箔表面的润湿能力提供了新的见解。     

Refractive index of soft contact lens materials measured in packaging solution and standard phosphate buffered saline and the effect on back vertex power calculation

PurposeTo measure the refractive index (RI) of commonly available soft contact lens (CL) materials, their packaging solutions and compare to the manufacturers’ nominal RI. The relationship between RI versus water content, and the effect of inaccurate RI when converting lens power measured in solution to in-air back vertex power were examined.MethodsThe RI of 18 single vision soft CL materials were measured using CLR 12–70 digital refractometer. Three lenses of each material were measured, in their packaging solution and then after soaking in standard phosphate buffered saline (PBS). The RIs of packaging solution were also measured. Accuracy requirements for correct wet to dry power conversion based on thick lens formula were projected.ResultsThe standard deviation between three samples was less than 0.005. The measured RI ranged from 1.3744 ± 0.001–1.4265 ± 0.0004 for PBS soaked and from 1.3739 ± 0.0003–1.4264 ± 0.0024 for packaging solution soaked materials. Comparing nominal with mean measured PBS and packaging solution RIs, 5 and 3 lens materials, respectively, fell outside ISO tolerance. The packaging solution RI of DailiesAquaComfortPlus had the largest difference of 0.0040, compared to RI of standard PBS. For converting lens power measured in PBS to in-air power, the difference between measured and nominal RI of 0.0104 would result in wrongly calculated in-air power 0.99 D for a -6.00 D lens.ConclusionThe CLR 12–70 is reliable and accurate refractometer for the measurement of soft CL materials. Accurate RI measurements are of relevance with increased use of wavefront sensors to measure lens power while they are immersed in solution. Even small errors in solution or material RI can lead to significant errors in converted in-air power. To obtain valid in-air lens power results, measurement conditions must match the material and solution RIs used for the conversion.     

The differences between patient and optometrist experiences of contact lens hygiene education from the perspective of a Scottish university teaching hospital

BackgroundContact lens related keratitis is a frequent presentation to acute ophthalmology services. Patients often do not recall being counselled regarding the safe use of contact lenses therefore fail to comply with guidance.This study aimed to identify the content and format of advice given to patients with contact lens keratitis concerning appropriate hygiene practices, determine their compliance with this and finally characterise optometrist practices regarding contact lens advice provided to patients.MethodsAll adult patients presenting with contact lens related keratitis to the acute ophthalmology clinic were asked to complete a survey. Information was collected on lens type, format of advice received and compliance.Community optometrists were asked to complete an electronic survey on their contact lens review practices and routine patient education.ResultsAll patients surveyed recalled counselling on initiation of contact lenses; however 12% (6/50) were given no advice on return visits. This advice was in written format for 20% (10/50) of patients on initiation increasing to 32% (16/50) on renewal.Many patients slept (22%), showered (44%) or swam (36%) in lenses. 92% cleaned their contact lenses appropriately, but cases were washed infrequently (19% of cases cleaned < monthly) or with tap water (27%).All optometrists surveyed claimed to provide advice to patients in either written or verbal format for new and returning contact lens users. 49% (16/33) of optometrists gave written advice to patients on initial contact lens fitting, but only 1/33 continued with written advice for repeat customers.ConclusionThis study identified that although most patients were informed of appropriate hygiene requirements, compliance was poor. Optometrists regularly provide verbal advice but do not routinely offer written support and there is a mismatch between patient recollection and self-reported optometrist practice. It is suggested that patient education needs greater emphasis and both verbal and written information should be regularly provided on initial review and follow up assessments.     

Study of pilot's comfortness in the cockpit seat of a flight simulator

Pilot's seat cushion parameters on seating comfort have been investigated using finite element approach. Various parameters such as stiffness and thickness have been considered to study the seating comfort. Uniaxial compression test has been conducted on seat cushion foam to establish the stress-strain relationship. This stress-strain test data has been used for selection of appropriate hyper-elastic model and extraction of material model parameter by using curve fitting. Simplified models of human buttock, pelvic bones and cushion foam have been developed to simulate the mechanical response of cushion foam under gravity load. The result of finite element analysis has been found in good agreement with computational results related to contact stress at interface of buttock-seat cushion available in literature.     

Eye care professionals’ perceptions of the benefits of daily disposable silicone hydrogel contact lenses

PurposeTo gain a better understanding of eye care professionals’ (ECPs) perceptions regarding the benefits of silicone hydrogel (SiH) daily disposable contact lenses (DDCL), particularly with respect to health, comfort and patient satisfaction.MethodsA survey was conducted with 300 ECPs in the United States, United Kingdom and Japan during November 2017. The survey comprised 34 statements relating to SiH DDCLs, to which the ECPs provided their level of agreement using a 6 point Likert scale. A minimum of 70% agreement was set to define majority agreement. Categories of statements included Health, Comfort, Patient Experience, and Standard of Care.ResultsECPs rated the highest levels of agreement to perceptions within the Patient Experiences and Health categories. The six statements receiving the highest ratings were “Silicone hydrogel 1 day lenses satisfy today’s patients’ demanding lifestyles” (93% agreement); “Silicone hydrogel 1 day lenses are the best choice to safeguard my patients’ eye health related to contact lens wear” (92%); “Silicone hydrogel 1 day lenses provide the best benefits to my patients” (92%); “Silicone hydrogel 1 day lenses provide better long term eye health for my patients than hydrogel 1 day lenses” (91%); “Silicone hydrogel is the healthiest lens material for my daily disposable patients” (90%); and “Silicone hydrogel 1 day lenses provide a better wearing experience for my patients than hydrogel 1 day lenses” (90%).ConclusionECPs perceive that SiH DDCLs offer long-term eye health and comfort for the patient and although the ECPs surveyed would not necessarily prescribe SiH DDCLs to all their patients, they would prescribe them to most of their patients. The results support the premise that while ECPs consider SiH 1 day contact lenses as the current “standard of care”; the principal barrier continues to be the perceived higher cost of these lenses.     

Identification of virulence factors in contact lens associated bacteria: A physiological approach

PurposeWearing contact lens requires awareness about possible contaminants, the causative agents of multiple complications. The present study focused on identification of potential pathogens and presence of virulence associated markers in contact lens associated bacteria.MethodsBacterial contaminants were isolated from contact lenses or cleaning solutions collected from University students. Isolates were identified using conventional methods followed by 16S rRNA gene sequencing and screened for the presence of virulence factors which included capsular presence, adhesion, serum resistance, iron chelation, haemagglutination and hemolysis. Moreover, antibiotic resistance profile was also monitored.ResultsContamination was observed in 79% (45 of 57) of lenses. Based on 16S rRNA sequencing Bacillus sp. was found to be most abundant (26%). The presence of at least three pathogenic characteristics was recorded in 75.8% isolates. Among the pathogenic characteristics, capsule presence was found to be the most prevalent character (73%) followed by hemolysin production (65%), serum resistance (61%), haemagglutination (56%), iron chelation (50%) and polystyrene adherence (42%). Multiple antibiotic resistance was recorded in 66.13% isolates. Cluster analysis on the basis of virulence markers separated all isolates in two groups. Potential pathogens and non-pathogens were found to be equally frequent among contaminants of contact lens cases.ConclusionThe present work provides evidence that pathogenic bacteria can adhere and survive in contact lens or lens solution. It highlights the need for the development of new methods to protect contact lenses and lens care accessories. Drugs targeting capsule formation may offer a good option for treatment or use in cleaning solution.