Lung-inspired, fractal flow-fields hold great potential in improving the performance of polymer electrolyte membrane fuel cells (PEMFCs) by providing uniform gas distribution across the electrodes ...and ensuring minimum entropy production in the whole system. However, the inherent susceptibility of the fractal flow-fields to flooding renders their use inadequate at high humidity conditions. In-depth understanding of water management in lung-inspired flow-fields is indispensable for the implementation of alternative outlet channel geometries or engineered water removal strategies to alleviate flooding. Here, liquid water formation and transport across the lung-inspired and serpentine flow-field based PEMFCs are evaluated using neutron radiography. The results reveal a propensity to flooding in the interdigitated outlet channels of the fractal flow-field with N = 4 generations as a result of slow gas velocity and narrow channel dimensions, which leads to significant performance deterioration. Neutron images also elucidate the importance of ensuring a well-defined internal channel structure of the fractal flow-fields to prevent backflow of liquid water via wicking and capillary pressure build-up arising from the narrow inlet gas channels and hydrophobic gas diffusion layer.
•Neutron radiographs are presented for the lung-inspired and serpentine flow-fields.•A well-defined channel structure of the fractal flow-field is indispensable.•Water removal strategies required to alleviate flooding in the fractal flow-field.
The relationship between the properties of geopolymers and the characteristics of metakaolin samples used in their preparation has been investigated. Three commercial metakaolin samples have been ...characterised using 27Al-NMR to determine the coordination number of Al (IV, V and VI), and by acid and alkali dissolution to determine the reactive Si and Al content. The setting and mechanical properties of geopolymers formed from the metakaolin samples under identical conditions are reported, using Weibull statistics to analyse strength data. Although the metakaolin samples contained different levels of five coordinated aluminium (Al (V)) the mechanical properties of the geopolymers formed were very similar. The reactive fraction of metakaolinite determined by dissolution in 8M NaOH provides the most relevant long-term indicator of geopolymer performance.
•Metakaolin characteristics are related to geopolymer properties.•No correlation was found between Al (V) content and geopolymer strength development.•Dissolution in 8M NaOH provides the preferred indicator of metakaolin reactivity.
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•Combined X-ray CT with Neutron imaging to characterize compression effect.•PEFC with medium compressed metal foam achieves the best performance.•Compression process decreases the ...pore size and narrows the PSD of metal foams.•Compression process facilitates effective water removal due to high pressure drop.•Medium compressed cell shows moderate water removal ability and parasitic power.
The mechanical compression of metal foam flow-field based polymer electrolyte fuel cells (PEFCs) is critical in determining the interfacial contact resistance with gas diffusion layers (GDLs), reactant flow and water management. The distinct scale between the pore structure of metal foams and the entire flow-field warrant a multi-length scale characterization that combines ex-situ tests of compressed metal foam samples and in-operando analysis of operating PEFCs using X-ray computed tomography (CT) and neutron radiography. An optimal ‘medium’ compression was found to deliver a peak power density of 853 mW cm−2. The X-ray CT data indicates that the compression process significantly decreases the mean pore size and narrows the pore size distribution of metal foams. Simulation results suggest compressing metal foam increases the pressure drop and gas velocity, improving the convective liquid water removal. This is in agreement with the neutron imaging results that demonstrates an increase in the mass of accumulated liquid water with minimum compression compared to the medium and maximum compression cases. The results show that a balance between Ohmic resistance, water removal capacity and parasitic power is imperative for the optimal performance of metal foam based PEFCs.
In-depth understanding of water management is essential for the optimization of the performance and durability of polymer electrolyte fuel cells (PEFCs). Neutron imaging of liquid water has proven to ...be a powerful diagnostic technique, but it cannot distinguish between ‘legacy’ water that has accumulated in the system over time and ‘nascent’ water recently generated by reaction. Here, a novel technique is introduced to investigate the spatially resolved water exchange characteristics inside PEFCs. Hydro-electrochemical impedance imaging (HECII) involves making a small AC-sinusoidal perturbation to a cell and measuring the consequential water generated, using neutron radiographs, associated with the stimulus frequency. Subsequently, a least-squares estimation (LSE) analysis is applied to derive the spatial amplitude ratio and phase shift. This technique provides a complementary view to conventional neutron imaging and provides information on the source and ‘history’ of water in the system. By selecting a suitable perturbation frequency, HECII can be used to achieve an alternative image ‘contrast’ and identify different features involved in the water dynamics of operational fuel cells.
•Hydro-electrochemical impedance imaging applied to water management of PEFC.•HECII distinguish between 'legacy' and 'nascent' water in the PEFC.•The perturbation frequency of HECII affects water dynamics features.
The encapsulation of caesium (Cs) and strontium (Sr) contaminated clinoptilolite in Na and K based metakaolin geopolymers is reported. When Cs or Sr loaded clinoptilolite is mixed with a metakaolin ...geopolymer paste, the high pH of the activating solution and the high concentration of ions in solution cause ion exchange reactions and dissolution of clinoptilolite with release of Cs and Sr into the geopolymer matrix. The leaching of Cs and Sr from metakaolin-based geopolymer has therefore been investigated. It was found that Na-based geopolymers reduce leaching of Cs compared to K-based geopolymers and the results are in agreement with the hard and soft acids and bases (HSAB) theory. Cs ions are weak Lewis acids and aluminates are a weak Lewis base. During the formation of the geopolymer matrix Cs ions are preferentially bound to aluminate phases and replace Na in the geopolymer structure. Sr uptake by Na-geopolymers is limited to 0.4 mol Sr per mole of Al and any additional Sr is immobilised by the high pH which causes precipitation of Sr as low solubility hydroxide and carbonate phases. There was no evidence of any other phases being formed when Sr or Cs are added to metakaolin geopolymers.
•Leaching.•Encapsulation of Cs and Sr.•Nuclear waste.•Clinoptilolite.
Magnox swarf contaminated with trace levels of Al metal is an important UK legacy waste originated from the fuel rod cladding system used in Magnox nuclear power stations. Composite cements made from ...Portland cement and blast furnace slag form a potential encapsulation matrix. However the high pH of this system causes the Al metal to corrode causing durability issues. Geopolymers derived from metakaolin are being investigated as an alternative encapsulation matrix for Magnox swarf waste and the corrosion kinetics and surface interactions of Al with metakaolin geopolymer are reported in this paper. It is shown that the pH of the geopolymer paste can be controlled by the selection of metakaolin and the sodium silicate solution used to form the geopolymer. A decrease in pH of the activation solution reduces corrosion of the Al metal and increases the stability of bayerite and gibbsite layers formed on the Al surface. The bayerite and gibbsite act as a passivation layer which inhibits further corrosion and mitigates H2 generation. The research shows that optimised metakaolin geopolymers have potential to be used to encapsulate legacy Magnox swarf wastes.
Limited data are available regarding the influence of thiamine supplementation on the incidence of polioencephalomalacia (PEM) in lambs fed diets containing increased concentrations of S in the diet ...(>0.7%). Therefore, our objective was to evaluate the influence of thiamine supplementation on feedlot performance, carcass quality, ruminal hydrogen sulfide gas concentrations, and incidence of PEM in lambs fed a finishing diet containing 60% distillers dried grains with solubles (DDGS; DM basis). Two studies were conducted using completely randomized designs to evaluate the influence of concentration of thiamine supplementation. Study 1 used 240 lambs fed in 16 pens, whereas study 2 used 55 individually fed lambs. Lamb finishing diets contained 60% DDGS, which resulted in a dietary S concentration of 0.73% (DM basis). Treatments diets were based on the amount of supplemental thiamine provided: 1) no supplemental thiamine (CON), 2) 50 mg/animal per day (LO), 3) 100 mg/animal per day (MED), or 4) 150 mg/animal per day (HI). Additionally, in study 2, a fifth treatment was included, which contained 0.87% S (DM basis; increased S provided by addition of dilute sulfuric acid) and provided 150 mg of thiamine/animal per day (HI+S). In study 1, ADG decreased quadratically (P = 0.04), with lambs fed the CON, LO, and MED diets gaining BW at a greater rate than lambs fed the HI diet. In study 1, DMI responded quadratically (P < 0.01), whereas G:F tended to differ linearly (P = 0.08) to concentration of thiamine supplementation, with MED lambs having greater DMI and decreased G:F. No differences (P ≥ 0.17) in lamb performance were observed in study 2. In both studies, most carcass characteristics were unaffected, with the exception of a tendency for decreased carcass conformation (study 1; P = 0.09) and greater flank streaking (study 2; P = 0.03). No differences in ruminal hydrogen sulfide concentration (P > 0.05) among treatments were apparent until d 10, at which point lambs fed the LO diet had less hydrogen sulfide concentrations than all other treatments. Lambs fed HI had the greatest concentrations of hydrogen sulfide on d 31 (1.07 g of hydrogen sulfide /m³; P < 0.009). Ruminal pH did not differ (P = 0.13) and averaged 5.6 ± 0.06. No clinical cases of PEM were observed during the course of either study. The use of thiamine as a dietary additive to aid in the prevention of PEM in finishing lambs does not appear to be necessary under the conditions of this study.
Sirolimus-eluting stents (SESs) recently proved to be superior to bare metal stents (BMSs) in decreasing the need for repeat revascularization in patients with ST-segment elevation myocardial ...infarction (STEMI) at 1 year. Whether this also holds for paclitaxel-eluting stents (PESs) is currently unclear and the long-term relatively efficacy of the 2 drug-eluting stents is currently unknown. We investigated the 3-year efficacy of SESs and PESs versus BMSs in patients with STEMI. Primary angioplasty was performed in a consecutive group of 505 patients (BMSs in 183, SESs in 186, PESs in 136). At 3 years, the cumulative mortality rate was comparable in the 3 groups: 13.3% in the BMS group, 11.5% in the SES group, and 12.4% in the PES group (nonsignificant for all). The rate of target vessel revascularization (TVR) was 12.0% in the BMS group compared with 8.0% and 7.7% in the SES and PES groups, respectively (p = 0.12 for BMS vs SES, 0.30 for BMS vs PES, 0.62 for SES vs PES). The cumulative incidence of death, MI, or TVR was 25.5% in the BMS group compared with 17.9% and 20.6% in the SES and PES groups, respectively (p = 0.06 for BMS vs SES, 0.32 for BMS vs PES, 0.45 for SES vs PES). Angiographic stent thrombosis occurred in 2.4% of all patients (BMS 1.6%, SES 2.7%, PES 2.9%). In conclusion, in this relatively small consecutive patient cohort, the use of SESs and PESs was no longer associated with significantly lower rates of TVR and major adverse cardiace events in patients with STEMI after 3 years of follow-up. A high frequency of stent thrombosis was observed in the 2 drug-eluting stent groups.
Aims To investigate the outcome of a real world diabetic patient cohort treated with bare metal stents (BMS), sirolimus-, or paclitaxel-eluting stents (SES and PES, respectively). Due to the ...different mechanisms of action of both drugs it is currently unknown which device is the best option to treat these high-risk patients.
Methods and results The study compares the 2-year clinical outcome of 708 consecutive diabetic patients (25% insulin treated) treated with either a BMS (n = 252), a SES (n = 206), or a PES (n = 250), as part of the RESEARCH and T-SEARCH registries. Target vessel revascularization was 19.5% in the BMS group, vs. 15.3% in the SES group and 9.7% in the PES group. PES (21.2%), but not SES (28.9%), were superior to BMS (29.7%) in reducing major adverse cardiac events. After propensity analyses, none of the differences remained significant. The incidence of stent thrombosis (ST) was high in both DES groups.
Conclusion There was a trend towards a more favourable outcome associated with the use of PES over BMS. There was no significant difference between SES and PES in each of the clinical endpoints, and neither in the NIDDM patients, which are hypothesized to be better-off with PES.
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