Numerical simulation of intermediate‐temperature disk type seal‐less SOFC fed with partially reformed methane

Since natural gas containing methane as major component is the most promising fuel for the solid oxide fuel cell (SOFC), development of a numerical simulation code of the intermediate‐temperature disk‐type seal‐less SOFC for methane fuel case is considered to be very useful. In this study, therefore, we develop a new simulation code for the single cell unit of this type of SOFC fed with partially reformed methane as the fuel gas, based on the existing simulation code for pure hydrogen. We calculate the current density versus single cell voltage (i–V ) curves of the single cell unit for various cases with a wide range of the cell temperature and prereformer temperature conditions and compare them with the corresponding experimental results. From the results, we confirm that the numerically obtained i–V curves coincide very well with the corresponding experimental ones in all cases. The variations of the i–V curves, which depend not only on the cell temperature but also on the prereformer temperature, are successfully simulated with a sufficiently high accuracy, indicating the validity of the newly developed simulation code. We also investigate the detailed influence of the cell temperature and prereformer temperature on the cell performance on the basis of the numerically obtained gaseous partial pressure profiles in the fuel channel and Nernst potential profiles in the cell, and clarify the reason why the prereformer temperature has obvious influence on the cell performance when the cell temperature is low, though the cell performance is almost independent of the prereformer temperature when the cell temperature is high. © 2013 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

Highly sensitive detection of net hydrogen charged into austenitic stainless steel with secondary ion mass spectrometry

Secondary ion mass spectrometry (SIMS) is used to detect local distributions of hydrogen in various materials. However, it has been well-known that it is extremely difficult to analyze net hydrogen (H(N)) in metals with SIMS. This was because hydrogen, which is originated from moisture (H(2)O), hydrocarbon (C(x)H(y)) or other organic materials (C(x)H(y)O(z)) existing on a sample surface or in the SIMS chamber, is simultaneously detected in the SIMS measurement of the H(N), and the H(N) and the background-originated hydrogen (H(BG)) cannot be distinguished in a SIMS profile. The effective method for reductions and determinations of the H(BG) in hydrogen measurements of metallic materials with the SIMS method has not been established. The present paper shows an effective method for reduction and estimation of H(BG) in SIMS analyses of hydrogen charged into type 316 L austenitic stainless steel, and an accurate estimation method of the net charged hydrogen. In this research, a silicon wafer is sputtered by a primary ion beam of a SIMS near an analyzed area (silicon sputtering method) to reduce H(BG). An uncharged type 316 L sample was prepared for estimation of H(BG) in SIMS measurements of the hydrogen-charged sample. The gross intensities of hydrogen between the hydrogen-charged sample and the uncharged sample were compared. The gross intensities of hydrogen of the uncharged sample (26.8-74.5 cps) were much lower than the minimal gross intensities of hydrogen of the hydrogen-charged sample (462-1140 cps). Thus, we could reduce the H(BG) enough to estimate the hydrogen charged into the type 316 L sample. Moreover, we developed a method to determine intensities of H(BG) in the measurement of the hydrogen-charged sample by estimating the time-variation of hydrogen intensities in the measurements of the uncharged sample. The intensities of the charged hydrogen can be obtained by subtracting the estimated intensities of the H(BG) from the gross intensities of hydrogen of the hydrogen-charged sample. The silicon sputtering method used to reduce H(BG) and the determination method for H(BG) in this research can be applied to the accurate hydrogen analysis for other various metallic materials.     

Evaluation of a Bacillus subtilis rec-assay for the detection of mutagens which may occur in water environments

A recombination-deficient mutant of Bacillus subtilis, NIG 45 and a wild-type strain NIG 17, were used as a mutagenicity test microorganism. The strain NIG 45 has a very high sensitivity to gamma rays, u.v. and chemical drugs. Kada et al. (Mutation Res. 31, 347–364, 1972), Tazima, et al. (Mutation Res. 32, 55–80, 1975) and Sadaie & Kada (J. Bacteriol. 125, 489–500, 1976) developed the rec-assay method of Bacillus subtilis, which showed more sensitive to mutagens than the Ames reversion tests of Salmonella. In this research, the liquid-cultivation method of Bacillus subtilis was applied rather than the originally developed plate-cultivation method, resulting in detection of mutagens in very low concentration. Among test heavy metals, chromium sexivalent indicated very strong mutagenicity and manganese heptavalent indicated weak mutagenicity. NIG 45 showed an adverse growth effect at the Cr(+6) concentration of 0.5 mg l⁻¹, while NIG 17 showed the adverse effect at 1.0 mg l⁻¹, indicating the rec-assay of Bacillus subtilis as a good method of monitoring mutagens in water environment. A test of finding the combination effect of two mutagenic substances Cr(+6) and Mitomycin showed an additive effect rather than multiple. The combination of Cr(+6) and a non-mutagenic substance Hg, showed no enhancing effect of Hg to a mutagenic effect of Cr(+6). Among test dyes, acridine orange, acridine yellow and methyl violet indicated strong mutagenicity. Application of the target and hit theory to experimental results showed that mutagenicity of Mitomycin-C and Cr(+6) fitted to the one-target-one-hit theory, and mutagenicity of acridine orange and acridine yellow fitted to the one-target-two-hits theory. The term, mean lethal concentration of chemical mutagens was introduced to evaluate the experimental results of one-target-one-hit and one-target-two-hits cases.     

Fertility of mice receiving vitrified adult mouse ovaries

Cryopreservation of the ovaries is a useful technology for preservation of germ cells from experimental animals, because if the female founder is infertile or has mutated mitochondrial DNA, preservation of female germ cells is necessary. Although it is possible to cryopreserve immature mouse ovaries with a high degree of viability by vitrification with a mixture of several cryoprotectants, the viability of cryopreserved adult mouse ovaries is still unknown. Here, we investigated the viability of mouse ovaries at various ages after cryopreservation by vitrification techniques. Donor ovaries were collected from 10-day-, 4-week-, 10-week- and 7-month-old, female, nulliparous, green fluorescence protein (GFP)-transgenic mice and cryopreserved by vitrification. The vitrified-warmed ovaries were orthotopically transplanted to 4- or 10-week-old mice. GFP-positive pups were obtained in all experimental groups. In the 4-week-old recipients, the percentages of GFP-positive pups among the total pups from recipients transplanted with ovaries of 10-day-, 4-week-, 10-week- and 7-month-old donors were 44%, 9%, 12% and 4% respectively. In the 10-week-old recipients, the percentages of GFP-positive pups among the total pups from recipients transplanted with ovaries of 10-day-, 4-week-, 10-week- and 7-month-old donors were 36%, 16%, 2% and 9% respectively. Furthermore, GFP-positive pups also were obtained from recipients transplanted with ovaries of donors without normal estrous cyclicity. Our results indicate that cryopreservation of mouse ovaries by vitrification is a useful method for the preservation of female germ cells from mice of various ages.     

Stabilization analysis of commercial‐scale subsonic diagonal‐type MHD generator considering loading conditions

In previous research on subsonic diagonal‐type MHD generators, the authors have proposed a conceptual design with relatively low Mach number in order to stabilize the MHD generator of commercial scale and have shown that the MHD generator works stably under constant‐current loading condition. In the present paper, effects of loading conditions on stability of the MHD generator are examined. A channel‐length scale linear stability analysis and time‐dependent calculations are carried out, where both gasdynamical boundary conditions and loading condition are taken into account. These analyses show that the MHD generator behaves stably under various loading conditions such as constant‐voltage loading condition and ohmic loading condition. Then the stability of the MHD generator connected with an ac power system is also analyzed by time‐dependent calculations. The analysis shows that the MHD generator stably provides the rated power to the ac power line. © 1999 Scripta Technica, Electr Eng Jpn, 128(4): 16–24, 1999     

ATR-FTIR and SEM Gradient Study of Poly(2-ethylhexyl acrylate)/Poly (vinylidene fluoride-co-hexafluoro acetone) Blends

The segregation structure and the gradient structure of poly(2-ethylhexylacrylate) (P2-EHA)/poly(vinylidene fluoride-co-hexafluoro acetone) [P(VDF-HFA)] blends were confirmed by ATR-FTIR and SEM. For the P2-EHA/P(VDF-HFA) (50/50) blend, the P(VDF-HFA) and P2-EHA layers were observed at the free surface side and bottom side, respectively. The gradient structure was obtained for the P2-EHA/P(VDF-HFA) (30/70) blend. The domain morphology of a cross section of the P2-EHA/P(VDF-HFA) (50/50) blend was dramatically changed by the thickness of the blend film. Finally, we propose that the segregation structure and gradient structure formed in P2-EHA/ P(VDF-HFA) blends were caused by surface tension difference, rate of phase separation, rate of solvent evaporation, and molecular weight difference.     

Free Volume of cis-1,4 polyisoprene/polybutadiene blends

Summary The number and radius of molecular order free space present in polybutadiene (PBD)/polyisoprene (PIP) blend were observed by positron life-time measurement, and apparent free volume fraction was estimated. The changes in the number and radius of the free space were not represented to be a linear function of blend composition. The apparent free volume fraction increased by mixing PBD with PIP and was approximated by a concave curve depicted against blend composition, even though the excess volume of mixing was proved to be negative. The change in the apparent free volume fraction was related to the variation of thermal expansion coefficient on blend composition. Received: 21 July 2000/Revised version: 21 August 2000/ Accepted: 24 August 2000