Three methods were explored to estimate the efficiency for the conversion of mechanical power to electrical power using synchronous generators in ships at low power factors. Generally, the generator efficiency data is provided by manufacturers as shop trial data and is measured by operating generators under power factor of 0.8 and 1.0. However, the efficiency of synchronous generators is not measured under low power factor of less than 0.8. In practice, onboard generators occasionally operate at low power factor and it is desirable to clarify their characteristics for power system designers of large vessels. By substituting the shop trial data into the proposed efficiency estimation formulas, the generator efficiency at low power factor was extrapolated. To evaluate the validity of these methods, the fuel consumption characteristics of diesel engines as prime movers was focused. The estimation of the generator efficiency was indirectly validated using a statistical analysis of long-term observational data of the generator in operation. As a result, the efficiency estimation method based on a power loss mechanism gave the most reliable result among the three estimation methods. The root mean squared error of the calculated specific fuel consumption was 3.5 g/kWh, which is approximately 1.66 % error rate.

In order to select candidate materials for the equipment of the 3rd and 4th reaction of Mg-I thermochemical hydrogen production cycle, screening test of metallic materials was conducted. The corrosive constituents concerned in the 3rd reaction are hydrogen iodide, iodine, and water, and in the 4th reaction, hydrogen iodide, iodine, water, and hydrogen. Therefore, for the 1st screening test, the testing environment was made up of hydrogen iodide, iodine, and water under the condition of linearly increasing temperature from 250C to 700C. The several materials which passed the 1st screening test were examined isothermally for 200hrs in the iodide and iodine atmosphere with and without hydrogen. The results are as follows: (1) Common engineering materials, such as the austenitic and ferritic stainless steels, nickel-base alloys, and cobalt-base alloys are unsuitable because of their inability to resist the high corrosive atmosphere. (2) Corrosion rates of niobium, zirconium, and tantalum are very low in the atmosphere at 200C, but they absorb hydrogen to some degree and then may be sensitive to hydrogen brittleness. (3) Corrosion rates of titanium and its alloys are negligible at 350C, but also may be sensitive to hydrogen brittleness. (4) Molybdenum is the best choice below 450C at present, because its corrosion rate is very low, and it does not absorb hydrogen. The oxide scale on the molybdenum shows the tendency of evaporation at 450C, but the rate is extremely low. (5) Chromium, tungusten, aluminum, gold, and platinum can withstand the corrosive atmosphere at higher temperature also. It is, however, impossible to use them because of expensiveness (Au, Pt), low tensile strength in high temperature (Al), or brittleness (Cr, W). (b) Several surface treatments such as plasmaspray coating of oxides, electroplating of chromium, and diffusion coating of aluminum and chromium are yet incredible at present. struction Materials for the Magnesium-Iodine Cycle of Thermochemical Hydrogen Production Process (Part 4))

In order to find out the construction materials for the process of reactions (3) and (4) of the magnesium-iodine thermochemical cycle the corrosion tests of ceramics (alumina, mullite, periclase, graphite, glass linings, etc.) and some jointing mortars were carried out for test durations up to 1000 hours and at temperatures up to 700C in the atmosphere of a HI-12-H20 mixed gas. The atmosphere was prepared without hydrogen, since hydrogen has little effect on the corrosion of ceramics. The corrosion resistance has been evaluated by observing the change in appearance, weight, and strength after the test. The test results were as follows: (1) The oxide materials (alumina, mullite, etc.) and graphites showed a good corrosion resistance at 500C and 700C. (2) Aluminum phosphate type jointing mortar was favorable. On the other hand, sodium silicate type mortar showed remarkable weight gain and decrease of bending strength accompanied by deposition of sodium iodide, and could not be assessable as candidate materials. (3) The pyroceram type glass lining specimens did not show any changes in its appearance and in weight at temperature range between 200C and 500C, while standard type were damaged.

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The corrosion behavior of mild steel was investigated in a culture where hydrogen gas was bubbled. A dual cell system was employed. That is, in the first cell the bacteria produced hydrogen sulfide, which was introduced into the second cell by hydrogen gas. The bacteria were cultured in autotrophic or heterotrophic conditions. The electrode potential and polarization resistance of the specimens in both of the cells were measured. The variations of electrode potential and corrosion rate of the steel in both of the cell could be explained, corresponding to the variation of the concentration of hydrogen sulfide.The weight loss of the steel in the first cell was smaller than that in the second cell.There was no evidence that hydrogen depolarization by the bacteria occured. It seems to be more resonable that the anodic and catholic reactions were stimulated catalytically by hydrogen sulfide, not by the bacteria.On the other hand, in autotrophic condition, the bacteria could not grow so much, and the amount of biogenic hydrogen sulfide was much smaller than that in heterotrophic condition.Organic substances is necessary for the biosynthesis of the bacteria and for the great evolution of hydrogen sulfide. Therefore, in order to prevent the corrosion by the bacteria, in practice, a desalting plant ought to be designed to eliminate organic substances as much as possible.

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