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The survey was conducted to clarify the succession of the epilithic algal communities in two small streams (the River Tsunaki and the River Zaru) during Apr.1997-Apr.1998. The riverhead of two streams is almost same. The River Tsunaki is a branch of the River Hirose, a symbolic river in Sendai City, receiving the ozonated sewage effluent. While the River Zaru is a branch of the River Natori, receiving the effluents from housing developments.The epilithic algae and water quality were investigated at eight sites (three in the R. Tsunaki and five in the R. Zaru) every month. The average of water temperatures were 11-18°C, velocities were 0.25-1.12m/s. The average concentrations of BOD were 0.7-1.2 (the River Tsunaki), 0.6-2.2 mg/l (the River Zaru) . The many nutrient concentrations were constantly high at the downstream site in the R. Tsunaki by the sewage effluent.The average amounts of chl.α were 76-470 mg/m2. The amounts of chl. α were tended to increase during winter. Among the algal species identified (77 species in the River Tsunaki) and (80 species in the River Zaru) Homoeothrix janthina, Stigeoclonium lubricum, Rhoicosphenia abbreviata, Nitzschia inconspicua and Cymbella minuta to dominated. At the site of rapid velocity the filamentous algae dominated, and at the sites of upper 0.5 m/s velocity the relative abundance of filamentous algae and the velocity related in high ratio (r=0.70) . And it was found that the epilithic algal communities in each river divided four groups during a year by cluster analysis bases on C∏ similarity and the sewage effluent effected the epilithic algal communities.The present results showed the efficiency of algal community for monitaring river environments.

The characteristics of heat exchangers with offset-type plate fins for space stations are studied for Reynolds numbers less than 300 based on the hydraulic diameter. A three-dimensional analysis is carried out to study the effects of the following parameters on the heat transfer and the flow characteristics: (a) the thermal boundary layer developing on the bottom plate and on the fins on the plate, (b) the aspect ratio (height/pitch) of the cross section of the flow passage, the fin thickness, the fin length in the direction of the flow, the thermal conductivity of the fluid and the fins, and the Prandtl number of the fluid. The results obtained are as follows. (1) The heat-transfer coefficient on the fin surface is characterized by the thermal-conductivity ratio of fluid to fin material. When the thermal conductivity of the fin material approaches that of the fluid, the heat-transfer coefficient on the fin surface becomes low. (2) The optimum condition of the aspect ratio depends on the value of the thermal-conductivity ratio between the fluid and the fins. (3) When the aspect ratio becomes large or small, the friction factor of offset fins approaches that of fully developed duct flow with the same aspect ratio as the Reynolds number decreases.

The development of a 300kW-class recuperative ceramic gas turbine (CGT301) for continuous load has been conducted by the New Energy and Industrial Technology Development Organization (NEDO) as one of the programs in the Moonlight Project. In this program, the development of a ceramic heat exchanger has been carried out under the cooperation of Ishikawajima-Harima Heavy Industries, Ltd. (IHI) and NGK Insulators, Ltd. (NGK). since 1988. In this paper, the process of the development of the ceramic heat exchanger is described. A three pass shell-and-tube type of heat exchanger is considered. As the heat exchanger is to be operated at gas temperature over 825°C, the reliability is expected to be improved by applying high-temperature resistant silicon-nitride ceramics to its hot tube-bundle. In consideration of the limitation in the size of the ceramic tube-bundle, the heat exchanger was designed as the assembly of six identical modules. Tests of a single module with ceramic tube-bundle were conducted. It was confirmed that the ceramic tube-bundle had reasonable structural reliability, and that the module gave a sufficient performance i.e., temperature effectiveness and pressure drop characteristics.