A threefold- or quadruple-effect still using 10 mm diffusion distances was examined experimentally. The still was tilted at a 12° angle from the horizontal, and heated on the bottom and cooled on the top by means of naturally convective evaporation. The experimental results were compared to theoretical results based on a one-dimensional steady-state model. The findings are summarized as (1) The evaporation rate is largest at the first effect and decreases at the effects farther from the first. This is also seen in the theoretical results. (2) The theoretical total evaporation rate increases exponentially a long with the bottom heating temperature, and this is supported by the measurements. (3) Measured evaporation rate from the outer-covering fabric are in fairly good agreement with the theoretical rates, while the measured evaporation rate from the other fabrics are smaller than the theoretical rates. As a result, the measured total evaporation rate is smaller than the theoretical rate by 15 to 18 ％. (4) Polyester baking coating of 50 to 70 μm thickness prevents corrosion of the steel plates in contact with hot seawater-soaked fabrics.
The effectiveness of seawater that contains air and nitrogen (N2) microbubbles was examined for its ability to repress biofilm formation and remove biofilm formed inside an aluminum brass pipe covered with iron film. As a result, biofilm formation was effectively repressed by the injection of N2 microbubbles into a continuous seawater flow running through the pipe. After three weeks, the fouling factor of the pipe was 9.0×10－5 m2・K W－1, while the value was 15.0×10－5 m2・K W－1 when seawater alone was delivered. The most effective result was obtained by using seawater after removal of injected N2 microbubbles. The value was 5.2×10－5 m2・K W－1. To remove biofilm already formed inside the pipe, a seawater flow containing N2 microbubbles reduced biofilm to 0.4 mg cm－2, as dry weight, from 0.9 mg cm－2 of the control. While the value was reduced to 0.6 mg cm－2 when seawater, from which injected N2 microbubbles had been removed, was delivered into the pipe.
Formation of iron film on the inner surface of an aluminum brass pipe was confirmed even when Fe2＋ was supplied to the seawater flow with injected N2 microbubbles. These results indicate that the seawater flow containing N2 microbubbles has the potential to remove biofilm formed inside the pipes. Seawater from which N2 microbubbles had been removed is applicable for the repression of biofilm formation during operation of machinery.