In designing a gas-insulated bus (GIB) using N 2 /SF 6 mixtures, there are many application problems, such as the mixture pressure needed in order to maintain the required dielectric and heat transfer performance. Problems of recycling SF 6 are also essential in applying N 2 /SF 6 mixtures. This paper presents the minimum breakdown field strength at lightning impulse and the temperature rise of the conductor and enclosure as measured for N 2 /SF 6 mixtures. Considering the dielectric and heat transfer properties, we clarify the problems of application of mixtures to a GIB and discuss the appropriate mixture ratio of SF 6 in designing a GIB comparable to the present dimensions. In addition, the lowest limit of SF 6 content in a liquefied recovering method is theoretically estimated for reference in practical SF 6 recovery from mixtures. It is important for design to consider both breakdown phenomena, including the area effect of electrode, and the heat transfer properties of mixtures.Key words: SF6; N 2 /SF 6 mixtures; breakdown field strength; area effect of electrode; heat transfer property; SF6 recovery.

The authors have observed flow patterns of ice/water slurry flow through horizontal circular pipes, and measured pressure loss for small diameter pipes, using three classes of ice particles. The slurry flows are classified into three patterns, dispersed-particle flow, cluster flow, and column flow. They are presented on a plane of two dimensionless parameters, the ice fraction f and the ratio of mixing energy to cohesion energy, πmix. The pressure loss for small diameter pipes is estimated accurately by the formula proposed in previous studies by the present authors based on experimental data for larger pipes.

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The authors have observed flow patterns of ice/water slurry flow through horizontal circular pipes, and measured pressure loss for small diameter pipes, using three classes of ice particles. The slurry flows are classified into three patterns, i.e. dispersed-particle flow, cluster flow and column flow, and they are presented on a plane of two dimensionless parameters, i.e. the ice fraction f and the ratio of mixing energy to cohesion energy, πmix. The pressure loss for small diameter pipes is well estimated by the formula proposed previously by the present authors.