This paper was presented at the general meeting for establishment of the society as an invited memorial lecture. The paper involves a review of multiphase flow appearing in civil engineering field.
First of all, the phenomena of multiphase flow in civil engineering are classified in Table 1, and especially features of mudflow in mountains and extremely high concentration flow in Yellow River are introduced as peculiar phenomena of one directional two-phase flows with water and sediment. Secondly sediment transport on the beach and beach deformation by waves are discussed as a typical two-phase flow problem in coastal engineering, and in addition, a pneumatic breakwater using air bubble curtain flow is introduced as an application of two-phase flow with air and water.

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Methods of measurement and data obtained for drop sizes and velocity in annular gas/liquid flow have been reviewed. In particular, possible sources of bias of bias in the results have been examined. The interrelation of data from different sources is considered and regions where different behaviour predominates are identified.

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A chronological table which is composed of columns of a gas-liquid two-phase flow research, formulae of critical heat flux in boiling heat transfer, progress of type of boilers, and type of heat transfer, progress of type of boilers, and type of nuclear reactors is presented. The relationship between the development of the two-phase flow and heat transfer researches and the related technology of boilers and nuclear reactors is discussed based on the chronological table. A historical aspect of the development of the two-phase flow research is described. The progress of the research is divided by four stages according to the feature of the researches in each stage. These periods are 1948-1959, 1960-1970, 1971-1979, and 1980-1988. In this first report are described an intension of the aurthor's research on the two-phase flow which was started in 1948, the progress of the two-phase flow researches in the first period, and also the state of electric power generation capacity at that period in Japan as a background for the development of the two-phase flow research.

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To examine the effect of the solid concentration and the particle diameter on the pressure fluctuation in solid-liquid flow, several investigations were made experimentally. The experiment was carried out in a transparent acrylic pipe of 49.7mm i.d., and six kinds of particles are used to investigate the effect of the particle diameter on the pressure fluctuation.
The following results are obtained in this experiment:
1) The maximum pressure fluctuation increases with an increase in the solid concentration increases. The maximum pressure fluctuation also increases as the particle diameter increases, but once it exceeds 2mm, the maximum pressure fluctuations are not affected by the particle diameter and nearly show constant values.
2) In the range of higher velocities, the distributions of the pressure fluctuation are expressed as the Gauss distribution from the results of Probability Density Function, Skewness, and Flatness. In the range of lower velocities, on the other hand, the distributions of the pressure fluctuation are different from the Gauss distribution.
3) In lower velocities and higher concentrations, the obvious periodicities are obtained in the auto-correlation function due to the movement of dune formed in the pipe.

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A device for constant current power source is proposed with which the electric current in upward two-phase flow channel is unaffected by the leakage current in downward flow channel. It is shown that the equivalent circuit for electrode is the parallel connection of series C-R and an electric noise cell. To eliminate the noises, a current with rectangular wave of 10KHz and a constant amplitude was used.
The electric resistance in a bubbly column is higher than that in a column in which a nonconductive rod with a same void fraction is inserted instead of bubbles. The coefficient, void fraction multiplier for current, is depend on both the void fraction and the bubble shape. The multiplier is estimated by assuming that bubbles are placed in the folw in the position of a face-centered cubic. The calibration curve obtained by the f.c.c. model is in good agreement with that determined by the experimental data in bubbly flow, and differ a little from that for a churn turbulent flow.
It is concluded that the constant current method is useful for the void faction measure ment in bubbly and churn turbulent flows.

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