The development of space is a great dream left to mankind. About 40 years have passed since the artificial satellite was launched for the first time in the world. At present, international telephone communication can be made through comsats and the image of clouds can be seen on television and newspapers through a meteorological satellite. With a greater power output in satellites and spaceships, the thermal control system must be considered for the recovery, transport, and disposal of waste heat. The change of phase of the working fluid results in lower electrical power requirement to operate pumps and gives a relatively isothermal sink temperature. Various system designs must be made to accomplish this two-phase thermal management capability. However, there is only little information available, as a restricting factor, on the fluid and heat transfer characteristics of two-phase flows such as pressure drop, flow pattern, and heat transfer in reduced-gravity environments. Here, the present status of investigation on gas-liquid two-phase flow under microgravity environments is outlined with a development of space radiator techniques for use in space.

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This paper presents a review on the current researches for the multiphase flow problems in turbomachinery, except for those caused by cavitation. Air-water two-phase flows are discussed from the aspects to define pump head and related characteristics, to predict the performance change using one-dimensional two-fluids models, to deepen our understanding of scale effect and unsteady flow phenomena, and to precisely simulate multidimensional flows inside the rotating impellers using turbulent and two fluids models. Solid-water two-phase flow problems are described from the viewpoints of precise prediction of erosion due to impingement of the solid particles entrained.

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Research and development activities for light water rector power plant have been reviewed focusing on those of multiphase technology in last ten years. In various fields such as reactor safety research, development of thermal-hydraulic analysis codes, improvement of reactor components, design of advanced, nextgeneration, or innovative light water reactors, researches related to multiphase technology have been performed. In future, demands for cost reduction and prevention for severe accident will be increased in development of future light water reactors. There will be increasing interest in replacing the current constitutive relation models with more mechanically or micro-mechanically-based models to make developmental work more efficient.

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Recent development on the subgrid scale modeling for the large eddy simulation (LES) of turbulent flows is reviewed. Special attention is focused on the dynamic models which use properties of the smallest resolved eddies to estimate the subgrid scale stresses. Taking into account the multiple scale structure of multiphase flows, the extension of subgrid scale model for turbulent multiphase flows is surveyed.

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Based on the assumption that the fundamental modes of the fluid transfer between subchannels are turbulent mixing, void drift and diversion cross flow, we have proposed and examined a treatment for the turbulent mixing in a hydrodynamic non-equilibrium two-phase flow. In this treatment, the turbulent mixing rate in such a flow is assumed to be equal to the rate in a hydrodynamic equilibrium state that the flow will attain. In order to obtain data needed for the examination, experiments on the axial variations in tracer concentrations for both phases were made in several non-equilibrium flows. An analysis of the data showed that the assumption and treatment are valid.

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Spatial distributions of bubbles in gas-liquid two-phase bubbly flow with various sizes of bubbles were obtained by using an image processing system in a vertical pipe. The test section was a 30.8mm I.D. and approximately 10m height. The equivalent sphere bubble diameters were between 2mm and 8mm. The relation between bubble diameter and radial distribution of volume fraction was investigated based on radial profiles of volume fraction of classified bubbles in sizes. It was assumed that radial profiles of volume fraction of gas-liquid two-phase bubbly flow with almost all the same size of bubbles could be estimated from radial profiles of volume fraction of each group of bubbles classified in size in bubbly flow with various sizes of bubbles. Radial profiles of volume fraction were obtained for each classified bubbles with three different steps: 1.0mm, 0.50mm and 0.25mm. As the results, it was clarified that the some radial profiles of volume fraction of each group of bubbles classified in size in bubbly flow with various sizes of bubbles agreed qualitatively with those of bubbly flow with almost all the same size of bubbles and there were some new types of radial profile. Moreover, effects of the step on radial profiles of volume fraction were investigated. It was confirmed that the radial profiles of volume fraction of each classified bubbles in size varied occasionally with the small step as 0.25 mm. The importance of step size was presented.

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Flow configurations of large particle-water two-phase flows in a vertical pipe of 30.3mm I. D. were observed and their flow patterns were classified into sparsely dispersed flow, cluster flow, bunch flow, slug flow and denselydispersed flow. Flow regime maps were presented for large particles of 8.12, 12.9, 17.8 and 24.8mm in mean diameter. The analogy of flow patterns between gas-liquid two-phase flow and liquid-solid two-phase flow was discussed.

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[in Japanese]

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