Microplastic wastes in ocean can include the harmful chemical material, and the harmful material is concentrated by marine species. The separation and collecting methods of microplastics in ocean are researched in the...Microplastic wastes in ocean can include the harmful chemical material, and the harmful material is concentrated by marine species. The separation and collecting methods of microplastics in ocean are researched in the world. The authors proposed the microplastics recovery device composed of the plates. Besides, the device consists of the tilted inlet/outlet and the horizontal part. In the water flow such as the tidal and ocean currents, the microplastics can be extracted from the main flow due to the vortex flow generated at the inner part of this device. In this research, the effects of the flow velocity and the inlet/outlet tilt angle on the capture performance were investigated experimentally and numerically. In the numerical simulations using the discrete phase model, the tilt angle was changed in a range between 30 degrees and 150 degrees in increments of 15 degrees, and the particle tracks of plastics were derived in steady condition. On the other hand, the capture performances in three cases of tilt angle 45 degrees, 120 degrees and 150 degrees were compared by circulation type water channel tests in which the plastics denser than the water were swept away 30 times every flow velocity. As the result, it seems that the tilt angle of 120 degrees is suitable for the wide range of the flow velocity in river and ocean.展开更多
The aim of this study is to investigate CO2 two-phase nozzle flow in terms of both experimental and analytical aspects for the optimum design of two-phase flow nozzle of CO2 two-phase flow ejector. In the experiment, ...The aim of this study is to investigate CO2 two-phase nozzle flow in terms of both experimental and analytical aspects for the optimum design of two-phase flow nozzle of CO2 two-phase flow ejector. In the experiment, it is measured that the temperature profile in the stream-wise direction of a divergent-convergent nozzle through which CO2 in the supercritical pressure condition is blown down into the atmosphere. In the analysis, a one-dimensional model which assumes steady, adiabatic, frictionless, and equilibrium is proposed. In the convergent part of the nozzle the flow is treated as single-phase flow of liquid, whereas in the divergent part the flow is treated as separated two-phase flow with saturated condition. The analytical results indicate that the temperature and the pressure decrease rapidly in the divergent part, and the void fraction increases immediately near the throat. Although this analysis is quite simple, the analytical results can follow the experimental results well within this study.展开更多
Prediction of inception of sheet cavitation on solid walls has been recognized to be very difficult, since it is significantly affected by the boundary layer flow characteristics, the population of free nuclei, the nu...Prediction of inception of sheet cavitation on solid walls has been recognized to be very difficult, since it is significantly affected by the boundary layer flow characteristics, the population of free nuclei, the nuclei held in the wall roughness, the amount of dissolved air in liquid and so on. It has not sufficiently been made clear how the inception is affected by the conditions of water qualities and background flow characteristics. In this study, high speed observation of inception of sheet cavity from free nuclei is conducted for a two-dimensional convergent-divergent nozzle flow, where the sheet cavity forms just downstream of the nozzle throat. The effects of the amount of dissolved air and the free stream velocity on the inception process of sheet cavitation is examined. In addition, the bubble nuclei density, which is well known to be important factor for cavitation inception, is passively controlled by the filter installed in the tunnel. From the observations, it is confirmed that the nuclei number density significantly affects the formation of sheet cavity rather than the other two parameters. In conditions with large nuclei number density, the sheet cavity does not form, and bubbly cavitation appears instead. In the case with small nuclei number density, the sheet cavity forms from a single flowing nucleus and develops streamwisely and spanwisely. In the conditions with medium nuclei number density, the sheet cavity also forms but is shorter/narrower streamwisely/spanwisely, due to interaction of other nuclei flowing near the formed sheet cavity.展开更多
文摘Microplastic wastes in ocean can include the harmful chemical material, and the harmful material is concentrated by marine species. The separation and collecting methods of microplastics in ocean are researched in the world. The authors proposed the microplastics recovery device composed of the plates. Besides, the device consists of the tilted inlet/outlet and the horizontal part. In the water flow such as the tidal and ocean currents, the microplastics can be extracted from the main flow due to the vortex flow generated at the inner part of this device. In this research, the effects of the flow velocity and the inlet/outlet tilt angle on the capture performance were investigated experimentally and numerically. In the numerical simulations using the discrete phase model, the tilt angle was changed in a range between 30 degrees and 150 degrees in increments of 15 degrees, and the particle tracks of plastics were derived in steady condition. On the other hand, the capture performances in three cases of tilt angle 45 degrees, 120 degrees and 150 degrees were compared by circulation type water channel tests in which the plastics denser than the water were swept away 30 times every flow velocity. As the result, it seems that the tilt angle of 120 degrees is suitable for the wide range of the flow velocity in river and ocean.
文摘The aim of this study is to investigate CO2 two-phase nozzle flow in terms of both experimental and analytical aspects for the optimum design of two-phase flow nozzle of CO2 two-phase flow ejector. In the experiment, it is measured that the temperature profile in the stream-wise direction of a divergent-convergent nozzle through which CO2 in the supercritical pressure condition is blown down into the atmosphere. In the analysis, a one-dimensional model which assumes steady, adiabatic, frictionless, and equilibrium is proposed. In the convergent part of the nozzle the flow is treated as single-phase flow of liquid, whereas in the divergent part the flow is treated as separated two-phase flow with saturated condition. The analytical results indicate that the temperature and the pressure decrease rapidly in the divergent part, and the void fraction increases immediately near the throat. Although this analysis is quite simple, the analytical results can follow the experimental results well within this study.
文摘Prediction of inception of sheet cavitation on solid walls has been recognized to be very difficult, since it is significantly affected by the boundary layer flow characteristics, the population of free nuclei, the nuclei held in the wall roughness, the amount of dissolved air in liquid and so on. It has not sufficiently been made clear how the inception is affected by the conditions of water qualities and background flow characteristics. In this study, high speed observation of inception of sheet cavity from free nuclei is conducted for a two-dimensional convergent-divergent nozzle flow, where the sheet cavity forms just downstream of the nozzle throat. The effects of the amount of dissolved air and the free stream velocity on the inception process of sheet cavitation is examined. In addition, the bubble nuclei density, which is well known to be important factor for cavitation inception, is passively controlled by the filter installed in the tunnel. From the observations, it is confirmed that the nuclei number density significantly affects the formation of sheet cavity rather than the other two parameters. In conditions with large nuclei number density, the sheet cavity does not form, and bubbly cavitation appears instead. In the case with small nuclei number density, the sheet cavity forms from a single flowing nucleus and develops streamwisely and spanwisely. In the conditions with medium nuclei number density, the sheet cavity also forms but is shorter/narrower streamwisely/spanwisely, due to interaction of other nuclei flowing near the formed sheet cavity.
