The behavior of interface between a water droplet dyed red to make clear its boundary and silicone oil surface on which the droplet falls was observed by using a high speed video recorder with 500 frames per second. Eleven kinds of silicone oil whose kinematic viscosity νT is 1 mm2/s to 105mm2/s were used as the target liquid. A droplet having 3.1mm diameter falls freely from a micropipet whose height was varied between 100mm and 1000mm. The configuration of silicone oil cavity at its deepest state and that of deformed droplet at its maximum spread were classified into seven and five respectively based on their observation results. Under some conditions disintegration of droplet were observed, which accompanied remarkable deformation of oil surface at lower viscosity νT≥≤10mm2/s, while it occurred on the plane oil surface at higher viscosity of νT≥5×10mm2/s.
Geysering may be induced during start-up in natural circulation boiling water reactors. It is necessary for simulation of this flow instability to model the coalescence mechanism and condensation process of slug bubbles. In this work, image data processing technique using a CCD digital camera has been developed to measure slug flow characteristics. The developed measurement technique of rising velocity of slug bubbles and liquid film thickness surrounding a bubble and its measurement accuracy are discussed in this paper.
Geysering may be induced during start-up in natural circulation boiling water reactors. It is necessary for simulation of this flow instability to model the coalescence mechanism and condensation process of slug bubbles. In this work, image data processing technique using a digital video camera has been developed to measure slug flow characteristics. In this technique, ultraviolet lighting with high frequency power source, laser sheet and stroboscope whose lighting frequency can be regulated are used as lighting and small nylon particles mixed into water are adopted for tracers. The developed measurement technique are applied for slug bubbles rising in stagnant water, and coalescence process of slug bubbles, liquid film velocity surrounding a slug bubble and velocity field in the wake region are measured. From these results, the capability of the developed measurement technique and the measurement accuracy are discussed.
The influence of the passage spacing of an installed corrugated wall duct on the flow and heat transfer characteristics was analyzed. First of all, a corrugated wall duct of the corrugation angle, θ=45°, was constructed. Then, flow visualization and flow characteristic measurements were conducted. Following this, a numerical simulation was performed for the same conditions. The factors, which influenced the characteristics of the flow in the corrugated wall channel, were clarified according to the results. Especially, a main factor, which determined the flow characteristic of the channel, was confirmed to be the passage spacing. Therefore, the influence of the passage width exerted on the heat transfer characteristics was confirmed by the experiment. Using this result the correlation between the flow and heat transfer characteristics were derived.
Pictures have been presented for oscillatory laminar flow in the inlet region of circular curved pipes with long, straight tangents. Visualization of the flow was realized by the hydrogen bubble method and the time-dependent velocity profiles were grasped with reasonable accuracy. Their features substantiate the behavior of the developing oscillatory flow in dependence on the Womersley number α. Influences of the curvature radius ratio Rc and the Dean number D on the development are also investigated. From LDV measurements executed with reference to the visualization data, moreover, the inlet lengths of both the curved pipe and the upstream tangent are obtained in a wide range of the parameters and the formulas for them are presented as a function of D/α 2·Rc1/2, which is effective when α>4. The inlet length of the upstream tangent is 1.5 times as long as one of the curved pipe.