Experimental study was made on the turbulence structure of vertical upward gas-liquid two-phase bubbly flow through 20-mm and 50-mm round tubes. In this study, the turbulence fluctuation velocity and the power spectral density on the basis of experimental data measured by a hot-film anemometer for various turbulent flow conditions were analyzed and they were considered by the void fraction distribution and the liquid single-phase flow. Furthermore the vortex scale, the wake size and the void interval were also discussed by those analytical results.
The branching flow characteristics of gas-liquid two-phase flow in separated narrow channel with T-junction were experimentally carried out. The one-sided flow at T-junction was observed. The characteristics of one-sided flow were evaluated by measuring mass flow rate of liquid phase for each separated channel and summarized “One-sided flow parameter.” The flow visualization at T-junction by high-speed video camera was also carried out. In addition, to improve the flow distribution characteristics to be the even flow separation, that means the averaged flow rate of each separated channel to be equal, a choking devices was attached to the outlet of each channel. The results show the mechanisms of the even flow separation and successful effect of choking at outlet on flow distribution characteristics.
The operating condition of the distillation column is strongly influenced by flow characteristics of counter-current two-phase flow in structured packings. Generally, the flooding and loading conditions determine the limitation of the operating condition. Thus, various investigations have been conducted so far, but most of those studies were based on the results which were obtained by using simple test section such as a round-tube. Consequently, the characteristics of the actual apparatus have not been fully understood so far. In this study, the influence of clearance between structured packings on flow characteristics of counter-current two-phase flow was experimentally investigated. In the investigations, liquid hold up, which was quantitatively estimated by using X-ray radiography, pressure drops and liquid distributions were measured under several clearances (0, 3 and 5 mm). As a result, when the clearance is 5 mm, influence of the clearance is clearly observed in the flow characteristics.
Gas-liquid interfacial flows, such as liquid film flows (also known as wetting flows on plates), are encountered in many industrial processes including absorption, distillation and so on. The present study focuses on detailed descriptions of the transition phenomena between the film flow and the rivulet flow, as well as how such phenomena are affected by surface texture treatments on plates. This study uses a numerical simulation of Computational Fluid Dynamics (CFD) with the Volume of Fluid (VOF) model as well as an experimental measurement technique. Through the comparison of two geometry cases (smooth surface and wavy surface) which are the models simplified from typical structured packings, the numerical and experimental results show that surface texture treatments can help to prevent the liquid channeling and can increase the wetted area. The main reason for increasing the wetted area on the wavy surface is that the liquid film break-up is inhibited due to the increasing of liquid film thickness on the plate as well as the spreading of the liquid flow in spanwise direction by the wavy surface geometry.
Large multi-stage compressors and blowers have been applied widely in the energy industry, such as oil and gas plants, for many years. In recent years, a compact blower with a high pressure difference and high flow rate (e.g., as the cooling system for a densely packed server) is anticipated with the development of miniaturization technology for machinery. Thus, this experimental study was conducted for the development of a novel compact multi-stage blower. The appropriate combinations of curved impellers and return vanes, which eliminate the swirling flow for a static pressure recovery and draw an operating fluid to the 2nd impeller from the 1st impeller, were investigated from the viewpoint of performance and efficiency. In addition, the velocity and pressure fluctuations of flow instabilities generated in the return vanes for a low flow rate were also investigated. The results indicated that the best combination of the impellers from the point of total efficiency, which was the backward-curved vane for the 1st impeller and the forward-curved vane for the 2nd impeller, in the case of present condition. In addition, flow instability in the return vanes circumferentially propagates with the cell structure.
Gravel-bed rivers are composed of a large variety of particle sizes and shapes.Large particles on the bed resist against flows, but they are picked up and move intermittently. Particle motions are different from those in sandy rivers where most of particles move continually. To estimate sediment transport rate in gravel-bed rivers, fundamental movement processes of particles with different sizes and shapes have to be examined. In this paper, three-dimensional numerical movable-bed simulations were conducted, and sediment transport rate and fundamental movement processes of particles were measured under three conditions of spheres, gravel particles and mixed particles. We found that particle shapes affected significantly pick-up processes and this resulted in great differences of sediment transport rate among particles with different shapes.
This study experimentally examined the drying characteristics of the waste gypsum powder using a permeation of heated air. The powder used was the waste gypsum which the particle diameter was classified into three kinds. As the experimental conditions, the particle diameter of dehydrate gypsum, the heating temperature, the initial mass of powder, the heating time and the mass flux of heated air were varied. When the initial mass of powder was an identical, it is found that the decrease in the time of change from the dehydrate gypsum to the hemihydrate gypsum depends on the increase in the particle diameter and the heating temperature. As the analysis of X-ray diffraction pattern, it can be confirmed a permeation test of heated air was an effectiveness for the evaluation of the change to hemihydrate gypsum. In addition, an effective thermal conductivity and heat flux of the packing bed of gypsum were estimated. It is found that a particle Reynolds number influenced to an effective thermal conductivity in the packing bed of waste gypsum. Also, an effective thermal conductivity including the flow of heated air was high in the case of large particle diameter. Furthermore, it is inferred that a high heat flux acting on the packing bed of gypsum influenced the time of change from the dehydrate gypsum to the hemihydrate gypsum.
Liquid infiltration is an important process for cleaning inside small size holes. However, it is difficult to infiltrate liquid into closed end holes having small diameter. Because the surface tension prevents the deformation of gas-liquid interface for entering the liquid. In this study, we observed the liquid infiltration process into a closed end hole by applying external pressure under two ways, i.e. gradual pressurization with a hand pump and impingement of a droplet train. As a result, it is found that the amount of dissolved air into liquid by applying pressure is small, and it has small effect for the liquid infiltration. In addition, it is also found that the high liquid infiltration rate can be achieved by applying a droplet train impact. The trapped bubbles inside the holes were ejected by repetition of droplet impingement. On the other hand, such the high liquid infiltration was not observed by the liquid column impact. Possible mechanisms of liquid infiltration by a droplet train impingement are discussed.
Gas-liquid flows driven by rotating rigid objects are numerically studied. The Volume-Of-Fluid (VOF) and Boundary Data Immersion (BDI) methods are employed to treat the gas-liquid and fluid-rigid interfaces, respectively. The basic equations are solved by means of finite difference method using a regular Cartesian mesh. Two types of systems are considered: one is a simple geometry composed of cylindrical disk and container to exhibit the validity of the numerical approach, and the other is a complex geometry including holes and/or caves to clarify the relevance to the two-phase mixing and forcing. Numerical simulations are performed for various angular speeds Ω and compared with the experiments. The simulated results demonstrate the capability in capturing the gas-liquid distribution, the torque on the disk and the velocity distribution obtained by Particle Image Velocimetry (PIV). For the complex system, the torque at low Ω is dependent mainly on Ω irrespective of the presence of the holes/caves, while beyond a certain Ω, the considerable jetting flow structure forms due to the presence of the holes on the disk, and therefore the geometry effect on the torque becomes significant.
Microbubble aeration is utilized usefully for chemical and biological processes which consume large amount of dissolved gas in liquid because the microbubbles have long residence time in liquid, large specific gas-liquid interfacial area and fast mass transfer rate. To design the industrial process using microbubble aeration, however, the fundamental characteristic and behavior of microbubbles have to be investigated at first. In this study, therefore, both shrinking and rising behaviors of a single microbubble are simultaneously observed. A single microbubble was induced from a fine nozzle into the bottom of a tall transparent vessel filled with ion-exchanged water in which dissolved gas was reduced previously with vacuum degassing. The single rising microbubble was chased with a high-speed video camera along the vessels height. The mass transfer rate was measured from the shrinking behavior of the single microbubble which was captured and analyzed from the video image. The smaller the diameter of a microbubble, the more rapidly it decreased. Finally, the microbubble was vanished. With reducing concentrations of oxygen and nitrogen dissolved in water, the shrinking rate of a microbubble became faster. The mass transfer from shrinking microbubble of either air or pure oxygen can be evaluated by the sum of oxygen transfer and nitrogen transfer, in which each mass transfer coefficient was estimated by the equation of Ranz and Marshall. The estimated behavior of the single shrinking microbubble was agreed well with the observation. It is understood in this study that both oxygen transfer and nitrogen transfer from shrinking microbubble into water occur independently in relatively low dissolved gas concentration in water.
This paper describes experimental investigation on the three-dimensional internal flow structures of the acoustic levitated volatile droplets by stereo PIV. The acoustic levitation is one of the effective techniques to levitate and manipulate droplets in air. In order to apply the acoustic levitation to various fields such as the material science, analytical chemistry, drug discovery and so on, it is essential to understand the flow structures and transport phenomena on the acoustically levitated droplet. Our observation shows the internal flow structure is changed with the increase of the saturated vapor pressure of the levitated droplets. In the case of decane, nonane, octane, heptane, hexane and pentane droplets, the rotational motion is generated in each droplet. In the case of ethanol and methanol droplets, there is the flow from the equator toward the center of the droplet in the horizontal plane. In addition, the two or four vortices are generated in the horizontal plane with the increase of the droplet diameter.