A mercury target system will be installed in Japan Proton Accelerator Research Complex (J-PARC) for MW class neutron sources. High intense proton beams injected into the target will induce cavitation by pressure waves. Injection of microbubbles with 50 to 200 μm in diameter into mercury may be effective to reduce cavitation damage. Bubble generation in mercury is difficult because of its poor wettability. Therefore, we artificially change wetting condition in water to simulate bubble formation in poor wetting conditions. Experimentally, visualization of bubble growth at an orifice type nozzle of 100 μm in diameter was done by a high-speed CCD camera. Wetting condition on the orifice surface was worsen by coating it with a water-repellent. Computational Fluid Dynamics (CFD) simulation was carried out under stagnant water to understand the effect of wettability on bubble formation from the orifice nozzle. It was found that the bubble diameter depends on contact angle and it increases as wetting conditions become worse, i.e. large contact angle.
Two types of swirl motions of a liquid jet occur when a liquid is injected through a centered bottom nozzle into a cylindrical bath of a constant depth: shallow-water and deep-water wave types. The water in the bath is drained and then circulated with a pump to keep the bath depth constant. Similar swirl motions can be observed when a liquid is continuously injected into a cylindrical bath without draining it from the vessel. The bath depth therefore increases linearly with time. The swirl motion of the deep-water wave type is useful for practical applications because it has very high mixing efficiency. In this study the trajectory of the swirling jet, the velocity vectors of water and air flows, and the period and amplitude of the swirl motion in a bath of varying depth are experimentally and numerically obtained The results are compared with those for a swirl motion generated in a bath of constant depth.
Contamination of semiclosed water areas is one of serious problems in the world. A novel agitation method is proposed for the treatment of contaminated sediment on the bottoms of bays and lakes using a swirl motion of a bubbling jet and ozonation. In this study, we focus on the lifting of small particles initially placed on the bottom of a cylindrical bath up into the bath by a swirl motion of a bubbling jet generated with a J-shaped lance. Investigation is carried out on the occurrence condition and the basic characteristics of the swirling bubbling jet.
Cross flow fans have extensive industrial applications, from air conditioning and ventilation to agricultural sprayers, as well as a wide variety of heat transfer applications. This fan is a unique type of fan with an eccentric vortex inside impeller which produces high pressure coefficient. However, some problems are not yet solved completely about the effects of fan geometry on the performance. The position and the circulation of the vortex are affected by the casing configuration of the fan. The vortex behavior has a large effect on the fan performance and fan noise level. In this paper a method of noise reduction of cross flow fan is experimentally investigated. The method involves varying the geometry of the dividing tongue through slight alterations in position and⁄or the introduction of axial variations in the tongue geometry. The visualization studies undertaken to ascertain the mechanism of the observed noise reduction is accomplished.
Swirling liquid jet is useful for agitating strongly a bath contained in a cylindrical vessel without using any mechanical devices such as an impeller in the bath. Many practical applications therefore are expected in a variety of fields such as materials, mechanical, chemical and food engineering. Swirling liquid jet can be generated by injecting a liquid into a cylindrical bath from a bottom nozzle. In this study, we introduce the flow visualization of a swirling liquid jet in a bath in two-phase stratification. We compare the experimental data of Particle Image Velocimetry (PIV) with the numerical results of Computational Fluid Dynamics (CFD).
Recently, fan noise is severely restricted by ISO standard 14000, such as about 40 [dB(A)] noise level at night. Usually, small type fan includes centrifugal fan, axial flow fan, cross flow fan and so on. Although centrifugal fan is considered as the most silent one among them, further reduction of noise level is required. Fan noise is generated with the coherence between the blade and the tongue of the fan. Therefore fan noise can be reduced when the blade is removed or the blade is kept away from the tongue. In this study, two types of new idea fans were developed. The first is the multi disk friction type fan which was developed from a viewpoint of no blade fan. The second is the multi disk fan with blade, which we call hybrid fan. This is a combination of the multi disk fan and the centrifugal fan. In case of the hybrid fan, the blade was kept away from the tongue. Hybrid fan is expected to achieve low noise and high performance characteristics. Experimental apparatus was constructed. Fan performance and noise level were measured. Furthermore, power spectrum analysis was conducted. Multi disk fan with no blade showed the lowest noise level characteristics among the fans experimented. Hybrid fan shows much lower noise level than that of centrifugal fan. Desired noise level characteristics and performance characteristics can be obtained with hybrid fan.
This experimental study is aimed at clarifying the vibration characteristics of tube bundle subject to vertical cross flow. Following our 1st report on in-line array of tubes, this paper reports on staggered array of tubes, another configuration of tube bundle commonly applied in shell-and-tube type of heat exchangers. Test section, comprising flexibly mounted tubes over the whole tube bundle, was built to simulate the vibrating state. For visualization of the flow field, the heat tubes were simulated by transparent glass rods and the channel walls were made of acrylic resin. Displacement of the vibrating rods was captured by high-speed video camera, whereas instantaneous velocity fields around the rods were obtained by Particle Image Velocimetry (PIV). Good agreement between the frequencies of the rod vibration and the fluctuation of the flow velocity component indicated a strong interaction between them.
An experimental study was conducted to investigate the flow-induced vibration characteristics of socket-supported (flexible) tube bundles in cross flow. In order to simulate the partial support of clearance holes of baffles in shell-and-tube heat exchangers, in-line and staggered bundles comprising glass rods mounted flexibly inside circular supporting socket in the channel wall were constructed. The two test sections were made transparent to facilitate flow visualization and whole-field measurement by PIV. Based on the results obtained in this study, it can be concluded that vortex shedding is the intrinsic excitation source for the vibration of flexible tube bundle. Vortex shedding creates instability in the flow field. The vortex shedding drives the oscillating motion of the tube, and the motion of the tube controls the vortex shedding. Thus a feedback path is established to sustain the tube vibration.
The flow characteristic of bubbly flow is very complex because interactions between bubble and fluid,bubble and bubble,and bubble and wall appear simultaneously.In order to simplify the problem,one interaction is taken and studied experimentally.The study deals with the bubble-wall interaction as an elementary process of bubbly flow.The bouncing motion of a single bubble in water was measured by using stereo image processing.The bubble of about 4 mm diameter flowed up spirally and moved toward the wall.After touching the wall,the bubble bounced and moved toward the center of the channel.After that,the bubble turned to the wall again.The experimental results showed the deformation, orientation and velocity of the bubble during the bouncing process,which were not obtained in the previous study using 2D image processing.The aspect ratio and velocity of the bubble synchronized the bubble motion.The minor axis of the bubble was parallel to its moving direction,which was supposed as the effect of the drag force of the water.
The authors have developed a new automatic technique of drawing the master curve from the experimental data measured by the Dynamic Measurement Tester. In this paper, the experimental conditions recommended by Japanese Industrial Standards are considered and modified from the perspective of drawing the master curve. To verify the effectiveness of the proposed technique and the experimental conditions, the storage and loss moduli of epoxy resins and rubber materials are measured, and the proposed technique is applied to the experimental data. From the results, it is confirmed that the master curves are obtained automatically and expeditiously.
The stress in granular media flowing from the 2D hopper with an orifice is visualized by experimental method using photoelasticity. Firstly, the characteristics of the granular flow are examined. The results show that critical outlet diameter of the granular flow is about five times larger than the diameter of the particle used in this study. Moreover, the characteristic of the mass flow rate nearly corresponds with that in general granular flow systems. Then, the stress in the granular flow is examined through the photoelastic experiment. The results show that dynamic arches are frequently observed near the orifice even if the granular flows out from the orifice continuously. The rate of arching during granular flowing and the frequency of clogging increase with decreasing the orifice bore. These results say that the static arching and clogging are caused by increasing of the rate of dynamic arching.
Bubble formation from a centered single-hole nozzle placed on the bottom of a water bath has been investigated using a high-speed video camera. Wetted and poorly wetted nozzles are used to understand the effect of wettability of nozzle on the bubble formation in the water. When the gas flow rate is lower than a certain critical value, the frequency of bubble formation is specified by the outer nozzle diameter. On the other hand, when the gas flow rate is raised above another critical value, the inner nozzle diameter governs the bubble formation. An empirical equation is proposed for the frequency of bubble formation in the water.