Toshihiko Shakouchi

Classification of ultra fine powder by a new pneumatic type classifier

Abstract Recently, there are great requirements for ultra fine powder in fields that use advanced materials, for example, electric parts in Information Technology (IT) industry. Especially, the request for the diameter control of ultra fine powder is increasing. Pneumatic type ultra fine powder separator, classifier, is one of the equipment which meet this request. But there is no clarified study on the flow condition that realizes high performance. In this study, a new pneumatic type ultra fine classifier is proposed and the relation between the performance and the flow condition is investigated by flow visualization with the tuft grid and oil dot methods and the measurement of gas velocity. Based on the results, it was known that the new classifier has a large swirling flow velocity which is able to classify ultra fine particles accurately.

Studies on Mixing Process and Performance Improvement of Jet Pump (Effects of Nozzle and Throat Shapes)

In order to improve the efficiency of a jet pump used in Boiling Water Reactors, the effects of nozzle and throat shapes on the mixing process between driving flow and induced flow in the throat and the pump efficiency were examined experimentally. The velocity profile and local skin-friction coefficient distribution in the throat were also obtained experimentally. Three kinds of nozzles, conventional throat and throat having a very gentle gradient were used. The following results were obtained. The circular nozzle with eight notches shified the efficiency to a bit high flow rate ratio region by reduced jet size. The flower-shaped nozzle decreased the efficiency by increasing skin-friction loss caused by enhanced mixing. The throat having a very gentle gradient reduced the skin-friction loss and enhanced the efficiency.

Gas Absorption, Aeration, by Fluidic Oscillator Operated by Gas-Liquid Two-Phase Flow

It is known that a conventional feedback type and other type of fluidic oscillators can be operated not only by gas or liquid single phase flow but also by gas(air)-liquid(water) two-phase flow (Shakouchi, 1989, 2001). The two-phase jet flow oscillates periodically of the oscillator under some conditions, and then the gas, air bubble, and liquid flows are mixed and stirred forcibly. The contact area and time between gas and liquid flows increase considerably and then the much increasing of mass transfer, the diffusion or absorption of gas into liquid, will be expected. It may be able to construct an entirely new compact type gas-absorber, aerator, with a simple construction. In this paper, first the performance of fluidic oscillator operated by gas-liquid two-phase flow is made clear experimentally. Next, the aeration performance of the oscillator, namely the diffusion or absorption rate of air, dissolved oxygen, into water under various kind of operation conditions are examined experimentally. The following major results will be shown. (1) The oscillatory frequency f increases linearly with increasing the Re number (= udf /ν, u: mean velocity of water flow at the nozzle exit, df : nozzle width, ν: kinematic viscosity) and the void fraction α. (2) The pressure loss, flow resistance, Δp of the oscillator or increases rapidly with increasing Ref and linearly increasing α. (3) Dissolved oxygen in water can be increased considerably by fluidic oscillator operated by air-water two-phase flow, and it was well known that a new compact type aerator can be constructed by fluidic oscillator.Copyright

Flow and Heat Transfer of Petal Shaped Double Tube—Effects of Pipe Geometry

Heat exchangers are widely used to transfer heat from one fluid flow to another. Over time, various types of heat exchangers have been developed to decrease energy consumption and increase efficiency, including compact fin tube and double tube with special inner pipe geometries (ribbed, spiral, and petal shapes) [1, 2]. In this study, we experimentally investigated the heat transfer efficiency of petal-shaped double tubes with a large wetted perimeter or heat transfer area. Moreover, the influence of the number of petals was studied. Our results show that a larger heat transfer area improves heat transfer rate in heat exchangers but the heat transfer efficiency of the five petal-shaped double tube (5P-tube) is much higher than that of the 6P-tube because of a smaller flow resistance of the 5P-tube.

Development of Rectangular Microblasting Nozzle

In this study, in order to improve the machining productivity of microblasting, the new rectangular microblasting nozzle with a large aspect ratio is proposed and the flow characteristics and cutting performance are examined precisely by experimental and numerical analyses. The main results show that (1) setting the circular vane in the nozzle can diffuse particle flow uniformly at the nozzle exit, making the high cutting accuracy, (2) larger cutting efficiency is obtained comparing with the conventional circular blasting nozzle.

Interaction Between Water or Air-Water Bubble Flow and Tube Bundle—Effects of Arrangement of Tube Bundle and Void Fraction

Water or air-water bubble flow passing through tube bundle can be seen in many industrial equipments such as heat exchanger and chemical equipment. In addition, tube bundle can be used as a flow-straightener, -mixer, -resistor, and -damping device. In this study, the effects of tube arrangement of equally or unequally spaced in-line and staggered tube bundle and of void fraction on the flow characteristics such as flow pattern and flow resistance of a tube or tube bundle are examined experimentally.

Loss Reduction of the Flow in the Reducing Elbow Duct by Using Weir Shaped Small Obstacle

Reducing elbow is \( 90^{\circ }\) bend or elbow pipe/duct which has smaller outlet than inlet. This type of element is frequently used in the industrial facilities. After the corner of this element separated flow from the corner flows away from the inner wall. And then, effective cross-sectional area of downstream pipe/duct near the corner is reduced. Reduction of effective cross-sectional area causes extremely large flow resistance. In this study, loss reduction method with weir-shaped obstacle for reducing elbow duct is newly proposed. To clarify the effects of obstacle on the flow in the reducing elbow, pressure measurement and flow visualization were carried out. As a result, it is made clear that the loss of reducing elbow is reduced by maximum of about 63 % by using obstacle.

Direct Numerical Simulation of Dynamic-Rotational Controlled Jet

In order to develop a new mixing procedure, we conduct DNS (direct numerical simulation) of dynamic controlled free jets. As the dynamic control, it is assumed that the inflow velocity of jet is alternately rotated around streamwise direction. To realize the high accurate computation, the discretization in space is performed with hybrid scheme in which sine or cosine series and 6th order compact scheme are used. From view of instantaneous vortex structures, it is found that the flow pattern considerably changes according to the rotating frequency, i.e., according to the increasing frequency, helical and entangled mode appear in turn. From the ensemble averaged flow properties such as jet width and entrainment, it is confirmed that the jet widely spreads perpendicular to the rotating axis and that the mixing of upstream jet is markedly enhanced due to the dynamic control. Further in order to quantify the mixing efficiency of the dynamic control, as another mixing measure, a statistical entropy is examined. Compared to the uncontrolled jet, it is confirmed that the mixing efficiency is markedly improved, suggesting that the dynamic control can be expected to be useful for the improvement of mixing performance.

Flow and heat transfer of petal shaped double tube

In this study, the flow and heat transfer characteristics of petal-shaped double tube with 6 petals are examined experimentally for a compact heat exchanger. As results, the heat transfer rate, Q, of the 6 petal shaped double tube (6-p tube) is much larger than that, Qp, of conventional circular double tube in all Reynolds number Rein,h (where, the reference length is hydraulic diameter) ranges. For example, at Rein,h =(0.5～1.0)× 104 it is about 4 times of Qp. The heat transfer enhancement of 6-p tube is by the increase of heat transfer area, wetting perimeter, and a highly fluctuating flow, and Q of the 6-p tube can be expressed by Q [kW/m] = 0.54Rein,h + 2245.

Jet Flow from Resonance Nozzle and Flow Control by Notched Nozzle

The jet flow from an orifice nozzle shows a particular velocity profile with a large velocity gradient at the edge of the jet. Setting an orifice nozzle, second one, with a resonance room just after the first orifice nozzle the jet causes resonance phenomena and the resonance frequency depends on the jet velocity and the volume of resonance room. In this study, a notched nozzle was used as the second one to enhance the flow disturbance or fluctuation, and the effects of the notched nozzle on the mean and fluctuating velocities and the mixing or diffusion characteristics of the jet itself and with the surroundings were examined experimentally using a hot wire measurements. As a result, it was made clear that under a same operation power the flow rate near the nozzle exit of a notched resonance jet is larger than those of an orifice and resonance jets, for example, at x/d = 0.2 (x: distance from the nozzle exit to the downstream, d: nozzle diameter) it is about 2.5 and 1.3 times of theirs, respectively, and others.