Tetsuhiro Tsukiji

Study on the cavitating flow in an oil hydraulic pump

In the present study, the computational fluid dynamics(CFD) is employed using a three-dimensional realizable k-ε turbulent model with cavitation model to estimate the occurrence and the region of the cavitation cloud of the cavitating jet flow issuing from a notch (V-shaped groove) in an oil hydraulic pump. On the other hand, test pump model is designed to visualize the jet flow near a notch of a valve plate in an axial piston pump using a high-speed video camera from the perpendicular direction to the axis. The CFD results are found to be in good agreement with the visualization results. The main aim of the present study is to investigate the influence of the number of notches on the pressure distribution, void fraction and the volume of the cavitation region. The erosion for those cases is discussed by investigating the pressure distribution on the inside surface of the cylinder.

CFD Analysis in a Non-Contact Holder

There are many devices that use air flow characteristics. Recently an electric fan without propeller using air jet flow and a vacuum cleaner using swirling air flow have been developed by Dyson Ltd. Furthermore, as one of the applications of such air flow, a non-contact holder that can hold a body such as a work piece, disc etc., using low-pressure region generated by air flow without contact was developed by a Japanese company. Some bodies such as work piece are brought without contact with the holder. The mechanism to hold them is explained by Bernoulli’s theorem. However, systematic research has not been done in the present stage and the effect of the geometry of the non-contact holder on the holding force is not clear. In this paper, we calculated the flow in a non-contact holder and obtained the force to hold a body by CFD analysis. The effect of the deflector and inside geometry of the holder on the velocity and pressure distribution, and holding force is investigated. The deflector is a device fixed with the holder to increase the holding force using low-pressure region. CFD was done using both incompressible and compressible flow, and k-e turbulent model was used. The calculated pressure distributions of a simpler model of the holder are compared with the previous experimental results to confirm our calculation method. The design policy of a non-contact holder is discussed based on the calculated results of velocity and pressure distributions and holding force. Consequently we show that the deflector is very useful to obtain high holding force and the concept to design the non-contact holder is required to get the holding force according to the weight of the body and to achieve high efficiency.Copyright

Influence of Electric Fields on Flow of Liquid Crystal Mixture in a Circular Tube With Electrode Surface

Liquid crystal is one of functional fluids to control an apparent viscosity using an electric field intensity. It is also called ER (Electro-rheological) fluids. In the present experiment a liquid crystal mixture made of some kinds of the nematic liquid crystal is used. The responses of the pressure drop are examined when the liquid crystal mixture flows in a circular tube with the electrode walls on some parts of the inner surface of the tube for the constant flow rates. The four pair of the electrode is used and the voltages are added in the peripheral direction. When the voltages are applied on the liquid crystal mixture and removed, the pressure responses of the inlet of the circular tube are measured with the pressure transducer. On the other hand, the pulse-wave voltages are added to the electrodes to control the pressure drop using the pulse width modulation or the pulse frequency modulation. The diameter of the circular tube is 1.0mm. The isotropic-nematic transition is 90.0°C and smectic-nematic transition is −44.0°C for the liquid crystal mixture. The open-loop test facility with the liquid crystal mixture is set in a pyrostat to keep the temperature constant.© 2003 ASME

Pump Using Nematic Liquid Crystalline Flow Under Direct Current Electric Field

This paper presentsa small pump for liquid crystal, herein called a liquid crystal pump. The mechanism of liquid crystalline flow by applying an electric field to the liquid crystal is used to generate one-directional flow in a pump. A liquid crystal pump has a cylindrical channel and a cylindrical electrode pair. In this study, direct current electric fields were used, and the pressure-flow rate characteristics of the pump were measured. In addition, the relationships between the non-dimensional flow rate and pressure of the pump were obtained. In order to achieve both high pressure and high flow rate, various shapes of electrodes and channels were investigated and the measured results were compared with each other. In addition, connecting pumps were designed to obtain the required pressure and flow rate. The structure of a liquid crystal pump is simple and the size can be decreased by further research. So this pump has the advantage of small source of actuator by changing electric power into fluid power. Furthermore, our pump has a good possibility for use in cooling system because it makes no noise and no mechanical vibrations.Copyright

Influence of Electric Fields on Pressure Drop of Liquid Crystal Mixture

Liquid crystal is one of homogeneous ER (Electrorheological) fluids in some range of temperature. In the present experiment a liquid crystal mixture is used. The responses of the pressure drop are examined when the liquid crystal mixture flows between two parallel-plate electrodes for the constant flow rates. When the voltages are applied on the liquid crystal mixture and removed, the pressure responses of the inlet electrodes are measured with the pressure transducer. At same time, the liquid crystal mixture between the transparent electrodes made of glass is visualized with the video camera investigate the time history of the director of the liquid crystal mixture. The AC voltages are also used to investigate dependence of the liquid crystal mixture on the frequency the voltages. Outlet of the flow channel with two parallel-plate electrodes is atmosphere. Relation between the flow visualization results and the changes of pressure drop investigated especially for transient period. On the other hand, the pulse-wave voltages are added to the electrodes to control the pressure drop using the pulse width modulation or the pulse frequency modulation. In the present study the flow rates change from 0.001cc/sec (velocity is lmm/sec) to 0.003cc/sec and the electric field intensity is from 0.2kV/mm to lkV/mm. The gap of the electrodes is 0.2mm.The isotropic-nematic transition is 90.0°C and smectic-nematic transition is −44.0°C for the liquid crystal mixture. The open-loop test facility the liquid crystal is set in a pyrostat to keep the temperature constant.Copyright

Characteristics of Pneumatic Non-Contact Holder With Two Swirling Flows

When products requiring careful handling such as semiconductor wafers and food (hereinafter called “workpieces”) are transported in manufacturing processes, problems can occur due to malfunctions that degrade sanitary conditions during the transport of workpieces through contact. An excellent device for transporting workpieces is a pneumatic non-contact holder (hereinafter called “cup”). This device holds a workpiece without contact by using pneumatic pressure, and so a workpiece doesn’t suffer damage or contamination. The purpose of this paper is to propose a method for overcoming the weaknesses in vortex-type non-contact holders, which is a cup that can hold a workpiece by using the negative pressure generated by the centrifugal force of a swirling flow, and propose a shape of cup which will generates a larger holding force from the point of view of energy saving. Specifically, we changed the shape of the chamfer in the swirling chamber exits and the number of the nozzles, and measured the holding force characteristics and the pressure distribution of the cup, thereby examining the performance of the cups. The experimental results indicate that the holding force is strongly related to both the shape of the chamfer in the swirling chamber exits and the number of the nozzles.Copyright

Study on EHD pump with multi-holes electrode

One of an electrohydrodynamics (EHD) phenomenon is the induced flow of a functional fluid in the presence of an electric field. In this paper, we describe a small pump in which the flow is generated by such an EHD phenomenon. In the case of pumps based on cylindrical electrodes, which thus far have been the focus of our research on EHD pumps, the total circumference length of the edge of the holes in the electrode that generates the rotational flow is small, leading to a small overall one-directional flow velocity. To increase this area, we produced two different electrode pumps in which the electrode (cylindrical; 6 mm diameter, 1 mm width) contains multiple holes. We measured the pressure-flow rate characteristics of our pumps and compared their performances.

STUDY ON LIQUID CRYSTALLINE FLOW INDUCED BY DIRECT CURRENT ELECTRIC FIELD

A functional fluid flows by itself when electric fields are applied to the functional fluid. This phenomenon is called EHD (electrohydrodynamics) phenomenon, and research and developments are being made to apply this phenomenon on to motors and pumps. We use a liquid crystal as a functional fluid and observe the behavior of the liquid crystal as well as flow in the flow channel when steady electric fields are generated through a direct current by two electrodes in the bottom of the flow channel. Moreover, we observe how the behavior and flow change as a result of the shape of the electrodes being changed. Furthermore, we research the possibility to design the motors using EHD phenomenon.

Experimental Studies on Wake-Induced Transition of Turbulent Boundary Layers

Wake-induced bypass transition of boundary layers on a flat plate subjected to favorable and adverse pressure gradients was investigated. Detailed boundary layer measurements were conducted using two hot-wire probes. A spoked-wheel-type wake generator was used to create periodic wakes in front of the flat plate. The main focus of this study was to reveal the effect of the Strouhal number, which changed by using different numbers of wake-generating bars, on the turbulence intensity distribution and the transition onset position of the boundary layer on the flat plate using two hot-wire probes.Copyright

Pump using Nematic Liquid Crystalline Flow under Application of Electric Field

This article is concerning a small pump for liquid crystal, which is called liquid crystal pump in this article. The mechanism of the induced flow of liquid crystal by application of electric fields on the liquid crystal is used to generate the rotational flow in the present pump. Liquid crystal pump has a channel to change rotational flow into one-way flow from inlet to outlet of the pump. Rotational electric fields are used in the present study. In our researches, a previous pump was cylindrical type with a long length in the axial direction. On the other hand, this article presents plate-type pumps with planar electrode, so it is short in the axial direction. The rotational electric fields are generated by circle-electrode structure fabricated on planar surface, which are applied three-phase alternating currents. Using integrated electrode plate, connection of pumps with plate type is easier than cylindrical one. The pressure–flow rate characteristics of the pump were measured. In addition, the relation between non-dimensional flow rate and pressure of the pump were obtained. In order to obtain a high pressure and high flow rate, various shapes of electrode and channel were investigated and the measured results were compared with each other. Besides connecting pumps with integrated circle electrode plate were designed to get the required pressure and flow rate. The structure of liquid crystal pump is simple and the size can be decreased by further researches. So this pump has the advantage of small source of actuator by changing electric power into fluid power. Furthermore, our pump has a good possibility of the cooling system’s source because this pump makes no noise and no mechanical vibration.