The validity of unsteady flow rate measurement with a plate orifice is examined for pulsating pipe flows and constant-acceleration pipe flows. The conventional steady state relationship between the flow rate and pressure loss through the orifice is applied to these kinds of unsteady flows. The flow rate thus measured is compared to that obtained by integrating the instantaneous velocity distribution over the pipe cross-section. The velocity distribution is measured by traversing a hot-wire probe. The two flow rates are in good agreement with each other.

View full abstract

Surfactant additives can greatly reduce the friction factors of a heat transfer medium flowing in a tube. This was because the generation or growth of turbulent vortices is suppressed by rod-like micelles in a surfactant solution. However, since they decrease the heat transfer coefficient, we investigated the heat transfer enhancement by gas-liquid two-phase flow, and the flow and heat transfer characteristics in gas-surfactant solution two-phase flows. Injecting air significantly enhanced the heat transfer coefficients because it destroyed rod-like micelles or caused surfactant additives to accumulate at the gas-liquid interface, decreasing the apparent micelle concentrations.

View full abstract

Experimental results of the transition to turbulence in a constant-acceleration pipe flow were reported in our previous studies where the effects of temporal acceleration on the critical Reynolds number and the propagation of turbulence were investigated in detail. Two patterns of propagation of turbulence were observed: the pattern where the flow transit to turbulence simultaneously and the pattern where the transition propagates downstream. Whereas, square duct flows seems to be different from that of circular duct. There is no paper reported the constant-acceleration square duct flow. In this paper, experimental investigation has been carried out using air as the working fluid to understand the transition to turbulence and critical Reynolds number in constant-acceleration square duct flows. The critical Reynolds number in the high-acceleration regime was compared to an empirical equation proposed originally for the critical Reynolds number in a constant-acceleration pipe flow and existing experimental results.

View full abstract

In order to investigate the applicability of fractal scale conception in characterization of oil-water two phase flow, six algorithms of fractal scale exponent are evaluated by the Weierestrass function time series with noise. The result shows that Detrended Fluctuation Analysis method is strong robustness. Based on the algorithm evaluated, we acquire 80 groups of conductance fluctuating signals from the experiment of oil-water two phase flow in vertical upward pipe, which diameter is 12.5cm. By extracting the fractal scale exponent at different flow conditions, we find that the extracted fractal scales are correlated with the flow pattern evolvement. It can be concluded that the fractal scale exponent from conductance fluctuating signals can reflect the oil-water two phase flow characteristics.

View full abstract

In the vertical upward gas-liquid two-phase flow under low liquid flow rate conditions, the flow patterns are divided into three main groups; annular flow, churn flow and slug flow. At high gas flow rate, the annular flow is formed with continuous gas core and liquid film on the wall. As the gas flow rate decreases, the liquid film flow on the wall becomes unstable owing to a reduction of the gas-liquid interfacial shear stress, which can trigger the flow pattern transition to the intermittent slug flow. In the intermediate region between annular and slug flows, the churn flow is observed. As the name "churn" implies, the flow is very complex and accompanied with oscillatory motions of the liquid in the tube.
In the present paper, a lumped parameter model is developed to predict the stability of annular flow and simulate the non-linear oscillation of churn flow. The model is based on the one-dimensional two-fluid model. According to the assumption of uniform flow, the annular flow is expressed by a set of ordinary differential equations. From the comparison between the linear stability analysis and the flow pattern map in the experiment, it is found that the flow pattern transition from annular to churn flow is in approximate agreement with the marginal stability boundary of the model, and the churn flow oscillation induces the formation of intermittent slug flow.

View full abstract

The effects of gas humidity on material temperature and changes in the moisture content of wet spherical porous materials are investigated both experimentally and theoretically. The experimental results show that the mean moisture content at the end of the surface evaporation period (the critical moisture content) is lower under higher gas humidity conditions for the same gas temperature. The gradient of local moisture content in the material, which is obtained by numerical calculations, is smaller under higher gas humidity conditions for the same constant drying rate.

View full abstract

Particles concentration in a fluidized bed with water pulsation for Lithium collection system in seawater has been measured using impedance method. As a result, the void fraction is increased in the lower layer and that is decreased in the upper layer as the frequency increases. Moreover, the void fraction in the lower layer has a reasonable agreement with the Richardson- Zaki equation. The amplitudes of vibration in the lower and upper layers increase as the frequency increases. However, it is not changed among the frequencies in the middle layer.

View full abstract

In order to develop a simulation method that can treat flows containing various multi-components as one fluid system, we propose a model which can represent the relation of interfacial tensions on three phase contact line faithfully. Our model is based on a front-tacking method. By comparing some schemes of interfacial tension representation, we found that three-point finite difference without extrapolation can represent the curvature and static balance of tension among interfaces very accurately. Then we performed a drop spreading on a solid surface by the proposed model and dynamic contact angles were represented.

View full abstract

A theoretical and experimental study is conducted to investigate the three-dimensional surface profile of a liquid droplet on a solid surface in the gravitational and centrifugal fields. Based on the behavior of the droplet, the profile of the contact line on the solid surface was assumed as a circle and an ellipse. The three-dimensional Laplace equation was simplified into an ordinary differential equation to calculate the profile of the droplet. The theoretical profiles agreed well with experimental ones for some test liquids and solid plates.

View full abstract

Flow characteristics of the radial inflow are investigated in a closed rotating cylinder. This cylinder consists of the outer rotating casing and the inner fixed body providing the flow inlet and outlet. The cylinder can rotate at the speed in range between 0 and 6000 rpm. The fixed body can have the stirrer blade on its top. This time, both type with and without the stirrer blade were investigated. Using a transparent acrylic for the upper part of the casing, fluid flows with tracer particles were shot with a high-speed camera (HSC). Then, the visualized flow images were measured by Particle Tracking Velocimetry (PTV) analysis. The analyzed results are helpful in investigating the heat transfer characteristics of a certain type of rotating cylinder cooling.

View full abstract

The flow from a large space into a pipe has a large annular separated vortex region just after the pipe inlet. This vortex region makes the drag of pipe inlet extremely large. In order to reduce the drag of pipe inlet, the control and suppression of the separated vortex region at the pipe inlet are needed. Generally, bellmouth is mounted at the pipe inlet. But, in this study, the reduction of the flow resistance of pipe inlet on the wall of a large reservoir tank by a simpler method is newly shown and examined. In this new method, a small ring shaped obstacle (see, Fig.1) on the wall of tank at the pipe inlet. It is expected that the separated flow from the obstacle flows along the pipe wall and the vortex region at the pipe inlet is suppressed or minimized. We measured the pressure and velocity distribution in the directions of pipe axis, and visualized a flow pattern of the flow just after pipe inlet. The test section is made by transparent acrylic resin in order to visualized the flow pattern and has many pressure taps on the pipe along the axis. The velocity distribution is measured by Laser Doppler Anemometer (LDA). Flow visualization is made by water solution of fluorescence sodium dye and Laser light sheet method. We also examined the effect of ring shaped small obstacle on the drag reduction. We examined the effect of obstacle with several heights, widths and mounting position. It is made clear that the vortex region just after the pipe inlet is suppressed and then the inlet loss or drag is reduced by about maximum 90% by mounting a ring shaped small obstacle.

View full abstract

The study deals with a new sponge ball cleaning system for a heat exchanger at an air conditioning system in industries. The new sponge ball cleaning system and the coolant-sponge separator using a centrifugal force were reported by the authors in the first symposium (ISEM 2006-Sapporo) and here, an improved separator or a compact-type one was designed and studied by a simulation experiment using the transparent scale-down model. The experimental results showed that the separation performance of the compact-type separator was better than that of the first model reported in the previous symposium, and that the pressure loss of the compact-type separator was larger than that of the first model. Furthermore, the demonstration of the new sponge ball cleaning system showed that the system was useful to clean the heating tubes.

View full abstract

This study deals with specific phenomena of boiling two phase flow in a helically coiled tube submerged in a bath held at a constant temperature. The two phase flow in a coiled tube under a low quality condition is strongly influenced by buoyancy and centrifugal forces. DNB (departure from nucleate boiling), CHF (critical heat flux) and dry-out on the tube wall are important characteristics for boiling flow. There are many studies conducted under a high quality condition but few under a low quality condition. Therefore, the investigations on detailed phenomena under a low quality condition are required for designing structure and safety operation of helically coiled tube heat exchangers.
The characteristics of boiling phenomena were experimentally investigated for an apparatus of scale model using water or nitrogen gas-water as working fluids. The helically coiled test section is made from a stainless steel tube with an internal diameter of 10mm, thickness of 1mm, a coil diameter of 200mm, an inclined angle of 5 degrees and 2.5 turns. The test section was submerged in an oil bath heated at a constant temperature of about 200°C. The temperatures of the external wall of tube were measured by K-type thermocouples at 10 cross-sections along the tube and 4 points around the circumference at each cross-section.
The temperature distributions in both the cross-section and the flow direction of the tube and the time variations were strongly influenced by flow rate conditions. Especially, the temperature changes like a saw-toothed wave were observed under a low flow rate conditions. That is, after the temperature on the external wall of the tube increased, it rapidly decreased. This fact suggests that the internal wall of the tube becomes in dry-out condition with boiling of water, then it is wetted again owing to arrival of liquid plug. Thus, DNB was supposed to occur repeatedly.

View full abstract

We have successfully demonstrated that the stress distribution of a metal substrate can be directly displayed by coating the surface of test objects with SrAl₂O₄:Eu (SAO), a strong mechanoluminescent material. An aluminum plate with the SAO sensing film was applied to experimental analysis of stress concentrations. This novel visualization technique can be applied to view stress concentration in various fields such as modeling, manufacturing and demonstration of industrial products.

View full abstract

New phase unwrapping algorithm is verified for its performance in unwrapping the isoclinic parameter. Both numerical and experimental photoelastic fringes of the circular ring under compression are generated for unwrapping. Comparisons between the numerical and experimental results show that the phase unwrapping algorithm is robust regardless the presence of the singularities in the isoclinic map. This shows an advance of the phase unwrapping for solving the complex fringe patterns.

View full abstract

The extraction of the singularities in the wrapped map of the isoclinic parameter photoelasticitally obtained is presented. The method involves the use of two wrapped maps of isoclinics and a map of modulated intensity. Two characteristics-the abrupt phase jumps around the singularities and the values of modulated intensity-are used to identify those positions. The technique developed herein is evaluated with the real phase maps of an eccentrically loaded split ring (C-shaped model) under compression and experimental results are also presented.

View full abstract

It is important to know mechanical properties of micro structures fabricated as a micro machine component by micro-stereolithography (μSL). In the previous study, we reported that elastic modulus of a micro-cantilever fabricated by μSL is controllable by irradiation laser power and postcure processing time. In this study, micro-cantilevers are formed by changing lamination pitch (10 μm to 25 μm) and lamination orientation. Then, the relation between the load and the deflection of the cantilever is evaluated. Experimental results show that the elastic modulus of the cantilever decreases with the increase of the lamination pitch.

View full abstract

Compressive stress-strain loops of several commercial engineering plastics at strain rates of up to 600⁄s are determined using the standard split Hopkinson pressure bar. Four different engineering plastics or typical thermoplastics: PA-6, PA-66, PC and POM are tested at room temperature. Cylindrical specimens with a slenderness ratio (= length l⁄diameter d) of 0.5 are used in the Hopkinson bar tests, and those with l⁄d = 1.5 as specified in the ASTM Designation E9-89a are used in the static tests. The stress-strain loops in compression at low and intermediate strain rates are measured on an Instron testing machine. The effects of strain rate on the Young's modulus, flow stress at 2.5% strain and dissipation energy are investigated. It is demonstrated that the area included within the stress-strain loop (or dissipation energy) increases with increasing strain rate as well as given strain, that is, all plastics tested exhibit intrinsic strain-rate dependent viscoelastic behavior and a high elastic aftereffect following complete unloading.

View full abstract

The use of a composite with an inorganic matrix as a structural material in high-temperature applications is investigated. The inorganic compound used as a matrix of the composite is easy to use because it can be cured at only 150 °C. In this study, an inorganic-based composite is filled with aluminum particles. The physical properties of the composite were tested before and after heat treatment. The results of high-temperature acoustic tests show that the elastic modulus of the composite containing aluminum particles becomes large after the heat treatment. Also, other results show that as the volume fraction of aluminum particles increases, the coefficient of linear expansion increases and the electric resistivity decreases.

View full abstract

Phase-shifting digital holographic interferometry can measure small displacement and strain distribution with high-precision, full-field and non-contact. A planar object is needed to be perpendicular to an optical axis of a camera in this strain measurement method. However, in a practical case, the object cannot be placed at the position, according to circumstances. An angle of the planar object is required in order to measure the distribution of the in-plane displacement. In this paper, an optical system which can measure shape and displacement of an object is proposed. In addition, a calculation method for strain distribution on surface of a tilted planar object is proposed. Shape measurement is performed using grating projection method. In-plane deformation and stain distribution of a cantilever was measured by this optical system. The results of the experiment demonstrated the effectiveness of this method.

View full abstract

Bubble formation from a centered single-hole nozzle placed on the bottom of a mercury bath has been investigated using an electroresistivity probe. The nozzle is made of brass and its surface is coated with fluororesin. Accordingly, the nozzle is poorly wetted by mercury. When the gas flow rate is lower than a certain critical value, the frequency of bubble formation is specified by the outer diameter of nozzle, d_no. On the other hand, when the gas flow rate is raised above another critical value, the inner diameter of nozzle, d_ni, governs the bubble formation. Empirical equations are proposed for the two critical gas flow rates. Bubble formation is affected by d_no and d_ni in the regime between the two critical gas flow rate values.

View full abstract

This paper presents the detection of surface crack in a woven fabric composite laminate using energy index method. A carbon fabric F3T-282⁄epoxy (DICY) is used to fabricate a plain woven laminate. In the first place, the unknown material properties can be obtained by employing inverse method through the finite element analysis. Three equivalent FE models, i.e. cross-ply [0⁄90]_ns , orthotropic and representative cell models are established to simulate the woven laminate. Experimental modal analysis is performed to obtain the modal displacements of the laminate before and after damage. The modal displacements are used to compute the modal strain energies. A damage index is defined by using the fractional modal strain energy and used to identify the surface crack location. Limited by grid points of measurement, a differential quadrature method is applied to compute the partial differential terms in strain energy formula. Only few measured mode shapes are required in this approach. This method provides a flexible, cost effective, nondestructive, and feasible of real-time detection of potential damage in woven fabric composite laminates.

View full abstract

This paper studies the machinability of BK7 optical glass by using conventional ultrasonic machining (USM) and rotary ultrasonic machining (RUM). For USM, the finer grit size gives low MRR, good surface finish, small chipping size and low opaqueness. In RUM, higher spindle speed gives good MRR, excellent surface finish, high opaqueness and small chipping size. Whilst higher feedrate gives high MRR, low surface finish, low opaqueness and small chipping size. The edge chipping size could be decreased with backing material.

View full abstract

In order to improve the conversion efficiency (up to a final target over 20% of conversion efficiency) of the photovoltaic cell with multi-crystalline silicon, it is necessary to optimize the casting conditions of silicon ingot such as purifications of mold, mold coating material, atmosphere gas and solidification rate. We have investigated the influence of solidification conditions on the microstructure by the experimental measurement of molten silicon temperature and the simulation of molten silicon flow and temperature distribution in rectangular crucible. It was detected that large supercooling in crucible bottom was effective in enlarging the crystal grain size. High quality silicon ingot was obtained by controlling the solidification rate. The diffusion length of the wafer (thickness 5mm, resistivity 0.65Ω·cm, at bare state) was attained to 350μm or longer from this silicon ingot. Consequently, the conversion efficiency of the cell reached to 18.3% (cell area 25cm²) and 20.3%(cell area 4cm²) using this silicon wafer.

View full abstract

The development of a simple, low-cost method for making wastewater polluted with dioxins⁄furans (dioxins) harmless is one of the important assignments in a waste incineration and a sewage disposal plants. The purpose of the present study is basically to develop a simple removal method of dioxins in wastewater and to evaluate a basic removal ratio of dioxins. Removal method of dioxins in wastewater has been investigated by using fluidized bed with polyolefin particles, which have adsorption ability for fly carbonaceous matters (C∗) including almost all dioxins. The fly C∗ including almost all dioxins in wastewater can be removed by adsorbing on polyethylene (PE) particles. The removal ratio of dioxins (R_DW) from wastewater by using fluidized bed with PE particles is estimated from the following equation: R_DW (%) = 100×{ 1−exp(−8×10⁻⁴•S_S•t_C)}, where S_S (cm²⁄cm³) is a specific surface area of particles, and t_C (s) is a contact time between particles and wastewater.

View full abstract

Volatile matter (V.M.) is released in the course of carbonization of coal under a rising temperature condition. The kind and amount of V.M. depend on the kind of coal. Components of V.M. are tar, hydrocarbons (CH₄, C₂H₄, C₂H₆, C₃H₈), CO, CO₂ and H₂, which are released in this order as a function of carbonization temperature. When the carbonization of coal under a rising temperature condition is interrupted at a maximum carbonization temperature, T_{C, max}, semi-coal-char with residual V.M. is obtained. If some optimum interruption-temperature is chosen, small but most suitable amount of V.M. is retained. When the semi-coal-char thus obtained is heated again under the same rising temperature conditions but up to more than T_{C, max}, the residual V.M. is released from just around T_{C, max}. We propose novel iron ore agglomerate bearing such semi-coal-char with some strength in order to decrease the initial temperature for reduction of iron oxide under a rising temperature condition, such as in a blast furnace shaft. The carbonization of Newcastle blend coal under a rising temperature condition was interrupted at T_{C, max} = 823, 873, 1073, 1173 and 1273 K, to obtain semi-coal-char with some residual V.M. Thus obtained semi-coal-char at T_{C, max} = 823 K retained much amount of V.M, most of which was H₂. The semi-coal-char was mixed with reagent grade hematite in the mass ratio of one to four, and added with a Bentonite of 1 mass% as a binder. The carbon composite pellets bearing the semi-coal-char were prepared and reduced from room temperature to maximum reduction temperatures, T_{R, max} = 873, 973, 1073, 1173 and 1273 K, at 3 K min^-1 in the nitrogen gas atmosphere. It was confirmed by the gas chromatography of gas generated by reduction of pellets that the carbon composite pellets bearing the semi-coal-char at T_{C, max} = 823 K had the highest reducibility of the iron oxide; the original Fe₂O₃ was mainly changed to Fe₃O₄ at T_{R, max} = 973 K and 1073 K, to FeO at 1173 K and to Fe at 1273 K.

View full abstract

Reactor vessels with batch operation have been widely used in ferrous and non-ferrous production. In the production processes, more than one liquid phase is usually contained in the vessel, and it is desirable to discharge each phase separately as fast as possible. In separating two co-existing liquids, the liquid of the bottom layer is usually discharged through a nozzle located at the bottom of the vessel. However, as the liquid-level lowers with discharging of the liquid, a swirling flow generates, and the discharging rate of the liquid decreases. Moreover, the liquid of the upper layer is caught by the swirling flow, and the upper liquid begins to discharge along with the bottom liquid. In the present study, a method to prevent the generation of swirling flow during the discharge of the liquid from the vessel has been examined by water-model experiments. The time taken for discharging water rapidly increases as the water level at which the air-core forms is higher. The prevention of the generation of the air-core is an essential factor in discharging and in separating two coexisting liquid phases at high speed. It is found that the installment of a cylindrical object around the nozzle entrance is very effective for preventing the generation of swirling flow and the formation of an air-core.

View full abstract

Effects of channel gap and channel attitude on the flow pattern of gas-liquid two-phase flow in rectangular millimeter-scale gap channels are investigated. The channel gap is varied from 0.5mm to 10.0mm. The observed flow patterns in horizontally placed channels are classified into three categories: bubbly flow, slug flow and annular flow. As the gap becomes small, the bubbly flow regime shifts to the slug flow regime. The boundary between the slug flow regime and the annular flow regime is hardly dependent on the gap. In the bubbly flow regime, the so-called channeling phenomenon of bubbles takes place. Concerning the effects of channel attitude on the flow pattern, a channel with a gap of 1.0mm is mainly used. The inclination angle of the channel is varied from 0° to 90° . The observed flow patterns for a vertically wide channel with an inclination angle of 0° are classified into three categories: bubbly flow, slug flow and stratified wavy flow. Those for an inclination angle of 90° are classified into bubbly flow, slug flow and annular flow. As the inclination angle increases form 0 to about 30°, the bubbly flow regime becomes wide. With a further increase in the inclination angle from about 30° to 90°, it becomes narrow. The slug flow regime changes with an increase in the inclination angle in a complicated manner.

View full abstract

A novel agitation method has been developed to extract useful materials from pig bones, chicken bones, and so on. A swirl motion of a liquid jet is chosen to agitate a bath containing the bones because any driving devices such as an impeller are not equipped with this agitation system. Preferable operation conditions are clarified on the basis of the amplitude of the swirl motion occurring in the bath.

View full abstract

This paper describes the frequency characteristics of dragonfly wings related to the aerodynamic characteristics. In the first stage, the higher speed flight of a dragonfly was analyzed with a high-speed video camera system. It was confirmed that insect wings undergo strong deformation during free flight. In the second stage, the surface roughness of dragonfly wing was measured by the three-dimensional, optical shape measuring system. It was clear that the difference of elevation is especially remarkable between the longitudinal veins at the part of leading edge. In the third stage, the dynamic responses of dragonfly wing to the excitation vibration were examined over the relatively wide range of frequency. The maximum amplitudes of insect wing oscillation were measured with the optical displacement detector system. It was found that the natural frequencies of dragonfly wings were related to the flapping frequency of the dragonfly. The deformable characteristics of dragonfly wings were related to the aerodynamic characteristics and structural strength of the dragonfly wing. Flexibility on the trailing edge of dragonfly wings was revealed experimentally.

View full abstract

The behavior of colon bacteria in liquid in microchannels that simulate the pouring lip of a new container, which has been developed by the authors and is capable of delaying the discoloration and decay of liquid food products, was observed using a light microscope. Rectangular and circular microchannels were used. Results indicate that the movement of colon bacteria in static fluid depends on the size of the microchannels.

View full abstract