Akira Kariyasaki

Characteristics of gas-liquid two-phase flow in a capillary tube

Abstract Gas-liquid two-phase phenomena in capillary tubes were investigated with special attention on the flow patterns, the time varying void fraction and pressure loss. The directions of flow were vertical upward, horizontal and vertical downward. Pipe inner diameters used were 1 mm, 2.4 mm and 4.9 mm. As a result it is made clear that due to the strong effects of surface tension the flow pattern is not severely affected by the direction of flow, the smaller the pipe inner diameter, the easier the formation of liquid slug and the pressure loss in a unit length takes much larger than the estimated value by the Chisholm equation.

Measurement of Liquid Film Thickness by a Fringe Method

A technique was developed and tested to measure the local thickness of a droplet or a liquid film on a surface of an opaque or thick single transparent plate by an interference fringe pattern that was easily formed by reflecting laser lights. Monochromatic epi-illumination through an objective lens of a conventional microscope was provided by a 5 mW or 300 mW laser and a filter to remove the noise caused by laser speckle. The incremental height difference of the liquid layer between neighboring maxima or minima of fringes was evaluated from the wavelength of the laser light and the refractive index of the liquid. Estimation error of a local inclination angle was discussed using ray tracing under parallel illumination approximation. Droplet profiles evaluated from the interferogram that were obtained by the present fringe method agreed well with those by Laser Focus Displacement Meter. Measurement was made to ensure the usefulness of the present technique. It was made clear that the contact angle of a liqu...

EFFECT OF INCLINATION ON DISTRIBUTION OF ENTRAINMENT FLOW RATE IN AN INCLINED UPWARD ANNULAR FLOW

The droplet entrainment in an annular flow plays an important role in heat and mass transfer. owever the fundamental experimental data such as film thickness, entrainment flow rate and disturbance wave velocity in the case of an inclined upward annular flow are very few compared with similar data in the case of two-phase flow in vertical and horizontal pipelines. In this paper, experimental data on the distribution of entrainment flow rate and the onset of liquid entrainment in an inclined upward annular flow are presented and the effects of the inclination angle are examined. In this experiment, the isokinetic sampling probe technique was used for the measurement of the entrained droplet flow rate and the ranges of inclination angle examined were 0, 30, 45, 60°and 75°from horizontal. As a result, it was clarified that the difference in droplet mass flux between the upper and lower tubes becomes small as pipe inclination increases, the entrainment fraction increases as both the flow rate and the inclination increase and the critical gas velocity for the onset of entrainment becomes small as the liquid film Reynolds number and the inclination increase. Furthermore, Ishii & Mishimas correlation for the entrainment fraction was modified for application to the inclined upward annular flow.

Fundamental Data on the Gas-Liquid Two-Phase Flow (Keynote)

It is needless to say the importance of doing research on multi-phase flows in micro- and mini-channels, which is clearly seen in the growing number of researchers in this field in recent years. We started about fifteen years ago to investigate on the gas-liquid two-phase flows in circular capillary tubes in order to get fundamental information with special attention on the flow patterns, the time varying hold-up and pressure loss. The directions of flow were vertical upward, horizontal and vertical downward. After that we also did research on the flows in rectangular mini channel in the similar experimental condition. In the present paper we will present and summarize these data.Copyright

Separation of Air From Two-Phase Air-Water Mixture Flowing in a Mini Channel

An air-water separator which uses the centrifugal force as a driving force was developed and tested for micro scale flow systems. The device is composed of a main-channel of return bend, a sub-channel running along the main-channel, and several connecting-channels which connect the main- and the sub-channel. When two-phase mixture flows through the curved main-channel, water drifts towards outside region of the curvature and partly into the sub-channel. Consequently air holdup in main-channel becomes large at its exit. The performance of the device was evaluated numerically and experimentally by means of water recovery, air recovery, and Newton efficiency.Copyright

Hydrophilic and Hydrophobic Modifications of Microchannel Inner Walls for Liquid-Liquid Laminar Layered Flows

Microchannels, which have a wide surface area per unit volume, have the potential for use in efficient chemical synthesis, separation and analysis. When microchannels are applied to mass transfer operations between immiscible liquids, a layered laminar flow is preferable because the two liquids can be spontaneously separated at the outlets. In this study, the flow of a water-octane system in a horizontal microchannel 200 ?m in width and 200 ?m in depth was simulated using CFD software. The simulation suggested that a stable layered flow was realized when the contact angle of octane on the hydrophobic inner walls was smaller than ca. 60 degrees and when that on the hydrophilic inner walls was larger than ca. 120 degrees irrespective of the inlet planes into which water and octane were introduced. To fulfill these requirements, PMMA plates were modified using five procedures, and the contact angles of one of the liquids were determined in the presence of the counterpart liquid. Measurement of the contact angles was carried out by lateral observation (in the case of spherical cap drops) and the fringe pattern of laser interference (in the case of thin films). When the two liquids coexisted, a combination of modification with 1-octadecanethiol for hydrophobicity and coating with TiO2 for hydrophilicity was the most workable of the treatments tested. Microchannels modified by this combination were then fabricated. When either water or octane were introduced into the hydrophilic and hydrophobic half-sections, respectively, a stable two-phase layered flow was obtained.

The Effects of Forced Vibration on Two-Phase Flow in a Small Diameter Tube

The effects of forced vibrations on the motion of air-water two-phase mixture were studied in 2.4mm I.D. horizontal tube over rather wide range of flow conditions (about 60 flows for lateral vibration, 4 flows and 1 stagnant mixture for longitudinal vibration). 13 different modes of sinusoidal vibration with 1–8mm amplitude and 1–7.7 Hz frequency were exerted on the test tube. Pressure drop, void fraction and flow pattern of the two-phase flow were compared to those of the flow without forced vibration. It was made clear that the lateral vibration exerted on the tube induced a self exciting fluctuation of the pressure drop for a specific flow condition and longitudinal vibration on the tube promoted the bubble coalescence.© 2003 ASME

Shifted crossed-beam (SCB) method for the measurement of local values of the characteristic parameters in a dispersed two-phase flow

Abstract A new method (SCB method) to measure the characteristic parameters such as the size, velocity, and passing frequency of the dispersed phase—i.e., solid particles or gas bubbles in a gas-solid, gas-liquid, or solid-liquid two-phase flow—is proposed. Two laser beams are used as a detector. They are arranged so as to be crossed at right angles with each other, with one beam being shifted at a small distance in a direction of flow. The autocorrelation of the output signal from the upstream beam and the cross-correlation between the upstream and downstream beams are calculated to determine the characteristic parameters. The SCB method is experimentally examined and compared with other conventional methods.

A Shifted-Cross-Beam Method (SCB-Method) for the Measurement of the Local Values of the Characteristic Parameters in a Dispersed Two-Phase Flow

A new noncontacting method (SCB method) to measure simultaneously the time averaged local values of the characteristic parameters such as the size, velocity and passing frequency (or void fraction) of the dispersed phase, i. e., solid particles or gas bubbles in a gas-solid, gas-liquid or solid-liquid two-phase flow is proposed. Two laser beams are used as a detector. They are arranged so as to be crossed at right angles with each other with one beam being shifted at a small distance in a direction of flow. The auto-correlation of the output signal from the upstream beam and the cross-correlation between the upstream and downstream beam are calculated to determine the characteristic parameters. The SCB method was experimentally examined by using spherical particles with a known equal diameter. The characteristic parameters measured by the SCB method agreed well with those values obtained by other conventional methods.