Gentaro Yamanaka

Visualization of clustering on nonmagnetic and ferromagnetic particles in magnetic fluids

Micro-cluster formation of the non-magnetic and ferromagnetic particles in a magnetic fluid was investigated. Using an optical microscope system with cardioid condenser lens, real-time visualization of the Brownian motions of both particles were carried out. The chain-like cluster formation of both particles were observed simultaneously under the magnetic field. Two types of magnetic fluid of a water-based and kerosene-based magnetic fluids were used as test liquids.

Measurement of Two-phase Flow using Multi-wave Ultrasound (Measurement of Bubble Rising Velocity using Correlation Method)

In this paper, two types of ultrasonic measurement techniques are attempted to obtain liquid and gas velocity distributions in bubbly flow. The first attempt is that the both of liquid and gas velocity distributions are obtained using an ultrasonic basic frequency and its echo signals. In order to separate the signals reflected on liquid-gas interfaces and particles, thresholding based on the ultrasonic echo intensity is applied. However, it is difficult to extract completely the echo signals reflected on the tracer particles. In order to overcome the difficulty, a multi-wave ultranonic transducer (TDX) is applied. The TDX consisted of two piezoelectric elements that have different basic frequency. The liquid velocity distribution is obtained using an ultrasonic velocity profiles (UVP) monitor at 8 MHz ultrasonic frequency, and the rising velocity of bubbles is measured using cross-correlation method at 2 MHz ultrasonic frequency. Using the technique, both of the liquid and gas velocity distributions are obtained accurately using the TDX.

Velocity Profile Measurement in Turbulent Pipe Flow Using Ultrasound Time-Domain Correlation Method

This paper presents a velocity profile measurement technique using a ultrasound time-domain correlation method (UTDC). The system is based on the cross correlation between two consecutive echoes of ultrasonic pulses to detect the velocity. The UTDC has two advantages over a conventional ultrasound pulse Doppler method. First, the system has a higher time resolution than the pulse Doppler method. Second, the system does not have a limitation in maximum measurable velocity, which is limited by Nyquist’s sampling theorem. In this paper, the velocity profile measurement in turbulent pipe flow using the UTDC is performed.Copyright

The clustering phenomena of magnetic and non-magnetic particles in magnetic fluids

Magnetic fluids are suspension of ferromagnetic particles less than 10nm in diameter and it is well-known for the chain(cluster) formation of the magnetic particles under the magnetic field. In the present paper, using the light scattering from the particles, direct visualization on the behavior of cluster formation of the ferromagnetic particle and non-magnetic particles have been made under the magnetic field.