ICONE15-10175 Measurement technique of surface tension using a Single-Tip Optical fiber Probe

Abstract

An optical fiber probe method is one of the efficient and reliable measurement methods for gas-liquid two-phase flows. Generally, simultaneous measurement of bubble diameters and velocities has been thought to need at least two optical fiber probes. To break through this situation, we newly developed a Single-Tip Optical fiber Probe (S-TOP) which realizes simultaneous measurement of diameters and velocities of minute bubbles/droplets. In the S-TOP measurement, the surface tension intensively influences the S-TOP signals. The main aim of this investigation is to strictly evaluate the influences of surface tension on the bubble measurement in order to develop the S-TOP which can take the surface tension into consideration. In the present study, we found out that the gradient of leading edge (or trailing edge) of the S-TOP signal is proportional to the gas-liquid interface velocity. In the measurement of gas-liquid interface velocity via S-TOP, this relationship is effectively utilized. The influences of surface tension and probe-surface wettability on this relationship were discussed. The gradients of the leading and trailing edges were changed with decrease in surface tension. At surface tension higher than about 50mN/m, the surface tension is dominant. On the other hand, at lower than this value, wettability is dominant.