Light Transmission Time Research Articles

Gas Bubbles and Slugs Crossover in Air–Water Two-phase Flow by Multifractals

Abstract Slugs and bubbles two-phase flow patterns dynamics in a minichannel are analysed. During the experiment, the volume flow rates of air and water were changed. We study transition of bubbles to slugs two-phase flow patterns using Fourier and multifractal approaches to optical transitivity signal. The sequences of light transmission time series are recorded by a laser-phototransistor sensor. Multifractal analysis helps to identify the two-phase structure and estimate the signal complexity. Especially, we discuss occurrence and identification of a self-aggregation phenomenon. These results are compared to corresponding Fourier spectra. The results indicate that the fractality is a an important factor influencing the distribution of the gas phase in water.

Study of dynamics of two-phase flow through a minichannel by means of recurrences

By changing air and water flow rates in the two-phase (air–water) flow through a minichannel, we observed the evolution of air bubbles and slugs patterns. This spatiotemporal behaviour was identified qualitatively by using a digital camera. Simultaneously, we provided a detailed analysis of these phenomena by using the corresponding sequences of light transmission time series recorded with a laser-phototransistor sensor. To distinguish particular patterns, we used recurrence plots and recurrence quantification analysis. Finally, we showed that the maxima of various recurrence quantificators obtained from the laser time series could follow the bubble and slugs patterns in studied ranges of air and water flows.

Dynamics of a two-phase flow through a minichannel: Transition from churn to slug flow

The churn-to-slug flow bifurcations of two-phase (air-water) flow patterns in a 2mm diameter minichannel were investigated. With increasing a water flow rate, we observed the transition of slugs to bubbles of different sizes. The process was recorded by a digital camera. The sequences of light transmission time series were recorded by a laser-phototransistor sensor, and then analyzed using the recurrence plots and recurrence quantification analysis (RQA). Due to volume dependence of bubbles velocities, we observed the formation of periodic modulations in the laser signal.

Dynamics of Two-Phase Flow through a Minichannel: Fourier and Multiscale Entropy Analyses

By changing a air flow rate of the two-phase (air-water) flow through a minichannel weidentified aggregation and partitioning of air bubbles and slugs of different sizes and air bubble arrangement into periodic patterns. The identification of these spatio-temporal behaviour was doneby digital camera. Simultaneously, we provide the detailed studies of these phenomena by using thecorresponding sequences of light transmission time series recorded by a laser-phototransistor sensor.To distinguish the instabilities in air slags and their breakups and aggregations we used the Fourierand multiscale entropy analysis.

Two phase flow bifurcation due to turbulence: transition from slugs to bubbles

The bifurcation of slugs to bubbles within two-phase flow patterns in a minichannel is analyzed. The two-phase flow (water-air) occurring in a circular horizontal minichannel with a diameter of 1 mm is examined. The sequences of light transmission time series recorded by laser-phototransistor sensor is analyzed using recurrence plots and recurrence quantification analysis. Recurrence parameters allow the two-phase flow patterns to be found. On changing the water flow rate we identified partitioning of slugs or aggregation of bubbles.

Self-aggregation Phenomenon and Stable Flow Conditions in a Two-Phase Flow Through a Minichannel

Abstract By increasing a water flow rate of the two-phase (air–water) flow through a minichannel, both the partitioning of air slugs into air bubbles of different sizes and small air bubbles aggregation into larger air bubbles were identified. These phenomena were studied in detail by using the corresponding sequences of light transmission time series recorded with a laser-phototransistor sensor. To distinguish any instabilities in air slugs along with their break-ups and aggregations, the recurrence plots and recurrence quantification analysis were applied.

Recognition of Bragg Wavelength Disturbed by Time Delay of Fiber Length in Prepositive Tunable Filter

The wavelength shift in fiber Bragg grating does not depend directly on the total light levels, losses in the connecting fibers and couplers, or source power. However, if the tunable Fabry-Perot filter is place on the end of incident fiber, the detected time delay of modulation light is occurred due to the unmatch between the scanning time and light transmission time in the transmission fiber. Consequently, the detected peak wavelength shifts with the length of transmission fiber. Thus, the peak wavelength shift effect of Bragg reflective light transmitted in fiber with different fiber length can be obvious in the demodulator with a prepositive tunable Fabry-Perot filter. The experiment indicates the shift rates of 0.109 - 0.126 nm/km increase approximately linearly with the original peak wavelength of 1532.917 - 1560.300 nm at the fiber length of 0 - 6 km. To certify the consistency of measurement data, the criterion correction is introduced. By using the differential method of two fiber Bragg gratings with an optical path, the differential worth is compensated from the disturbance modulated by the time delay of fiber length.

Poly(ethylene terephthalate). I. Study of crystallization kinetics

Cast amorphous one mil films of poly(ethylene terephthalate)were allowed to crystallize isothermally in silicone oil over the temperature range 25–240°C. The crystallization paths were followed by recording the percent of transmission of 4000 A. light through the films as a function of time at specific temperatures. At temperatures between 70 and 90°C. the transmission increased to a value higher than the initial transmission and did not decrease with time. From about 95 to 125°C. the curves showed a similar increase, followed by a decrease to a minimum and then an increase to a new maximum before leveling off. The shapes of these curves were interpreted in terms of the sizes of the growing spherulites. The first detectable signs of crystallization were observed at 96.5°C., as evidenced by density and densitometer measurements. It is shown that the polymer passed through a temperature range beginning at the glass transition point (66°C.) and extending to about 95°C., where molecular and chain rearrangements occurred without crystallization. Half lives and rate constants were found to increase exponentially over the range 96.5–119.5°C. Above approximately 125°C., the crystallization process took place at such a rapid rate that accurate data were impossible to obtain. Activation energies were calculated from the rate constants and from an estimation of induction times from the light transmission–time curves. These values were found to be 37 and 30 kcal./mole, respectively. The density–time data were also fitted to the Avrami relationship. Evaluation of the constants indicated that the initial crystallization growth was lineal.