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In order to improve the understanding of transient behavior of gas-liquid plug two-phase flow in a horizontal pipe, CFD simulations and experimental studies on the relevant phenomena were carried-out. The pipe diameter and pipe length were 26 and 9.5 m respectively. The transient calculations were carried out using a Volume of Fluid (VoF) multiphase flow model of the commercial CFD code of FLUENT 6.3. The corresponding CFD solution has been obtained by using the Best Practice Guidelines of CFD for thermal engineering purposes. In the present works, the series of high quality experimental data was used to validate the CFD calculations in terms of time and space. A comparison with the high-speed video observations shows a good qualitative agreement. The results indicate also a quantitative agreement between calculations and experimental data for the elongated bubble length and the time variation of the liquid hold-up. [ABSTRACT FROM AUTHOR]

The bubble breakup pattern on a swirl-type bubble generator (MBG) with water and air fluids was experimentally studied. The bubble breakup pattern was analyzed visually and characterized using several parameters such as Pressure Drop (ΔP), Kolmogorov Entropy, Standard Deviation, and DWT (Discrete Wavelet Transform), which were taken from the extraction of pressure signals at the water inlet and outlet of the bubble generator. The wavelet spectrum of the measured signal was shown to identify the overall bubble breakup pattern, and the wavelet variance vector is proposed as a character vector to identify the bubble breakup pattern. The results show that there were three types of different flow breakup patterns: (1) static breakup, (2) dynamic breakup, and (3) tensile breakup. The observed bubble breakup sub-patterns can be categorized into tensile, moderate tensile, high tensile, dynamic, low dynamic, static, and high static sub-patterns. The static clustered breakup pattern has the highest wavelet energy compared to the tensile and dynamic clustered breakup. [ABSTRACT FROM AUTHOR]

The purpose of the present study was to investigate the performance and flow structure of an airlift pump-bubble generator during the lifting of gas-water-solid particles three-phase flow experimentally. Here, a mechanistic model was also developed to predict the performance of an airlift pump bubble-generator on the basis of power balance. In the experimental part, the flow structure was analyzed visually, and taken from the extraction of the differential pressure signal at both the bottom and top test sections. Time series of differential pressure normalization was analyzed by using wavelet transform to determine the wavelet energy distribution. The wavelet energy was used as input the artificial neural network method to clustering the flow regime. The results indicate that under a constant of superficial gas velocity, the discharged both the water and particle increase with the submergence ratio (SR). SR is defined as the ratio of the distance from the injector to the water surface and the distance from the injector to the outlet side. Next, under a constant gas superficial velocity, the increase of SR will increase the solid fraction, but the fractions of both gas and water will decrease. The flow patterns were classified in the clustered bubble, homogeneous bubble, cap bubble, bubbly-stable slug, bubble unstable slug, and slug churn. Furthermore, the bubble flow is indicated by the peak wavelet energy on an eighth-level decomposition of approximation signal (a8), and the energy of the fourth-level decomposition of detail signal (d4) closes to the energy of the fifth-level decomposition (d5). The wavelet energy concentrated on the seventh and/or eighth level decomposition of detail signal (d7 and/or d8) is the indicator of slug flow in the riser pipe. The clustering flow patterns by using the ANN with input from wavelet energy gives a better approach than that of stochastic parameters of time series of the pressure differential. Moreover, the developed mechanistic model shows a good agreement with the experimental data. • The flow structure of air-water-solid particles in the airlift pump-bubble generator was identified. • The flow patterns are clustered bubble, homogeneous bubble, cap bubble, bubbly-stable slug, bubble unstable slug, and slug churn. • The submergence ratio has a significant effect on the fraction of solid, gas and water. • The clustering flow patterns by using the ANN with input from wavelet energy gives a better approach. • The developed mechanistic model shows a good agreement with the experimental data. [ABSTRACT FROM AUTHOR]

The Lattice Boltzmann Method (LBM) was implemented to simulate the two-dimensional (2-D) Rayleigh–Taylor instability (RTI) during the mixing of the immiscible fluids. Two important parameters of the density and the viscosity as represented respectively by the Atwood and the Reynolds numbers were considered. In the calculation the density of two immiscible fluids was calculated by using the equation of state (EOS). In the present simulations, both Atwood and Reynolds numbers were varied in order to investigate the time variations of the interfacial behavior during RTI, the position of bubbles and spikes, and the horizontal average density. The results indicate that the Atwood number has a higher effect than the Reynolds number in the mixing process during RTI. The bubbles and spikes positions go farther in the displacement with the increase of both Reynolds and Atwood numbers. Moreover, the increase of both Reynolds and Atwood numbers accelerate the mixing process during RTI. • Rayleigh–Taylor instability (RTI) was simulated using The Lattice Boltzmann Method. • Two important parameters such as density and viscosity were considered. • The density of two immiscible fluids was calculated by using the equation of state (EOS). • The Atwood number is more influential in the mixing process of RTI than the Reynolds number. • The increase of both Reynolds and Atwood numbers accelerate the mixing process during RTI. [ABSTRACT FROM AUTHOR]

An experimental study to assess the accuracy of wire-mesh sensors in dependence of bubble sizes and flow rates has been performed in a 50 mm × 50 mm transparent rectangular channel. The liquid superficial velocities were ranging from 0 m/s up to 0.62 m/s with the obtained bubble size ranging from 3 mm to 7 mm. A single wire-mesh sensor with 16 × 16 electrode wires was used with a temporal and spatial resolution of 10 kHz and 3.1 mm (lateral distance between two wires), respectively. Single bubbles with known bubble size, subsequently called reference bubble size, was injected into the test section via bubble injector approx. 25 cm upstream of the wire-mesh sensor. The bubble size measurement by using wire-mesh sensor cannot be obtained directly since it requires the information of bubble velocity which is not available only by installing a single sensor. Therefore, a stereoscopic observation was conducted to obtain the bubble velocity by tracking the successive frames as well as to study the intrusiveness of the sensor. This configuration gave an advantage that the registered bubble will be assigned with its real approach velocity and a better agreement is expected. As the result, a direct comparison of all individual bubbles with the reference bubble size showed an agreement within ±10%. However, a deceleration effect was found for low superficial and observed to disappear as the liquid superficial velocity increased then vanish at observed J L = 0.62 m/s. [ABSTRACT FROM AUTHOR]