In this study, we investigate the electro-osmotic flow pattern of two immiscible fluids through a microchannel with nonuniform wall potential, considering the impact of the surface tension along the liquid-liquid interface. The main objective of this work is to identify and predict the effects of the heterogeneous wall characteristics on the flow field and the deformation of the liquid-liquid interface. Both the Maxwell stress and the hydrodynamic stress are considered along the liquid-liquid interface with no charge accumulation, to predict the flow dynamics and interface deformation along the core due to the external electric field. For the flow analysis, the height of the channel is assumed to be much larger than the thickness of the electric double layers; hence Smoluchowski slip velocity conditions are applied along the channel walls to predict the electro-osmotic flow variation. Additionally, the transient deformation of the interface is considered when the flow field is considered to be quasisteady, predicting that the effects of inertia are minimal. The governing equations for the potential field and the flow field are solved analytically, using domain perturbation analysis for small deformations of the interface and a small amplitude of the wavy wall. Our results show that the heterogeneous wall topology generates swirling flow dynamics within the microchannel, and depending on the asymmetry in the zeta potential, the disturbances along the interface are enhanced or suppressed with the wavelength of the wavy microchannel.

In this work several computational approaches are tested for the two-phase simulation of the ELUBSYS bearing chamber in the high-speed regime-a four-equation Eulerian multifluid model, a steady-state Eulerian integral thin film (EITF) approach, a discrete parcel method (DPM) approach, and a simplified EITF-DPM coupled approach. While computationally expensive, the multifluid model captured the global liquid dynamics in the chamber and predicted that most of the oil is in the form of a thin film that flows on the stationary walls. The much more cost-efficient EITF approach achieved accurate results for the oil thickness distribution at the counter-current region but did not account for the large amounts of oil flowing out through the top vent. The DPM approach was used to assess the dispersed phase dynamics in both one-way and two-way coupling configurations, outlining a significant influence of the latter on the gas phase dynamics. Finally, the coupled EITFDPM approach was able to overcome some of the limitations observed by its individual counterparts by predicting a continuous film throughout the chamber circumference and a higher vent outflow, while still retaining most of the expected film distribution characteristics in the bearing chamber.

Shale gas is playing an increasingly important role in the global energy market. For shale gas wells, optimization of gas production depends on accurate pressure prediction with two-phase flow models. Pressure measurements were carried out in 15 horizontal gas wells at a major shale gas field in China. Classic two-phase flow models were assessed against field measurements. The results show the Mukherjee-Brill method produces relatively low errors in most cases, while the Beggs-Brill method produces relatively high errors in six wells.

The effects of tissue stiffness on the growth and collapse of a laser-induced bubble and the cavitation cloud formation by high intensity focused ultrasound (HIFU) in tissue-mimicking phantoms were investigated. First, the growth and collapse of a laser-induced bubble were observed with a high-speed video camera, which showed that the maximum bubble radius decreases with increase in the stiffness of agarose gels. The period of bubble collapse becomes shorter as the stiffness increases in agarose gels. However, the period in 0.3% agarose is longer than that in 7% gelatin, although both Young's moduli are similar to each other. In 0.3% and 0.5% agarose gels, the laser-induced bubble enlarged with the generation of wrinkles on its interface. Experiments were also conducted for the cavitation cloud formation due to the backscattering of HIFU from the residual microbubbles which remain after the laser-induced bubble collapses. In 0.3%, 0.7%, and 1.5% agarose phantoms, the cavitation clouds developed along with the propagation axis of HIFU, while a dense cavitation bubble cloud was not observed in 3.0% agarose. As the gel stiffness increases, the size of the cavitation cloud decreases due to the high stiffness of the surrounding medium. Also, the collapse time of a cavitation cloud becomes shorter with increase in the stiffness of agarose gels. Although the Young's modulus of 6% gelatin is smaller than 0.3% agarose, the collapse time of the bubble cloud is shorter than that in 0.3% agarose.

It has been pointed out that cavitation inside a fuel injector plays an important role in the fuel spray characteristics, which affects the thermal efficiency and exhaust gas emissions. Recently, it was pointed out that when needle lift is low, not only orifice wall cavitation but also single string cav-itation may occur in the mini-sac and valve-covered orifice (VCO) nozzles, which increases largely the spray cone angle. However, the mechanism and condition of the appearance of single string cav-itation have not been clarified yet. In this study we carry out high-speed visualization of orifice wall cavitation and single string cavitation in various transparent injectors with a single orifice and a simple rectangular sac, whose gap <i>Z</i>, sac width <i>W</i>, orifice diameter <i>D</i>, liquid kinematic viscosity ν, and mean liquid velocity <i>V</i> in the orifice are varied, to investigate the governing dimensionless parameters and to examine whether we can quantitatively predict the formation criteria of single string cavitation or not. Moreover, particle image velocimetry (PIV) analysis is conducted to measure the velocity distribution, to clarify the flow structure, and to quantify the circulation in the sac. As a result, we conclude that regardless of the shape and size of the fuel injectors, the length of cavitation in an orifice can be predicted by using the modified cavitation number σ<sub>c</sub>. The appearance of single string cavitation and circulation in the sac are possible to be predicted quantitatively by using a dimensionless Re<sub>1</sub> proposed in this study, which is the ratio among the inertial and viscous forces.

In several industries, specifically in the petroleum industry, single and multiphase flows through restrictions are commonly found. The restrictions are installed for multiple purposes, e.g., to control the flow and measurement. This research focuses on an experimental study of two-phase (air-water, air-oil) flows through orifice plates, with different restriction sizes (β) to better understand the effects of viscosity in three flow patterns: elongated bubble, slug flow, and annular flow. The experimental setup allows us to visualize the flow with a high-speed camera and measure the differential pressure signature, allowing a detailed discussion on the influence of Reynolds, Froude, and aspect ratio (β) for each flow pattern. This research demonstrates that with simple data analysis (PDF, PSD) of a low-frequency pressure drop sensor installed in the of singularity, it is possible to determine not only the flow pattern upstream the restriction, which has been done before in the literature, but also to determine several properties of the flow upstream and downstream, such as the intermittent factor of the flow and the oscillation wave downstream of the restriction, among others. This paper shows that any restriction properly instrumented can be used to determine the flow pattern in a system, which is usually an unknown variable. The analysis shows how the transition of flow patterns can be observed based on both probability density functions and the power spectrum density of the differential pressure signature.

In this work, we report our experiments of capturing the shape change, spiral and spinning motion and trajectory of the vapor bubbles rising in subcooled boiling flow in a vertical heated channel of natural circulation boiling loop using a high-speed video camera at 500 fps. We have measured bubble diameter, velocity and trajectory of the moving vapor-bubble at various surface temperatures and degrees of subcooling. The measured bubble diameter, bubble velocity and trajectory are in good agreement with the existing theories. The trajectories of moving bubbles in subcooled flow boiling have been analyzed experimentally and numerically. We observed an irregular shape change of the bubble during its motion in subcooled liquid and a spiral-spinning trajectory of non-spherical bubbles at higher fluxes. The non-spherical bubbles lends to a path instability of spiralling-and-zigzag trajectory and rotations (spinning) of the bubbles because of the coupling effect of the hydrodynamic forces and torques generated by the oscillating liquid flow surrounding the bubble. This is also confirmed by periodic variation of bubble velocity. The aspect ratio of vapor bubble, as the shape changes during its rise, is satisfactory experimentally and theoretically, and comparable with the captured bubble images.

The authors present the development of the lattice Boltzmann method (LBM) for application to gas--liquid flows, gas mixture, and gas--solid flows. The LBM scheme is constructed using a simple procedure that takes into account collision and propagation processes. The fluid density is calculated using the sum of the distribution function with respect to number of the discrete velocity. Since all distribution functions exist in the computational region with adequate boundary conditions, the LBM is effective for mass conservation and can be adjusted to the multiphase flow simulation. For the multiphase flow simulation, the color-gradient model is first proposed, and then the Shan--Chen and free energy models were implemented using the LBM. Then, the phase-field model, which is commonly used in LBMs, was investigated. The phase-field method easily captures the complicated interface and calculates multiphase flows with high density and viscosity ratios. For multicomponent flows, the LBM can calculate the Stefan--Maxwell equation. The present model calculates multicomponent phenomena, including uphill diffusion, without interpolating the distribution function. For particulate flows, we list the momentum exchange method and the immersed boundary --lattice Boltzmann method (IB-LBM) and explain the occurrence of boundary slip. Finally, we introduce models for wettability, including three phases: gas, liquid, and solid.