In this work, the effects of the presence of surfactants in the liquid phase and the hydrodynamic regime of the bubble flow on the oxygen transfer rate were investigated in an electroflotation process in batch mode. The volumetric mass transfer coefficient KLa and the oxygenation capacity were evaluated to improve the performances of the electroflotation process in terms of oxygenation. In order to evaluate the liquid-side mass transfer coefficient KL, the volumetric mass transfer coefficient KLa was dissociated into KL and the specific interfacial area (a) since the last one was obtained from the gas hold-up and the bubble diameter. The effect of Reynolds number which define the hydrodynamic of the bubble flow has been also studied. Models of KLa and KL have been established to show the effects of the hydrodynamic parameters and liquid phase characteristics on the oxygen transfer rate.

This paper studies the formation mechanism and the evolution characteristics of the mushroom-like vortex generated by a submerged laminar round jet based on experiments, CFD simulation and a theoretical model. The results of the numerical simulations agree well with those obtained by the experiments, and three distinct stages are identified in the formation and evolution processes of the mushroom-like vortex: the starting, developing and decaying stages. Three non-dimensional parameters for such a mushroom-like vortex: the length of the jet L*, the vortex radius R* and the circulation length d*, are introduced, and the variation characteristics of these parameters with respect to the non-dimensional time t* are quantitatively analyzed. In the starting stage, L* and d* increase linearly with t* while R* approximately remains a constant. In the developing stage, a considerable self-similarity is observed, and L*, R*, d* have the same proportional relationship with respect to t*¹/² regardless of the variations of the Reynolds number and the injection duration time. In the decaying stage, L* and R* are approximately proportional to t*¹/⁵, while d* nearly levels off at a constant. Furthermore, a theoretical model is proposed for the time evolution characteristics of the jet length, with predictions in good agreements with numerical and experimental results.

This study employed a rotating flume to examine the Powdered Activated Carbon (PAC) transport with water flow. The initial PAC concentration was 10 mg/L-30 mg/L, and PAC concentration versus time under a specified cross-sectional averaging fluid shear was observed. Results show that compared with PAC deposition in still water, PAC is depleted to zero faster under a fluid shear of 0.02 Pa, due to PAC agglomeration with the fluid shear. However, since PAC floc size only ranges from a single particle (2 μm) to approximate 6 μm, an increasing of instantaneous turbulent fluctuations could counteract the force of PAC floc settling downward, and as a result the steady PAC concentration increases with the increase of shear stress. It is found that the critical shear stress for PAC deposition is about 0.60 Pa, and further the PAC deposition probability is presented according to the experimental scenarios between 0.02 Pa and 0.60 Pa. Combining the PAC transport and deposition formula with PAC-pollutant removal model provides an insight into PAC deployment in raw water aqueduct for sudden open water source pollution.

The tip vortex cavitation and its relevant noise has been the subject of extensive researches up to now. In most cases of experimental approaches, the accurate and objective decision of cavitation inception is primary, which is the main topic of this paper. Although the conventional power spectrum is normally adopted as a signal processing tool for the analysis of cavitation noise, a faithful exploration cannot be made especially for the cavitation inception. Alternatively, the periodic occurrence of bursting noise induced from tip vortex cavitation gives a diagnostic proof that the repeating frequency of the bursting contents can be exploited as an indication of the inception. This study, hence, employed the Short-Time Fourier Transform (STFT) analysis and the Detection of Envelope Modulation On Noise (DEMON) spectrum analysis, both which are appropriate for finding such a repeating frequency. Through the acoustical measurement in a water tunnel, the two signal processing techniques show a satisfactory result in detecting the inception of tip vortex cavitation.

The surge tank plays an important role in ensuring the stability of a water flow standard device. To study the influence of the structure and the working conditions on the regulator performance of a surge tank, a three-dimensional model, including a surge tank, the pipeline and the water tank is built, and the VOF model in the Fluent software is used to simulate the two-phase pulsatile flow in the surge tank. The inlet flow pulsation is defined by the User Defined Functions (UDF), and the outlet flow is set to be a free jet. By calculating the flow fluctuation coefficient of the variation under different flow conditions, the influences of the pulse frequency, the initial water level height and the baffle plate structure on the flow stability are analyzed. It is shown that the surge tank has a good attenuation effect on high-frequency pulsations, there is an optimal initial water level to suppress the fluctuations, the round holes of the baffle should ensure a certain circulation area with the bore diameter small enough to have the necessary damping effect.

In an effort to develop methods of solving the issue of cuttings bed in horizontal wells, a 3-D transient model is established to simulate the distribution features and the transport mechanism of cuttings bed. The CFD calculation results show that the cuttings at the cross-sectional area of the mutation location such as the drilling pipe connector would easily settle down to build up a cuttings bed and the transport performance of the cuttings in a horizontal well can only be improved to some extent by adjusting the working parameters without using any destruction tools for the cuttings bed, thus the issue of a cuttings bed can not be solved in general. Accordingly, a new approach to effectively prevent and actively destroy the cuttings bed by using the Cuttings Bed Impeller (CBI) is proposed, the sensitivity analysis of which is conducted to determine the optimal structural parameters and the best matched working parameters from a perspective of the wellbore cleaning. Results show that the use of the CBI produces a number of benefits, including the reduced drill string torque to avoid the stuck pipe incidents with corresponding improvement in hole quality, a shorter trip time, and less wear on the drill string, the top drive and the casing. This research offers theoretical guidelines for the design of destruction tools for the cuttings bed and for the wellbore cleaning control in the horizontal drilling.

A 2-D Finite Volume Model (FVM) is developed for shallow water flows over a complex topography with wetting and drying processes. The numerical fluxes are computed using the Harten, Lax, and van Leer (HLL) approximate Riemann solver. Second-order accuracy is achieved by employing the MUSCL reconstruction method with a slope limiter in space and an explicit two-stage Runge-Kutta method for time integration. A simple and efficient method is introduced to deal with the wetting and drying processes without any correction of the numerical flux term or the source term. In this new method, a switch of alternative schemes is used to compute the water depths at the cell interface to obtain the numerical flux. The model is verified against benchmark tests with analytical solutions and laboratory experimental data. The numerical results show that the model can simulate different types of flood waves from the ideal flood wave to cases over complex terrains. The satisfactory performance indicates an extensive application prospect of the present model in view of its simplicity and effectiveness.

This paper presents a comparison among different hydrodynamic models for the analysis of the unsteady loads delivered by a marine propeller working in an axial, non-uniform inflow. Specifically, for a propeller subjected to a wake-field dominated by local high-frequency changes in space, the unsteady hydroloads predicted by the Nakatake formulation are compared with those given by the Theodorsen and Sears theories, respectively. Drawbacks and potentialities of these approaches are highlighted to assess a computationally efficient hydrodynamic solver for the analysis of operating conditions where propeller blades are significantly perturbed by a multi-harmonic onset-flow. Guidelines coming from this investigation may drive the choice of a fast and reliable unsteady propeller modeling that represents a good trade-off between accuracy of simulation and cost of computation within implementation in Computational Fluid Dynamics (CFD) solvers. The hydrodynamic formulations herein proposed are validated through numerical comparisons with the (accurate but computationally expensive) propeller loads predicted by a fully 3-D panel-method Boundary Element Method (BEM) solver, suited for the analysis of propellers operating in a complex hydrodynamic environment.

Hydrodynamic effects play a very important role in the contaminants release from sediments. Experiments were performed to study contaminants releasing characteristics due to resuspension. The time-dependent variation of COD concentration and relative roles under static and dynamic state of the overlying water were analyzed. Experimental results showed that COD concentration in the water column got a striking increment on the dynamic conditions, mainly by reducing the thickness of concentration boundary layer near sediment-water interface and destructing the surface structure of sediment. Hydrodynamics increased contaminants release rates and flux in unit time. Before reaching an equilibrium stage, the dynamic release caused by the resuspension was more effective than static one due to molecular diffusion. The release rate of COD increased with flow velocity and decreased with water depth. But at a shallow water depth, wave effects would dominate the causing resuspension, resulting in contaminants release in large quantity. The intensity of pollutant release increased with time in a rather circuitous process. The diffusion of pollutant from internal sediment to the sediment-water interface would maintain the endogenous release effects.

Generation of the transient flexural- and capillary-gravity waves by impulsive disturbances in a two-layer fluid is investigated analytically. The upper fluid is covered by a thin elastic plate or by an inertial surface with the capillary effect. The density of each of the two immiscible layers is constant. The fluids are assumed to be inviscid and incompressible and the motion be irrotational. A point force on the surface and simple mass sources in the upper and lower fluid layers are considered. A linear system is established within the framework of potential theory. The integral solutions for the surface and interfacial waves are obtained by means of the Laplace-Fourier transform. A new representation for the dispersion relation of flexural- and capillary-gravity waves in a two-layer fluid is derived. The asymptotic representations of the wave motions are derived for large time with a fixed distance-to-time ratio with the Stokes and Scorer methods of stationary phase. It is shown that there are two different modes, namely the surface and interfacial wave modes. The wave systems observed depend on the relation between the observer's moving speed and the intrinsic minimal and maximal group velocities.