Liquid Flow Dynamics Research Articles

Model validation for low and high superficial gas velocity bubble column flows

In the present work, gas–liquid flow dynamics in a bubble column are simulated with CFDLib using an Eulerian–Eulerian ensemble-averaging method in a two-dimensional Cartesian system. The two-phase flow simulations are compared to experimental measurements of a rectangular bubble column performed by Mudde et al. [1997. Role of coherent structures on Reynolds stresses in a 2-D bubble column. A.I.Ch.E. Journal 43, 913–926] and a cylindrical bubble column performed by Rampure et al. [2003. Modeling of gas–liquid/gas–liquid–solid flows in bubble columns: experiments and CFD simulations. The Canadian Journal of Chemical Engineering 81, 692–706] for low and high superficial gas velocities, respectively. The objectives are to obtain grid-independent numerical solutions using CFDLib to reconcile unphysical results observed using FLUENT with increasing grid resolutions [Law, D., Battaglia, F., Heindel, T.J., 2006. Numerical simulations of gas–liquid flow dynamics in bubble columns. In: Proceedings of the ASME Fluids Engineering Division, IMECE2006-13544, Chicago, IL], and to validate computational fluid dynamics (CFD) simulations with experimental data to demonstrate the use of numerical simulations as a viable design tool for gas–liquid bubble column flows. Numerical predictions are presented for the local time-averaged liquid velocity and gas fraction at various axial heights as a function of horizontal or radial position. The effects of grid resolution, bubble pressure (BP) model, and drag coefficient models on the numerical predictions are examined. The BP model is hypothesized to account for bubble stability, thus providing physical solutions.

Local characteristics of hydrodynamics in draft tube airlift bioreactor

Airlift column reactors have been widely used in bioprocesses. The design, scale-up, and performance evaluation of such reactors all require extensive and accurate information about the gas–liquid flow dynamics, particularly as computational fluid dynamics (CFD) has become more popular in the last decade. However, due to the limitation of most conventional techniques for gas–liquid flow dynamics measurement, only global hydrodynamic parameters (e.g., cross-sectionally averaged liquid circulation velocity, overall gas holdup, and overall mass transfer rate) have been extensively studied. The local flow characteristics (e.g., the macro-mixing and the turbulence intensity) remain unclear. In this study, we use the computer automated radioactive particle tracking (CARPT) technique to investigate the details of the multiphase flow dynamics in a draft tube airlift bioreactor, such as the liquid velocity field, turbulent kinetic energy field, distributions of shear stresses, etc. The flow structures in the whole reactor, as well as the structure in individual regions, i.e., the top, the bottom, the riser, and the downcorner are also characterized. We found significantly large turbulent kinetic energy in the top and the bottom regions, with spots of very high shear stress, which were also found in the vicinity of the sparger. The results also suggest that the top and bottom clearances have significant effects on the flow structures, which may have substantial effects on the bioreactor performance.

レドックスフロー電池の充放電切換え動特性に関する実験的検討

Characteristics of a Redox Flow (RF) battery are discussed for the transient state near practical operating setups. The RF battery has an ability of high-speed response. However, the transient characteristics have not been clearly understood because of the conjugated system structure in electric circuits, chemical reactions, and liquid flow dynamics. This research aims to serve the design of the charge/discharge cell and the optimization of the control for the dynamic operation of RF batteries.

Liquid flow texture analysis in trickle bed reactors using high-resolution gamma ray tomography

Abstract Trickle bed reactor performance and safety may suffer from radial and axial liquid maldistribution and thus from non-uniform utilization of the catalyst packing. Therefore, experimental analysis and fluid dynamic simulation of liquid–gas flow in trickle bed reactors is an important topic in chemical engineering. In the present study for the first time a truly high-resolution gamma ray tomography technique was applied to the quantitative analysis of the liquid flow texture in a laboratory cold flow trickle bed reactor of 90 mm diameter. The objective of this study was to present the comparative analysis of the liquid flow dynamics for two different initial liquid distributions and two different types of reactor configurations. Thus, the hydrodynamic behavior of a glass bead packing was compared to a porous Al2O3 catalyst particle packing using inlet flow from a commercial spray nozzle (uniform initial liquid distribution) and inlet flow from a central point source (strongly non-uniform initial liquid distribution), respectively. The column was operated in downflow mode at a gas flow rate of 180 L h−1 and at liquid flow rates of 15 and 25 L h−1.

Development of a Mechanistic Model to Represent the Dynamics of Liquid Flow Out of the Rumen and to Predict the Rate of Passage of Liquid in Dairy Cattle

A mechanistic and dynamic model was developed to represent the physiological aspects of liquid dynamics in the rumen and to quantitatively predict liquid flow out of the reticulorumen (RR). The model is composed of 2 inflows (water consumption and salivary secretion), one outflow (liquid flow through the reticulo-omasal orifice (ROO), and one in-and-out flow (liquid flux through the rumen wall). We assumed that liquid flow through the ROO was coordinated with the primary reticular contraction, which is characterized by its frequency, duration, and amplitude during eating, ruminating, and resting. A database was developed to predict each component of the model. A random coefficients model was used with studies as a random variable to identify significant variables. Parameters were estimated using the same procedure only if a random study effect was significant. The input variables for the model were dry matter intake, body weight, dietary dry matter, concentrate content in the diet, time spent eating, and time spent ruminating. Total water consumption (kg/d) was estimated as 4.893×dry matter intake (kg/d), and 20% of the water consumed by drinking was assumed to bypass the RR. The salivary secretion rate was estimated to be 210g/min during chewing. During ruminating, however, the salivation rate was assumed to be adjusted for the proportion of liquid in the rumen. Resting salivation was exponentially related to dry matter intake. Liquid efflux through the rumen wall was assumed to be the mean value in the database (4.6kg/h). The liquid outflow rate (kg/h) was assumed to be a product of the frequency of the ROO opening, its duration per opening, and the amount of liquid passed per opening. Simulations of our model suggest that the ROO may open longer for each contraction cycle than had been previously reported (about 3s) and that it is affected by dry matter intake, body weight, and total digesta in the rumen. When compared with 28 observations in 7 experiments, the model accounted for 40, 70, and 90% of the variation, with root mean square prediction errors of 9.25kg, 1.84kg/h, and 0.013h−1 for liquid content in the rumen, liquid outflow rate, and fractional rate of liquid passage, respectively. A sensitivity analysis showed that dry matter intake, followed by body weight and time spent eating, were the most important input variables for predicting the dynamics of liquid flow from the rumen. We conclude that this model can be used to understand the factors that affect the dynamics of liquid flow out of the rumen and to predict the fractional rate of liquid passage from the RR in dairy cattle.

Numerical studies of bubble formation dynamics in gas–liquid–solid fluidization at high pressures

A discrete phase simulation (DPS) is conducted to investigate multi-bubble formation dynamics in gas–liquid–solid fluidization systems. A numerical technique based on computational fluid dynamics (CFD) with the discrete particle method (DPM) and volume tracking represented by the volume-of-fluid (VOF) method is developed and employed for the simulation. A bubble-induced force (BIF) model, a continuum surface force (CSF) model, and Newton's third law are applied to account for the couplings of particle–bubble, bubble–liquid and particle–liquid interactions, respectively. A close-distance interactive effect between colliding particles is considered in the formulation of the particle–particle collision model. Two-dimensional simulations of the behavior of bubble formation from multi-orifices in liquids and liquid–solid suspensions are conducted at high pressures up to 19.4 MPa under constant gas flow conditions. Experiments are also conducted in this study to quantify the bubble formation behavior from a single orifice under comparable gas flow conditions. The study indicates that the liquid flow dynamics induced by adjacent bubbles and bubble wake significantly affects the multi-bubble formation process. The simulation results on the initial bubble size and bubble formation time under various pressures and solids hold-up are found to be in good agreement with those obtained experimentally as well as those predicted based on the analytical model developed earlier by the authors.

Understanding the Nonlinear Dynamics of Liquid Flow with Surge Tanks

The problem considered here is that of a pressurized surge tank with a constant inlet mass flow rate and an outlet mass flow rate through a circular channel. The dynamic behaviour of this system can be influenced by the liquid height inside the surge tank, the inlet and outlet mass flow rates, the gas pressure in the surge tank, and the liquid kinetic energy that is often neglected in textbooks and fluid dynamics literature. The model considers a constant density liquid in laminar flow and investigates the nonlinear effects of liquid height in the pressurized surge tank, mass flow rates, gas pressure, and kinetic energy on the system behaviour. Also, the model is investigated for scenarios that manifest in oscillatory behaviour.

Monofiber optical probes for gas detection and gas velocity measurements: conical probes

Optical probes are a very common tool for the investigation of gas–liquid flow dynamics. A single sensitive tip gives access to the phase indicator function, while using two tips some distance apart provides estimates of the gas velocity. Recently, it has been shown that the gas velocity could also be inferred from a monofiber probe provided that its latency length is known. To improve the capabilities of this new technique, an optimisation of the probe geometry, based on optical simulations and controlled piercing experiments, has been undertaken. In this first paper, conical probes (1C) produced using a new manufacturing technique are considered. Although they are effective for simultaneous gas velocity measurements, their actual response is sensitive to small geometrical defects occurring at their tips. Therefore, calibrations on well controlled interfaces appear necessary both to check the presence of pre-signals responsible for incorrect phase detections, and to establish a significant rise-time/velocity correlation.

Fluorescence depolarization as a probe of molecular dynamics within liquid jets

Preliminary results are presented from a study of fluorescence depolarization within a thin laminar jet of rhodamine 6 G in ethylene glycol. A large number of polarization measurements taken across the jet have enabled us to build up a detailed polarization map of the liquid flow. Relating the degree of depolarization to molecular alignment caused by the presence of shear forces within the jet, we propose that this method may be used as a sensitive probe of the molecular dynamics of liquid flow.

Dynamics of liquid flow in an up‐flow reactor‐used for anaerobic treatment of wastewater

AbstractBy means of stimulus‐response experiments with a Li+ tracer, a description of the fluid flow in a 30 m3 reactor, used for anaerobic treatment of wastewater, was derived. It appeared that of the three parts that could be distinguished in the reactor (the sludge bed. The sludge blanket, and the settler), the sludge bed could be described as a combination of two perfectly mixed regions with bypassing and return flows; the sludge blanket was perfectly mixed, while the fluid flow in the settler could be described as plug flow. From experiments performed under different conditions it was concluded that 60 m3 gas/day were sufficient to provide good mixing and also that the height of the sludge bed should be 2–3 m. From this last conclusion it follows, e.g., that scale‐up of the 30 m3 reactor should be done by increasing the cross section of the reactor while homogeneously distributing the influent over the bottom.

Unsteady state behavior of multicomponent distillation columns: Part I: Simulation

AbstractA very general form of the basic column equations is presented which allows a wide choice in the form of the specifications of variables required to define the column operation. Variable plate holdups, variable plate efficiencies, heat losses from the column, and finite time liquid flow dynamics are some of the specifications considered. The values of the implicit column variables during the unsteady state period are found by a method which is independent of the numerical procedure chosen to solve the differential equations. Computer runs with the Kutta‐Merson method used to solve the differential equations were made for a column approaching steady state at total reflux. The effect of different variable specifications on this computer column are discussed.