Turbulent Liquid Research Articles

Numerical prediction of dispersed turbulent liquid–solid flows in vertical pipes

ABSTRACTA mathematical model for the simulation of dispersed turbulent liquid–solid flows in vertical pipes is presented. The model is based on the Eulerian–Eulerian approach and solves the averaged mass and momentum conservation equations for both phases, coupled by means of interfacial momentum transfer terms. Its distinctive feature is the modelling of interphase friction and turbulence modulation. In particular, specific source terms which generalize some existing correlations originally developed for gas–solid flows are introduced in the conservation equations for the turbulent kinetic energy of the fluid and its dissipation rate to account for turbulence modulation. By comparison with experimental data available in the literature for different flow conditions, the model revealed that it is capable of reproducing the main features of the flow. Moreover, it proved capable of predicting the effect of particle size on turbulence modulation in liquid–solid flows.

Performance analysis and parameter optimization of an inner spiral in-pipe robot

SUMMARYA novel micro in-pipe robot using an internally threaded profile for propulsion is proposed in this paper, and the dynamic model of the robot in the turbulent liquid pipeline is established, and the computational fluid dynamics method is used to solve the influence of environmental parameters and operating parameters on the robotic performance. By the orthogonal experimental optimization method, the optimal inner spiral structural parametrical combination is obtained. According to the working principle of the inner spiral robot, an inner spiral driving device is designed and fabricated, and the running experiment in the pipeline full of 201 methyl silicone oil verifies the feasibility of the proposed robot. Adopting the pulsating blood flow function as the inlet condition, in a pulsating period, the robotic performance is numerically analyzed.

Modelling of ultrasonic propagation in turbulent liquid sodium with temperature gradient

The use of ultrasonic instrumentation in sodium-cooled fast reactors requires to understand and to predict how ultrasonic waves can be deflected, slowed down or speeded up, depending on the thermo-hydraulic characteristics of the liquid sodium. These thermo-hydraulic characteristics are mainly the local temperature and flow speed of the sodium. In this study we show that ray theory can be used to simulate ultrasonic propagation in a medium similar to the core of a sodium-cooled fast reactor, in order to study ultrasonic instrumentation and prepare it installation and utilisation in the sodium of the nuclear reactor. A suitable model has been developed and a set of thermo-hydraulics data has been created, taking account of the particularities of the sodium flow. The results of these simulations are then analysed within the framework of acoustic thermometry, in order to determine which disturbance must be taken into account for the correct operation of the temperature measurement.

Study on mass transfer of turbulent air flow sweeping liquid surface

Different forces in interface of gas–liquid in the process of turbulent air flow sweeping liquid surface were analyzed. Characteristics of flowing section were done and Prandtl mixing length theory was used, the principle of turbulent flow mass transfer in the process of turbulent air flow sweeping liquid surface was studied. Effect of Reynolds number, gas flow structure and Prandtl mixing length on the mass transfer were analyzed. It indicated that the turbulent flow mass diffusion coefficient and mass transfer coefficient were involved with the state of gas flow and was affected by gas flow structure. The results are in favor of lucubrate study and engineering application of mass transfer in gas–liquid interface.

Optimization of magnetic amplification by flow constraints in turbulent liquid sodium

Direct measurements of the vector turbulent emf in a driven two-vortex flow of liquid sodium were performed in the Madison Dynamo Experiment [K. Rahbarnia et al., Astrophys. J. 759, 80 (2012)]. The measured turbulent emf is anti-parallel with the mean current and is almost entirely described by an enhanced resistivity, which increases the threshold for a kinematic dynamo. We have demonstrated that this enhanced resistivity can be mitigated by eliminating the largest-scale eddies through the introduction of baffles. By tailoring the flow to reduce large-scale components and control the helical pitch, we have reduced the power required to drive the impellers, doubled the magnetic flux generated by differential rotation, and increased the decay time of externally applied magnetic fields. Despite these improvements, the flows remain sub-critical to the dynamo instability due to the reemergence of turbulent fluctuations at high flow speeds.

Statistical analysis of measured and computed thickness and interfacial temperature of free-falling turbulent liquid films

This study examines the evolution of film thickness and interfacial temperature in turbulent, free-falling water films that are subjected to sensible heating. Measured temporal records of film thickness and interfacial temperature are subjected to thorough statistical analysis to understand the influence of interfacial waves on the distribution, periodicity and interdependence of these two parameters. A computational model of the film is constructed and its predictions subjected to similar statistical analysis. The statistical tools employed in this study include probability density, auto-covariance, cross-covariance, auto-spectrum and cross-spectrum. Probability density of film thickness shows an increase in substrate thickness and amplitude with increasing Reynolds number, while auto-covariance of thickness captures dominant frequencies corresponding to the large waves. Cross-covariance of film thickness and interfacial temperature difference captures a clear phase shift between the two parameters, with the temperature reaching a maximum in the relatively thin film region between the substrate and wave peak. Statistical results for both parameters exhibit clear dependence on axial location in the thermal entrance region, and point to fully developed wave structure downstream. The statistical results based on computed film thickness and interfacial temperature difference agree well with the results based on the measured, which demonstrates the effectiveness of the adopted computational tools at predicting the complex transport phenomena associated with wavy liquid–vapor interfaces.

Numerical study on modulation of microbubbles on turbulence frictional drag in a horizontal channel

Although many investigations on the drag reduction by microbubbles have been conducted, a general mechanism guiding the design of the drag reduction system has not been achieved yet. The drag reduction by microbubbles was investigated in detail with the Euler–Lagrange two-way coupling method in order to understand the drag reduction mechanism by microbubbles in this paper. The liquid velocity field was solved with direct numerical simulations (DNS), and the bubble trajectory was calculated by Newtonian motion equation. The mutual momentum transfer between gas and liquid phases was bridged by interphase forces. The computational results show that a low drag-reduction rate is obtained, the liquid-phase velocity is slightly increased in the region away from the channel wall (i.e., the channel side containing microbubbles), and the turbulence intensity and Reynolds shear stress of the liquid phase are changed along the whole channel height. The present analysis shows that the drag reduction depends on mutual interactions between microbubbles and the liquid turbulence with the help of interphase forces.

Review on convection heat transfer in channel flow with discrete heater arrays for electronic cooling

A review on three convection modes, forced, natural or free and mixed, is made related to laminar and turbulent direct air and liquid cooling channel flow, for application to cooling of electronic systems, and with emphasis on useful correlations. The scope covers single-phase flow over plain heaters, protruded heaters and wall heating. For forced convection, the review continues from the previous review, and describes work from 1995 onward. It is observed that protruded heater distorts the flow in the channel, causing a substantial increase in heat transfer. In natural convection, the methods of cooling and channel aspect ratio strongly affect the heat transfer. In the mixed regime, the location of the heater is less important, and at low Reynolds number, heat transfer is mainly controlled by the Grashof number. However, there are still inconsistent findings among reported results. Keywords : Forced, Natural and Mixed Convection Heat Transfer, Discrete Heat Sources, Electronics Cooling, Channel Flow.

Numerical investigation of the interphase forces and turbulence closure in 3D square bubble columns

3D time dependent numerical study has been performed to predict the flow hydrodynamics in bubble columns by employing explicit algebraic Reynolds stress (EARSM), re-normalization group (RNG) and RNG bubble induced turbulence (BIT) k–ε models and the computational fluid dynamics (CFD) results are compared with experimental work of Deen (2001). This work shows the comparison between different drag force models (Ishii and Zuber, 1979; Schiller and Nauman, 1935; Grace et al., 1976) and drag coefficient). Moreover, the effects of the lift, virtual mass and suchlike other imperative non drag forces inclusive of wall lubrication as well as the turbulent dispersion have been examined. All the results show good quantitative agreement with experiments in case of turbulent kinetic energy, axial gas and liquid velocity profiles. EARSM k–ε has found to perform better than both the RNG k–ε modalities in estimating the turbulent kinetic energy profiles, but gave poor predictions of axial velocity profiles. Comparatively, RNG and RNG BIT models have successfully predicted the averaged flow field. Whereas the turbulent kinetic energy profiles at some locations, have been slightly under estimated by the RNG models. The inclusion of bubble induced turbulence led to slight improvement in estimation of the turbulent kinetic energy profiles. The advanced performance of RNG models stems in the better estimation of rate of turbulent dissipation and turbulent viscosity. Thus, both RNG and RNG BIT models can be readily utilized for the analysis of average flow fields and turbulent flow structures.

The feedback effect caused by bed load on a turbulent liquid flow

Experiments on the effects due solely to a mobile granular layer on a liquid flow are presented (feedback effect). Nonintrusive measurements were performed in a closed conduit channel of rectangular cross section where grains were transported as bed load by a turbulent water flow. The water velocity profiles were measured over fixed and mobile granular beds of same granulometry by Particle Image Velocimetry. The spatial resolution of the measurements allowed the experimental quantification of the feedback effect. The present findings are of importance for predicting the bed-load transport rate and the pressure drop in activities related to the conveyance of grains.

Study on Liquid Turbulence Modulation by Microbubbles in Different Turbulence Layers

Bubbly flows exist extensively in industrial processes. To enhance efficiencies of industrial processes, it is very necessary and important to understand detailedly mechanisms of liquid turbulence modulation by bubbles. To understand mechanisms of the liquid turbulence modulation by microbubbles, an Euler-Lagrange two-way model was used to investigate and analyze deeply the liquid turbulence modulation by microbubbles in the subviscous, buffer, and outer layers, respectively. The present results show that the liquid turbulence modulation by microbubbles is related to microbubble locations; the liquid turbulence is intensified when microbubbles are in the outer layers, whereas the liquid turbulence is suppressed when microbubbles are in the subviscous and buffer layer; and the drag reduction occurs only when microbubbles are in the buffer layer.

Nonlinear Analysis of Bubble Formation Dynamics in Shear-Thinning Fluids

The dynamics of bubble generating in carboxymethylcellulose (CMC) aqueous solution were studied using chaos method. The results show that for low position (P) and gas flowrate (Qg), the characteristic frequency of axial and radial velocities are both consistent to bubble periodic shear frequency; but for high position, power spectrums are of broad coverage within low frequency range. The magnitudes of radial characteristic peaks increase with gas flowrate. Phase portraits of reconstructed phase space of velocity time series display certain features of chaotic attractor. For lowPandQg, phase portrait takes on uniform elliptical shape due to liquid periodic motion caused by bubble periodic rising. Whereas for highPandQg, the liquid turbulence is reinforced by bubble increasing velocity and large-scale turbulent intensity around bubble increases, consequently, leading to significant compression of phase portrait.

Measurements of Turbulence in a Liquid-Metal Two-Phase Flow by Using a Miniature Electro-Magnetic Probe

A nitrogen gas-lead bismuth two-phase flow was experimentally studied as a two-phase flow with large liquid-to-gas density ratio. Experiments were performed to understand turbulent structure in a liquid-metal two-phase flow by using a miniature electro-magnetic probe. Radial profiles of axial liquid velocity and turbulence intensity were measured by using the electro-magnetic probe. Turbulence is induced mainly by rising bubbles in the liquid-metal. Measurement results show that the turbulence intensity at the tube center was proportional to the void fraction to the power of 0.8 for higher void fraction at the present experimental conditions.

Dynamical analysis of turbulent liquid phase in two-phase pipe flow

An experimental study was conducted to evaluate dynamic structures embedded in a liquid and turbulent characteristics of slug flow in a horizontal pipe. Initially, single liquid phase flow was considered at a flow rate of 120 l/m and later on slug flow was generated by the introduction of a gas phase at the rate of 40 l/m keeping the liquid phase flow at the same rate. Particle image velocimetry was employed to calculate the two-dimensional instantaneous velocity field of the liquid phase. The turbulent velocity fields and dynamics of the liquid phase flow were investigated by proper orthogonal decomposition analysis. The structures containing the most energy were successfully revealed. The energy distributions of the spatial and temporal modes were also obtained.

Experimental approaches to universal out-of-equilibrium scaling laws: turbulent liquid crystal and other developments

This is a brief survey of recent experimental studies on out-of-equilibrium scaling laws, focusing on two prominent situations where nontrivial universality classes have been identified theoretically: absorbing-state phase transitions and growing interfaces. First the paper summarizes the main results obtained for electrically driven turbulent liquid crystals, which exhibited the scaling laws for the directed percolation class at the transition between two turbulent regimes, and those for the Kardar–Parisi–Zhang class in the supercritical phase where one turbulent regime invades the other. Other experimental investigations on these universality classes and related situations are then overviewed and discussed. Some remarks on analyses of these scaling laws are also given from the practical viewpoint.

A Mechanism on Liquid-Phase Turbulence Modulation by Microbubbles

Although bubbly flows have been extensively applied to many industrial fields, efficiency improvements of bubbly equipments are greatly limited due to the absence of accurate understandings of liquid turbulence modulation by bubbles. In order to obtain an accurate mechanism explanation, an Euler-Lagrange two-way method was used to investigate and analyze deeply the liquid turbulence modulation by microbubbles in this paper. The present investigation shows that for the bubbly flow laden with microbubbles the liquid turbulence modulation is mainly caused by the drag force, and the turbulence modulation level is related to the microbubble diameter. A detailed mechanism explanation on the physical phenomenon was presented here.

Pool Fires Of Biofuels And Their Blends With Petroleum Diesel

The combustion characteristics of pool fires of biofuels, canola methyl ester (CME), soy methyl ester (SME), and their blends with a petroleum fuel (No. 2 diesel) were studied. The fuels were burned in cups of two sizes (0.042 m and 0.057 m in diameter and 0.038 m height) that simulated convection-dominated small pool fires of liquids. Blends of CME and SME with diesel fuel were tested with biofuel concentrations of 25, 50, and 75% by volume. The mass burn rate, the fuel surface regression rate, the radiation emission from the flames, the flame temperature field, and the emission indices of CO and NOx were recorded. The fuel surface regression rate in both containers was comparable. Both the fuel mass burning rate and surface regression rate varied non-monotonically with the volume concentration of biofuel in the blend. The radiation fraction of heat release and the temperature profiles were similar for all the flames. The CO emission index decreased with the biofuel content in the fuel. The NOx emission index did not show a systematic and significant dependence on the fuel blend; however, it was smaller than that measured in the turbulent gas jet and liquid spray flames of the corresponding fuels.

Direct analysis of eight chlorophenols in urine by large volume injection online turbulent flow solid-phase extraction liquid chromatography with multiple wavelength ultraviolet detection

A novel method for determining eight chlorophenols (CPs) by large volume injection online turbulent flow solid-phase extraction high performance liquid chromatography in urine samples was developed. An aliquot of 1.0 mL urine sample could be analyzed directly after centrifugation. The analytes were preconcentrated online on a Turboflow C18-P SPE column, eluted in back-flush mode, and then separated on an Acclaim PA2 analytical column. Major parameters such as SPE column type, sample loading flow rate and elution time were optimized in detail. Eight CPs from monochlorophenol to pentacholophenol were measured by multiple-wavelength UV detection at four different wavelengths. The limits of detection (LODs) were between 0.5 and 2 ng/mL. The linearity range was from the limit of quantification to 1000 ng/mL for each compound, with the coefficients of determination (r(2)) ranging from 0.9990 to 0.9996. The reproducibility of intraday and interday relative standard deviations (RSDs) ranged from 0.6% to 4.5% (n=5). The method was successfully applied to analyze eight CPs in urine samples. Good recoveries, ranging from 76.3% to 122.9%, were obtained. This simple, sensitive and accurate method provides an alternative way to rapidly analyze and monitor CPs in urine samples, especially for matters of occupational exposure.

A statistical model for the average volume fraction profile through the mixing zone in turbulent stratified gas–liquid flow

A phenomenological model was developed for the average volume fraction profile through the mixing zone between turbulent gas and liquid in horizontal, layered flow. A probability distribution (PDF) of the height of the interface was defined in terms of a ratio between the interfacial energy (system energy) and the turbulent kinetic energy (driving energy), representing an analogy to the Boltzmann distribution in statistical physics. A potential advantage with this modelling approach is that it offers an alternative to (often inaccurate) entrainment correlations that are used in boundary conditions for dispersion models. A unified PDF and dispersion model was tested against X-ray tomography data, with satisfactory results.

Large Eddy Simulation of Liquid-Jet Primary Breakup in Air Crossflow

A robust two-phase-flow large-eddy-simulation methodology is applied to simulate the primary breakup of an axisymmetric liquid jet injected into an air crossflow at atmospheric pressure. The coupled level-set and volume-of-fluid method is implemented for accurate interface tracking. To deal with high liquid/gas density ratio, an extrapolated liquid-velocity field is created and used for momentum-equation discretization in the vicinity of the interface. Based on the local level-set value, sharp jumps in fluid density and viscosity are assumed across the interface. By simulating the nonturbulent inflow of a liquid jet into a nonturbulent gaseous crossflow, regular surface waves are observed in the large-eddy-simulation predictions on the upstream side of the liquid jet, with the wavelength agreeing well with experimental measurements. The predicted wavelength decreases as the gaseous Weber number increases, implying that the surface waves arise from a Rayleigh–Taylor-type instability. The simulated velocity field shows that, as the instability grows, gaseous vortices develop in the wave troughs, further enhancing the breakup of the liquid core. The turbulent inflow of a liquid jet into a turbulent gas crossflow is also simulated, and the effect of turbulent eddies on the liquid-jet primary breakup is examined. The rescaling/recycling method for large-eddy-simulation inlet-condition generation is implemented to generate realistic (i.e., physically correlated) turbulent inflows. It is found that it is the liquid rather than the gaseous turbulence that determines the initial liquid-jet instability and interface characteristics; further downstream, the turbulent liquid jet disintegrates more chaotically than the nonturbulent jet due to strong aerodynamic and turbulence effects. When appropriate turbulent inflows are specified, the liquid-jet penetration into the air crossflow (and the subsequent spread of the spray) is correctly predicted by the current large-eddy-simulation methodology, which displays good numerical robustness and accuracy for high liquid/gas density-ratio two-phase systems.