Liquid Flow Characteristics Research Articles

Calculation of flow characteristics of liquid fuel supplied through pressure jet atomizers of small-sized gas turbine engines

The paper presents the results of studying the flow characteristics of liquid fuel in pressure jet atomizers of small-sized gas turbine engines with nozzle diameters of 0.4-0.6 mm for various operating and design parameters. The study was carried out using experimental measurements, semi-empirical correlations and CFD (computational fluid dynamics) methods. The Euler approach, the volume- of- fluid (VOF) method, was used to model multiphase flows in CFD simulations. Good agreement was obtained between experimental and predicted data on the fuel coefficient and the primary spray cone angle at the nozzle outlet. Besides, the assessment of the applicability of semi-empirical techniques for the nozzle configurations under consideration is given. In the future, the flow characteristics in question (the nozzle flow rate, the fuel film thickness, and the primary spray cone angle) can be used to determine the mean diameter of the droplets (SMD) required to fully determine the boundary conditions of fuel injection when modeling combustion processes in combustion chambers of small-sized gas turbine engines.

3D CFD simulation of the liquid flow in a rotating packed bed with structured wire mesh packing

An in-depth understanding of the liquid flow characteristics in rotating packed beds (RPBs) is very important for the optimization and modelling of RPB reactors. However, the complex and dense packing makes it very difficult to accurately obtain the dynamic and detailed characteristics of liquid flow in RPBs through experimental methods. Therefore, this paper carried out a 3D gas–liquid flow CFD simulation of an RPB with structured wire mesh packing to obtain detailed liquid flow information. Detailed macro and micro characteristics of the liquid flow in the packing region of the RPB are obtained. The dynamic evolution processes of droplets are observed and analysed. A new flow pattern of “branch flow” is observed in the packing region. In addition, two typical liquid disintegration modes of liquid ligament-droplet disintegration and liquid bridge-droplet disintegration are observed, and the disintegration mechanisms are analysed. Finally, the effects of contact angle and rotational speed on the characteristic parameters are investigated, and the interfacial areas between different phases in the RPB are analysed. In both hydrophilic and hydrophobic packings, the wetted packing surface area is always less than the gas–liquid interfacial area, and their ratio decreases with the increases of contact angle and/or rotational speed, but increases with the increase of the liquid viscosity.

Experimental Study of Flow Boiling and Condensation in Tubes with Pin-Fin and Metallic Foam Structures

Appropriate arrangement of the fin structures in the evaporator and condenser not only enhances the heat transfer coefficient but also suppresses the increase of pressure drop. Due to this reason, a new method of using large-scale pin fins is explored to increase the heat transfer area and to modify the liquid film flow characteristics in the enhanced tubes. In the present study, four enhanced tubes and one plain tube were manufactured by selective laser melting. The working fluid is R407C and the enhanced tubes are eight short pin fins tube, five long pin fins tube, twisted pin fins tube and a tube filled with metallic foam. The results show that the shorter fin tube has the largest heat transfer coefficient for condensation at 3967 W/m2⋅K and the metallic foam tube demonstrates the largest heat transfer coefficient for boiling at 10606 W/m2⋅K. However, the shorter fins have the highest efficiency indices based on the heat transfer coefficient-pressure drop evaluation criterion and the heat transfer coefficient-area evaluation criterion. For condensation, the indices are 1.28 and 1.35, respectively. For boiling, the indices are 2.55 and 1.62, respectively.

First law of thermodynamics on the boundary for flow through a carbon nanotube.

The definition of boundary at the nanoscale has been a matter of dispute for years. Addressing this issue, the nonequilibrium molecular dynamics (NEMD) simulations in this work investigate the flow characteristics of a simple liquid in a single-walled carbon nanotube (SWCNT), and equilibrium molecular dynamics simulations support the range of the NEMD results. The inconsistencies in defining the flow boundary at the nanoscale are understood through the first law of thermodynamics: Local thermodynamic properties (the effects of the density distribution, pressure, viscosity, and temperature) define the boundary. We have selected different boundary positions in the CNT to demonstrate the probability of density distribution that also indicates the coexistence of multiple thermodynamic states. Altering the interaction parameters, we produce convergence between the NEMD result and the no-slip Hagen-Poiseuille assumptions. Meanwhile, the results indicate that the boundary position varies between the innermost solid wall and peak density position of the CNT as a function of the input energy or work done in the system. Finally, we reveal that the ratio between the potential energy barrier and the kinetic energy is proportional to the shift of the boundary position away from the innermost solid wall.

Photogrammetry based computational fluid dynamics of erosion of sand particles in water pipeline: Dynamic shape factors of 3D particles and minimization of erosion activity

Extraction and delivery of raw materials in engineering industries are inevitably polluted with sand particles that caused several flow assurance problems. Besides, designing a pipeline and estimating sand erosion is very complex in a multiphase flow due to several important factors needed to be considered, such as impact velocity, impact angle, size of particle, shape of particle, properties of particle, and properties of the target material. In this work, a modified E/CRC erosion model was developed to address the shape randomness in sand particles distribution. The photogrammetry technique was adopted to digitize sand particles into 3D models within the range of 400–500 μm. After quantitative and qualitative analysis, a database of shape factor for different spherical and roundness of sand particles was tabulated. Meanwhile, a high-fidelity simulation of a 90-degree elbow pipeline was conducted using the CFD-DEM method. Hydrodynamic characteristics of liquid flow, sand particle trajectories, the sensitivity of velocity, shape factor, and flow rate were comprehensively explored. Modification of the particle shape factor based on the generated database from photogrammetry resulted in overestimated erosion rate of the original E/CRC model with 124.4% accuracy improvement in predicting erosion rate on pipe bend at different collision angles. Lastly, through response surface methodology (RSM), a flow threshold condition was established to achieve minimum erosion damage.

Seepage Time Soft Sensor Model of Nonwoven Fabric Based on the Extreme Learning Machine Integrating Monte Carlo.

Nonwoven fiber materials are materials with multifunctional purposes, and are widely used to make masks for preventing the new Coronavirus Disease 2019. Because of the complexity and particularity of their structure, it becomes difficult to model the penetration and flow characteristics of liquid in nonwoven fiber materials. In this paper, a novel seepage time soft sensor model of nonwoven fabric, based on Monte Carlo (MC), integrating extreme learning machine (ELM) (MCELM) is proposed. The Monte Carlo method is used to expand data samples. Then, an ELM method is used to establish the prediction model of the dyeing time of the nonwoven fiber material overlaps with the porous medium, as well as the insertion degree and height of the different quantity of hides. Compared with the back propagation (BP) neural network and radial basis function (RBF) neural network, the results show that the prediction model based on the MCELM method has significant power in terms of accuracy and prediction speed, which is conducive to the precise and rapid manufacture of nonwoven fiber materials in practical applications between liquid seepage characteristics and structural characteristics of porous media. Furthermore, the relationship between the proposed models has certain value for predicting the behavior and use of nonwoven fiber materials with different structural characteristics and related research processes.

Drag coefficient modification for turbulent gas-liquid two-phase flow in a rotodynamic pump

An appropriate drag coefficient model is necessary for the simulation to better predict gas–liquid flow characteristics in a multiphase rotodynamic pump. However, most of the drag coefficient models are derived based on bubbles rising through a stagnant or laminar liquid, which are not applicable for turbulent flow in pumps. In this study, the drag coefficient in the quiescent flow is correlated with the drag coefficient in the turbulent flow through the Stokes number, and the drag coefficient model proposed by Ishii and Zuber (1979) is modified. By comparing the simulation results with experimental data of a rotodynamic pump, it is found that the pump performance predicted by the simulation with the modification is larger than without it, and has better accuracy. After the correction, the bubble accumulation near the suction side of the impeller blade is reduced, the gas volume fraction in the diffuser also decreases. When the rotational speed of the pump is 2350 r/min, the drag coefficient after the correction near the suction side of the impeller blade is much larger than before the correction. At the highest turbulent kinetic energy, the drag coefficient with the modification is more than 20 times greater than the corresponding ones without it. When the rotational speed increases to 2650 r/min or 2950 r/min, the frequency of the eddies are too high to affect the bubble motion, which makes the increasing degree of the drag coefficient decreases.

Experimental investigation of critical suction velocity of coarse solid particles in hydraulic collecting

Hydraulic collecting and pipe transportation are regarded as an efficient way for exploiting submarine mineral resources such as the manganese nodules and ores. Coarse particles on the surface of the sea bed are sucked by a pipe during the mining and crushing of the mineral. In this paper, the critical suction velocity for lifting the coarse particles is investigated through a series of laboratory experiments, and the solid–liquid two-phase flow characteristics are obtained. Based on the dimensional analysis, the geometric similarity is found between actual exploitation process and model test with the same kind of material. The controlling dimensionless parameters such as the hydraulic collecting number, the relative coarse particle diameter, the relative suction height, and the density ratio are deduced and discussed. The results show that the logarithm in base 10 of the hydraulic collecting number increases approximately linearly with the increase of the relative suction height, while decreases with the relative particle diameter. A fitting formula for predicting the critical suction velocity is presented according to the experimental results.

Characteristics of turbulent liquid flow produced by mechanically rotating impeller for agitation

Characteristics of turbulent liquid flow produced by mechanically rotating impeller for agitation

Characteristics of unsteady liquid flow produced by forward-reverse rotating impeller for agitation

Characteristics of unsteady liquid flow produced by forward-reverse rotating impeller for agitation

Comparing flow characteristics of viscoelastic liquids in long and short capillaries (entrance effects)

This study is devoted to the analysis of the physical meaning of the difference in the results of the viscosity measurements obtained by using the two-capillary method—carrying on the same flow rate through two circular parallel capillaries of different lengths but the same diameter. Furthermore, there is the other approach for using short capillaries for determination of a value, known as “elongational viscosity,” based on the concept of domination extension at the convergent flow along the inlet of a capillary. The theory of this method dates back to the publication of Cogswell. However, it was shown that this approach is inadequate for polymeric liquids that demonstrate time-dependence effects. In this study, we present experimental data for melts of two polyethylenes of different molecular weights and their mixtures. The data of capillary viscometry are accompanied by measuring their viscoelastic properties. The obtained data showed that the two-capillary method cannot give a chance to estimate “elongational viscosity” for elastic liquids. The difference between the losses in flow through long and short capillaries is treated in the terms of “end correction,” which is determined by the Weissenberg number. Hence, elasticity is the main physical parameter responsible for additional losses in the flow through a short capillary.

Solid–liquid two-phase flow and erosion calculation of butterfly valves at small opening based on DEM method

Purpose The study aims to decrease the effect of solid particles on a butterfly valve, which will cause seal failure and leakage, providing a reference for anti-wear design. Design/methodology/approach In this paper, computational fluid dynamics discrete element method (CFD-DEM) simulation was conducted to study the solid–liquid two-phase flow characteristics and erosion characteristics of a butterfly valve with a different opening. Findings Abrasion at 10% opening is affected by high-speed jets in upper and lower parts of the pipeline, where the erosion is intense. The impact of the jet on the upper part of 20% opening begins to weaken. With the top backflow vortex disappearing, the effect of lower jet is enhanced. Meanwhile, the bottom backflow vortex phenomenon is obvious, and the abrasion position moves downward. At 30% opening, the velocity is further weakened, and the circulation effect of lower flow channel is more obvious than that of the upper one. Originality/value It is the first time to use DEM to investigate the two-phase flow and erosion characteristics at a small opening of a butterfly valve, considering the effect of inter-particle collision. Therefore, this study carries on the thorough analysis and discussion. At the same opening degree, with increasing of the particle size, the abrasion of valve frontal surface increases when the size is less than 150 µm and decreases when it is greater than 150 µm. For the valve backflow surface, this boundary value becomes 200 µm. Peer review The peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-07-2020-0264/

A critical review of filmwise natural and forced convection condensation on enhanced surfaces

The use of enhanced surfaces is an efficient method to improve filmwise condensation. Due to their immense potential, many enhanced structures were developed and investigated with the aim of improving natural and forced convection condensation heat transfer coefficients. This has resulted in large collections of predictive models and experimental data being reported. In this review, the developments in this field of research in the past few decades and the recent advances are collated and examined. This paper focuses on the review of natural convection condensation on the external surfaces of enhanced flat plates and tubes and forced convection condensation in enhanced tubes. The various models predicting the heat transfer coefficients on plain and enhanced surfaces are evaluated. For natural convection condensation, the liquid film-based models, semi-empirical models and numerical modes are reviewed whereas, for forced convection condensation, the gravity-dominated and vapor shear-dominated models are discussed. The effects of these enhanced structures on the liquid film and two-phase flow characteristics are analyzed and the various types of enhanced tubes and flat plates investigated are categorized. The manufacturing techniques employed to fabricate these surfaces are identified. A detailed evaluation of the heat transfer and pressure drop performances of the various enhanced surfaces is performed. In addition, their thermal performances are summarized and compared, and their associated heat transfer mechanisms are elucidated. For external condensation on a single tube row, three-dimensional fin structures were found to provide better thermal performance than two-dimensional structures, with some three-dimensional fin structures exhibiting more than 6 times the heat transfer coefficients of a plain surface. However, in a tube bundle, the heat transfer coefficient of three-dimensional fin tubes decreases more significantly with increasing tube row as compared to two-dimensional fin tubes. For convective condensation in circular tubes, the herringbone and pin fin tubes demonstrated better thermal and pressure drop performances than other internally enhanced tubes. Their efficiency indices were between 1.25 and 1.28. Based on the literature surveyed, the various experimental results are compared, existing research gaps are identified and frameworks for future research work are provided.

Study on gas–liquid flow characteristics in stirred tank with dual-impeller based on CFD-PBM coupled model

Study on gas–liquid flow in stirred tank with two combinations of dual-impeller (six-bent-bladed turbine (6BT)+six-inclined-blade down-pumping turbine (6IT D ), the six-bent-bladed turbine (6BT)+six-inclined-blade up-pumping turbine (6IT U )) was conducted using computational fluid dynamics (CFD) and population balance model (PBM) (CFD-PBM) coupled model. The local bubble size was captured by particle image velocimetry (PIV) measurement. The gas holdup, bubble size distribution and gas–liquid interfacial area were explored at different conditions through numerical simulation. The results showed that the 4 mm bubbles accounted for the largest proportion of 33% at the gas flow rates Q = 0.76 m 3 ⋅h −1 and 22% at Q = 1.52 m 3 ⋅h −1 for combined impeller of 6BT + 6IT U , while the bubbles of 4.7 mm and 5.5 mm were the largest proportion for 6BT + 6IT D combination, i . e . 25% at Q = 0.76 m 3 ⋅h −1 and 22% at Q = 1.52 m 3 ⋅h −1 , respectively, which indicated that 6BT + 6IT U could reduce bubble size effectively and promote gas dispersion. In addition, the gas holdup around impellers was increased obviously with the speed compared with gas flow rate. So it was concluded that 6IT U impeller could be more conductive to the bubble dispersion with more uniform bubble size, which embodied the advantages of 6BT + 6IT U combination in gas–liquid mixing.

Numerical simulation and experimental study of the characteristics of packing feature size on liquid flow in a rotating packed bed

Rotating packed bed has high efficiency of gas–liquid mass transfer. So it is significant to investigate fluid motion in rotating packed bed. Numerical simulations of the effects of packing feature size on liquid flow characteristics in a rotating packed bed are reported in this paper. The particle image velocimetry is compared with the numerical simulations to validate the turbulent model. Results show that the liquid exists in the packing zone in the form of droplet and liquid line, and the cavity is droplet. When the radial thickness of the packing is less than 0.101 m, liquid line and droplets appear in the cavity. When rotational speed and radial thickness of the packing increase, the average diameter of the droplets becomes smaller, and the droplet size distribution becomes uniform. As the initial velocity of the liquid increases, the average droplet diameter increases and the uniformity of particle size distribution become worse. The droplet velocity increases with the radial thickness of the packing increasing, and gradually decreases when it reaches the cavity region. The effect of packing thickness is most substantial through linear fitting. The predicted and simulated values are within ±15%. The cumulative volume distribution curves of the experimental and simulated droplets are consistent with the R-R distribution.

Evolution and Interaction Characteristics of Liquid Flow and Bubbles in a Jet Bubbling Column

The jet bubbling column is a new type of gas–liquid two-phase reactor with excellent mixing ability. The evolution and interaction characteristics of liquid flow and bubbles in a jet bubbling colum...

Free-Surface Liquid Lithium Flow Modeling and Stability Analysis for Fusion Applications

Liquid metal plasma facing components are considered an attractive design choice for fusion devices including pilot plants. Virtual prototyping of such devices includes modeling of free-surface flow of the electrically conductive liquid, which requires computational fluid dynamics (CFD) and magnetohydrodynamics (MHD) simulations. Numerical tools capable of simulating flows and heat transfer in the free-surface MHD flow were developed at PPPL based on the customized ANSYS CFX. MHD is introduced using a magnetic vector potential approach. Free-surface flow capabilities are available in the code and were tested. Special stabilization procedures were derived and applied to improve convergence of the momentum equations with the source terms due to the Lorentz force and surface tension. Important characteristics of the fusion-relevant liquid metal flow is free surface smoothness and stability. Heat flux from the plasma impacts the liquid surface at a very acute angle, so any change of the free surface from axisymmetry can dramatically increase the local heat flux density and thus create excessive evaporation of liquid lithium into the plasma, which is detrimental to operations. Stability analysis of the liquid metal film flow was performed to determine applicable flow regimes. Thin film flow along horizontal wall is considered. Effects of gravity, magnetic field, and surface tension are included in the analysis.

CFD simulation of liquid flow characteristics in a rotor-stator spinning disc reactor

In this work, the CFD approach is employed to analyse the liquid hydrodynamic behaviour in the rotor-stator spinning disc reactor (RSSDR). The effect of rotational speed (N) and volume flow rate (Q) on the liquid-liquid flow pattern and its transition are investigated. It is found that there are two typical flow pattern (film flow and filament flow) observed in the RSSDR. Increasing N and decreasing Q turn the film flow into the filament flow. The flow pattern criterion for transition of filament flow to film flow is also obtained. The simulation data show a good agreement with our previous published experimental results. In addition, the influence of N and Q on liquid holdup rate (ε) and liquid velocity distribution in the RSSDR are also studied. The results show that ε keeps stable and then decreases with the increase of N, increases and then keeps consistent with increasing Q. While the mean liquid velocity increases as increasing N, Q, and radial radius (r). The mean radial velocity increases with increasing N, Q, and decreasing r. This work leads a deep understanding of the liquid flow characteristics in the RSSDR and its optimization design and scaling up.

Effect of self-excited instability on single liquid swirl injector flow characteristics

Owing to their simple structure and high performance, swirl injectors have been used as propellant injectors for rocket engines in various countries, starting from Russia. However, when a swirl injector is used in combustion, flow instability becomes important because of its relation to combustion instability. Because the external flow of a swirl injector is a thin liquid sheet, wave-forming self-excited instability could occur. In this study, the effect of self-excited instability on the flow characteristics of a swirl injector was investigated. Moreover, through the use of a mechanical pulsator, the effect of self-excited instability frequency on the dynamic characteristics of the swirl injector was examined. As a result, self-excited instability was determined to cause the periodic breakup of the spray sheet. In addition, large droplets generated immediately after breakup are confirmed to be periodically concentrated with a specific frequency equal to the self-excited instability frequency. With external pulsation, breakup length was observed to be shortened with pulsation and had minimum value when pulsation of frequency equal to the self-excited instability frequency was applied. Droplet characteristics with pulsation were also investigated, and external pulsation was determined to cause mean droplet diameter (D10) and Sauter mean diameter (SMD) to be smaller. When SMDs at pulsations of different frequencies were compared, the SMD at pulsation with self-excited instability frequency was observed to be larger because this frequency causes droplet distribution to be more non-uniform. Through this study, self-excited instability was confirmed to be able to change the static and dynamic characteristics of a swirl injector. This result can serve as a reminder of the importance of the self-excited instability of a sheet in the design of a swirl injector.

CFD analysis of the hydrodynamic characteristics in a rotating packed bed with multi-nozzles

Rotating packed bed (RPB) has been widely noted for its good mass transfer performance and tangible size savings, and its advantages are especially obvious in space-intensive scenarios, such as purification of natural gas on offshore platforms. Liquid maldistribution in RPBs has a serious impact on mass transfer performance. However, it is difficult to accurately obtain and predict the liquid flow characteristics and liquid distribution in RPBs by experimental methods. Therefore, the liquid flow characteristics and liquid distribution analysis of multi-nozzle RPBs based on computational fluid dynamics (CFD) models is performed in this paper. The simulation results indicate that increasing of the number of nozzles and nozzle width at two different rotational speeds increases the liquid holdup and decreases the degree of liquid dispersion. In addition, a liquid maldistribution index within RPBs is proposed and investigated. The circumferential distribution of the liquid becomes uniform as the number of nozzles increase, but the uniformity gets worse as the width of nozzle increases, under the same total liquid flow rate. The more the number of nozzles, the more uniform the overall liquid distribution; on the contrary, the larger the nozzle width, the more uneven the overall liquid distribution.