Liquid Bridge Force Research Articles

A coarse grain model with parameter scaling of adhesion forces from liquid bridge forces and JKR theory in the discrete element method

The discrete element method (DEM) is a reliable tool for analyzing powder processes. However, the DEM is problematic for fine particle simulations owing to its huge computational cost. Coarse grain models, where multiple original particles are replaced with one large particle, are a promising solution. In such a model, scaling laws for forces acting on a coarse-grained particle are used to make its behaviors match the behaviors of the original particles. While various scaling laws have been proposed, there is not enough insight into combining several scaling laws and the relationship between scaled parameters. This study newly proposes a coarse grain model with a systematic parameter scaling law for adhesion forces, especially liquid bridge forces. Simulation results are compared with experimental results. Good agreements are achieved for macroscopic particle behaviors such as cascading angles and lifted heights. The adequacy of the proposed coarse grain model is also verified. The behaviors of the coarse-grained particles well match the corresponding behaviors of the original particles. Consequently, this study demonstrates the superiority of the coarse grain model by comparing its results with those obtained without the model.

Interfacial Adhesion Forces of Hydrate Particles in the Presence of Hydrate Inhibitors

Hydrate inhibitors are traditionally utilized to prevent hydrate plugging. In this study, the adhesion forces of cyclopentane (CP) hydrates with thermodynamic inhibitors (ethanol, urea, and NaCl) and anti-agglomerant inhibitors [sorbitan monooleate (Span 80) and lecithin] were measured to understand the effects of hydrate inhibitors on the adhesion forces of hydrates. It was found that the thermodynamic inhibitors increased the early hydrate interparticle adhesion force due to the enhanced liquid bridge force. However, the liquid bridge acted as a lubricant layer to prevent the irreversible agglomeration of hydrate after long-term contact. The hydrate adhesion forces decreased by 90.5-93.0% and 76.6-92.7% with an increase in the concentration of Span 80 and lecithin, respectively, from 0.1 to 1 wt %. Both rough morphology and low interfacial tension contributed to the adhesion force decrease of hydrate after the addition of anti-agglomerant inhibitors. The results may be helpful for understanding the mechanism of influence and quantifying the impact of hydrate inhibitors on hydrate interparticle adhesion force.

Influence of liquid bridge force on physical stability during fuel storage and transportation

The physical stability of solid‒liquid fuel is a factor that needs to be considered for fuel product practicability for storage and transportation. To determine the Influence of liquid bridge force on physical stability, two detection devices were designed. The laws obtained from microscopic experiments are used to verify the physical stability of fuel under different component ratios. The liquid bridge force is found to increase with the droplet volume. Multiliquid bridges above one critical saturation can generate significant resultant forces compared to single-liquid bridges of the same volume. There exist four states of solid‒liquid mixed fuel with increasing liquid saturation rate. The liquid bridge force between the solid and liquid plays a dominant role in the physical stability of the first three states. There may be two stages involved in the stratification process for state 4 fuel, and the liquid viscosity is another factor that cannot be ignored. In the process of selecting a fuel ratio, a larger liquid bridge force between the components can be obtained by properly improving the wetting effect so that the fuel shows better physical stability.

Airborne high oil-content coal particles suppression via the electrolyte accelerated application of hydrocarbon and short-chain fluorocarbon surfactants

This paper studied the wetting and agglomerating behaviour of high oil-content coal particles, during the electrolyte accelerated synergistic application of hydrocarbon and short-chain fluorocarbon surfactants. The addition of short-chain fluorocarbon contributed 42.91 % ∼ 71.71 % reduction on surface tension and 51.08 % to 59.54 % reduction on immersing time. The short-chain fluorocarbon surfactant also achieves 29.17 % ∼ 258.93 % improvement on TSI and 48 % ∼ 104 % improvement on dust suppression rate. The presence of electrolytes further enhanced those performances by contributing an extra 7.95 % ∼ 18.41 % reduction on surface tension, 54.99 % ∼ 75.73 % reduction on immersing time for oil-rich and oil-high coal particles, 1.95 ∼ 19.16 times higher TSI and 23.35 % ∼ 31.85 % increasement on dedusting rate. The agglomerating behaviour is more accurate in predicting the dedusting rate. The increased oil content led to significant reduction on static and total liquid bridge force, and finally resulted in deteriorated dedusting rate due to the diminished wetting and agglomerating performance.

Effect of Surfactants with Different Hydrophilic–Lipophilic Balance on the Cohesive Force between Cyclopentane Hydrate Particles

Effective control of the cohesive force between hydrate particles is the key to prevent their aggregation, which then causes pipeline blockage. The hydrophilic–lipophilic balance (HLB) value of surfactants was proposed as an important parameter for the evaluation and design of hydrate anti-agglomerants. A microscopic manipulation method was used to measure the cohesive forces between cyclopentane hydrate particles in the presence of Tween and Span series surfactants with different HLB values; moreover, the measured cohesive force was compared with the results of calculations based on the liquid bridge force model. Combined with the surface morphology and wettability of the hydrate particles, we analyzed the mechanism by which surfactants with different HLB values influence the cohesion between hydrate particles. The results show that for both Tween (hydrophilic, HLB > 10) and Span (hydrophobic, HLB < 10) surfactants, the cohesive force between cyclopentane hydrate particles decreased with decreasing HLB. The experimental results were in good agreement with the results of calculations based on the liquid bridge force model. The cohesive force between hydrate particles increased with increasing concentration of Tween surfactants, while in the case of the Span series, the cohesive force decreased with increasing surfactant concentration. In the formation process of cyclopentane hydrate particles, the aggregation of low-HLB surfactant molecules at the oil–water or gas–water interface increases the surface roughness and hydrophobicity of the hydrate particles and inhibits the formation of liquid bridges between particles, thus reducing the cohesion between particles. Therefore, the hydrate aggregation and the associated blockage risks can be reduced.

Particle fluidization characteristics and transition in a hot gas-solid fluidized bed with liquid injection

The particle fluidization characteristics and transition in a hot gas-solid fluidized bed with liquid injection were investigated on the basis of pressure drop of fluidized bed, the side wall temperature distribution and the weight fraction of agglomerates. It was found that the particle fluidization behavior was controlled by liquid bridge force under low induction heating power, whereas both solid bridge force and liquid bridge force take control of fluidization under higher induction heating power. With increasing liquid injection flowrate, the particle fluidization behavior experienced four types, named fast defluidization, gradual defluidization, agglomerating fluidization and stable fluidization, respectively. Further the transition behaviors between different fluidization types of particles were investigated, and four fluidization regions were distinguished. A dimensionless number ζ was proposed based on the theoretical analysis of interparticle forces and bubble expansion force, thereby establishing the connection between lab-scale experiments and industrial fluidized beds, and providing guidelines for their safe operation. • The combined effect of both solid bridge force and liquid bridge force were investigated on fluidization behaviors. • Four types of particle fluidization behaviors from stable fluidization to defluidization were distinguished. • The transition boundary of different particle fluidization types was determined. • The stable operating domain of the reactor was determined. • A dimensionless number was proposed to classify particle fluidization behaviors.

Insight into the interaction mechanism between liquid action and cone structure in liquid-containing gas-solid spouted fluidized bed reactors

Liquid action and cone structure can significantly change fluidization characteristics via cooperation or competition in liquid-containing gas-solid spouted fluidized bed reactors (LGSFBR), which deserves in-depth study. The CFD-DEM method coupling with liquid bridge force model was adopted to investigate the fluidization, circulation and mixing characteristics, and thus a correlation analysis among the above multiple aspects was proposed to systematically explore interaction mechanism between the liquid action and the cone structure. The multiple analysis results show that the increase of inclination angle will cause a clear transition in the dominated interaction mechanism, i.e., the fluidization characteristics are firstly dominated by liquid action with lower inclination angle, then co-dominated by liquid action and cone structure, finally by cone structure with higher inclination angle. In conclusion, the overall fluidization state and characteristics can be associated with the cooperation and competition relationship between the liquid bridge force and the shear mixing action.

Properties of Ceramic Coating on Heating Surface of Waste Incineration Boiler Prepared by Slurry Method.

In order to alleviate the problem of high-temperature fly ash corrosion and slag on the heating surface of a high-parameter waste incinerator, a ceramic coating material that can be prepared in situ on the heating surface by the slurry method was studied. The ceramic coating can be formed by sintering at a lower temperature of 750 °C. Its surface and profile are very dense, and the porosity is less than 1%. The mechanical properties test results show that the ceramic coating can withstand 60 cycles of water-cooled thermal shock at 700 °C, and the bonding strength is 25.14 ± 2.21 MPa. It will not fall off in a large area when subjected to pressure load, and it has a certain degree of processable plasticity. High-temperature wettability experiments show that the ceramic coating has lower liquid-bridge force, smaller adhesion area, and shorter fouling cycle for molten corrosive fouling, and potential self-cleaning properties. Its practical mechanical properties make the coating valuable for production applications and meet expectations, and excellent antifouling properties to reduce average fouling thermal resistance and corrosion.

Mathematical study on gravity effect of the liquid bridge between two rigid spheres

To better understand how gravity affects the evolution of capillary force and meniscus shape of the vertical liquid bridge between two millimeter-size spheres, an explicit mathematical model was built using Surface Evolver software. In this study, the rupture behavior of liquid bridge in the equilibrium state was studied using the energy minimization method, and the validity of the mathematical method followed was verified by comparing with existing research results. In addition, the gravity effect on the meniscus shape and geometric parameters were systematically studied. Finally, the gravity effect on the residual liquid volume after the liquid bridge ruptures was examined, and a calculation method for the residual liquid volume on the sphere was proposed, which was proven by mathematical methods and experiments. The relative error was <16% when the liquid dripping error was neglected, proving the feasibility of the calculation method.

Geometric similarity on interparticle force evaluation for scaled-up DEM particles

The scaled-up particle model, which is also commonly known as the coarse grain model or discrete parcel model, is frequently used to reduce the computational cost in Discrete Element Method (DEM). In the direct force scaling approach, the forces acting on original particles are first estimated and then directly scaled to apply to scaled-up particles. It is therefore crucial to appropriately evaluate the variables of the original particles, e.g. overlap and separation distance, from the scaled-up particles particularly when estimating complex interparticle forces. The present work proposes the use of geometric similarity for the evaluation of the original particle overlap and separation distance. It is demonstrated that the proposed method can provide an almost identical stress-strain curve between the original and scaled-up particles during uniaxial compression of a packed particle bed, whilst the conventional method in the literature gives significant overestimation of the stress. In addition, the scaled-up particles can reasonably replicate the original velocity distributions of cohesive particles with both liquid bridge and JKR surface adhesion forces in a dynamic flow system (vertical mixer). The simulation results suggest that the method proposed can be applied to any type of interparticle forces. A scaling of time step limit is also derived theoretically and discussed.

Investigation of agglomerating and wetting behaviour during coal dust suppression via the synergistic application of hydrocarbon and short-chain-fluorocarbon surfactants in the presence of electrolytes

This paper investigated the agglomerating and wetting behaviour during coal dust suppression via the synergistic application of hydrocarbon and short-chain-fluorocarbon surfactants in the presence of electrolytes. A maximum 51.01% and 53.12% reduction in surface tension is achieved after compounding FS-50 and FS-3100 with SDBS and FMEE. Short-chain fluorocarbon surfactants reduced the immersing time of coal particles from maximum 637.03 s to minimum 28.06 s, and further diminished to 9.33 s in the presence of electrolytes. The addition of short-chain fluorocarbon and electrolytes can significantly promote the agglomeration behaviour among treated coal particles. After the addition of NaCl and NaAc, the maximum dust suppression rate reaches 95.12%, which is 1.21–1.33 times of binary surfactants and 1.59–2.01 times of the solely application of hydrocarbon ones. The agglomerating behaviour is more sufficient in predicting the dust suppression rate. The larger the coal particles, the higher liquid bridge force and stronger agglomerated coal particle clusters.

Experimental Study on Fluidization Behaviors of Wet Rice Threshed Materials with Hot Airflow

Among food crops, rice has the largest planting area, the highest yield per unit area and the largest total yield in China. However, cleaning performance is reduced by the high moisture content of rice during the harvesting process. In order to decrease the adhesion among wet rice threshed mixtures and improve the cleaning performance, the method of hot airflow cleaning was proposed. Firstly, the fluidization characteristics of wet sticky rice under the action of hot air were compared with those of dry particles. In this work, the minimum suspension velocity and the fastest suspension time were used and quantified to characterize the fluidization characteristics. It was found that the minimum suspension velocity and the fastest suspension time of the wet rice threshed mixture are both higher than those of dry particles due to the liquid bridge force. Moreover, the dispersion degree of the wet rice threshed mixture can be improved by the hot airflow due to the decrease in the surface water content of impurities. Secondly, the influence of the temperature and vibration frequency in the air-and-screen cleaning device on the dispersion characteristics of the wet rice threshed mixture were investigated. The accumulation mass was measured to quantify the dispersion degree. It was found that the increase in vibration frequency has little effect on the dispersion of the wet rice threshed mixture. The accumulation mass on the front of the sieve decreases slightly with the increase in the gas temperature range from ambient temperature to 30 °C. Then, the dispersion degree increases rapidly when the temperature exceeds 40 °C. The dispersion effect is the best when the temperature is 50 °C and the vibration frequency is 5 Hz. These results provide a basis for the cleaning of the wet rice threshed mixture in a combine harvester.

CFD–DEM simulation of wet granular-fluid flows and heat transfer in an integral multi-jet spout-fluidized bed

The hydrodynamic and heat transfer characteristics of dry and wet particles in quasi-two-dimensional integral multi-jet spout-fluidized bed (IMJSFB) and conventional spouted bed (CSB) were numerically studied using Computational Fluid Dynamics-Discrete Element Method (CFD-DEM), where the effect of wet content of particles is realized by introducing the liquid bridge force. In addition, the agglomeration, particle mixing, circulation, collision and heat transfer of IMJSFB and CSB under different moisture content were quantitatively studied. It is found that with the increase of gas velocity, the circulation capacity of particles in both spouted beds increases first and then decreases, and particle circulation characteristics of IMJSFB are obviously better than those of CSB. The appropriate moisture content of particles is beneficial to enhance the heat transfer effect, and compared with CSB, IMJSSFB has more obvious advantages in dealing with wet particles. This study has important significance for the mixing and heat transfer of class D wet particles, which is less studied in fluidization technology, and provides theoretical and technical reference for the actual design and operation of spouted bed.

Controlling particle adhesion of synthetic and sewage sludge ashes in high temperature combustion using metal oxide nanoparticles

During combustion, ash particles can adhere to the internal walls of the plant due to partial melting and generate a liquid bridge force at the high operating temperatures. The adhered ashes inhibit energy recovery and stable operation of the plant. To achieve highly efficient energy recovery during combustion, it is necessary to investigate suitable methods to control adhesiveness according to each operational case. Herein, the ability of small amount (1–3 wt%) of nanoparticles (NPs: SiO2 NPs, Al2O3 NPs, and Fe3O4 NPs) as additives to control the adhesiveness at high temperatures was investigated. The controllability of each type of NP with respect to the adhesiveness of various synthetic ashes, which served as model compounds, was evaluated to clarify the role played by the different NPs. To demonstrate the practical utility of the NPs as additives, ash samples derived from the incineration of sewage sludge were investigated. Given the chemical complexity of the ash systems, it was discovered that a chemical effect and an increase in the porosity of the powder bed can effectively decrease the adhesiveness of ash particles produced at high temperatures.

Liquid component effect on the dispersion and explosion characteristics of solid-liquid mixed fuel

The adhesion of liquid fuel is an important factor hindering the disengagement of solid fuel particles. And the liquid component characteristics of mixed fuel also have a significant impact on the final combustion and explosion reaction result. The liquid bridge force was detected by a self-assembled device. And the influence of the liquid fuel on the dispersion and explosion characteristics of solid–liquid fuel (nitromethane-diethyl ether-aluminum) was investigated by a laser particle size analyzer and a 20 L explosion vessel. The liquid bridge force result from the liquid fuel decreases with decreasing surface tension and liquid fuel volume effectively reduce the hindering of liquid adhesion on dispersion. And the increase in spray pressure also alleviate fuel agglomeration. The smaller the fuel particle size, the higher the explosive overpressure and the (dp/dt) max. Effectively coping with the impact of the liquid fuel adhesion on fuel dispersion could significantly accelerate the fuel reaction rate and promote energy transfer.

Liquid bridges between particles and the hydrophobic or hydrophilic surfaces of solar photovoltaic glass

Photovoltaic (PV) power generation technology is one of the most important methods for reaching the carbon peak and achieving carbon neutralization. Dust accumulation on the surface of PV glass greatly reduces the working performance and power generation efficiency of PVs. The hydrophobic or hydrophilic surfaces on the PV glass have substantial self-cleaning potential. In this study, the liquid bridges formed between particles and the hydrophobic or hydrophilic surfaces of solar PV glass are investigated. The effects of the liquid bridge force and the influencing factors for these two surfaces on particle dynamics behaviours are studied. Furthermore, the self-cleaning abilities of these two surfaces are also discussed. The results indicate that the liquid bridges formed between a particle and a hydrophilic PV glass placed horizontally or obliquely exhibit similar saddle shapes, but the liquid bridges wrap the particle on the surface of hydrophobic PV glass. The influence of the liquid bridges causes particles to adhere to the tilted hydrophilic or hydrophobic surfaces at liquid bridge volumes (VL) < 6 μL, making initially moving particles stay on these two tilted surfaces with 6 μL ≤ VL ≤ 20 μL and even achieving self-cleaning properties at VL > 20 μL. Both hydrophobic and hydrophilic surfaces increase the self-cleaning forces resulting from the liquid bridge formation with increasing VL, thus completing the self-cleaning process. Increasing the self-cleaning forces and decreasing the friction force and the liquid bridge force improves the self-cleaning abilities of the surface. These research findings have important theoretical significance and commercial engineering value in preventing and reducing dust accumulation on glass.

Influence mechanism of liquid bridge evaporation on the dynamic behaviour of dust particles on solar photovoltaic panels

Solar photovoltaics (PVs) are one of the most promising renewable energy sources to solve the global environmental and energy crises. Dust agglomeration on PV panels greatly affects their operation life and power generation efficiency. In this study, the evaporation mechanism and laws of liquid bridges as well as the evaporation time and interaction forces for liquid bridges and particles are investigated. The effects of liquid bridge evaporation and its influencing factors on dust dynamic behaviour are discussed. Liquid bridge evaporation in the muddy state with small particle spacing can cause particle agglomeration on PV panels. However, it is very difficult for the capillary, the ribbon, and the pendulum states or the muddy state with large particle spacing to affect particle motion. In the muddy state, the interaction force for a small particle spacing consists of not only the liquid bridge force but also the drag force caused by liquid bridge evaporation, and that for a large particle spacing consists of only the drag force; in the other three states, the interaction force consists of only the liquid bridge force. Liquid bridge evaporation can greatly intensify particle agglomeration and even scaling processes with decreasing particle size. These findings can provide important theoretical guidance and value for engineering improvements in power generation and safe operation of PV panels.

Influence of H2O and SO3 on fine particles coagulation for sintering flue gas after desulfurization in an alternating electric field.

Electric coagulation of fine particles has been studied in the simulated sintering flue gas after semi-dry desulfurization to quantify the influence of H2O and SO3. The electric coagulation platform has a DC charging zone and an AC coagulation zone. Fine particles were divided into different diameter intervals to deeply explore the impact of H2O and SO3, including less than 0.15μm (PM0.15), 0.15-0.5μm (PM0.15-0.5) and 0.5-1μm (PM0.5-1). The particle charge, mass fractions of fine particles, and the mean diameter are measured and compared under water and SO3 atmosphere. The experiments showed that the increasing AC voltage helps particles larger than 0.5μm to coagulate but has little effect on the rest particles without H2O or SO3. Both H2O and SO3 enhance the PM1.0 AC coagulation. When flue gas relative humidity went up from 20 to 80%, the charge per particle maximally increased by 120%, as well as the mass fraction of PM0.5-1, PM0.15-0.5, and PM0.15 decreased by 83.2%, 64.5%, and 66.6%, respectively. When the SO3 concentration rose up from 0ppm to 12.3ppm, the charge per particle maximally increased by 100%, as well as the mass fractions of PM0.5-1, PM0.15-0.5, and PM0.15 decreased by 54.5%, 28.6%, and 33.3%, respectively. The impact of water and sulfuric mist on the particle intervals was sequenced as: PM0.5-1 > PM0.15 > PM0.15-0.5. The influence on PM1.0 AC coagulation was sequenced as H2O > sulfuric mist > AC voltage. Through data regression, H2O had approximate linear correlation with the particle mass fractions while the impact of sulfuric mist was non-linear. The interparticle forces were calculated to analyze the dominant force of particle AC coagulation with water: liquid bridge force > Coulomb force > > van der Waals force. The liquid bridge force indicated that liquid film was form on the surface of fine particles when water or sulfuric mist was added into the system which was the main reason enhancing the AC coagulation.

Experimental study on bulk modulus and dissipation of dry and wet granular samples under vertical vibration

Dry granular materials are composed of a dense random packing of macroscopic grains. As a small amount of liquid is added to granular samples, the liquid bridge forces, i.e. the forces between liquid and the grains, have an influence on the mechanical properties of wet granular material, and some of these properties are quite different from those of dry granular materials. In this work, by measuring the acceleration of the sample chamber and the force exerted on it by the shaker, the variations of bulk modulus and energy dissipation of both dry and wet glass bead samples with pressure and viscosity under vertical vibration are studied. The results are shown below. 1) Under low saturation, the bulk modulus of dry and wet glass bead sample are both described by a power law scaling law with pressure, which is close to the power law relationship predicted by the efficient medium theory on the basis of Hertz contact potential. A small amount of liquid can increase the bulk modulus of glass bead sample. At the same pressure and liquid content, the bulk modulus of wet glass bead sample increases with liquid viscosity increasing. Based on Hertzian contact mechanics, an efficient elastic network model is proposed to illustrate the mechanism of increasing bulk modulus of wet glass bead samples. 2) The energy dissipation of dry and wet glass bead sample decrease following the power law of pressure, and the energy dissipation of wet glass bead samples is proportional to the kinematic viscosity of liquid. 3) With the increase of strain amplitude, the softening behavior of the wet glass bead sample is similar to that of the dry glass bead sample, when the strain amplitude is higher than the strain threshold value. The kinematic viscosity of liquid inhibits the softening behavior of glass bead sample.

Effects of Time-Varying Liquid Bridge Forces on Rheological Properties and Resulting Extrudability and Constructability of 3d Printing Concrete

Effects of Time-Varying Liquid Bridge Forces on Rheological Properties and Resulting Extrudability and Constructability of 3d Printing Concrete