Liquid Bridge Force Research Articles

The simplification and analytical verification of the static liquid bridge force model for particle adhesion in inferior seedling substrates

This study examines the adhesion mechanism in varying water contents of inferior seedling substrate blocks, focusing on the adhesion between particles‒particles and particles‒wall of the seedling tray. A simplified static liquid bridge force model based on the Young–Laplace equation is proposed. The correlation between the liquid bridge force and volume is derived and validated against existing experimental. The results indicate that the static liquid bridge force between particles decreases as the distance increases. A critical distance region is identified, where below this distance, a smaller liquid bridge volume results in a greater static liquid bridge force, and beyond this, the trend reverses, except when the solid–liquid contact angle is 50°. Additionally, the solid‒liquid contact angle has a minimal influence on the liquid bridge force between the particles and the inner sidewall of the seedling tray. This study also analyses the change in critical rupture distance during the transition of liquid bridges from pendulum to ring rope type, and this change increases with the liquid bridge volume.

Understanding particle adhesion of sewage sludge incineration ash at high temperatures: Effect of physical characteristics

Ash particle adhesion at high temperatures in thermochemical processes is a serious problem, and adhered ashes cause operational problems for processing plants, resulting in inefficient and unstable operation. A major mechanism of adhesion is the formation of a liquid phase due to melting of the ash components with low melting points, which results in a liquid bridge force, which is an attractive force. Therefore, the chemical characteristics of the ashes have been carefully studied to understand the adhesion phenomenon. However, each ash is also characterized by its physical properties such as particle size and packing ability. In this study, we focused on the physical characteristics of sewage sludge incinerated ashes collected from commercial incineration plants and carefully examined their relationship to adhesion. We found good correlations between particle size or porosity of the powder bed and adhesiveness at both ambient temperature and 800 °C. Understanding particle adhesion based on physical characteristics is simpler than considering complicated chemical characteristics and is useful for predicting particle adhesion at high temperatures.

An investigation of the filtration performance and mechanism of oil-solid mixed particles on filter materials with different wettability

In the process of air filtration, filter materials may encounter oil-solid mixed particles from various sources such as industry and household, and the influence of filter material with different wettability on the filtration performance of oil-solid mixed particles has not been fully reported. The objective of this study was to prepare filter materials with varying wettability properties and investigate their filtration performance for oil-solid mixed particles with diverse oil contents. In this study, four filter materials were prepared using the impregnation method, exhibiting 0° (superoleophilic), 46° (oleophilic), 90° and 122° (oleophobic) oil contact angles. The oil-solid mixed particles with varying oil contents were loaded on the four different filter materials. The loading behavior of the filter materials was characterized from two aspects: macroscopic loading behavior (changes in pressure drop and DHC) and microscopic particle deposition behavior. The results demonstrated that, under the conditions of 25% and 50% oil content, the enhanced liquid bridge force between the oil-solid mixed particles on the oleophobic filter material facilitated the formation of a loose and porous cake layer structure compared with other filter materials, resulting in a lower growth rate of pressure drop and a higher dust holding capacity (DHC). However, in 75% and 100% oil content environments, the superoleophilic filter material owned a remarkably high affinity for oil particles compared with other filter materials, leading to the gradual formation of an oil film structure on the filter material, yielding lower the growth rate of pressure drop and higher DHC. These findings shed light on the mechanism of particle deposition under diverse filtration conditions and are applicable to the filtration of various oil-solid mixed particles over a wide range of oil contents.

Effect of Temperature on the Liquid Bridging Force while Maintaining Physical Stability in Solid-Liquid Mixed Fuel.

The temperature factor is an important factor affecting the intercomponent forces while maintaining the physical stability of solid-liquid mixed fuels. Through self-designed experimental equipment, feedback was provided on the fuel stratification and density distribution uniformity with solid-liquid volume ratios of 1.25:1 and 1:1 under different temperature conditions. As the viscosity of the liquid increased with decreasing temperature, the ability of the fuel to overcome particle deposition was enhanced. Although none of the three fuel ratios with a solid-liquid volume ratio of 1.25:1 showed stratification, the differences in the liquid bridging forces of the components resulted in an increasingly uneven distribution of density with increasing surface tension of the liquid components. By analyzing the imaging results and measuring the liquid bridge force, it was found that the fuel with a nitromethane mass ratio of 40% had the lowest temperature effect on the solid-liquid contact area and the most uniform density distribution. Properly reducing the surface tension of liquid components could effectively resist the influence of the temperature on the liquid bridge force while maintaining the physical stability of the fuel.

Cohesive particle–fluid systems: An overview of their CFD simulation

AbstractSolid particles may experience different kinds of cohesive forces, which cause them to form agglomerates and affect their flow in multiphase systems. When such systems are simulated through computational fluid dynamics (CFD) programs, appropriate modelling tools must be included to reproduce this feature. In this review, these strategies are addressed for various systems and scales. After an introduction of the different forces (van der Waals, electrostatic, liquid bridge forces, etc.), the modelling approaches are categorized under three methodologies. For diluted slurries of very fine particles, many researchers succeeded with pseudo‐single phase approaches, employing a model for the non‐Newtonian rheology. This was especially popular for sludges in anaerobic digestions or certain types of soils. In other cases, continuum‐based approaches seem to be more adequate, including cohesiveness in the kinetic theory of granular flows or the restitution coefficient. Geldart‐A particles experiencing van der Waals forces are the primary focus of such studies. Finally, when each particle is modelled as a discrete element, the cohesive force can be directly specified; this is especially widespread for the wet fluidization case. For each of these approaches, a general overview of the main strategies, achievements, and limits is provided.

The interactive force between fat, oil, and grease (FOG) deposits and the effect of food waste disposers on kitchen drainage systems

Food waste disposers (FWDs) streamline kitchen waste management and facilitate waste classification, whether they would increase the potential of blockage in kitchen drainage system is still unknown. This study conducted a theoretical analysis of the interactive forces between fat, oil, and grease (FOG) deposits and their aggregation on pipe walls. The study involved grading food waste particles processed by FWDs using sieving and weighing techniques to determine the mean weight diameter (MWD) of various aggregations. A full-scale experimental system, implemented in a 60-m high test tower, simulated blockages in horizontal pipes of high-rise buildings. The effect of pipeline materials and particle sizes on blockage were examined by measuring the adhesion of deposits on horizontal pipes. Energy dispersive spectrometer (EDS) analysis suggested that liquid bridge force is a primary factor in aggregate formation. Hand-cut particles formed aggregates with the highest MWD value. Particle size analysis revealed that sizes ranging from 2.36 to 4.75 mm, 1.18–2.36 mm, and 0.60–1.18 mm constituted over 80 % of particles ground by FWDs, with an average size of 2.16 mm. Results of full-scale experiment indicate particle diameters, friction coefficients and lipophilic coefficient significantly affected the propensity of these aggregates to adhere to pipes. Notably, particles processed by FWDs tended to cause blockages more frequently than hand-cut particles. These findings elucidate the deposition mechanism of FOG deposits and offer strategies to reduce blockages in kitchen drainage systems, such as reducing current grinding particle size by 18 % to 1.77 mm or selecting pipes like cast iron and high-density polyethylene.

Numerical Study on Effect of Aggregate Moisture on Mixing Process.

During the concrete mixing process, the transition of aggregates from a dry to a moist state introduces a crucial dynamic that significantly influences particle interaction, consequently impacting mixing homogeneity. In this paper, based on the discrete element method, the effect of aggregate moisture on the mixing process of sand and stone was investigated. The interaction between dry particles was described by the Hertz-Mindlin model, while the interaction between wet particles was calculated by the linear cohesion model considering the liquid bridge force. Additionally, a functional relationship between the moisture content and the parameters of the linear cohesive contact model was established. The results show that the numerical method can be employed to simulate the mixing process. Notably, when the moisture content of pebbles ranges from 0% to 0.75% and that of sand ranges from 0% to 10.9%, the linear cohesion model is deemed suitable. The standard deviation of the mixing homogeneity of wet particles is lower than that of dry particles for short mixing time, indicating that a small amount of liquid enhances mixing homogeneity. However, moisture has no obvious effect on mixing homogeneity for a long mixing time. This nuanced understanding of the interplay between moisture, particle interactions, and mixing duration contributes valuable insights to optimize concrete mixing processes.

Investigation on tillage resistance and soil disturbance in wet adhesive soil using discrete element method with three-layer soil-plough coupling model

To reveal the interaction between plough and wet adhesive soil, it's essential to establish an accurate coupling model of the soil-plough system. Traditional Edinburgh elasto-plastic adhesive contact model neglects the adhesion effect when two interactive particles are separated, leading to lower simulation accuracy. Here, an improved contact model of wet adhesive soil by introducing the adhesive force is proposed. Then a novel discrete element model of a three-layer soil-plough coupling system is established, where the liquid bridge force and the adhesion effect are considered. Furthermore, the corresponding soil bin tests are also conducted to demonstrate the effectiveness of the proposed model. Finally, the effect of soil adhesion, ploughing speeds and ploughing depths on the tillage resistance and soil disturbance is analyzed. Results show that the prediction accuracy of the proposed model increases by about 7%, moreover, the soil disturbed area decreases, while the tillage resistance increases with increasing soil adhesion.

The role of adding nanoparticles and surfactant to the enzyme liquid binder in fluidized bed granulation process

The influence of enzyme liquid binder properties on wet granulation process was evaluated at both micro- and macro-scales. The micro-scale phenomena, including binder droplet spreading on and penetration into the powder bed, as well as liquid bridge shape and force, were analyzed by introducing SiO2 nanoparticles and SDS surfactant into the liquid binder containing a protease enzyme and 1 wt% of NaCMC. Moreover, the simultaneous effect of formulation variables, including NPs and SDS concentrations, and process conditions, such as binder spray rate and air temperature, was investigated using design of experiments. The average size and the span were considered as the responses. Nanofluid binder without SDS exhibited lower spreading and penetration times and a stronger bridge force. All formulation and process factors significantly influenced granule size distribution. Notably, increasing nanoparticle concentration and binder flow rate, while decreasing SDS concentration and air temperature, resulted in larger granules and a narrower size distribution.

Clay minerals separation in soft rock driven by the liquid bridge force during water–rock interaction

Clay minerals separation in soft rock driven by the liquid bridge force during water–rock interaction

A machine learning model of liquid bridge force and its application in discrete element method

Developing an accurate and efficient contact model for discrete element method (DEM) simulation that can describe the microscopic dynamics of low moisture content wet granular systems continues to be a major challenge. In this study, a improved energetic approach based on the traditional linear unit discretization method is introduced to solve liquid bridge problems. This improved approach significantly ameliorates the efficiency of constructing the databases while ensuring high data accuracy. Using this method, we generated databases consisting of 163,440,000 and 2043,000 data points for the sphere-sphere and sphere-wall systems, respectively. Machine learning capillary force models (ML-Capillary) are trained using the Catboost algorithm. These models demonstrate excellent performance in predicting capillary force between particles as well as between particles and walls, considering different particle sizes, moisture levels, and contact angles, while neglecting the influence of gravity. The corresponding relative errors are below 1.5% and 2%, respectively, which are lower than existing simulation models. We incorporated the obtained models into the discrete element method and calculated capillary force between particle pairs and simulated wet granular column collapse tests. The simulation results show good agreement with experimental results in terms of parameters such as inter-particle capillary forces and particle column collapse run-out length. This study will provide an accurate and efficient numerical model for simulating low saturation wet granular systems using the discrete element method.

Importance of liquid bridge forces in dynamics of rock-ice avalanches: insights from discrete element simulations

Rock-ice avalanches imminently threaten high-mountain and glacierized regions. The wet rock-ice particle flow exhibits dependence on pendular liquid bridges; however, its mechanisms are unclear. This paper focuses on the influence of interstitial water in the pendular regime on the dynamics of rock-ice avalanches. A scheme was proposed to incorporate capillary and viscous liquid bridge forces into the discrete element method (DEM) for simulating the wet rock-ice particle flow. Numerical results indicate that the proposed scheme could well reproduce the key experimental outcomes of small flume tests. The liquid bridges could reduce the mixture mobility remarkably via pseudo-cohesion, which was mainly attributed to the capillary force. The pseudo-cohesion effect could alter the collision-dominant flow regime to the shear-dominant regime through buffering collisions and suppress the segregation through impeding the downward penetration of gravels. A very small amount of water, too little to form liquid bridges, could lubricate the sliding surface, and increase the mixture mobility. The role of the critical inter-element separation distance was deterministic in DEM for wet particles. This paper demonstrated the crucial impact of the liquid bridges in the dynamics of rock-ice avalanches and offered a promising scheme for deeply understanding the solid–liquid interactions in wet rock-ice avalanches.

Effects of time-varying liquid bridge forces on rheological properties, and resulting extrudability and constructability of three-dimensional printing mortar

Effects of time-varying liquid bridge forces on rheological properties, and resulting extrudability and constructability of three-dimensional printing mortar

Wet fluidization characterization of potash particles in a pulsation-assisted fluidized bed

In order to improve fluidization behavior, pulsed airflow was employed to break agglomeration and eliminate channeling in a fluidized bed with wet potash particles. The effects of pulsation frequency, pulsed air to continuous flow ratio (r), and inlet relative humidity of the air on bubbling behavior were investigated via an electrical capacitance tomography system. A frequency of 1.0 Hz and an r of 0.33 with 0.1 s opening time were found to be the optimum condition, leading to the lowest minimum fluidization velocity (umf) and generation of homogeneous bubbles in size and shape. A new theoretical model was developed to predict the umf of wet particles in a fluidized bed by considering both the liquid bridge force and resonant force resulting from the pulsation. Average absolute deviation percentage values between the predicted umf and the experimental data were 13.8 and 20.7 for the dry and wet particles, respectively, indicating good agreement.

Mechanisms of rheological modifiers for quick mixing method in 3D concrete printing

Quick mixing technology at the nozzle is a potential approach to avoiding the opposing requirements for pumpability and buildability and improving productivity in 3D concrete printing. However, the addition of rheological modifiers poses a challenge in quickly achieving a uniform mix while minimizing mixing energy. This study investigated two common rheological modifiers, including polymeric carboxymethylcellulose (CMC) and nano-clay. Their effects on the liquid bridge of mixing water and the mixing evolution and yield stress of concrete were investigated. Results show that the resistance of mixing concrete with CMC reduced with mixing time after a peak whereas that with nano-clay exhibited an opposite trend. An increase in modifier dosages enhanced the liquid bridge force and rupture energy, increasing mixing resistance; the CMC was more influential than nano-clay. Furthermore, the quick mixing method resulted in better dissolution (or dispersion) of these modifiers and higher yield stress but cost more mixing energy.

CFD-DEM investigation of the gas-solid flow characteristics in a fluidized bed dryer

Wet granules drying in a fluidized bed is a complex process and the process involves heat and mass transfer between gas and solid phases as well as the moisture changes in the granules. CFD-DEM model was employed to investigate the wet granule flow characteristics, the heat and mass transfer process in a fluidized bed drying process. The proposed model considered the liquid bridge force varying with granule moisture content and was validated by experimental data. Due to the computational capability restriction, pseudo 2D model simulations were first employed for the whole drying process and then 3D model simulations were performed at certain moisture contents to investigate the flow dynamics in more detail. The effects of granule number and the changing liquid bridge force on the drying process were further analyzed. Granule agglomeration was generated in the drying process at high moisture content due to the liquid bridge force, which affects the fluctuations of pressure and bed height. Moreover, the heat and mass exchange between the gas and solid phases mainly occurred in the interface of bubble phase and granule phase. With the increase of bed height, the granule volume fraction decreased and the transfer coefficients between these two phases decreased.

The effect of short-chain fluorocarbon and electrolyte on simultaneous dedusting and explosion prevention performance when applied to coal particle with high oil-content

The fully mechanized mining faces in underground oil-rich coal mines are exposed to the serious dust pollution and the high risk of dust explosion. Traditional materials cannot effectively realize the removal and inerting of coal particles with high oil content. Thus, this paper innovated new materials to eliminate the occupational disasters and explosion accident in underground coal mines by achieving simultaneous dedusting and explosion prevention of coal particles with high oil content. Compare with traditional materials, the presence of short-chain fluorocarbon surfactants and electrolytes achieved 76.30–84.92% improvement on dedusting rate, a maximum 22 times improvement on MIE, 4.20–8.90% improvement on MIT, and 50% improvement of MEC. Mechanism analysis revealed the better performance is attributed to the optimized wetting and agglomerating behaviour. Kinetic analysis showed that the new materials reduced the heat release and inhibit combustion process. The NaCl outperforms NaHCO3 in achieving better dedusting and explosion suppression performance in most cases for its higher TSI and more efficient explosion prevention mechanisms. Studies also demonstrated that the oil content could moderate the dedusting and explosion prevention performance due to the reduction of static liquid bridge force in terms of the increased proportion of saturated hydrocarbons and aromatic hydrocarbons, the reduced concentration of polar functional group, and the corresponding increased contact angle “θ”. The Findings of this paper provide an efficient and environmental-friendly choice for ensuring occupational health and safe production in underground oil-rich coal mines by achieving simultaneous dedusting and explosion prevention. It will also guide the innovation and development of multiple protective materials for coal mine safety protection.

A novel water film enhanced electrostatic agglomeration process to remove fine particles: performance and mechanism

Wet electrostatic agglomeration (WEA) is a very promising method in fine particle removal, however, it is still a challenging problem to avoid short-circuiting of the equipment caused by spraying water during traditional WEA. In this work, a novel WEA process based on a water film was established for the first time, and the fine particle removal and process mechanism were investigated. The influence of discharge and ground electrodes on the particle agglomeration performance was studied, indicating that a much better agglomeration performance was obtained by the spike plate (discharge electrode) thanks to the stronger electric field covering the entire agglomeration area. The corrosion-resistant and low-priced polyvinyl chloride (PVC) plate could significantly improve the water distribution effect after surface grooving modification, and its agglomeration as a grounding electrode under wet conditions was comparable to that of the wet metal plate. The mechanism of the water film enhanced WEA process lay in the fact that the high-voltage electric field greatly promotes the evaporation of the water film, which increased the humidity in the agglomeration space, resulting in liquid bridge force between the water-absorbing particles. In summary, this work provides an alternative novel idea for enhancing the agglomeration performance of the traditional WEA process.

CFD-DEM simulations of a gas-solid-liquid fluidization system: Effects on the flow field and particle behavior of semi-dry desulfurization fluidized bed

Gas-solid-liquid multiphase flow systems have been widely applied in energy engineering, petrochemical industries, biochemical industries and food industries, etc., which usually involve multi-physical processes and multi-reaction stages. As a typical gas-solid-liquid multiphase flow system, the semi-dry flue gas desulfurization fluidized bed has been widely applied by small and medium-scale thermal power plants for its advantages of excellent mixing effect, relatively high efficiency and low cost. This study focused on the fluid hydrodynamics, wet particle motions and the transfer efficiency (SO2 removal efficiency) in a fluidized bed via two-way coupled CFD-DEM numerical simulations with the implementation of different semi-dry desulfurization stages (“constant-rate” absorption stage, “falling-rate” absorption stage and solid absorption stage) as well as the liquid bridge force. To avoid the fast evaporation of small droplets, simulations based on larger particles (Geldart group D) were also conducted to clarify the influence of varying liquid volume contents. Results revealed that the existence of liquid layers would partly enhance the desulfurization efficiency, while in this case the bed exhibits poor fluidization characteristics. Adding humification water in the solid absorption stage would transform the reaction stage from solid absorption stage to “constant-rate” absorption stage, which improves the desulfurization efficiency significantly. It could also be summarized that the increase of Ca/S molar ratio would enhance the desulfurization efficiency partly, but the improvement would not be obvious when the Ca/S molar ratio is greater than a certain range.

Development of a High-Function Fiber Stylus for Microstructure Measurement with Water-Repellent and Antistatic Coatings

The precise measurement of microstructures and other micron-sized materials has garnered considerable interest in recent years. We have developed a measurement system that uses an etched small diameter optical fiber as a stylus to measure microstructures with low contact force. However, when the diameter of the stylus tip is less than a few tens of micrometers, the surface forces between the measured surface and the stylus tip become larger than the gravity of the stylus tip, causing the stylus tip to stick to the measured surface. This adhesion leads to an increase in measurement time and a decrease in measurement accuracy. In this study, we fabricated a high-function stylus with water-repellent and antistatic coatings applied to the stylus tip to reduce the adhesion between the stylus tip and measured surface due to surface forces, and conducted performance evaluation tests. As a result, the average separation distance was 13.8 µm when a fluorinated resin coating with a contact angle of 105° was used, confirming that the influence of liquid bridge forces could be reduced by approximately 78%. Additionally, when static elimination experiments were conducted by scanning the charged surface at a pitch of 0.5 µm using an antistatic coating stylus with a gold on the stylus surface, the average adsorption distance was 3.6 µm, confirming that the effect of electrostatic force could be reduced by 71%.