Sticky Wall Research Articles

Hydrothermal carbonization of sludge: Effect of steam release on products properties and wall sticking phenomenon

In order to understand hydrothermal carbonization (HTC) process more effectively, the effect of steam-release process at different temperatures (160, 180, 200, and 220 °C) on product properties and wall sticking phenomenon were studied. Experimental results indicated that the approximate equilibrium moisture content (AEMC) of hydrochar obtained with (SRHC) and without (HC) steam-release process were both negatively correlated with zeta potential (R = −0.96326 for HC and R = −0.95825 for SRHC). More importantly, the absolute value of the zeta potential of SRHC was lower than HC indicating steam-release process significantly improve dewatering performance of sludge after HTC treatment. The results of FE-SEM and N2 adsorption–desorption experiments indicated steam-release process was favorable for the formation of porous hydrochar. The variation of surface functional groups showed that the intensity of all peaks in SRHC was significantly lower than HC, indicating steam-release process which significantly affects surface chemical properties of samples. As for liquid, TOC, TN and COD value of the condensate were lower than filtrate, indicating steam-release process which produces “cleaner” condensed liquid with less organic matter content. The wall sticking phenomenon in the steam-release process became more severe with increasing temperature and the amount of sticky wall sample (SWS) increased from 0.392 g at 160 °C to 2.131 g at 220 °C, which indicated that temperature was key factor affecting the sticking phenomenon on the inside wall of the reactor. The contact angle of SWS and SRHC decreased from 60.083° and 77.283° at 160 °C to 51.317° and 67.967° at 220 °C, and the polar free energy of SWS (12.52–14.00 mN/m) was significantly higher than that of SRHC (1.85–4.53 mN/m), indicating increasing hydrophobicity and reducing polar free energy of sample were key factors in improving sticking phenomenon.

Metastability for expanding bubbles on a sticky substrate

We study the dynamical behavior of a one dimensional interface interacting with a sticky impenetrable substrate or wall. The interface is subject to two effects going in opposite directions. Contacts between the interface and the substrate are given an energetic bonus while an external force with constant intensity pulls the interface away from the wall. Our interface is modeled by the graph of a one-dimensional nearest-neighbor path on Z+, starting at 0 and ending at 0 after 2N steps, with the wall being the horizontal axis. At equilibrium each path ξ=(ξx)x=02N is given a probability proportional to λH(ξ)exp(σNA(ξ)), where H(ξ):=#{x:ξx=0} and A(ξ) is the area enclosed between the path ξ and the x-axis. We then consider the classical heat-bath dynamics which equilibrates the value of each ξx at a constant rate via corner-flip. Investigating the statics of the model, we derive the full phase diagram in λ and σ of this model, and identify the critical line which separates a localized phase where the pinning force sticks the interface to the wall and a delocalized one, for which the external force stabilizes ξ around a deterministic shape at a macroscopic distance of the wall. On the dynamical side, we identify a second critical line, which separates a rapidly mixing phase (for which the system mixes in polynomial time) to a slow phase where the mixing time grows exponentially. In this slowly mixing regime, we obtain a sharp estimate of the mixing time on the log scale, and provide evidences of a metastable behavior.

Research on atomization evaporation characteristics and parameter optimization of a novel spray evaporation desalting system

Rotary spray evaporation technology has received particular attention due to its superiority in high-salinity wastewater's zero liquid discharge (ZLD). This research develops a new type of high-efficiency and low-energy-consumption rotary spray evaporation tower. The effects of atomization speed, feed flow, feed liquid concentration, hot air temperature, and hot air velocity on high-salinity wastewater's atomization and evaporation characteristics were studied. The numerical results show that the atomization speed can reduce the droplet spraying to the tower wall to reduce the sticky wall phenomenon and prolong the droplet residence time to increase the evaporation rate. By controlling the atomization speed, feed flow, and feed concentration, the droplet SMD can be reduced by 6.0 % to 37.3 % so that the droplets are evenly dispersed. With reasonable hot air temperature and speed, the outlet temperature drops by 19.1 % to 29.0 %, and the evaporation rate increases by 8.7 % to 11.8 %. The optimal working conditions are 16,000 r/min atomization disk speed, 10 kg/h feed flow, 433 K hot air temperature, 10 m/s hot air flow rate, and 93.2 % evaporation rate at this time. The results show that the rotary spray evaporation technology can be a powerful means of ZLD of high-salinity wastewater.

One-dimensional Coulomb system in a sticky wall confinement: Exact results.

This work investigates a one-component one-dimensional Coulomb system in sticky wall confinement. Sticky wall is introduced as an alternative and intuitive depiction of charge regulation, the notion that a surface charge is not a fixed but a fluctuating quantity in dynamic equilibrium with its immediate environment. Emphasis is placed on intuitive derivation and expressions are obtained by observing that the partition function of a charge regulated system can be decomposed into a collection of independent equilibriums with different fixed surface charges. Adsorbed particles behave as ideal-gas particles in a one-dimensional box whose length corresponds to the parameter of stickiness. Among various scenarios considered are a single- and two-wall confinement as well as the case of sticky counterions capable of associating into pairs. Exact solutions provide a view of the role and behavior of surface charge fluctuations, which is an important step in the "beyond-mean-field" analysis. Consequently, the model serves as a simple paradigm of the mechanism that gives rise to the Kirkwood-Shumaker interactions detected in real systems.

Particles in a Box with One Sticky Wall: From ODE to PDE

We present noncompetitive adsorption as “particles in a box with one sticky wall.” We start with a general model that can be modeled as a simple ordinary differential equation (ODE). To verify the ODE students run a computer simulation. The ODE’s solution imperfectly fits the simulation’s data. This leads to the diffusion partial differential equation. We show how to determine the diffusion constant from theory; how to determine how many terms in the Fourier series solution need to be summed; and the use of nonlinear regression. As a bonus, the physics of the model will lead us to a series representation of π.

Flocking Behaviors of a Cucker--Smale Ensemble in a Cylindrical Domain

We study the Cucker--Smale (C-S) type model in a cylindrical domain with a specular reflection boundary condition. When there exist flocking forces along the normal direction to the boundary, then a “sticky wall" effect is numerically observed such that particles aggregate in a region near the wall of a cylinder. To avoid this sticky wall phenomenon, we adopt a flow-directional flocking force which has no force component normal to the boundary. As a result, we obtain the flocking behavior of particles along the flow direction. Moreover, the emergence of flocking also holds for the corresponding kinetic C-S model. We present a global existence of the classical solution to the kinetic C-S model with the specular reflection boundary condition. In addition, we perform numerical simulations for the particle and kinetic C-S models to demonstrate the aggregation behavior of flocking particles interacting with the boundary.

Correlation between chemical compositions of traditional Chinese medicine extracts and phenomenon of wall stickiness in spray drying

To explore the correlation between chemical compositions (organic acids, small molecule sugars, protein and others) of traditional Chinese medicine extracts and the wall stickiness in spray drying. In this study, 55 types of most common used Chinese herbs were selected to determine the content of 7 chemical components such as citric acid and fructose from plant extraction. The status of wall stickiness was observed during the drying process. The principle component analysis (PCA-X), hierarchical clustering analysis(HCA) and orthogonal partial least squares-discriminant analysis (OPLS-DA) were then used to evaluate the correlation between each chemical compositions and wall stickiness, so as to look for the essential chemical compositions associated with the wall stickiness. All of the above 3 statistical analysis methods showed significant results in distinguishing the two groups (sticky or non-sticky). PCA-X score chart and HCA clustering scatter plot suggested that the small molecular substance was the main factor causing wall stickiness, which was then proved by the reality where some of the traditional herb extracts were in non-sticky state after drying but in sticky state after alcohol precipitation. OPLS-DA results revealed that L-malic acid, citric acid, fructose and glucose were the difference factors for the wall stickiness of the extracts. Under small molecular components, L-malic acid, citric acid, fructose and glucose were the crucial factors that directly led to the hot melt sticky wall of the herbal extracts, and macromolecular substances might ameliorate the function of wall stickiness.

Wall effects in entrained particle-laden flows: The role of particle stickiness on solid segregation and build-up of wall deposits

Particle–wall interaction is relevant to the performance of entrained-flow slagging gasifiers. Different micromechanical char–slag interaction patterns may establish, depending on the stickiness of the wall layer and of the impinging char particle. The main goal of this study is to improve the mechanistic understanding of particle–wall interactions, by using the tool of physical modeling. The idea behind this research campaign is to use molten wax as a surrogate of fuel ash. The wax had rheological/mechanical properties resembling those of a typical coal slag. Experiments have been carried out in a 0.10m-ID lab-scale cold entrained-flow reactor, optically accessible, and equipped with a nozzle whence molten wax atomized into a mainstream of air. Reactor lengths in the range 0.1–0.6m were investigated, while the wax was atomized at a temperature of 100–110°C. Two interaction regimes were investigated: the “sticky wall–sticky particle” regime was simulated by setting the air mainstream and the wall temperatures at values beyond the wax melting range (160°C and 140°C, respectively); the “nonsticky wall–nonsticky particle” regime was simulated by setting both temperatures at 30°C, i.e. well below the wax softening range. Assessment of the flow and segregation patterns was based on direct visual observation by means of a progressive scan CCD video camera, while the partitioning of the wax droplets into the different phases was characterized by their selective collection at the reactor exhaust. The micromechanics of particle–wall interactions in the “nonsticky–nonsticky” regime was analyzed on the basis of particle impact and of hydrodynamics of gas mainstream and jet flows. Threshold gas velocities for particle detachment were evaluated for the characterization of particle resuspension phenomena.

An exact solution of two friendly interacting directed walks near a sticky wall

We find the exact solution of two interacting friendly directed walks (modelling polymers) on the square lattice. These walks are confined to the quarter plane by a horizontal attractive surface, to capture the effects of DNA-denaturation and adsorption. We find the solution to the model’s corresponding generating function by means of the obstinate kernel method. Specifically, we apply this technique in two different instances to establish partial solutions for two simplified generating functions of the same underlying model that ignore either surface or shared contacts. We then subsequently combine our two partial solutions to find the solution for the full generating function in terms of the two simpler variants. This expression guides our analysis of the model, where we find the system exhibits four phases, and proceed to delineate the full phase diagram, showing that all observed phase transitions are second-order.

A lab-scale cold flow model reactor to investigate near-wall particle segregation relevant to entrained-flow slagging coal gasifiers

This paper reports on preliminary results of an experimental investigation aimed at the development of a phenomenological model of the fate of coal/ash particles in entrained-flow slagging coal gasifiers. The study specifically addresses the interaction between the lean-dispersed particle phase and the reactor walls, and the establishment of a particle segregated phase in the near-wall region of the gasifier. Better mechanistic understanding of particle–wall interaction patterns in entrained-flow gasifiers is pursued using the tool of physical modeling. To this end a lab-scale cold flow reactor (0.04m-ID) has been designed and set up, where molten wax is air-atomized (droplets of 50–100μm size) into a mainstream of air to simulate the near-wall fate of char/ash particles in a real hot environment. Preliminary characterization of the hydrodynamics of the lean-dispersed phase, of its interaction with the wall, of the build-up of the liquid wall layer has been accomplished with a focus on the “sticky wall–sticky particle” subregime.The particle deposition rate at the wall and the partitioning of wax droplets between the lean-dispersed phase and the wall liquid layer have been assessed under a range of operating conditions. Temperatures of the atomized wax, of the mainstream air and of the reactor wall have been set in a range of values (120–155°C) at which the wax was fluid. Experiments with wax feeding rate of 0.2gs−1 and flow rate of atomizing air in the order of 0.30m3h−1 demonstrated that the fractional mass of wax in the dispersed phase decreased from 91% to 12% as the reactor length increased from 0.03m to 0.27m. The velocity of the descending wall liquid layer, whose thickness was in the order of 0.2mm, ranged between 3mms−1 and 6mms−1. The effects of the flow rate of atomization air and of the nozzle temperature were limited.

Pulling a polymer with anisotropic stiffness near a sticky wall

We solve exactly a two-dimensional partially directed walk model of a semi-flexible polymer that has one end tethered to a sticky wall, while a pulling force away from the adsorbing surface acts on the free end of the walk. This model generalizes a number of previously considered adsorption models by incorporating individual horizontal and vertical stiffness effects, in competition with a variable pulling angle. A solution to the corresponding generating function is found by means of the kernel method. While the phases and related phase transitions are similar in nature to those found previously the analysis of the model in terms of its physical variables highlights various novel structures in the shapes of the phase diagrams and related behaviour of the polymer. We review the results of previously considered sub-cases, augmenting these findings to include analysis with respect to the model’s physical variables—namely, temperature, pulling force, pulling angle away from the surface, stiffness strength and the ratio of vertical to horizontal stiffness potentials, with our subsequent analysis for the general model focusing on the effect that stiffness has on this pulling angle range. In analysing the model with stiffness we also pay special attention to the case where only vertical stiffness is included. The physical analysis of this case reveals behaviour more closely resembling that of an upward pulling force acting on a polymer than it does of a model where horizontal stiffness acts. The stiffness–temperature phase diagram exhibits re-entrance for low temperatures, previously only seen for three-dimensional or co-polymer models. For the most general model we delineate the shift in the physical behaviour as we change the ratio of vertical to horizontal stiffness between the horizontal-only and the vertical-only stiffness regimes. We find that a number of distinct physical characteristics will only be observed for a model where the vertical stiffness dominates the horizontal stiffness.

Exact solution of two friendly walks above a sticky wall with single and double interactions

We find, and analyse, the exact solution of two friendly directed walks, modelling polymers, which interact with a wall via contact interactions. We specifically consider two walks that begin and end together so as to imitate a polygon. We examine a general model in which a separate interaction parameter is assigned to configurations where both polymers touch the wall simultaneously, and investigate the effect this parameter has on the integrability of the problem. We find an exact solution of the generating function of the model, and provide a full analysis of the phase diagram that admits three phases with one first-order and two second-order transition lines between these phases. We argue that one physically realizable model would see two phase transitions as the temperature is lowered.

Study of the Desulfurization Process and Gas-Solid-Liquid Phase Distribution under the Complex Humidification Conditions in Dense Tower

In making the gas-solid-liquid phase analysis, based on the collaborative study of the internal and external humidification ratio of desulfurization efficiency, determine the humidifier ratio within 60% to 75%, that can make the best balance between the respective merits of a simple tower humidifiers tower humidifier way, optimizing the overall desulfurization reaction, effectively reducing the sticky wall, stick in the desulfurization efficiency and reduce the wall to achieve a balance between the balance, without increasing the sorbent and process water, under the premise can promote the desulfurization reaction, improve the desulfurization sorbent utilization and efficiency, help desulfurization reaction system is stable, efficient and economic operation, the gas-liquid-solid three-phase to achieve better synergy.

Modeling magnetic microcapsules that crawl in microchannels

Using computational modeling, we probe how to design microfluidic systems in which magnetic microcapsules could autonomously crawl along channel walls. The polymeric microcapsules are fluid-filled elastic shells with embedded superparamagnetic nanoparticles and, thereby, can be controlled by external magnetic fields. We show that when a magnetic force circulates normal to a sticky microchannel wall, capsules can propel in a steady, autonomous manner. The unidirectional capsule propulsion is facilitated by hydrodynamic interactions between the capsules and channel walls, and is most effective when the magnitudes of magnetic and adhesive forces are equal to each other. Furthermore, the propulsion efficiency is greater for compliant capsules. Our findings could be useful for designing novel microfluidic devices where mobile magnetic microcapsules could be harnessed as microscale transport vehicles.

Efficient Brownian dynamics simulation of particles near walls. II. Sticky walls.

In this paper we treat a boundary condition, the "sticky boundary," which appears to be quite useful in mesoscopic models. The sticky boundary is modeled as an infinitely deep, infinitely narrow, potential well adjacent to a reflecting boundary. The free energy corresponding to this boundary is finite. The boundary condition, which can be viewed as an intermediate between the absorbing and reflecting boundary condition, may have many applications, e.g., for the simulation of the partial adsorption of polymer molecules to walls and for the modeling of solvent quality. We will derive an efficient Brownian dynamics algorithm, capable of handling interactions of a diffusing particle with a sticky wall. Our approach avoids the large discretization errors that occur in the simulation of boundary interactions within the "standard" Brownian dynamics approach. The essence of our method was presented before [E. Peters and T. Barenbrug, Phys. Rev. E (to be published)]. The treatment of the wall as proposed here is quite general, and therefore not limited to the use within Brownian dynamics. In other simulation techniques which aim at treating the dynamics of mesoscopic particles near walls, we expect it to be of use as well.

Average diffusion-to-the-wall times for laser-tagged molecules in a long cylinder

An approximate closed-form expression is derived for the average wall-reaching rate kW or time τW=kW-1 of laser-tagged molecules diluted in an inert carrier gas migrating to the wall of a long cylinder where they are removed with sticking coefficient ηW. The exact equation for the sticky wall problem requires a trial-and-error solution of a transcendental relation with Bessel–functions. With the aid of the Fermi–Amaldi albedo theory, an explicit “compromise” relation is derived which approximates the exact diffusion curve of kW versus ηW rather well. The result is applied to obtain curves of kW versus ηW at different gas mix pressures for UF6 diluted in N2.

Appearance and interaction of pollen and pistil pathway proteins in Gasteria verrucosa (Mill.) H. Duval

Patterns of proteins excreted during pollen germination, of germinating pollen and of the stylar and placental fluids excreted by cells along the pistil pathway of Gasteria verrucosa were analyzed by electrophoresis. The medium from germinating pollen contains several pollen exudate proteins as well as glycoproteins from the sticky pollen wall coating. No protein could be detected in the stigmatic exudate. The stylar fluid shows a protein pattern different from that of the placental fluid. The placental fluid contains some glycoproteins. After pollination, three pollen proteins begin to appear in the stylar fluid. Two of these pollen proteins remain present in the placental fluid. Some placental fluid proteins and glycoproteins are modified after pollination. The difference in protein patterns demonstrates the heterogeneity of proteins in the pollen tube pathway and suggests that proteins excreted by the pollen tube interact with other proteins in the pistil pathway, especially those in the placental fluid.

The filtration characteristics of the aqueous outflow system

To determine the filtration characteristics of the aqueous outflow system, microspheres (0·18 μm–1·1 μm) were perfused through enucleated human and bovine eyes. The microspheres were smaller than morphologically determined flow dimensions, and yet a significant fraction of all sizes of microspheres were captured. The bovine (calf) aqueous outflow system was found to be a far more efficient filter than was the human outflow system. Combining the experimental results with morphological observations and theoretical calculations leads to the conclusion that ‘sticky wall’ interactions are responsible for much of the microsphere capture, and that the site of filtration may be distinct from the site of flow resistance. Consequently, the dimension of the sites generating flow resistance cannot be determined from filtration studies.

A numerical simulation of particle deposition in turbulent boundary layers

A Lagrangian random-walk approach to modeling particle deposition in turbulent duct flows is presented. The inhomogeneous boundary layer turbulence is simulated by a discrete eddy field, characterized by a random normal velocity (drawn from a Gaussian probability distribution) and a random time scale (drawn from an exponential probability distribution). A mean streamwise velocity profile is superposed upon the turbulence field using the law-of-the-wall relations. The turbulent r.m.s. velocity and time scale profiles are obtained from experimental data. The particle equations of motion include Stokes' drag and shear-induced (Saffman) lift. The equations are numerically solved for particle relaxation times ( τ + ) ranging from 0.3 to 1000 and particle-fluid density ratios of 500—5000. Approximately 500—10,000 particle trajectories are computed for each case, simulating particle deposition in pipe flow with a sticky wall. Deposition velocity predictions compare favorably with measurements, showing that inertial impaction is dominant at lower values. A predicted decrease in deposition velocity occurs for large particle. ( τ − > 30 ) due to reduction in particle fluctuating velocity. Shear-induced lift increases particle deposition rate, most significantly for 1 < τ + < 10 . Particle concentration profiles reveal that smaller particles (τ + < 10) tend to accumulate in the near-wall region due to the sudden damping of fluid turbulence. Predicted particle r.m.s. velocity profiles compare favorably with measurements, showing a decrease in magnitude with increasing inertia.

Localized adsorption at solid-liquid interfaces: the sticky site-hard wall model

The interface between a structured solid and a liquid is modelled by a flat surface with sticky sites placed on a regular lattice. It is shown that this three-dimensional adsorption model can be mapped into a two-dimensional lattice-gas model with the interaction energies of the particles on the sites related to the potential of mean force in the inhomogeneous fluid. In the simple case of a liquid of hard spheres, the first layer of liquid at contact with the solid exhibits an order-disorder phase transition and the total surface excess shows a maximum as the bulk density increases.