Liquid Contact Research Articles

A Simple Approach to Characterize Gas-Aqueous Liquid Two-phase Flow Configuration Based on Discrete Solid-Liquid Contact Electrification.

In this study, we first suggest a simple approach to characterize configuration of gas-aqueous liquid two–phase flow based on discrete solid-liquid contact electrification, which is a newly defined concept as a sequential process of solid-liquid contact and successive detachment of the contact liquid from the solid surface. This approach exhibits several advantages such as simple operation, precise measurement, and cost-effectiveness. By using electric potential that is spontaneously generated by discrete solid–liquid contact electrification, the configurations of the gas-aqueous liquid two-phase flow such as size of a gas slug and flow rate are precisely characterized. According to the experimental and numerical analyses on parameters that affect electric potential, gas slugs have been verified to behave similarly to point electric charges when the measuring point of the electric potential is far enough from the gas slug. In addition, the configuration of the gas-aqueous liquid two-phase microfluidic system with multiple gas slugs is also characterized by using the presented approach. For a proof-of-concept demonstration of using the proposed approach in a self-triggered sensor, a gas slug detector with a counter system is developed to show its practicality and applicability.

Interfacial area measurements and surface area quantification for spray absorption

Abstract Sprays are widely used in the chemical industry for absorption operations such as gas conditioning and flue gas desulphurization. Despite the wide usage, spray absorption is poorly understood. For absorption applications, the rate of transfer of solute gas into all of the liquid drops is a strong function of the surface area of drops and hence the dropsize. Experimental measurements of dropsize at multiple locations within the spray plume and robust computation of the cumulative surface area of the drops is required to ascertain the liquid surface area availability. Further, the efficiency of spray contactors can be conveniently expressed in terms of the effective gas–liquid interfacial area measured using the standard chemical technique. The liquid surface area and the effective gas–liquid contact area inside spray columns can differ from each other on account of the large degree of absorption occurring during the process of atomization, and the internal stagnancy of small drops. Further, drop break-up, drop-drop interactions, collision of the spray plume with the column wall, and wall flow affect the liquid surface area availability and the effective gas–liquid contact area to varying degrees. As a result, it is essential to quantify both, the liquid surface area as well as the effective gas–liquid area inside spray columns to gain a fundamental understanding. Present study addresses this gap. Dropsize measurements using a Phase Doppler Interferometer (PDI), robust cumulative drop surface area quantification, and effective interfacial area measurements with the CO2-0.1 N NaOH system inside a 0.2 m ID laboratory spray column are presented. The effect of L/G ratio and gas–liquid contact height on the effective interfacial area and the cumulative drop surface area are elucidated. The effective interfacial area measurements are compared to results of previous researchers. Further, a methodology to compare the cumulative drop surface area with the effective interfacial area measurements is presented. Results from the study shows that a great degree of mass transfer does occur in the region in the vicinity of the nozzle tip. A large difference is observed in the cumulative drop surface area and the effective interfacial area on account of the large degree of CO2 absorption taking place during the process of atomization and the large number of internally stagnant drops. This work provides a fundamental insight into spray absorption and will guide in nozzle selection and robust design of spray columns.

Spray absorption of CO2 into monoethanolamine: Mass transfer coefficients, dropsize, and planar surface area

Spray columns show potential to absorb CO2 into aqueous amine solvents such as monoethanolamine (MEA). Low gas phase pressure drop, less susceptibility to corrosion due to the absence of internals, and greater tolerance to use of precipitating solvents, are some of the favorable attributes associated with spray columns. At present, there is a need for robust spray absorption data with the CO2-MEA system. Experimental dropsize measurements with MEA as the test solvent have never been reported. Measurement of dropsize distributions can help ascertain the surface area available for absorption. In this spray study, absorption rates in terms of overall mass transfer coefficients, drop size data, and planar surface area for the CO2-MEA system, quantified in a 0.2m ID, lab-scale column are presented. The dropsize measurements are made with a Phase Doppler Interferometry (PDI) system. The effects of liquid rate, inlet loading, MEA concentration, and gas–liquid contact height on the performance of a full-cone nozzle are elucidated. Results from the study show an increase in mass transfer coefficients with MEA concentration and liquid rate. The mass transfer data, dropsize data and surface area quantification indicate that the free MEA content dominates spray absorption. The data also indicate the occurrence of a great degree of mass transfer in the region immediate downstream of the nozzle tip. The study provides fundamental insight into spray absorption phenomena and can aid in more robust, application specific design of spray columns.

Micro–macro transition and simplified contact models for wet granular materials

Wet granular materials in a quasistatic steady-state shear flow have been studied with discrete particle simulations. Macroscopic quantities, consistent with the conservation laws of continuum theory, are obtained by time averaging and spatial coarse graining. Initial studies involve understanding the effect of liquid content and liquid properties like the surface tension on the macroscopic quantities. Two parameters of the liquid bridge contact model have been identified as the constitutive parameters that influence the macroscopic rheology (i) the rupture distance of the liquid bridge model, which is proportional to the liquid content, and (ii) the maximum adhesive force, as controlled by the surface tension of the liquid. Subsequently, a correlation is developed between these microparameters and the steady-state cohesion in the limit of zero confining pressure. Furthermore, as second result, the macroscopic torque measured at the walls, which is an experimentally accessible parameter, is predicted from our simulation results with the same dependence on the microparameters. Finally, the steady- state cohesion of a realistic non-linear liquid bridge contact model scales well with the steady-state cohesion for a simpler linearized irreversible contact model with the same maximum adhesive force and equal energy dissipated per contact.

Oil sorption behaviors of porous polydimethylsiloxane modified collagen fiber matrix

ABSTRACTA facial and cost‐effective synthesis method of converting the leather protein solid wastes into a value‐added collagen matrix oil sorbent is successfully established for the first time. Hide powder fiber (HPF) was firstly prepared by using the pre‐tanned fleshing wastes from the leather industry, and then cross‐linked with epoxy‐terminated polydimethylsiloxane (PDMS) to produce hydrophobic collagen fiber, which was verified by the FT‐IR spectrum and contact angle analysis. Subsequently, a series of porous PDMS modified collagen‐based sorbents with roughness surface was successfully fabricated by solvent‐ and freeze‐drying methods respectively. The oil sorption capacity, sorption saturated time and retention capacity of the prepared sorbents was investigated. Combined with the SEM images, liquid displacement method and contact angle analysis, the results revealed that oil sorption capacities of the sorbent with lower pore size, higher porosity and rougher surface for silicone oil, motor oil and vegetable oil were approximate to 13.60, 12.50, and 11.92 g/g, respectively. Additionally, the sorption of oils is a quasi‐instantaneous process and also showed excellent oil retention capacity. It exhibited acceptable oil sorption performances as compared to commercial biomass sorbents. These findings indicated its potential as an eco‐friendly oil sorbent material. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 42727.

Pulsed Corona Discharge in Water Treatment: The Effect of Hydrodynamic Conditions on Oxidation Energy Efficiency

Water treatment by gas-phase pulsed corona discharge (PCD) relies mainly on utilization of ozone and OH radicals as oxidizing agents. In a configuration where the treated solution is showered through the plasma zone, the gas–liquid contact surface is the primary OH-radical formation site and the interface in the mass transfer of ozone. Its significance to overall process efficiency is therefore notable. In this study, the effect of varying contact surface area at different discharge powers was investigated from the perspective of efficient utilization of the two prime oxidants in slow reaction with oxalate. It is seen that increasing the area of the contact surface improves OH-radical utilization up to the point where the pollutant oxidation efficiency abruptly decreases presumably because of unfavorable pulse energy distribution in the gas–liquid mixture. The existence of an optimal area for a given power has implications for future studies in the design of pulsed plasma applications for water treatment.

Comments on “Surface energy of parylene C”

In this short communication, we comment the results recently reported by Ch. Chindam et al. [“Surface energy of parylene C” Materials Letters, available online on the 8th of April 2015, doi: 10.1016/j.matlet.2015.04.009]. The surface energy of parylene C, a widely investigated polymer, is one of the critical parameters for its application as a micrometer biomaterial coating. The surface energy was obtained from single liquid (water) contact angle measurements using the Li–Neumann theoretical model. We comment on the relevance of the reported absolute value of the surface energy as well as the methodology used for its determination.

Flow boiling and critical heat flux in horizontal channel with one-sided and double-sided heating

This study explores flow boiling of FC-72 along a 5-mm high by 2.5-mm wide rectangular channel that is fitted with top and bottom heating walls. By activating one wall at a time, the opposing influences of gravity are examined for inlet velocities from 0.11 to 2.02m/s. Results for top wall and bottom wall heating are then compared to those for double-sided heating. For top wall heating, high speed video imaging proves gravity effects are dominant at low velocities, accumulating vapor along the heated wall and resulting in low critical heat flux (CHF) values. For bottom wall heating, buoyancy aids in vapor removal and liquid replenishment of the heated wall, resulting in higher CHF values. Higher velocities result in fairly similar interfacial behavior for top wall and bottom wall heating, and double-sided heating exhibiting greater symmetry between interfacial behaviors along the opposite walls. Overall, CHF values for all three configurations converge to one another above 1.5m/s. This convergence is clearly the result of high inertia negating the influence of gravity. It is shown that interfacial instability theory provides an effective means for assessing the influence of velocity on CHF for top wall versus bottom wall heating. For top wall heating, a stable interface at low velocities causes vapor accumulation against the top wall resulting in very low CHF. Instability theory shows that top wall heating becomes unstable above 1.03m/s, allowing liquid contact with the wall and improved wall cooling. For bottom wall heating, the interface is always unstable and favorable for liquid contact. Instability theory also shows that inertia dwarfs gravity around 1.5m/s, where critical wavelengths for top wall and bottom wall heating converge. Convergence of the CHF values for top wall and bottom wall heating also occurred at a similar value.

Contaminant adhesion (aerial/ground biofouling) on the skin of a gecko.

In this study, we have investigated the micro- and nano-structuring and contaminant adhesional forces of the outer skin layer of the ground dwelling gecko--Lucasium steindachneri. The lizard's skin displayed a high density of hairs with lengths up to 4 μm which were spherically capped with a radius of curvature typically less than 30 nm. The adhesion of artificial hydrophilic (silica) and hydrophobic (C18) spherical particles and natural pollen grains were measured by atomic force microscopy and demonstrated extremely low values comparable to those recorded on superhydrophobic insects. The lizard scales which exhibited a three-tier hierarchical architecture demonstrated higher adhesion than the trough regions between scales. The two-tier roughness of the troughs comprising folding of the skin (wrinkling) limits the number of contacting hairs with particles of the dimensions used in our study. The gecko skin architecture on both the dorsal and trough regions demonstrates an optimized topography for minimizing solid-solid and solid-liquid particle contact area, as well as facilitating a variety of particulate removal mechanisms including water-assisted processes. These contrasting skin topographies may also be optimized for other functions such as increased structural integrity, levels of wear protection and flexibility of skin for movement and growth. While single hair adhesion is low, contributions of many thousands of individual hairs (especially on the abdominal scale surface and if deformation occurs) may potentially aid in providing additional adhesional capabilities (sticking ability) for some gecko species when interacting with environmental substrates such as rocks, foliage and even man-made structuring.

Wetting & Wicking Effects of Superhydrophilic Nano-Structured Coatings

Superhydrophilic Nano-Structured Coatings (SHNC) were discovered during pool boiling experiments using nanofluids with alumina nanoparticles. During nucleate boiling, the nanoparticles are deposited on the heater surface, forming a uniform oxide coating. These coatings have been demonstrated to greatly decrease the liquid contact angle observed on the surfaces, both by increased surface roughness and increased surface energy. An illustration of this roughness, within 1 μm thickness, can be seen in the 3-D optical microscope mapping of a SHNC surface, top right. These highly wetting structures can greatly enhance macro-level mass transfer effects, such as capillary action. The series of images on the left depict the wickability enhancement achieved by SHNC coating inside a 0.92 mm internal diameter aluminum tube. In the tube coated with SHNC, a 21 μl water droplet disappeared in 183 milliseconds, resulting in an average wicking speed along the pipe of 17 cm/sec. The bare aluminum tube does not wick at all, even as it is pushed into the droplet. The bottom right sequence shows the wettability enhancement responsible for this behavior; an 8 μl water droplet is dropped onto both a SHNC-coated and a bare aluminum surface from a height of 1 cm. The droplet on the SHNC-coated surface spreads instantaneously due to the high wettability of the SHNC, while the droplet on the bare aluminum remains aggregated as a hemisphere.

Three‐dimensional numerical simulation of coalescence and interactions of multiple horizontal bubbles rising in shear‐thinning fluids

The dynamics of multiple horizontal bubbles rising from different orifice arrangements in shear‐thinning fluids was simulated numerically by three‐dimensional Volume of Fluid method. The effects of bubble size, rheological properties of shear‐thinning fluids, and orifice structure arrangements on multiple bubbles interaction and coalescence were analyzed, and the mechanisms of bubble coalescence and breakup were fully discussed and elucidated. The variation of bubble rising velocity during coalescence process and freely rising processes for different orifice arrangements was also deeply investigated. The critical initial horizontal intervals for coalescence of multiple horizontal bubbles with various orifice arrangements were attained by simulation, which could serve as the critical criterion of bubble coalescence or noncoalescence. Furthermore, the critical bubble interval was predicted based on the film drainage model, the prediction accords well with the simulation result and is quite conducive for the design and optimization of perforated gas–liquid contact equipment. © 2015 American Institute of Chemical Engineers AIChE J, 61: 3528–3546, 2015

Characteristics of Absorption/Regeneration of AMP/MEA Using Hybrid Packing for the Improvement of CO2 Absorption Performance

The development of new packing materials and absorbents for use in CO2 recovery is urgently needed as a means of reducing greenhouse gases. In this study, we evaluated the absorbents 2-amino-2-methyl-1-propanol (AMP) and monoethanolamine (MEA) in combination with random packing materials (ceramic Raschig rings and Berl saddles) and a structured gauze packing material. To improve the CO2 absorption efficiency, we developed hybrid packing materials comprising Raschig rings and the structured packing material in various ratios. The effects of the ratio on the gas flow rate, absorbent liquid flow rate, and CO2 absorption/regeneration efficiencies over time were evaluated. The overall mass-transfer coefficients were also calculated. The height of the tower corresponding to one theoretical plate in the absorptive tower design and the available gas–liquid contact area were calculated. This fundamental research will help support efforts to improve the efficiency of CO2 absorption from various industrial exhaust streams.

A level set method for materials with texturally equilibrated pores

Textural equilibrium controls the distribution of the liquid phase in many naturally occurring porous materials such as partially molten rocks and alloys, salt–brine and ice–water systems. In these materials, pore geometry evolves to minimize the solid–liquid interfacial energy while maintaining a constant dihedral angle, θ, at solid–liquid contact lines. We present a level set method to compute an implicit representation of the liquid–solid interface in textural equilibrium with space-filling tessellations of multiple solid grains in three dimensions. Each grain is represented by a separate level set function and interfacial energy minimization is achieved by evolving the solid–liquid interface under surface diffusion to constant mean curvature surface. The liquid volume and dihedral angle constraints are added to the formulation using virtual convective and normal velocity terms. This results in an initial value problem for a system of non-linear coupled PDEs governing the evolution of the level sets for each grain, using the implicit representation of the solid grains as initial condition. A domain decomposition scheme is devised to restrict the computational domain of each grain to few grid points around the grain. The coupling between the interfaces is achieved in a higher level on the original computational domain. The spatial resolution of the discretization is improved through high-order spatial differentiation schemes and localization of computations through domain composition. Examples of three-dimensional solutions are also obtained for different grain distributions networks that illustrate the geometric flexibility of the method.

Comparison of cryogenic flow boiling in liquid nitrogen and liquid hydrogen chilldown experiments

This paper presents a comparison between experimental results from recent liquid hydrogen (LH2) transfer line chilldown experiments at high Reynolds (Re) numbers versus liquid nitrogen (LN2) experiments conducted at low Re numbers. Parasitic heat leak, inner wall temperatures, inner wall heat fluxes, and heat transfer coefficients are computed to compare between the two systems. Analysis of temperature traces and flow visualization indicates that the chilldown process evolves much more rapidly at higher Re numbers due to a quick transition from vapor flow to annular liquid flow and near immediate liquid contact along the pipe walls. The lower kinematic viscosity and surface tension of LH2, along with reduced parasitic heat leak and higher Re numbers relative to the LN2 experiments, causes chilldown to proceed almost immediately into the nucleate boiling regime, in comparison to low Re flows where >75% of the chilldown is spent in vapor film boiling.

Investigation on the liquid contact angle and its influence for liquid desiccant dehumidification system

The liquid desiccant dehumidification system (LDDS) is promising by removing extra air moisture effectively with absorption. By significantly affecting the film wetted area, the desiccant contact angle of the liquid/air interface on the working plate is critical for the system performance. Its value accuracy also seriously impacts the prediction accuracy of theoretical models. However, previous research on the liquid desiccant contact angle was limited, and the results of current predictions were questionable. This paper tested the contact angle of commonly used desiccants, Lithium Chloride (LiCl) and Lithium Bromide (LiBr) aqueous solution, on the stainless steel plate, and developed empirical formulas for predicting the angle. For both desiccants, the contact angle increased with the solution mass concentration and decreased with temperature. With the increase of plate surface roughness, the angle first increased and then decreased. These parameters showed much obvious effects on the angle of LiCl. For the effect of roughness, the maximum changing rate of LiCl was 0.13°/nm compared with 0.07°/nm of LiBr. Errors between new formulas and experiment ones were acceptable, showing an average absolute error of 12.3% for LiCl and 9.4% for LiBr. Furthermore, the effects of contact angle on the film wetted area were investigated experimentally with a single channel regenerator. When the plate surface was hydrophilic, the initial film width was significantly enlarged, with a rate of −2.0×10−3m per degree, and film contraction along the flow direction was restrained due to the small contact angle. So, the film wetted area increased with an average changing rate of −9.7×10−4m2 per degree, and the mass transfer was effectively enhanced by 2–3 times. Effective measures to reduce the contact angle were also proposed.

Controlling picolitre droplet impact dynamics by tailoring the solid subsurface

The oscillatory dynamics of picolitre water droplets following impact onto a range of hydrophobic surfaces is found to be influenced by the underlayer stiffness and thickness. The relative contributions of surface functionality versus subsurface hardness have been decoupled by utilising plasmachemical surface functionalisation and underlayer crosslinking respectively. Higher oscillation frequencies are measured for softer and thicker films, which correlates to a larger surface deformation around the liquid droplet contact line.

Dynamics of spreading on ultra-hydrophobic surfaces

Despite the extensive variety of applications for ultra-hydrophobic surfaces in industry, technology, and biology, due to their wetting characteristics, there has not been considerable attention in the area of dynamics of wetting on ultra-hydrophobic surfaces. In this research, the experimental investigations have been done by applying forced spreading of several polyethylene-glycol/water mixtures in different weight ratios on Teflon plates and ultra-hydrophobic sprayed glass substrates. Hydrodynamics theory and molecular-kinetic theory have been applied to investigate the dynamics of wetting on these substrates. It has been found that the dynamics of receding motion of liquid contact line on ultra-hydrophobic surfaces could be described perfectly with the molecular-kinetic theory. In the case of advancing motion on an ultra-hydrophobic surface, dynamic contact angle is independent of liquid contact line velocity. The advancing and receding motions of liquid contact line on smooth Teflon plates followed molecular-kinetic theory.

Key Technologies of Spraying Machine with Wireless Remote Control

In this research, a wireless remote-controlled (RC) spraying machine is developed based on the S3C6410 embedded controller. This spraying machine is composed of a rotary pesticide selection unit, a real-time mixing unit, a multi-angle spraying unit, an image acquisition module, an embedded control module, a wireless communication module, and an intelligent mobile platform. It is especially designed for hilly areas, greenhouses, orchards, and other environments that are not accessible to large and medium-sized spraying machines. The wireless RC machine achieves precise proportional and multi-angle flexible spraying while avoids liquid waste and direct operator–liquid contact.

A comparative study of solid and liquid inner contact paroxetine hydrochloride ion-selective electrode membranes

A comparative study was made between two designs of paroxetine-selective electrodes: a polyvinyl chloride membrane (liquid inner contact) called electrodes PME1 and PME2 and a solid contact called electrodes CWE1 and CWE2 based on paroxetine–phosphotungstate and paroxetine–phosphomolybdate as ion exchangers. The four electrodes, PME1, PME2, CWE1 and CWE2, show linearity over the concentration range from 1 × 10−5 to 1 × 10−2 M, with slopes of 56.7, 54.4, 59.8 and 55.3 mV/decade, meanwhile the limits of detection were 2.5 × 10−6, 4 × 10−6, 5.6 × 10−6 and 6.2 × 10−6 M, respectively. PME1 and PME2 showed better limit of detection than electrodes CWE1 and CWE2. The present electrodes show clear discrimination of Prx.HCl from several inorganic, and organic species. The sensors were applied efficiently for determination of Prx.HCl in its pharmaceutical preparations using standard addition and the calibration curve methods.

Application of vacuum impregnation with anti-freezing proteins to improve the quality of truffles

Vacuum impregnation (VI) with anti-freezing proteins was studied with the aim to minimize the loss in consistency occurring on truffles after thawing. Particularly, vacuum level, vacuum time and the relaxation time were modulated by using a Box-Behnken design. The results showed a significant weight increase of truffle samples in the range between 0.02 and 0.29 g/g proving that the impregnation occurred in all experimental conditions although the truffles showed a low porosity fraction (~6.33 %). After thawing, the samples submitted to pressure values lower than 150 mbar and vacuum times greater than 6.5 min, showed a consistency similar to the fresh samples, stating that the application of VI with a solution of anti-freezing proteins can be a useful method to reduce the loss in consistency probably caused by ice crystal formation. Moreover, after VI the samples showed an increase of porosity fraction probably due to the formation of new fractures as a consequence of the high rigidity of truffles. This phenomenon probably increased the absorption of anti-freezing proteins as a consequence of the improvement of solid–liquid surface contact area.