Air-water System Research Articles

Wireless microwave-to-optical conversion via programmable metasurface without DC supply

Microwave-optical interaction and its effective utilization are vital technologies at the frontier of classical and quantum sciences for communication, sensing, and imaging. Typically, state-of-the-art microwave-to-optical converters are realized by fiber and circuit approaches with multiple processing steps, and external powers are necessary, which leads to many limitations. Here, we propose a programmable metasurface that can achieve direct and high-speed free-space microwave-to-laser conversion. Moreover, it supports reverse conversion, achieving bidirectional operations. The programmable metasurface converter is realized by integrating subwavelength microwave resonant structures, MS junction and photoelectric PN junction components together, without connecting any direct-current supplies to provide driving bias. We further demonstrate the enormous potentials of the metasurface converter in cross-media links and develop a full-duplex air-water wireless communication system. Experimental results show that the bidirectional real-time data transmissions and exchanges are established through the air-water boundary. This work represents a decisive step towards microwave-optical interconversion on wireless and battery-free interfaces.

Effect of Gas Holdup and Gas Velocity on Volumetric Mass Transfer Coefficient in Bubble Column

Bubble columns are widely used in various industrial processes such as wastewater treatment, fermentation, and gas-liquid reactions due to their simplicity and effectiveness in mass transfer operations. In this study, we investigate the influence of gas holdup and gas velocity on the volumetric mass transfer coefficient in a bubble column reactor. The volumetric mass transfer coefficient is a critical parameter that affects the efficiency of gas-liquid mass transfer processes. Through experimental analysis and computational modeling, we systematically examine the relationship between gas holdup, gas velocity, and the volumetric mass transfer coefficient. In this study, volumetric mass transfer coefficient kL.a was calculated using air in water. The data obtained are in the range of superficial gas velocity (0.03-0.2398) m/s for air water system. The experiments were carried out using 0.1 m column diameter with 2 mm hole diameter and 79 holes gas distributor. From the experimental data it was found that kL.a increased with increasing of gas holdup and increasing of superficial gas velocity.

Pseudosteady shock refractions over an air–water interface

Shock refraction in a gas–liquid interface is ubiquitous in nature and engineering. This study investigates the shock refraction phenomena in air–water interfaces for various inclination angles. The interface inclination angles are achieved using a tiltable vertical shock tube. The time-resolved schlieren images are compared with numerical simulations performed using the BlastFoam solver in the OpenFOAM software. The stiffened gas equation of state is used to model water in the simulations. The shock polar analysis using modified shock relations for a stiffened gas is used to elucidate the refraction patterns. A regular refraction pattern with a reflected shock wave and a bound precursor refraction with a regular reflection are observed experimentally for the first time in an air–water system. Further, a new free precursor refraction pattern with a Mach reflection is observed. The transition criteria and the corresponding boundaries for each refraction pattern are demarcated in the ( $M_S, \theta _w^c$ )-plane. The refraction sequence and the range for various incident shock strength regimes are also identified.

A novel approach for measuring the void fraction in stratified air-water systems utilizing an 8-blade capacitance-based sensor, sinogram, and a deep neural network

A novel approach for measuring the void fraction in stratified air-water systems utilizing an 8-blade capacitance-based sensor, sinogram, and a deep neural network

Fluodynamics of a column filled with glass rings using the air-water system

In the present work, the fluidynamics of an absorption tower with a filling of glass rings is shown. The study was done by the variation in pressure drop with the flow rates of liquid (water) and gas (atmospheric air). The influences of the two flows were analyzed and ranges were identified where the flooding and the dragging of the liquid occur. A critical point is also presented, indicating the maximum limit of the combination between the two flows, Qwater/Qair, which must be used in the operation of the tower

Numerical Simulation of Effects of Previous PVD Treatment on Second Vacuum-PVD Improvement

The influence of the initial improvement through prefabricated vertical drains (PVD) and surcharge embankment on the second improvement by vacuum PVD has not been comprehensively explored in the existing literature. The expansion of the Second Bangkok International Airport (Suvarnabhumi Airport) underwent initial treatment with PVD and surcharge, followed by further soft ground improvement with vacuum PVD, which serves as a valuable case study for understanding the impact of the initial PVD improvement. This study highlights the effects of the initial PVD improvement through a comparison of two case studies: the first improvement by vacuum PVD on Taxiway Extension D at Zone 27 and the second vacuum PVD improvement on the Third Extension North at Zone 7. Extensive back analysis results reveal significantly higher flow parameters and reduced settlements for the second improvement at Zone 7 compared to the first improvement at Zone 27. The water contents, void ratios, and compression indices decreased while the undrained shear strengths and maximum past pressures increased. These results demonstrated the effectiveness of the vacuum PVD improvement with a modified field-distributed air-water separation system. Numerical studies further corroborated these findings and confirmed the observed crack patterns at the surface resulting from inward lateral movement.

A multivariable submersible sensor for monitoring in real-time industrial flotation cells

This paper describes the development and validation of a submersible sensing technology for industrial flotation cells. The sensor provides simultaneous real-time measurements of gas and solid holdups, as well as the density and viscosity of the slurry in the pulp zone of flotation machines. The submersible device comprises a gas exclusion cell, which resembles an inverted truncated cone assembled to a single-straight tube Coriolis meter. When the sensor device is vertically immersed in the aerated slurry, a continuous bubble-free flow of slurry is induced through the device, which allows the Coriolis meter to provide measurements of the slurry flow, density, and viscosity. The magnitude of the induced flow is a primary function of the sensor’s geometry and gas holdup. Applying the Bernoulli equation reveals that gas holdup can be expressed as the square of the induced flow velocity. A discharge coefficient parameter is introduced to compensate for variations in the velocity profile and flow losses. This coefficient is a function of the fluid Reynolds number, calculated in real-time based on the Coriolis measurements. The sensing technology was assessed in a pilot column operated in a water–air system and industrial forced-air and self-aspirated large flotation cells. Results demonstrate the sensor’s capabilities to provide reliable, accurate, real-time, long-term continuous gas dispersion and solid suspension-related variables, which could be used for supervision, control, and optimization applications.

Heat Transfer Performance Studies of Packed Bed Distillation Setup

Heat transfer performance studies done in a setup involving a stirred tank reactor and packed bed distillation column. Stirred tank reactor consists of double pitch blade impeller with rotational speeds varied from 40-120 rpm. The water-air system was taken into consideration. The reactor is jacketed with Therminol 55 as a heating medium. Therminol 55 is used as a heating medium because of its higher specific heat and boiling point. Column comprises of 3 packed bed segments, each of 1m in height and jacketed with Therminol 55. Therminol 55 is used as a source of indirect heating to negate any heat losses in the column. The column is randomly packed with Mellapak250Y packing. The data collected by experiments especially characterizes the packed bed distillation setup and heat transfer performance. The work evaluates effect of agitation on overall heat transfer coefficient and mass flow/ boil up rate calculated theoretically and experimentally. Use of efficient correlations along with various necessary dimensionless numbers and rudimentary parameters were clubbed to form a MATLAB model useful for verification of theoretical data. The comparison of theoretical and experimental overall heat transfer coefficient and mass flow/boil up rate is done. The study done on the setup used shows conclusions regarding overall heat transfer coefficient and mass flow/boil up rate with respect to agitator speed and Reynolds number. The theoretical calculated values of overall heat transfer coefficient and mass flow/boil up rate are compared with the experimental ones and conclusions taken out regarding the reactor and column contribution. Finally, the Reynolds number and mass flow/boil up rate relation is shown

Mechanistic Insights into Chloric Acid Production by Hydrolysis of Chlorine Trioxide at an Air-Water Interface.

Chlorine oxides play crucial roles in ozone depletion, and the final oxidation steps of chlorine oxide potentially result in the formation of chloric acid (HClO3) or perchloric acid (HClO4). Herein, the solvation and reactive uptake of three stable isomers of chlorine trioxide (Cl2O3), namely, ClOCl(O)O, ClClO3, and ClOOOCl, at the air-water interface were investigated using classical and hybrid quantum mechanics/molecular mechanics (QM/MM) molecular dynamics (MD) coupled with advanced free energy methods. Two distinct mechanisms were revealed for the hydrolysis of ClOCl(O)O and ClClO3: molecular and ionic mechanisms. A comparison of the computed free-energy profiles for the gaseous and air-water interfacial systems indicated that the air-water interface could markedly lower the free-energy barrier for or HClO3 formation while stabilizing the product state. In particular, the hydrolysis of ClClO3 at the air-water interface was barrierless. In contrast, our calculations showed that the hydrolysis of ClOOOCl was very slow, indicating that ClOOOCl was inert to water at the air-water interface. This study provides theoretical evidence for the hypothesis that HClO3 is a sink for chlorine oxides and for the widespread distributions of HClO3 recently observed in the Arctic region.

Physical qualities of acid sulfate soil: its limitations and implications for oil palm production

ABSTRACT Global demand has pressured the extension of oil palm production areas in Thailand to acid sulfate soils. Besides their severe acidity and nutrient imbalance, the soil physical quality is expected to restrict production. This research defined the critical physical limitations of acid sulfate soils for oil palm production. The soil parameters of physical quality were assessed, covering 32 points in both the topsoil (Ap) and subsoil horizons. These parameters consisted of penetration resistance in the wet and dry seasons, saturated hydraulic conductivity (Ksat), bulk density (BD), the water characteristic curve, available water capacity (AWCA), available water content (AWCO), infiltration, and the S-index (a single indicator of soil physical quality derived from the parameters of the van Genuchten equation). The results showed critical physical quality constraints, particularly concerning the S-index and water shortage. The poor physical quality was more distributed in the Ap horizon (S-index = 0.024) than in the subsoil (S-index = 0.033). The penetration resistance was moderately restricted (3.26 Mpa) to the plant roots only in the dry season. Corresponding to the S-index data, the Ap horizon had a lower AWCA (0.21) than the subsoil (0.30). Most negative AWCO values in the subsoils (78%) during the wet season suggested a severe water shortage for oil palm production. Further research is needed to refine a specific partial drainage technique under oil palm canopies, focusing on the air-water balance system.

Effect of gas distributors on hydrodynamics in molten-metal bubble column reactors for fluorinated gas removal using computational fluid dynamics

Fluorinated gases (F-gases) emitted by semiconductor industry have high global warming potential. Repurposing F-gases into valuable metal fluorides using molten-metal bubble column reactors (MMBCRs) is a promising alternative for their removal. Many researchers have reported hydrodynamics of bench-scale MMBCRs using computational fluid dynamics (CFD). However, the effect of the gas distributor type on hydrodynamics in large-scale MMBCRs has not been addressed. This study investigated hydrodynamics of pilot-scale MMBCRs with different gas distributors in a N2-Sn system including 1 % CF4 by using a volume-of-fluid (VOF) CFD model. The VOF-CFD model was validated against the experimental bubble sizes in air-water and Ar-Fe systems. Using the CFD model, the gas holdup (αG), Sauter mean bubble size (d32), and specific interfacial area (as) of three gas distributors (20 spargers, and perforated plates without and with tip) were evaluated in the pilot-scale MMBCR at 650 °C. The bubble size distributions near the gas distributor were significantly different for the three MMBCRs but were similar in the upper zone of the reactor. αG and d32 were approximately 15 % and 22 mm, respectively. as for the three MMBCRs ranged from 55 to 59 m2/m3. The VOF-CFD model predicted the crucial hydrodynamic parameters for reactor design and optimization.

Investigations on transport behaviours of rotating packed bed for CO2 capture by chemical absorption using CFD simulation

A rotating packed bed (RPB) has been proposed to overcome the limitations of high operating and capital costs involved in conventional columns which are used for chemical absorption-based carbon dioxide (CO2) capture. The design of large-scale RPBs depends on their transport characteristics. Owing to the difficulties in predicting the transport characteristics of RPBs experimentally, Computational Fluid Dynamics (CFD) simulation has been implemented. In this study, a two-dimensional (2D) volume of fluid (VOF) simulation is conducted to predict transport characteristics of RPB including, hydrodynamics, and physical and reactive mass transfers. To predict hydrodynamics of RPBs accurately, the liquid holdup by CFD simulation is compared against experimental prediction, showing a strong agreement between simulation and experimentation. Various liquid phase flow patterns within RPB are observed and these are cross-referenced with findings in the existing literature. Additionally, the impacts of rotational motion and flow rate are further assessed in the study. For the mass transfer performance, the prediction of the volumetric mass transfer coefficient, kLae of the air-water system from CFD simulation is studied. Two different mass transfer theories such as surface renewal theory and penetration theory are studied to predict kLae. It is observed that the kLae from the penetration theory closely follows the trend of the experimental data. Finally, a 2D simulation of the reactive absorption of CO2 by diethylenetriamine (DETA) in RPB is developed and compared with the existing available data in the literature. The present model underpredicts CO2 capture efficiency in RPB, which needs further improvement in reaction kinetics. In general, the present CFD model has the capability of predicting the transport characteristics of RPB.

Experimental Investigation of Liquid Holdup in a Co-Current Gas–Liquid Upflow Moving Packed Bed Reactor with Porous Catalyst Using Gamma-Ray Densitometry

This study explores the dynamics of liquid holdup in a lab-scale co-current two-phase upflow moving packed bed reactor, specifically examining how superficial gas velocity influences the line average external liquid holdup at a fixed superficial liquid velocity. Utilizing gamma-ray densitometry (GRD) for precise measurements, this research extends to determining line average internal porosity within catalyst particles. Conducted with an air–water system within a bed packed with 3 mm porous particles, the study presents a novel methodology using Beer–Lambert’s law to calculate liquid, gas, and solid holdups and catalyst porosity that is equivalent to the internal liquid holdup that fills the catalyst pores. Findings reveal a decrease in liquid holdup corresponding with increased superficial gas velocity across axial and radial locations, with a notable transition from bubbly to pulse flow regime at a critical velocity of 3.8 cm/sec. Additionally, the lower sections of the packed bed exhibited higher external liquid holdup compared to the middle sections at varied gas velocities. The liquid holdup distribution appeared uniform at lower flow rates, whereas higher flow rates favored the middle sections.

Turbulent natural convection in an air–water system with evaporation across the free surface

In this paper we report on direct numerical simulations of turbulent convection in a cuboidal pool that contains liquid water in the lower part and air in the upper one. The bottom wall is uniformly heated and natural convection is established in both phases, accompanied by water evaporation across the free surface of the water. The descent of the free surface due to evaporation is computed via a newly developed tracking algorithm based on the ghost-fluid method. We present results for three different cases which correspond to different pool heights. In all of them, the natural convection in the water lies in the soft-turbulence regime. Whereas in the gas, it lies in the laminar, transitional and soft-turbulence regimes, respectively. Our analysis focuses on the characteristics of the convective patterns in the two phases and the statistics of the various flow quantities of interest. According to our simulations, the flow in the water is organized in a single-roll Large-Scale Circulation (LSC). In the gas, it is organized in single or dual-roll LSCs, depending on the aspect ratio of the pool. Interestingly, the impingement points of the LSCs of the two phases at the free surface remain very close to one another, which is attributed to the continuity of the shear stresses across the free surface. Further, after the initial transient period, both the free-surface temperature and the evaporative mass flux are stabilized and remain almost constant, but they exhibit small-scale fluctuations in time due to turbulence. Also, the transport of water vapor in air has similar properties as the heat transport, and the ratio between the Sherwood and Nusselt numbers is very close to the Lewis number for air.

Salinity and flow pattern independent flow rate measurement in a gas-liquid flow with optimum feature selection and novel detection geometry using ANNs

This paper presents a study on the salinity determination and flow rate estimation in a two-phase air-water system. For this purpose, an automated air-water test loop capable of generating different flow patterns in a horizontal pathway was utilized to do numerous experiments at varying flow rates. A nuclear measuring setup, comprising Cs-137 and Am-241 as radiation sources, one NaI (Tl) scintillation detector to register transmission counts of Cs and three scintillator detectors for registering transmission and scattering counts from Am, was prepared. A pressure drop pipe was also employed for flow rate measurement, with MLPs were selected as the processing element. Notable innovations of this paper can be considered from two perspectives. Firstly, a novel paradigm in nuclear measurement geometry. This novelty uses the benefits of three scintillator detectors to extract features with the maximum potential for classifying and determining salinity. Secondly, there is a new method in data processing and utilizing optimum features to achieve the best performance in predicting flow rates. Results in flow rate prediction independent of salinity and flow regime indicate that the proposed paradigm and method are reliable for using in industrial fields related to multi-phase metering.

Lift force on single bubbles in subcooled pool boiling systems: Experimental measurements and CFD simulations

Lift coefficient has been evaluated for a subcooled pool boiling system with water as continuous phase and vapor (steam) bubble as dispersed phase generated on vertical walls with constant heat flux for a specific Rayleigh number (Ra) range (8x1012 < Ra < 2x1013) for the first time. Experimental investigation has been done with High Speed Camera while two phase CFD simulations have been performed using Volume of Fluid (VOF) method. The Morton number (M) for this system is log10M = -10.6 and Eötvös number (Eo) range is 0.2 < Eo < 1.3 while the shear rates have been maintained in the range 2 ≤ Sr ≤ 2.8. Bubble size of the bubbles arising from the sites on vertical surface have been determined by both experiments and simulations. The CFD predictions for bubble size and lift coefficients agree well with experimental measurements with a deviation of less than 10%. Further, empirical expressions from experimental data for the estimation of bubble size and lift coefficients have also been presented. The data for lift coefficients obtained is different from the ones of bubbles generated by single sparger in air-water systems.

Fluodynamics of a Column Filled with Glass Rings Using the Air-Water System

In the current study, we present the fluid dynamics of an absorption tower equipped with glass rings as fillings. The research involved investigating the variations in pressure drop concerning liquid (water) and gas (atmospheric air) flow rates. We thoroughly examined the impacts of these two flows, identifying specific ranges where flooding and liquid entrainment take place. Additionally, we pinpoint a critical threshold that signifies the maximum allowable combination of the two flows, denoted as Qwater/Qair, for effective tower operation.

Fluodynamics of a Column Filled with Glass Rings Using the Air-Water System

In the current study, we present the fluid dynamics of an absorption tower equipped with glass rings as fillings. The research involved investigating the variations in pressure drop concerning liquid (water) and gas (atmospheric air) flow rates. We thoroughly examined the impacts of these two flows, identifying specific ranges where flooding and liquid entrainment take place. Additionally, we pinpoint a critical threshold that signifies the maximum allowable combination of the two flows, denoted as Q&lt;sub&gt;water&lt;/sub&gt;/Q&lt;sub&gt;air&lt;/sub&gt;, for effective tower operation

Modeling and Robust Optimization of Commercial Air-Water HVAC System

Modeling and Robust Optimization of Commercial Air-Water HVAC System

Numerical Study of Bubble Column Water-Air System by the VOF Method

This paper aims to present a comprehensive study of the dynamics of a bubble using the Volume of Fluid (VOF) model in Fluent software. The simulation of two-phase flows is carried out by calculating the terminal velocity, bubble flow contours at different column heights, and the evolution of bubble circularity and Reynolds number at different times. The calculation was carried out on an air bubble with a diameter equal to 10 mm and zero introduction velocity by modifying the simulation parameters, such as the surface tension, to study their influence on the deformation of the bubble. This study will present four different shape regimes, which are obtained by varying the Bo (Bond number) and Mo (Morton number) values within the corresponding ranges of 1 &lt; Bo &lt; 103 and 5×10-8 &lt; Mo &lt; 102 . In addition, simulations are performed using large density and viscosity ratios of 1000 and 100, respectively. The results are comparable with great precision to the numerical simulation and experimental data.