scholarly journals Fluidic Oscillators Mediating Generation of Microbubbles (Survey)

Fluids ◽  
2021 ◽  
Vol 6 (2) ◽  
pp. 77
Author(s):  
Václav Tesař
Keyword(s):  
Wastewater Treatment ◽  
Mass Transport ◽  
Gas Flow ◽  
Liquid Surface ◽  
Working Life ◽  
External Effects ◽  
Fluidic Oscillator ◽  
Size Discrepancy ◽  
Gas Volume ◽  
Device Simple

If a gas volume is distributed into many microbubbles of a sub-millimetre size, the total gas/liquid surface becomes very large. This increases overall heat and/or mass transport across the sum of surfaces. The paper discusses several applications in which the use of microbubbles increases efficiency of various processes, especially in wastewater treatment and in growing microorganisms such as algae, yeast, bacteria, or primitive fungi. The problem of microbubble generation by percolation in aerator is their coalescence into larger bubbles, whatever small are the pores in the aerator in which the microbubbles are generated. The solution of this size discrepancy question was found in agitating the gas flow by a fluidic oscillator prior to its injection through the aerator. The oscillator is a no-moving-part device, simple, inexpensive, resistant to external effects like acceleration or heat, and with long maintenance-free working life.

Improving Mass Transport of Titanium Hollow Fibre Electrodes through Gas Flow Stimulated Hydrodynamics

2020 ◽  
Vol MA2020-02 (15) ◽  
pp. 1410-1410
Author(s):  
Ronald P.H. Jong ◽  
Piotr M. Krzywda ◽  
Guido Mul
Keyword(s):  
Mass Transport ◽  
Gas Flow ◽  
Hollow Fibre

Measuring the rate of local evaporation from the liquid surface under the action of gas flow

2015 ◽  
Vol 41 (7) ◽  
pp. 665-667 ◽  
Author(s):  
Yu. V. Lyulin ◽  
D. V. Feoktistov ◽  
I. A. Afanas’ev ◽  
E. S. Chachilo ◽  
O. A. Kabov ◽  
...  
Keyword(s):  
Gas Flow ◽  
Liquid Surface

scholarly journals DEMONSTRATION TASKS OF LIQUID AND GAS PROPERTIES AND THEIR RATIONALE SENSE

2010 ◽  
Vol 7 (1) ◽  
pp. 29-37
Author(s):  
Violeta Šlekienė ◽  
Loreta Ragulienė
Keyword(s):  
Gas Flow ◽  
Liquid Surface ◽  
Flow Speed ◽  
Pressure Reduction ◽  
Physics Teaching ◽  
Liquid Surface Tension ◽  
Air Stream ◽  
Logical Sense ◽  
Physical Phenomena ◽  
Gas Properties

The article reveals the importance of demonstration tasks in physics teaching in secondary schools. Four demonstration of the liquid and gas properties are presented and analyzed. They are: Pressure dependence of gas flow speed; Pressure reduction in air-stream; Wing lift; Liquid surface tension. Reasoning schemes for giving a logical sense to these physics demo tasks are developed. The proposed reasoning schemes reach to activate students' thinking, understanding the demonstrations during the observed physical phenomena, i.e. help students to: understand the nature of the demo task, determine cause - effect relationships and dependencies, compare conditions and findings, summarize the results, do conclusions. Such using of demonstration tasks is useful to both of teacher and pupil: teacher controls the content of teaching and a learning of pupils, pupils - are focused to self-activities, encouraged to think, analyze, summarize and do conclusions. Key words: physics teaching, demonstration task, liquid and gas properties, reasoning schemes.

scholarly journals Macroscopic Model for Passive Mass Dispersion in Porous Media Including Knudsen and Diffusive Slip Effects

2021 ◽  
Vol 3 ◽  
Author(s):  
Francisco J. Valdés-Parada ◽  
Didier Lasseux
Keyword(s):  
Boundary Condition ◽  
Porous Media ◽  
Mass Transport ◽  
Gas Flow ◽  
Macroscopic Model ◽  
Type Model ◽  
Pore Scale ◽  
Advective Transport ◽  
Apparent Permeability ◽  
Slip Effects

In this work, a macroscopic model for incompressible and Newtonian gas flow coupled to Fickian and advective transport of a passive solute in rigid and homogeneous porous media is derived. At the pore-scale, both momentum and mass transport phenomena are coupled, not only by the convective mechanism in the mass transport equation, but also in the solid-fluid interfacial boundary condition. This boundary condition is a generalization of the Kramers-Kistemaker slip condition that includes the Knudsen effects. The resulting upscaled model, applicable in the bulk of the porous medium, corresponds to: 1) A Darcy-type model that involves an apparent permeability tensor, complemented by a dispersive term and 2) A macroscopic convection-dispersion equation for the solute, in which both the macroscopic velocity and the total dispersion tensor are influenced by the slip effects taking place at the pore-scale. The use of the model is restricted by the starting assumptions imposed in the governing equations at the pore scale and by the (spatial and temporal) constraints involved in the upscaling process. The different regimes of application of the model, in terms of the Péclet number values, are discussed as well as its extents and limitations. This new model generalizes previous attempts that only include either Knudsen or diffusive slip effects in porous media.

Domestic wastewater treatment by a submerged MBR (membrane bio-reactor) with enhanced air sparging

2003 ◽  
Vol 47 (12) ◽  
pp. 149-154 ◽  
Author(s):  
I.-S. Chang ◽  
S.J. Judd
Keyword(s):  
Wastewater Treatment ◽  
Membrane Fouling ◽  
Gas Flow ◽  
Domestic Wastewater ◽  
Air Sparging ◽  
Air Jet ◽  
Dead End ◽  
Membrane Tube ◽  
Cake Layer ◽  
Air Lift

The air sparging technique has been recognised as an effective way to control membrane fouling. However, its application to a submerged MBR (Membrane Bio-Reactor) has not yet been reported. This paper deals with the performances of air sparging on a submerged MBR for wastewater treatment. Two kinds of air sparging techniques were used respectively. First, air is injected into the membrane tube channels so that mixed liquor can circulate in the bioreactor (air-lift mode). Second, a periodic air-jet into the membrane tube is introduced (air-jet mode). Their applicability was evaluated with a series of lab-scale experiments using domestic wastewater. The flux increased from 23 to 33 lm−2h−1 (43% enhancement) when air was injected for the air-lift module. But further increase of flux was not observed as the gas flow increased. The Rc/(Rc+Rf), ratio of cake resistance (Rc) to sum of Rc and Rf (internal fouling resistance), was 23%, indicating that the Rc is not the predominant resistance unlike other MBR studies. It showed that the cake layer was removed sufficiently due to the air injection. Thus, an increase of air flow could not affect the flux performance. The air-jet module suffered from a clogging problem with accumulated sludge inside the lumen. Because the air-jet module has characteristics of dead end filtration, a periodic air-jet was not enough to blast all the accumulated sludge out. But flux was greater than in the air-lift module if the clogging was prevented by an appropriate cleaning regime such as periodical backwashing.

Evaluation of a four year experience with a fully instrumented anaerobic digestion process

2002 ◽  
Vol 45 (4-5) ◽  
pp. 495-502 ◽  
Author(s):  
J.P. Steyer ◽  
J.C. Bouvier ◽  
T. Conte ◽  
P. Gras ◽  
P. Sousbie
Keyword(s):  
Wastewater Treatment ◽  
Anaerobic Digestion ◽  
Gas Flow ◽  
Volatile Fatty Acids ◽  
Fixed Bed ◽  
Total Alkalinity ◽  
Wastewater Treatment Process ◽  
Loop Control ◽  
Anaerobic Digestion Process ◽  
Digestion Process

For several years, a 1 m3 fixed bed anaerobic digestion process has been operated for the treatment of distillery vinasses. This reactor has been fully instrumented with the following variables available on-line: pH, temperature, liquid and gas flow rates, gas composition (i.e., CH4, CO2 and H2), concentration of bicarbonate, chemical oxygen demand, total organic carbon, volatile fatty acids and partial and total alkalinity, these last four variables being measured twice by different techniques (i.e., using a TOC analyzer, a titrimetric sensor and an infrared spectrometer). The purpose of this paper is to compare the respective benefits of advanced instrumentation for the monitoring of wastewater treatment processes in general, and for anaerobic digestion in particular. It will also provide some statistical analysis of the time required to operate a fully instrumented wastewater treatment process. It is indeed well admitted in the literature that instrumentation is usually the main limitation step for using closed-loop control. However, it is our opinion that, in the near future, this situation will change. This point is discussed based on our four years practical experience.

scholarly journals State Primary Standard of Gas Volume and Flow Rate Units for the Pressure Range of 1 MPa to 5 MPa (PVTt-15)

2020 ◽  
pp. 3-12
Author(s):  
M. S. Rozhnov ◽  
Yu. V. Kuzmenko ◽  
D. M. Melnyk ◽  
O. S. Levbarg ◽  
A. M. Rak ◽  
...  
Keyword(s):  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Gas Flow ◽  
Pressure Range ◽  
General View ◽  
Measurement Standard ◽  
Functional Scheme ◽  
Filling Time ◽  
Gas Volume

For the first time in Ukraine a primary measurement standard of gas volume and flow rate units in a pressure range of 1 MPa to 5 MPa has been created. The standard is based on realisation of the units by PVTt principle and units dissemination using critical Venturi nozzles. Gas passing through the nozzle during its calibration fills an evacuated collection tank located downstream the nozzle, and the respective time interval is measured. Mass flow rate is calculated by multiplying the volume of the collection tank by the gas density change and dividing by the tank filling time. Density values are determined by the equation of state and the measured initial and final pressure and temperature values. The structural and functional scheme of the measurement standard is shown in Figure 3. The standard consists of two units. The first unit is intended to realise, keep and transfer the units of gas volume and flow rate. The general view of the block is shown in Figure 4. The unit contains high pressure collection tank, precision water thermostat, vacuum pump, piston gas pressure gauge, flow switch, fine filter, a set of seven Venturi nozzles with diameters from 0.1 mm to 3.0 mm. The second unit is designed to form a stationary gas flow and provide a critical gas flow rate (at the speed of sound) at the nozzle throat. In the case of an elementary reversible adiabatic (isoentropic) process at a critical velocity, the mass flow rate of gas passing through the nozzle is maximally possible. The unit consists of equipment for reducing the pressure from 150 bar to 70 bar and from 70 bar to 10 bar, the heat exchanger and the instruments measuring the pressure and temperature of the gas flow. The created measurement standard will assure metrological traceability of the measurements of gas volume and volume flow rate at high pressures for the flow rate up to 100 m3/h and calibration of the primary reference nozzles with a throat diameter from 0.1 mm to 3 mm.

Two-dimensional simulation of mass transport in polymer removal from a powder injection molding compact by thermal debinding

2001 ◽  
Vol 16 (8) ◽  
pp. 2436-2451 ◽  
Author(s):  
Ying Shengjie ◽  
Y. C. Lam ◽  
S. C. M. Yu ◽  
K. C. Tam
Keyword(s):  
Injection Molding ◽  
Mass Transport ◽  
Liquid Flow ◽  
Gas Flow ◽  
Powder Injection Molding ◽  
Forced Flow ◽  
Powder Injection ◽  
Two Dimensional ◽  
Thermal Debinding ◽  
Dimensional Simulation

Two-dimensional simulation of thermal debinding in powder injection molding based on mass and heat transfer in deformable porous media is proposed. The primary mechanisms of mass transport, i.e., liquid flow, gas flow, vapor diffusion, and convection, as well as the pyrolysis of polymers, and their interactions, are included in the model. The simulated results revealed that polymer removal process is primarily affected by liquid flow, which is mainly dominated by pressure-forced flow rather than capillary-driven flow. A significant phenomenon, enrichment with liquid polymer in the outer surface regions of the compact, is explained.

Micromixing Characteristics in an Aerated Stirred Tank with Half Elliptical Blade Disk Turbine

2014 ◽  
Vol 12 (1) ◽  
pp. 231-243
Author(s):  
Wanbo Li ◽  
Xingye Geng ◽  
Yuyun Bao ◽  
Zhengming Gao
Keyword(s):  
Energy Dissipation ◽  
Specific Energy ◽  
Dissipation Rate ◽  
Gas Flow ◽  
Liquid Surface ◽  
Energy Dissipation Rate ◽  
Reaction Scheme ◽  
Stirred Tank ◽  
Wall Region ◽  
Superficial Gas Velocity

Abstract The parallel-competing iodide-iodate reaction scheme was used to investigate the micromixing efficiency in an aerated stirred tank of 0.30 m diameter agitated by a half elliptical blade disk turbine. The mean specific energy dissipation rate Pm ranged from 0.5 to 2.2 W/kg, while the superficial gas velocity VS ranged from 0.015 to 0.047 m/s. Four sub-surface feed positions were considered. When the tank is fed just under the liquid surface or in the near-wall region, the micromixing efficiency can be enhanced by introducing gases with superficial gas velocities higher than 0.031 m/s. The effects of gas on the micromixing performance become complicated, while the tank is fed in the impeller discharging region. The increase of gas flow rate does not always have good effects on the micromixing performance. Moreover, the way to feed sulfuric acid can strongly affect the efficiency of the reaction scheme. For a single liquid phase, the micromixing time tm according to the incorporation model varies from 5 × 10−3 to 3 × 10−2 s. The dimensionless local specific energy dissipation rate Φ near the liquid surface is almost independent of Pm, while Φ in the impeller discharging area decreases with increasing Pm.

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