Study of Bubble Size and Velocity in a Vibrating Bubble Column

2016 ◽  
Author(s):  
Shahrouz Mohagheghian ◽  
Brian R. Elbing
Keyword(s):  
Mass Transfer ◽  
Void Fraction ◽  
Bubble Size ◽  
Gas Flow ◽  
Bubble Column ◽  
Mass Transfer Rate ◽  
Superficial Velocity ◽  
Bubble Velocity ◽  
Published Data ◽  
Two Phase

Bubble columns are two-phase and three-phase reactors in which a gas flow drives a liquid flow and allows transport phenomena’s to take place. With a broad application from aeration of organic organisms in bio-rectors to hydrogenation of coal slurries in the Fischer-Tropsch process and production of synthetic fuel, bubble column reactors are cheap and easy to operate. In this work bubble size was studied in a bubble column and effect of injector size and gas superficial velocity was investigated. Results showed larger bubble size as gas superficial velocity was increased. It was previously shown that vibration increases the mass transfer between phases, which one active mechanism is that vibration increases the void fraction and with more gas in contact with liquid mass transfer rate increases. To check that a shaker table setup capable of generating vibration in the range of 5–15 Hz of frequency at 5 mm of amplitude using an eccentric drive mechanism was refurbished to study the bubble velocity and void fraction under vibration. The experimental setup was first verified to check if tests are repeatable and also the results are in agreement with literature. Void fraction, bubble size and velocity was measured and comparison with previously published data showed good agreement. Bubble size measurements in a stationary column showed that over the range tested bubble size increases with increasing gas superficial velocity. Bubble velocity decreases when gas superficial velocity was increased. Vibration showed a gradual reduction in bubble velocity as vibration frequency was increased.

Uncertainty Quantification of Low Void Fraction Measurements Using Wire-Mesh Sensors in Horizontal Air-Water Flows

2016 ◽  
Author(s):  
Étienne M. Lessard ◽  
Robert C. Bowden ◽  
Sun-Kyu Yang
Keyword(s):  
Uncertainty Quantification ◽  
Void Fraction ◽  
Physical Theory ◽  
Gas Flow ◽  
Superficial Velocity ◽  
Wire Mesh ◽  
Flow Loop ◽  
Two Phase ◽  
Flow Measurements ◽  
Void Fractions

The need for a revised methodology and uncertainty quantification for wire-mesh sensor void fraction measurements in horizontal low void fraction flow conditions was identified. Two-phase flow measurements were performed at a low-pressure, adiabatic and horizontal flow loop using wire-mesh sensors over a range of water superficial velocities from 3.5 to 5.5 m/s, air superficial velocities from 0.05 to 0.9 m/s and volumetric void fractions from 1 to 16% Using this proposed analysis, a corrected trend with average percent differences of 36, 21 and 6% was obtained for the low, medium and high gas flow rate cases, respectively, when comparing the wire-mesh sensor void fractions to two-phase pipe flow models. By combining these measurements of the void fraction with those of the interfacial velocity, the gas superficial velocity was calculated based on the physical theory, and compared to the superficial velocity measured by the flowmeters for validation purposes. An estimation of the uncertainty of these parameters showed that most of the measured parameters agreed reasonably with physical theory within 20%.

Investigating the Effect of Pipe Inclination on Two-Phase Gas-Liquid Flows Using Advanced Instrumentation

2011 ◽  
Author(s):  
Abolore Abdulahi ◽  
Lokman A. Abdulkareem ◽  
Safa Sharaf ◽  
Mukhtar Abdulkadir ◽  
Valente Hernandez Perez ◽  
...  
Keyword(s):  
Time Series ◽  
Void Fraction ◽  
Flow Rate ◽  
Gas Flow ◽  
Oil And Gas ◽  
Silicone Oil ◽  
Flow Characteristics ◽  
Superficial Velocity ◽  
Wire Mesh ◽  
Two Phase

Pipes that make up oil and gas wells are not vertical but could be inclined at any angle between the vertical and the horizontal which is a significant technology of modern drilling. Hence, this study has been undertaken to look at the effect of inclination on flow characteristics especially at 10 degrees from both horizontal and vertical. Air/silicone oil flows in a 67 mm slightly deviated pipe have been investigated using advanced instrumentation: Wire Mesh Sensor Tomography (WMS) and Electrical Capacitance Tomography (ECT). They provide time and cross-sectionally resolved data on void fraction. Both the ECT probes and WMS were mounted on the inclined pipes upstream just at the point where flows were fully developed. By keeping the liquid flow rate constant at 10 litres/min (or liquid superficial velocity of 0.052m/s), gas flow rate was varied from 10 litres/min to 1000 litres/min (or gas superficial velocity from 0.05m/s to 4.7m/s). Then other values of liquid superficial velocity were considered. Visual observations were considered. Time series and void fraction were then measured for WMS while time series and liquid holdup were measured for ECT. The raw data were processed and then interpreted for proper analysis. From an analysis of the output from the tomography equipment, flow patterns were identified using both the reconstructed images as well as the characteristic signatures of Probability Density Function (PDF) plots of the time series of cross-sectionally averaged void fraction as suggested by some authors. Bubbly, slug and churn flows were observed for 10° from vertical pipe while bubbly, plug as well as slug flow when the pipe was inclined at 10° from horizontal. Examples of the PDFs are well illustrated which compares the use of ECT with WMS. In addition, statistical data such as Power Spectral Density (PSD), dominant frequency, mean void fraction as well as the structure velocities from cross correlation of the two planes of ECT have been identified.

Axial Variation of Mass Transfer Volumetric Coefficients in Bubble Column Bioreactors

2010 ◽  
Vol 5 (1) ◽  
Author(s):  
Elizabeth León-Becerril ◽  
Rafael Maya-Yescas
Keyword(s):  
Mass Transfer ◽  
Transfer Coefficient ◽  
Mass Transfer Coefficient ◽  
Bubble Size ◽  
Transfer Rate ◽  
Bubble Column ◽  
Mass Transfer Rate ◽  
Gas Bubbles ◽  
Transfer Rates ◽  
Metabolic Reactions

Bubble column bioreactors used to perform aerobic fermentations consist of a liquid medium containing microorganisms that uptake oxygen for metabolic reactions and gas bubbles that supply this oxygen. Mass transfer rate from gas to liquid phase is a crucial factor for the performance of bioreactors because microorganisms’ life and metabolic reactions depend directly upon it. The maximum transfer rate of oxygen from gas bubbles to the liquid medium is a function of two important parameters: the specific interfacial area and the mass transfer coefficient. These two parameters are lumped into the volumetric specific transfer coefficient. Since size of gas bubbles is not constant along the bioreactor, gas-liquid mass transfer rate changes continuously. In order to optimize mass transfer rates, it is essential to know the bubble size distribution and the interfacial phenomena in each particular system at different operating conditions. Due to the complexity of hydrodynamics and bubble interphase characteristics, the current state of the problem does not consider a universal model to evaluate mass transfer rates in gas-liquid systems; moreover, information about bubble size and its distribution is often neglected. This work presents a model to evaluate axial distribution of values of volumetric mass transfer coefficients considering changes in bubble size and its influence on bubble area along the reactor in homogeneous regime. Simultaneously, this model evaluates changes of volumetric mass transfer coefficient and its effect on the fermentation kinetics, which influences performance of the bioreactor.

Numerical Investigation of Air/Water and Hydrogen/Diesel Flow Across Tube Bundles With Baffles

2017 ◽  
Vol 139 (9) ◽  
Author(s):  
Diego N. Venturi ◽  
Waldir P. Martignoni ◽  
Dirceu Noriler ◽  
Henry F. Meier
Keyword(s):  
Void Fraction ◽  
Volume Fraction ◽  
Tube Bundle ◽  
Superficial Velocity ◽  
Intermittent Flow ◽  
Two Phase ◽  
Operational Conditions ◽  
Horizontal Flows ◽  
Tube Bundles ◽  
Experimental Approaches

Two-phase flows across tube bundles are very commonly found in industrial heat exchange equipment such as shell and tube heat exchangers. However, recent studies published in the literature are generally performed on devices where the flow crosses the tube bundle in only a vertical or horizontal direction, lacking geometrical fidelity with industrial models, and the majority of them use air and water as the working fluids. Also, currently, experimental approaches and simulations are based on very simplified models. This paper reports the simulation of a laboratory full-scale tube bundle with a combination of vertical and horizontal flows and with two different baffle configurations. Also, it presents a similarity analysis to evaluate the influence of changing the fluids to hydrogen and diesel in the operational conditions of the hydrotreating. The volume of fluid (VOF) approach is used as the interface phenomena are very important. The air/water simulations show good agreement with classical correlations and are able to show the stratified behavior of the flow in the horizontal regions and the intermittent flow in the vertical regions. Also, the two baffle configurations are compared in terms of volume fraction and streamlines. When dealing with hydrogen/diesel flow using correlations and maps made for air/water, superficial velocity is recommended as similarity variable when a better prediction of the pressure drop is needed, and the modified superficial velocity is recommended for prediction of the volume-average void fraction and the outlet superficial void fraction.

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