scholarly journals Measurement of local effective diffusivity in heterogeneous biofilms

1998 ◽  
Vol 38 (8-9) ◽  
pp. 171-178 ◽  
Author(s):  
H. Beyenal ◽  
A. Tanyolaç ◽  
Z. Lewandowski
Keyword(s):  
Flow Velocity ◽  
Liquid Flow ◽  
Empirical Equation ◽  
Effective Diffusivity ◽  
Mixed Population ◽  
Limiting Current ◽  
Biomass Density ◽  
Fast Evaluation ◽  
Novel Technique ◽  
Electroactive Species

We have developed a novel technique to measure local effective diffusivity distribution in heterogeneous biofilms. Mobile microelectrodes (tip diameter 10 μm) and the limiting current technique were employed to measure the effective diffusivity of electroactive species introduced to natural and artificial biofilms. We calibrated the microelectrodes in artificial biofilms of known effective diffusivity and known density. In mixed population biofilms, local effective diffusivity varied from one location to another and decreased toward the bottom of the biofilm. We related local effective diffusivity to local biofilm density using an empirical equation. Surface-averaged biomass density depended on liquid flow velocity at which the biofilms were grown. The higher the flow velocity, the denser were the biofilms. Our technique permits fast evaluation of local effective diffusivity and biofilm density in heterogeneous biofilms.

Acetate and ammonium diffusivity in membrane-aerated biofilms: improving model predictions using experimental results

2005 ◽  
Vol 52 (7) ◽  
pp. 121-126 ◽  
Author(s):  
J.W. Shanahan ◽  
A.C. Cole ◽  
M.J. Semmens ◽  
T.M. LaPara
Keyword(s):  
Population Stratification ◽  
Fluid Velocity ◽  
Effective Diffusivity ◽  
Substantial Variation ◽  
Biomass Density ◽  
Bacterial Populations ◽  
Modified Model ◽  
Biofilm Reactors ◽  
Model Predictions ◽  
High Fluid

Membrane-aerated biofilm reactors (MABRs) are advantageous for wastewater treatment because of their ability to achieve both nitrification and denitrification in a single bioreactor. The stratification of membrane aerated biofilms, however, needs to be better understood so that MABRs can be properly designed and implemented. In this study, we present a modified multi-population model that accounts for variation in effective diffusivity in biofilms of variable biomass density. For biofilms grown at a low fluid velocity (2 cm s−1), the variation in effective diffusivity had a profound effect on the predicted stratification and activity of bacterial populations. For biofilms grown at a high fluid velocity (14 cm s−1), biomass density was relatively constant as a function of depth and thus there was less substantial variation in effective diffusivity; our modified model, therefore, predicted a population stratification that was similar to its original version under these conditions.

Effect of liquid flow velocity on corrosion behavior of 20# steel at initial stage under gas-liquid two-phase plug flow condition

2020 ◽  
Vol 67 (4) ◽  
pp. 415-425
Author(s):  
Guirong Yang ◽  
Wenming Song ◽  
Zibo Zhu ◽  
Ying Ma ◽  
Yuan Hao
Keyword(s):  
Corrosion Rate ◽  
Flow Velocity ◽  
Liquid Flow ◽  
Pipe Wall ◽  
Liquid Velocity ◽  
Plug Flow ◽  
Corrosion Products ◽  
Two Phase ◽  
Content Type ◽  
Corrosion Time

Purpose The paper aims to study the effect of liquid flow velocity on corrosion behavior of 20# steel at initial stage under (CO2/aqueous solution) gas–liquid two-phase plug flow conditions. Design/methodology/approach Weight loss, scanning electron microscopy, energy-dispersive X-ray spectroscopy and XPS methods were used in this study. Findings The corrosion rate increased with the increasing liquid flow velocity at any different corrosion time. The corrosion rate decreased with the extension of corrosion time at the same liquid flow velocity. There was no continuous corrosion products film on the whole pipe wall at any different corrosion time. The macroscopic brown-yellow corrosion products on the pipe wall surface decreased with the increasing liquid flow velocity and the loose floccus corrosion products decreased gradually until these products were transformed into un-continuous needle-like dense products with the increasing liquid velocity. The main elements among the products film were Fe, C and O, and the main phases of products film on the pipe wall were Fe3C, FeCO3, FeOOH and Fe3O4. When the corrosion time was 1 h under different liquid–velocity condition, the thickness of local corrosion products film was from 3.5 to 3.8 µm. Originality/value The ion mass transfer model of corrosion process in pipe was put forward under gas–liquid two-phase plug flow condition. The total thickness of diffusion sublayer and turbulence sublayer decreased as well as the turbulence propagation coefficient increased with the increasing liquid velocity, which led to the increasing velocity of ion transfer during corrosion process. This was the fundamental reason for the increase of corrosion rate with the increasing liquid velocity.

A hybrid method of debris flow velocity estimation based on empirical equation

2017 ◽  
Vol 35 (1) ◽  
pp. 147-152 ◽  
Author(s):  
Shuwen Tian ◽  
Changming Wang ◽  
Zhimin Zhang
Keyword(s):  
Debris Flow ◽  
Flow Velocity ◽  
Hybrid Method ◽  
Empirical Equation ◽  
Velocity Estimation

scholarly journals Tungsten oxide electrode for measurement of ultralow liquid flow velocity

2015 ◽  
Vol 215 ◽  
pp. 459-463
Author(s):  
Yizhang Wen ◽  
Xiaoping Wang ◽  
Peijun Cai ◽  
Bing Zhang
Keyword(s):  
Flow Velocity ◽  
Tungsten Oxide ◽  
Liquid Flow ◽  
Oxide Electrode

Liquid Flow in Rectangular Microchannels with Gradient Wettability Inner Surface Driven by Capillary Force and Gravity

2011 ◽  
Vol 233-235 ◽  
pp. 1152-1156
Author(s):  
Jiang Cheng ◽  
Yuhong Tao ◽  
Yong Zhang ◽  
Zhi Qi Cai ◽  
Pi Hui Pi ◽  
...  
Keyword(s):  
Mathematical Model ◽  
Flow Velocity ◽  
Liquid Flow ◽  
Capillary Force ◽  
Driving Force ◽  
Flow Front ◽  
Rectangular Microchannel ◽  
Inner Surface ◽  
Channel Surface ◽  
Moving Path

A mathematical model for predicting liquid flow velocity in a rectangular microchannel driven by capillary force and gravity is derived. The model takes into account the additional driving force arising from the wettability gradient on inner surface of a microchannel. The results of model prediction show that the velocity of liquid flow decreases with the length of microchannel and the wettability gradient on channel surface will accelerate the motion of the liquid when the flow-front approaches to the end of the microchannel. The analysis of driving force along the moving path matches well with the flow velocity predicted by the model.

CRITICAL FLOW VELOCITY FOR COLLAPSE OF A CLAMPED-CLAMPED PIPE CONVEYING GAS-LIQUID FLOW

2018 ◽  
Author(s):  
David Castillo ◽  
L. Enrique Ortiz-Vidal ◽  
Quino Valverde
Keyword(s):  
Flow Velocity ◽  
Liquid Flow ◽  
Critical Flow ◽  
Critical Flow Velocity ◽  
Gas Liquid Flow

Corrosion Evaluation for Aluminum Alloy (6262) in Aerated 3.5% NaCl Solutions under Hydrodynamic Conditions

2010 ◽  
Vol 154-155 ◽  
pp. 1846-1849
Author(s):  
Ahmed Y. Musa ◽  
Abdul Amir H. Kadhum ◽  
Abu Bakar Mohamad ◽  
Mohd Sobri Takriff
Keyword(s):  
Aluminum Alloy ◽  
Flow Velocity ◽  
Flow Condition ◽  
Sea Water ◽  
Electrochemical Impedance ◽  
Limiting Current ◽  
Corrosion Mechanism ◽  
Mixed Control ◽  
Limiting Current Density ◽  
Corrosion Evaluation

The corrosion of aluminum alloy (6262) in artificial sea water under flow condition was evaluated using electrochemical impedance spectroscopy (EIS) and potentiodynamic methods. The flow condition experiments were simulated using rotating cylinder electrode (RCE). Results showed that the increasing of the flow velocity enhances the corrosion kinetic of the system and changes the corrosion mechanism. Limiting current density was increased with increasing in the flow velocity. This behavior was due to the presence of a mixed control on the corrosion process related with the formation and stabilization of corrosion product layers on the electrode surface.

Modelling of the Near-Wall Liquid Velocity Field in Subcooled Boiling Flow

2005 ◽  
Author(s):  
Franz Ramstorfer ◽  
Bernd Breitscha¨del ◽  
Helfried Steiner ◽  
Gu¨nter Brenn
Keyword(s):  
Experimental Data ◽  
Surface Roughness ◽  
Flow Velocity ◽  
Liquid Flow ◽  
Axial Velocity ◽  
Velocity Profiles ◽  
Subcooled Boiling ◽  
Test Channel ◽  
Boiling Flow ◽  
Near Wall

The subject of the present work is the modelling of the liquid streamwise flow velocity in the two-phase boundary layer in subcooled boiling flow under the influence of the vapor bubbles. Subcooled boiling flow experiments were carried out in a horizontal test channel in order to investigate the interaction between the bubbles and the liquid phase. The heater surface was located at the bottom of the test channel. The near-wall liquid flow velocity was measured using a two-component laser-Doppler anemometer. Based on the experimental data a model is proposed to describe the impact of the gaseous phase on the motion of the liquid in the subcooled boiling regime. It was observed that the axial velocity profiles near the wall follow a logarithmic law similar to that used in turbulent single-phase flow over rough surfaces. Based on this finding it is suggested to model the influence of the bubbles on the liquid flow analogously to the effect of a surface roughness. The correlation developed for an equivalent surface roughness associated with the bubbles yields good agreement of the modeled axial velocity profiles with the experimental data.

Sign in / Sign up

Export Citation Format

Share Document