Influence of horizontal return bend on the two‐phase flow pattern in a 6.9 mm diameter tube

The two‐phase flow pattern for air‐water mixtures inside a 6.9 mm U‐tube is reported to have curvature ratios of 3?7.1. At a lower total mass flux of 50 kg/m²·s and a quality of 0.1, or at a larger curvature ratio of 7.1, no influence on the flow patterns is seen. However, if the curvature ratio is reduced to 3, the flow pattern in the recovery region just after the return bend is temporally turned from stratified flow into annular flow. For a quality larger than 0.4, the annular flow pattern prevails in the entire tube. For G = 400 kg/m²·s and x < 0.01, the size of the plug in the downstream is usually larger than that in the upstream due to the coalesce in the return bend. This coalescence phenomenon continues to further increase the total mass flux at the lower quality region. For a total mass flux above 500 kg/m²·s, the bubbly flow pattern in the upstream region may become intermittent.     

Effect of tube diameter on two‐phase flow patterns in mini tubes

The effect of tube diameter on two‐phase flow patterns was investigated in circular tubes with inner diameters of 0.6, 1.2, 1.7, 2.6, and 3.4 mm using air and water. The gas and liquid superficial velocity ranges were 0.01–50 and 0.01–3 m/s, respectively. The gas and liquid flow rates were measured and the two‐phase flow pattern images were recorded using high‐speed CMOS camera. The flow patterns observed were dispersed bubbly, bubbly, slug, slug‐annular, wavy‐annular, stratified, and annular flows. These flow patterns were not observed in all the test diameters, but were found to be unique to particular tube diameters, confirming the effect of tube diameter on the flow pattern. The data obtained were compared to existing experimental data and flow regime transition maps which show generally reasonable overall agreement at the larger diameters, but significant differences were observed with the smaller diameter tubes.     

CFD analysis of two‐phase turbulent flow in internal airlift reactors

The hydrodynamic performance of three internal airlift reactor configurations was studied by the Eulerian–Eulerian k–ε model for a two‐phase turbulent flow. Comparative evaluation of different drag and lift force coefficient models in terms of liquid velocity in the riser and downcomer and gas holdup in the riser was highlighted. Drag correlations as a function of Eötvös number performed better results in comparison to the drag expressions related to Reynolds number. However, the drag correlation as a function of both Reynolds and Eötvös numbers fitted well with experimental results for the riser gas holdup and downcomer liquid velocity in configurations I and II. Positive lift coefficients increase the liquid velocity and decrease the riser gas holdup, while opposite results were obtained for negative values. By studying the effects of bubble size and their shape, the smaller bubbles provide a lower liquid velocity and a gas holdup. The effects of bubble‐induced turbulence and other non‐drag closure models such as turbulent dispersion and added mass forces were analysed. The gas velocity and gas holdup distributions, liquid velocity in the riser and downcomer, vectors of velocity magnitude and streamlines for liquid phase, the dynamics of gas holdup distribution and turbulent viscosity at different superficial gas velocities for different reactor configurations were computed. The effects of various geometrical parameters such as the draft tube clearance and the ratio of the riser to the downcomer cross‐sectional area on liquid velocities in the riser and the downcomer, the gas velocity and the gas holdup were explored. © 2011 Canadian Society for Chemical Engineering     

Characteristics of air–water two‐phase flow in a 3‐mm smooth tube

Two‐phase flow pattern and friction characteristics for an air–water system in a 3.17 mm smooth tube are reported in this study. The range of mass flux is between 50 and 700 kg/m²s. The experimental data show that the two‐phase friction multipliers are strongly related to the flow pattern. For a stratified‐wavy flow pattern, a mass‐flux dependence of the two‐phase multipliers is seen. For a non‐stratified flow pattern, the two‐phase frictional multipliers are comparatively independent of mass flux. Correlations of the frictional multipliers are developed for stratified and non‐stratified flow. To use the appropriate correlation in different regime, a simple criterion is proposed.     

Oil–water two‐phase flow in microchannels: Flow patterns and pressure drop measurements

This paper investigates oil–water two‐phase flows in microchannels of 793 and 667 µm hydraulic diameters made of quartz and glass, respectively. By injecting one fluid at a constant flow rate and the second at variable flow rate, different flow patterns were identified and mapped and the corresponding two‐phase pressure drops were measured. Measurements of the pressure drops were interpreted using the homogeneous and Lockhart–Martinelli models developed for two‐phase flows in pipes. The results show similarity to both liquid–liquid flow in pipes and to gas–liquid flow in microchannels. We find a strong dependence of pressure drop on flow rates, microchannel material, and the first fluid injected into the microchannel.     

Pressure drop for single and two‐phase flow of non‐newtonian liquids in helical coils

New experimental results on pressure loss for the single and two‐phase gas‐liquid flow with non‐Newtonian liquids in helical coils are reported. For a constant value of the curvature ratio, the value of the helix angle of the coils is varied from 2.56° to 9.37°. For single phase flow, the effect of helix angle on pressure loss is found to be negligible in laminar flow regime but pressure loss increases with the increasing value of helix angle in turbulent flow conditions. On the other hand, for the two‐phase flow, the well‐known Lockhart‐Martinelli method correlates the present results for all values of helix angle (2.56‐9.37°) satisfactorily under turbulent/laminar and turbulent/turbulent conditions over the following ranges of variables as: 0.57 ≤ n′ ≤ 1; Re′ < 4000; Re_l < 4000; Re_g < 8000; 8 ≤ x ≤ 1000 and 0.2 ≤ De′ ≤ 1000.     

Influence of liquid viscosity and bed porosity on two‐phase pressure drop in concurrent gas‐liquid upflow through packed beds

It was observed in the experimental investigations that the concurrent upflow of air‐Monoethanol amine system through the packed bed gave higher pressure drop in bubble flow regime than the air‐water system. But when the flow regime changed to spray flow, air‐water system showed higher pressure drop than the other. This phenomenon was observed for the two column packing used in this study. An attempt is made to explain this phenomenon.     

Gas holdup in a two‐phase reversed flow jet loop reactor

Experimental investigations have been carried out in Reversed Flow Jet Loop Reactor (RFJLR) to study the influence of liquid flow rate, gas flow rate, immersion height of two‐fluid nozzle in reactor and nozzle diameter on gas holdup without circulation, that is, gas–liquid mixture in draft tube only (E_gd) and gas holdup with circulation loop (E_g). Also critical liquid flow rate required for transition from draft tube to circulation loop has been determined. Gas holdup was measured by isolation valve technique. Gas holdup in draft tube and circulation loop increased with increase in liquid flow rate and gas flow rate. It is observed that the increased flow rate is required for achieving a particular value of gas holdup with larger nozzle diameter. Nozzle at the top edge of draft tube have higher gas holdup as compared to other positions. It has been noted that, no significant recirculation of gas bubbles into the top of draft tube from annulus section has been observed till a particular liquid flow rate is reached. A plot of gas holdup with no circulation and with circulation mode determines minimum liquid flow rate required to achieve complete circulation loop. Critical liquid flow rate required to achieve complete circulation loop increases with increase in gas flow rate and is minimum at lowest immersion height of two‐fluid nozzle.     

Polymer–solute interactions in solid–liquid two‐phase partitioning bioreactors

BACKGROUND: Biphasic systems with immiscible solvents have been studied for in situ product removal, and have shown improvements in bioreactor performance, however, problems associated with solvent biocompatibility, bioavailability and operation have been identified. One alternative is the solid–liquid system in which polymer beads are used, absorbing and removing target compounds from the aqueous phase while maintaining equilibrium conditions. This work aims to identify polymer properties that may be important in polymer selection for selected biotransformation molecules including 2‐phenylethanol, cis‐1,3‐indandiol, iso‐butanol, succinic acid and 3‐hydroxybutyrolactone. RESULTS: Relatively hydrophobic compounds (e.g. 2‐phenylethanol) tend to be absorbed by polymers better than hydrophilic ones (e.g. iso‐butanol) based on partition coefficient tests; values as high as 80 were obtained for the former and < 3 for the latter. Owing to the presence of polar functional groups on these compounds, polar polymers such as Hytrel® performed better than non‐polar ones such as Kraton®. Crystallinity and intermolecular hydrogen‐bonding were also found to be important polymer properties. CONCLUSION: Polymers showed excellent results in absorbing hydrophobic compounds such as aromatic alcohols, and positive results in absorbing hydrophilic compounds but to a lesser extent. Grafting hydrophilic functional groups onto polymers may be a promising approach for extending polymer uptake capabilities and is currently being investigated. Copyright © 2009 Society of Chemical Industry     

Prediction of liquid height for onset of slug flow

An experimental investigation is carried out to study the transition from stratified to slug flow and the development of slug flow. The variation of Lockhart–Martinelli parameter with the non‐dimensional liquid height is established based on the experimental data. A correlation is developed for the liquid height as a function of superficial gas and liquid Reynolds number. The liquid height is observed to increase up to some level depending on the mass flow rate, beyond which there is a sudden jump in the height leading to the formation of slug. This critical liquid height is the limiting condition for the evolution of slug. Below the critical height a stable stratified flow is observed. The critical height for stability limit of stratified flow is established experimentally for various combinations of mass flow rates of the primary and secondary phases. © 2011 Canadian Society for Chemical Engineering     

Modeling and simulation of conditionally volume averaged viscoelastic two‐phase flows

Conditional volume averaging is used to develop a model capable of simulating two‐phase flows of viscoelastic fluids with surface tension effects. The study is started with the single‐phase mass and momentum balances, which are subsequently conditionally volume averaged. In doing so, we arrive at a set of equations having unclosed interfacial terms, for which closure relations for viscoelastic fluids are presented. The resulting equations possess a structure similar to the single‐phase equations; however, separate conservation equations are solved for each phase. As a result, each phase has its own pressure and velocity over the entire domain. Next, our numerical implementation is briefly outlined. We find that a Poiseuille single‐phase flow is predicted correctly. The closure terms are examined by considering a two‐phase shearing flow and a quiescient cylinder with surface tension. A convergence analysis is performed for a steady stratified two‐phase flow with both phases being viscoelastic. © 2013 American Institute of Chemical Engineers AIChE J, 59: 3914–3927, 2013     

Liquid‐liquid two‐phase flow patterns in a new helical microchannel device

Flow patterns of liquid‐liquid two‐phase fluids in a new helical microchannel device were presented in this paper. Three conventional systems were considered: kerosene‐water, n‐butyl acetate‐water, and butanol‐water. Six different flow patterns, slug flow, continuous parallel flow, discontinuous deformation parallel flow, discontinuous deformation parallel‐droplet flow, droplet‐slug flow, and filiform‐droplet flow, were observed. The influence of interfacial tension, microchannel structure, and rotation rate on two‐phase flow patterns were studied, and a universal flow pattern map was presented and discussed. The systems without mass transfer (0.1 g/g (10 %) tri‐n‐butyl phosphate (TBP)‐water, 0.2 g/g (20 %) TBP‐water, and 0.8 g/g (80 %) TBP‐water) and the system with mass transfer (0.8 g/g (80 %) TBP‐0.62 g/g (62 %) H₃PO₄) were used to verify the validity of the proposed universal flow pattern map in predicting flow patterns. The results showed that the former compared with the latter can be predicted more accurately by the universal flow pattern map.     

A new mechanistic model to predict gas–liquid interface shape of gas–liquid flow through pipes with low liquid loading

Devising a new mechanistic method to predict gas–liquid interface shape in horizontal pipes is concerned in this article. An experiment was conducted to find the pressure gradients of air–water flow through a 1‐in. pipe diameter. Comparing results of model with some experimental data available in the literature demonstrates that the model provides quite better predictions than existed models do. This model also predicts flow regime transition from stratified to annular flow better than Apparent Rough Surface and Modified Apparent Rough Surface models for both 1‐ and 2‐in. pipe diameters. The model also leads to reliable predictions of wetted wall fraction experimental data. Although one parameter of new model was evaluated based on air–water flow pressure loss experimental data for 1 in. pipe, it was considerably successful to predict pressure drop, liquid holdup, stratified‐annular transition and wetted wall fraction for other gas–liquid systems and pipe diameters. © 2014 American Institute of Chemical Engineers AIChE J, 61: 1043–1053, 2015     

Corrosion inhibition of carbon steel under two‐phase flow (water‐petroleum) simulated by turbulently agitated system

The corrosion of carbon steel in single‐phase (water with 0.1N NaCl) and two immiscible phases (kerosene‐water) using turbulently agitated system was investigated. The experiments were carried out for Reynolds number (Re) range of 38 000 to 95 000 using circular disc turbine agitator at 40°C. In two‐phase system, test runs were carried out in aqueous phase (water) concentrations of 1% vol, 5% vol, 8% vol, and 16.4% vol mixed with kerosene at various Re. The effect of Re, percent of dispersed phase, dispersed droplet diameter, and number of droplets per unit volume on the corrosion rate were investigated and discussed. Test runs were carried out using two types of inhibitors: sodium nitrite of concentrations 20, 40, and 60 ppm and sodium hexapolyphosphate of concentrations 485, 970, and 1940 ppm in a solution containing 8% vol aqueous phase (water) mixed with kerosene (continuous phase) at 40°C for the whole range of Re. It was found that increasing Re increased the corrosion rate and the presence of water enhanced the corrosion rate by increasing the solution electrical conductivity. For two‐phase solution containing 8% vol and 16% vol of water, the corrosion rate was higher than single phase (100% vol water). The main parameters that play the major role in determining the corrosion rate in two phases were concentration of oxygen, solution electrical conductivity, and the interfacial area between the two phases (dispersed and continuous). Sodium nitrite and sodium hexapolyphosphate were found to be efficient inhibitors in two‐phase solution for the investigated range of Re.     

Medium composition effects on solute partitioning in solid–liquid two‐phase bioreactors

Biphasic systems such as two‐phase partitioning bioreactors (TPPBs) have been used to alleviate biological inhibition by sequestering inhibitory compounds within an immiscible phase. The use of solid polymer beads as this auxiliary phase provides a fully biocompatible alternative to potentially toxic organic solvents. While guidelines exist for the rational selection of the polymer phase, the effect of the aqueous phase composition on molecular sequestration has not been explored in the literature. This work aims to identify aspects of medium composition that influence the partitioning of target molecules into the sequestering phase. Using benzaldehyde as the target molecule and Hytrel G3548L (DuPont) as the polymer phase, pH, temperature, salt and glucose concentrations, as well as ethanol concentrations, were examined for their effects on the partition coefficient. pH and temperature were observed to have no significant effect on benzaldehyde partitioning. Salt and glucose additions increased the partition coefficient by 173% and 30%, respectively, compared with pure reverse osmosis (RO) water, while increasing ethanol concentration was found to decrease the partition coefficient from 44 ( ± 1.6) to 1 ( ± 0.3). Strategic changes to the aqueous phase can be made to improve affinity of the sequestering phase for target molecules. This provides a simple and cost‐effective method to potentially improve TPPB system performance. Copyright © 2010 Society of Chemical Industry     

A mechanistic model for roll waves for two‐phase pipe flow

A new two‐phase roll wave model is compared with data from high pressure two‐phase stratified pipe flow experiments. Results from 754 experiments, including mean wave speed, wave height, pressure gradient, holdup and wave length, are compared with theoretical results. The model was able to predict these physical quantities with good accuracy without introducing any new empirically determined quantities to the two‐fluid model equations. This was possible by finding the unique theoretical limit for nonlinear roll amplitude and applying a new approach for determining the friction factor at the gas‐liquid interface. © 2009 American Institute of Chemical Engineers AIChE J, 2009     

Dynamic effects in capillary pressure relationships for two‐phase flow in porous media: Experiments and numerical analyses

Well defined experiments and numerical analyses are conducted to determine the importance of dynamic effect in capillary pressure relationships for two‐phase flow in porous media. Dynamic and quasi‐static capillary pressure‐saturation (P^c‐S_w) and, ?S_w/?t‐t curves are determined. These are then used to determine the dynamic effects, indicated by a dynamic coefficient (τ) in the porous domains which establishes the speed at which flow equilibrium (?S_w/?t = 0) is reached. τ is found to be a nonlinear function of saturation which also depends on the medium permeability. Locally determined τ seems to increase as the distance of the measurement point from the fluid inlet into the domain increases. However, the functional dependence τ‐S_w follows similar trends at different locations within the domain. We argue that saturation weighted average of local τ‐S_w curves can be defined as an effective τ‐S_w curve for the whole domain which follows an exponential trend too. © 2012 The Authors. AIChE Journal, published by Wiley on behalf of the AIChE. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited. AIChE J, 58: 3891–3903, 2012