Bubble Residence Time Research Articles

Optimization of bubble column performance for nanoparticle collection

Fibrous media embody the most effective and widely used method of separating ultrafine particles from a carrier fluid. The main problem associated with them is filter clogging, which induces an increasingly marked pressure drop with time and thus imposes regular media cleaning or replacement. This context has prompted the idea of investigating bubble columns, which operate at constant pressure drop, as alternatives to fibrous filters. This study examines the influence of different operating conditions, such as liquid height, air flow rate, bubble size and presence of granular beds on ultrafine particle collection. Experimental results show that bubble columns are characterised by high collection efficiency, when they feature a large liquid height and small diameter bubbling orifices, while their efficiencies remain lower than those of fibrous filters. Gas velocity does not greatly influence collection efficiency, but the inclusion of a granular bed, composed of beads, increases the bubble residence time in the column, thereby increasing the column collection efficiency.

Initial Experimental and Theoretical Investigation of Solar Molten Media Methane Cracking for Hydrogen Production

Previous work assessed the fundamental technical and market risks associated with the development and deployment of solar fuels technology in Alberta. It identified methane cracking in solar-molten media as the hydrogen production technology featuring the best combination of technical risk, market acceptance, and breakthrough potential of all the techniques covered in the study. Alberta Innovates – Technology Futures (AITF) plans to advance the technology from a conceptual stage to a proof-of concept over a span of 4 years. The ultimate goal is to design, build and test a prototype solar receiver/reactor in a suitable solar simulator.The paper outlines the activities to date concerning the initial bench-scale testing of methane cracking in molten media at temperatures ranging from 1023 to 1373K. The design and construction of an experimental apparatus used to establish the fundamental thermo-chemical performance of the process is presented, along with preliminary results and lessons from the first testing campaign. A transient, non-isothermal, preliminary mathematical model of a reacting bubble within the molten metal has been developed using MATLAB. The model accounts for the chemical reactions, diffusion of the gases in the bubble and heat transfer from the molten metal to the reacting gases. The model can be used to predict the minimum bubble residence time needed to achieve a given hydrogen yield. The simulation tool will be used to numerically estimate methane conversions in the reactor at various conditions.

Assessment of Mass-Transfer Effects during Polyether Production from 1,3-Propanediol

A mathematical model is developed to simulate condensation polymerization of 1,3-propanediol to produce polytrimethylene glycol (PO3G) polyether. The model includes improved mass-transfer expressions that account for nonzero concentrations of water and monomer inside nitrogen bubbles and for increasing overall bubble surface area due to increases in bubble residence time. An objective function that accounts for the mole fractions of evaporated monomer, water and propanal is considered for parameter estimation. Improvements in the predicted monomer and water concentrations in the polymer and evaporation rates of monomer and water can be observed compared to a previous model.[5, 6] However, predictions of degree of polymerization do not improve noticeably. Recommendations including revisions of the chemical mechanism to include additional reactions and accounting for evaporation of linear and cyclic oligomers in future models are suggested.

Simulation on Gas Injection Refining Process with Mechanical Stirring

Basing on the new method of in-situ desulfurization with gas injection and mechanical stirring, the effect of bubble dispersion and disintegration of three type impellers are numerically simulated by commercial CFD software Ansys Fluent 12.0. Numerical simulations of three-dimensional multiphase turbulence in gas injection and mechanical stirring are performed by adopting unsteady SM method coupled with Eulerian multiphase model and two-phase turbulence model. The information of gas-liquid fluid flow, velocity, turbulent kinetic energy and the power consumption are investigated and the results show that the SSB impeller can make bubbles get best dispersion and disintegration，and its power consumption is lower than VB impeller. The disk on the impeller blades can weaken the swirl flow in the upper zone of the impeller. Therefore, the bubble residence time is extended, and the bubble dispersing zone is also increased. DOI: http://dx.doi.org/10.11591/telkomnika.v10i8.1659 Full Text: PDF

Influence of magma ascent rate on carbon dioxide degassing at oceanic ridges: Message in a bubble

In order to quantify the magma ascent rate beneath oceanic ridges, we propose a new method based on vesicle size distribution (VSD) and volatiles measurements (CO2 and H2O) on 65 fresh glasses from the global Mid-Ocean Ridge system. Comparisons of VSD between the main oceanic basins reveal that Mid-Ocean-Ridge-Basalts (MORB) from the Pacific Ocean have significantly higher bubble densities (148−124+739 bubbles/cm2) and initial population densities ln(n0)=19.6±2.8cm−4 but lower vesicularities (∼0.1%). We determine the residence time of bubbles in the magma using the linear relationship between the logarithm of the density population and the vesicle diameters. Assuming a constant bubble growth rate (G=1.5×10−7cm/s), we suggest that the transit times of the magmas through the oceanic crust are shorter beneath Pacific ridges (∼2 h) than elsewhere (∼15 h). In addition, the CO2 and H2O contents of the studied glasses allow the carbon saturation pressure to be calculated. Pacific MORB display a significantly lower carbon dioxide saturation pressure (Psat=843−221+300bars) than Atlantic and Indian MORB (Psat=1898−827+1466bars) but identical pressures of eruption (Pe∼310bars). Consequently, the distance traveled by bubbles from the vesiculation depth to the seafloor is shorter for the Pacific (∼1.9km) than for the Atlantic and Indian oceans (∼5.2km): the longer the transit time, the longer the distance traveled. A closer inspection of the data revealed that the decompression rate (dP/dt) varied from 5.0×102 to 2.3×104Pa/s and correlated positively with the measured bubble densities (nb/m3) as expected from experimental data and numerical modeling. At the global scale, most of the Pacific samples are characterized by high ascent rates (0.25−0.13+0.26m/s) relative to those from the Atlantic (0.11−0.06+0.15m/s) and the Indian samples (0.09−0.03+0.05m/s). However, at the local scale some samples from the Mid-Atlantic Ridge at 37 °N (where the reflections of seismic waves from crustal magma chamber have been observed) are not distinguishable from the Pacific data set having high ascent rates and large bubble densities. We suggest that the method presented in this study could be used to identify spots along the Mid-Oceanic-Ridge system where magma chambers are possibly present.

Investigating Primary Marine Aerosol Properties: CCN Activity of Sea Salt and Mixed Inorganic–Organic Particles

Sea spray particles ejected as a result of bubbles bursting from artificial seawater containing salt and organic matter in a stainless steel tank were sampled for size distribution, morphology, and cloud condensation nucleus (CCN) activity. Bubbles were generated either by aeration through a diffuser or by water jet impingement on the seawater surface. Three objectives were addressed in this study. First, CCN activities of NaCl and two types of artificial sea salt containing only inorganic components were measured to establish a baseline for further measurements of mixed organic–inorganic particles. Second, the effect of varying bubble residence time in the bulk seawater solution on particle size and CCN activity was investigated and was found to be insignificant for the organic compounds studied. Finally, CCN activities of particles produced from jet impingement were compared with those produced from diffuser aeration. Analyses indicate a considerable amount of organic enrichment in the jet-produced particles relative to the bulk seawater composition when sodium laurate, an organic surfactant, is present in the seawater. In this case, the production of a thick foam layer during impingement may explain the difference in activation and supports hypotheses that particle production from the two methods of generating bubbles is not equal.

A new dynamic model for highly efficient mass transfer in aerated bioreactors and consequences for kLa identification

Gas-liquid mass transfer is often rate-limiting in laboratory and industrial cultures of aerobic or autotrophic organisms. The volumetric mass transfer coefficient k(L) a is a crucial characteristic for comparing, optimizing, and upscaling mass transfer efficiency of bioreactors. Reliable dynamic models and resulting methods for parameter identification are needed for quantitative modeling of microbial growth dynamics. We describe a laboratory-scale stirred tank reactor (STR) with a highly efficient aeration system (k(L) a ≈ 570 h(-1)). The reactor can sustain yeast culture with high cell density and high oxygen uptake rate, leading to a significant drop in gas concentration from inflow to outflow (by 21%). Standard models fail to predict the observed mass transfer dynamics and to identify k(L) a correctly. In order to capture the concentration gradient in the gas phase, we refine a standard ordinary differential equation (ODE) model and obtain a system of partial integro-differential equations (PIDE), for which we derive an approximate analytical solution. Specific reactor configurations, in particular a relatively short bubble residence time, allow a quasi steady-state approximation of the PIDE system by a simpler ODE model which still accounts for the concentration gradient. Moreover, we perform an appropriate scaling of all variables and parameters. In particular, we introduce the dimensionless overall efficiency κ, which is more informative than k(L) a since it combines the effects of gas inflow, exchange, and solution. Current standard models of mass transfer in laboratory-scale aerated STRs neglect the gradient in the gas concentration, which arises from highly efficient bubbling systems and high cellular exchange rates. The resulting error in the identification of κ (and hence k(L) a) increases dramatically with increasing mass transfer efficiency. Notably, the error differs between cell-free and culture-based methods of parameter identification, potentially confounding the determination of the "biological enhancement" of mass transfer. Our new model provides an improved theoretical framework that can be readily applied to aerated bioreactors in research and biotechnology.

CFD-DPM Modeling of Gas-Liquid Flow in a Stirred Vessel

Gas-liquid flow in a stirred vessel was simulated numerically with computational fluid dynamics(CFD). Gas was treated as discrete phase and described by discrete phase model (DPM), while the liquid was considered as a continuum and solved under Euler reference frame. The liquid velocity, gas holdup and gas residence time distribution in the stirred vessel were predicted. The simulation results show that gas dispersion in the stirred vessel is very non-uniformity and high gas holdup is found in the centre of the stirred vessel and vortexes while relatively low in bottom region and region between two impellers. Liquid velocity has great influence on bubble residence time and size distributions.

Agitation of a gas-solid-liquid system in a vessel with high-speed impeller and vertical tubular coil

AbstractExperimental results of gas hold-up, power consumption and residence time of gas bubbles in a gas-solid-liquid system produced in an agitated vessel equipped with a high-speed impeller and a vertical tubular coil are presented in this paper. Critical agitator speed, needed for the dispersion of gas bubbles and solid particles in liquid were also identified. The studies were carried out in an agitated vessel of the inner diameter D = 0.634 m and the working liquid volume of about 0.2 m3. A tubular coil of the diameter of 0.7D, consisting of 24 vertical tubes of the diameter of 0.016D, was located inside the flat-bottomed vessel. The agitated vessel was equipped with a Rushton turbine with six blades or an A 315 impeller with four blades. Both impellers had diameter, d, equal to 0.33D. The vessel was filled with liquid up to the height H = D. In this study, air and particles of sea sand with the mean diameter of 335 μm and the concentration of up to 3.0 mass % were dispersed in distilled water as the liquid phase. The measurements were carried out within the turbulent regime of the fluid flow in the agitated vessel. Results of the measurements were processed graphically and mathematically. Lower values of the critical agitator speed, n JSG, needed for simultaneous dispersion of gas bubbles and particles with the solids concentration from 0.5 mass % to 2 mass %, were obtained for the vessel equipped with the A 315 impeller. Higher values of the specific power consumption were reached for the vessel with the Rushton turbine. Higher values of the gas hold-up and residence time of the gas bubbles in the fluid were obtained for the system equipped with the Rushton turbine. Results of the gas hold-up as a function of the specific power consumption, superficial gas velocity and solids concentration were approximated with good accuracy using Eq. (5).

Experimental analysis of the hydrodynamics of a three-phase system in a vessel with two impellers

AbstractResults of experimental analysis concerning gas hold-up and average residence time of gas bubbles in a three-phase gas-solid-liquid system produced in a baffled, double-impeller vessel are presented. Measurements were carried out in a vessel with the internal diameter of 0.288 m. Two different double-impeller configurations were used for agitation: Rushton turbine (lower) — A 315 (upper) and Rushton turbine (lower) — HE 3 (upper). Upper impellers differed in the fluid pumping mode. Coalescing and non-coalescing systems were tested. Liquid phases were distilled water (coalescing system) and aqueous solutions of NaCl (non-coalescing systems). The ability of gas bubbles to coalesce in the liquid was described using parameter Y. Dispersed phases were air and particles of sea sand. The experiments were conducted at seven different gas flow rates and two particle loadings. Effects of the ability of gas bubbles to coalesce (liquid phase properties), operating parameters (superficial gas velocity, impeller speed, solids loadings), and of the type of the impeller configuration on the investigated parameters were determined. The results were approximated mathematically. For both impeller configurations tested, significantly higher gas hold-up values were obtained in the non-coalescing gas-solid-liquid systems compared to the coalescing one. Out of the tested impeller systems, the RT-A 315 configuration proved to have better performance ensuring good gas dispersion in the liquid in the three-phase systems.

Removal of Impurity Elements from Molten Aluminum: A Review

In the current paper, the technical progress of aluminum refining over the past 30 years has been summarized, including the improvement of batch reactor and in-line continuous reactors, the evolution of gas purging methods by nozzle, porous plug, and rotating impellor, and the use of fluxing by using gas mixtures (including argon, nitrogen, and chlorine) and solid salts (such as AlF3, MgCl2, and KCl). The mathematical models developed for the removal of impurity elements from molten aluminum were also reviewed. Thermodynamic factors were summarized, including the Gibbs free energy of the chemical reactions, activity coefficients of the impurity elements, and the melting and boiling points of impurity elements and related compounds. Kinetic factors used and derived by researchers are also reviewed, such as mass transfer coefficient of impurity elements, mixing power and mixing time in reactors stirred by gas, impellor and circulation of the fluid, and the size, residence time, and terminal velocity of bubbles. The current review provides useful information for the future study of the removal of impurity elements from aluminum.

Numerical prediction of critical heat flux in pool boiling with the two-fluid model

Three-dimensional numerical simulations of the atmospheric saturated pool boiling are performed with the aim of predicting the critical heat flux. The two-phase mixture in pool boiling is described with the transient two-fluid model. The transient heat conduction in the horizontal heated wall is also solved. Dynamics of vapor generation on the heated wall is modeled through the density of nucleation sites and the bubble residence time on the wall. The heater’s surface is divided into zones, which number per unit area equals the density of nucleation sites, while the location of nucleation site within each zone is determined by a random function. The results show a replenishment of the heater’s surface with water and surface wetting for lower heat fluxes, while heater’s surface dry-out is predicted at critical heat flux values. Also, it is shown that the decrease of nucleation site density leads to the reduction of critical heat flux values. Obtained results of critical heat flux are in good agreement with available measured data. The presented approach is original regarding both the application of the two-fluid two-phase model for the prediction of boiling crisis in pool boiling and the defined boundary conditions at the heated wall surface.

Gas holdup and single bubble velocity profile

Single bubble velocity profile (velocity vs. distance) has been measured for a 1.45mm diameter bubble to try to explain reported differences in gas holdup in two systems: F150 vs. 1-pentanol, and MIBC vs. NaCl. It was found that in F150 the bubble slowed rapidly to reach the terminal velocity stage of the profile while in 1-pentanol the bubble remained in the deceleration stage and was consequently moving faster, at almost twice the speed. The lower rise velocity in F150 means longer bubble residence time and corresponding higher gas holdup than with 1-pentanol, as reported. In the second system, the bubble in MIBC reached terminal velocity more rapidly than in NaCl which agrees with the reported higher gas holdup in MIBC compared to NaCl. An implication for gas holdup evaluation is that the value may depend on the part of the velocity profile over which it is measured. Possible exploitation of this reagent effect on bubble rise velocity in flotation is considered.

Process characteristics for a gas—liquid system agitated in a vessel equipped with a turbine impeller and tubular baffles

AbstractResults of the experimental research on gas hold-up, power consumption for liquid phase and gas—liquid systems, and on residence time of the gas bubbles are presented in the paper for an agitated vessel with a turbine impeller. Distilled water or aqueous solutions of NaCl were used as the liquid phase. Air was dispersed into liquid as the gas phase. The studies were carried out in an agitated vessel of the inner diameter D = 0.634 m. Tubular baffles of the diameter of 0.7D, consisting of 24 vertical tubes of the diameter of 0.016D, were located inside a flat-bottomed tank. Turbines with six blades and the pitch of 90°, 60°, or 45°, respectively, were used for agitation. Measurements were carried out in the range of good dispersion of gas bubbles in the liquid within the turbulent regime of the liquid flow. Effects of the gas bubbles capability to coalesce on the gas hold-up, residence time of the gas bubbles, and power consumption were analyzed. Results of the power consumption (P G-L/P o = f 1(Kg, Fr)) and gas hold-up (φ= f 2(Kg, We, Y)) were approximated mathematically, using Eqs. (5) and (6), respectively. In Eq. (6), parameter Y was introduced in order to describe the influence of the bubbles capability to coalesce on the gas hold-up. The results of the study show that power consumption does not depend on the capability of bubbles to coalesce, but the pitch of the turbine impeller affects the power characteristics in such a physical system significantly. However, the residence time of the gas phase in agitated liquid depends on the pitch of the impeller blade and on the capability of bubbles to coalesce.

Laboratory-generated primary marine aerosol via bubble-bursting and atomization

Abstract. A range of bubble and sea spray aerosol generators has been tested in the laboratory and compared with oceanic measurements from the literature. We have shown that the method of generation has a significant influence on the properties of the aerosol particles produced. Hence, the validity of a generation system to mimic atmospheric aerosol is dependent on its capacity for generating bubbles and particles in a realistic manner. A bubble-bursting aerosol generator which produces bubbles by water impingement was shown to best reproduce the oceanic bubble spectral shapes, which confirms previous findings. Two porous bubblers and a plunging-water jet system were tested as bubble-bursting aerosol generators for comparison with a standard nebulizer. The methods for aerosol production were evaluated by analysing the bubble spectrum generated by the bubble-bursting systems and the submicron size distribution, hygroscopicity and cloud condensation nucleus activity of the aerosols generated by the different techniques. Significant differences in the bubble spectrum and aerosol properties were observed when using different aerosol generators. The aerosols generated by the different methods exhibited similar hygroscopicity and cloud condensation nucleus activity behaviour when a sample of purely inorganic salts was used as a parent seawater solution; however, significant differences in the aerosol properties were found when using samples of filtered natural seawater enriched with biogenic organics. The presence of organics in the aerosol caused suppression of the growth factor at humidities above 75% RH and an increase in the critical supersaturation with respect to the generation from artificial seawater devoid of organics. The extent of the effect of organics on the aerosol properties varied depending on the method of particle production. The results of this work indicate that the aerosol generation mechanism affects the particles organic enrichment, thus the behaviour of the produced aerosols strongly depends on the laboratory aerosol generator employed. Comparison between bubble lifetimes in several laboratory simulations and the oceanic conditions indicated that it would require a considerable extension of the dimensions of the currently used bubble-bursting laboratory systems in order to replicate the characteristic oceanic bubble lifetimes. We analyzed the implications derived from the reduced bubble residence times in scaled systems, regarding marine surfactants adsorption on rising bubbles, and found that adsorption equilibrium is reached on a timescale much shorter than the bubble lifetime in small-scale laboratory generators. This implies that adsorption of marine surface-active material is not limited by surfactant transport to the bubble surface.

Solid suspension and gas dispersion in gas-solid-liquid agitated systems

AbstractThe aim of the research work was to investigate the effect of superficial gas velocity and solids concentration on the critical agitator speed, gas hold-up and averaged residence time of gas bubbles in an agitated gas-solid-liquid system. Experimental studies were conducted in a vessel of the inner diameter of 0.634 m. Different high-speed impellers: Rushton and Smith turbines, A 315 and HE 3 impellers, were used for agitation. The measurements were conducted in systems with different physical parameters of the continuous phase. Liquid phases were: distilled water (coalescing system) or aqueous solutions of NaCl (non-coalescing systems). The experiments were carried out at five different values of solids concentration and gas flow rate. Experimental analysis of the conditions of gas bubbles dispersion and particles suspension in the vessel with a flat bottom and four standard baffles showed that both gas and solid phases strongly affected the critical agitation speed necessary to produce a three-phase system. On the basis of experimental studies, the critical agitator speed for all agitators working in the gas-solid-liquid systems was found. An increase of superficial gas velocity caused a significant increase of the gas hold-up in both coalescing and non-coalescing three-phase systems. The type of the impeller strongly affected the parameters considered in this work. Low values of the critical impeller speed together with the relatively short average gas bubbles residence time tR in three phase systems were characteristic for the A 315 impeller. Radial flow Rushton and Smith turbines are high-energy consuming impellers but they enable to maintain longer gas bubbles residence time and to obtain higher values of the gas hold-up in the three-phase systems. Empirical correlations were proposed for the critical agitator speed, mean specific energy dissipated and the gas hold-up prediction. Its parameters were fitted using experimental data.

Motor oil removal from water by continuous froth flotation using extended surfactant: Effects of air bubble parameters and surfactant concentration

The objective of this study was to correlate the air bubble parameters in a flotation column and the surfactant concentration to the efficiency of motor oil removal from water by continuous froth flotation. C 14–15(PO) 5SO 4Na (branched alcohol propoxylate sulfate, sodium salt) was used to form microemulsions with motor oil. From the microemulsion phase diagram, the minimum surfactant concentration, known as the critical microemulsion concentration (CμC), to form a Winsor Type III microemulsion, was preliminarily selected for the froth flotation experiments. An increase in surfactant concentration was found to reduce the size and rising velocity of air bubbles in the froth flotation column, whereas the specific surface area, bubble surface area flux, bubble number flux, and residence time of the air bubbles increased with increasing surfactant concentration. The maximum removal of both motor oil and surfactant was found to correspond to the CμC. Beyond the CμC, the oil removal decreased with increasing the surfactant concentration because increasing the micelle concentration results in increasing oil stabilization.

Bubble Motion through a Generalized Power‐Law Fluid Flowing in a Vertical Tube

Intravascular gas embolism may occur with decompression in space flight, as well as during cardiac and vascular surgery. Intravascular bubbles may be deposited into any end organ, such as the heart or the brain. Surface interactions between the bubble and the endothelial cells lining the vasculature result in serious impairment of blood flow and can lead to heart attack, stroke, or even death. To develop effective therapeutic strategies, there is a need for understanding the dynamics of bubble motion through blood and its interaction with the vessel wall through which it moves. Toward this goal, we numerically investigate the axisymmetric motion of a bubble moving through a vertical circular tube in a shear-thinning generalized power-law fluid, using a front-tracking method. The formulation is characterized by the inlet Reynolds number, capillary number, Weber number, and Froude number. The flow dynamics and the associated wall shear stresses are documented for a combination of two different inlet flow conditions (inlet Reynolds numbers) and three different effective bubble radii (ratio of the undeformed bubble radii to the tube radii). The results of the non-Newtonian model are then compared with that of the model assuming a Newtonian blood viscosity. Specifically, for an almost occluding bubble (effective bubble radius = 0.9), the wall shear stress and the bubble residence time are compared for both Newtonian and non-Newtonian cases. Results show that at low shear rates, for a given pressure gradient the residence time for a non-Newtonian flow is higher than that for a Newtonian flow.

Experimental determination of Henry's law constant of perfluorooctanoic acid (PFOA) at 298 K by means of an inert-gas stripping method with a helical plate

The Henry's law constant ( K H) of perfluorooctanoic acid (PFOA, C 7F 15C(O)OH) was determined at 298 K in aqueous sulfuric acid solutions and in aqueous sodium chloride and sulfuric acid mixtures by an inert-gas stripping method in which a helical plate was used to increase the residence time of the gas bubbles in the solutions. The partial pressures of C 7F 15C(O)OH in the purge gas ( P PFOA) were determined by means of Fourier-transform infrared spectroscopy. Time-courses of P PFOA and concentrations of PFOA in the test solutions ( C PFOA) differed from those typically obtained by an inert-gas stripping, indicating both the presence of C 7F 15C(O)OH aggregates, even at low concentrations of C 7F 15C(O)OH in aqueous sulfuric acid solutions, and the adsorption of gaseous C 7F 15C(O)OH on the walls of the experimental apparatus. We derived overall gas-to-water partition coefficients ( K H′) by simulating the time-courses of P PFOA and C PFOA simultaneously to optimize parameters of the model relating to the partitioning, the aggregation, and the adsorption. The K H′ value for 0.31 mol dm −3 sulfuric acid solutions at 298 K was determined at 3.8 ± 0.1 mol dm −3 atm −1. From the relationship between K H′ and the ionic strength of aqueous sulfuric acid solutions, the K H values of C 7F 15C(O)OH at 298 K were determined at 9.9 ± 1.5 mol dm −3 atm −1 for p K a = 2.8 and 5.0 ± 0.2 mol dm −3 atm −1 for p K a = 1.3. The p K a value of 1.3 seems to be most probable among the reported three values for C 7F 15C(O)OH, taking into account dependence of K H′ on sulfuric acid concentrations for aqueous sodium chloride and sulfuric acid mixtures. Despite the low p K a value, the relatively small K H of C 7F 15C(O)OH obtained at 298 K suggests a substantial partitioning of C 7F 15C(O)OH in air in the environment.

Characterisation and control of bubbling behaviour in gas–solid fluidised beds

Bubbling fluidised beds are often exploited for the good mixing of phases they promote, which is required in many chemical processes. However, the bubbles cause heterogeneity in the fluidised system, and their dynamics must be understood for good process control. In this paper, the dynamic behaviour of the bubbles in a planar gas–solid fluidised bed is described analytically and experimentally validated. The bed resembles a temporary buffer of gas for which the bubble residence time in the bed is important. Subsequently, a closed-loop controller was developed using visual feedback to regulate the process.