Aerated desserts have shown a great market potential. Mousse is an airy dessert had stable foamy structure. In this study the effect of different concentrations of albumin, sodium caseinate, whey protein concentrate and gelatin on texture feature (stiffness and fractal force), and microstructure (bubble size distribution and equivalent bubble diameter) of chocolate mousse were evaluated. Result of bubble size distribution showed at samples including albumin, most of bubble was in smaller 5 pixel part and section of larger than 20 pixel had low effect on microstructure mousse chocolate. Also samples including high amount gelatin had lesser portion in section on more than 20 pixels. Equivalent bubble diameter increased during aging but samples including albumin and high amount gelatin had little increasing. Totally increasing amount of protein caused equivalent bubble diameter decreased. Stiffness was more in sample including high amount gelatin. Fractal force had no significant different.

One of the effective factors on the efficiency of the flotation process, is bubble size distribution. Bubble size influences the bubble/particle collision, attachment and detachment probability. In this paper, size distribution of bubbles produced in a laboratory mechanical flotation cell, has been investigated by the direct image analysis method. In addition, effect of some important parameters such as frother concentration, pH value and temperature on bubbles size have been studied. In order to sample bubbles for imaging, bubble viewer with a viewing chamber was designed and made. Images were analyzed using Image J Ver. 1.44 software. To reduce number of bubbles in imaging zone and minimizing bubble overlap, the tube diameter was chosen small as much as possible so that quality and accuracy of image analysis were improved. In addition, by covering side walls of viewing chamber, light entrance from these walls was prevented and images quality was enhanced. Moreover, by photography field depth adjustment and also applying suitable lens, existing problems in previous studies such as bubble overlap and error induced by perspective were improved. To minimize bubble diameter standard deviation, 200 images per experiment were taken and some of them were randomly chosen analyzed. Study of frother effect on bubble size showed that with increase of frother concentration from 10 ppm to 60 ppm, Sauter diameter (d32) of bubbles decreased from 910 mm to 706 mm. with increasing pH from 4 to 10.4, in sync with increase of zeta potential absolute value, d32 of bubbles decreased from 1020 mm to 754 mm and bubble size distribution curve became similar to normal distribution. Furthermore, increase of temperature from 10 °C to 47 °C, resulted enlargement of Sauter diameter of bubbles from 611 mm to 830 mm.

In this research, the effect of carboxy methyl cellulose (CMC) addition into pure water as pseudo-plastic non-Newtonian fluid and its concentration on bubble diameter and gas hold-up were investigated. For this purpose, four different concentrations of CMC (0.05, 0.1, 0.15 and 0.2 w/v%) as the non-Newtonian fluid and five different superficial gas velocities (0.2, 0.4, 0.6, 0.8 and 1 cm/s) as the gas phase were examined in an airlift reactor. Bubble size distribution in the airlift reactor was measured by photography and picture analysis at various concentrations of CMC and various velocities of gas. Increasing in gas velocity created a wider bubble size distribution and thereby an increase in bubble diameter and gas hold-up in both riser and down-comer. However, the bubbles diameter in pure water was larger than those of the CMC solutions (in the riser and down-comer), but CMC concentration enhancement increased bubbles diameter and gas hold-up in the down-comer. Bubbles diameter expansion in the riser by CMC concentration enhancement took place from concentrations of 0.05 to 0.15 (w/v)% and then it suddenly decreased. Furthermore, gas hold-up decreased from concentrations of 0.05 to 0.15 (w/v)% and increased at concentration of 0.2 (w/v)%. The gas hold-up increases (more than that in the concentrations of 0.1 and 0.15%) when bubbles diameter decreases in concentration of 0.2%. The overall gas hold-up trend was similar to the gas hold-up in the riser.

The purpose of the present study was investigation of effect petroleum contaminants and surfactants on hydrodynamics and oxygen transfer as important parameters for treatment of crude contaminated wastewaters. Gas hold-up (εg), bubble size distribution and oxygen transfer coefficient (kLa) were evaluated for petroleum contaminants (C13 and C16) in water at concentrations of 0.1 and 0.5 vol.% over the range of superficial gas velocity (ug) of 1.18-23.52×10-3 m/s in bubble column reactor. A type of anionic surfactant (SDS) was utilized in the experiments for studying of surfactants on wastewater parameters. The bubble size distribution becomes bimodal with increasing of gas velocity and gas hold-up, mass transfer coefficient and Sauter mean diameter is increased. The petroleum contaminants and surfactants lead to delayed regime transition from the homogeneous to heterogeneous by decreased surface tension and by the coalescence inhibition, and also, Sauter mean diameter is decreased in the presence of petroleum contaminants. These changes increased in the presence of surfactants. Also, petroleum contaminants enhanced mass transfer coefficient and gas hold-up, especially at higher superficial gas velocity. Increasing of mass transfer and hold-up were more at higher concentrations of contaminants. Also, presence of surfactants on bubble surfaces, decreases oxygen transfer due to the enhanced mass transfer resistance. Empirical correlations were proposed for evaluating gas hold-up and mass transfer coefficient as a function of superficial gas velocity and interfacial surface tension.

Hypothesis: 

One of the existing challenges in the foam production industry is to achieve the desired mechanical and thermal insulation properties required, which are directly related to cellular density, size, and distribution of bubbles. Therefore, predicting the bubble size distribution in each foam production system significantly contributes to the final properties of the desired foam. Nucleation, growth, coalescence of bubbles, and their final stabilization are influential stages in the ultimate properties of the foam that should be considered in predicting the bubble size distribution and laboratory testing phase.

Initially, a modified classical nucleation model was used for predicting cell nucleation, and then a population balance model was employed to predict the size distribution of bubbles in a batch system for the production of polystyrene foam. The modeling of this process was one-dimensional, and changes in bubble diameter were included as the characteristic variable of the system's equations. The foam production stage was carried out at temperatures of 70°C, 90°C, and 110°C, under a pressure of 20 MPa, and the consolidation stage was performed within 0.1 s and 1 s and without consolidation. To calculate the average cell size and size distribution, SEM images and software tools such as Axiovision.v4.82.SP2 and SPSS 26 were used, and the results were compared with the modeling outcomes.

Using the bubble size distribution obtained from modeling, the average bubble size at a saturation temperature of 70°C and a consolidation time of 1 s was 4.3 µm. With an increase in temperature from 70°C to 90°C, the average bubble size increased to 36.7 µm due to the higher rate of gas diffusion into the bubbles. With an increase in the amount of gas in polystyrene, the free volume increased, and glass transition temperature decreased. At 110°C, the average size of bubble cells increased to 78.1 µm. Since this temperature was higher than the glass transition temperature of polystyrene, in addition to the high gas diffusion rate into the bubble cells, the growth process did not stop, and gas diffusion and coalescence between the bubbles continued. Finally, the model predictions were compared with experiments under various conditions and demonstrated acceptable agreement.

Venturi bubble generators have been extensively studied because of having a simple structure and high foaming efficiency, while producing a uniform bubble size. The effect of a noncondensable gas on hydraulic cavitation was considered to improve the Zwart-Gerber-Belamri cavitation model. This improved model and a population balance model were used to study the effect of cavitation on bubble fragmentation. The CFD-PBM results were compared with experimental results, and the accuracy of the improved calculation method was verified in terms of the distributions for the cavitation cavity, gas phase, and bubble size. The calculation results showed that increasing the noncondensable gas content over a certain range promoted the development of hydraulic cavitation, and the cavitation intensity could be indirectly controlled by adjusting the noncondensable gas content. With increasing cavitation intensity, the average bubble size decreased, and the bubble size distribution became narrower. Therefore, a high-pressure pulse generated by cavitation could effectively break bubbles. The development process of microbubbles was studied. The main controlling factors for bubble formation were determined to be the turbulent shear force of the fluid and the collapse impact force of the cavitation group, which provides a theoretical basis for optimizing the design of bubble generators.

Scoria cones are one of the main parts of East of Kurdistan volcanoes. Olivine, Pyroxene, Plagioclase and Biotite are main phonocrystals with Amygdaloidal-glassy matrix. This paper was studied processes of bubbles nucleation and grow during the eruption of scoria's unite using the Bubble Size Distribution (BSD) method including study of population density, bubbles volume, 3D modeling, nucleation and bubble growth. For selected sample from different cone, in total was measured 3623 bubbles and drawn that bubbles volumes calculated from 40 to 85 percent. Using the 2D bubbles shape renovated 3D bubbles schematic shape and compared together. Most population for four samples bubbles shapes are near to sphere and for other four samples are ellipsoid. Longest ellipsoid bubbles shape has 1:3.2:8 diagonals ratio that it’s flat ellipsoid. The longest diameter (L) is perpendicular to the surface and parallel to lower pressure dictated on magma and bubbles could be growth more than other sides. Presence of 2-5 peaks in frequency distribution versus bubble size diagram, suggesting unimodal, polymodal, exponential and power low events for bubbles generation in the east of Kurdistan Scoria's. Nucleation density increased from first to lasts generation but bubbles growth reduced. Recur of bubble forming in macroscopic samples, microscopy, SEM and nucleation and grow model suggested fractal model.

Membrane bioreactor (MBR) is an effective technology for wastewater treatment and water reuse which is becoming increasingly popular due to its numerous applications and advantages over conventional activated sludge process. This novel technology have advantages of small footprint, high concentration of mixed liquor suspended solids (MLSS), high removal efficiency of chemical oxygen demand (COD), less production of excess sludge and to be reliable and simple to operate. Membrane fouling and its consequences, regarding plant maintenance and operating costs, has gained attention in recent years as a major obstacle for development of this technology. Various methods have been used to reduce membrane fouling and new solutions are frequently proposed and used. Among different operational variables, aeration is the most effective factor on membrane fouling mitigation. Despite its major role in membrane fouling reduction, the energy consumption of aeration is the main operating cost for MBRs, such that approximately 30-50% of consumed energy in a submerged MBR is used for aeration. Hence, operation improvement by optimizing hydrodynamic conditions has a high technical and economic significance. Computational fluids dynamics (CFD) is a powerful tool for understanding the relationship between hydrodynamics and fouling in MBRs. Researches have been conducted to assess hydrodynamic and its effect on the system efficiency. Most of design, operational and geometrical variables, like bubble diameter, membranes distance, presence of baffles and walls in flat-sheet modules require evaluation and optimization. Membranes are mostly assumed to be rigid in CFD simulations of MBRs. In this study, effect of hydrodynamic characteristics of a submerged membrane bioreactor on membrane fouling was investigated using computational fluid dynamics simulation. In this study, effect of hydrodynamic characteristics on fouling in an airlift MBR was investigated using CFD simulation. Three-dimensional two and three-phase simulation was implemented using Eulerian approach and k-ε turbulent model. Results indicated that by increasing air flow rate and MLSS concentration, shear stress on membrane surface increase and membrane fouling decreases. Also effect of considering population balance model in simulation was studied. In addition results indicated that using granular model in three-phase simulation would lead to a more realistic simulation. Simulation results were in good agreement with experimental data which demonstrate the ability of this CFD approach and population balance model as an efficient tool. Materials and methods Experiments were carried out in a submerged membrane bioreactor which is 70 cm in height, 23 cm in length and 21 cm in width with operating volume of 20 L for activated sludge. A flat-sheet chlorinated polyethylene membrane with mean pore size of 0.45 μm and effective membrane area of 0.11 m2 was used. Two baffles were located at both sides of membrane. The required air was pumped through a sparger located beneath the membrane, and its flow rate was measured using a flow meter. The biomass was obtained from a municipal wastewater treatment plant in Tehran, Iran. The driving force for filtration was created by vacuum. In all experiments, the system was fed by a synthetic influent, glucose, ammonium sulfate, and ammonium phosphate which are the sources of carbon, nitrogen, and phosphorus, respectively. The tests were carried out at four different air flow rates of 0.2, 0.4, 0.6 and 0.8 m3/h and at two MLSS concentrations of 8 and 12 g/L. The permeate flow rate, MLSS concentration and membrane resistance were measured. Total gas hold-up was also estimated by visual determination of bed expansion. A three-dimensional two- and three-phase model was used to investigate the hydrodynamics of the MBR. In order to describe liquid and gas properties in multiphase flow, an Eulerian-Eulerian approach was implemented. The standard k-ε turbulent model was used for phases to model turbulence. A fine mesh was generated between the membranes. However, to decrease the number of computational cells, only a quarter of the set-up was considered as the simulation domain due to the symmetry from both sides. The projected area of the air spargers at the bottom of the system were considered as the air velocity inlet boundary condition. The boundary condition at the top of the MBR was set to open to atmosphere in order to let the air exit to the atmosphere. Also a bubble size distribution with ten bubble classes and the possibility of coalescence and breakage was used in some of the simulations. In this work, phase-coupled simple with pressure based solver was applied for the Eulerian multiphase simulations. The velocities were solved coupled by phases, but in a discrete method. This method solves momentum and pressure based continuity equations simultaneously, thus the rate of convergence improves compared to the segregated method which solves the governing equations sequentially. - The effect of bubble size distribution in MBR Due to importance of bubble characteristics and their distribution in bioreactors, a simulation was carried on in which the bubble size distribution, based on experimental data, was used. MBR was simulated at TMP of 40 kPa, MLSS concentration of 8 g/L and four different air flow rates of 0.2, 0.4, 0.6 and 0.8 m3/h. Ten bubble classes are studied with possibility of accumulation and breakage. Bubble size distribution in 5 stages of bioreactor was investigated. Results indicate that by increasing the aeration intensity, ratio of larger bubbles increases in the system. After formation of air bubbles at the sparger, their coalescence and breakage occur during their movement towards the free liquid surface and gradual increase of bubble diameter can be observed. Larger bubbles are commonly seen at higher levels, near the membrane surface and the wall. Average bubble diameter from both simulation and experimental results were compared. Simulation results correlate with experimental data which verified bubble size distribution in simulation. So a mean bubble diameter was used in other following simulations. - The effect of MLSS concentration and aeration intensity In order to investigate the effect of aeration as the main effective factor in membrane fouling reduction, simulation was done at various air flow rates of 0.2, 0.4, 0.6 and 0.8 m3/h. Gas holdup was measured experimentally and was compared with simulation results. Results demonstrate that increasing the aeration intensity, and consequent growth in average bubble diameter, causes a greater gas holdup in the bioreactor. Although the growth in the average bubble diameter leads to reduction of the gas holdup due to higher rise velocity, the overall effect of increasing the aeration intensity and average bubble diameter is higher gas holdup in the system. Also by increasing MLSS concentration and consequence increase in the activated sludge viscosity, more bubbles are trapped in the riser which leads to more gas holdup. In airlift bioreactors, flow of air is the main cause of liquid motion and circulation. Therefore, by increasing the aeration intensity, the liquid velocity increases in both riser and down comer which leads to a greater shear stress on the membrane surface. Also, at higher MLSS concentrations, which correspond to greater liquid viscosity, air and liquid shear rates increase. However at lower aeration intensities, changing the MLSS concentration does not make a significant change in the shear stress. This is due to the fact that aeration cannot impose the necessary rate of mixing in the bioreactor and provide the force required for particles movement. Exerting more shear stress on membrane surface in higher aeration intensity leads to a decrease in cake formation on membrane surface and membrane fouling resistance. Also gas shear stress contours on membrane surface at various air flow rates was investigated. It was seen that a greater shear stress is exerted on the surface in the middle and upper half of the membrane which is owing to higher velocity and turbulence of gas and liquid mixture in this region. Also, at air flow rate of 0.2 m3/h, the maximum shear stress is exerted on a small part of the membrane surface, while by increasing the air flow rate to 0.8 m3/h, a greater surface area is exposed to the maximum shear stress. - Validation of the model In order to validate simulation results, gas shear stress and its effect on MBR operation and membrane resistance was studied under different conditions. Results indicate that by increasing air flow rate, resistance reaches its lowest amount. By increasing aeration intensity stress changes resulting from gas and liquid becomes ascending. It should be mentioned that both stresses influence cake formation and total resistance on surface tension, But it cannot be specifically said which effect is more. Other studies indicate that in constant pressure systems much change is not observed after reaching semi-constant condition. As mentioned before, aeration causes cross flow on membrane in air lift bioreactor and the more aeration causes more flow circulation velocity and lifting force on particles, which leads to membrane resistance reduction. Liquid shear stress changes on membrane surface in different air flow rates, shows a similar trend. Also gas hold up was measured experimentally and was compared to simulation results. It was seen that simulation results are in good agreement with experimental data which indicates model accuracy and ability of computational fluid dynamics for investigation and prediction of bioreactor hydrodynamic. - The effect and behavior of solid particles distribution Three-phase simulation was studied in order to approach real conditions and identification of solid particles aggregate. Three-phase simulation in aeration intensity of 0.8 m3/h and MLSS concentration of 8 g/L was done. Average particle diameter was determined by microscopic image of active sludge and image analysis of 6 µm. Eulerian approach was used to model three-phase simulation. Volume fraction distribution of solid phase particles of sludge, liquid and air were investigated. Results show that solid particles accumulate less near membrane and are accumulated more in bottom of bioreactor due to more aeration and liquid circulation around baffles. In order to achieve more uniform distribution of solid particles, air distributor can be placed at the bottom in order to prevent particle accumulation in that area. Conclusion A submerged membrane bioreactor was investigated using CFD simulation. A two- and three-phase simulation using Eulerian approach was implemented. In addition, the effect of permeate flux was considered in simulation. Simulation results were validated against the experimental data. From the results reported here, the following conclusions can be drawn: - By using bubble size distribution, bubbles behavior during their movement in system can be investigated. Results show that bubble size increases during their movement from sparger to free surface of liquid and bigger bubbles tend to accumulate near membrane surface and walls. - By increasing aeration intensity and MLSS concentration in system, gas and liquid shear stress on membrane surface increases. - Simulation results were in good agreement with experimental data which indicates model accuracy and ability of computational fluid dynamics for investigation and prediction of bioreactor hydrodynamic. - Application of granular model in three-phase simulations causes reactor conditions come closer to actual one. Results indicate that solid particles tend to accumulate more in bottom of bioreactor and less near membrane and around baffles.

Scoria is one of the main pyroclastic units in Damavand volcano, which its main crystals are plagioclase, olivine and pyroxene. In this study, characterization of bubbles and their formation during the eruption considered using Bubble Size Distribution (BSD) method including study of volume, 3D modeling, nucleation and bubble growth. For ed sample, thebubbles investigated in 3 perpendicular dimensions (X-Y-Z) and in total 16830 bubbles (X=7357, Y=5385, Z=4088) were measured and drawn. The Bubbles volumes calculated in 3 dimensions are X=47.21, Y=40.27, Z=40.01 percent. The Bubbles axes were calculated: X=1:1:4, Y=Z=1:1:3.4 and the 3D schematic shape is ellipsoid which the longest axis (L) is about 4 times longer than the other two axes (I, S). The L axis is parallel to the lowest pressure dictated on magma and the bubbles could be grown 4 times more in that direction. The bubbles shape of Damavand scoria is an ellipsoid with an average of 1:1:3.7 for its axes. The presence of 3 peaks in frequency distribution versus bubble size diagram, suggesting polymodal events of bubbles generation and in the Damavand volcano the bubbles nucleation occurred in 3 events(F1, F2, and F3). The nucleation density increased F1 to F3 but the bubbles growth reduced in the same direction. The first group of bubbles formed in the magma chamber and the second group formed during the magma ascent. The third group of bubbles could form either in the space between earlier groups or in the last stage of magma eruption.

In melting process of lead silicate glasses containing 70 wt% PbO, the bubble size distribution, and the manner of formation and elimination of gas bubbles of glass melt at different temperatures and times were investigated. The lead silicate glass was manufactured by melting, fritting and milling of glass powder for several stages. At first, 50 grams of lead silicate glass powder was poured into each alumina crucible for maintaining the batches separately at temperatures of 900, 950, 1000, 1050 and 1100˚C for 15, 30 and 45 minutes, to study the effects of time and temperature on the bubble nucleation, growth and ascension from the lead silicate glass melt. Because of the dissolution of air molecules inside the glass melt and owing to the achievement of super-saturation, gas bubbles were nucleated and grown. Due to the density of the gradient between the gas bubbles and glass melt, the bubbles ascended to the surface of the melt where they ruptured afterwards. The density of alumina crucibles and the glass inside them were measured. The volume and the mean value of the diameter of bubbles were determined by images from the lateral cross section of glass inside crucibles and from the images taken from the surface of the bubbly glassy layer on the surface of the samples.