Gas Pocket Formation Research Articles

Study of the factors affecting growth of Celerinatantimonas sp. and gas pocket formation in Spanish-style green olives

The defect of gas pocket formation still leads to substantial losses of yield and quality of Spanish-style green olives worldwide. This spoilage has recently been associated with the growth of Celerinatantimonas sp., and this study was aimed at investigating the influence of several factors on the growth of Celerinatantimonas , both in synthetic media as well as in the olive brines of the three olive cultivars Gordal, Manzanilla and Hojiblanca. Using synthetic media, it was found that the concentration of NaCl within current industrial levels (3.5–7.0%) did not affect the growth of Celerinatantimonas , whereas the pH was a crucial factor, the range of growth being 4.5–7.5 units. Among the acids tested, lactic acid presented the highest inhibitory action against this microorganism. The assays carried out with olive brines disclosed that the population of Celerinatantimonas and its normal fermentation products (acetic acid and ethanol) increased in all of the inoculated brines, while the reduction of gas pocket defect depended on the combined use of several factors including addition of lactic acid, control of pH and inoculation with a lactic acid bacteria starter. Hence, the maintenance of a pH below 4.5 units at the beginning of fermentation along with the addition of 0.2–0.8% lactic acid was considered necessary to inhibit growth of Celerinatantimonas and to prevent gas pocket defect. The tools proposed as conclusions of this work should be used by table olive processors in the future to reduce the incidence of this olive spoilage. • Celerinatantimonas caused gas pocket defect in processed green olives. • NaCl up to 10% did not inhibit the growth of Celerinatantimonas . • Celerinatantimonas grew in a pH range of 4.5–7.0 units. • Lactic acid at 0.2–0.8% retarded growth of Celerinatantimonas . • The combined use of pH and lactic acid may control growth of Celerinatantimonas .

Formation of gas pocket defect in Spanish-style green olives by the halophile Celerinatantimonas sp.

Gas pocket defect causes substantial losses every season to Spanish-style green table olive processors. This defect has been thought to be caused by microorganisms that are able to produce gaseous compounds that break the flesh and/or the epidermis of olive fruits. This study was focused on the search for the microorganism actually responsible for this spoilage. Metataxonomy analysis of industrial spoiled brines demonstrated the presence of Celerinatantimonas as the most probable source leading to gas pocket formation. Several bacterial isolates were obtained from different industrial spoiled brines whose 16S rRNA sequence closest homologue was Celerinatantimonas diazotrophica (94–96% similarity). Vigorous gas production (H 2 and CO 2 ) by these isolates in broth cultures was confirmed. Inoculation of microbial pellets from one of these spoiled brines did indeed provoke gas pocket formation in fresh batches of Spanish-style green olives. Although the species C. diazotrophica has been previously reported in metataxonomy studies in samples of table olives, this is the first time that it was isolated from fermenting table olive samples. In addition, this is the first report that associates this species to the gas pocket defect in table olives. Thus, inoculation with one of the wild-type isolates identified as C. diazotrophica in table olive brines confirmed the involvement of this microorganism in the formation of the gas pocket defect in Spanish-style green olives. • Celerinatantimonas was detected by metataxonomy in every spoiled table olive brine. • Celerinatantimonas was isolated from brines of table olives with gas pockets. • Gas pocket defect in olives was reproduced by Celerinatantimonas inoculation. • Celerinatantimonas yields acetic acid-ethanol-H 2 -CO 2 disturbing lactic acid fermentation.

Experimental Analysis of Gas–Liquid Flows in a Centrifugal Rotor

Abstract This work presents an experimental analysis of gas–liquid flows in a centrifugal rotor prototype. Pressure rise curves are evaluated considering a wide range of liquid and gas flowrates and different rotating speeds. An innovative apparatus including a dynamic sealing system, back illumination, and filming in a rotating frame of reference is employed to visualize gas–liquid flow patterns at different operating conditions. Volume fraction measurement and bubble-size evaluation are also taken into account. The experimental apparatus allowed analyzing details of the gas-phase dynamics inside the rotor channels. That includes preferential bubble paths and zones of agglomeration, gas pocket formation, coalescence and breakup, and the effect of flow pattern transition on different degrees of performance degradation that centrifugal rotors are subject to when working with gas–liquid flows. Also, important information about the effect of the gas flowrate and the rotating speed on the performance of the assumed rotor prototype could be gathered. Discussions in this work should contribute to comprehend the behavior of gas–liquid flow in centrifugal pumps, a topic that is still far from being well understood. Qualitative and quantitative data here presented could also be valuable to guide the development of numerical models to solve this problem.

Polyvinyl alcohol/magnesium phosphate composite coated Mg–Ca alloy for biodegradable orthopaedic implant applications

Magnesium-Calcium (Mg–Ca) alloys are suitable candidate materials for developing degradable metallic implants. However, the degradation rate of these alloys in the physiological environment needs to be controlled to avoid the loss of mechanical integrity of the implant and hydrogen gas pocket formation. In this work, the degradation rate of low Ca containing Mg alloy was controlled using polyvinyl alcohol (PVA)/magnesium phosphate (Mg–P) composite coating. The sample surfaces were subjected to hydrothermal treatment prior to coating. Mg–P was developed using magnesium nitrate [Mg(NO3)2 · 6H2O] and diammonium phosphate [(NH4)2HPO4] as precursors were dispersed in PVA solution prior and was spin coated on the sample surfaces. The in vitro biodegradation and biomineralization of the samples were tested in supersaturated simulated body fluid (SSBF). The immersion test results showed that composite coating on hydrothermally pretreated samples reduced the degradation rate and enhanced biomineralization in the physiological environment. The hydrothermal treatment made the coating-substrate interface stable. The combination of hydrothermal pretreatment and PVA/Mg–P composite coating can be used as a surface modification technique to enhance biomineralization and control the rapid degradation rate of Mg alloys in the physiological environment.

A Review of Design Considerations of Centrifugal Pump Capability for Handling Inlet Gas-Liquid Two-Phase Flows

Most of the pumps working under two phase flows conditions are used in petroleum industry applications, like electrical submersible pumps (ESP) for hydrocarbon fluids, in chemistry, nuclear industries and in agriculture for irrigation purposes as well. Two-phase flows always deteriorate overall pump performances compared with single flow conditions. Several papers have been published aiming to understand flow physics and to model all the main mechanisms that govern gas pocket formation and surging phenomena. These mechanisms depend on the pump type, the impeller geometry, the rotational speed, design and off-design liquid flow rate conditions, the volumetric gas fraction, the fluid properties and the inlet pressure. In the present paper, a review on two phase performances from various centrifugal pumps designs is presented, mainly based on experimental results. The main focus is devoted to detect the significant geometrical parameters that: (1) Modify the pump head degradation level under bubbly flow regime assumption; (2) Allow single stage centrifugal pumps keep working under two-phase flow conditions with high inlet void fraction values before pump shut down, whatever the pump performance degradations and liquid production rates should be. Because most of the published experimental studies are performed on dedicated laboratory centrifugal pump models, most of the present review is based on air-water mixtures as the working fluid with inlet pressures close to atmospheric conditions. The following review supposes that gas phase is considered as a non-condensable perfect gas, while the liquid phase is incompressible. Both phases are isolated from external conditions: neither mass nor heat transfer take place between the phases.

A numerical study on flow patterns inside an electrical submersible pump (ESP) and comparison with visualization experiments

This paper presents a numerical study of flow pattern recognition inside the rotating impeller of an electrical submersible pump (ESP) using the transient multiphase Computational Fluid Dynamics (CFD) simulations. The calculation domain is constructed based on the previous experimental facility for visualizing flow patterns in an ESP (Barrios (2007)). The high-quality structured mesh comprising hexahedral grids is generated using multi-block technique in ANSYS ICEM. For CFD simulations, the realizable k-ε turbulence model with volume of fluid (VOF) and Eulerian-Eulerian multiphase models is successfully implemented in ANSYS Fluent solver. The sliding mesh technique is applied to interfaces where rotating and stationary parts interact. By incorporating the same boundary conditions as Barrios experimental study, three flow cases with constant gas flow rates and varying liquid flow rates are selected to conduct numerical simulations. The comparison of simulation results with Barrios’ observations shows that the Eulerian-Eulerian multiphase model is superior to VOF model for simulating gas-liquid two-phase flow in a rotating ESP. The single-phase simulation results match catalog curves, which validates the numerical methodology. For two-phase simulations, the simulated flow patterns using Eulerian-Eulerian model agree well with visualization experiments. Different flow patterns prevailing inside the rotating ESP impeller are captured. At low gas flow rate, bubbles are dispersed in liquid phase, and the flow pattern is categorized as dispersed bubble flow. As gas flow rate increases, bubbles can accumulate and coalesce, causing large gas-pocket formation leading to intermittent/slug flow. Transient multiphase CFD simulation is an efficient and reliable tool to predict flow patterns inside ESPs.

In vivo study of self-assembled alkylsilane coated degradable magnesium devices.

Magnesium (Mg) and its alloys are candidate materials for resorbable implantable devices, such as orthopedic devices or cardiovascular stents. Mg has a number advantages, including mechanical properties, light weight, its osteogenic effects and the fact that its degradation products are nontoxic and naturally present in the body. However, production of H2 gas during the corrosion reaction can cause formation of gas pockets at the implantation site, posing a barrier to clinical applications of Mg. It is therefore desirable to develop methods to control corrosion rate and gas pocket formation around the implants. Here we evaluate the potential of self-assembled multilayer alkylsilane (AS) coatings to control Mg device corrosion and formation of gas pockets in vivo and to assess effects of the AS coatings on the surrounding tissues in a subcutaneous mouse model over a 6 weeks' period. The coating significantly slowed down corrosion and gas pocket formation as evidenced by smaller gas pockets around the AS coated implants (ANOVA; p = 0.013) and decrease in the weight loss values (t test; p = 0.07). Importantly, the microCT and profilometry analyses demonstrated that the coating inhibited the pitting corrosion. Specifically, the roughness of the coated samples was ∼30% lower than uncoated specimen (p = 0.02). Histological assessment of the tissues under the implant revealed no inflammation or foreign body reaction. Overall, our results demonstrate the feasibility of use of the seld assembled AS coatings for reduction of gas pocket formation around the resorbable Mg devices. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 107B: 342-351, 2019.

In vivo degradation of magnesium plate/screw osteosynthesis implant systems: Soft and hard tissue response in a calvarial model in miniature pigs

Biodegradable magnesium plate/screw osteosynthesis systems were implanted on the frontal bone of adult miniature pigs. The chosen implant geometries were based on existing titanium systems used for the treatment of facial fractures. The aim of this study was to evaluate the invivo degradation and tissue response of the magnesium alloy WE43 with and without a plasma electrolytic surface coating. Of 14 animals, 6 received magnesium implants with surface modification (coated), 6 without surface modification (uncoated), and 2 titanium implants. Radiological examination of the skull was performed at 1, 4, and 8 weeks post-implantation. After euthanasia at 12 and 24 weeks, X-ray, computed tomography, and microfocus computed tomography analyses and histological and histomorphological examinations of the bone/implant blocks were performed. The results showed a good tolerance of the plate/screw system without wound healing disturbance. In the radiological examination, gas pocket formation was found mainly around the uncoated plates 4 weeks after surgery. The micro-CT and histological analyses showed significantly lower corrosion rates and increased bone density and bone implant contact area around the coated screws compared to the uncoated screws at both endpoints. This study shows promising results for the further development of coated magnesium implants for the osteosynthesis of the facial skeleton.

Experimental studies of bubbly flow in a pseudo-2D micro-structured bubble column reactor using digital image analysis

A novel micro-structured bubble column reactor (MSBC) is studied experimentally in this work. Micro-structuring is realized by using a wire mesh inserted in a pseudo-2D bubble column reactor. Different flow configurations of the wire mesh are evaluated by means of visual observation. Three different regimes with bubble cutting, bubble cutting followed by re-coalescence and gas pocket formation were observed for different wire meshes for superficial gas velocities ranging from 5 to 50mm/s. An advanced digital image analysis technique (DIA) was used to determine the effect of wire mesh on the bubble size distribution, gas holdup and interfacial area. Detailed experiments were performed for wire meshes with mesh openings of 3.3mm, 3.7mm and 5.6mm for superficial gas velocities ranging from 5 to 30mm/s. Bubble cutting is observed at 3.7mm mesh opening for superficial gas velocities up to 15mm/s. At higher superficial gas velocities, the bubble breaks up to very small bubbles and bypasses the wire mesh unaffected.

Modeling Approach for the Determination of Material Flow and Welding Conditions in Porthole Die Extrusion with Gas Pocket Formation

The material flow in porthole dies is of crucial importance with regard to the seam weld quality in aluminum extrusion. Thus, experimental as well as numerical investigations on the effect of die geometry on the material flow were conducted. The experimental tests were performed on a 10 MN laboratory extrusion press. During the experimental trials, the extrusion ratio was varied by means of exchangeable die plates. Since the modular die allows removal of the aluminum in the welding chamber as well as in the feeders after the process, the material flow could be inspected in detail. The experimental results were used to improve the accuracy of FEA simulations, which were also conducted by commercial software. An attempt was made to improve the result quality of Eulerian FEA model regarding the simulation of an extrusion process with a gas pocket in the welding chamber. The influence of the modeling approach on the predicted material flow and on the contact pressure was analyzed and finally linked to the seam weld quality.

Biodegradable poly(lactide-co-glycolide) coatings on magnesium alloys for orthopedic applications

Polymeric film coatings were applied by dip coating on two magnesium alloy systems, AZ31 and Mg4Y, in an attempt to slow the degradation of these alloys under in vitro conditions. Poly(lactic-co-glycolic acid) polymer in solution was explored at various concentrations, yielding coatings of varying thicknesses on the alloy substrates. Electrochemical corrosion studies indicate that the coatings initially provide some corrosion protection. Degradation studies showed reduced degradation over 3 days, but beyond this time point however, do not maintain a reduction in corrosion rate. Scanning electron microscopy indicates inhomogeneous coating durability, with gas pocket formation in the polymer coating, resulting in eventual detachment from the alloy surface. In vitro studies of cell viability utilizing mouse osteoblast cells showed improved biocompatibility of polymer coated substrates over the bare AZ31 and Mg4Y substrates. Results demonstrate that while challenges remain for long term degradation control, the developed polymeric coatings nevertheless provide short term corrosion protection and improved biocompatibility of magnesium alloys for possible use in orthopedic applications.

Analysis of Gas Pocket Formation during Extrusion of Al Hollow Profiles and Establishing an Extrusion Seam Weld Limit Diagram

In extrusion of aluminium alloys, using porthole dies, the billet metal is split into separate metal streams during flow into the ports. After that, the streams join by seam pressure welding in the weld chamber of the die and finally flow through the die exit emerging as the desired extrusion. Because of re-joining of the metal streams the extrusion will contain as many extrusion seam welds as there are bridges in the die. Dependent on the die design the metal will flow in such a way that a gas pocket may form behind the die bridge and remain stable here throughout the course of the extrusion process. If, at this stage of the process, the feed of metal into the region behind the bridge is increased the space behind the bridge may fill up completely and the gas pocket will disappear. In this work we have investigated how finite element modeling can be used (for a simple idealized case of 2-D extrusion welding) to understand the extrusion seam welding process, and to characterize what extrusion conditions will provide stable gas pocket formation behind a bridge, and when the pocket will disappear. The geometry of the welding chamber and the die opening was varied in a number of simulations to study this phenomenon using the FEM-code Deform 2D®. Based on these simulations we have been able to propose an “extrusion seam weld limit diagram (ESWLD)”. The ESWLD shows when extrusion will occur with a gas pocket present behind the bridge and when there is transfer to a state where the pocket disappears and the die fills up completely with metal. By curve-fitting the results can be presented by a mathematical model, i.e. by an equation allowing the reduction in extrusion at the point of transfer from a state of presence of the pocket to a state of complete die filling, to be computed from the dimensions of the porthole and the weld chamber, for a given billet size and a given bridge geometry. The model also shows which geometrical extrusion parameters of the die will favor complete filling of the space behind a die bridge instead of gas pocket formation there.

Fermenting yeasts associated with softening and gas-pocket formation in olives.

Fermenting, pectolytic yeasts were isolated from a massive commercial outbreak of softening and gas-pocket formation in olives that had been stored in acidified, low-salt brines in an attempt to reduce the problem of brine disposal. The suspected yeasts represented three different species: Saccharomyces oleaginosus, S. kluyveri, and Hansenula anomala var. anomala. All pectolytic cultures produced pectin esterase and polygalacturonase but no pectic acid trans-eliminase when grown in nutrient glucose broth. Crude, cell-free dialyzed enzyme preparations measured viscosimetrically exhibited optimal activity on sodium polygalacturonate at pH 6.0 and 45 C and were active in the range of pH 4.0 to 9.0 and 10 to 60 C.

Fermenting Yeasts Associated with Softening and Gas-Pocket Formation in Olives

Fermenting, pectolytic yeasts were isolated from a massive commercial outbreak of softening and gas-pocket formation in olives that had been stored in acidified, low-salt brines in an attempt to reduce the problem of brine disposal. The suspected yeasts represented three different species: Saccharomyces oleaginosus, S. kluyveri, and Hansenula anomala var. anomala. All pectolytic cultures produced pectin esterase and polygalacturonase but no pectic acid trans-eliminase when grown in nutrient glucose broth. Crude, cell-free dialyzed enzyme preparations measured viscosimetrically exhibited optimal activity on sodium polygalacturonate at pH 6.0 and 45 C and were active in the range of pH 4.0 to 9.0 and 10 to 60 C.