On-line characterization of single bubbles in multiphase reactors

ECCE 7 - 7th European Congress of Chemical Engineering, CHISA 2010 - 19th International Congress of Chemical and Process Engineering (CD-ROM of Full Texts)This paper presents an on-line method to identify automatically the single bubbles (isolated bubbles without influence of surrounded bubbles) in multiphase reactors. Based on image analysis technique (IA), the method combines the information given by IA with the Discriminant factorial analysis leading to results that allow the identification of single bubbles and the study of bubble population complexity. By this way, it is possible to characterize the single bubbles on different conditions and to understand their influence on mass transfer. Agreement between automated and manual classification, measured in terms of a performance index, is 90% on average. Further, it describes the application of such methodology to the study of the influence of bubble characteristics (size, shape, bubble population complexity, etc) on the individual parameters of volumetric liquid side mass transfer coefficient, kLa. The experiments were done at different temperatures (25-35ºC) and superficial gas velocities (up to 14 mm/s) in a bubble column.info:eu-repo/semantics/publishedVersio

Effect of solids on gas-liquid mass transfer

The effect of the solids on the mass transfer characteristics in a bubble column was studied experimentally for the systems air/water/Polyvinyl chloride (PVC) and air/water/glass beads. Volumetric liquid side mass transfer coefficient, kLa, was determined under different solid concentrations, gas flow rates and solid sizes. The presence of solids affects negatively kLa being this effect more pronounced for the largest particles. For smaller size particles, surface properties play an important role in mass transfer as opposite effects in kLa are observed for the hydrophobic and hydrophilic particles

Relational contracting and its combination with the BIM methodology in mitigating asymmetric information problems in construction projects

Project management in the construction sector is a complex and uncertain process and companies tend to look for the lowest value in the procurement of services and materials. However, contractors do not share the necessary information with the contracted parties and thus give rise to the asymmetric information (AI) phenomenon. The aim of this study is to perform an analysis of the determining factors in the adoption of relational contracting (RC) in combination with Building Information Modelling (BIM) to reduce AI. The results of a questionnaire survey, which was e-mailed to 14 specialists with solid experience (over twenty years) and knowledge in construction projects, revealed that the probability of the AI phenomenon occurring in Portugal is very high, and its impact on construction projects is equally high. The results also show that RC in combination with the BIM methodology contributes very positively to the mitigation of AI problems in construction projects in Portugal. Approximately 85% of respondents consider that the government should seek to reduce AI in the public works sector through the use of RC and its combination with the BIM methodology in the Portuguese Public Contracts Code

Enhancement of oxygen mass transfer in pneumatical bioreactors using n-dodecane as oxygen-vector

In biotechnology, oxygen mass transfer is a key parameter involved in the design and operation of bioreactors and it can be analyzed by means of the oxygen mass transfer coefficient (kLa). Due to the fact that oxygen has a very low solubility in an aqueous media (8–10 ppm at 20°C), actively growing cells can consume all the dissolved oxygen very fast, therefore, it has to be supplied continuously into the broths. In conventionally aerated bioreactors, low oxygen solubility combined with slow oxygen transfer rates often results in reduced growth and culture productivity. Due to their higher oxygen solubility, non-toxicity to microbes, antifoaming action, oxygen-vectors addition is one of the most effective methods to improve oxygen mass transfer rate in aerobic fermentations. The aim of this study was to investigate the use of n-dodecane as oxygen-vector in bubble column and air-lift bioreactors, under different working conditions (air superficial velocity, volumetric fraction of the organic phase, medium temperature). The results show that volumetric fraction of oxygen-vector (φ) has a great influence on kLa; in the presence of low volumetric fraction (φ=0.005 (v/v)), the oxygen mass transfer coefficient’s value in bubble column bioreactor was increased by almost 100% at 35°C and for φ=0.02 (v/v) by 5% at 25°C, while in air-lift bioreactor, at 25°C and φ=0.005 (v/v), the kLa value was enhanced by approximately 50%.his paper was supported by the project PERFORM-ERA "Postdoctoral Performance for Integration in the European Research Area" (ID-57649), financed by the European Social Fund and the Romanian Government

pH influence on oxygen mass transfer coefficient in a bubble column. Individual characterization of kL and a

Experiments were performed in a laboratory scale bubble column (10 L), to investigate the pH influence on oxygen mass transfer coefficient, in order to achieve a better control of biological processes. The liquid-side mass transfer coefficient, kL, and the specific interfacial area, a, were studied individually. The specific interfacial area was obtained using the new automatic image analysis technique developed by Ferreira et al. (2012). The pH was changed by the addition to the system of the most common acids and base used in biological process: hydrochloric acid (HCl), phosphoric acid (H3PO4) and potassium hydroxide (KOH). The results show that aqueous systems containing HCl, H3PO4 or KOH present lower volumetric liquid side mass transfer coefficient, kLa, in relation to pure systems (distilled water), this decrease being not linear. It was found that the specific interfacial area presents higher values in KOH and HCl solutions in comparison with distilled water. However, an opposite behavior was observed in the liquid-side mass transfer coefficient values. The kL behavior on the impure systems was explained based on bubble surface contamination. Higbie's and Fröessling's equations were adapted in the present work in order to be used in bubble dispersion systems

Temperature and solids effect on gas‐liquid mass transfer

The temperature and solids effect on the mass transfer characteristics in a bubble column was studied experimentally for the systems air/water/polyvinyl chloride (PVC) beads and air/water/expandable polystyrene (EPS) beads. Volumetric liquid side mass transfer coefficient, kLa, was determined under different temperatures (20, 25, 30, 35ºC), solid concentrations (up to 5%), gas flow rates (up to 7.4 mm/s) and solid sizes (549 and 210 μm for PVC beads, and 591 μm for EPS beads). The results show that the temperature plays an important role on mass transfer phenomena, by increasing kLa and, simultaneously, promoting the solids influence on kLa. The presence of solids affects negatively kLa being this effect more pronounced for the largest particles (PVC case). In addition, a decrease in kLa occurs when the solid loading increases (observed in both cases, PVC and EPS). Comparing the PVC and EPS effects on kLa, it can be concluded that physical and chemical properties of solids are important parameters to be taken into account on this kind of studies. An empirical correlation for kLa on the experimental variables was developed

GIS for the determination of bioenergy potential in the centre region of Portugal

Every activity performed by mankind is directly or indirectly dependant on the use of energy. Fossil fuels are the main source used nowadays, a presumably limited energy source that may end in the near future (Boyle, 2004). World total annual consumption of all forms of primary energy increased drastically, and in the year 2006 it reached an estimated 10,800 Mtoe (million tons of oil equivalent) (U.S. Energy Information Administration [USEIA], 2009). The annual average energy consumption per person of the world population in 2006 was about 1.65 toe (ton of oil equivalent) (Population Reference Bureau, 2010). In 2010, the consumption of this energy may reach 12,800 Mtoe (USEIA, 2009) and in 2050 it is expected to achieve a range of 14,300 Mtoe to 23,900 Mtoe (International Energy Agency for Bioenergy [IEAB], 2009). We can also assume that it might possibly never end. The current energy crisis is affecting great part of the world population (U.S. Department of Energy, 2009).(undefined

Structure determination of Split-soret Cytochrome from a Desulfovibrio species isolated from a human abdominal abcess

The determined structure of the split-soret cytochrome (SSC) isolated from Desulfovibrio desulfuricans ATCC 27774 (D.d.) revealed a new Heme arrangement, which suggests that this protein constitutes a new cytochrome class.. SSC is a 52.6kDa homodimer containing four hemes at one end of the molecule. In each monomer the two hemes have their edges overlapped within van der Waals contacts. The polypeptide chain of each monomer supplies the sixth ligand to the heme-iron of the other monomer. A similar protein was recently purified from a homologous Desulfovibrio clinical strain isolated from an abdominal wall abscess in human patient2. Crystals of this SSC were grown using vapour diffusion method in the presence of agarose gel. Diffraction data were collected using X-ray synchrotron radiation at the ESRF, beamline, ID 14-1. The structure will be solved by molecular replacement using the structure of the D.d. as a starting model