CFD Simulation of Two-phase and Three-phase Flows in Internal-loop Airlift

Airlift reactors are pneumatically agitated reactors that have been widely used in chemical, petrochemical, and bioprocess industries, such as fermentation and wastewater treatment. Computational Fluid Dynamics (CFD) has become more popular approach for design, scale-up and performance evaluation of such reactors. In the present work numerical simulations for internal-loop airlift reactors were performed using the transient Eulerian model with CFD package, ANSYS Fluent 12.1. The turbulence in the liquid phase is described using κ- ε the model. Global hydrodynamic parameters like gas holdup, gas velocity and liquid velocity have been investigated for a range of superficial gas velocities, both with 2D and 3D simulations. Moreover, the study of geometry and scale influence on the reactor have been considered. The results suggest that both, geometry and scale have significant effects on the hydrodynamic parameters, which may have substantial effects on the reactor performance. Grid refinement and time-step size effect have been discussed. Numerical calculations with gas-liquid-solid three-phase flow system have been carried out to investigate the effect of solid loading, solid particle size and solid density on the hydrodynamic characteristics of internal loop airlift reactor with different superficial gas velocities. It was observed that averaged gas holdup is significantly decreased with increasing slurry concentration. Simulations show that the riser gas holdup decreases with increase in solid particle diameter. In addition, it was found that the averaged solid holdup increases in the riser section with the increase of solid density. These produced results reveal that CFD have excellent potential to simulate two-phase and three-phase flow system.

Modeling of water/steam circulation in Circulating Fluidized Bed boiler

A distinctive design feature of steam boiler with natural circulation is the presence of the steam drum which plays a role of the separator of vapor from the flow of water-and-steam mixture coming into steam drum from the furnace tubes. Steam drum with unheated downcomer tubes, deducing from it, and riser (screen/furnace tubes) inside the furnace is a closed circulation loop in which movement of water (downcomer tubes) and water-and-steam mixture (riser tubes) is organized. The movement of the working fluid is appears due to occurrence of the natural pressure, determined by the difference in hydrostatic pressure and the mass of water and water-and-steam mixtures in downcomer and riser tubes and called the driving pressure of the natural circulation: S drive = H steam (ρ down + ρ mix) g where: ρ down - density of water in downcomer tubes; ρ mix - density of water in riser tubes; H steam - height of steam content section; g - acceleration of gravity. In steam boilers with natural circulation the circulation rate is usually between 10 and 30. Thus, consumption of water in the circulation circuit “circulation rate times” more than steam output of the boiler. There are two aspects of the design of natural water circulation loops. One is to ensure a sufficient mass flux of circulating water to avoid burnout of evaporator tubes. The other is to avoid tube wall temperature fluctuation and tube vibration due to oscillation of circulation velocity. The design criteria are therefore reduced, in principle, to those of critical heat flux, critical flow rate for burnout, and flow instability. In practical design, however, the circulation velocity and the void fraction at the evaporator tube outlet are used as the design criteria (Seikan I., et. al., 1999). This study has been made with assumption that the heat flux in the furnace of the boiler even all the time. The target of the study was to define the circulation rate of the boiler, thus average heat flux do not change it. I would like to acknowledge professionals from “Foster Wheeler” company for good and comfortable cooperation.

Methods and Models for Accelerating Dynamic Simulation of Fluid Power Circuits

The objective of this dissertation is to improve the dynamic simulation of fluid power circuits. A fluid power circuit is a typical way to implement power transmission in mobile working machines, e.g. cranes, excavators etc. Dynamic simulation is an essential tool in developing controllability and energy-efficient solutions for mobile machines. Efficient dynamic simulation is the basic requirement for the real-time simulation. In the real-time simulation of fluid power circuits there exist numerical problems due to the software and methods used for modelling and integration. A simulation model of a fluid power circuit is typically created using differential and algebraic equations. Efficient numerical methods are required since differential equations must be solved in real time. Unfortunately, simulation software packages offer only a limited selection of numerical solvers. Numerical problems cause noise to the results, which in many cases leads the simulation run to fail. Mathematically the fluid power circuit models are stiff systems of ordinary differential equations. Numerical solution of the stiff systems can be improved by two alternative approaches. The first is to develop numerical solvers suitable for solving stiff systems. The second is to decrease the model stiffness itself by introducing models and algorithms that either decrease the highest eigenvalues or neglect them by introducing steady-state solutions of the stiff parts of the models. The thesis proposes novel methods using the latter approach. The study aims to develop practical methods usable in dynamic simulation of fluid power circuits using explicit fixed-step integration algorithms. In this thesis, twomechanisms whichmake the systemstiff are studied. These are the pressure drop approaching zero in the turbulent orifice model and the volume approaching zero in the equation of pressure build-up. These are the critical areas to which alternative methods for modelling and numerical simulation are proposed. Generally, in hydraulic power transmission systems the orifice flow is clearly in the turbulent area. The flow becomes laminar as the pressure drop over the orifice approaches zero only in rare situations. These are e.g. when a valve is closed, or an actuator is driven against an end stopper, or external force makes actuator to switch its direction during operation. This means that in terms of accuracy, the description of laminar flow is not necessary. But, unfortunately, when a purely turbulent description of the orifice is used, numerical problems occur when the pressure drop comes close to zero since the first derivative of flow with respect to the pressure drop approaches infinity when the pressure drop approaches zero. Furthermore, the second derivative becomes discontinuous, which causes numerical noise and an infinitely small integration step when a variable step integrator is used. A numerically efficient model for the orifice flow is proposed using a cubic spline function to describe the flow in the laminar and transition areas. Parameters for the cubic spline function are selected such that its first derivative is equal to the first derivative of the pure turbulent orifice flow model in the boundary condition. In the dynamic simulation of fluid power circuits, a tradeoff exists between accuracy and calculation speed. This investigation is made for the two-regime flow orifice model. Especially inside of many types of valves, as well as between them, there exist very small volumes. The integration of pressures in small fluid volumes causes numerical problems in fluid power circuit simulation. Particularly in realtime simulation, these numerical problems are a great weakness. The system stiffness approaches infinity as the fluid volume approaches zero. If fixed step explicit algorithms for solving ordinary differential equations (ODE) are used, the system stability would easily be lost when integrating pressures in small volumes. To solve the problem caused by small fluid volumes, a pseudo-dynamic solver is proposed. Instead of integration of the pressure in a small volume, the pressure is solved as a steady-state pressure created in a separate cascade loop by numerical integration. The hydraulic capacitance V/Be of the parts of the circuit whose pressures are solved by the pseudo-dynamic method should be orders of magnitude smaller than that of those partswhose pressures are integrated. The key advantage of this novel method is that the numerical problems caused by the small volumes are completely avoided. Also, the method is freely applicable regardless of the integration routine applied. The superiority of both above-mentioned methods is that they are suited for use together with the semi-empirical modelling method which necessarily does not require any geometrical data of the valves and actuators to be modelled. In this modelling method, most of the needed component information can be taken from the manufacturer’s nominal graphs. This thesis introduces the methods and shows several numerical examples to demonstrate how the proposed methods improve the dynamic simulation of various hydraulic circuits.

Comparative analysis between identified injuries of victims of fall from height and other mechanisms of closed trauma

OBJECTIVE: To analyze the lesions diagnosed in victims of falls, comparing them with those diagnosed in other mechanisms of blunt trauma.METHODS: We conducted a retrospective study of trauma protocol charts (prospectively collected) from 2008 to 2010, including victims of trauma over 13 years of age admitted to the emergency room. The severity of injuries was stratified by the Abbreviated Injury Scale (AIS) and Injury Severity Score (ISS). Variables were compared between the group of victims of falls from height (Group 1) and the other victims of blunt trauma (Group 2). We used the Student t, chi-square and Fisher tests for comparison between groups, considering the value of p <0.05 as significant.RESULTS: The series comprised 4,532 cases of blunt trauma, of which 555 (12.2%) were victims of falls from height. Severe lesions (AISe"3) were observed in the extremities (17.5%), in the cephalic segment (8.4%), chest (5.5%) and the abdomen (2.9%). Victims of Group 1 had significantly higher mean age, AIS in extremities / pelvis, AIS in the thoracic segment and ISS (p <0.05). The group 1 had significantly (p <0.05) higher incidence of tracheal intubation on admission, pneumothorax, hemothorax, rib fractures, chest drainage, spinal trauma, pelvic fractures, complex pelvic fractures and fractures to the upper limbs.CONCLUSION: Victims of fall from height had greater anatomic injury severity, greater frequency and severity of lesions in the thoracic segment and extremities.

Comparative analysis between identified injuries of victims of fall from height and other mechanisms of closed trauma

OBJECTIVE:to identify predictors of death in blunt trauma patients sustaining pelvic fractures and, posteriorly, compare them to a previously reported series from the same center.METHOD: Retrospective analysis of trauma registry data, including blunt trauma patients older than 14 y.o. sustaining pelvic fractures admitted from 2008 to 2010. Patients were assigned into group 1 (dead) or 2 (survivors). We used Student's t, qui square and Fisher's tests for statistical analysis, considering p<0.05 as significant. Posteriorly, we compared predictors of death between both periods.RESULTS: Seventy-nine cases were included. Mean RTS, ISS and TRISS were, respectively, 6.44 + 2.22, 28.0 + 15.2 e 0.74 + 0.33. Nineteen patients died (24,0%). Main cause of death was hemorrhage (42,1%). Group 1 was characterized by (p<0.05) lower systolic blood pressure and Glasgow coma scale means on admission, higher heart rate, head AIS, extremity AIS and ISS means, as well as, higher frequency of severe head injuries and complex pelvic fractures. Comparing both periods, we notice that the anatomic and physiologic severity of injury increased (RTS and ISS means). Furthermore, there was a decrease in the impact of associated thoracic and abdominal injuries on the prognosis and an association of lethality with the presence of complex pelvic fractures.CONCLUSION: There were significant changes in the predictors of death between these two periods. The impact of thoracic and abdominal associated injures decreased while the importance of severe retroperitoneal hemorrhage increased. There was also an increase in trauma severity, which accounted for high lethality.

Sellutehtaan vedenkäytön vähentäminen

Työn tarkoituksena oli etsiä mahdollisia kohteita sellutehtaan veden käytön vähen-tämiseksi. Analyysien avulla selvitettiin voidaanko havaittujen kohteiden tällä hetkellä menetettyjä vesivirtoja käyttää uudelleen. Lopuksi arvioitiin miten kierrä-tettävät vedet vaikuttaisivat raakaveden laatuun, mikäli ne yhdistettäisiin tämän joukkoon. Veden käytön vähentämiskohteita etsittiin tutkimalla tehtaan prosessi-kaavioita osastokohtaisesti sekä selvittämällä näin havaittuja kohteita osastoilla. Työn kokeellinen osa koostui vesianalyyseistä. Vesianalyyseissä määritettiin seu-raavat arvot sellutehtaalle tulevasta vedestä: sameus (FTU), kiintoaine, sähkönjoh-tavuus, pH, CODCr, BOD7ATU, kokonaisfosfori P, Mn, Cl, K, Ca, Mg ja AOX. Nämä tehtiin valituista kohteista havaituista tällä hetkellä tehtaalta pois johdetuista mutta mahdollisesti kierrätettävistä vesistä. Työn tuloksien perusteella havaittiin, että seuraavissa tarkasteluun valituissa koh-teissa vedet olivat hyvin puhtaita ja talteen otettavia kierrätykseen. Näitä olivat savukaasupesurin vedet, sekundäärilauhdesäiliön vedet sekä tiivistevedet. Haih-duttamon lämminvesisäiliön sekä kuivauskone 4 kiertovesitornin vedet olivat hieman likaantuneet mutta hyvin kierrätettävissä. Koivulinjan D0-vaiheen, havu-linjan D1-vaiheen sekä kuivauskone 4 lajittamon vesivirtoja ei likaantumisen vuoksi kannattanut kerätä hyötykäyttöön.

Kaivoslastauskoneen hybridisointianalyysi virtuaali- ja in-loop -simuloinnin avulla

Työssä tutkitaan raskaiden työkoneiden hybridisointimitoitusta simuloimalla. Työssä esitetään simulation-in-the-loop-simulointiin perustuva järjestelmä, jolla esimerkkitapauksena oleva kaivoslastauskone työympäristöineen voidaan mallintaa mekaaniselta osaltaan monikappaledynamiikkaan perustuvalla ohjelmistolla ja hybridijärjestelmän osalta Simulinkissa. Yhdistetty simulointi mahdollistaa hybridityökoneen virtuaalimallin ohjaamisen käyttäjän toimesta reaaliajassa. Simuloinnista saadaan tuloksena mm. työsykli, jota voidaan käyttää hybridisointimitoitukseen. Hybridisointi toteutetaan kahdella erilaisella kokoonpanolla, joista analysoidaan suorituskykyä sekä polttoaineen kulutusta. Tuloksia verrataan pelkästään dieselmoottoria voimanlähteenä käyttävään lastauskoneeseen. Työssä tehty tutkimus osoittaa, että (sarja-) hybridisoinnilla voidaan saavuttaa merkittäviä etuja raskaiden työkoneiden polttoainetehokkuudessa. Dieselmoottoria voidaan ajaa sellaisessa staattisessa toimintapisteessä, jonka hyötysuhde on korkea riippumatta työkoneen kuormituksesta. Saavutettu hyöty on toteutetussa tutkimuksessa parhaimmillaan jopa 56 % vähennys polttoaineenkulutuksessa. Lisäksi tarvittava dieselin nimellisteho pienenee huomattavasti. Tutkimuksen osana esitellään myös Hardware-in-the-Loop -laitteisto, jonka avulla voidaan liittää oikea sähkömoottori ja taajuudenmuuttaja osaksi virtuaalisesti simuloitua työkonetta.

Development and evaluation of a loop-mediated isothermal amplification (LAMP) assay for rapid detection of Actinobacillus pleuropneumoniae based the dsbE-like gene

This paper reports on the development and validation of a loop-mediated isothermal amplification assay (LAMP) for the rapid and specific detection of Actinobacillus pleuropneumoniae (A. pleuropneumoniae). A set of six primers were designed derived from the dsbE-like gene of A.pleuropneumoniae and validate the assay using 9 A. pleuropneumoniae reference/field strains, 132 clinical isolates and 9 other pathogens. The results indicated that positive reactions were confirmed for all A. pleuropneumoniae strains and specimens by LAMP at 63ºC for 60 min and no cross-reactivity were observed from other non-A.pleuropneumoniae including Haemophilus parasuis, Escherichia coli, Pasteurella multocida, Bordetella bronchiseptica, Streptococcus suis, Salmonella enterica, Staphylococcus, porcine reproductive and respiratory syndrome virus (PRRSV), and Pseudorabies virus. The detection limit of the conventional PCR was 10² CFU per PCR test tube, while that of the LAMP was 5 copies per tube. Therefore, the sensitivity of LAMP was higher than that of PCR. Moreover, the LAMP assay provided a rapid yet simple test of A. pleuropneumoniae suitable for laboratory diagnosis and pen-side detection due to ease of operation and the requirement of only a regular water bath or heat block for the reaction.

Rapid and sensitive detection of Bordetella bronchiseptica by loop-mediated isothermal amplification (LAMP)

Bordetella bronchiseptica causes acute and chronic respiratory infections in diverse animal species and occasionally in humans. In this study, we described the establishment of a simple, sensitive and cost-efficient loop-mediated isothermal amplification (LAMP) assay for the detection of B. bronchiseptica. A set of primers towards a 235 bp region within the flagellum gene of B. bronchiseptica was designed with online software.. The specificity of the LAMP assay was examined by using 6 porcine pathogens and 100 nasal swabs collected from healthy pigs and suspect infected pigs. The results indicated that positive reactions were confirmed for all B. bronchiseptica and no cross-reactivity was observed from other non-B. bronchiseptica. In sensitivity evaluations, the technique successfully detected a serial dilutions of extracted B. bronchiseptica DNA with a detection limit of 9 copies, which was 10 times more sensitive than that of PCR. Compared with conventional PCR, the higher sensitivity of LAMP method and no need for the complex instrumentation make this LAMP assay a promising alternative for the diagnosis of B. bronchiseptica in rural areas and developing countries where there lacks of complex laboratory services.

Connexin domains relevant to the chemical gating of gap junction channels

Most cells exchange ions and small metabolites via gap junction channels. These channels are made of two hemichannels (connexons), each formed by the radial arrangement of six connexin (Cx) proteins. Connexins span the bilayer four times (M1-M4) and have both amino- and carboxy-termini (NT, CT) at the cytoplasmic side of the membrane, forming two extracellular loops (E1, E2) and one inner (IL) loop. The channels are regulated by gates that close with cytosolic acidification (e.g., CO2 treatment) or increased calcium concentration, possibly via calmodulin activation. Although gap junction regulation is still unclear, connexin domains involved in gating are being defined. We have recently focused on the CO2 gating sensitivity of Cx32, Cx38 and various mutants and chimeras expressed in Xenopus oocytes and studied by double voltage clamp. Cx32 is weakly sensitive to CO2, whereas Cx38 is highly sensitive. A Cx32 chimera containing the second half of the inner loop (IL2) of Cx38 was as sensitive to CO2 as Cx38, indicating that this domain plays an important role. Deletion of CT by 84% did not affect CO2 sensitivity, but replacement of 5 arginines (R) with sparagines (N) at the beginning of CT (C1) greatly enhanced the CO2 sensitivity of Cx32. This suggests that whereas most of CT is irrelevant, positive charges of C1 maintain the CO2 sensitivity of Cx32 low. As a hypothesis we have proposed a model that involves charge interaction between negative residues of the beginning of IL1 and positive residues of either C1 or IL2. Open and closed channels would result from IL1-C1 and IL1-IL2 interactions, respectively

The role of autolysis loop in determining the specificity of coagulation proteases

We recently demonstrated that the substitution of the autolysis loop (residues 143 to 154 in the chymotrypsin numbering system) of activated protein C (APC) with the corresponding loop of factor Xa (fXa) renders the APC mutant (APC/fX143-154) susceptible to inhibition by antithrombin (AT) in the presence of pentasaccharide. Our recent results further indicated, that in addition to an improvement in the reactivity of APC/fX143-154 with AT, both the amidolytic and anti-factor Va activities of the mutant APC have also been significantly increased. Since the autolysis loop of APC is five residues longer than the autolysis loop of fXa, it could not be ascertained whether this loop in the mutant APC specifically interacts with the activated conformation of AT or if a shorter autolysis loop is responsible for a global improvement in the catalytic activity of the mutant protease. To answer this question, we prepared another APC mutant in which the autolysis loop of the protease was replaced with the corresponding loop of trypsin (APC/Tryp143-154). Unlike an ~500-fold improvement in the reactivity of APC/fX143-154 with AT in the presence of pentasaccharide, the reactivity of APC/Tryp143-154 with the serpin was improved ~10-fold. These results suggest that both the length and structure of residues of the autolysis loop are critical for the specificity of the coagulation protease interaction with AT. Further factor Va inactivation studies with the APC mutants revealed a similar role for the autolysis loop of APC in the interaction with its natural substrate.

Alloxan-induced diabetes delays repair in a rat model of closed tibial fracture

A closed fracture was performed on the left tibia of 3-month-old Wistar rats weighing 250 to 350 g that were either healthy (N = 24) or made diabetic with alloxan (N = 24) to investigate the effect of alloxan-induced diabetes on the course of bone fracture healing. Histomorphometric analysis of the fracture site was performed at 7, 14, 25, and 35 days. After 7 days, diabetic rats had significantly less cartilage (P = 0.045) and greater fibrous connective (P = 0.006) tissue formation at the fracture site compared to controls. In contrast, marked callus formation was seen in diabetic rats with significant osteogenesis (P = 0.011, P = 0.010, P = 0.010, respectively, for 14, 25, and 35 days) and chondrogenesis (P = 0.028, P = 0.033, P = 0.019) compared to controls. Radiographic analysis revealed a displaced fracture with poor bone fragment alignment and delayed consolidation at these times in the diabetic group. The levels of alkaline phosphatase were significantly higher in diabetic rats at 25 days (P = 0.009). These results suggest that the initial excessive formation of fibrous connective tissue associated with delay in chondrogenesis and osteogenesis may not provide suitable stability of the fractured site, contributing to the inappropriate alignment of fragments and an increase in the volume of callus in later stages of repair. The resulting displaced fracture in diabetic rats requires long periods for remodeling and complete bone consolidation.