Failed fuel refers to the breach in the fuel-clad of an irradiated fuel assembly in a nuclear reactor. Neutron detection or gamma detection is commonly used in Failed Fuel Detection and Locating (FFDL) system to monitor the activity of the coolant. Though these methods offer specific advantages under different conditions of the coolant, providing both types of detectors in FFDL system is impractical. This limitation is the motivation for the detector system developed in the present work. In the present work, effort has been made for realising a detector system for simultaneous measurement of neutron and gamma activity of the coolant, thus offering a two-parameter basis for failed fuel detection. NE213 liquid scintillator was chosen for this work as it has good detection capability for both neutrons and gammas. Additionally, the neutrons and gammas interacting with NE213 detector can be separated based on pulse shape discrimination. The work reported in this thesis includes fabrication details and different steps followed in assembling the NE213 detector. Details of experimental set-up developed for pulse height analysis and pulse shape analysis are covered. Results of experiments carried out to study the response of the NE213 detector to gamma and neutron sources using pulse height analyser are presented. The absolute gamma efficiency and relative gamma efficiency of NE213 detector are calculated. Neutron–gamma separation capability of NE213 detector based pulse shape analysis system is reported. Application of the developed detector system to analyse the coolant activity in FFDL system in a reactor is described. Response of the detector is compared with the existing FFDL system at different power levels of the reactor. Since failed fuel is a rare event, it was simulated using neutron and gamma sources. Pulse shape analysis spectra obtained under simulated failed fuel condition are presented.

In India, the expansion of industries and two-fold increase in motor vehicles over the last decade are posing a serious environmental crisis in the form of urban air pollution. Common pollutants include carbon monoxide, sulfur dioxide, chlorofluorocarbons (CFCs), and nitrogen oxides produced by industry and motor vehicles. Air pollution results from a variety of sources. The natural sources include volcanoes, forest fire, scattering soil, biological decay, lightning strikes, dust storms etc. and man-made sources include thermal power plants, vehicular exhausts, incinerators and various other industrial emissions. More than 60% of the air pollution is contributed by these man-made sources. Amongst the gaseous pollutants, the major concern and a challenging task is to control oxides of nitrogen, commonly referred to as NOx. In case of diesel engines, despite the modification in engine design and improvement in after treatment technologies, large amount of NOx continues is get emitted and attempts to develop new catalyst to reduce NOx have so far been less successful. Further, with the emission standards becoming more stringent, estimates are that NOx and particulate matter emission must be reduced by as much as 90%. In this context, the emergence of electrical discharge plasma technique in combination with the few existing technologies is providing to be economically viable and efficient technology. In this thesis emphasis has been laid on the discharge based non-thermal plasma for NOx removal. NOx from simulated gas mixture and actual diesel engine exhaust has been treated. The thesis mainly addresses the following issues. . • Performance evaluation of pipe-cylinder and wire-cylinder reactor for NOx removal . • Study of effect of plasma assisted adsorbent reactor on NOx removal . • Study of effect of adsorption and plasma based desorption using different adsorbent material and electrode configuration The first chapter provides introduction about the air pollutants and the existing NOx control technologies, a brief history of electric discharge plasma, a detailed literature survey and scope of the work. A detailed experimental setup consisting of voltage sources, gas system (simulated flue gas and diesel exhaust), gas analyzers, adsorbent materials are discussed in the second chapter. In the third chapter, NOx is treated by three different methods and are described in separate parts. In first part we have done a comparative study of NO/NOx removal using two different types of dielectric barrier discharge electrodes: a) wire-cylinder reactor, b) pipe-cylinder reactor. Investigations were first carried out with synthetic gases to obtain the baseline information on the NO/NOx removal with respect to the two geometries studied. Further, experiments were carried out with raw diesel exhaust under loaded condition. A high NOx removal efficiency 90% was observed for pipe-cylinder reactor when compared to that with wire-cylinder reactor, where it was 53.4%. In second part an analysis has been made on discharge plasma coupled with an adsorbent system. The cascaded plasma-adsorbent system may be perceived as a better alternative for the existing adsorbent based abatement system in the industry. During this study the exhaust is sourced from a diesel generator set. It was observed that better NO removal in a plasma reactor can be made possible by achieving higher average fields and subsequent NO2 removal can be improved using an adsorbent system connected in cascade with the plasma system. This part describes the various findings pertaining to these comparative analyses. The third and last part of chapter 3 consists of gas desorption from an adsorbent by non-thermal plasma, which is an alternative to conventional thermal desorption, has been studied in relation to diesel engine exhaust. In this process saturated adsorbent material is regenerated using high energetic electrons and excited molecules produced by non thermal plasma. The last Chapter lists out the major inferences drawn from this study.

In India, with the increase in the number of industries and vehicles the environment is getting more and more polluted. More than industries it is the rapid growth of vehicles which causes serious environmental crisis in the form of air pollution and has become alarming particularly in cities. The industrial and vehicular growth cannot be neglected, as the country’s economic and social well being is largely dependent on them. But this should not come at the cost of our health and eco system. The industrial and vehicular emissions must be controlled in order to keep our air clean. Continued efforts in this direction are being taken up across the globe to investigate an efficient and economical technique. There are many air pollutants being emitted from both natural and manmade sources. The major air pollutants identified as hazardous to human health are nitrogen oxides (NOx), carbon monoxide (CO), particulate matter (PM), volatile organic compounds (VOC), and sulfur dioxides (SOx). Among these, nitrogen oxides are considered to be difficult to remove. The sources of NOx are thermal power plants, stationary and mobile diesel engines, gasturbine engine, ironore sintering plants and various other smallscale utilities. There are conventionally available technologies to remove NOx such as chemical scrubbing, catalysis etc. But these techniques are either difficult to operate or do not bring down the level of NOx to the required norms imposed by the government. The failure of conventional techniques to remove NOx to the expected limit led to the development of alternative nonconventional techniques. Prominent among these new alternative techniques is electric discharge plasma, where the gas is partially ionized and temperature of electrons is considerably higher than that of ions and background gas molecules. Diesel engines are getting popular due to their inherent merits and their number is increasing considerably. Unfortunately, the exhaust of diesel engine being complex with high oxygen content makes the existing pollution control techniques insufficient particularly with regard to removal of NOx. So there is a need for investigating better technology which can effectively abate the pollutants from diesel engine exhaust. Electric Discharge plasma is one such alternative technique which has been very successful in large volumes of flue gas cleaning and hence, its potential is being explored in the cleaning of small volumes of vehicular exhausts, in particular, diesel engine exhaust. In the present work we investigated the relative performance of different electric discharge plasma reactors, with different type of voltages like AC, DC and pulse. The reactors were evaluated for NOx removal efficiency and NO conversion. This research work is a feasibility study to find whether electric discharge plasma can be used more effectively as an alternative technology for the after treatment of diesel engine exhaust in cascade with some cheaper adsorbents, if necessary. The scope of this qualitative experimental study can briefly be summarized as below: . • To study different reactors for NO conversion and NOx removal . • To study the effect of dielectric pellets in enhancing the radical production which in turn will have a bearing on the chemical reactions . • To study the effect of different types of voltages on the cleansing process . • To propose an efficient reactor system subject to the experimental conditions studied.

This thesis is concerned with investigations on two related issues of turbulent jet diffusion flame, namely (a) stabilization at liftoff and (b) autoignition in a turbulent jet diffusion flame. The approach of Conditional Moment Closure (CMC) has been taken. Fully elliptic first order CMC equations are solved with detailed chemistry to simulate lifted H2/N2 flame in vitiated coflow. The same approach is further used to simulate transient autoignition process in inhomogeneous mixing layers. In Chapter 1, difficulties involved in numerical simulation of turbulent combustion problems are explained. Different numerical tools used to simulate turbulent combustion are briefly discussed. Previous experimental, theoretical and numerical studies of lifted jet diffusion flames and autoignition are reviewed. Various research issues related to objectives of the thesis are discussed. In Chapter 2, the first order CMC transport equations for the reacting flows are presented. Various closure models that are required for solving the governing equations are given. Calculation of mean reaction rate term for detailed chemistry is given with special focus on the reaction rates for pressure dependent reactions. In Chapter 3, starting with the laminar flow code, further extension is carried to include kε turbulence model and PDF model. The code is validated at each stage of inclusion of different model. In this chapter, the code is first validated for the test problem of constant density, 2D, axisymmetric turbulent jet. Further, validation of PDF model is carried out by simulating the problem of nonreacting jet of cold air issuing into a vitiated coflow. The results are compared with the published data from experiments as well as numerical simulations. It is shown that the results compare well with the data. In Chapter 4, numerical results of lifted jet diffusion flame are presented. Detailed chemistry is modelled using Mueller mechanism for H2/O2 system with 9 species and 21 reversible reactions. Simulations are carried out for different jet velocities and coflow stream temperatures. The predicted liftoff generally agrees with experimental data, as well as joint PDF results. Profiles of mean scalar fluxes in the mixture fraction space, for different coflow temperatures reveal that (1) Inside the flamezone, the chemical term balances the molecular diffusion term, and hence the structure is of a diffusion flamelet for both cases. (2) In the preflame zone, the structure depends on the coflow temperature: for low coflow temperatures, the chemical term being small, the advective term balances the axial diffusion term. However, for the high coflow temperature case, the chemical term is large and balances the advective term, the axial diffusion term being small. It is concluded that, liftoff is controlled (a) by turbulent premixed flame propagation for low cofflow temperature while (b) by autoignition for high coflow temperature. In Chapter 5, the numerical results of autoignition in inhomogeneous mixing layer are presented. The configuration consists of a fuel jet issued into hot air for which transient simulations are performed. It is found that the constants assumed in various modelling terms can severely influence the results, particularly the flame temperature. Hence, modifications to these constants are suggested to obtain improved predictions. Preliminary work is carried out to predict autoignition lengths (which may be defined by Tign × Ujet incase of jet- and coflowvelocities being equal) by varying the coflow temperature. The autoignition lengths show a reasonable agreement with the experimental data and LES results. In Chapter 6, main conclusions of this thesis are summarized. Possible future studies on this problem are suggested.

For an engine running at a constant speed, both exhaust and intake processes are periodic in nature. This inspires the muffler designer to go for the much easier and faster frequency domain modeling. But analogous to electrical filter, as per Thevenin’s theorem, the acoustic filter or muffler requires prior knowledge of the load-independent source characteristics (acoustic pressure and internal impedance), corresponding to the open circuit voltage and internal impedance of an electrical source. Studies have shown that it is not feasible to evaluate these source characteristics making use of either the direct measurement method or the indirect evaluation method. Hence, prediction of the radiated exhaust or intake noise has been subject to trial and error. Making use of the fact that pressure perturbation in a duct is a superposition of the forward moving wave and the reflected wave, a simple hybrid approach has been proposed making use of an interrelationship between progressive wave variables of the linear acoustic theory and Riemann variables of the method of characteristics. Neglecting the effect of nonlinearities, reflection of the forward moving wave has been duly incorporated at the exhaust valve. The reflection co-efficient of the system downstream of the exhaust valve has been calculated by means of the transfer matrix method at each of the several harmonics of the engine firing frequency. This simplified approach can predict exhaust noise with or without muffler for a naturally aspirated, single cylinder engine. However, this proves to be inadequate in predicting the exhaust noise of multi-cylinder engines. Thus, estimation of radiated noise has met only limited success in this approach. Strictly speaking, unique source characteristics do not exist for an IC engine because of the associated non-linearity of the time-varying source. Yet, a designer would like to know the un-muffled noise level in order to assess the required insertion loss of a suitable muffler. As far as the analysis and design of a muffler is concerned, the linear frequency-domain analysis by means of the transfer matrix approach is most convenient and time saving. Therefore, from a practical point of view, it is very desirable to be able to evaluate source characteristics, even if grossly approximate. If somehow it were possible to parameterize the source characteristics of an engine in terms of basic engine parameters, then it would be possible to evaluate the un-muffled noise before a design is taken up as a first approximation. This aspect has been investigated in detail in this work. A finite-volume CFD (one dimensional) model has been used in conjunction with the two-load or multi-load method to evaluate the source characteristics at a point just downstream of the exhaust manifold for the exhaust system, and upstream of the air filter (dirty side) in the case of the intake system. These source characteristics have been extracted from the pressure time history calculated at that point using the electro-acoustic analogy. Systematic parametric studies have yielded approximate empirical expressions for the source characteristics of an engine in terms of the basic engine parameters like engine RPM, capacity (swept volume or displacement), air-fuel ratio, and the number of cylinders. The effect of other parameters has been found to be relatively insignificant. Unlike exhaust noise, the intake system noise of an automobile cannot be measured because of the proximity of the engine at the point of measurement. Besides, the intake side is associated with turbocharger (booster), intercooler, cooling fan, etc., which will make the measurement of the intake noise erroneous. From the noise radiation point of view, intake noise used to be considered to be a minor source of noise as compared to the exhaust noise. Therefore, very little has been done or reported on prediction of the intake noise as compared to the exhaust noise. But nowadays, with efficient exhaust mufflers, the un-muffled intake noise has become a contributing factor to the passenger compartment noise level as a luxury decisive factor. Therefore, in this investigation both the intake and the exhaust side source characteristics have been found out for the compression ignition as well as the spark ignition engines. Besides, in the case of compression ignition engines, typical turbocharged as well as naturally aspirated engines have been considered. One of the inputs to the time-domain simulation is the intake valve and exhaust valve lift histories as functions of crank angle. It is very cumbersome and time-consuming to measure and feed these data into the program. Sometimes, this data is not available or cannot be determined easily. So, a generalized formula for the valve lift has been developed by observing the valve lift curves of various engines. The maximum exhaust valve lift has been expressed as a function of the swept volume of the cylinder. This formulation is not intended for designing a cam profile; it is for the purpose of determining approximate thermodynamic quantities to help a muffler designer for an initial estimation. It has also been observed during the investigation that from the acoustic point of view, sometimes it is better to open the exhaust valve a little earlier, but very slowly and smoothly, and keep it open for a longer time. Although the exact source characteristics for an automobile engine cannot be determined precisely, yet the values of source characteristics calculated using this methodology have been shown to be reasonably good for approximate prediction of the un-muffled noise as well as insertion loss of a given muffler. The resultant empirical expressions for the source characteristics enable the potential user to make use of the frequency-domain cum-transfer matrix approach throughout; the time consuming time-domain simulation of the engine exhaust source is no longer necessary. Predictions of the un-muffled sound pressure level of automotive engines have been corroborated against measured values as the well as the full scale time-domain predictions making use of a finite-volume software.

Numerical studies of two-dimensional laminar conjugate natural convection flow and heat transfer in horizontal annuli formed between inner heat generating solid cylinders and outer isothermal circular boundary are performed with and without the effect of surface radiation. The two configurations of the concentrically placed inner cylinder are a circular cylinder (CC configuration) and a square cylinder (SOS, i.e., Square-On-Side, configuration). The mathematical formulation consists of the continuity equation, momentum equations with Boussinesq approximation and the solid and fluid energy equations. Numerical solutions are obtained by discretising the governing equations on a collocated mesh (non-staggered mesh) and the pressure-velocity coupling is taken into account via the SIMPLE (Semi-Implicit Method for Pressure-Linked Equations) algorithm. A cylindrical polar coordinate system is employed for CC configuration and a Cartesian coordinate system is used for the SOS configuration. The convective terms are discretised with donor-cell differencing scheme and the diffusion terms, with central differencing scheme. The algebraic equations resulting from the discretisation of the governing equations are solved using the line by line TDMA (Tri-Diagonal Matrix Algorithm). A global iteration scheme over each time step is used for better coupling of temperature and the flow variables and steady-state solutions are obtained by time-marching. Steady-state results of conjugate pure natural convection are obtained for the volumetric heat generation and outer radius based Grashof number ranging from 104 to 1010, for solid-to-fluid thermal conductivity ratios of 1, 5, 10, 50 and 100, and for the aspect ratios of 0.2 and 0.4, with air as the working medium (Pr=0.708) for the CC and SOS configurations. The flow and temperature distributions are presented in terms of isotherms and streamline maps. Results are presented for several quantities of interest such as local and average Nusselt numbers on the inner and outer boundaries, dimensionless local temperatures on the inner boundary and dimensionless maximum and average solid cylinder temperatures. The results show that the flow in the annulus is characterized by double or quadruple vortex patterns. Of the dimensionless maximum solid temperature, average solid temperature and average inner boundary temperature, the first two are much sensitive to solid-to-fluid thermal conductivity ratio. Surface radiation effects are studied numerically in conjugation with natural convection. The coupling with surface radiation arises through the solid-fluid interface thermal condition. To account for the radiation effects, configuration factors among the subsurfaces of the inner and outer boundaries formed by the computational mesh are determined. Results are obtained for CC and SOS configurations for emissivities ranging from 0.2-0.8, with the other parameters as in pure natural convection case. It is found that even at low surface emissivity, radiation plays a significant role in bringing down the convective component and enhancing the total Nusselt numbers across the annulus. The presence of radiation is found to reduce the dimensionless temperatures inside the solid and homogenise the temperature distribution in the fluid. The radiative Nusselt number is about 50-70 % of the total Nusselt number depending on the radiative parameters chosen. This factor emphasizes the need for taking into account the coupling of radiation and natural convection for the accurate prediction of the flow and heat transfer characteristics in the annulus. The solution of the conjugate problem facilitates the determination of the solid temperature distribution, which is important in connection with the safety aspects of various thermal energy systems. Correlations as functions of Grashof number and thermal conductivity ratio are constructed for the estimation of various quantities of interest for the two configurations and aspect ratios for pure natural convection and for combined natural convection and radiation cases. The results are expected to be useful in the design of thermal systems such as spent nuclear fuel casks during transportation and storage, underground transmission cables and cooling of electrical and electronic components.

Solar energy is a virtually inexhaustible energy resource, and thus, has great potential in helping meet many of our future energy requirements. Current technology used for solar energy conversion, however, is not cost effective. In addition, solar thermal power systems are also generally less efficient as compared to fossil fuel based thermal power plants. There is a large variety of systems for solar thermal power generation, each with certain advantages and disadvantages. A distinct advantage of solar thermal power generation systems is that they can be easily integrated with a storage system and/or with an auxiliary heating system (as in hybrid power systems) to provide stable and reliable power. Also, as the power block of a solar thermal plant resembles that of a conventional thermal power plant, most of the equipment and technology used is already well defined, and hence does not require major break through research for effective utilisation. Manufacturing of components, too, can be easily indigenized. A solar collector field is generally used for solar thermal energy conversion. The field converts high grade radiation energy to low grade heat energy, which will inevitably involve energy losses as per the laws of thermodynamics. The 2nd law of thermodynamics requires that a certain amount of heat energy cannot be utilised and has to be rejected as waste heat. This limits the efficiency of solar thermal energy technology. However, in many situations, the waste heat can be effectively utilized to perform refrigeration and desalination using absorption or solid sorption systems, with technologies popularly known as “polygeneration”. There is extensive research done in the area of solar collectors, including but not limiting to thermal analysis, testing of solar collectors, and economic analysis of solar collectors. Exergy and optimization analyses have also been done for certain solar collector configurations. Research on solar thermal power plants includes energy analysis at system level with certain configurations. Research containing analysis with insolation varying throughout the day is limited. Hence, there is scope for analysis incorporating diurnal variation of insolation for a solar thermal power system. This thesis centres on the thermodynamic analysis at system level of a solar thermal power system using a concentrating solar collector field and a simple Rankine cycle power generation (with steam as the working fluid) for Indian conditions. The aim is to develop a tool for thermodynamic analysis of solar thermal power systems, with a generalised approach that can also be used with different solar collector types, different heat transfer fluids in the primary loop, and also different working fluids in the secondary loop. This analysis emphasises the solar collector field and a basic sensible heat storage system, and investigates the various energy and exergy losses present. Comparisons have been made with and without a storage unit and resulting performance issues of solar thermal power plants have been studied. Differences between the system under consideration and commercially used thermal power plants have also been discussed, which brought out certain limitations of the technology currently in use. A solution from an optimization analysis has been utilized and modified for maximization of exergy generated at collector field. The analysis has been done with models incorporating equations using the laws of thermodynamics. MATLAB has been used to program and simulate the models. Solar radiation data used is from NREL’s Indian Solar Resource Data, which is obtained using their SUNY model by interpreting satellite imagery. The performance of the system has been analysed for Bangalore for four different days with different daylight durations, each day having certain differences in the incident solar radiation or insolation received. A particular solution of an optimization analysis has been modified using the simulation model developed and analysed with the objective of maximization of exergy generated at collector field. It has been found that the performance of the solar thermal power system was largely dependent on the variation of incident solar radiation. The storage system provided a stableperformance for short duration interruptions of solar radiation occurred on Autumn Equinox (23-09-2002).The duration of the interruption was within the limits of storage unit capacity. The major disruption in insolation transpired on Summer Solstice (21-06-2002) caused a significantly large drop in the solar thermal system performance; practically the system ceased to function due to lack of energy resource. Hence, the use of an auxiliary heating system hasbeen considered desirable. The absence of a storage unit has been shown to cause a significant loss in gross performance of the power system. The Rankine cycle turbine had many issues coping with a highly fluctuating energy input, and thus caused efficiency losses and even ceased power generation. A storage unit has been found to be ideal for steady power generation purposes. Some commercial configurations may lack a storage system, but they have been compensated by the auxiliary heating system to ensure stable power generation. The optimization of the solar collector determines that optimal collector temperatures vary in accordance to the incident solar radiation. Hence, the collector fluid outlet temperature must not be fixed so as to handle varying insolation for optimal exergy extraction. The optimal temperatures determined for Bangalore are around 576 K which is close to the values obtained by the simulation of the solar thermal power system. The tools for analysis and simulation of solar thermal power plants developed in this thesis is fairly generalised, as it can be adapted for various types of solar collectors and for different working fluids (other than steam), such as for Organic Rankine Cycle (ORC). The model can also be easily extended to other types of power cycles such as Brayton and Stirling cycles.

PETROBRAS / Ao longo dos últimos anos a utilização de bombas centrífugas submersas (BCS) se tornou o segundo método de elevação artificial mais usado na indústria petrolífera. Como a produção típica dos poços petrolíferos submarinos consiste em misturas contendo óleo e gás, as bombas centrífugas estão sujeitas a operar com escoamento bifásico. A presença de gás livre no escoamento provoca instabilidades e degradação da curva de ganho de pressão da bomba. Essa degradação se torna muito grande quando ocorre o fenômeno de surging. Este fenômeno é caracterizado por um grande acúmulo de gás nos canais do rotor, sendo seu início identificado como um ponto na curva de ganho de pressão a partir do qual o desempenho cai de forma abrupta com a diminuição da vazão do líquido. Dependendo da fração de gás na entrada da bomba, pode ocorrer o bloqueio dos canais do rotor, fenômeno conhecido como gas locking, fazendo com que a vazão de líquido e o incremento de pressão sejam praticamente nulos. Portanto, é fundamental o conhecimento das condições operacionais e padrões de escoamento ligados à ocorrência de surging para uma operação adequada da bomba. Nesse cenário, o presente trabalho tem por objetivo avaliar o desempenho de uma bomba centrífuga operando com escoamento bifásico ar-água. Para esse fim, foram levantadas as curvas de ganho de pressão de uma bomba centrifuga convencional de dois estágios com rotores de tipo radial. Os testes foram feitos utilizando água e ar como fluidos de trabalho, com frações volumétricas de gás entre 0 e 10%, velocidades de rotação entre 300 e 600 rpm, com vazões de água entre 0,2 e 1,5 vezes o ponto de máxima eficiência e uma pressão de sucção de 160 kPa. Ao mesmo tempo, foram identificados os diferentes padrões de escoamento dentro do rotor em diferentes condições operacionais. Para construção da bancada, a carcaça da bomba e o rotor original de seu primeiro estágio foram substituídos por outros de material transparente, o que permitiu fotografar a distribuição de gás na bomba com a ajuda de uma câmera de alta velocidade. Além de se utilizar o modelo homogêneo (não deslizamento) como referência para calcular a fração de vazio de entrada em cada teste, um sensor de malha de eletrodos (wire mesh) foi instalado na sucção da bomba com o objetivo de medir frações de vazio reais, que posteriormente foram comparadas com os resultados do modelo homogêneo e o de deslizamento (drift flux). As imagens obtidas foram associadas às instabilidades observadas nas curvas de desempenho da bomba, como forma de se compreender os fenômenos relacionados à queda de desempenho em operação com escoamento bifásico, em especial nas condições de surging. Esse procedimento, associado à medida da fração de vazio real na entrada da bomba, não apenas contribui com o entendimento do escoamento bifásico líquido-gás em bombas, como também oferece uma fonte interessante de dados de entrada e de validação de modelos teóricos e numéricos para outros trabalhos. / Over the last years the use of electric submersible centrifugal pumps (ESPs) has become the second most widely used artificial elevation method in the oil industry. As the typical production of submarine oil wells consists of mixtures containing oil and gas, the centrifugal pumps are subjected to operate with two-phase flow. The presence of free gas in the flow causes instabilities and degradation of the pump pressure-rise curve. This degradation becomes severe when the surging phenomenon occurs, which is characterized by large gas accumulations inside the impeller, with its initiation identified as the point in the pressure-rise curve from which the performance falls abruptly with the decrease of the liquid flow rate. Depending on the intake gas fraction, the rotor channels can be completely blocked (gas locking), causing the liquid flow rate and the pressure-rise to be almost null. Therefore, knowledge of operating conditions and flow patterns linked to the occurrence of surging for proper pump operation is critical. In this scenario, the present work aims to evaluate the performance of a centrifugal pump operating with two-phase air-water flow. To this end, the pressure-rise curves of a conventional two-stage centrifugal pump with radial rotors were measured. The tests were done using water and air as working fluids, with volumetric gas fractions between 0 and 10%, rotational speeds between 300 and 600 rpm, water flow rates between 0.2 and 1.5 times the best efficiency point and a suction pressure of 160 kPa. At the same time, different flow patterns were identified inside the rotor under different operating conditions. For this purpose, the pump casing and the original rotor of its first stage were replaced by equivalent transparent pieces, which allowed photographing the gas distribution inside the pump with the help of a high-speed camera. In addition to using the homogeneous (non-slip) model as a reference to calculate the inlet gas volume fraction in each test, a wire mesh sensor was installed in the intake pipe in order to measure the actual void fractions, which were later compared with the results from the homogeneous and the drift flux models. The images obtained were associated with the instabilities observed in the performance curves of the pump, as a way to understand the phenomena related to the performance degradation in two-phase flow operation, especially under surging conditions. This procedure, together with the measurement of the actual gas volume fractions in the pump intake, not just contributes to the understanding of gas-liquid flows in pumps, but also provides an interesting source of data for input and validation of theoretical and numerical models for other investigations.

CNPq / O bloqueio de linhas de produção devido à formação de hidratos é uma das principais preocupações na garantia do escoamento em operações de produção de óleo e gás devido aos altos custos associados às paradas de produção. Os hidratos são formados pelo aprisionamento de moléculas de gás em uma gaiola de moléculas de água formada por ligações de hidrogênio. As condições de alta pressão e baixa temperatura necessárias para a formação de hidratos são frequentemente encontradas em cenários de produção no mar, sendo que o escoamento em golfadas é considerado o padrão de escoamento predominante. O presente trabalho utiliza uma abordagem em regime permanente para modelar a formação de dispersões homogêneas de hidrato-em-água durante o escoamento em golfadas em tubulações horizontais. O consumo das fases para a formação de hidratos é estimado em função da área interfacial gás-água e da temperatura de subresfriamento do sistema. O modelo de escoamento em golfadas é acoplado com: (i) termos de transferência de massa para recalcular as velocidades das estruturas das golfadas e (ii) termos de geração de calor, visto que a formação de hidratos é um processo exotérmico. O modelo foi implementado em linguagem Fortran90, utilizando lógica nodal de marcha. Comparações do modelo com dados experimentais da literatura apresentam desvios de aproximadamente ±20%. O modelo foi utilizado para analisar os efeitos da formação de hidratos sobre a hidrodinâmica e transferência de calor do escoamento em golfadas, analisando: velocidades (superficiais e das estruturas do escoamento em golfadas), pressão, temperatura, coeficiente de transferência de calor e geometria da célula unitária do escoamento em golfadas (comprimento das regiões características e frações de fase). O modelo também foi utilizado para analisar a influência das condições de entrada do escoamento (velocidade superficial da mistura, razão de líquido/mistura, pressão, uso de inibidores químicos) e de geometria da tubulação (diâmetro interno, espessura da parede, condutividade da parede) que retardam a formação de hidratos. Ao final, a influência da deposição de camadas de hidratos sobre o escoamento em golfadas (pressão, temperatura, velocidades, geometria da geometria da célula unitária) é analisado. / Hydrate formation is one of the main flow assurance concerns in offshore oil and gas production due to the high cost of production interruptions or impairments. Hydrates are formed by the imprisonment of gas molecules into hydrogen bonded cages of water molecules. The high pressure and low temperature conditions needed for hydrate formation are frequently found in offshore production scenarios, where slug flow is often the prevailing flow regime. The present work uses a steady-state approach for modeling homogeneous hydrate-in-water dispersion formation on horizontal slug flow in pipelines. The consumption of the phases during hydrate formation is estimated by a kinetic model in terms of the gaswater interfacial surface and the subcooling of the system. The slug flow model is coupled with: (i) mass transfer terms so as to recalculate the velocities of the slug flow structures and (ii) heat generation terms, since hydrate formation is an exothermic process. Comparisons of the model with experimental data present an average deviation of ±20%. The model was used to analyze the effects brought by hydrate formation over the slug flow hydrodynamics and heat transfer, analyzing: velocities (superficial and structure velocities), pressure, temperature, heat transfer coefficient and unit cell geometry (region lengths and phase fractions). The model was also used to analyze the influence of the pipe inlet conditions (mixture superficial velocity, liquid loading, pressure, use of chemical inhibitors) and of the pipeline geometry (internal diameter, wall width, wall thermal conductivity) in delaying hydrate formation. Finally, the influence of hydrate deposits on the slug flow behavior (pressure, temperature, velocities, unit cell geometry) is analyzed.

PETROBRAS / O presente trabalho contempla a análise do desenvolvimento de filme de líquido em escoamento ascendente sob a ação dos campos centrífugo e gravitacional, localizado em uma câmara ciclônica de um sistema de distribuição. No estudo foi analisada a dinâmica de um escoamento bifásico líquido-gás a partir de simulações numéricas, tridimensionais e transientes. Na modelagem numérica do escoamento foi utilizado o modelo de dois fluidos euleriano-euleriano junto com o esquema compressivo para a captura da interface líquido-gás e o modelo de turbulência SST (Shear Stress Transport). As equações de balanço foram discretizadas utilizado o método dos volumes finitos baseados em elementos finitos. As simulações numéricas foram realizadas no software comercial ANSYS-CFX 15.0. O modelo numérico desenvolvido foi validado com base em dados experimentais fornecidos pelo NUEM (Núcleo de Escoamento Multifásico). Os resultados obtidos neste trabalho possibilitaram o entendimento da dinâmica do escoamento (formação, espalhamento, estabilidade e desenvolvimento) e como a variação das velocidades superficiais do líquido e do gás (0,5; 1,0; 1,5 e 2,0 m/s para ambas as fases) influenciam na estabilidade e no comportamento do escoamento de filme de líquido ascendente. Foi elaborado ainda um modelo matemático capaz de fornecer condições de comportamento médio de um escoamento no padrão golfadas para os casos analisados. / Flows with free surface compose an important class of two-phase flows in the fluids mechanics. In various applications a thin film of liquid builds up on horizontal or vertical surfaces. This type of flow is denominated as liquid film flow. The present work contemplates the analysis of the development of liquid film in ascendant flow under the action of the centrifugal and gravitational fields, located in a cyclonic chamber of a distribution system. In the study, the dynamics of a liquid film flow were analyzed with the aid of three-dimensional and transient numerical simulations. The numerical model developed was validated based on experimental data provided by NUEM (Centre for Multiphase Flows). In the numerical modeling of the flow, were used the EulerianEulerian two fluid model coupled with the compressive discretization scheme for the capture of the liquid-gas interface and the Shear Stress Transport turbulence model. The balance equations were discretized using the finite volume based on finite elements method. Numerical simulations were supported by the commercial software ANSYS-CFX 15.0. The results obtained in this work enabled the understanding of flow dynamics (formation, spreading, stability and development) and how the superficial velocities of liquid and gas (0.5, 1.0, 1.5 and 2.0 m/s for both phases) influence on the stability and behavior of the ascendant liquid film flow. A mathematical model capable of providing conditions that represent the average behavior of a slug flow pattern was also elaborate.