Academic literature on the topic 'Suction and pressurization'

To provide a comprehensive understanding of the pressure fluctuation–vortex interaction in non-cavitation and cavitation flow, in this article, the unsteady flow in an ultra-low specific-speed centrifugal pump was investigated by numerical simulation. The uncertainty of the numerical framework with three sets of successively refined mesh was verified and validated by a level of 1% of the experimental results. Then, the unsteady results indicate that the features of the internal flow and the pressure fluctuation were accurately captured in accordance with the closed-loop experimental results. The detailed pressure fluctuation at 16 monitoring points and the monitoring of the vorticity suggest that some inconsistent transient phenomena in frequency spectrums show strong correlation with the evolution of vortex, such as abnormal increasing amplitudes at the monitoring points near to the leading edge on the suction surface and the trailing edge on the pressure surface in the case of lower pressurization capacity of impeller after cavitation. Further analysis applies the relative vortex transport equation to intuitionally illustrate the pressure fluctuation–vortex interaction by the contribution of baroclinic torque, viscous diffusion and vortex convection terms. It reveals that the effect of viscous diffusion is weak when the Reynolds number is much greater than 1. Pressure fluctuation amplitude enlarges on the suction side of blade near to the leading edge due to the baroclinic torque in cavitation regions, whereas the abnormal increase of pressure fluctuation after cavitation on the pressure surface of blade approaching the trailing edge results from the vortex convection during vortices moving downstream with the decrease of available net positive suction head at the same instance.

The operation of a high-pressure, piston-plunger fuel pump oriented for use in the common rail circuit of modern diesel engines for providing fuel to the injectors is investigated in this study from a numerical perspective. Both the suction and pressurization phases of the pump stroke were simulated with the overall flow time being in the order of 12 × 10−3 s. The topology of the cavitating flow within the pump configuration was captured through the use of an equation of state implemented in the framework of a barotropic, homogeneous equilibrium model. Cavitation was found to set in within the pressure chamber as early as 0.2 × 10−3 s in the operating cycle, while the minimum liquid volume fraction detected was in the order of 60% during the second period of the valve opening. Increase in the in-cylinder pressure during the final stages of the pumping stroke leads to the collapse of the previously arisen cavitation structures and three layout locations, namely, the piston edge, the valve and valve-seat region and the outlet orifice, were identified as vulnerable to cavitation-induced erosion through the use of cavitation aggressiveness indicators.

Tip clearance has a great effect on the flow and pressure fluctuation characteristics in a multiphase pump, especially at multiple operating points. The phase distribution and pressure fluctuation in tip clearance in a multiphase pump are revealed using the CFD (computational fluid dynamics) technology and high-speed photography methods. In this paper, the phase distribution, the gas-liquid two-phase velocity slip, and the pressure fluctuation intensity are comprehensively analyzed. Results show with the increase of the tip clearance, the multiphase pump pressurization performance is obviously deteriorated. In the meantime, the gas accumulation mainly occurs at the hub, the blade suction side (SS), and the tip clearance, and the maximum gas-liquid two-phase velocity difference is near the impeller streamwise of 0.4. In addition, the tip clearance improves the gas-liquid two-phase distribution in the pump, that is, the larger the tip clearance is, the more uniform the gas-liquid distribution becomes. Furthermore, the gas leads to the maximum pressure fluctuation intensity in the tip clearance which is closer to the tip leakage flow (TLF) outlet, and has a greater effect on the degree of flow separation in the tip clearance.

A fixed-wing aircraft (Beechcraft KingAir B200 C) fitted as an airborne intensive care facility is described. It completed 2000 missions from 1987–1992, for distances up to 1300 km. Features include: 1. Space for carriage of two stretchers, medical cabin crew of up to five persons and equipment and two-pilot operation if necessary. A third stretcher may be carried in emergencies. 2. Two CARDIOCAP™ fixed monitors for ECG, invasive and noninvasive pressures, pulse oximetry and end-tidal CO2 plus SIEMENS 630™/PROPAQ™ compact monitors for the ground transport phase of missions, or the total duration. 3. A medical oxygen reservoir of 4650 litres, sufficient for two patients on IPPV with FiO2 = 1.0 for a four-hour trip. The medical suction system is powered from the engine or a vacuum pump. 4. Other medical equipment and drugs in portable packs, for ground transport and resuscitation needs and for replenishment by nursing staff at the parent hospitals. 5. Stretchers compatible with helicopter and road ambulance vehicles used. 6. A stretcher loading device energized from the aircraft, operating through a wide (cargo) door. 7. Provision of 240v AC (alternating current) and 28v DC (direct current) electrical energy. 8. Pressurization and climate control. 9. Satisfactory aviation performance for conditions encountered, with single-pilot operation.

In the petroleum industry, multiphase transport pumps are a crucial technology for petroleum extraction. Therefore, the pressure fluctuation and internal-flow characteristics of multiphase transport pumps with different inlet-gas-volume fractions (IGVFs) have become an important research topic. Studying the pressure fluctuation and its effects on the performance of mixed-transport pumps under different IGVFs is significant for improving the running stability of pumps. In this work, steady and transient flow with different IGVFs was solved using the Navier–Stokes equation applied to a structured grid and the Shear Stress Transport (SST) turbulence model. The effects of IGVFs on the pressure pulsation and the performance of a three-stage, mixed-transport pump were studied. Results indicated that the numerical calculation results agreed well with the experimental data. The numerical method could predict the gas and liquid two-phase flow in the mixed-transport pump accurately. The pressure increase of this pump decreased with the increased flow quantity and the IGVFs. The efficiency improvement of the pump was limited by the increasing the flow rate. Under the rated-flow condition, a quantitative relationship was established between the relative discharge of the IGVF and the decrease in the pump head; when the IGVF exceeded 15%, the pressurization capacity decreased by more than 30%. Along the blade centerline direction, the pressure fluctuation amplitude near the suction surface of the impeller blade head gradually increased. Numerical simulation results showed that the dominant frequency of the pressure fluctuation of the impeller and diffuser was ten and seven times that of the rotation frequency, respectively. Thus, the IGVFs greatly influenced the dominant frequency of the pressure fluctuation. The air in the impeller primarily piled up at the suction surface of the blade head near the front cover. Under a centrifugal force, water was pushed to the back cover plate, making the gas-volume fraction near the front cover plate higher. Consequently, the distribution of gas content in the impeller became uneven. On the blade suction surface near the front cover plate, a low-velocity area caused by flow separation was generated, which further affected the pressure pulsation in the impeller. There were obvious vortices in the diffuser, and the vortex position had a tendency to move toward the inlet of the diffuser with an increased gas content. The flow pattern in the impeller was consistent, which indicated the great transport performance of this pump. In conclusion, through numerical simulation and experimental research, this study revealed the effects of the IGVFs on the performance and pressure pulsation of a mixed-transport pump under a gas–liquid two-phase flow condition. Our findings may serve as a guide for the optimization of a multiphase pump.

This work aimed to study the bubble distribution in a multiphase pump. A Euler-Euler inhomogeneous two-phase flow model coupled with a discrete particle population balance model (PBM) was used to simulate the whole flow channel of a three-stage gas-liquid two-phase centrifugal pump. Comparison of the computational fluid dynamic (CFD) simulation results with experimental data shows that the model can accurately predict the performance of the pump under various operating conditions. In addition, the liquid phase velocity distribution, gas-phase distribution, and pressure distribution of the second stage impeller at a 0.5 span of blade height under three typical working conditions were compared. Results show that the region with high local gas volume fraction (LGVF) mainly appears on the suction surface (SS) of the blade. With the increase in inlet gas volume fraction (IGVF), vortices and low velocity recirculation regions are generated at the impeller outlet and SS of the blade, the area with high LGVF increases, and gas–liquid separation occurs at the SS of the blade. The liquid phase flows out of the impeller at high velocity along the pressure surface of the blade, and the limited pressurization of fluid mainly happens at the impeller outlet. The average bubble size at the impeller outlet is the smallest while that at the impeller inlet is the largest. Under low IGVF conditions, bubbles tend to break into smaller ones, and the broken bubbles mainly concentrate at the blade pressure surface (PS) and the impeller outlet. Bubbles tend to coalesce into larger ones under high IGVF conditions. With the increase in IGVF, the bubble aggregation zone diffuses from the blade SS to the PS.

Dissertação de Mestrado Integrado em Engenharia de Mecânica
No âmbito do projeto desenvolvido na empresa Ferespe – Fundição de Ferro e Aço, Lda. surge esta Dissertação de Mestrado, cujo tema passa pelo desenvolvimento e conceção de um equipamento que permita a injeção de gases e pós no banho de metal líquido. Sendo o principal objetivo a promoção da sua limpeza e homogeneização da composição do metal fundido. Com o intuito de obter conhecimento relativamente às práticas, equipamentos e recursos utilizados nesta fase do processamento do metal fundido, recorreu-se a pesquisas bibliográficas bem como foi realizada uma visita à Siderurgia Nacional, S.A. e paralelamente efetuou-se um acompanhamento in loco do processo na empresa. O estudo dos diversos dispositivos utilizados na injeção de gás e pós, as variáveis operacionais com influência na hidrodinâmica do banho, os processos de transporte e a gama de elementos normalmente utilizados nas práticas de refinação no forno, serviram de suporte ao desenvolvimento do projeto apresentado nesta dissertação. A definição do modo operativo do equipamento, bem como os diferentes passos para a sua construção, foram os alicerces essenciais para o desenvolvimento do trabalho. Com base nas práticas aplicáveis na empresa em conjunto com a informação recolhida, definiram-se diversos fatores do processo, como a determinação do árgon e da cal, elementos a insuflar. No seguimento destas opções foram definidos os principais subsistemas do equipamento de injeção, como o invólucro refratário, a tipologia de alimentação e o circuito de insuflação. Um primeiro esboço da lança, em particular a extremidade de injeção, possibilitou o início dos passos de experimentação para o dimensionamento dos subsistemas da lança. Foram realizados diversos testes, complementados por métodos numéricos, que permitiram estudar o sistema de insuflação. Numa primeira fase contemplando apenas a aspiração dos pós para posteriormente ser coadjuvado pela pressurização do depósito. Após os ensaios de todos os subconjuntos efetuou-se a sua assemblagem, originando a estrutura do protótipo final para o trabalho experimental no forno. O processo evolutivo de todos os componentes, ao longo do projeto, foi conseguido graças aos inúmeros testes realizados na fundição do metal líquido, onde foram adaptadas e otimizadas as técnicas de construção do refratário. Devido aos obstáculos presentes, como a frequente obstrução da lança, houve a necessidade de redefinir os valores teóricos da pressão a injetar, para posteriormente conjugá-los com a velocidade do fluxo, de modo a conferir estabilidade no comportamento de homogeneização do banho. Na sequência dos testes realizados para a otimização do protótipo, concluiu-se que os efeitos das suas ações sobre o banho são inofensivos. A consequente análise química e física às amostras recolhidas evidenciou os progressos na limpeza do banho fundido, em resultado das reações ao nível da composição das inclusões de óxidos e sulfuretos. Por fim foi realizada a automatização e dimensionamento do equipamento otimizado.
Under the project developed in FERESPE company - Iron and Steel Foundry Ltd. has appeared this Master's Thesis, which the main subject involves the development and design of an equipment that allows the injection of gases and powders in the liquid metal bath. The main goal is the promotion of its cleanliness and the homogenization of the molten metal composition. In order to obtain knowledge regarding to this application, equipments and resources were used at this phase of the molten metal processing, literature research and a visit to the National Steel Mill, SA were made and in the meantime makes a in loco process monitoring in the company. They were made studies to support the development of the presented project, such as, several devices were used during the gas injection and after that, operating variables which influence in the hydrodynamic bath, the transport processes and the range of elements normally utilized in oven refining practices. The setting of the operating equipment mode and the different steps for its construction, were crucial for the development work. Based on the company practices and information gathered, the process factors were defined, such as, argon flow and lime like the elements to insufflate. After get the major subsystems of the injection equipment they were defined the refractory casing, the feed type and the blowing circuit. A first draft of the spear, in particular the extremity of the injection, it made possible starting the experimental steps for the spear subsystems designing. Several tests were made, complemented by numerical methods, allowed studying the insufflation system. Initially looking only on the aspiration of the powders and later to be assisted by pressurizing the deposit. After testing all the system subsets its assembly has been made, creating the structure of the final prototype for the realization of the experimental work in the oven. Evolutionary process of all components throughout the project, was achieved due to the numerous tests performed on the fusion of the liquid metal, which have been adapted and optimized the refractory construction techniques. Due to present obstacles, like the frequent obstruction of the spear, there was the necessity to redefine the theoretical values of the pressure to inject for later conjugate them with the speed of the flow, in order to establish stability in the homogenization of the bath behavior. Following the tests carried out to achieve the main objective, it was concluded the optimization of the prototype, that the effects of their actions on the bath are inoffensive. The chemical and physical analysis results to the collected samples shows progress in the cleaning of the molten bath, as a result of the reactions in terms of the composition of inclusions of oxides and sulphides. Finally, the automation and the design of the optimized equipment was performed.

A detailed unsteady numerical simulation has been carried out to investigate the shock and unsteady flow in the low pressure (LP) rotor in a 1+1/2 counter-rotating turbine (vaneless counter-rotating turbine (VCRT)). Through analyzing the distribution of static pressure and Mach number etc. in the VCRT, it can be found that, when the outer-extending shock (OES) of high pressure (HP) rotor moving from one LP rotor leading edge into the next, the inflow condition of LP rotor will vary. In the process, there are two typical inflow conditions. One is subsonic, but sufficiently near 1.0, and the other is slightly above unity i.e. the OES impinges on the LP rotor leading edge. Such inflow conditions of LP rotor will result in two different shock systems at different time. When the OES impinges on the LP rotor leading edge, a bow shock appears upstream of the LP rotor, and a normal shock produces at roughly 70% axial chord on the suction surface of LP rotor, and between the bow shock and normal shock, a group of expansion waves exist. After the OES sweeps the LP rotor leading edge i.e. the inflow of LP rotor is subsonic, the bow shock upstream of the LP rotor disappears, and a normal shock, that is weaker than the above, produces at the same location, and in front of the normal shock, a group of expansion waves exist. This distribution of shock in the VCRT LP rotor is similar to that in a compressor double-circular-arc (DCA) airfoil cascade in the same inflow condition, but in the VCRT LP rotor, the shocks are confined to the suction surface side of passage and its intensity weaker. The reason of the difference of the shock systems between the VCRT and the DCA airfoil cascade is that in the cascade the flow is of pressurization while in the VCRT the flow is of decompression. When the wake of the HP rotor sweeps the LP rotor, the static pressure on the suction surface of LP rotor will fluctuate, and a variational lower pressure area appears on the suction surface, which will result in a clear adverse pressure gradient on the suction surface in the LP rotor.

Lungmen Nuclear Power Plant in Taiwan is a twin-unit Advanced Boiling Water Reactor (ABWR) plant. In this study, a long-term GOTHIC model for the Lungmen ABWR primary containment response analysis is established. The wetwell space is vertically divided into several volumes to catch the pool temperature stratification effect. The long-term containment responses for a double-ended feedwater line break (FWLB) accident are calculated. The fuel decay heat is absorbed by the reactor coolant, and the coolant flows to the containment via the broken line. The suppression pool is gradually heated up by the high-temperature gas-water mixture following through horizontal vents. To reduce the pool temperature, the Residual Heat Removal (RHR) system will be required to operate in the suppression pool cooling mode. The RHR pumps have suction flow from suppression pool and discharge it to the RHR heat exchangers for cooling. The cooled water then returns to the pool. An elevated RHR return line is desired to avoid the cooled water being directly sucked again. The wetwell temperature stratification associated with the RHR return line elevation is investigated in this study. Effects of the RHR return line elevation on the pool temperature can be determined since the whole wetwell space is not lumped as a node only. The calculated peak pool temperature is 92.6°C based on the plant piping configuration. The peak temperature can be reduced to 88.9°C by returning the water via the wetwell spray spargers located in the top of the wetwell. However, it should be noted that using the wetwell spray also pressurizes the wetwell because the pool water temperature is higher than that of airspace during the late period of the event. Returning the pool water via the wetwell spray spargers is not suggested because it causes long-term wetwell pressurization.