Os ejetores são dispositivos largamente utilizados nos mais diversos ramos da engenharia. Este trabalho foi desenvolvido no Laboratório de Hidráulica da Escola de Engenharia de São Carlos - USP, com o propósito de avaliar experimental e teoricamente o desempenho de ejetores de baixo custo, projetados e construídos em conexões do tipo \"tê\" de PVC, onde água foi utilizada tanto como fluido prmário como secundário. Os ensaios foram realizados com ejetores de diâmetros nominais de 25 mm e de 32 mm com relações de áreas de 0,25; 0,35 e 0,53. Foi utilizado também, para cada diâmetro, um ejetor mais compacto e sem câmara de mistura, com a relação de áreas de valor intermediário. Os ejetores comuns apresentaram rendimentos mais elevados do que os compactos, sendo o máximo de 30,52% alcançado com o ejetor de 25 mm e relação de áreas de 0,35. Os coeficientes de perda de carga em cada componente dos ejetores foram ajustados através de um modelo unidimensional. O fenômeno da cavitação também foi analisado. Os resultados mostraram que os ejetores de baixo custo apresentam funcionamento similar ao dos ejetores convencionais. / The ejectors are devices widely used in the most several branches of the engineering. This work was developed at the Laboratory of Hydraulics of the School of Engineering of São Carlos - SP, with the purpose of evaluating experimentally and theoretically the acting of low cost ejectors, projected and built in connections of the type \"tee\" of PVC, where water was used as much primary fluid as secondary. The experiments were accomplished with ejectors of nominal diameters of 25 mm and of 32 mm with area ratio of 0,25; 0,35 and 0,53. It was also used, for each diameter, a more compact ejector and without mixing chamber, with the area ratio of intermediate value. The common ejectors presented higher efficiencies than the compact ones, being the maximum of 30,52% reached with the ejector of 25 mm and area ratio of 0,35. The coefficients of head loss in each component of the ejectors were adjusted through one-dimensional model. The phenomenon of the cavitation was also analyzed. The results showed that the low cost ejectors present similar operation to the conventional ejectors.

Os ejetores são dispositivos largamente utilizados nos mais diversos ramos da engenharia. Este trabalho foi desenvolvido no Laboratório de Hidráulica da Escola de Engenharia de São Carlos - USP, com o propósito de avaliar experimental e teoricamente o desempenho de ejetores de baixo custo, projetados e construídos em conexões do tipo \"tê\" de PVC, onde água foi utilizada tanto como fluido prmário como secundário. Os ensaios foram realizados com ejetores de diâmetros nominais de 25 mm e de 32 mm com relações de áreas de 0,25; 0,35 e 0,53. Foi utilizado também, para cada diâmetro, um ejetor mais compacto e sem câmara de mistura, com a relação de áreas de valor intermediário. Os ejetores comuns apresentaram rendimentos mais elevados do que os compactos, sendo o máximo de 30,52% alcançado com o ejetor de 25 mm e relação de áreas de 0,35. Os coeficientes de perda de carga em cada componente dos ejetores foram ajustados através de um modelo unidimensional. O fenômeno da cavitação também foi analisado. Os resultados mostraram que os ejetores de baixo custo apresentam funcionamento similar ao dos ejetores convencionais. / The ejectors are devices widely used in the most several branches of the engineering. This work was developed at the Laboratory of Hydraulics of the School of Engineering of São Carlos - SP, with the purpose of evaluating experimentally and theoretically the acting of low cost ejectors, projected and built in connections of the type \"tee\" of PVC, where water was used as much primary fluid as secondary. The experiments were accomplished with ejectors of nominal diameters of 25 mm and of 32 mm with area ratio of 0,25; 0,35 and 0,53. It was also used, for each diameter, a more compact ejector and without mixing chamber, with the area ratio of intermediate value. The common ejectors presented higher efficiencies than the compact ones, being the maximum of 30,52% reached with the ejector of 25 mm and area ratio of 0,35. The coefficients of head loss in each component of the ejectors were adjusted through one-dimensional model. The phenomenon of the cavitation was also analyzed. The results showed that the low cost ejectors present similar operation to the conventional ejectors.

This research study considered subsonic short air-air ejectors with multi-ring entraining diffusers. Many references can be found for the design of air-air ejectors with solid diffusers. However, a limited amount of work has been published specially addressing the performance of short ejectors with entraining diffusers. This study was an experimental and computational investigation of how ejector performance is affected by ejector geometry (i.e. nozzle, mixing tube and diffuser), flow inlet swirl conditions and flow temperature. Ejector performance was quantified in terms of pumping, pressure recovery, wall temperature and velocity and temperature distribution at the diffuser exit. The experiments were conducted on one cold flow wind tunnel and one hot gas wind tunnel. In total, eight ejector systems were tested for this research. Five different swirl conditions and two primary air flow temperatures were studied. Ejector inlet conditions were measured using four fixed 7-hole pressure probes in the annulus. Ejector exit flow conditions were measured using a traversing 7-hole pressure probe with a thermocouple. A parallel computational study was conducted along with the experimental study. The commercial CFD packages, Gambit 2.3 and Fluent 6.2, were selected for meshing and flow solutions. The objective of the computational study was to determine the utility of RANS based CFD model for predicting device performance as design changes were implemented. The computational study was intended to provide practitioners with guidance as to when CFD will provide practical answers to specific questions relating to the ejector performance including ejector pumping, pressure recovery, wall temperatures and velocity and temperature distribution at the diffuser exit. In total, twenty-six complete cold flow experiments and twenty complete hot flow experiments have been completed. A detailed CFD model study has been performed to select the suitable computational domain, mesh density, boundary conditions, turbulence model and near wall treatment. Twenty-four CFD cases were selected to compare with the corresponding experimental data. The experimental results showed that the inlet swirl conditions and the diffuser bent angle had significant effects on the ejector performance. In general, the maximum ejector performance was achieved with the 20° inlet swirl condition. This level of swirl enhanced pressure recovery in the ejector. As the diffuser bent angle increased, the total pumping decreased due to the flow impingement in the diffuser. The oblong ejector generally had better flow mixing performance than the round ejector. For the CFD simulations, the Realizable k-ε turbulence model was found to give reasonable predictions for most of the bulk flow properties such as the total pumping, velocity profiles, swirl levels and back pressure. These were achieved at a reasonable cost in terms of the human efforts and computational resources. The RSM was able to give slightly improved predictions but at a much higher cost in terms of the efforts and computing resources. All of the turbulence models had difficulty predicting the pressure recovery in the mixing tube and diffuser because of their inability to accurately predict flow separation in the core of the swirling primary flow. As a result of this, the turbulence models considered in this work overpredicted the pumping of the mixing tube and underpredicted the pumping of the entraining diffuser. This unresolved issue with the CFD models is an important consideration when designing such devices. / Thesis (Ph.D, Mechanical and Materials Engineering) -- Queen's University, 2008-01-08 00:26:54.931 / This project has been funded by joint contribution from the National Sciences and Engineering Research Council of Canada (NSERC), the Department of National Defence (DND)and W.R. Davis Engineering Ltd.

Refrigeration systems, air-conditioning units and heat pumps have been recognized as indispensable machines in human life, and are used for e.g. food storage, provision of thermal comfort. These machines are dominated by the vapor compression refrigeration system and consume a large percentage of world-wide electricity output. Moreover, CO2 emissions related to the heating and cooling processes contribute significantly to the total amount of CO2 emission from energy use. The ejector refrigeration system (ERS) has been considered as a quite interesting system that can be driven by sustainable and renewable thermal energy, like solar energy, and low-grade waste heat, consequently, reducing the electricity use. The system has some other remarkable merits, such as being simple and reliable, having low initial and running cost with long lifetime, and providing the possibility of using environmentally-friendly refrigerants, which make it very attractive. The ERS has received extensive attention theoretically and experimentally. This thesis describes in-depth investigations of vapor ejectors in the ERS to discover more details. An ejector model is proposed to determine the system performance and obtain the required area ratio of the ejector by introducing three ejector efficiencies. Based on this ejector model, the characteristics of the vapor ejector and the ERS are investigated from different perspectives. The working fluid significantly influences the ejector behavior and system performance as well as the ejector design. No perfect working fluid that satisfies all the criteria of the ERS can be found. The performance of nine refrigerants has been parametrically compared in the ERS. Based on the slope of the vapor saturation curve in a T-s diagram, the working fluids can be divided into three categories: wet, dry and isentropic. A wet fluid has a negative slope of the vapor saturation curve in the T-s diagram. An isentropic expansion process from a saturated vapor state will make the state after the expansion to fall inside the liquid-vapor area of the T-s diagram which will result in droplet formation. Generally, an isentropic expansion for a dry fluid will not occur inside the liquid-vapor area, and consequently no droplets will form. An isentropic fluid has a vertical slope of the vapor saturation curve in the T-s diagram and an isentropic expansion process will hence follow the vapor saturation curve in the T-s diagram, ideally without any droplet formation. However, when the saturation condition is close to the critical point, it is possible that the isentropic expansion process of a dry fluid and an isentropic fluid occurs inside the liquid-vapor area of the T-s diagram, resulting in formation of droplets. In order to avoid droplet formation during the expansion, a minimum required superheat of the primary flow has been introduced before the nozzle inlet. Results show that the dry fluids have generally better performance than the wet fluids and the isentropic fluid. Hence the thesis mostly focuses on the features of vapor ejectors and the ERS using dry fluids. Exergy analysis has been proven to be very useful to identify the location, magnitude, and sources of exergy destruction and exergy loss, and to determine the possibilities of system performance improvement. This method is applied to the ejector and the ERS. The ejector parameters are closely interacting. The operating condition and the ejector area ratio have a great impact on the ejector overall efficiency and system COP. The ejector efficiencies are sensitive to the operating conditions, and they significantly influence the system performance. A so-called advanced exergy analysis is adopted to quantify the interactions among the ERS components and to evaluate the realistic potential of improvement. The results indicate that, at the studied operating condition, the ejector should have the highest priority to be improved, followed by the condenser, and then the generator. Thermoeconomics, which combines the thermodynamic analysis and economic principles, is applied to reveal new terms of interest of the ERS. The economic costs of the brine side fluids (fluids that supply heat to the generator and evaporator and remove heat from the condenser) play very essential roles in the thermoeconomic optimization of the ERS. Depending on different economic conditions, the system improvement from a thermodynamic point of view could be quite different from the thermoeconomic optimization. The ERS is economically sound when using free heat sources and heat sink. An ejector test bench has been built to test the entrainment ratio of different ejectors. Although the experiments do not achieve the desired results, they could still be discussed. The insignificant effect of the superheat of the secondary flow found in the theoretical study is validated. The assumption of neglecting the velocities at the ejector inlets and outlet are confirmed. The quantification of the ejector efficiencies shows that they largely depend on the operating conditions and the ejector dimensions. / <p>QC 20141102</p>

The application of an ejector nozzle integrated with a reaction drive rotor configuration for a vertical takeoff and landing rotorcraft is considered in this research. The ejector nozzle is a device that imparts energy from a high speed airflow source to a lower speed secondary airflow inside a duct. The overall nozzle exhaust mass flow rate is increased through fluid entrainment, while the exhaust gas velocity is simultaneously decreased. The exhaust gas velocity is strongly correlated to the jet noise produced by the nozzle, making the ejector a good candidate for propulsion system noise reduction. Ejector nozzles are mechanically simple in that there are no moving parts. However, coupled fluid dynamic processes are involved, complicating analysis and design. Geometric definitions of the ejector nozzle are determined through a reduced fidelity, multi-disciplinary, representation of the rotary wing ejector. The resulting rotary wing ejector geometric sizing procedure relates standard vehicle and rotor design parameters to the ejector. Additionally, a rotary wing ejector performance procedure is developed to compare this rotor configuration to a conventional rotor. Performance characteristics and aerodynamic effects of the rotor and ejector nozzle are analytically studied. Ejector nozzle performance, in terms of exit velocities, is compared to the primary reaction drive nozzle; giving an indication of the potential for noise reduction. Computational fluid dynamics are paramount in predicting the aerodynamic effects of the ejector nozzle located at the rotor blade tip. Two-dimensional, steady-state, Reynolds-averaged Navier-Stokes (RANS) models are implemented for sectional lift and drag predictions required for the rotor aerodynamic model associated with both the rotary wing ejector sizing and performance procedures. A three-dimensional, unsteady, RANS simulation of the rotary wing ejector is performed to study the aerodynamic interactions between the ejector nozzle and rotor. Overall performance comparisons are made between the two- and three-dimensional models of the rotary wing ejector, and a similar conventional rotor.

Thesis (M. S.)--Mechanical Engineering, Georgia Institute of Technology, 2009. / Committee Chair: Dr. Yogendra Joshi; Committee Member: Dr. S. Mostafa Ghiaasiaan; Committee Member: Dr. Sheldon Jeter. Part of the SMARTech Electronic Thesis and Dissertation Collection.

Orientador: Vivaldo Silveira Junior / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia de Alimentos / Made available in DSpace on 2018-08-24T19:17:01Z (GMT). No. of bitstreams: 1 Oliveira_CintiaCarlaMelgacode_M.pdf: 2012386 bytes, checksum: 17e9e513690eaa1341a66b69e6b22a64 (MD5) Previous issue date: 2014 / Resumo: A busca por equipamentos de refrigeração eficientes e acessíveis é crescente no mercado. Grandes empresas buscam instalar termoacumuladores, armazenamento de energia a baixa temperatura, em suas instalações por fatores econômicos. Com isso, este processo pode ser efetuado em horários fora de pico de energia e ser usado em horário de maior demanda energética, projetando-se então, equipamentos menores para acoplar ao sistema principal e melhorar o dimensionamento do espaço físico. Atualmente, um dos meios utilizado no sistema de resfriamento evaporativo é o uso de bomba de vácuo ou ejetores. Este trabalho tem como objetivo construir e avaliar energeticamente um sistema de resfriamento evaporativo com uso de ejetor, tendo água como fluido que circulará no seu interior, permitindo ser instalado em locais com abundância de água em circulação, perante a substituição ao sistema de resfriamento com uso de dispositivos mecânicos ou geradores. Ejetores são dispositivos usados para arrastar amostras por um jato de um fluido auxiliar, que constam essencialmente de um tubo aspirador e um bocal convergente, alimentando um compartimento convergente-divergente. Após a montagem mecânica e elétrica do sistema, estudou o comportamento do mesmo perante a mudança da vazão volumétrica e da temperatura da água de circulação, temperatura da água de reposição, presença de cavitação e avaliou o coeficiente de desempenho de acordo com as diferentes potências térmicas aplicadas no reservatório de resfriamento. O maior vácuo obtido no reservatório de resfriamento foi de 8,5 kPa nas condições operacionais nominais de 4,1 ± 0,1 m³/h e 5 ± 0,5 °C da água de circulação, atingindo 9,7 ± 0,5 °C a água de resfriamento. Não houve presença de cavitação no bocal do hidroejetor pois a pressão atingida no mesmo não foi inferior a pressão de saturação da água nas condições operacionais da água de circulação. A perturbação gerada, tipo pulso, no reservatório de resfriamento com a reposição da água de resfriamento em diferentes momentos de funcionamento do sistema, não resultou em mudanças expressivas quanto a desestabilidade do vácuo ou do aumento de temperatura no reservatório de resfriamento. O coeficiente de desempenho (COP), avaliado no sistema na maior inserção de potência térmica, 92,27 W pela água de resfriamento, foi de 0,077, sendo subestimado devido a possíveis problemas de eficiência da bomba. O sistema em estudo não foi ideal para resfriamento de fluido a baixas temperaturas nas condições operacionais estudadas, mas pode ser muito bom quando utilizado para resfriamento de fluido a patamares de temperatura maior, podendo ser complementar aos sistemas de refrigeração principal / Abstract: The search for efficient and affordable cooling equipment is increasing in the market. Big companies are always seeking to use thermal storage as a way to storage energy at low temperatures in their facilities due to economic factors. Therefore, this process can be done in off-peak energy periods and the energy stored can be used in times of high demand. This allows the design of smaller equipment, which can be coupled to the main system, improving the design of the physical space. Currently, evaporative cooling is conducted through the use of vacuum pumps or ejectors. This work aimed to construct and evaluate energy evaporative cooling system using an ejector, using water as the inner circulating fluid, which allows it to be installed in places plenty of water circulation, through the replacement of the cooling system using generators or mechanical devices by ejectors systems. Ejectors are devices used to drag samples by a jet of an auxiliary fluid, built essentially with a sniffer and a converging nozzle, which feeds a convergent-divergent compartment. After mechanical and electrical assembly of the system, the behavior of the system was evaluated by changing the volumetric flow rate and temperature of the circulation water, temperature of makeup water and cavitation water. The performance coefficient was also evaluated according to the different thermal inputs applied in the reservoir cooling. The higher vacuum obtained in the cooling tank was 8.5 kPa in a nominal volumetric flow rate of 4.1 ± 0.1 m³/h and circulating water at 5 ± 0.5 °C. In situation, the cooling water reached 9.7 ± 0.5 °C. There was no cavitation observed in hidroejector nozzle, since the pressure reached was not less than the saturation pressure of water in the operating conditions of the circulating water. The disturbance generated, like pulse, in the cooling reservoir with the replacement of the cooling water at different times, did not result in significant changes in vacuum destabilization or in the temperature rising in the cooling reservoir. The coefficient of performance (COP), evaluated at the greater inclusion of thermal power for cooling water (92.27 W) was 0.077. This value was underestimated due to problems of pump efficiency. The system studied was not ideal for cooling fluids at low temperatures the studied operating conditions, but it can be good enough when used for cooling fluids with higher temperatures, which may be complementary to the main refrigeration systems / Mestrado / Engenharia de Alimentos / Mestra em Engenharia de Alimentos

Condensing ejectors utilize the beneficial thermodynamics of condensation to produce an exiting static pressure that can be in excess of either entering static pressure. The phase change process is driven by both turbulent mixing and interphase heat transfer. Semi-empirical models can be used in conjunction with computational fluid dynamics (CFD) to gain some understanding of how condensing ejectors should be designed and operated. The current work describes the construction of a multidimensional simulation capability built around an Eulerian pseudo-fluid approach. The transport equations for mass and momentum treat the two phases as a continuous mixture. The fluid is treated as being in a non-thermodynamic equilibrium state, and a modified form of the homogenous relaxation model (HRM) is employed. This model was originally intended for representing flash-boiling, but with suitable modification, the same ideas could be used for condensing flow. The computational fluid dynamics code is constructed using the open-source OpenFOAM library. Fluid properties are evaluated using the REFPROP database from NIST, which includes many common fluids and refrigerants. The working fluids used are water and carbon dioxide. For ejector flow, simulations using carbon dioxide are more stable than with water. Using carbon dioxide as the working fluid, the results of the validation simulations show a pressure rise that is comparable to experimental data. It is also observed that the flow is near thermodynamic equilibrium in the diffuser for these cases, suggesting that turbulence effects present the greatest challenge in modeling these ejectors.

An Axisymmetric Rocket Ejector Simulation (ARES) was developed to numerically analyze various configurations of an air augmented rocket. Primary and secondary flow field visualizations are presented and performance predictions are tabulated. A parametric study on ejector geometry is obtained following a validation of the flow fields and performance values. The primary flow is calculated using a quasi-2D, irrotational Method of Characteristics and the secondary flow is found using isentropic relations. Primary calculations begin at the throat and extend through the nozzle to the location of the first Mach Disk. Combustion properties are tabulated before analysis to allow for propellant property selection. Secondary flow calculations employ the previously calculated plume boundary and ejector geometry to form an isentropic solution. Primary and secondary flow computations are iterated along the new pressure distributions established by the 1D analysis until a convergence tolerance is met. Thrust augmentation and Specific Impulse values are predicted using a control volume approach. For the validation test cases, the nozzle characteristic net is very similar to that of previous research. Plume characteristics are in good agreement but fluctuate in accuracy due to flow structure formulation. The individual unit processes utilized by the Method of Characteristics are found to vary their outputs by up to 0.025% when compared to existing sources. Rocket thrust and specific impulse are increased by up to 22% for a static system and 15% for an ejector flow at Mach 0.5. Evidence of Fabri conditions were observed in the flow visualization and graphically through the performance predictions. It was determined that the optimum ejector divergence angle for an air augmented rocket greatly depends on the stagnation pressure ratio between the primary and secondary flows.

No description available.