An experimental and numerical study of air-air bent exhaust ejectors was carried out. The objective of the study was to determine the effect of a bend on the performance of exhaust ejectors. The ejectors consisted of nozzles, mixing tubes and in some cases entraining diffusers. As part of this study the effect of swirl in the primary flow and the temperature ratio of the primary to the secondary flow were also investigated. The study included testing of round and oblong sectioned ejectors with and without entraining diffusers. The experimental testing was performed on two different wind tunnels capable of blowing air at a maximum mass flow rate of 2.2 kg/s at ambient and elevated temperatures. Flow measurements were made upstream of the nozzle, at the nozzle exit and at the exit of the ejector. Pumping, pressure rise and total efficiency of the ejector were studied with respect to the bend angle, swirl angle and the primary to secondary flow temperature ratio. A commercial CFD code was used to evaluate the effectiveness of commercial CFD using limited resources for designing of such devices. The pumping ratio and pressure rise decrease with the increase in the degree of bend. Swirl up to a certain angle has a useful effect on the performance of a bent ejector. The entraining diffuser enhances the performance of a bent ejector. The CFD models based on commercial solver were able to predict the flow structures and the variation of the performance parameters with the bend and swirl angle. However, generally the CFD models were not able to predict the exact values of the performance parameters. / Thesis (Ph.D, Mechanical and Materials Engineering) -- Queen's University, 2008-03-31 05:53:54.89 / NSERC DND WR Davis

Thesis (M. S.)--Civil and Environmental Engineering, Georgia Institute of Technology, 2010. / Committee Chair: Jacobs, Laurence; Committee Co-Chair: Kurtis, Kimberly; Committee Member: Kim, Jin-Yeon. Part of the SMARTech Electronic Thesis and Dissertation Collection.

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.

The most prevalent method for the prevention of freeze-thaw and salt scaling damage in cement based materials is through the entrainment of air voids using air entraining chemical admixtures (AEA's). However, the common field methods for measuring air content in fresh concrete cannot distinguish between entrained and entrapped air voids, and the actual air content in the hardened concrete can vary from that determined by these tests due to a variety of factors such as workability, placing operations, consolidation efforts, and environmental conditions. Previous research has shown the ability of ultrasonic attenuation to distinguish between entrained and entrapped air voids in hardened cement paste, providing a foundation for an inversion procedure to calculate the size and volume content of the two scatterer sizes. While additional challenges are present with measurements in fresh paste, the use of an immersion setup can overcome the limitations of cement paste containment vessels and provide a means to measure air content from batching to placement. An immersion apparatus to monitor ultrasonic wave attributes including attenuation in fresh cement paste is designed and built. Results comparing air entrained and non-air entrained cement pastes are presented. Ultrasonic wave attributes are studied as a function of time and level of chemical air entrainer. Finally, recommendations are made to improve the accuracy of the immersion apparatus in order to develop an in situ, quality control procedure to quantify the air content of fresh cement paste from batching to placement.

No description available.

<p dir="ltr">Air-entraining agents (AEA) were introduced in the 1930s to improve concrete's resistance to cyclic freezing-thawing exposure. Over the past 90 years, there has been extensive discussion about how traditional AEAs contribute to durability improvements. However, the issue of strength loss associated with conventional AEA use remains unresolved unless the cement is overdosed. Moreover, the effectiveness of traditional AEAs in entraining air voids has proven inconsistent, as it is influenced by various factors. As a result, the increased costs and carbon footprint associated with AEA use continue to be ongoing concerns for the industry.</p><p dir="ltr">Hollow polymeric microspheres have emerged as a promising solution for enhancing concrete's cyclic freezing-thawing resistance by providing encapsulated air without compromising mechanical performance or durability. In this study, the hydration, fresh properties, hardening performance, and freezing-thawing resistance of air-entrained cement mortar and concrete were investigated using the novel hollow polymeric microspheres and a traditional aqueous AEA, respectively. Additionally, the dynamic modulus of elasticity change and surface spalling damage of concrete beams following cyclic freezing-thawing exposure were evaluated. The air-void system and capillary pore structure of cement mortar and concrete, air-entrained with the traditional AEA and microspheres, respectively, were examined through various characterization methods, including optical microscopy (OM), scanning electron microscopy (SEM), mercury intrusion porosimetry (MIP), and 3D X-ray microscopy (micro-CT, or XCT). The properties of mortar and concrete with varying dosages of AEA and microspheres were assessed, and the mechanisms behind the enhanced freezing-thawing resistance were explored.</p><p dir="ltr">The microspheres used in this study were found to have a 'curing' effect, enhancing the hydration, workability, and mechanical strength of the mortar compared to both plain mortar without air entrainment and mortar air-entrained with the traditional aqueous AEA. Evaluating the mechanical strength changes and mass loss of mortar specimens demonstrated that the freezing-thawing resistance of mortar air-entrained with microspheres was superior to that achieved with aqueous AEA. The small size and compressibility of the microspheres resulted in a fine and well-distributed air void system, offering improved freezing-thawing resistance in the mortar specimens.</p><p dir="ltr">Additionally, due to the potential 'curing' and nucleation effects of the microspheres, the strength of air-entrained concrete with microspheres was slightly higher than that of plain concrete without air entrainment. In contrast, the traditional air-entraining method led to a 7.0% to 8.4% strength loss in concrete with 1% entrained air. Furthermore, concrete air-entrained with microspheres exhibited significantly less surface spalling damage compared to plain concrete, thanks to its well-distributed air void system and enhanced strength. On the other hand, although traditionally air-entrained concrete maintained its dynamic modulus throughout the 300 cycles of freezing-thawing exposure, it still suffered severe surface spalling damage, likely due to its reduced strength.</p><p dir="ltr">This study provides valuable insights into the practical application of polymeric microspheres for enhancing the freezing-thawing resistance of concrete.</p>

In the present study, possible scale effects on the formation of air-entraining vortices at horizontal intakes are studied experimentally. Basic dimensionless parameters that govern the onset of vortices at a horizontal intake in a model and a prototype are stated by dimensional analysis. Series of experiments are conducted on four intake pipes of different diameters located in a large reservoir. The relationship of critical submergence ratio with other dimensionless parameters is considered for a given Froude number and it is found out that the critical submergence ratio is affected by model length scale ratio and its natural result of side-wall clearance ratio and Reynolds number differences between model and prototypes. It is observed that, side-wall clearance ratio is not effective on the critical submergence ratio after it exceeds about 6. In addition to this, Reynolds number limit, beyond which viscous forces do not affect the vortex flow, is found out to be increasing with the increase in Froude number. An empirical relationship, which gives the critical submergence ratio as a function of Froude number, side-wall clearance ratio and Reynolds number is obtained by using data collected in the experiments.

Made available in DSpace on 2014-12-17T14:07:07Z (GMT). No. of bitstreams: 1 IrantecioMF_DISSERT_Parcial.pdf: 354207 bytes, checksum: e43a8d49123a8e937d996a1e4e80ba39 (MD5) Previous issue date: 2012-09-28 / Lightweight oilwell cement slurries have been recently studied as a mean to improve zonal isolation and sheath-porous formation adherence. Foamed slurries consisting of Portland cement and air-entraining admixtures have become an interesting option for this application. The loss in hydrostatic pressure as a consequence of cement hydration results in the expansion of the air bubbles entrapped in the cement matrix, thus improving the sheath-porous formation contact. Consequently, slurries are able to better retain their water to complete the hydration process. The main objective of the present study was to evaluate the effect of the addition of an air-entraining admixture on the density, stability and permeability of composite slurries containing Portland cement and diatomite as light mineral load. Successful formulations are potential cementing materials for low fracture gradient oilwells. The experimental procedures used for slurry preparation and characterization were based on the American Petroleum Institute and ABNT guidelines Slurries containing a pre-established concentration of the air-entraining admixture and different contents of diatomite were prepared aiming at final densities of 13 to 15 lb/gal. The results revealed that the reduction of 15 to 25% of the density of the slurries did not significantly affect their strength. The addition of both diatomite and the air-entraining admixture increased the viscosity of the slurry providing better air-bubble retention in the volume of the slurry. Stable slurries depicted bottom to top density variation of less than 1.0 lb/gal and length reduction of the stability sample of 5.86 mm. Finally, permeability coefficient values between 0.617 and 0.406 mD were obtained. Therefore, lightweight oilwell cement slurries depicting a satisfactory set of physicochemical and mechanical properties can be formulated using a combination of diatomite and air-entraining admixtures for low fracture gradient oilwells / Atualmente, busca-se a formula??o de pastas de cimento leves para prevenir o fraturamento de forma??es de baixa resist?ncia ou depletadas e combater a perda de circula??o, com boa ader?ncia e isolamento hidr?ulico entre cimento e meio poroso. O cimento espumado composto pela mistura de cimento com incorporador de ar ? um material alternativo para essa aplica??o. A perda de press?o hidrost?tica durante o processo de hidrata??o causa expans?o das bolhas de g?s, mantendo o grau de contato cimento-meio poroso, diferentemente do que ocorre apenas com o uso do cimento tradicional. A ader?ncia entre o cimento e o meio poroso (forma??o rochosa) faz com que haja estabilidade da pasta, impedindo a perda de ?gua do cimento no estado fresco para o meio. O presente trabalho tem como objetivo estudar a estabilidade e a permeabilidade de comp?sitos ciment?ceos contendo diatomita (carga leve) e incorporador de ar, verificando se o uso desses aditivos ? vi?vel para cimentos projetados para ambientes de baixo gradiente de fratura. A metodologia empregada no trabalho consiste na prepara??o e avalia??o de pastas comp?sitas, por meio de procedimentos adotados pelo American Petroleum Institute e pela Associa??o Brasileira de Normas T?cnicas. Partiu-se de uma dosagem fixa do incorporador de ar e variou-se a concentra??o de diatomita. As densidades calculadas foram 13,0 lb/gal, 14,0 lb/gal e 15,0 lb/gal, com o intuito de observar a contribui??o do fator ?gua/cimento na estabiliza??o das espumas geradas pela adi??o do incorporador de ar em rela??o a uma pasta padr?o, sem incorporador de ar. Os resultados revelaram que as pastas tiveram suas densidades reduzidas entre 15% e 25%, com a adi??o do incorporador de ar e diatomita e boa resist?ncia mec?nica. O aumento da viscosidade nas formula??es com diatomita proporcionou maior reten??o das bolhas, visto que houve redu??o acentuada da migra??o de ar para a superf?cie do cimento durante cura em repouso. Observou-se que pastas est?veis apresentaram varia??o entre o valor de densidade de fundo e topo de 0,96 lb/gal e rebaixamento de topo de 5,86 mm, al?m de baixos coeficientes de permeabilidade (0,617 mD a 0,406 mD). Concluiu-se que ? poss?vel formular pastas ciment?ceas espumadas de baixa densidade com propriedades mec?nicas e reol?gicas satisfat?rias, al?m de boa estabilidade e baixa permeabilidade, a partir de uma combina??o de cimento, diatomita e incorporador de ar. Os materiais resultantes s?o adequados visando ? cimenta??o de po?os de petr?leo com forma??es de baixa resist?ncia ou depletadas / 2020-01-01

The thesis deals with the possibility of specific weight lowering of kaolin suspensions using air-entraining agents. These agents are usually used as concrete admixtures. The goal of the thesis is to verify an alternative possibility of creating porous structure in kaolin suspensions in order to prepare heat insulating moulded refractory concretes without using lightweight fillers. The effect of several air-entraining agents was compared, after that the dosage of agent and mixing conditions were optimized. The stabilization of prepared foams and practical application of selected agents were also part of the thesis.

Geopolymers are amorphous to semi-crystalline aluminosilicate polymers which are formed from inorganic polycondensation reaction of a solid aluminosilicate precursor with an alkaline sodium hydroxide or silicate. The resulting materials exhibit high durability, resistance to aggressive environments, high temperature resistance and many other properties that make them have received much attention in recent years, not only in construction. This thesis describes the influence of additives commonly used in concrete and mortar (water reducing, superplasticizer, air-entraining, foamer and defoamer, anti-shrinkage, stabilization) on the behavior of metakaolin in geopolymer fresh and hardened state. It describes metakaolin geopolymer effect on rheological properties of fresh mixtures, compressive strength and flexural strength after 28 days and a density in the fresh and hardened state.