Fluid flow and gas absorption in an ejector venturi scrubber

Empirical models were developed to describe the fluid flow characteristics and gas absorption efficiency of an ejector venturi scrubber. The empirical constants were determined experimentally using stop action photographs of the spray, static pressure measurements, and sulfur dioxide absorption efficiencies. To take photographs of the spray, a 2 foot high, clear plastic ejector venturi scrubber was used, with a 4 inch diameter gas entrance port. Photographic equipment included a Hasselblad camera, Xenon flash lamp, and Polaroid 667 ASA 3000 film. Exposure duration was about 1 microsecond, resulting in complete stop-action of the spray droplets at liquid rates up to 6 gpm. Droplet size ranged from 34 to 563 microns, with a volume mean diameter of 155 microns, at a liquid rate of 6 gpm. The sulfur dioxide mass transfer coefficient (Kga) varied from 0.6 to 796 lb-moles/hr-ft3 as the liquid delivery rate was varied from 1 to 8 gpm (i.e. from no atomization to complete atomization)

Aeronautical Engineering, a continuing bibliography with indexes, supplement 173

This bibliography lists 704 reports, articles and other documents introduced into the NASA scientific and technical information system in March 1984

Advanced Numerical Simulations of Two-phase CO2 Ejectors

Over the last decade, Carbon dioxide (R744) a natural fluid has gained significant interest as a potential substitute for synthetic refrigerants commonly used in refrigeration, air-conditioning, and heat pump systems. Because of CO2 properties, such cycles generally operate in transcritical conditions. Moreover, their Coefficient Of Performance (COP) is relatively low compared to conventional cycles using synthetic refrigerants, because of higher entropy production of C02 along an isenthalpic expansion from a supercritical state to a subcritical state. Integrating a two-phase ejector, as an expansion device, is a promising technology to significantly improve the system efficiency, which would make CO2 adequate for HVAC applications. For example, in a CO2 ejector-expansion system, an ejector replaces the classical throttling valve to partly recover the throttling losses and provides a compression work reducing the compressor load. As a result, the COP and cooling capacity can be improved. However, many complex physical phenomena occur within a two-phase CO2 ejector and they are not yet fully understood, such as the turbulent mixing between the primary and the secondary flows, the flashing in the primary nozzle, shock waves-shear layer interactions, as well as phase-change processes. In this thesis, a numerical approach was developed by combining an efficient look-up table method for CO2 properties, density-based solvers, and characteristic Navier-Stokes boundary conditions (NSCBC) in order to correctly predict those complex flow features. This look-up table method allows to compute vapor, liquid, supercritical and two-phase properties of CO2 from 217K to 1000K and pressures up to 50MPa. It was coupled to three density-based solvers which allow to perform inviscid simulations, Reynolds-Averaged Navier-Stokes Simulations (RANS), and Large-Eddy Simulations (LES). Validations and verifications were performed for these three solvers. Then, Converging-diverging nozzles and ejectors were investigated by using RANS simulations. The developed solver was used to conduct an exergy tube analysis for a two-phase CO2 ejector and the sensibility of the method to the numerics was discussed. Finally, the compound-choking theory was extended for real gas flows and it was used to check the choking condition of the investigated ejector.L’objectif principal de ce travail de thèse est de développer une approche numérique complète capable de simuler de manière précise et rapide l’écoulement et les transferts exergétiques au sein d’éjecteurs transcritiques au CO2. Tout d’abord, une méthode tabulée basée sur l’équation d’état de Span-Wagner (SW) est développée pour calculer les propriétés du CO2 [59] à l’état de vapeur, liquide, supercritique et diphasique. Cette approche est précise et efficace. Les écarts relatifs maximaux par rapport à l’équation d’état de SW sont de 0.23% et 1.2% pour la pression et la vitesse du son, respectivement et l’écart absolu maximal pour la température est de 0.06 K. Dans le cas d’un tube à choc 1D, cette approche s’avère de 66.6 à 90 fois plus rapide que si on utilise l’équation d’état de SW. Deuxièmement, cette méthode tabulée est couplée à trois solveurs basés sur la densité : CLAWPACK pour les simulations d’écoulements inviscides, rhoCentralFoam pour des modélisations RANS (Reynolds-Average Navier-Stokes) essentiellement et AVBP pour des simulations des grandes échelles. Différents cas tests en 1D et 2D sont effectués pour valider l’implémentation de la méthode dans ces trois solveurs. Ces cas incluent les problèmes du tube à choc, de la dépressurisation et de la cavitation. Troisièmement, afin de se rapprocher des éjecteurs, les tuyères convergentes-divergentes de Nakagawa et al. dans des conditions supercritiques et sous-critiques sont simulées à l’aide des solveurs CLAWPACK et rhoCentralFoam. On constate que le modèle de turbulence a une influence significative sur les résultats numériques, en particulier pour les tuyères ayant un petit angle divergent. La tuyère de Berana et al. est étudiée également. Un choc épais est prédit, ce qui correspond bien aux mesures expérimentales. Quatrièmement, l’éjecteur de Li et al. est examiné via le solveur rhoCentralFoam pour une condition on-design. L’analyse des tubes d’exergie proposée par Lamberts et al. pour un éjecteur à air est appliquée. La sensibilité de la méthode est discutée. La résolution des gradients a une influence significative sur les termes de destruction. Par conséquent, le maillage et les schémas numériques peuvent affecter fortement l’analyse des tubes d’exergie. Enfin, la théorie de “compound-choking” est étendue à l’écoulement diphasique au CO2. Elle prédit que l’écoulement est choqué au début de la section de mélange, tandis que selon la ligne sonique, l’écoulement est choqué à la fin de cette section. Finalement, des calculs RANS d’un éjecteur complet sont comparées à de nouvelles mesures faites sur le banc expérimental développé au Laboratoire des Technologies de l’Énergie (LTE, Shawinigan). Un bon accord est obtenu pour le profil de pression pariétale. Les tubes de transport de quantité de mouvement et d’énergie cinétique sont analysés et révèlent une zone de recirculation à l’entrée du flux secondaire. Cependant, la condition de fonctionnement n’est pas appropriée pour les cycles d’éjecteur à expansion (régime off-design)

Supersonic wind tunnel nozzles: A selected, annotated bibliography to aid in the development of quiet wind tunnel technology

This bibliography, with abstracts, consists of 298 citations arranged in chronological order. The citations were selected to be helpful to persons engaged in the design and development of quiet (low disturbance) nozzles for modern supersonic wind tunnels. Author, subject, and corporate source indexes are included to assist with the location of specific information

Aeronautical Engineering: A continuing bibliography with indexes (supplement 177)

This bibliography lists 469 reports, articles and other documents introduced into the NASA scientific and technical information system in July 1984

The Fifth Annual Thermal and Fluids Analysis Workshop

The Fifth Annual Thermal and Fluids Analysis Workshop was held at the Ohio Aerospace Institute, Brook Park, Ohio, cosponsored by NASA Lewis Research Center and the Ohio Aerospace Institute, 16-20 Aug. 1993. The workshop consisted of classes, vendor demonstrations, and paper sessions. The classes and vendor demonstrations provided participants with the information on widely used tools for thermal and fluid analysis. The paper sessions provided a forum for the exchange of information and ideas among thermal and fluids analysts. Paper topics included advances and uses of established thermal and fluids computer codes (such as SINDA and TRASYS) as well as unique modeling techniques and applications

Aeronautical Engineering. A continuing bibliography with indexes, supplement 156

This bibliography lists 288 reports, articles and other documents introduced into the NASA scientific and technical information system in December 1982

An understanding of ejector flow phenomena for waste heat driven cooling

In an attempt to reduce the dependence on fossil fuels, a variety of research initiatives has focused on increasing the efficiency of conventional energy systems. One such approach is to use waste heat recovery to reclaim energy that is typically lost in the form of dissipative heat. An example of such reclamation is the use of waste heat recovery systems that take low-temperature heat and deliver cooling in space-conditioning applications. In this work, an ejector-based chiller driven by waste heat will be studied from the system to component to sub-component levels, with a specific focus on the ejector. The ejector is a passive device used to compress refrigerants in waste heat driven heat pumps without the use of high grade electricity or wear-prone complex moving parts. With such ejectors, the electrical input for the overall system can be reduced or eliminated entirely under certain conditions, and package sizes can be significantly reduced, allowing for a cooling system that can operate in off-grid, mobile, or remote applications. The performance of this system, measured typically as a coefficient of performance, is primarily dependent on the performance of the ejector pump. This work uses analytical and numerical modeling techniques combined with flow visualization to determine the exact mechanisms of ejector operation, and makes suggestions for ejector performance improvement. Specifically, forcing the presence of two-phase flow has been suggested as a potential tool for performance enhancement. This study determines the effect of two-phase flow on momentum transfer characteristics inside the ejector while operating with refrigerants R134a and R245fa. It is found that reducing the superheat at motive nozzle inlet results in a 12-13% increase in COP with a 14-16 K decrease in driving waste heat temperature. The mechanisms of this improvement are found to be a combination of two effects: the choice of operating fluid (wet vs. dry) and the effect of two-phase flow on the effectiveness of momentum transfer. It is recommended that ejector-based chillers be operated such that the motive nozzle inlet is near saturation, and environmentally friendly dry fluids such as R245fa be used to improve performance. This work provides critical methods for ejector modeling and validation through visualization, as well as guidance on measures to improve ejector design with commensurate beneficial effects on cooling system COP.Ph.D