Thesis (M.Sc.). / Written for the School of Computer Science. Title from title page of PDF (viewed 2008/01/15). Includes bibliographical references.

Thesis (Chem.E)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, 1980. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND SCIENCE. / Includes bibliographies. / by Kenneth George Hellyar. / Chem.E

Thesis--M. Phil., University of Hong Kong.

published_or_final_version / Mechanical Engineering / Master / Master of Philosophy

Vortex Tube (VT) is a simple device having no moving mechanical parts, in which compressed gas at high pressure is injected through one or more tangential nozzles into a vortex chamber resulting in the separation of the inlet flow into two low pressure streams. One of the streams is the peripheral flow that is warmer than the inlet stream while the other is the central (core) flow that is colder than the inlet stream. This separation of the inlet flow into high and low temperature streams is known as temperature or energy separation. It is suggested by many investigators that compressed air of few atmospheres pressure and at room temperature can produce temperatures as high as +200ºC at the hot end (peripheral flow exit) and as low as -50ºC at the cold end (core flow exit) of the VT. Though VTs have large potential for simple heating and cooling applications, the mechanism of energy separation is not clear so far. Based on their studies, many investigators have suggested various theories, different from each other, but having specific lacunas and is an unresolved issue. Also, till date, experimental and industrial designs of the VTs are based purely on empirical correlations. Apart from heating and cooling applications, VTs can also be used for separation of binary gas mixtures and separation of oxygen from two-phase precooled air stream. The conceptual futuristic cryogenic launch vehicle designs are being attempted with in-flight liquid oxygen (LOX) collection system that significantly improves the pay load fraction. Vortex tube technology is one of the few promising technologies for futuristic in-flight LOX separation based launch vehicles. This technology has significant advantages over its counterparts as it is a simple, compact and light weight, and most importantly have no moving parts and unaffected by gravity and orientation. In order that VTs become an acceptable technology for in-flight LOX separation system, it is necessary to achieve minimum oxygen purity of 90% with more than 60% yield (separation efficiency) for the oxygen enriched stream in the VT. A survey of the available open literature has shown very little reported details, in particular, on achieving the required specifications for in-flight LOX separation systems. Till date, the highest LOX purity of 60% with 40% separation efficiency has been reported with VT technology. In view of the above mentioned facts, the work carried out has been focused on to: • Optimize the critical parameters of the VT to achieve maximum energy separation by CFD and experimental studies. • Understand the flow behaviour in the VT by estimating the velocity, temperature and pressure profiles at various locations in the VT and validation of secondary circulation flow and its effect on the performance of energy separation in VT. • Estimation of the energy transfer between the core and the peripheral layers of fluid flow in VT by analytical and CFD methods to propose the most appropriate mechanism of energy separation in VT. • Design and development of a dedicated experimental setup for both energy separation and LOX separation studies in VTs. • Design and fabrication of straight and conical VTs and experimental programme on energy separation and LOX separation. • Development of the VT air separation technology to achieve the required specifications of in-flight LOX separation system for futuristic launch vehicles. With these specific objectives and motivations, the total work was carried out with the following planned and sequential steps: • The first step was the CFD modeling of the VT with the available CFD software (Star-CD) and obtain the energy separation phenomena for a 12mm diameter VT. After gaining sufficient confidence level, optimization of the critical parameters like the air injection nozzle profile, number of nozzles, cold end orifice diameter dc, length to diameter (L/D) ratio, hot gas fraction etc of the VT was carried out through CFD and experimental studies. • The studies show that 6 convergent nozzles perform better in comparison to other configurations like circular helical, rectangular helical, 2 convergent and 6 straight nozzles. The studies also show that cold end orifice diameter (dc) plays an important role on energy separation and bring out the existence of secondary circulation flow with improper design of cold end orifice diameter. Through our studies, the effect of cold end diameter on the secondary circulation flow has been evaluated for the first time. Also, the mechanism of energy transfer in VT based on heat pump mechanism enabled by secondary circulation flow as suggested by some investigators has been evaluated in our studies. The studies show that cold end orifice diameter dc = 7mm is optimum for 12mm diameter VT, which matches fairly with the correlations given by other investigators. The studies confirms that CFD modeling carried out in this work is capable of selecting the correct dc value for a VT, without resorting to the empirical correlations as a design guide or a laborious experimental programme. • Through the CFD and experimental studies on different length to diameter (L/D) ratios and hot gas fractions, maximum hot gas temperature of 391K was obtained for L/D = 30 with hot gas fraction of 12-15 % and minimum cold gas temperature of 267K for L/D = 35 was obtained for cold gas fraction ≈ 60% (lowest cold gas fraction possible with the present experimental system). • CFD analysis has been carried out to investigate the variation of static and total temperatures, static and total pressures as well as the velocity components of the particles as it progresses in the flow field, starting from the entry through the nozzles to the exit of the VT by tracking the particles to understand the flow phenomenon and energy transfer mechanism inside the VT. The studies indicate that the mechanism of energy transfer from the core flow to the peripheral flow in VT is predominantly occurs by the tangential shear work. Thus the investigations reported in the thesis have given a clear understanding of the contributing mechanism for energy separation in VT, which has been an unresolved issue for long time. The net energy transfer between the core and the peripheral fluid has been calculated analytically and compared with the values obtained by CFD model for VTs of L/D ratios equal to 10 and 30. The net energy transfer by analytical and CFD model for VT with L/D = 10 is 159.87W and 154.2W respectively whereas the net energy transfer by analytical and CFD model for VT with L/D = 30 is 199.87W and 192.3W respectively. The results show that CFD results are in very good agreement with the analytical results and CFD can be used as a tool for optimization of the critical parameters and to analyze the flow parameters and heat transfer analysis for VTs. Also, the net energy transfer between the core and peripheral fluids calculated analytically matches very well with that of the net energy transfer by CFD analysis, without considering the effect of acoustic streaming. Thus acoustic streaming may not be the mechanism of energy separation in VT as suggested by some investigators. • By optimizing the critical parameters of the 12mm diameter straight VT through CFD and experimental studies, LOX separation studies have been carried out using both straight and conical VTs of dc = 7mm and of different L/D ratios for high LOX purity and separation efficiency. It is observed that conical (3º divergence) VTs perform better as compared to straight VTs for LOX separation whereas straight VTs perform better for energy separation. The better performance of conical VT as compared to straight VTs can be attributed to its increased surface area for condensation-evaporation phenomenon of oxygen and nitrogen molecules. Experimental studies have been conducted to evaluate the influence of the inlet pressure and the inlet temperature (liquid fraction) on LOX purity. Studies indicate that for achieving high LOX purity for the studied experimental system, the inlet pressure is to be in the range of 6-6.5bar and there exists a very narrow band of inlet temperature zone in which high LOX purity can be achieved. Experimental studies on VTs show that VT can be optimized suitably either for high LOX purity with low separation efficiency or low LOX purity with high separation efficiency by adjusting the hot end mass fraction accordingly. It is also observed that it is not possible to obtain both high purity and high separation efficiency simultaneously with the single VT. Staging approach has to be adapted to achieve higher LOX purity with higher separation efficiency. By staging the VTs, the enriched air stream (hot end outlet flow) from the first stage of VTs is introduced to the inlet of the second stage of VTs. Experimental studies have been conducted to evaluate the design parameters on staging of VTs. LOX purity of 48% with 89% separation efficiency has been achieved for conical first stage VT of L/D = 25. LOX purity of about 94% with separation efficiency of 84% has been achieved for 50% oxygen content at the inlet of the second stage VT. Similarly, LOX purity of 96% with separation efficiency of 73.5% has been achieved for 60% oxygen content at the inlet of the VT. This is the highest LOX purity and separation efficiency reported so far indicating that, conical VT of optimized diameter, L/D ratio and orifice diameter can yield the hot end flow very close to the target value of futuristic in-flight LOX separation based launch vehicles. The present investigation has focused the optimization of the critical parameters of VTs through CFD and experimental studies. It has also given an insight to the mechanism of energy transfer between the core and peripheral flow in VT by evaluating two of the existing theories on mechanism of energy transfer in VT. The studies also highlighted the fact that custom designed and precision fabricated VTs can be very useful for obtaining maximum / minimum temperatures of fluid flow as well as LOX separation with high purity and high separation efficiency needed for futuristic in-flight LOX separation based space launch vehicles.

Thesis (Ph. D.)--Rutgers University, 2009. / "Graduate Program in Mechanical and Aerospace Engineering." Includes bibliographical references (p. 111-115).

Large eddy simulation is used to study the large-scale structures in a low subsonic mixing layer and their breakdown to small scales. For 3-D simulations, different finite-difference and pseudo-spectral schemes are tested. The (2, 4) MacCormack Scheme developed by Gottlieb and Turkel (1976) shows the best overall performance. It is very fast and supplies enough but not excessive artificial dissipation. Though slower than MacCormack scheme, the pseudo-spectral method has its advantage: high resolution of the high-wavenumber range when adequate de-aliasing scheme is used. When efficient fast Fourier transform routines are available, this method can be a very good alternative to the MacCormack scheme. Most of the simulations use a modified Smagorinsky-type model (Erlabacher et al. 1992). The effect of different models and model constants is also studied. It is found that the two subgrid-scale (SGS) models, the Smagorinsky model and the linear combination model (Bardina et al. 1983), show significant difference even at the low wavenumber range of the spectra. In the study of three-dimensional subsonic temporal mixing layers, it is found that the streamwise vortex tubes play an important role in the transition process. The vortex interaction of the streamwise vortex tubes and undulated spanwise vortex structures proves to be the dominant mechanism in the development of three-dimensionality and the subsequent generation of small-scale motions. In the absence of pairing of the spanwise vortex tubes, this vortex interaction causes uneven distribution of vorticity along the span of the spanwise vortex tubes and the breaking of the large structures. Following the breaking of the spanwise vortex tubes, the secondary streamwise vortex tubes become the dominant vortex structures. In the case involving pairing, it is found that the relative motion of the spanwise vortex tubes in the pre-pairing process creates much stronger strain rate field between the pairing vortex tubes than the case without pairing. The stronger strain rate field leads to the formation of streamwise vortex tubes with very high vorticity and low induced pressure. This also leads to much stronger vortex interaction between the spanwise and streamwise vortex tubes due to the increased strength of the streamwise vortex tubes. / Ph. D.

Os sistemas de ar condicionado automotivos sempre se utilizaram do conceito de operação do ciclo termodinâmico por compressão de vapor, sendo necessário para isso componentes básicos tais como fluído refrigerante, trocadores de calor e compressor. Apesar de diversas décadas de pesquisa e desenvolvimento desse sistema, algumas dificuldades ainda permanecem nos dias de hoje. Dessa forma, a investigação de outros mecanismos de refrigeração, que possam ser aplicados em sistemas automotivos de ar condicionado, é bem vinda. Uma dessas possibilidades é a aplicação dos tubos de vórtices, utilizados atualmente para fins industriais. Os tubos de vórtices são dispositivos que operam através da introdução de um fluxo de ar comprimido, sendo que ele possibilita a divisão deste fluxo em duas parcelas: um fluxo de alta temperatura e um fluxo de baixa temperatura. Tal dispositivo apresenta vantagens tais como a não necessidade da utilização de trocadores de calor e de fluídos refrigerantes. Desta forma, ele possibilita uma maior flexibilidade de posicionamento de saídas de ar em pontos do habitáculo do veículo os quais não são permitidos atualmente. A alimentação do tubo de vórtices se dá exclusivamente com fluxo de ar comprimido, que pode ser armazenado para consumo conforme necessidade. Adicionalmente, devido a esta característica, surge a possibilidade de executar o reaproveitamento de energia cinética, que no processo de frenagem é dissipada ao ambiente. O reaproveitamento energético pode ser efetuado através do redirecionamento dessa energia cinética para o compressor de ar. Baseado nessa possibilidade, foram inicialmente obtidos os dados de operação de um sistema de ar condicionado convencional, além do potencial de regeneração energética, sendo estes dados obtidos através de publicações técnicas e cálculos teóricos. Estabeleceu-se uma proposta de configuração dos componentes, assim como modos de operação do sistema. Posteriormente seguiu-se com uma pré-seleção dos componentes que influem diretamente na viabilidade do sistema. Os resultados mostraram a dificuldade de implementação dessa filosofia de sistema para veículos leves (automóveis de passeio), mostrando maior viabilidade para veículos comerciais de grande porte (tais como caminhões), principalmente aqueles dotados de sistema pneumático para a operação dos freios a ar e suspensão pneumática. / Automotive air conditioning systems have always utilized the thermodynamic vapor-compression cycle concept, with the necessity of some basic components as refrigerant fluid, heat exchangers and compressor. Although research and development of these systems have been made along many decades, some difficulties still remain nowadays. Then, the investigation of other mechanisms of refrigeration that could be applied to automotive air conditioning systems are welcome. One of these possibilities is the application of the Vortex Tubes, utilized nowadays for industrial applications. Vortex Tubes are devices that work with the introduction of an air compressed flow. These devices enable the division of the inlet flow in two flow fractions: one high and one low temperature flow. The application of these devices brings advantages, as an example no necessity of heat exchangers and refrigerant fluids. Then it enables a higher flexibility in the positioning of air outlets in some cabin position, that are not possible nowadays. The feeding of vortex tubes occurs only with compressed air flow, which can be stored for consumption when necessary. In addition, because of this characteristic, there is the possibility of the kinetic energy reutilizing, that is dissiped to the environment in the braking process currently. This possibility of energetic reutilizing can be made through the transfer of this kinetic energy to the air compressor. Based on this possibility, it was obtained data about the operation of a conventional air conditioning system, besides the energetic regeneration potential data. These data were obtained through technical publications and theoretical calculations. It was established a configuration proposal for the components, as well as the system operation modes. Later, it was made a first selection of the components that have direct influence in the system viability. The results showed the difficulties in the application of this philosophy for light vehicles (passenger cars) with more viability for commercial vehicles use (for example trucks), mainly those vehicles that are equiped with a pneumatic system to the air brakes and air suspension.

The present work draws together all current literature on particle separating devices and presents a review of the current research on rotor downwash-induced dust clouds. There are three types of particle separating device: vortex tube separators; inlet barrier filters; and inlet particle separators. Of the three, the latter has the longest development history; the former two are relatively new retrofit technologies. Consequently, the latter is well-represented in the literature, especially by computational fluid dynamics simulations, whereas the other two technologies, with specific application to rotorcraft, are found to be lacking in theoretical or numerical analyses. Due to their growing attendance on many rotorcraft currently in operation, they are selected for deeper investigation in the present work.The inlet barrier filter comprises a pleated filter element through which engine bound air flows, permitting the capture of particles. The filter is pleated to increase its surface area, which reduces the pressure loss and increases the mass retention capability. As particles are captured, the filter's particle removal rate increases at the expense of pressure loss. The act of pleating introduces a secondary source of pressure loss, which gives rise to an optimum pleat shape for minimum pressure drop. Another optimum shape exists for maximum mass retention. The two optimum points however are not aligned. In the design of inlet barrier filters both factors are important. The present work proposes a new method for designing and analysing barrier filters. It is found that increasing the filter area by 20% increases cycle life by 46%. The inherent inertial separation ability of side-facing intakes decreases as particles become finer; for the same fine sand, forward-facing intakes ingest 30% less particulate than side-facing intakes. Knowledge of ingestion rates affords the prediction of filter endurance. A filter for one helicopter is predicted to last 8.5 minutes in a cloud of 0.5 grams of dust per cubic metre, before the pressure loss reaches 3000 Pascals. This equates to 22 dust landings.An analytical model is adapted to determine the performance of vortex tube separators for rotorcraft engine protection. Vortex tubes spin particles to the periphery by a helical vane, whose pitch is found to be the main agent of efficacy. In order to remove particles a scavenge flow must be enacted, which draws a percentage of the inlet flow. This is also common to the inlet particle separator. Results generated from vortex tube theory, and data taken from literature on inlet particle separators permit a comparison of the three devices. The vortex tube separators are found to achieve the lowest pressure drop, while the barrier filters exhibit the highest particle removal rate. The inlet particle separator creates the lowest drag. The barrier filter and vortex tube separators are much superior to the inlet particle separator in improving the engine lifetime, based on erosion by uncaptured particles. The erosion rate predicted when vortex tube separators are used is two times that of a barrier filter, however the latter experiences a temporal (but recoverable post-cleaning) loss of approximately 1% power.

Os sistemas de ar condicionado automotivos sempre se utilizaram do conceito de operação do ciclo termodinâmico por compressão de vapor, sendo necessário para isso componentes básicos tais como fluído refrigerante, trocadores de calor e compressor. Apesar de diversas décadas de pesquisa e desenvolvimento desse sistema, algumas dificuldades ainda permanecem nos dias de hoje. Dessa forma, a investigação de outros mecanismos de refrigeração, que possam ser aplicados em sistemas automotivos de ar condicionado, é bem vinda. Uma dessas possibilidades é a aplicação dos tubos de vórtices, utilizados atualmente para fins industriais. Os tubos de vórtices são dispositivos que operam através da introdução de um fluxo de ar comprimido, sendo que ele possibilita a divisão deste fluxo em duas parcelas: um fluxo de alta temperatura e um fluxo de baixa temperatura. Tal dispositivo apresenta vantagens tais como a não necessidade da utilização de trocadores de calor e de fluídos refrigerantes. Desta forma, ele possibilita uma maior flexibilidade de posicionamento de saídas de ar em pontos do habitáculo do veículo os quais não são permitidos atualmente. A alimentação do tubo de vórtices se dá exclusivamente com fluxo de ar comprimido, que pode ser armazenado para consumo conforme necessidade. Adicionalmente, devido a esta característica, surge a possibilidade de executar o reaproveitamento de energia cinética, que no processo de frenagem é dissipada ao ambiente. O reaproveitamento energético pode ser efetuado através do redirecionamento dessa energia cinética para o compressor de ar. Baseado nessa possibilidade, foram inicialmente obtidos os dados de operação de um sistema de ar condicionado convencional, além do potencial de regeneração energética, sendo estes dados obtidos através de publicações técnicas e cálculos teóricos. Estabeleceu-se uma proposta de configuração dos componentes, assim como modos de operação do sistema. Posteriormente seguiu-se com uma pré-seleção dos componentes que influem diretamente na viabilidade do sistema. Os resultados mostraram a dificuldade de implementação dessa filosofia de sistema para veículos leves (automóveis de passeio), mostrando maior viabilidade para veículos comerciais de grande porte (tais como caminhões), principalmente aqueles dotados de sistema pneumático para a operação dos freios a ar e suspensão pneumática. / Automotive air conditioning systems have always utilized the thermodynamic vapor-compression cycle concept, with the necessity of some basic components as refrigerant fluid, heat exchangers and compressor. Although research and development of these systems have been made along many decades, some difficulties still remain nowadays. Then, the investigation of other mechanisms of refrigeration that could be applied to automotive air conditioning systems are welcome. One of these possibilities is the application of the Vortex Tubes, utilized nowadays for industrial applications. Vortex Tubes are devices that work with the introduction of an air compressed flow. These devices enable the division of the inlet flow in two flow fractions: one high and one low temperature flow. The application of these devices brings advantages, as an example no necessity of heat exchangers and refrigerant fluids. Then it enables a higher flexibility in the positioning of air outlets in some cabin position, that are not possible nowadays. The feeding of vortex tubes occurs only with compressed air flow, which can be stored for consumption when necessary. In addition, because of this characteristic, there is the possibility of the kinetic energy reutilizing, that is dissiped to the environment in the braking process currently. This possibility of energetic reutilizing can be made through the transfer of this kinetic energy to the air compressor. Based on this possibility, it was obtained data about the operation of a conventional air conditioning system, besides the energetic regeneration potential data. These data were obtained through technical publications and theoretical calculations. It was established a configuration proposal for the components, as well as the system operation modes. Later, it was made a first selection of the components that have direct influence in the system viability. The results showed the difficulties in the application of this philosophy for light vehicles (passenger cars) with more viability for commercial vehicles use (for example trucks), mainly those vehicles that are equiped with a pneumatic system to the air brakes and air suspension.