Vortex tube (VT) is a mechanical device with no moving parts. The fundamental principle of Vortex Tube is that it can split an incoming fluid flow of a constant pressure and constant temperature gas stream into two separate low pressure streams, one having higher enthalpy and the other having lower enthalpy than the inlet flow. So this device essentially works as a temperature separator. On separation from the device, a warmer flow exits through a terminal which is called the “hot end” and a low temperature stream comes out from another terminal known as the “cold end”. Just with a few bar pressure of compressed air at room temperature can produce a hot stream temperature of about 150°C and a cold stream temperature of about - 40°C. This temperature separation scheme allows us to get cooling and heating effect simultaneously using the same device which makes the Vortex tube one of the popular mechanical equipment and is used in many fields of engineering. The cooling or heating effect produced by this device is largely dependent on geometric parameters of the device itself. Since no exact theoretical correlation is there between the geometric parameters and the cooling (or heating) effect produced, VT design is solely based on empirical relations. There are quite a few geometric parameters which affect the cooling effect of this device and all the empirical correlation are needed to design the optimum VT for maximum cooling/heating effect. These relations can be derived in two ways, either by numerical methods or by experimental investigations. The first part of the thesis important geometric parameter of the VT namely the ratio of the “cold end” diameter (to the “tube diameter” , which has been numerically optimized in this work to achieve maximum temperature separation. In our efforts to design a VT based refrigeration system, optimization of the VT itself is not enough. A suitable heat exchanger (HX) which can extract the cold enthalpy from the VT also needs to be designed and cascaded with the VT to get the complete refrigeration system. The second part of the thesis is solely dedicated to the design of a suitable HX that can be used alongside a VT to produce refrigeration. The HXs design can be approached from two directions, dimensional aspect and material aspect. Rather than focusing on the dimensional aspect in this work we have concentrated of the material aspect of HX design. It is fairly obvious that the thermal conductivity (TC) of the HX material will play a crucial role on the cooling effect of the refrigeration system. Conventional metals with high TC can be used to design HXs but the downsides of using pure metals such as Copper, Iron are that they are heavy, quite expensive and highly reactive to corrosive fluids. Because of this, high TC ceramic material such as Aluminium Nitride (AlN) is quite often used to fabricate HXs and they are used for spot cooling in electronic systems. AlN has TC of 160 W/m-K which is high but not as high as of Copper or Iron. TC of AlN can be increased by mixing the right volume fraction of metal powder (such as pure Aluminium) with it to a great extent. So in a nutshell, instead of using pure AlN, if we use the particle reinforced binary composite [AlN + Al (powder)] to design a HX, we would achieve the benefits of having high TC as well as properties such as anti-corrosiveness, cost effectiveness and weight reduction. In the above context, prediction of TC of particle reinforced composite materials containing a base material of low TC and a filler material of high TC is of utmost importance. Till now a very few analytical heat transfer models are available in the literature that can accurately predict the TC value of such composites especially when high volume fraction of filler particles is added to the base material or if more than one type of filler particles are added. So in this thesis, three analytical heat transfer models have been developed that can predict the TC of binary as well as tertiary particle reinforced composites. The third and the final segment of the thesis deals with the performance study of a refrigeration system comprised of the optimized VT cascaded with a suitable HX made out of a particle reinforced composite material. The numerical results show how the HX effectiveness improves as the volume fraction of the filler particles in the composite increases. The key results of the works described in the thesis are as follows: • Through extensive numerical simulations it is shown that for = 0.5, the temperature separation in a VT is maximum. • The heat transfer models developed to predict the thermal conductivity of binary composites, shows the trend of how thermal conductivity varies with increasing volume fraction of filler. It has been shown that initially the thermal conductivity increases linearly with a small slope, then after a critical volume fraction an abrupt increment of slope is observed due to the formation of continuous heat conduction paths within the composite. Further increase in volume fraction shows linear increment of thermal conductivity with lesser slope as before. • The heat transfer model developed to predict the thermal conductivity of tertiary composites is suitable for low volume fraction (< 20 %). The model shows the addition of one component into the base matrix affects the distribution of the other component which is observed through the covariance. • The last part of the thesis shows that compared to a pure AlN heat exchanger, a heat exchanger made of AlN + 30 % volume fraction of pure Aluminium powder, has increased heat exchanger effectiveness by more than 50 %. Thesis outline is as follows: • Chapter 1 is a brief introduction to Vortex Tube. • Chapter 2 deals with the necessary literature review related to Vortex Tube as well as presently available heat transfer models that are equipped to handle composite materials to predict their TC. • Chapter 3 elaborates numerical modeling and optimization of a critical parameter ( to achieve maximum temperature separation in a VT. • Chapter 4 presents a stochastic heat transfer model to estimate the TC of Binary particle reinforced composites containing low volume fraction of filler particles. • Chapter 5 describes the development of a computational heat transfer model to predict the TC of Particle Reinforced Binary Composite materials containing high volume fraction of filler element. • Chapter 6 deals with a stochastic heat transfer model to calculate TC of Particle Reinforced Tertiary Composite materials containing low volume fractions of filler elements. • Chapter 7 consolidates all the necessary concepts and data from previous chapters to design the final cascaded VT based refrigeration system and presents a performance study. • The last chapter summarizes the entire work along with scope for future work.

abstract: ABSTRACT A vortex tube is a device of a simple structure with no moving parts that can be used to separate a compressed gas into a hot stream and a cold stream. Many studies have been carried out to find the mechanisms of the energy separation in the vortex tube. Recent rapid development in computational fluid dynamics is providing a powerful tool to investigate the complex flow in the vortex tube. However various issues in these numerical simulations remain, such as choosing the most suitable turbulent model, as well as the lack of systematic comparative analysis. LES model for the vortex tube simulation is hardly used in the present literatures, and the influence of parameters on the performance of the vortex tube has scarcely been studied. This study is aimed to find the influence of various parameters on the performance of the vortex tube, the best geometric value of vortex tube and the realizable method to reach the required cold out flow rate 40 kg/s . First of all, setting up an original 3-D simulation vortex tube model. By comparing experiment results reported in the literature and our simulation results, a most suitable model for the simulation of the vortex tube is obtained. Secondly, we perform simulations to optimize parameters that can deliver a set of desired output, such as cold stream pressure, temperature and flow-rate. We also discuss the use of the cold air flow for petroleum engineering applications. / Dissertation/Thesis / M.S. Mechanical Engineering 2013

CoordenaÃÃo de AperfeiÃoamento de Pessoal de NÃvel Superior / This paper aims to scale, build and test a new vortex tube, operating from the use of compressed air at pressures below the pressure ranges typical of this unconventional cooling device for the purpose of obtaining drafts cold for air conditioning. For that were originally studied theoretical and experimental aspects of flow processes through tests performed in the laboratory with a commercial vortex tube. Known influence of geometric parameters (such as the ratio between the length and internal diameter of the tube and the diameter of the diaphragm hole) and the thermophysical properties (such as inlet pressure gauge in the compressed air tube and the mass flow rate of the stream cold) air in the performance of the vortex tube, gave up the step of sizing the same. After engineered and designed parts of the tube, the final steps were the manufacture of pipe and conducting experimental tests, beyond the selection of a photovoltaic array to provide the power required to drive the compressor. The results of the laboratory tests with a vortex tube counter-current type, internal diameter D equal to 16.5 mm and a length equal to fifteen times this value, and configured diaphragm orifice diameter of 0.5D showed that temperatures of the cold air flow of 9.5 ÂC at a mass flow of 40% of the mass flow input are obtained when delivered by the compressor inlet gauge pressure of 3 bar and volumetric flow rate of 3.15 L/s compressed air. / O presente trabalho tem como objetivos dimensionar, construir e testar um novo tubo de vÃrtice, que opere a partir da utilizaÃÃo de ar comprimido em pressÃes abaixo das faixas de pressÃo tÃpicas deste dispositivo de refrigeraÃÃo nÃo-convencional, com o propÃsito de obter correntes de ar frio para climatizaÃÃo. Para tanto, foram inicialmente estudados aspectos teÃrico-experimentais dos processos de escoamento, atravÃs de testes realizados em laboratÃrio com um tubo de vÃrtice comercial. Conhecida a influÃncia dos parÃmetros geomÃtricos (tais como a razÃo entre o comprimento e diÃmetro interno do tubo e o diÃmetro do orifÃcio do diafragma) e das propriedades termofÃsicas (tais como a pressÃo manomÃtrica de entrada no tubo do ar comprimido e o percentual de vazÃo mÃssica da corrente de ar frio) no desempenho do tubo de vÃrtice, deu-se a etapa de dimensionamento do mesmo. Depois de projetadas e desenhadas as peÃas do tubo, as etapas finais foram a fabricaÃÃo do tubo e a realizaÃÃo de testes experimentais, alÃm da seleÃÃo de um arranjo fotovoltaico que forneÃa a potÃncia necessÃria para o acionamento do compressor. Os resultados dos testes em laboratÃrio com um tubo de vÃrtice do tipo contra-corrente, de diÃmetro interno D igual 16,5 mm e comprimento igual a quinze vezes esse valor, e configurado com diafragma de diÃmetro do orifÃcio de 0,5D, mostraram que sÃo obtidas temperaturas da corrente de ar frio de 9,5 ÂC a uma vazÃo mÃssica de 40% da vazÃo mÃssica de entrada, quando fornecido pelo compressor pressÃo manomÃtrica de entrada de 3 bar e vazÃo volumÃtrica de 3,15 L/s de ar comprimido.

CoordenaÃÃo de AperfeÃoamento de Pessoal de NÃvel Superior / A busca por novos sistemas de refrigeraÃÃo vem se tornando o alvo de estudo de diversos pesquisadores, com o objetivo de diminuir impactos ambientais referentes à destruiÃÃo da camada de ozÃnio e efeito estufa que trazem consigo diversos malefÃcios à vida no planeta. Sistemas de refrigeraÃÃo convencionais respondem por boa parte do consumo de energia elÃtrica de uma residÃncia ou uma empresa (de 20 ou atà 25%), e sÃo normalmente ligados durante o dia , quando a demanda à maior e as tarifas mais caras. Dispositivos de refrigeraÃÃo sÃo indispensÃveis nas atividades humanas, como conservaÃÃo de alimentos, medicamentos, etc. Sistemas fotovoltaicos sÃo fontes de energia elÃtrica confiÃveis e independentes. Por essas razÃes, atualmente, hà um aumento no uso de sistemas de refrigeraÃÃo acionados por energia solar fotovoltaica nas zonas rurais. Tubos de Ranque-Hilsch ou tubos de vÃrtice sÃo geralmente utilizados para refrigeraÃÃo local de baixo custo, onde hà a disponibilidade de ar comprimido. Nesse trabalho, um tubo de vÃrtice foi concebido, testado e otimizado para operaÃÃo em pressÃes inferiores Ãs convencionais, de modo a ser alimentado por um compressor acionado por mÃdulos fotovoltaicos, suprindo as necessidades de esfriamento em localidades desprovidas de energia elÃtrica. Nas mediÃÃes experimentais, foram obtidas temperaturas abaixo do ponto de congelamento da Ãgua por meio da combinaÃÃo de certos parÃmetros, possibilitando a esse sistema de climatizaÃÃo ser utilizado de maneira eficiente e racional em localidades remotas, podendo contribuir para a soluÃÃo da questÃo energÃtica e ambiental da sociedade. / The search for new refrigeration systems has become the target of various researchers. Their goal is to reduce the environment impacts resulting from the destruction of the ozone layer and the greenhouse effects that harm life in the planet Earth. Vapor-compression refrigeration systems represent a big fraction of the world energy consumption in houses and commercial stores (between 20 to 25%) and these systems usually run during the day, when the energy demand and the prices are higher. Refrigeration systems are necessary to todayâs human activities, such as food and medicament conservation, air conditioning, etc. Photovoltaic systems are reliable energy sources and they can operate separately from the distribution energy grid. For these reasons, there is an increase in the use of refrigeration systems powered by solar photovoltaic panels in rural areas. Ranque-Hilsch tubes or vorticity tubes are commonly used for low cost local refrigeration, where compressed air is available. In this study, a vortex tube was designed, tested, and optimized to operate at pressure levels lower than the conventional values. The purpose is to allow its operation by a compressor system powered by solar photovoltaic panels and, therefore, its installation in locations where there is no electrical grid. In the experimental measurements, temperatures below the water freezing point were reached due to the combination of a number of tube parameters. These low temperature values support the use of the vortex tube in air cooling applications in a more efficient and rational energy use, particularly in remote locations, and can contribute to the solution of the energy demand and environmental problems.

A pressurized vortex tube is used to generate streamwise vortices in a wind tunnel and the resulting flow behavior is analyzed. The apparatus is intended to verify computational data from the AFRL by offering a method of conducting real-world counterpart experiments. The apparatus design process and other considered approaches are discussed. The vortex tube is operated at pressures of 20, 30 and 40 psi while the wind tunnel is operated at 3, 5, 10 and 20% capacity. Flow measurements are performed using particle image velocimetry to observe vortices and freestream interactions from which velocity and vorticity data is comparatively analyzed. Results indicate that vortex velocity greater than freestream flow velocity is a primary factor in maintaining vortex structures further downstream, while increased supply pressure and reduced freestream velocity also reduce vortex dissipation rate. A brief analysis of the vortex interaction with a downstream airfoil is presented to support future work.

No description available.

No description available.

Helicopter turboshaft engines may ingest large amounts of foreign particles (most commonly sand/dust), which can cause significant compressor blade damage and even engine failure. In many helicopters, this issue is mitigated by separating the particles from the intake airstream. An effective device for engine air-particle separation is the vortex tube separator (VTS), which uses centrifugal forces in a vortical flow to radially filter foreign particles from a duct with an annular exit. Dozens or hundreds of these devices are linked together on a shared manifold known as a VTS array. There is a distinct lack of scientific literature regarding these arrays, which likely feature significantly more complex flowfields than singular VTSs due to aerodynamic interactions between the devices. The research presented in this dissertation identifies and explains flow features unique to arrays by means of an experimental investigation downstream of various VTS configurations in a wind tunnel. Mean PIV flowfields reveal that the VTS array rapidly generates a strong central recirculation zone while a single VTS does not, implying the existence of axial flow gradients within associated separators that could affect filtration efficiency. The key factor here is the global swirl intensity, which is increased in array flows due to high angular momentum contributions from separators that are radially distant from the duct center. A preliminary momentum integral model is constructed to predict the onset of recirculation in VTS flows. Analysis is then extended to the unsteady flowfield, where it is shown that VTS-generated turbulence contains only low levels of anisotropy. Spectral proper orthogonal decomposition is conducted on the array flow; it reveals the existence of low-frequency harmonic behavior composed of back-and-forth pumping motions downstream of the central VTS. Additionally, a unique precession motion is found in the same region at a slightly higher frequency. Similar precessing vortex cores have been shown to reduce separation efficiency in other cyclone separators. Both of these coherent structures may be associated with the central recirculation zone and may interfere with VTS array filtration given their timescales relative to potential particle relaxation timescales. This dissertation opens the door for future experimental and computational studies of fluid and particle dynamics in VTS flows with the goal of improving VTS array-specific design philosophies. / Doctor of Philosophy / Vortex tube separators (VTSs) help protect helicopter engines by filtering harmful particles (sand, dust, snow, ash, sea spray, etc.) they would otherwise ingest. This is done by creating a vortex in which centrifugal forces eject particles outwards, separating them from the main airstream. These devices are effective when dozens are grouped together into VTS arrays, but little is understood of the complex air and particle dynamics that result from the many interacting vortices both in and around such arrays. This dissertation describes an early effort to study these aerodynamics and open the door for subsequent particle dynamics research. A laser-based measurement technique called particle image velocimetry is used to determine flow velocities downstream of a VTS array placed in a wind tunnel. When velocities are averaged together over time, they reveal a central recirculation zone (a known feature of intensely swirling flows) downstream of the VTS array that vanishes when only a single separator in the array is active. A mathematical model is developed to predict such recirculation. It demonstrates that a VTS array comprises many separators that are far from the center of the duct they are contained within, and these contribute greatly to the overall swirl intensity. Other data analysis techniques are used to investigate the instantaneous velocity flowfield, which differs significantly from averaged quantities. One such technique is spectral proper orthogonal decomposition, which extracts so-called "coherent structures" from the flow - correlated high-energy motions that exist at certain frequencies and may not be visible in the raw data. This analysis finds two interesting structures at the very center of the duct, possibly associated with the recirculation zone: a back-and-forth pumping motion at a very low frequency (and some of its harmonic frequencies), and a "precessing" (unsteadily rotating) vortex at a slightly higher frequency. These motions, as well as the central recirculation zone itself, are impactful because they may affect the filtration process within the VTS upstream of where they were measured. Such effects will be investigated in future experiments and, if confirmed, may influence the design of VTS arrays.

The purpose of this diploma thesis was to find optimal operational parameters of Ranque–Hilsch vortex tube that would give the best results of temperature separation, and to create a numerical model of the device. Firstly, extensive research of current literature was done and analytical model of the tube was created. Then, the numerical model of the vortex tube was designed using Star-CCM+ software. Afterward, best fitting turbulence model was chosen to do the calculation and optimal geometrical parameters of the tube were obtained as a result of CFD simulation. Then, inlet nozzles for the tube were designed and manufactured. Experimental evaluation of the vortex tube and description of its optimal settings form a substantial part of the project. Finally, the data obtained from the experiment were compared to the results of numerical analysis and conclusions were deduced.

Thesis (MScEng (Mechanical and Mechatronic Engineering))--University of Stellenbosch, 2010. / ENGLISH ABSTRACT: The Pebble Bed Modular Reactor (PBMR) is a Generation IV graphite-moderated helium cooled nuclear reactor which is being developed in South Africa. The PBMR design is based on the German Arbeitsgemeinschaft Versuchreaktor (AVR). The AVR was decommissioned in December 1988 due to operational and safety problems. The PBMR project has put a lot of emphasis on safety and therefore all safety issues relating to the AVR have to be addressed before this technology can be implemented. After the decommissioning of the AVR plant, technicians found radioactive isotopes of cesium 55Cs137, 55Cs134, silver 44Ag110 and strontium 38Sr90 as well as graphite dust in the primary coolant loop of the reactor. These isotopes as well as the graphite dust have to be removed from the helium coolant stream because it can be potentially harmful to equipment, personnel and the general public. The main objective of this thesis is therefore to investigate a separation method for removing the graphite dust (and with it the radioactive isotopes) from the helium coolant stream and also test this method under different operating conditions and geometrical configurations to determine its dust separation efficacy. The device chosen to investigate is the Ranque-Hilsch vortex tube. The Ranque-Hilsch vortex tube (RHVT) is a simple device having no moving parts that produces a hot and cold air stream simultaneously at its two ends from a compressed air source. The vortex generated by the vortex generator located at the inlet of the RHVT causes strongly rotating flows similar in speed to that of a gas centrifuge. The gas centrifuge is used for isotope separation. The RHVT, in theory, can therefore be implemented to separate the graphite/silver isotopes from the helium coolant with the added benefit of either cooling or heating the coolant and was thus selected as the separation technique to be tested experimentally. The dust separation efficiency of the RHVT was tested experimentally using different grades of graphite dust, different fluids, various inlet volumetric flow rates and volume fractions and different RHVT geometries. The experimental results showed that the RHVT has a dust separation efficiency of more than 85 %. A regression analysis was also done with the experimental data to obtain a correlation between the different operating conditions (such as volumetric flow rate) and the dust separation efficiency that can be used to predict the dust efficiency under different operating and geometric conditions (such as the PBMR environment). An analytical model is also presented to describe the ‘temperature separation’ phenomenon in the RHVT, using basic thermo-physical principals to gain a better understanding of how the RHVT works. A CFD analysis was also attempted to supplement the analytical analysis but the solution did not converge and therefore only the preliminary results of the analysis are discussed. / AFRIKAANSE OPSOMMING: Die “Pebble Bed Modular Reactor” (PBMR) is `n vierde generasie grafiet gemodereede en helium verkoelde reaktor wat in Suid-Afrika ontwikkel word. Die PBMR ontwerp is gebaseer op the Duitse Arbeitsgemeinschaft Versuchreaktor (AVR) wat buite werking gestel is in Desember 1988 as gevolg van operasionele en veiligheidsprobleme. Die PBMR projek lê baie klem op veiligheid en daarom moet alle veiligheidskwessies van die AVR eers aangespreek word voor die tegnologie geimplementeer kan word. Nadat die AVR buite werking gestel is, het AVR tegnisie radioaktiewe isotope van cesium 55Cs137, 55Cs134, silwer 44Ag110 en strontium 38Sr90 asook grafiet stof in die primêre stroomkring van die reaktor gevind. Hierdie isotope sowel as die grafiet stof moet uit die helium verkoelingsmiddel in die primere stroomkring van die reaktor verwyder word aangesien dit dalk skadelik kan wees vir toerusting, personeel en die publiek. Die hoofdoelwit van hierdie tesis is dus om `n skeidingstekniek te ondersoek wat die stof (en dus ook die radioaktiewe isotope) uit die helium verkoelingsmiddel kan verwyder. Hierdie tegniek moet dan getoets word onder verskillende operasionele en geometriese toestande om die skeidingsbenuttingsgraad te bepaal. Die toestel wat gekies is om ondersoek te word is die “Ranque-Hilsch Vortex Tube”. Die “Ranque-Hisch Vortex Tube” (RHVT) is a eenvoudige uitvindsel wat geen bewegende parte bevat nie en wat warm en koue lug gelyktydig produseer vanaf `n saamgepersde lugbron. ‘n Baie sterk roteerende vloei word gegenereer in die RHVT wat dieselfde snelhede bereik as die lug in `n gas-sentrifugeerder. Die gas- sentrifugeerder word gebruik as `n isotoopskeidingsapparaat. In teorie kan die RHVT dus ook gebruik word om partikels te skei as gevolg van die sterk roteerende vloei, met die voordeel dat dit ook die lug kan verhit en verkoel. As gevolg van hierde redes is die RHVT gekies as die skeidingstegniek om te ondersoek en dus experimenteel te toets. Die benuttingsgraad van die RHVT se vermoë om die grafiet stof van die lug te skei was gevolglik eksperimenteel getoets deur gebruik te maak van verskillende gehaltes grafiet stof, verskillende vloeistowwe (lug of helium), verskillende inlaat volumevloeitempos en volume fraksies en RHVT geometrieë. Die experimentele resultate het getoon dat die RHVT `n benuttingsgraad van meer as 85 % het. `n Regressie analise was ook gedoen met die eksperimentele data om `n korrelasie tussen die verskillende opersionele toestande (soos volumevloeitempo) en die stof skeiding benuttingsgraad te kry. Hierdie korrelasie kan dan gebruik word om die stofskeidingsbenuttingsgraad onder ander operasionele en geometriese omstandighede, soos die PBMR omgewing, te voorspel. `n Analitiese model word ook voorgestel om die “temperatuur-skeidings” meganisme in die RHVT te verduidelik, met die hulp van basiese termo-fisiese beginsels, om beter te verstaan hoe dit werk. Daar was ook gepoog om `n CFD analise te doen wat die analitiese model kon aanvul, maar die numeriese oplossing het nie gekonvergeer nie en dus word net die voorlopige resultate van dié analise bespreek.