Academic literature on the topic 'Numero di Reynolds'
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Journal articles on the topic "Numero di Reynolds"
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ANNET, LIHAVI, Dr Virginia Kitetu, and Dr Mary wainaina. "The Effect of Varying Magnetic Number, Reynolds Number and Pressure Gradient on Velocity Profiles in an MHD Flow." International Journal of Innovative Science and Research Technology 5, no. 7 (2020): 387–94. http://dx.doi.org/10.38124/ijisrt20jul395.
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Magnetohydrodynamic ow of a hot viscous electrically conducting incompressible uid through parallel plates is studied. In the study, the e ect of Hartmann number (M), pressure gradient and Reynolds number (Re) on the velocity eld is investigated. The Navier-stokes equations were coupled with Ohms law and then solved using nite di erence method (FDM). The velocity eld was computed for various values of the physical parameters and shown graphically. It was found that as the Hartmann number M increases, the velocity pro les decreased due to increased Lorents force while an increase in Reynolds number causes an increase in the velocity of the uid. All these analysis was done using MATLAB program and the results were presented in tables and graphs.
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Mohammadzadeh, K., E. M. Kolahdouz, E. Shirani, and M. B. Shafii. "Numerical Investigation on the Effect of the Size and Number of Stages on the Tesla Microvalve Efficiency." Journal of Mechanics 29, no. 3 (2013): 527–34. http://dx.doi.org/10.1017/jmech.2013.29.
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AbstractIn the present study, the effect of the number of stages of Tesla Micro-Valve (TMV), as well as the dependency of Reynolds number, Re, on the valve performance has been analyzed. For this purpose, different layouts include one to four-stage with different sizes are investigated numerically. The main criterion for evaluation of valves performance is diodicity, Di. Unsteady and steady flow in valve have been simulated and compared. It is shown that although there are some difference but the trend is similar for both responses. Finally, 2-D and steady state computations of the fluid flow have been utilized that reveal a strong dependence of Di on Re and pressure drop, ΔP. The results showed that the maximum Di of the two-stage microvalve is approximately 1.45 times of that of one-stage. Additional stages increase the complexity, and they do not change Di appreciably. It is concluded that two-stage layout of Tesla type valve is the best option. Also, the two-stage valve performance for three different sizes is compared with Nozzle-Diffuser type Micro-Valve (NDMV). Comparisons, which are performed based on calculation Di in applicable range of Re, showed that Di as a function of Re is independent of the valve size. Also, the superiority of the Tesla type valve at higher Re and its weakness at lower Re is observed.
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ALI, ABDUL-FATTAH, and Mohanad M-Ridha. "ANALYSIS AND CORRELATIONS OF DIMENSIONLESS NUMBERS RELEVANT TO ORIFICES’ CAVITATING FLOW." IIUM Engineering Journal 21, no. 2 (2020): 41–54. http://dx.doi.org/10.31436/iiumej.v21i2.1306.
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The aim of this work was to establish a general design basis for pilot-scale units to treat textile dyeing wastewater containing recalcitrant organic chemicals by hydrodynamic cavitation (HC) using orifices of various geometries. Relevant tabulated data available in the literature were analyzed and correlated to obtain universal relationships to this end. In spite of extensive effort, most of the obtained correlations were system-specific, which still can be used for design using their respective orifice geometries as demonstrated. However, one salient general relationship links the pipe’s dimensionless loss coefficient (KLP) to the pipe’s Reynolds number (ReP), encompassing all data under consideration, which may serve as an additional design option to optimize such units. The implication of this relationship is a lower upstream pressure (P1) value with an increase in pipe diameter while using the same specified orifice and achieving the same desired cavitation number (Cv). The ratio of P1 value in the larger pipe to its value in the smaller pipe is a function of the smaller pipe diameter (DS) to the larger pipe diameter (DL) ratio: (P1 in DL) / (P1 in DS) = (DS /DL)2.33. A lower P1 value will increase the cavitation yield by decreasing the expended energy, especially if the required number of passes is large. Additionally, the variation of the orifices’ hole loss coefficient (KLh) with the ratio of the holes area to the pipe cross-sectional area (Ah/Ap) for cavitating flow is compared with that for non-cavitating/incipient cavitation flow reported in the literature. ABSTRAK: Tujuan kajian ini diadakan bagi mereka bentuk dasar umum unit skala-pandu bagi merawat pewarnaan air buangan tekstil yang mengandungi kimia organik rekalsitran daripada peronggaan hidrodinamik (HC) menggunakan orifis pelbagai geometri. Data berjadual berkaitan yang ada dalam kajian lepas dianalisa dan dikaitkan bagi mendapatkan kaitan universal hingga akhir. Walaupun pelbagai usaha telah dijalankan, banyak kaitan didapati mengguna pakai sistem-tertentu, di mana boleh digunakan bagi mereka cipta menggunakan geometri orifis yang ditunjukkan. Walau bagaimanapun, bagi menghubung kait pekali langsung tanpa dimensi (KLP) kepada paip nombor Reynolds (ReP), meliputi semua data di bawah pertimbangan, di mana membantu pilihan rekaan tambahan bagi mengoptimum unit tersebut. Implikasi hubungan ini adalah nilai tekanan hulu sungai bawah (P1) dengan penambahan diameter paip dengan menggunakan orifis sama yang sebenar dan mendapati nombor peronggaan yang sama diingini (Cv). Nisbah nilai P1 dalam paip besar kepada nilai paip kecil adalah berkadaran pada nisbah diameter paip kecil (DS) kepada diameter paip besar (DL): (P1 dalam DL) / (P1 in DS) = (DS /DL)2.33.
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Liu, Xiao Heng, Hong Mei Yin, Yi Lai, and Long Juan Xue. "Mechanical Properties of Living Cells: Interaction of the Adherent Endothelial Cell and the Fluid Shear Flow." Key Engineering Materials 361-363 (November 2007): 1157–60. http://dx.doi.org/10.4028/www.scientific.net/kem.361-363.1157.
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In present study a theoretical model was established to simulate the interaction between the adherent endothelial cell and fluid shear flow. A two-dimensional computational fluid dynamics (CFD) was conducted to solve the model equations. The results showed that the model cell was deformed under steady shear flow. It spread along the flow direction, and decreased its height. The deformation index (DI) increased with Reynolds number of applied fluid flow. The DI of the cell increased greatly when the initial contact angle (α) was smaller than 130°, and then it was less important with the increase of α. These results suggest that the fluid shear flow may play a particular role in the mechanism of cell activation and in the regulation of endothelial cells functions.
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Tsai, Sheng Hong, and Yu Tang Chen. "Experiment Study and Numerical Analysis of Flow and Heat Transfer in (110) Silicon Base Microchannel." Materials Science Forum 594 (August 2008): 351–56. http://dx.doi.org/10.4028/www.scientific.net/msf.594.351.
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Microchannel heat sink is fabricated on silicon wafer by anisotropic etching, and used Pyrex #7740 as a transparent cover that integrated by anodic bonding. Rectangular microchannel presents the flow phenomena of fluid in micro scale, and this study focus on the boundary conditions which hydraulic diameter (Dh) is from 80m to 350m and Aspect ratio is from 0.24~7.8 of working fluid (DI water). While the size of microchannel is decreasing, laminar flow occurs on the low Reynolds number, which caused by the interaction of viscosity and friction on boundary layer. Sequentially, the influence of dimension decreasing on microchannel that induced transition and turbulent flow in early stage as Reynolds number is still in the range of 600~800. Pressure drop is high (2 bar) when fluid flows through the micro channel, and flux is constrained by the flow resistance during experiment operating. In this study, it takes effect by increasing aspect ratio to reduce pressure drop and enlarge the conductive surface. Geometry of microchannel, hydraulic diameter, and aspect ratio are the key factors in flow phenomena investigation. This research presents the difference between micro scale flow and traditional pipe flow by consideration of Reynolds number. By using computer aided engineering to optimize the aspect ratio of microchannel, which can find the maximum conductive surface under the limitation of pressure drop. The best value of aspect ratio is 0.88~1.22. The simulation result makes good sequence with experiment data. Based on this methodology, numerical analysis can be used to design the optimal microchannel on wafer for cooling hot spot.
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Raghu, Palani, M. Senthamil Selvan, K. Pitchandi, and N. Nallusamy. "Experimental Study on Diesel Engine and Analysis the Spray Characteristics of Diesel and Biodiesel by Varying Injection Pressure." Advanced Materials Research 984-985 (July 2014): 932–37. http://dx.doi.org/10.4028/www.scientific.net/amr.984-985.932.
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— The spray characteristic of the injected fuel is mainly depends upon fuel injection pressure, temperature, ambient pressure, fuel viscosity and fuel density. An experimental study was conducted to examine the effect of injection pressure on the spray was injected into direct injection (DI) diesel engine in the atmospheric condition. In Diesel engine, the window of 20 mm diameter hole and the transparent quartz glass materials were used for visualizing spray characteristics of combustion chamber at right angle triangle position. The varying Injection pressure of 180 - 240 bar and the engine was hand cranked for conducting the experiments. Spray characteristics for Jatropha oil methyl ester (JOME) and diesel were studied experimentally. Spray tip penetration and spray cone angle were measured in a combustion chamber of Direct Injection diesel engine by employing high speed Digital camera using Mie Scattering Technique and ImageJ software. The study shows the JOME gives longer spray tip penetration and smaller spray cone angle than those of diesel fuels. The Spray breakup region (Reynolds number, Weber number), Injection velocity and Sauter Mean Diameter (SMD) were determined for diesel and JOME. SMD decreases for JOME than diesel and the Injection velocity, Reynolds Number, Weber Number Increases for JOME than diesel.
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Putra, Randi Purnama, Bahrul Amin, Dori Yuvenda, and Nuzul Hidayat. "Karakteristik Aliran pada Saluran Udara dengan Penambahan Square dan Circular Turbulator di Dekat Silinder Sirkular Tunggal." INVOTEK: Jurnal Inovasi Vokasional dan Teknologi 19, no. 1 (2019): 1–8. http://dx.doi.org/10.24036/invotek.v19i1.351.
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Penggunaan silinder sirkular banyak ditemukan pada bentuk kontruksi aplikasi teknik seperti; heat exchanger, struktur penyangga anjungan lepas pantai, jembatan dermaga, sistem perpipaan dan sebagainya. Di dalam beberapa aplikasi teknik, silinder sirkular ditempatkan di dalam saluran dengan berbagai pengaturan. Penggunaan silinder sirkular di dalam saluran tentunya mengakibatkan perbedaan karakteristik aliran dan membuat bertambahnya pressure drop. Penelitian ini bertujuan melihat karakteristik aliran dengan penggunaan variasi turbulator didekat silinder sirkular. Karakteristik aliran yang di tinjau adalah pressure drop, distribusi tekanan pada silinder sirkular dan Koefisien drag pressure. Penelitian dilakukan secara eksperimen. Turbulator ditempatkan di depan dari silinder sirkular. Turbulator yang digunakan berbentuk square dan circular cylinder. Saluran udara memiliki penampang bujur sangkar dengan luas penampang 125 x 125 mm. Rasio blockage sebesar 36,4 %. Variasi posisi sudut turbulator adalah dengan sudut α = 200, 300, 400, 500, dan 600. Pengujian dilakukan pada Reynolds number 11,6 x 104 (Re berdasarkan diameter hidrolik). Hasil dari penelitian menunjukkan penggunaan square turbulator lebih efektif mereduksi pressure drop pada saluran dibandingkan circular turbulator. Variasi posisi sudut square turbulator yang efektif mereduksi pressure drop ada pada sudut α = 300. Reduksi pressure drop pada sudut ini sebesar 23,33 %. Separasi aliran pada silinder sirkular terjadi pada sudut 1100 dan koefisien drag pressure sebesar 0,62.
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Klistafani, Yiyin. "Studi Numerik Steady RANS Aliran Fluida di Dalam Asymmetric Diffuser." INTEK: Jurnal Penelitian 4, no. 1 (2017): 20. http://dx.doi.org/10.31963/intek.v4i1.100.
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Research on fluid flow becomes a necessity to develop technology and for the welfare of human beings on earth. One of them is study of fluid flow in the diffuser. The example of diffuser application is used as a flue gas duct in the car or motorcycle. In addition, diffuser is also applied in air conditioning systems. Diffuser is a construction that able to control the behavior of the fluid. The increasing of cross section area in the diffuser will generate a positive pressure gradient or also called adverse pressure gradient (APG). The greater APG that happens, the greater energy required by the fluid to fight it, because APG will lead to separation. This study aimed to evaluate the numerical fluid flow in the asymmetric diffuser with divergence angle (θ) = 10 ° (upper wall) and widening one vertical side (α) of 20 ° (front wall). The Reynolds number is 8.7 x 104 by high inlet diffuser and the maximum velocity at the inlet diffuser. Turbulence models used are standard k-ɛ, realizable k-ε, and shear stress transport (SST) k-ω. Numerical study of steady RANS used Fluent 6.3.26 software. Results of numerical visualizations show that huge vortex established in diffuser, that’s why performance of diffuser is not optimal. In addition the location of separation point shown by SST k-ω is earlier than other turbulence models (standard k-ε and realizable k-ε).
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Syahrul, Syahrul, Siti Mechram, Purwana Satrio, and Agus A. Munawar. "Simulasi Model Aliran Fluida Dan Kebutuhan Daya Pompa Pada Sistem Hidrodinamika." Rona Teknik Pertanian 9, no. 1 (2016): 40–49. http://dx.doi.org/10.17969/rtp.v9i1.4383.
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Abstrak. Sistem hidrodinamika merupakan suatu kesatuan sistem dimana di dalamnya terdapat air yang mengalir dari suatu tempat ke tempat lain dimana tempat tersebut bisa berupa tangki, bak atau tempat penampungan lain. Sistem ini banyak diterapkan di bendungan, saluran-saluran irigasi, industri air minum dan bahkan industri-industri pengolahan pangan dan hasil pertanian. Para ilmuwan dan insinyur mempelajari sistem ini untuk menganalisa perubahan energi yang terjadi di sepanjang pipa akibat friksi di sepanjang pipa, katup, belokan, keran, dan perubahan diameter pipa. Tujuan utama dari studi ini adalah untuk membangun sistem model simulasi dalam program Visual Basic yang dapat digunakan untuk menganalisa karakteristik fluida dan menghitung kebutuhan daya pompa yang optimum pada sistem. Hasil studi menunjukkan bahwa sistem yang dibangun dapat menganalisa sistem hidrodinamika dengan cepat dan akurasi simulasi mencapai 0.99, 1 dan 0.99 untuk analisa bilangan Reynold, head loss, dan daya pompa yang diperlukan sistem. Modeling Simulation To Determine Fluids Flow And Power Requirement In Hydrodynamic System Abstract. Hydrodynamic system is a whole system where the water as the fluid is flow through pipe from a reservoir to another. This system can be find in an irrigation channels, water supply industries and even though in food processing industries. Scientist and engineers were analyze this system especially in head loss which caused by the friction in pipes, valves, elbows, joints and change of pipe areas. The objective of this study is to build a simulation program in microsoft visual basic which can be use to analyze and compute fluids flow characteristic and the required power pump. The result shows that hydrodynamic simulation program can analyze the system fastly and from the regression analyzes were given a high values for coefficient of correlation (r) whereas 0.9995 for reynold number prediction, 1 and 0.9972 both for system head loss and power requirement prediction respectively.
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Tanner, F. X., G. S. Zhu, and R. D. Reitz. "A Nonequilibrium Turbulence Dissipation Correction and Its Influence on Pollution Predictions for DI Diesel Engines." Journal of Engineering for Gas Turbines and Power 125, no. 2 (2003): 534–40. http://dx.doi.org/10.1115/1.1501917.
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A correction for the turbulence dissipation rate, based on nonequilibrium turbulence considerations from rapid distortion theory, has been derived and implemented in combination with the RNG k-ε model in a KIVA-based code. This correction reflects the time delay between changes in the turbulent kinetic energy due to changes in the mean flow and its turbulence dissipation rate, and it is shown that this time delay is controlled by the turbulence Reynolds number. The model correction has been validated with experimental data in the compression and expansion phase of a small diesel engine operated in motored mode. Combustion simulations of two heavy-duty DI diesel engines have been performed with the RNG k-ε model and the dissipation rate correction. The focus of these computations has been on the nitric oxide formation and the net soot production. These simulations have been compared with experimental data and their preditions are explained in terms of the turbulence dissipation effect on the transport coefficients for mass and heat diffusion. It has been found, that the dissipation correction yields consistent results with observations reported in previous studies.
Dissertations / Theses on the topic "Numero di Reynolds"
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Savelli, Nicola. "Misure sperimentali di nuove leggi di scala sull'attrito di parete generato da flussi turbolenti ad elevato numero di Reynolds." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2021. http://amslaurea.unibo.it/22704/.
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L’attrito generato dal moto di un fluido a contatto con una parete solida gioca un ruolo cruciale in svariate applicazioni di stampo ingegneristico, con ricadute sui consumi energetici e le emissioni di sostanze inquinanti. La stima corretta dell’attrito nei flussi turbolenti wall-bounded è strettamente legata all’evoluzione del profilo di velocità media vicino a parete dove si considera la Logarithmic Law of the Wall come universale e indipendente dal numero di Reynolds. Un’indagine sulla bontà dei termini “universale” e “indipendente” per quanto riguarda la Log-Law si rende però necessaria per migliorare la stima dell’attrito attraverso codici di calcolo numerico. Il presente elaborato vuole presentare l’attività sperimentale portata avanti presso il laboratorio CICLoPE, nato con lo scopo di rispondere a quelle domande ancora in sospeso riguardanti proprio i flussi turbolenti ad elevati valori del numero di Reynolds. In particolare flussi wall-bounded all’interno di pipe lisci. La caratteristica fondamentale del laboratorio CICLoPE sta nel garantire elevati numeri di Reynolds e allo stesso tempo preservare la risoluzione spaziale grazie alle dimensioni del suo Long-Pipe. Esplorando un range del numero di Reynolds che va da 9,3\times{10}^3 a 22,6\times{10}^3 si vuole caratterizzare, con l’utilizzo di un anemometro a filo caldo di tipo CTA, il profilo di velocità media e stimare i coefficienti che ne descrivono l’andamento secondo la log-law. Per far ciò sfruttiamo la caratteristica principale che deriva dall’avere un flusso turbolento completamente sviluppato all’interno di un pipe, ovvero il poter legare il gradiente di pressione costante lungo la direzione assiale alla friction velocity. Le misure hanno prodotto una buona caratterizzazione del flusso, mostrando però una certa variabilità sulla stima in funzione del numero di Reynolds delle costanti \kappa e B che definiscono la log-law, in accordo con le evidenze sperimentali di altri studi.
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Sanfilippo, Giorgia. "Turbulence in not fully filled vessel." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2020.
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In many chemical and biotechnological processes, mixing represents one of the fundamental unit operations, object of interest in chemical, pharmaceutical and food industries. Mixing efficiency is strongly influenced by the design and operating conditions chosen. The flow field study is important to understand which mechanism takes place in the fluid inside the stirred tank, in particular to characterize the property of the fluid and, to do that, a widely investigation techniques are used.
This experimental work was carried out during the “Erasmus + for traineeship” project carried out at the Chemical Engineering department of the University of Birmingham. It aims to investigate some parameters that influence the fluid dynamics of an agitated system, understanding how they influence it and possibly finding new parameters to define the turbulence of a system.
To achieve this aim, the characteristic parameters of a traditional single-phase system mechanically stirred and their behaviour during mixing have been experimentally studied. To understand the flow field generated in the various operating configurations adopted, an optical diagnostic technique, 2-D PIV, was used.
The work ends with the final considerations developed after analyzing the system both by changing the physical and geometric parameters and how these can affect the turbulence of an agitated system.
Conference papers on the topic "Numero di Reynolds"
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Mandelli, Simone, Sara Muggiasca, and Stefano Malavasi. "Numerical Simulation of an Oscillating Cylinder at High Reynolds Number." In ASME 2013 32nd International Conference on Ocean, Offshore and Arctic Engineering. American Society of Mechanical Engineers, 2013. http://dx.doi.org/10.1115/omae2013-11362.
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In this work a numerical investigation of the main flow field characteristics around a free oscillating rigid circular cylinder immersed in a turbulent flow is proposed (Re ≈ 5 · 104). The cylinder is characterized by high value of mass ratio and mass damping (m* = 145; ξ = 0.6 ÷ 1.14 · 10−3; m*ξ = 0.1 ÷ 0.25). The numerical results are compared with experimental data obtained in the wind tunnel under very similar fluid dynamic conditions. There are few works in literature that consider both numerical and experimental results under these conditions. This is probably due to the experimental facilities limitations and the computational difficulties correlated to modeling the flow at high Reynolds number. A numerical URANS model was developed through a CFD commercial code using a k–ω SST turbulence model in a 3D domain with the aim of matching the experimental results in the last years in the Politecnico di Milano Wind Tunnel on a suspended oscillating cylinder. The numerical setup is characterized by the use of the DFBI-Morphing (Dynamic Fluid Body Interaction) model that allows reproducing the body motion in response to fluid forces treating the cylinder as a mass-damping-spring system by introducing spring and damping forces acting on it. A preliminary check of this numerical setup was provided by a benchmark case involving a simple case of fixed cylinder at the same Reynolds number, where the movements of the cylinder were disabled. The numerical results of this case have been compared with experimental and numerical results reported in literature in terms of Drag and Lift coefficients and Strouhal number at high Reynolds numbers (Re ≈ 5 · 104). After that benchmark, the full setup has been checked by considering specific fluid dynamic conditions out of the lock in region in which the oscillations of the cylinder are negligible. Finally two points of the cylinder steady state response curve in the lock in region were investigated. The numerical model gave good results in terms of amplitude response of the cylinder and aerodynamic forces in agreement with experimental results. The analysis of the numerical reconstruction of the flow field evolution are therefore considered to have more information on the vortex shedding mode especially in the transition region between 2S and 2P mode.
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Wang, Y., S. J. Chung, J. P. Leonard, et al. "Cooling Performance of Nanofluids in a Microchannel Heat Sink." In ASME 2009 Second International Conference on Micro/Nanoscale Heat and Mass Transfer. ASMEDC, 2009. http://dx.doi.org/10.1115/mnhmt2009-18511.
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This paper describes an experimental study on microchannel heat sink performance where ZnO nanoparticle suspended fluids are used as coolant. The microchannel heat sink has 65 parallel microchannels branched out from an inlet reservoir and then collected into an outlet reservoir. Its fabrication process is based on the standard photolithographic microfabrication technology. A main feature of the heat sink has an array of on-chip temperature sensors on the channel bottom surface along the channel. Thus, the channel wall temperatures are directly measured. Heat transfer coefficient for the nanofluid is measured and compared with that of DI water as reference. The experiments show that the heat transfer coefficient of the ZnO nanofluid is 13% higher than that of the base fluid at the Reynolds number of 3.8, although it is comparable with that of DI water at lower Re numbers. The experiments also show that the heat transfer coefficient as well as the Nusselt number increases as the Reynolds number increases.
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Peyrard, Christophe, Marco Belloli, Pierre Bousseau, et al. "CFD Modeling of Flow Induced Vibration on a Mobile Cylinder for a 30 K-60 K Reynolds Number Comparison Between Simulation and Experimental Results." In ASME 2009 Pressure Vessels and Piping Conference. ASMEDC, 2009. http://dx.doi.org/10.1115/pvp2009-77534.
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Fatigue and aging of electrical overhead transmission lines is a major concern nowadays in developed countries with ever increasing difficulties to build new lines and an already quite aged network. An important degradation phenomenon of overhead line cables is fretting fatigue close to the suspension clamps due to vortex induced vibrations (VIV). These VIV are generally observed for wind speeds in the range of 1 to 7 m/s. The existing industrial practice for predicting how prone cables are to VIV fatigue is based on a balance between the power generated by the wind and the power dissipated by the cable system. The power generated by the wind has been evaluated through measurements on real line spans and through wind tunnel experiments on rigid and flexible cylinders as a function of frequency and vibration amplitude. The wind tunnel measurement results are mainly performed for constant flow speed. Corresponding results show a scattering from simple to double. Furthermore, complementary investigations are required to better evaluate the power with wind speed variations across and along the overhead line span. EDF R&D (with Code_Saturne open source software) and Politecnico di Milano have evaluated CFD modeling on a mobile rigid cylinder with comparison to detailed wind tunnel measurement results performed by Politecnico di Milano on a 20 cm diameter rigid cylinder equipped with a pressure scanner. This paper presents the steps, the different questions raised, the difficulties and limitations for the setting and the realization of the CFD modeling approach. The comparison between experimental results and simulation results is presented for the mobile rigid cylinder with k-ω SST turbulence model.
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Park, Chan Hyun, and Jorge L. Alvarado. "Thermal Performance of Poly Alpha Olefin Nanofluid With Spherical and Non-Spherical Nanoparticles." In ASME 2012 Heat Transfer Summer Conference collocated with the ASME 2012 Fluids Engineering Division Summer Meeting and the ASME 2012 10th International Conference on Nanochannels, Microchannels, and Minichannels. American Society of Mechanical Engineers, 2012. http://dx.doi.org/10.1115/ht2012-58319.
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In this study, several heat transfer fluids consisting of Poly-Alpha-Olefin (PAO) as base fluid and non-spherical alumina (Al2O3) nanoparticles such as nanorods and nanoplatelets have been used to formulate thermally enhanced nanofluids. Thermal properties such as thermal conductivity and viscosity have been measured, and the corresponding thermal conductivity enhancement has been calculated. The heat transfer coefficient under laminar flow under constant heat flux conditions has been measured experimentally. Results indicate that nanofluids containing spherical and non-spherical nanoparticles depict a Newtonian behavior at low concentrations. Nanofluids containing non-spherical alumina nanoparticles exhibit the greatest thermal conductivity enhancement when compared to pure PAO. Moreover, heat transfer enhancement was also observed when non-spherical nanoparticles were used. Likewise, the percentage enhancement in convective heat transfer coefficient was shown to increase non-linearly with axial distance (x/Di) in a circular heat transfer section. Nanofluids containing non-spherical nanoparticles exhibits a lower Re*Ra (Reynolds number*Rayleigh number) than pure PAO under laminar flow constant heat flux conditions indicating that nanoparticle morphology and composition are the two main factors responsible for convective heat transfer enhancement at low Reynolds number. Convection and axial conduction can explain the increase in Nusselt number when x/Di is greater than 400. The expected radial movement of nanoparticles within the fluid at relatively low Reynolds number could explain the enhanced convection when factoring in changes in viscosity and the effect of buoyancy.
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Fabbri, Matteo, Shanjuan Jiang, and Vijay K. Dhir. "Experimental Investigation of Single-Phase Micro Jets Impingement Cooling for Electronic Applications." In ASME 2003 Heat Transfer Summer Conference. ASMEDC, 2003. http://dx.doi.org/10.1115/ht2003-47162.
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Impinging jets for cooling of electronic equipment have been used by many researchers. Only few studies using arrays composed of a small number of jets are available in the literature. When very small jet diameters are used, the jet Reynolds number becomes quite small and no data are available for Reynolds number values below 500. In this work attention has been focused on circular arrays of free surface micro jets. Experiments were conducted by employing three jet pitches, 1, 2 and 3 mm and four jet diameters 50, 100, 150 and 250 μm and two different fluids, DI water and FC 40. The jet Reynolds number range was varied between 90 and 2000 while the Prandtl number varied from 6 to 84. Heat fluxes as high as 250 W/cm2 could be removed when water was utilized. Experimental data have been correlated within ±20%.
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Mashali, Farzin, Ethan M. Languri, Jim Davidson, David Kerns, and Fahad Alkhaldi. "An Experimental Study on the Convective Heat Transfer Behaviour of Diamond Nanofluids in Electronic Cooling Applications." In ASME 2018 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2018. http://dx.doi.org/10.1115/imece2018-87481.
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This study presents the convective heat transfer coefficient of 0.05 wt.% diamond nanofluids containing functionalized nanodiamond dispersed in a base fluid deionized (DI) water flowing in a conduction cold plate under turbulent flow conditions, experimentally. The conduction cold plate was heated via six cartridge heaters with a constant heat transfer rate. The primary experimental study has been implemented to investigate the thermal conductivity of diamond nanofluids which showed a higher effective thermal conductivity than that of the base fluid. In addition, nanofluid was flowed in a closed system with heating at the heat exchanger and cooling via a cooling tank to keep the inlet temperature constant to explore the convection heat transfer properties of diamond nanofluids. Results indicate that the convective heat transfer coefficient and Nusselt number of diamond nanofluid are higher than that of the DI water in a same flow rate, and these properties increased with increase in Reynolds number.
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John, T. J., B. Mathew, and H. Hegab. "Experimental Analysis of Poiseuille Number in Square Microchannels." In ASME 2009 International Mechanical Engineering Congress and Exposition. ASMEDC, 2009. http://dx.doi.org/10.1115/imece2009-11810.
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The applications involving fluid flow through microchannels in industry and research have increased significantly with the evolution of microfluidic devices such as lab-on-chip systems. Most of the previous studies concerning fluid flow were done using circular microchannels. However, there is an increased usage of noncircular microchannels, especially square microchannels, in microfluidic devices. Thus there is need for experimental studies on the behavior of fluid flow in square microchannels, and the comparison of the results with the results obtained from the conventional fluid flow equations is relevant. In this study the authors are focusing on the analysis of the friction factor associated with square microchannels of rounded edges under laminar flow conditions. Microchannels with hydraulic diameters of 200, 300, 400 and 500 micrometers and length of 10 cm and 5 cm are used in the analysis. DI-water and ethylene glycol at room temperature is used as the liquid for experiments. A constant liquid flow rate is achieved in the channels using a syringe pump that can pump from 50 μl/hr to 7,500 ml/hr using a 60 ml syringe, and a high precision pressure gauge is used to measure the pressure drop across the channel. The Reynolds number of the liquid flow in all the channels is kept constant between 20 and 120 by varying the flow rate. The friction factor at each Reynolds number is calculated and the results are compared with the friction factor of conventional channels. Experiments are conducted to measure the pressure drop across the channels. The pressure drop obtained across the 5 cm channel is subtracted from the pressure drop obtained across the 10 cm channel so that the effect of entrance effect can be eliminated from the results. The fiction factor obtained from the experiments is used to calculate the Poiseuille number. The experimental values of Poiseuille number are showing a median deviation of around 9% from the conventional values for all the different channels. The uncertainty is observed to be ca.9% for all the channels at all values of Reynolds numbers. The major factor contributing towards the total uncertainty is the uncertainty in the measurement of liquid flow rate.
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Me´ndes, Tilmer, Marco A. Ciaccia, Jorge E. Torres, and Sergio E. Di´az. "On the Amount of Air Entrainment Into Finite Length Squeeze Film Dampers." In ASME/STLE 2007 International Joint Tribology Conference. ASMEDC, 2007. http://dx.doi.org/10.1115/ijtc2007-44330.
Full textAbstract:
Squeeze Film Dampers (SFDs) are routinely employed to reduce vibration amplitudes and isolate structural components in gas jet engines, high performance compressors and, occasionally, water pumps. Most open-ended squeeze film dampers in practice present the phenomenon of air entrapment. It is generally accepted that the presence of air reduces the damping capability of the SFD, especially at large amplitudes and high frequencies of vibrations. Thus, there is a need for a reliable model of practical use in the analysis of high performance turbomachinery SDFs operating with air entrainment. Di´az and San Andre´s advance a model for estimation of air entrapped into the film lands. This model is based on a dimensionless number that relates geometric and operational parameters, but is strictly valid only for infinitesimal length bearings. The present research has by objective extending the previous work of Di´az and San Andre´s for prediction of air entrainment and entrapment on finite length bearings. The Reynolds lubrication equation for a homogeneous mixture is solved using the finite volume method. The results are shown in a map that allows determining air volume content in the film as a function of the dimensionless parameter created by Di´az and San Andre´s (Squeeze-Feed Flow Number, γ) and the length-diameter ratio (L/D). This work represents a significant step towards a better understanding of air entrainment in finite length Squeeze Film Dampers.
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Rajab, Husam, Da Yin, and Hongbin Ma. "Effects of Al2O3-Water Nanofluid and Angular Orientation on Entropy Generation and Convective Heat Transfer of an Elliptical Micro-Pin-Fin Heat Sink." In ASME 2014 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2014. http://dx.doi.org/10.1115/imece2014-40335.
Full textAbstract:
This paper presents an investigation of the effect of nanofluid on the heat transfer performance in an elliptical micro-pin-fin heat sink including the influence of entropy generation and pin orientation. The orientation angle of pins is decreased with the number of pins in the array with a 90 degree angle for the first pin and a 0 degree angle for the last pin. To study the flow and heat transfer behaviors in a micro-pin-fin heat sink, steady Navier-Stokes and energy equations were discretized using a finite volume approach and were solved iteratively. Deionized (DI) water was used as a base coolant fluid while aluminum oxide (Al2O3) nanoparticles were used in the present study with mean diameters of 41.6 nm. The results showed that (1) changing the angular orientation of pins can cause significant enhancement in heat transfer, (2) a significant enhancement of heat transfer can be attained in the system due to the suspension of Al2O3 nanoparticles in the base fluid in comparison with pure water, (3) enhancement of heat transfer is intensified with increasing volume fraction of nanoparticles and Reynolds and Prandtl numbers, (4) increasing volume fraction of nanoparticles, which is responsible for higher heat transfer performance, leads to a higher pressure drop, (5) using nanofluids as coolant can cause lower heat transfer entropy generation due to their high thermal properties, and (6) with increasing volume fraction and Reynolds and Prandtl numbers, overall entropy generation rate decreases.
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Gaetani, P., G. Persico, A. Spinelli, and A. Mora. "Impact of the Expansion Ratio on the Unsteady Aerodynamics and Performance of a HP Axial Turbine." In ASME Turbo Expo 2016: Turbomachinery Technical Conference and Exposition. American Society of Mechanical Engineers, 2016. http://dx.doi.org/10.1115/gt2016-56650.
Full textAbstract:
In the frame of the European research project RECORD, the flow field within a HP axial-flow turbine model was investigated experimentally for several operating conditions. A number of studies on stator-rotor interaction in HP turbines for subsonic as well as transonic/supersonic conditions were proposed in the last decades, but none of them compared different conditions for the same geometry. In this paper, the transonic condition is investigated and compared to three subsonic ones, in the frame of an entirely new experimental campaign. The research was performed at the Laboratorio di Fluidodinamica delle Macchine of the Politecnico di Milano (Italy), where a cold-flow, closed-loop test rig is available for detailed studies on turbines and compressors. The boundary conditions resulted in keeping constant both the turbine inlet temperature and the stage outlet absolute flow direction; so far, while the expansion ratio was varied, the rotational speed was also modified accordingly. The analysis was performed by means of a conventional five hole probe in the stator – rotor axial gap and by a fast response aerodynamic probe downstream of the rotor. The local time-averaged and phase-resolved flow field was then derived and used to analyze the stage aerodynamics and performance. Results show that the stage expansion ratio has a dramatic impact on both the rotor aerodynamics and stage performance. In particular, Mach number effects are recognized in the stator cascade that passes from transonic to low subsonic conditions. On the rotor cascade the reduction of expansion ratio reduces significantly the Mach and Reynolds numbers and increases the incidence angle as well; the rotor loss mechanics as well as the vane-rotor interaction are greatly amplified. Correspondingly a significant variation of stage overall efficiency is recorded.