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Zeitschriftenartikel zum Thema "Nu80"
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Eiamsa-ard, S., und P. Promthaisong. „Counter-rotation vortex flows and heat transfer mechanisms in a V-spirally-corrugated tube“. Proceedings of the Institution of Mechanical Engineers, Part A: Journal of Power and Energy 233, Nr. 7 (13.02.2019): 928–52. http://dx.doi.org/10.1177/0957650919829367.
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The flow and heat transfer behavior of newly designed V-corrugated tubes with various numbers of starts ( N = 2, 3, 4, and 5), depth ratios ( DR = 0.02–0.14), and pitch ratios ( PR = 1.0–2.0) were studied in the turbulent flow region (5000 ≤ Re ≤ 20,000). The friction factor ( f), friction factor ratio ( f/ f0), Nusselt number ( Nu), Nusselt number ratio ( Nu/ Nu0), and thermal enhancement factor ( TEF) values are reported. The computational results indicate that the conventional spirally-corrugated tube create swirl flows while V-corrugated tubes generate a counter-rotating vortex flow that impinges upon the lower zone of the tubes and enhances fluid transfer between tube core and near-wall regions. The results also show that the f, Nu, f/ f0, Nu/ Nu0 monotonically increase with decreasing PR, increasing DR and N, while the TEF is dependent on a tradeoff between f/ f0 and Nu/ Nu0. Over the studied range, the f/ f0, Nu/ Nu0, and TEF were in the ranges of 1.36–43.82, 1.00–5.35, and 0.80–2.11, respectively. The maximum TEF, 2.11, was achieved with a V-corrugated tube with an N of 4, DR of 0.06, and PR of 2.0 at Re = 5000.
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Liu, Jing, und Jie Li. „Numerical Prediction of Flow Structure and Heat Enhancement with Different Dimple Depth“. Applied Mechanics and Materials 574 (Juli 2014): 147–53. http://dx.doi.org/10.4028/www.scientific.net/amm.574.147.
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Aim at finding the relation between flow structure and heat enhancement, this paper change the dimple depth to print diameter from 0.06 to 0.3, with an interval of 0.02, and keep the print diameter constant. Through vortex structure analysis and Nu number integration, find out that: Vortex structure varies with dimple depth. Shallow depth dimple induces horseshoe vortex; middle depth dimple induces symmetric tornado-like vortex; deep depth dimple induces tornado-like vortex. Heat enhancement is closely related to vortex structure. Where spiral separation focus point exists, there the lowest Nu/Nu0 exists. Flow impingement at the windward side of dimple and new viscous layer generation at immediate plane after the dimple enhance heat transfer. The highest Nu/Nu0 exists in the sharp rearward dimple edge. From Fig 6, the deeper the dimple is, the higher the average Nu/Nu0 is, so does the pressure drop. But from 0.06 to 0.2 dimple, heat enhancement increased because of vortex structure changed. From 0.2 to 0.3 heat enhancement increased because of the increased area.
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PLIVA, J. „The difference bands nu11-nu4 and nu10-nu18 of benzene at high resolution“. Molecular Physics 87, Nr. 4 (01.03.1996): 859–63. http://dx.doi.org/10.1080/00268979650027216.
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Yang, De Zhi, Meng Long Dong, Xin Wei Lu und Zhao Yao Zhou. „Numerical Investigation of Convection Heat Transfer in Pipes with Sintered Porous Metal Rings“. Applied Mechanics and Materials 556-562 (Mai 2014): 4275–79. http://dx.doi.org/10.4028/www.scientific.net/amm.556-562.4275.
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Fully developed turbulence single phase convection heat transfer of water in pipes filled with sintered porous metal inner rings or solid inner rings was investigated numerically respectively. Numerical calculations were conducted with the Fluent 6.3 code, using the SST k-ω turbulence model. Comparing to solid-ring turbulator pipes, porous-ring turbulator pipes have better comprehensive heat transfer effect. The maximum PEC for porous-ring turbulator pipes is 4.4 and the PEC of solid-ring turbulator pipes is less than 1. It was also analyzed effect of geometric structures on porous-ring turbulator pipe performance. f/f0 for porous-ring turbulator pipes increases with the increasing of Re while Nu/Nu0 decreases with the increasing of Re ,and PEC decreases with the increasing of Re. With the same Re, if the width of the porous ring is equal to the width of groove, f/f0, Nu/Nu0 increases and PEC decreases with the increasing height of porous ring. When the height of porous ring is constant, the f/f0, Nu/Nu0 and PEC decreases with the increasing height of porous ring under the same Re.
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Yang, Yang, Siddharth Koushik Mohanakrishnan, David S.-K. Ting und Steve Ray. „DELTA WINGLETS FOR ENHANCING SOLAR ENERGY: TURBULENT STRAIN RATE-HEAT CONVECTION RELATIONSHIP“. Journal of Green Building 16, Nr. 2 (01.03.2021): 97–114. http://dx.doi.org/10.3992/jgb.16.2.97.
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ABSTRACT Delta winglets are an effective means for enhancing heat exchange and thus the performance of renewable energy technologies, including solar energy. A pair of 0.1 mm thick, 15 mm high (h) and 30 mm long aluminum winglets separated with transversal spacing, s, of 2h, h and 0 were scrutinized in a closed-loop wind tunnel at a Reynolds number based on h of 6300. The turbulent flow was characterized using a 3D hotwire probe, and the heat convection augmentation was quantified in terms of the normalized Nusselt number (Nu/Nu0), indicating the heat transfer improvement compared to the reference case without the winglets. The interaction of the organized counter-rotational vortices intensifies and they become indiscernible at s = 0. The peak strain rate at 10h downstream increased from 390 s–1, to 478 s–1, to 514 s–1, when the spacing decreased from 2h to h to 0, respectively. The zero-spaced winglet pair provided the largest Nu/Nu0, of around 1.21, at X/h = 10 and Y/h = 0, approximately 21% higher than that of 2h-spaced winglet pair, due to the strongest strain rate and the absence of upwash flow. On the other hand, the 2h-spaced winglet pair provided the largest span-averaged Nu/Nu0, which is of practical significance.
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Xu, Tao, Dongbo Shi, Di Zhang und Yonghui Xie. „Flow and Heat Transfer Characteristics of the Turbine Blade Variable Cross-Section Internal Cooling Channel with Turning Vane“. Applied Sciences 13, Nr. 3 (21.01.2023): 1446. http://dx.doi.org/10.3390/app13031446.
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The gas turbine blades are scoured by high temperature gas sustainedly and long-term in harsh environment. It is of great significance to explore effective cooling methods to lower the turbine blade temperature so as to ensure safe and stable operation of the gas turbine. However, there are few studies on the cooling channel considering the turning vane, variable cross-section characteristics, and rotation effect. In this paper, five kinds of serpentine cooling channel models with variable cross-section properties and different thickness guide vanes are constructed. The effects of different thickness guide vanes on the overall performance of the channel under stationary and rotating conditions are discussed and compared by numerical method. The result shows that when stationary (Re = 10,000-50,000), the turning vane with suitable thickness can increase the Nu/Nu0 by 56.5%. The f/f0 is decreased by 14.2%, and the comprehensive thermal performance is increased by 4.5%. When rotating (Re = 10,000, Ro = 0-0.5), the turning vane with suitable thickness can increase the Nuup/Nu0 and Nuall/Nu0 by 33.0% and 4.0%, respectively. The comprehensive performance of the variable cross-section serpentine channel can be greatly improved by arranging the turning vane structure with appropriate thickness.
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Machida, Shinichi, David Depierre, Heng-Chang Chen, Suzie Thenin-Houssier, Gaël Petitjean, Cecile M. Doyen, Motoki Takaku, Olivier Cuvier und Monsef Benkirane. „Exploring histone loading on HIV DNA reveals a dynamic nucleosome positioning between unintegrated and integrated viral genome“. Proceedings of the National Academy of Sciences 117, Nr. 12 (11.03.2020): 6822–30. http://dx.doi.org/10.1073/pnas.1913754117.
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The aim of the present study was to understand the biology of unintegrated HIV-1 DNA and reveal the mechanisms involved in its transcriptional silencing. We found that histones are loaded on HIV-1 DNA after its nuclear import and before its integration in the host genome. Nucleosome positioning analysis along the unintegrated and integrated viral genomes revealed major differences in nucleosome density and position. Indeed, in addition to the well-known nucleosomes Nuc0, Nuc1, and Nuc2 loaded on integrated HIV-1 DNA, we also found NucDHS, a nucleosome that covers the DNase hypersensitive site, in unintegrated viral DNA. In addition, unintegrated viral DNA-associated Nuc0 and Nuc2 were positioned slightly more to the 5′ end relative to their position in integrated DNA. The presence of NucDHS in the proximal region of the long terminal repeat (LTR) promoter was associated with the absence of RNAPII and of the active histone marks H3K4me3 and H3ac at the LTR. Conversely, analysis of integrated HIV-1 DNA showed a loss of NucDHS, loading of RNAPII, and enrichment in active histone marks within the LTR. We propose that unintegrated HIV-1 DNA adopts a repressive chromatin structure that competes with the transcription machinery, leading to its silencing.
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Lau, S. C., J. C. Han und Y. S. Kim. „Turbulent Heat Transfer and Friction in Pin Fin Channels With Lateral Flow Ejection“. Journal of Heat Transfer 111, Nr. 1 (01.02.1989): 51–58. http://dx.doi.org/10.1115/1.3250657.
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Experiments were conducted to study the effects of lateral flow ejection on the overall heat transfer and pressure drops for turbulent flow through pin fin channels. The two test sections of the investigation were rectangular channels with staggered arrays of six and eight streamwise rows of pins, respectively. The pin length-to-diameter ratio was one and both the streamwise and spanwise pin spacings were 2.5 times the pin diameter. Heat transfer and friction data were obtained for various ejection exit geometries, for ejection ratios between 0 and 1, and for Reynolds numbers between 6000 and 60,000. The results of the study show that, for any given ejection ratio, the overall Nusselt number increases with increasing Reynolds number. However, the overall Nusselt number is reduced by as much as 25 percent as the ejection ratio is increased from 0 to 1 over the range of Reynolds number studied. The Nu–Re–ε relationship, which is insensitive to varying the ejection exit geometry, can be correlated by the equation (Nu/Nu0) = (Nu1/Nu0)ε, where Nu0 = c0Rem and Nu1 = c1Ren are the overall Nusselt numbers in the 0 and 100 percent lateral flow ejection cases, respectively. The results also show that the overall friction factor is independent of the flow Reynolds number over the range of Reynolds number studied. However, the friction factor is strongly dependent on the ejection ratio as well as the geometries of the straight flow exit and lateral ejection flow exit.
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Takashima, M. „Article“. Canadian Journal of Physics 76, Nr. 12 (01.12.1998): 937–47. http://dx.doi.org/10.1139/p98-062.
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The stability of combined plane Poiseuille and Couette flow of an electricallyconducting fluid under a transverse magnetic field is investigated using linear stability theory.In deriving the equations governing the stability, the so-called magnetic Stokes approximationis made using the fact that the magnetic Prandtl number Prm for most electrically conductingfluids is extremely small. The Chebyshev collocation method is adopted to obtain theeigenvalue equation, which is then solved numerically. The critical Reynolds number Rec,the critical wave number αc, and the critical wave speed cc are obtained for wide ranges ofthe Hartmann number Ha and the parameter k = U0 / (U0 + nu0), where U0 is the maximumvelocity of pure Couette flow and nu0 is the maximum velocity of pure Poiseuille flow. It isfound that a transverse magnetic field has both stabilizing and destabilizing effects on theflow depending on the value of k.PACS Nos. 47.20
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Zhao, Zhen, Liang Xu, Jianmin Gao, Lei Xi, Qicheng Ruan und Yunlong Li. „Multi-Objective Optimization of Parameters of Channels with Staggered Frustum of a Cone Based on Response Surface Methodology“. Energies 15, Nr. 3 (08.02.2022): 1240. http://dx.doi.org/10.3390/en15031240.
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In this study, Response Surface Methodology (RSM) and multi-objective genetic algorithm were used to obtain optimum parameters of the channels with frustum of a cone with better flow and heat transfer performance. Central composite face-centered design (CCF) was applied to the experimental design of the channel parameters, and on this basis, the response surface models were constructed. The sensitivity of the channel parameters was analyzed by Sobol’s method. The multi-objective optimization of the channel parameters was carried out with the goal of achieving maximum Nusselt number ratio (Nu/Nu0) and minimum friction coefficient ratio (f/f0). The results show that the root mean square errors (RSME) of the fitted response surface models are less than 0.25 and the determination coefficients (R2) are greater than 0.93; the models have high accuracy. Sobol’s method can quantitatively analyze the influence of the channel parameters on flow and heat transfer performance of the channels. When the response is Nu/Nu0, from high to low, the total sensitivity indexes of the channel parameters are frustum of a cone angle (α), Reynolds number (Re), spanwise spacing ratio (Z2/D), and streamwise spacing ratio (Z1/D). When the response is f/f0, the total sensitivity indexes of the channel parameters from high to low are Re, Z1/D, α and Z2/D. Four optimization channels are selected from the Pareto solution set obtained by multi-objective optimization. Compared with the reference channel, the Nu/Nu0 of the optimized channels is increased by 21.36% on average, and the f/f0 is reduced by 9.16% on average.
Bücher zum Thema "Nu80"
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Critical Care Manual of Clinical Procedures and Competencies. Wiley & Sons, Limited, John, 2013.
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Planning Health Promotion Programs: An Intervention Mapping Approach. Wiley & Sons, Incorporated, John, 2016.
Den vollen Inhalt der Quelle findenBuchteile zum Thema "Nu80"
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Paschotta, R. „acousto-optic tunable filters“. In RP Photonics Encyclopedia. RP Photonics AG, 2004. http://dx.doi.org/10.61835/nu0.
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Shlonsky, Ur. „Pronouns“. In Clause Structure And Word Order In Hebrew And Arabic, 204–28. Oxford University PressNew York, NY, 1997. http://dx.doi.org/10.1093/oso/9780195108668.003.0010.
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Abstract Alongside the agreement suffixes or “clitic” forms discussed in chapter 9, both Hebrew and Arabic possess sets of unattached or free standing pronouns. The internal structure of nominative pronouns is discussed in chapter 7, where it is argued, following Ritter (1995), that first and second person pronouns are D0 elements while third person (or more precisely, nonperson) pronouns belong to the category Num0. Example (10-1) below lists the forms of the nominative series in Hebrew.
Konferenzberichte zum Thema "Nu80"
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Xu, Wei-jiang, Pei-yao Zhang, Xiao-fei Ma, Hui-ren Zhu und Li Zhang. „Experimental Study of Heat Transfer in a Converging Duct With Ribs“. In ASME Turbo Expo 2016: Turbomachinery Technical Conference and Exposition. American Society of Mechanical Engineers, 2016. http://dx.doi.org/10.1115/gt2016-56422.
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Heat transfer characteristics on the inner surface of a converging duct with ribs are investigated by conducting transient heat transfer experiments using thermochromic liquid crystals. In particular, features associated with the smooth duct are addressed as reference. The parameters studied are: the non-dimensional rib pitch (p/w = 10, 20, 50, p is the rib pitch, w is the rib width), the rib blockage ratio (e/H = 10%, 20%, e is the rib height, H is the channel height) and the inlet Reynolds number Re (Re = 6000∼20000). The results are presented on the top wall and its center line. Due to the converging shape of channel, the value of Nu/Nu0 increases downstream the channel, especially near the side wall. The effects of these parameters are: Firstly, the heat transfer improves with the increasing rib height whose influence decreases with the rise of Re number. Secondly, the value of Nu/Nu0 rises firstly, reaching its maximum at p/w = 20, and then declines with an increasing rib pitch. Thirdly, the value of Nu/Nu0 rises firstly and decreases afterwards with the Re number, as the Re number is within the range of Re≤12000.
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Molki, Majid, und Tannaz Harirchian. „The Enhancement Effect of Corona Discharge on Natural Convection Heat Transfer in Triangular Channels“. In ASME 2005 International Mechanical Engineering Congress and Exposition. ASMEDC, 2005. http://dx.doi.org/10.1115/imece2005-80070.
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A numerical research was conducted to investigate the effect of corona discharge on natural convection heat transfer in a triangular channel. The channel side walls were isothermal, the lower wall was adiabatic, and the fluid was air at the atmospheric pressure. The electric field was generated by a positive corona discharge from a charged wire electrode located at the center of the channel. The governing equations of the electric and flow fields were solved by a finite-volume technique. Three cases were considered: (1) natural convection; (2) corona-induced convection; and (3) combined natural and corona-induced convection. The computations encompassed Rayleigh numbers from 3,737 to 37,377 and applied voltages from 7 to 9 kV in the laminar regime. Computations for the applied voltage of 7.5 kV indicated that the heat transfer was enhanced from Nu/Nu0 = 1.01 to 1.04, or 1–4%, for different values of Ra. The enhancement at Ra = 3,737 and the applied voltage of 7 to 9 kV was Nu/Nu0 = 1.01 to 1.40, or 1–40%.
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Saha, Krishnendu, Sumanta Acharya und Chiyuki Nakamata. „Heat Transfer and Pressure Drop in a Converging Lattice Structure for Airfoil Trailing Edge Cooling“. In ASME 2008 International Mechanical Engineering Congress and Exposition. ASMEDC, 2008. http://dx.doi.org/10.1115/imece2008-68152.
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Lattice-matrix structures have distinct advantages in enhancing heat transfer in the cooling channels of a gas turbine blade. Lattice structures not only enhance heat transfer coefficient but also provide structural rigidity to the turbine blade. Stationary tests were performed for a 12 times scaled up model at four Reynolds numbers (4,000 < Re < 20,000) in a converging lattice structure. A narrow band liquid crystal technique is used to determine the heat transfer coefficient in the channel. The results shows very high heat transfer coefficient enhancement in the impingement regions. The average heat transfer coefficient enhancement for a channel with lattice structures is also higher (Nu/Nu0 = 1.9–3) than a pin fin cooling configuration channel (Nu/Nu0 = 1.7–2.2). The heat transfer coefficient enhancement decreases with increasing Reynolds number. Pressure data are taken at some specific points throughout the channel. High pressure drop due to the turning of the flow in the lattice structure is observed. Friction factor and overall thermal performance factor are calculated. The overall thermal performance factor lies in the range 0.64–1.
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Lan, Jibing, Yonghui Xie und Di Zhang. „Heat Transfer Enhancement in a Rectangular Channel With the Combination of Ribs, Dimples and Protrusions“. In ASME 2011 Turbo Expo: Turbine Technical Conference and Exposition. ASMEDC, 2011. http://dx.doi.org/10.1115/gt2011-46031.
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Rib turbulators can enhance the heat transfer successfully, but in most cases this is associated with large pressure loss penalties. Recently, dimple techniques become an attractive method for gas turbine blade internal cooling because dimples enhance heat transfer with low pressure penalty. In the present paper, a compound heat transfer enhancement technique, heat transfer enhancement in rectangular channel (Aspect ratio = 4) with the combination of ribs, dimples and protrusions, are investigated. The calculations are conducted on five different channel configurations. Case 1 which is the baseline configuration is a rectangular channel with rectangular ribs (e/Dh = 0.078, P/e = 10). In case 2, one row of dimples are placed between two ribs. In case 3, instead of dimples, one row of protrusions are placed between two ribs. In case 4, three rows of dimples are place between two ribs. Case 5 places three rows of protrusions between two ribs instead of dimples. The present paper focuses on Reynolds numbers (based on the channel hydraulic diameter) ranging from 10000 to 60000. In all configurations, the non-dimensional dimple/protrusion depths are 0.2. The results show that the rib+dimple cases provide minor increase in Nu/Nu0, f/f0 and thermal performance. Within the Reynolds number range studied, the Nu/Nu0 values of the three row rib+protrusion case is 17% ∼ 7% higher than that of the baseline case, and the decrease in f/f0 is about 10%. The thermal performance of the three row rib+protrusion case is about 16% higher than that of the baseline case. The Nu/Nu0 values of the one row rib+protrusion case is about 9% higher than that of the baseline case, and the decrease in f/f0 is about 12%. The thermal performance of the one row rib+protrusion case is about 14% higher than that of the baseline case. It can be concluded that rib+protrusion technique in rectangular channel has the potential to provide heat transfer enhancement with low pressure penalty.
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Qiu, Lu, Yanan Chen, Hongwu Deng und Jianqin Zhu. „The Counteractive Flow and Heat Transfer in a Narrow Straight Channel With Sidewall Bleeding Slots“. In ASME Turbo Expo 2018: Turbomachinery Technical Conference and Exposition. American Society of Mechanical Engineers, 2018. http://dx.doi.org/10.1115/gt2018-75606.
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In the internal cooling passages of the first stage turbine blade in the modern advanced gas turbines, the dense bleeding holes are arranged in order to supply the cold air for the external film cooling. The fluid extractions dramatically vary the flow field and convective heat transfer in the internal channels. In the current work, the flow and heat transfer in a high aspect ratio channel (AR = 4) with the side wall bleeding slots are investigated. Unlike the traditional single inlet channel, the cooling air is supplied into the channel from two entrances located at the both ends of the long straight channel. Therefore, a counteractive flow pattern is generated. The effects of the flow rate ratio of the two streams (MR = ṁ2/ṁ1) on the flow and heat transfer inside the channel are investigated, where ṁ1 and ṁ2, are the flow rate of the two streams at the two entrances. The local heat transfer is found to be zigzagging with an increase in the flow rate ratio. Interestingly, once a local flow ratio, MRx, is defined, which is based on the predicted local flow rate, all the data at different locations are converged to the same trend in the Nu/Nu0 - MRx space, where Nu is the measured local Nusselt number normalized with the Dittus-Boelter correlation, Nu0. Based on the numerical simulations, the detailed flow structure is analyzed and reported. The thermal boundary conditions in the simulations mimic the heating scheme in the experiments, where the channel wall is segmented into a matrix of copper plates which are separated by the insulations. It shows that the segmental heating scheme influences the heat transfer significantly.
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Tamunobere, Onieluan, Christopher Drewes und Sumanta Acharya. „Heat Transfer to an Actively Cooled Shroud With Blade Rotation“. In ASME Turbo Expo 2014: Turbine Technical Conference and Exposition. American Society of Mechanical Engineers, 2014. http://dx.doi.org/10.1115/gt2014-27103.
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In this paper, an experimental study of the shroud heat transfer behavior and the effectiveness of shroud cooling under the conditions of rotation is undertaken in a single stage turbine at low rotation speeds. The shroud consists of a periodic distribution of cooling holes that are 1 mm in diameter (D). The holes are angled at 45 degrees in a repeating pattern consisting of 5 unique hole pitches around the shroud circumference. Measurements of the normalized Nusselt number and film cooling effectiveness are done using liquid crystal thermography. These measurements are reported for the no coolant case, nominal blowing ratios of 1.0, 1.5, 2.0, 2.5 and 3.0, and rotation speeds of 300, 400, 500, 600 and 700 RPM. The results with no coolant injection show that the high Nu/Nu0 region migrates upstream toward the shroud leading edge with increasing rotation. The cooling results show that increasing the blowing ratio increases the area-averaged film cooling effectiveness in the shroud hole region for all rotation speeds studied. Furthermore, increasing the blade rotation speed increases the area-averaged Nusselt numbers and decreases the area-averaged film cooling effectiveness in the shroud hole region for all blowing ratios studied. As in the no-coolant case, with increasing rotation speeds, the high Nu/Nu0 region migrates upstream toward the shroud leading edge and disrupts the cooling effectiveness in this region. Finally, the results show that decreasing the shroud coolant hole spacing changes the lateral heat transfer profile from a periodic sinusoidal distribution for a shroud hole spacing of P/D = 10.4 to a more even distribution for a smaller P/D = 4.8.
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Issa, Johnny, Najib Saliba und Bchara Sidnawi. „A Numerical Investigation of the Effect of Inlet Velocity Oscillation on Heat Transfer in a Two-Dimensional Laminar Jet Impinging on an Isothermal Surface“. In ASME 2016 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2016. http://dx.doi.org/10.1115/imece2016-65144.
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Heat transfer in a laminar confined oscillating slot jet impinging on an isothermal surface is numerically investigated. A uniform inlet velocity profile, oscillating with an angle φ, is used at the jet exit. The angle φ changes in a sinusoidal form. The height-to-jet width ratio is fixed at 5. The working fluid is air with constant physical properties corresponding to Prandtl number, Pr, equal to 0.74 at ambient conditions. Reynolds number, Re, is defined based on the jet hydraulic diameter and is varied in the self-stable range between 100 and 400. Strouhal number, St, is also varied between 0.05 and 0.75. Oscillating the jet at Reynolds number equal to 100 showed no heat transfer improvement over the steady state case, regardless of the used Strouhal number values. The vortices generated by the oscillation were too weak and could barely reach the wall. The flow showed a high vulnerability to severe oscillations which drastically reduced the jet heat removal ability. The vorticity contours showed a perfect symmetry which resulted in instantaneous and average Nusselt number distributions that are symmetric about the center of the isothermal surface at x = 0. The average stagnation Nusselt number, Nu0, decreased by about 1.25% as Strouhal number is increased from 0.4 to 0.625 then dipped by 44.1% as St is further increased to 0.75, a fact that was attributed to reduction in the bulk momentum by the relatively high frequency. With Reynolds number at 250, the lowest two frequencies corresponding to St of 0.05 and 0.1, resulted in a flow field that is more developed to the right side of the channel, a phenomenon that was linked to the direction of the first jet swing. The corresponding average Nusselt number distributions were consequently asymmetric, with a significant shift to the right. This asymmetric behavior gradually disappeared as the frequency is increased. At St of 0.4 and 0.5, the average stagnation Nusselt number Nu0, showed a 2.2% increase over the steady jet case. As Strouhal number is further increased beyond 0.5, the average Nu0 gradually decreased, since the oscillation period became too short for a vortex to be strong enough to reach the wall. For Reynolds number set at 400, the oscillating condition at the inlet engaged the jet into flapping. The jet showed a tendency to a permanent lean towards one side of the channel, for all used frequencies. Flapping was more one-sided which led to a shift in the average Nusselt number distribution at low frequencies. As Strouhal number is increased to 0.75, flapping became more stable and the generated vortices were expectedly weaker due to the higher frequency. Also, at this Strouhal number value, the average Nu distribution showed the best symmetry with a 2.45% improvement of the average stagnation Nusselt number, over that of the steady state case.
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Islam, Md, L. Guangda, S. Ainane und S. Bojanampati. „Heat Transfer Enhancement With Vortex Generators“. In ASME 2019 Gas Turbine India Conference. American Society of Mechanical Engineers, 2019. http://dx.doi.org/10.1115/gtindia2019-2560.
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Abstract In this research, heat transfer and pressure drop from a tube with vortex generators (VGs) insert are numerically investigated. The effects of heights, attack angles of VGs inside a tube on heat transfer and flow behavior are investigated. CFD simulations, with and without VGs insert, are done for an air flow range (Reynolds numbers 6000 to 33000) and for a constant heat flux on the tube model surface. Four VGs are fitted in a circular pattern on the inner surface of the tube. We studied the characteristics of the delta winglet VGs for different attack angles and blockage ratios. The Nusselt number and friction factor results show the influence of the VGs insert on heat transfer and frictional factor. The maximum Nusselt number increment (Nu/Nu0) was achieved to be 1.75 while the maximum friction factor increment (f/f0) was 3.21. In order to understand the flow behavior and different vortices, path lines released by the VGs surface and details of the vortices are also studied.
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Christensen, Lasse U., Stefan Holebæk, Nisanthan Thanabalasingham, Jakob Hærvig und Henrik Sørensen. „Fully-Developed Convective Heat Transfer and Pressure Drop in a Square Duct With Baffle Inserts Using CFD Analysis“. In ASME 2020 18th International Conference on Nanochannels, Microchannels, and Minichannels collocated with the ASME 2020 Heat Transfer Summer Conference and the ASME 2020 Fluids Engineering Division Summer Meeting. American Society of Mechanical Engineers, 2020. http://dx.doi.org/10.1115/icnmm2020-1066.
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Abstract The scope of this project is to investigate how the geometry of baffles affect heat transfer and pressure loss of a fluid flow at Re = 1000 through a square duct. For this purpose, Large Eddy Simulations are performed to investigate the effect of baffle height and baffle width. Focus is on the fully-developed flow that repeats itself at streamwise stations. The flow field predicted by Computational Fluid Dynamics simulations was validated using Particle Image Velocimetry. The different designs are evaluated in terms of Nusselt number, Nu and a loss coefficient, f, which are normalised using a reference geometry consisting of a square duct without baffles. The two parameters are additionally combined into a performance parameter eta η = (Nu/Nu0)/(f / f0)(1/3). It was found that adding baffles can result in a quadrupling of η. Reducing the height of baffles decreases heat transfer, while significantly reducing pressure loss and ultimately leading to a higher η. Reducing baffle height was also found to increase the temperature gradient at the upper wall and reduce it at the lower wall. Reducing baffle width resulted in the largest temperature gradient, but lead to poor heat transfer within the fluid.
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Saha, Krishnendu, Shengmin Guo, Sumanta Acharya und Chiyuki Nakamata. „Heat Transfer and Pressure Measurements in a Lattice-Cooled Trailing Edge of a Turbine Airfoil“. In ASME Turbo Expo 2008: Power for Land, Sea, and Air. ASMEDC, 2008. http://dx.doi.org/10.1115/gt2008-51324.
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An experimental study of the heat transfer distribution and pressure drop through a converging lattice-matrix structure has been performed. This structure represents a gas turbine blade trailing-edge cooling passage. Stationary tests were performed on a scaled up model under three Reynolds numbers (24000<Re<60000). To obtain the wall temperature, the narrow band liquid crystal technique was used, and the heat transfer coefficient value was obtained using the transient method. It’s found that the Nusselt number ratio (Nu/Nu0) is around 4–5, comparing to the channel flow of similar hydraulic diameter and Re, for the whole lattice-matrix structure. Under the impingement and turning areas, the ratio can be as high as 7–8. Pressure data are taken throughout the lattice structure following the flow direction. The pressure drop increases with Reynolds number and as a result there is a decrease in the thermal performance factor at higher Reynolds number. In the present study thermal performance factor is found to be around 1–1.2. For comparison, pin fin based trailing edge configuration has a typical thermal performance factor of 0.7 to 0.85 under the same Reynolds numbers.