Academic literature on the topic 'Spacing over diameter ratio'
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Journal articles on the topic "Spacing over diameter ratio"
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Carter, R. E., I. M. Miller, and K. Klinka. "Relationships Between Growth Form and Stand Density in Immature Douglas-fir." Forestry Chronicle 62, no. 5 (October 1, 1986): 440–45. http://dx.doi.org/10.5558/tfc62440-5.
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Stem form of the whole tree and branching characteristics at whorls 6 to 10 were examined in 27-year-old Dougias-tir (Pseudoisuga menziesii [Mirb.] Franco) trees established at each of three spacings (1.8 × 1.8 m, 3.6 × 3.6 m, and 4.6 × 4.6 m) and replicated across two blocks. A total of 30 trees from each spacing were analysed. Spacings were found to affect stem, crown, and branching characteristics. Tree height, diameter at breast height, and stem diameter at the base of the live crown all increased significantly with spacing (p < 0.01), while age and height at the base of the live crown both decreased (p < 0.01). Increased spacing resulted in significantly greater branch diameters at whorls 6 to 10; and, in some whorls, an increase in branch number. Swelling of the stern at branch whorls, the number of lammas whorls, knottiness ratio, and a subjective index of stem form (higher index indicates poorer form) all increased with increased spacing (p < 0.01).The considerations involved with choosing high or low initial stocking levels are discussed and the study concludes that intensive management practices such as thinning and pruning will be necessary in all regimes if clear wood is to be produced over short rotations.
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Cook, Kevin L., and Leonard M. Pike. "OPTIMUM SPACING AND HARVEST TIME FOR `INTERMEDIATE LEAF' HYBRID PICKLING CUCUMBERS FOR ONCE-OVER MECHANICAL HARVEST." HortScience 26, no. 5 (May 1991): 488e—488. http://dx.doi.org/10.21273/hortsci.26.5.488e.
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An `intermediate leaf' hybrid pickling cucumber (TAMU 884304 X ARK H-19 `little leaf') was direct-seeded at four plant densities (94,570; 48,440; 32,290; 25,375 plants/ha) using four within-row spacings (15, 30, 45, 60cm) at two locations and two seasons. Optimum yield based on marketable fruit number, grade distribution and fruit quality occurred with 94,570 plants/ha. Optimum harvest time depended on location and season. Delayed harvest times were also evaluated. Harvests with fruit >5.1cm in diameter had severely reduced brining quality. Fruit did not enlarge or enlarged slowly to oversize. This resulted in a mixture of fruit ages within the largest marketable fruit grades. It is recommended that `little leaf' lines and their hybrids such as `intermediate leaf' be harvested when fruit 3.8 to 5.1cm in diameter appear and before oversize fruit are produced. Spacing did not significantly effect length/diameter ratio(LDR) but LDR was significantly greater for delayed harvests.
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Larocque, Guy R., and Peter L. Marshall. "Crown development in red pine stands. I. Absolute and relative growth measures." Canadian Journal of Forest Research 24, no. 4 (April 1, 1994): 762–74. http://dx.doi.org/10.1139/x94-101.
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The crown development of red pine (Pinusresinosa Ait.) plantations originating from different initial spacings was studied between 13 and 33 years of age. First, the effect of spacing on models used to predict crown width and crown ratio from diameter at breast height (DBH) and height was examined. Models for trees of different ages that included all the spacings were found to predict crown growth measures as well as separate models derived for each spacing. Second, the following crown relative growth measures were studied: crown width/crown length (crown shape ratio), crown surface/crown volume, and foliage biomass/crown volume. The way such measures changed over time under different initial spacings was studied; these findings were compared with changes in relative growth rate (RGR), which can be used to evaluate the effect of competitive stress. Crown shape ratio decreased with an increase in DBH in the absence of severe competition, and increased with DBH under severe competitive stress. The other two crown relative growth measures were always negatively correlated with DBH; this shows that large trees use their aerial growing space less efficiently than small trees at all stages of stand development. Only crown shape ratio changed in the same way as RGR.
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Nourmohammadi, Khosrow, P. K. Hopke, and J. J. Stukel. "Turbulent Air Flow Over Rough Surfaces: II. Turbulent Flow Parameters." Journal of Fluids Engineering 107, no. 1 (March 1, 1985): 55–60. http://dx.doi.org/10.1115/1.3242440.
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The objective of the present study was to examine experimentally the turbulent flow structure in a repeated rib geometry rough wall surface as a function of the ratio of the roughness height to the pipe diameter (K/D), the ratio of the spacing between the elements to the roughness height (P/K), the axial position within a rib cycle, and the Reynolds number. For small P/K values, the turbulent intensities and Reynolds shear stress variations were similar to those found for smooth wall pipe flow. Unique relationships for the u′ and v′ were found that were valid in the outer layer of the flow for all axial positions and all values of P/K and K/D.
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Zhang, Yunyan, Pingmei Ming, Runqing Li, Ge Qin, Xinmin Zhang, Liang Yan, Xinchao Li, and Xingshuai Zheng. "Numerical Analysis and Experimental Study on Fabrication of High Aspect Ratio Tapered Ultrafine Holes by Over-Growth Electroforming Process." Micromachines 10, no. 12 (November 27, 2019): 824. http://dx.doi.org/10.3390/mi10120824.
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High aspect ratio (HAR) ultrafine tapered holes (diameter ≤5 μm; AR ≥5) are the most important elements for some high-tech perforated metallic products, but they are very difficult to manufacture. Therefore, this paper proposes a nontraditional over-growth electroforming process. The formation mechanism of the HAR ultrafine tapered holes is investigated, and the factors controlling the geometric shape evolution are analyzed numerically. It was found that the geometric shape and dimensions of the holes are highly dependent on the diameter and thickness of the photoresist film patterns, but are hardly affected by the spacing between two neighboring patterns; the achievable diameter for a given hole depth becomes small with the increasing pattern diameter, but it becomes big with the increasing pattern thickness. These correlations can be well interpreted by the established two empirical equations that characterize the relationship between the minimum orifice of the tapered hole and the structural parameters of the photoresist film patterns previously formed on the substrate. Application of the fabricated 1500 tapered holes with 3-μm diameter and 17-AR as the nozzles of the medical precision nebulizer is also examined. The studies show that the over-growth electroforming process is highly applicable in fabricating the perforated metallic plate with HAR ultrafine tapered holes.
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Zhao, Guang. "Aerodynamics Study of Flow Past Two Tandem Bluff Bodies at Low Reynolds Number." Applied Mechanics and Materials 668-669 (October 2014): 138–41. http://dx.doi.org/10.4028/www.scientific.net/amm.668-669.138.
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Aerodynamics of flow past two tandem bluff bodies is a critical problem in fluid mechanics. In this work, the flow over two circular cylinders with unequal diameters in tandem arrangement is numerical investigated using lattice Boltzmann method. The diameter of the bigger one is adopted as the characteristic length, the diameter ratio is fixed as 2, and the Reynolds number is 100. Spacing between two cylinders (scaled by the characteristic length) are varied from 0 to 3 characteristic diameter, and the effects of which on the flow patterns of such a system are studied. The results show that flow patterns behind two tandem unequal circular cylinders are significantly different from that behind a single one. Due to the downstream cylinder, two classic vortex interaction modes are observed, known as destruction interaction mode and construction mode.
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Bowers, Morris B., and Issam Mudawar. "Two-Phase Electronic Cooling Using Mini-Channel and Micro-Channel Heat Sinks: Part 1—Design Criteria and Heat Diffusion Constraints." Journal of Electronic Packaging 116, no. 4 (December 1, 1994): 290–97. http://dx.doi.org/10.1115/1.2905700.
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Mini-channel (D = 2.54 mm) and micro-channel (D = 510 μm) heat sinks with a 1-cm2 heated surface were tested for their high heat flux performance with flow boiling of R-113. Experimental results yielded CHF values in excess of 200 W cm−2 for flow rates less than 95 ml min−1 (0.025 gpm) over a range of inlet subcooling from 10 to 32°C. Heat diffusion within the heat sink was analyzed to ascertain the optimum heat sink geometry in terms of channel spacing and overall thickness. A heat sink thickness to channel diameter ratio of 1.2 provided a good compromise between minimizing overall thermal resistance and structural integrity. A ratio of channel pitch to diameter of less than two produced negligible surface temperature gradients even with a surface heat flux of 200 W cm−2. To further aid in determining channel diameter for a specific cooling application, a pressure drop model was developed, which is presented in the second part of the study.
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Zheng, Shaokai, and Ellen K. Longmire. "Perturbing vortex packets in a turbulent boundary layer." Journal of Fluid Mechanics 748 (April 29, 2014): 368–98. http://dx.doi.org/10.1017/jfm.2014.185.
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AbstractA zero pressure gradient turbulent boundary layer of $\textit {Re}_{\tau }=2500$ was perturbed by a single spanwise array of finite cylinders mounted on the bounding surface and extending through the logarithmic region. The cylinder height was $H/\delta =0.2$ ($H^{+}=500$), where $\delta $ is the boundary layer thickness, with an aspect ratio ($AR$) (height/diameter) of four. Streamwise–spanwise ($x\text {--}y$) planes of the flow were examined by particle image velocimetry (PIV) up to $7\delta $ downstream at a wall-normal location of $z^{+}=300$ for cylinder array spacings ranging from $0.2\delta $ to $0.8\delta $. Average streamwise velocity fields showed a splitting, then merging pattern of cylinder wakes which occurred further downstream as the cylinder spacing increased. Based on measurements at the furthest downstream location, both the spanwise variation of average streamwise velocity and the Fourier content in the instantaneous fields suggested that the case with $0.6\delta $ cylinder spacing, which matched the dominant spanwise scale in the unperturbed flow, yielded the most persistent downstream flow organization. A flying PIV method was implemented to track specific packet structures over a range $-2<x/\delta <7$ with respect to the cylinder array, corresponding to a time scale of $12.4\delta /U_{\infty }$. Packets approaching the $0.2\delta $ spacing array first lost their organization but then regained it a distance $2\delta $ downstream, suggesting that a persistent outer layer organization propagated inwards into the log region. For arrays with larger spanwise spacing, approaching packets were generally redirected into the spanwise location midway between cylinders and sometimes enhanced.
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Abdlrahem, Maged A., and M. Hesham El Naggar. "Axial performance of micropile groups in cohesionless soil from full-scale tests." Canadian Geotechnical Journal 57, no. 7 (July 2020): 1006–24. http://dx.doi.org/10.1139/cgj-2018-0695.
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Hollow bar micropile (HBMP) groups are used for supporting large loads as an alternative foundation option to large diameter drilled shafts. In such cases, it may be necessary to increase the micropile’s diameter by increasing the drill bit diameter (Db). This paper investigates experimentally and numerically the effect of increasing Db and micropile spacing on the group performance. A field load testing program was conducted on four groups of HBMPs installed in sand; each group comprised four micropiles arranged in a square configuration. All micropiles were constructed with the same size hollow bar, Dh = 51 mm; two groups comprised micropiles constructed with drill bit, Db = 115 mm, and two groups comprised micropiles constructed with drill bit, Db = 152 mm. One group of each set was installed with spacing to micropile diameter ratio, S/Db = 3 and the other group with S/Db = 5. In addition, full 3D finite element model (FEM) was developed and calibrated to simulate the behaviour of micropile groups and to evaluate the failure load for groups that were not loaded to failure. The results demonstrated that micropile groups constructed with the large diameter drill bits displayed higher stiffness and load carrying capacity than the groups constructed with small diameter bits, which confirms the effectiveness of using a larger drill bit. In addition, the group efficiency ratio values at both working load and ultimate capacity were found to be close to unity for all groups. The ultimate skin friction values of grouted micropiles obtained from this study were higher than the values suggested by the US Federal Highway Administration for medium to very dense sand. It was also found that the settlement of the 4-HBMP group increased by 25% to 33% over that of a single HBMP due to group effect.
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Ligrani, P. M., and S. W. Mitchell. "Effects of Embedded Vortices on Injectant From Film Cooling Holes With Large Spanwise Spacing and Compound Angle Orientations in a Turbulent Boundary Layer." Journal of Turbomachinery 116, no. 4 (October 1, 1994): 709–20. http://dx.doi.org/10.1115/1.2929464.
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Experimental results are presented that describe the effects of embedded, longitudinal vortices on heat transfer and film injectant downstream of a single row of film cooling holes with compound angle orientations. Holes are spaced 7.8 hole diameters apart in the spanwise direction so that information is obtained on the interactions between the vortices and the injectant from a single hole. The compound angle holes are oriented so that their angles with respect to the test surface are 30 deg in a spanwise/normal plane projection, and 35 deg in a streamwise/normal plane projection. A blowing ratio of 0.5 is employed and the ratio of vortex core diameter to hole diameter is 1.6–1.67 just downstream of the injection holes (x/d=10.2). At the same location, vortex circulation magnitudes range from 0.15 m2/s to 0.18 m2/s. The most important conclusion is that local heat transfer and injectant distributions are strongly affected by the longitudinal embedded vortices, including their directions of rotation and their spanwise positions with respect to film injection holes. To obtain information on the latter, clockwise rotating vortices R0–R4 and counterclockwise rotating vortices L0–L4 are placed at different spanwise locations with respect to the central injection hole located on the spanwise centerline. With vortices R0–R4, the greatest disruption to the film is produced by the vortex whose downwash passes over the central hole (R0). With vortices L0–L4, the greatest disruption is produced by the vortices whose cores pass over the central hole (L1 and L2). To minimize such disruptions, vortex centers must pass at least 1.5 vortex core diameters away from an injection hole on the upwash sides of the vortices and 2.9 vortex core diameters away on the downwash sides of the vortices. Differences resulting from vortex rotation are due to secondary flow vectors, especially beneath vortex cores, which are in different directions with respect to the spanwise velocity components of injectant after it exits the holes. When secondary flow vectors near the wall are in the same direction as the spanwise components of the injectant velocity (vortices R0–R4), the film injectant is more readily swept beneath vortex cores and into vortex upwash regions than for the opposite situation in which near-wall secondary flow vectors are opposite to the spanwise components of the injectant velocity (vortices L0–L4). Consequently, higher Stanton numbers are generally present over larger portions of the test surface with vortices R0–R4 than with vortices L0–L4.
Dissertations / Theses on the topic "Spacing over diameter ratio"
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Coltrin, Ian S. "The Influence of Nozzle Spacing and Diameter on the Acoustic Emissions of Closely Spaced Supersonic Jet Arrays." BYU ScholarsArchive, 2012. https://scholarsarchive.byu.edu/etd/2935.
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The acoustic emissions from supersonic jets represent an area of significant research needs; not only in the field of aero-acoustics, but in industry as well where high pressure let down processes have been known to cause acoustically induced vibrations. A common method to reduce the acoustic emissions of such processes involves dividing the single larger supersonic flow into several smaller ones. Though this is common practice, there is not yet a current model which describes the reduction of acoustic emissions from an array of smaller supersonic jets. Current research which studies supersonic jet arrays are mainly focused on the effects of screech. Though screech is important, due to its high amplitude acoustic pressure, this research focuses on the overall acoustic emissions radiated from supersonic jet arrays which can cause severe acoustic loadings. This research investigated the acoustic emissions and shock formations from several eight by eight arrays of axisymmetric jet experimentally. The array nozzle diameters investigated ranged from 1/8 inch to 1/4 inch and the spacing over diameter ratio ranged from 1.44 to 3. The net pressure ratios investigated ranged from 2 to 24. Results revealed a strong correlation between the acoustic emissions and the shock formations of the flow. Up until a critical net pressure ratio, the overall sound pressure levels were comparable to that of a single jet within an array. At net pressure ratios beyond the critical the overall sound pressure levels transitioned to higher decibel levels; equivalent to a single jet with an equivalent exit area of an entire array. Also, the characteristic acoustic frequency emitted from a nozzle array remained ultrasonic (above 20 kHz) at lower net pressure ratios and then shifted to audible levels (between 20 Hz to 20 kHz) at net pressure ratios beyond the critical. Also, before the critical net pressure ratio the shock cells from the jets within the array remained unmerged, but at net pressure ratios beyond the critical the shock cells merged and formed lattices of weak oblique shocks at first and then strong oblique shocks as the net pressure ratio continued to increase. The critical net pressure ratio was investigated by non-dimensional analysis. The non-dimensional analysis revealed that the critical net pressure ratio was a strong linear function of the spacing over diameter ratio. A linear model was derived which is able to predict the critical net pressure ratio, and in turn, predict a critical shift in the acoustic emissions of a nozzle array.
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Nicholas, Allen Christo. "A stochastic analysis of Turbulence Intensity influence over various sizes of HAWT : Study of hypothetical relationship between Rotor Diameter and influence level of Turbulence Intensity." Thesis, Högskolan i Halmstad, Energivetenskap, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:hh:diva-31096.
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This disquisition aims for the study of turbulence intensity influence over the power performance of different sizes of turbines with the intent to validate a hypothesis. The hypothesis formulated for the analysis is the relationship between the rotor diameter (turbine size) and turbulence intensity. The hypothetical relationship is that the smaller turbines tend to experience more influence on the power performance from the turbulence in comparison with larger ones. For this examination, three different wind turbines of models Vestas V90, V100, V126 were chosen from three Swedish wind farms. The power performance of turbines at various levels of turbulence intensity were analyzed and the power deviation from the mean value due to influence of turbulence were assessed. The power deviation values of different turbines were compared at same level of wind speeds and also the power coefficients at same level of tip speed ratios were compared to validate the hypothesis. It was observed that the hypothesis seemed to appear true as higher influence on power curves were observed on V90 compared to others. Nevertheless, there were some obscene results which might be due to several factors such as influence of variation in hub height, site and inadequacy of data.Detta examensarbete syftar till att studera hur ett vindkraftverks storlek påverkar inflytande från turbulens på effektuttaget. Hypotesen är att vindkraftverk med mindre rotordiameter påverkas mer av turbulens än de större. Tre vindkraftverksmodeller (Vestas V90, V100 och V126) från svenska vindkraftsparker valdes ut. De olika modellernas effektuttag för olika grader av turbulens analyserades och avvikelsen från effektmedelvärdet jämfördes. Effektavvikelserna samt verkningsgradsavvikelsen för de olika vindkraftverksmodellerna jämfördes vid samma vindhastighet respektive löptal för att kunna testa hypotesen. Hypotesen styrks då den mista modellen (Vestas V90) påverkas mest av turbulens. Resultatet har dock troligtvis påverkats av andra faktorer såsom tornhöjd, terräng och en begränsad mängd data.
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Zhao, Shi-Bin, and 趙士賓. "Optimum Ratio of Jet Spacing-to-Jet Diameter for Confined Impinging Jets with Staggered Arrays in Heat Transfer Applications." Thesis, 1999. http://ndltd.ncl.edu.tw/handle/41234148471718844391.
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碩士國立中興大學
機械工程學系
87
The heat transfer of equilaterally staggered arrays of five confined jets vertically impinging on a flat plate is investigated. The jet diameter is 3mm. The considered ratios of s/d are individually 4, 6, 8, 12, 16 and 24. The ratios of H/d are individually 2, 3 and 4. The difference of jet total temperature and room temperature is controlled within 1℃. The ratio of heating width-to-jet diameter, (w/d), are respectively 12.5, 29.17 and 37.50. The surface heat flux on the heated area is . The Reynolds number of the center jet is 30,000. The Reynolds number of the neighboring jets are individually considered to be 30,000, 20,000, 10,000 and 0. An optimum ratio of jet spacing-to-jet diameter, (s/d)opt, is obtained for various ratios of jet height-to-jet diameter (H/d). Two numerical examples illustrating the applications of jet impingement for cooling are represented.
Book chapters on the topic "Spacing over diameter ratio"
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Kumar, K. Karthik Selva, and L. A. Kumaraswamidhas. "Wake Interaction Using Lattice Boltzmann Method." In Advances in Computer and Electrical Engineering, 223–61. IGI Global, 2018. http://dx.doi.org/10.4018/978-1-5225-4760-0.ch007.
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In this chapter, a brief discussion about the application of lattice Boltzmann method on complex flow characteristics over circular structures is presented. A two-dimensional computational simulation is performed to study the fluid flow characteristics by employing the lattice Boltzmann method (LBM) with respect to Bhatnagar-Gross-Krook (BGK) collision model to simulate the interaction of fluid flow over the circular cylinders at different spacing conditions. From the results, it is observed that there is no significant interaction between the wakes for the transverse spacing's ratio higher than six times the cylinder diameter. For smaller transverse spacing ratios, the fluid flow regimes were recognized with presence of vortices. Apart from that, the drag coefficient signals are revealed as chaotic, quasi-periodic, and synchronized regimes, which were observed from the results of vortex shedding frequencies and fluid structure interaction frequencies. The strength of the latter frequency depends on spacing between the cylinders; in addition, the frequency observed from the fluid structure interaction is also associated with respect to the change in narrow and wide wakes behind the surface of the cylinder. Further, the St and mean Cd are observed to be increasing with respect to decrease in the transverse spacing ratio.
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Ikram, Muhammad, Ali Raza, Atif Shahbaz, Haleema Ijaz, Sarfraz Ali, Ali Haider, Muhammad Tayyab Hussain, Junaid Haider, Arslan Ahmed Rafi, and Salamat Ali. "Carbon Nanotubes." In Sol Gel and other Fabrication Methods of Advanced Carbon Materials [Working Title]. IntechOpen, 2020. http://dx.doi.org/10.5772/intechopen.95442.
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Carbon nanotubes (CNTs) are referred to as carbon nano-architecture allotropes, with wrapped graphene sheets forming a cylindrical structure. CNTs are either developed by metals or narrow-band semiconductors with rolling graphene sheets in various ways. Researchers have dedicated a great deal of attention to understanding the fascinating properties of CNTs over the years, and possess certain peculiar properties, such as a high degree of stiffness, a wide ratio of length to diameter, and remarkable toughness, and are employed in a number of applications. These properties can be enhanced by scheming the diameter, nature of walls, chirality, length of CNTs which is rolled up, and depending on the synthesis process. This chapter extensively covers the various properties of CNTs and how it influences to desired applications and also explains numerous methods of synthesis and processing of CNTs with advantages and some drawbacks.
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Hillerdal, Gunnar. "Health Problems Related to Environmental Fibrous Minerals." In Geology and Health. Oxford University Press, 2003. http://dx.doi.org/10.1093/oso/9780195162042.003.0025.
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Very early in the history of mining and with the industrial applications of asbestos, it was known that a variety of mineral fibers were hazardous to health. By the 1940s, the potential risk of lung cancer, in addition to the fibrosis disorder asbestosis, one of the pneumoconioses, was described. Within twenty years, another malignant disease, mesothelioma, cancer of the tissues that surround the lung, was ascribed to asbestos exposure. It is now common knowledge that inhalation of certain mineral fibers can cause disease (Skinner et al. 1988). Because the fibers are inhaled, the lung and surrounding tissues are the primary targets, but there may be subsequent reactions in many other parts of the body. The information on disease related to fibrous materials emanates from studies of occupational environments where the dose or exposure is likely to be high and continued over long periods of time. However, it has been increasingly realized that domestic or general environmental exposure is also possible and can pose grave dangers. For a mineral fiber to be inhalable it should be less than one micron in diameter, but the length can be 10 microns or greater because the particle can align with the air stream in the bronchi and penetrate far into the lung. The ratio between length and diameter of the fiber is critical. The most dangerous fibers are very thin (one tenth of a micron in diameter or less) with a high length-diameter ratio. Another important factor is biodurability. Typically, the dangerous fibers are not broken down at all or only very slowly, with half-lives in the body of many years. They may remain in situ throughout life and can be found at autopsy. There are many varieties of fibers in the environment today, both naturally occurring and man-made. Only a few, however, fulfill the above criteria and occur in amounts where human exposure is possible. The problem fibers are collectively known as asbestos and the fibrous zeolite, erionite. There are many other fibers (Skinner et al. 1988), but their contributions to human disease are not recognized. Asbestos is not a mineralogical but a commercial term.
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Quevedo-Rojas, Ana, and Mauricio Jerez-Rico. "Mixed Forest Plantations with Native Species for Ecological Restoration in Cloud Forests of the Venezuelan Andes." In Silviculture [Working Title]. IntechOpen, 2020. http://dx.doi.org/10.5772/intechopen.95006.
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Tropical cloud forests play a fundamental role in the hydrological cycle of mountain watersheds having the largest biodiversity per unit area. In Venezuela, cloud forests are subject to intense deforestation and fragmentation by farming and cattle-ranching causing soil erosion, water cycle alteration, and biodiversity loss. Reforestation projects used exotic species as Pines and Eucalyptus, native species were rarely planted by lacking knowledge on species requirements and management. We report the performance of 25 native cloud forest species differing in shade-tolerance, planted in mixed assemblies on degraded areas. Tree survival and the individual tree variables: total height, root-collar diameter, tree-slenderness, and crown-ratio were evaluated at 1, 2, 4.5 and 7 years-old. Data was analyzed with a repeated measures analysis of variance mixed model considering species shade-tolerance, light intensity at planting and age as explanatory factors. Survival was over 80%. Shade-intolerant species displayed faster height and root-collar diameter growth. Shade-tolerant species had larger crown ratios due to persistence of lower branches; whereas, shade-intolerant showed signs of crown recession at age 7. Slenderness values from age 4.5 were indicative of good trees stability and health across treatments. The positive results have motivated landowners to establish native species plantations in critical areas with our support.
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Lee, Jun Ho, Min Soo Byun, Dahyun Yi, Kang Ko, So Yeon Jeon, Bo Kyung Sohn, Jun-Young Lee, Younghwa Lee, Haejung Joung, and Dong Young Lee. "Long-Term Exposure to PM10 and in vivo Alzheimer’s Disease Pathologies." In Advances in Alzheimer’s Disease. IOS Press, 2021. http://dx.doi.org/10.3233/aiad210012.
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Background: Previous studies indicated an association between Alzheimer’s disease (AD) dementia and air particulate matter (PM) with aerodynamic diameter <10 μm (PM10), as well as smaller PM. Limited information, however, is available for the neuropathological links underlying such association. Objective: This study aimed to investigate the relationship between long-term PM10 exposure and in vivo pathologies of AD using multimodal neuroimaging. Methods: The study population consisted of 309 older adults without dementia (191 cognitively normal and 118 mild cognitive impairment individuals), who lived in Republic of Korea. Participants underwent comprehensive clinical assessments, 11C-Pittsburg compound B (PiB) positron emission tomography (PET), and magnetic resonance imaging scans. A subset of 78 participants also underwent 18F-AV-1451 tau PET evaluation. The mean concentration of PM with aerodynamic diameter <10 μm over the past 5 years (PM10mean) collected from air pollution surveillance stations were matched to each participant’s residence. Results: In this non-demented study population, of which 62% were cognitively normal and 38% were in mild cognitive impairment state, exposure to the highest tertile of PM10mean was associated with increased risk of amyloid-β (Aβ) positivity (odds ratio 2.19, 95% confidence interval 1.13 to 4.26) even after controlling all potential confounders. In contrast, there was no significant associations between PM10mean exposure and tau accumulation. AD signature cortical thickness and white matter hyperintensity volume were also not associated with PM10mean exposure. Conclusion: The findings suggest that long-term exposure to PM10 may contribute to pathological Aβ deposition.
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Frolov, Vladimir. "Optimization of Lift-Curve Slope for Wing-Fuselage Combination." In Aerodynamics. IntechOpen, 2021. http://dx.doi.org/10.5772/intechopen.89056.
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The paper presents results obtained by the author for wing-body interference. The lift-curve slopes of the wing-body combinations are considered. A 2D potential model for cross-flow around the fuselage and a discrete vortex method (DVM) are used. Flat wings of various forms and the circular and elliptical cross sections of the fuselage are considered. It was found that the value of the lift-curve slopes of the wing-body combinations may exceed the same value for an isolated wing. An experimental and theoretical data obtained by other authors earlier confirm this result. Investigations to optimize the wing-body combination were carried within the framework of the proposed model. It was revealed that the maximums of the lift-curve slopes for the optimal midwing configuration with elliptical cross-section body had a sufficiently large relative width (more than 30% of the span wing). The advantage of the wing-fuselage combination with a circular cross section over an isolated wing for wing aspect ratio greater than 6 can reach 7.5% at the relative diameter of fuselage equal to approximately 0.2.
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Jung, Chau-Ren, Yu-Ting Lin, and Bing-Fang Hwang. "Ozone, Particulate Matter, and Newly Diagnosed Alzheimer’s Disease: A Population-Based Cohort Study in Taiwan." In Advances in Alzheimer’s Disease. IOS Press, 2021. http://dx.doi.org/10.3233/aiad210002.
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Several studies with animal research associate air pollution in Alzheimer’s disease (AD) neuropathology, but the actual impact of air pollution on the risk of AD is unknown. Here, this study investigates the association between long-term exposure to ozone (O3) and particulate matter (PM) with an aerodynamic diameter equal to or less than 2.5 μm (PM2.5), and newly diagnosed AD in Taiwan. We conducted a cohort study of 95,690 individuals’ age ≥ 65 during 2001–2010. We obtained PM10 and O3 data from Taiwan Environmental Protection Agency during 2000–2010. Since PM2.5 data is only accessible entirely after 2006, we used the mean ratio between PM2.5 and PM10 during 2006–2010 (0.57) to estimate the PM2.5 concentrations from 2000 to 2005. A Cox proportional hazards model was used to evaluate the associations between O3 and PM2.5 at baseline and changes of O3 and PM2.5 during the follow-up period and AD. The adjusted HR for AD was weakly associated with a raised concentration in O3 at baseline per increase of 9.63 ppb (adjusted HR 1.06, 95% confidence interval (CI) 1.00–1.12). Further, we estimated a 211% risk of increase of AD per increase of 10.91 ppb in O3 over the follow-up period (95% CI 2.92–3.33). We found a 138% risk of increase of AD per increase of 4.34 μg/m3 in PM2.5 over the follow-up period (95% CI 2.21–2.56). These findings suggest long-term exposure to O3 and PM2.5 above the current US EPA standards are associated with increased the risk of AD.
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Basiji, David. "Multispectral Imaging in Flow: A Technique for Advanced Cellular Studies." In Flow Cytometry for Biotechnology. Oxford University Press, 2005. http://dx.doi.org/10.1093/oso/9780195183146.003.0008.
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Flow cytometry is one of the most sophisticated technologies for the study of cellular biology, with the unique ability to analyze cell populations numbering in the millions. In addition to their great speed, flow cytometers can be configured with 10 or more detectors, so each cell can be characterized by multiple parameters corresponding to light scattered or emitted as they pass through the system. These capabilities have led to the development of a wide variety of applications for flow cytometry in cell biology, hematology, immunology, oncology, cell culture, and other fields. Nevertheless, a wide range of applications are not suited to flow cytometric analysis because the resulting data fail to capture cell morphology or the spatial distribution of signals within a cell. In contrast to conventional flow cytometry, microscopy can elucidate cell morphology by a number of means, including absorbed light imaging (brightfield), scattered light imaging (darkfield), and fluorescence imaging. An image of a typical mammalian cell measuring approximately 10 mm in diameter will cover over 300 pixels, assuming a detector resolution of 0.5mm per pixel. Hence, even a single cell image represents orders of magnitude more data than is acquired by a flow cytometric analysis of that same cell and therefore may represent far more information about that cell. In theory, a set of brightfield, darkfield, and fluorescence images of each cell would provide all the information of flow cytometry plus morphological features, such as the nuclear to cytoplasmic ratio, membrane texture, the distribution of a fluorescent probe, and so forth. However, as a practical matter, it is difficult to acquire and compare more than a few images of a cell because of the need to change fluorescence filter combinations, reconfigure the microscope for brightfield and darkfield imaging, and register the various images to compensate for shifts and distortion from the different optical arrangements. As a result, flow cytometry and microscopy have remained complementary techniques. The goal of imaging cells in flow has been elusive, despite several approaches that have achieved various levels of success over the last several decades.
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Chen, Jen-Hau, Tsung-Yu Kuo, Hwa-Lung Yu, Charlene Wu, Su-Ling Yeh, Jeng-Min Chiou, Ta-Fu Chen, and Yen-Ching Chen. "Long-Term Exposure to Air Pollutants and Cognitive Function in Taiwanese Community-Dwelling Older Adults: A Four-Year Cohort Study." In Advances in Alzheimer’s Disease. IOS Press, 2021. http://dx.doi.org/10.3233/aiad210022.
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Background: Previous studies have assessed limited cognitive domains with relatively short exposure to air pollutants, and studies in Asia are limited. Objective: This study aims to explore the association between long-term exposure to air pollutants and cognition in community-dwelling older adults. Methods: This four-year prospective cohort study recruited 605 older adults at baseline (2011–2013) and 360 participants remained at four-year follow-up. Global and domain-specific cognition were assessed biennially. Data on PM2.5 (particulate matter ≤ 2.5 μm diameter, 2005–2015), PM10 (1993–2015), and nitrogen dioxide (NO2, 1993–2015) were obtained from Taiwan Environmental Protection Administration (TEPA). Bayesian Maximum Entropy was utilized to estimate the spatiotemporal distribution of levels of these pollutants. Results: Exposure to high-level PM2.5 (>29.98 μg/m3) was associated with an increased risk of global cognitive impairment (adjusted odds ratio = 4.56; β = −0.60). High-level PMcoarse exposure (>26.50 μg/m3) was associated with poor verbal fluency (β = −0.19). High-level PM10 exposure (>51.20 μg/m3) was associated with poor executive function (β = −0.24). Medium-level NO2 exposure (>28.62 ppb) was associated with better verbal fluency (β = 0.12). Co-exposure to high concentrations of PM2.5, PMcoarse or PM10 and high concentration of NO2 were associated with poor verbal fluency (PM2.5 and NO2: β = −0.17; PMcoarse and NO2: β = −0.23; PM10 and NO2: β = −0.21) and poor executive function (PM10 and NO2: β = −0.16). These associations became more evident in women, apolipoprotein ε4 non-carriers, and those with education > 12 years. Conclusion: Long-term exposure to PM2.5 (higher than TEPA guidelines), PM10 (lower than TEPA guidelines) or co-exposure to PMx and NO2 were associated with poor global, verbal fluency, and executive function over 4 years.
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"Marine Artificial Reef Research and Development: Integrating Fisheries Management Objectives." In Marine Artificial Reef Research and Development: Integrating Fisheries Management Objectives, edited by Daniel J. Pondella, Jonathan P. Williams, Chelsea M. Williams, Jeremy T. Claisse, and David Witting. American Fisheries Society, 2018. http://dx.doi.org/10.47886/9781934874516.ch10.
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<em>Abstract</em>.—The subtidal rocky reefs that surround the Palos Verdes Peninsula in Los Angeles County, California, USA are subject to multiple anthropogenic impacts, including many (at least partially) human-induced landslides over the past half century, which have resulted in chronic sedimentation (e.g., reef burial and scour) and associated turbidity effects along a major stretch of this coastline. The amount of rocky reef habitat has significantly decreased; as such, determining the optimum technique for restoring this lost habitat is the focus of this study. Over the past decade, we mapped and intensively surveyed the nearshore physical and biological characteristics both inside this impacted area and in surrounding reference areas that contain extensive rocky reef habitat with established kelp forests. Notable among all survey locations is a relatively high-relief (~5 m) area of reef within the sediment impacted area that consistently has the highest fish biomass density among anywhere on the peninsula. The high structural relief prevents sediment accumulation, scour, and subsequent reef burial, and this reef ultimately served as the example for the design of sets of quarry rock reef “blocks” that together form the proposed restoration reef. Our primary objective was to use the 63,500 metric tons of quarry rock the budget would allow us to create the most productive habitat by restoring the natural reef environment while balancing scientific study design considerations (i.e., replicated reef components at multiple spatial scales) with maximizing the potential for an effective restoration effort across the range of important species and overall kelp forest biodiversity. To meet this objective, we considered multiple criteria that incorporated engineering specifications and biological performance and were informed by the scientific literature and results of natural and artificial reef surveys in this region. Ultimately, the design incorporated heterogeneity at multiple spatial scales while attempting to maximize high relief components, surface area to volume ratio, perimeter, ecotones, and small-scale current flow features and nutrient flux and while being consistent with the size of natural reefs along the Palos Verdes Peninsula. Further, placement and spacing of individual reef blocks (i.e., 2 × 48 m heterogeneous quarry rock reefs) included space for sand channels between blocks to permit sediment transport and create sand/rock ecotone habitats while remaining close enough to each other and existing natural reefs to maintain biological connectivity. Reef blocks were also located at the depth (15–20 m) where the most productive reef habitat in the region was observed. Finally, we discuss a proposed pre- and post-construction monitoring program and additional studies that could be performed that would leverage the replicated elements in the restoration reef design to inform future reef restoration programs.
Conference papers on the topic "Spacing over diameter ratio"
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Mohany, Atef, and Samir Ziada. "A Parametric Study of the Resonance Mechanism of Two Tandem Cylinders in Cross-Flow." In ASME 2006 Pressure Vessels and Piping/ICPVT-11 Conference. ASMEDC, 2006. http://dx.doi.org/10.1115/pvp2006-icpvt-11-93085.
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A parametric study has been performed to investigate the effect of cylinder diameter on the acoustic resonance mechanism of two tandem cylinders exposed to cross-flow in a duct. Three spacing ratios corresponding to different flow regimes inside the “proximity interference” region are considered, L/D = 1.5, 1.75 and 2.5, where L is the spacing between the cylinders and D is the diameter. For each spacing ratio, six cylinder diameters in the range of D = 7.6 mm to 27.5 mm, have been tested. For small diameter cylinders, the acoustic resonance mechanism of the tandem cylinders seems to be similar to that observed for single cylinders. However, for larger diameter cylinders, the resonance of a given acoustic mode occurs over two different ranges of flow velocity. The first resonance range, the pre-coincidence resonance, occurs at flow velocities much lower than that of frequency coincidence. The second resonance range, the coincidence resonance, is initiated near the condition of frequency coincidence. Thus, the occurrence and the intensity of the pre-coincidence resonance are found to be strongly dependent on the diameter of the cylinders. It is shown that increasing the cylinder diameter affects several flow parameters, which make the tandem cylinders more susceptible to the pre-coincidence acoustic resonance.
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Siroka, Shawn, Melissa Shallcross, and Stephen Lynch. "Unsteady Heat Transfer Around Low Aspect Ratio Cylinders in an Array." In ASME 2016 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2016. http://dx.doi.org/10.1115/imece2016-66783.
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Cylindrical pins, often called pin fins, are used to create turbulence and promote convective heat transfer within many devices, ranging from computer heat sinks to the trailing edge of jet engine turbine blades. Previous experiments have measured the time-averaged heat transfer over a single pin as well as the flow fields around the pin. However, in this study, focus is placed on the instantaneous heat flux around the centerline of a low aspect-ratio pin within an array. Time-mean and unsteady convective heat flux are measured around the circumference of an isothermal heated test pin via a microsensor located at the surface. The pin is positioned at various locations within a staggered array in a large-scale wind tunnel. Reynolds numbers from 3,000 to 50,000, based on pin diameter and maximum velocity between pins, are tested with a streamwise spacing of 1.73 diameters between rows, a spanwise spacing of 2 diameters, and a pin height of 1 diameter. The time-averaged and standard deviation of convective heat flux around the pin is higher over most of the pin surface for pins in downstream row positions of an array relative to the first row pin, except in the wake which has similar levels for all rows. For a given pin position in the array, as the Reynolds number increases, the point of minimum heat transfer moves circumferentially upstream on the pin fin, corresponding to earlier transition of the pin boundary layer. Also, for a given Reynolds number, the minimum heat transfer point on the pin circumference moves upstream for pins further into the array, due to the high turbulence levels within the array which cause early transition. For a single pin row with no downstream pins, heat transfer fluctuations are very high on the backside of the pin due to the significant unsteadiness in the pin wake, but heat transfer fluctuations are suppressed for a pin with downstream rows due to the confining effects of the close spacing. The results from this study can be used to design pin-fin arrays that take advantage of unsteadiness and increase overall convective heat transfer for various industry components.
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Shevade, Shantanu S., Muhammad M. Rahman, and Rasim O. Guldiken. "Turbulent Multi-Jet Air Impingement for Applications in Commercial Cooking." In ASME 2018 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2018. http://dx.doi.org/10.1115/imece2018-88635.
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Convective heat transfer coefficient and its interdependency with various key parameters is analyzed for turbulent multi-jet impingement. Air is used as the working fluid impinging on the flat surface via a three-nozzle arrangement. A thorough investigation of velocity and temperature distribution is performed by varying Nozzle Velocity, Height over Diameter ratio (H/D) and Spacing over Diameter ratio (S/D). Convective heat transfer coefficient, average impingement surface temperature, and heat transfer rate are calculated over the impingement surface. It was found that higher S/D ratios result in higher local heat transfer coefficient values near stagnation point. However, increased spacing between the neighboring jets results in less coverage of the impingement surface reducing the average heat transfer. Lower H/D ratios result in higher heat transfer coefficient peaks. The peaks for all three nozzles are more uniform for H/D ratios between 6 and 8. For a fixed nozzle velocity, heat transfer coefficient values are directly proportional to nozzle diameter. For a fixed H/D and S/D ratio, heat transfer rate and average impingement surface temperature increase as the nozzle velocity increases until it reaches a limiting value. Further increase in nozzle velocity causes drop in heat transfer rate due to ingress of large amounts of cold ambient air in the cooking space.
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Chyu, Minking K., Sean C. Siw, and Hee Koo Moon. "Effects of Height-to-Diameter Ratio of Pin Element on Heat Transfer From Staggered Pin-Fin Arrays." In ASME Turbo Expo 2009: Power for Land, Sea, and Air. ASMEDC, 2009. http://dx.doi.org/10.1115/gt2009-59814.
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A pin-fin array is a compact heat exchanger and widely used for cooling of turbine airfoils. This study is to experimentally examine the effects of pin height or height-to-diameter ratio (H/D) on the heat transfer from a pin-fin array. The test models are designed to facilitate three different H/D ratios, from 2 to 4, with a staggered pin-fin array of inter-pin spacing 2.5 times the pin diameter (S/D = X/D = 2.5) in both longitudinal and transverse directions. The Reynolds number ranges from 10,000 to 30,000. The experiment uses a hybrid technique based on the transient liquid-crystal imaging to obtain detailed local heat transfer coefficients over both the pin-fin surface and endwalls. Overall array-averaged heat transfer increases with the H/D value or pin height. Most of the heat transfer contribution for H/D>2 comes from the pins rather than the endwall. However, higher H/D leads to a greater pressure loss. As a measure of heat transfer enhancement per pressure loss, H/D = 2 leads to the highest performance index and H/D = 4 is the lowest.
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Voet, Michael T., Craig P. Fernandes, Zachary Little, Erik Fernandez, and Jay Kapat. "Effect of Density Ratio on Multi-Row Film Cooling Performance." In ASME Turbo Expo 2017: Turbomachinery Technical Conference and Exposition. American Society of Mechanical Engineers, 2017. http://dx.doi.org/10.1115/gt2017-64097.
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This study is an investigation into the effects of density ratio on the jet structure of different film cooling configurations. A simple-shaped cylindrical hole is tested at a tight spacing, which has a lateral and streamwise pitch-to-hole-diameter ratio of 7.5. Each of the holes are 3.8mm in diameter, and have a hole length-to-diameter ratio of 11.2. The holes are inclined at 20°. The cylindrical hole shapes were machined from an aluminum plate. Two different density ratios of nominally 1 and 1.5, are achieved by alternating the coolant gas between air and CO2 respectively, while maintaining a constant freestream velocity of 36.2 m/s. In order to compare cases between different densities, various ratios are independently matched for both density ratios. Blowing ratios comparisons made at 0.3 and 0.5, accompanied by comparisons of momentum flux ratio and velocity ratio at 0.1 and 0.3, respectively. Particle image velocimetry (PIV) is utilized to measure the flow field of the centerline planes of the film cooling arrays over the two density ratios. This data is then used to investigate flow interactions as coolant leaves the film cooling hole, and structure of the jet as it enters and mixes with the freestream. When comparing density ratio effects at low blowing and momentum flux ratios, increased turbulence intensities are seen closer to the surface for CO2 injection. This suggests that the overall performance of the film decreases with increasing density ratio at these low mass flux and momentum flux cases. However, when increasing blowing ratio, the higher density injection is seen to have lower levels of turbulence in the near wall region, when compared to that of the lower density fluid. This suggests that as blowing ratio increases, the higher density fluid out performs the lower density fluid. When a low constant velocity ratio is observed, the higher density fluid is seen to have decreased levels of turbulence, again suggesting that the higher density fluid out performs the low density fluid.
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Alzahrani, Yasser S., Lesley M. Wright, Andrew Chen, and Je-Chin Han. "Jet Impingement Heat Transfer in a Rectangular Channel With Smooth and Pinned Target Walls." In ASME Turbo Expo 2021: Turbomachinery Technical Conference and Exposition. American Society of Mechanical Engineers, 2021. http://dx.doi.org/10.1115/gt2021-59343.
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Abstract An experimental study was completed to quantify heat transfer enhancement, pressure loss, and crossflow effect within a channel of inline impinging jets. The jet diameter is 5.08 mm and the jet-to-jet spacing in the streamwise and spanwise directions is fixed at x/d = 11.1 and y/d = 5.9, respectively. The effect of jet-to-target surface spacing was considered with z/d = 3 and 6. For both of the jet-to-target surface spacings, a smooth surface, the reference case, and a surface roughened with partial height pins were investigated. The roughened surface has a staggered array of 120 partial height copper pin fins. The pin to jet diameter and the pin height to diameter ratios are D/d = 0.94 and H/D = 1.6, respectively. Regionally averaged heat transfer coefficient distributions were measured on the target surface, and these distributions were coupled with pressure measurements through the array. The heat transfer augmentation and pressure penalty were investigated over a range of jet Reynolds numbers (10K–70K). The results show high discharge coefficients for all the cases. The channels with the tight jet-to-target surface spacing experience double the cross-flow effect of its increased spacing counterpart. The addition of surface roughness showed a negligible effect on the crossflow. The best heat transfer performance was observed in the impingement channel with the pinned target surface at z/d = 3.
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Donahoo, E. E., C. Camci, A. K. Kulkarni, and A. D. Belegundu. "A Computational Visualization of Three Dimensional Flow: Finding Optimum Heat Transfer and Pressure Drop Characteristics From Short Cross-Pin Arrays and Comparison With Two Dimensional Calculations." In ASME 1999 International Gas Turbine and Aeroengine Congress and Exhibition. American Society of Mechanical Engineers, 1999. http://dx.doi.org/10.1115/99-gt-257.
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There are many heat transfer augmentation methods that are employed in turbine blade design, such as impingement cooling, film cooling, serpentine passages, trip strips, vortex chambers, and pin fins. The use of crosspins in the trailing edge section of turbine blades is commonly a viable option due to their ability to promote turbulence as well as supply structural integrity and stiffness to the blade itself. Numerous crosspin shapes and arrangements are possible, but only certain configurations offer high heat transfer capability while maintaining taw total pressure loss. This study preseots results from 3-D numerical simulations of airflow through a turbine blade internal cooling passage. The simulations model viscous flow and heat transfer over full crosspins of circular cross-section with fixed height-to-diameter ratio of 0.5, fixed transverse-to-diameter spacing ratio of 1.5, and varying streamwise spacing. Preliminary analysis indicates that endwall effects dominate the flow and heat transfer at lower Reynolds numbers. The flow dynamics involved with the relative dose proximity of the endwalls for such short crosspins have a definite influeoce on crosspin efficiency for downstream rows.
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Ligrani, Phillip M., and Stephen W. Mitchell. "Effects of Embedded Vortices on Injectant From Film Cooling Holes With Large Spanwise Spacing and Compound Angle Orientations in a Turbulent Boundary Layer." In ASME 1993 International Gas Turbine and Aeroengine Congress and Exposition. American Society of Mechanical Engineers, 1993. http://dx.doi.org/10.1115/93-gt-211.
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Experimental results are presented which describe the effects of embedded, longitudinal vortices on heat transfer and film injectant downstream of a single row of film cooling holes with compound angle orientations. Holes are spaced 7.8 hole diameters apart in the spanwise direction so that information is obtained on the interactions between the vortices and the injectant from a single hole. The compound angle holes are oriented so that their angles with respect to the test surface are 30 degrees in a spanwise/normal plane projection, and 35 degrees in a streamwise/normal plane projection. A blowing ratio of 0.5 is employed and the ratio of vortex core diameter to hole diameter is 1.6–1.67 just downstream of the injection holes (x/d=10.2). At the same location, vortex circulation magnitudes range from 0.15 m2/s to 0.18 m2/s. The most important conclusion is that local heat transfer and injectant distributions are strongly affected by the longitudinal embedded vortices, including their directions of rotation and their spanwise positions with respect to film injection holes. To obtain information on the latter, clockwise rotating vortices R0-R4 and counter-clockwise rotating vortices L0-L4 are placed at different spanwise locations with respect to the central injection hole located on the spanwise centerline. With vortices R0-R4, the greatest disruption to the film is produced by the vortex whose downwash passes over the central hole (R0). With vortices L0-L4, the greatest disruption is produced by the vortices whose cores pass over the central hole (L1 and L2). To minimize such disruptions, vortex centers must pass at least 1.5 vortex core diameters away from an injection hole on the upwash sides of the vortices and 2.9 vortex core diameters away on the downwash sides of the vortices. Differences resulting from vortex rotation are due to secondary flow vectors, especially beneath vortex cores, which are in different directions with respect to the spanwise velocity components of injectant after it exits the holes. When secondary flow vectors near the wail are in the same direction as the spanwise components of the injectant velocity (vortices R0-R4), the film injectant is more readily swept beneath vortex cores and into vortex upwash regions than for the opposite situation in which near-wall secondary flow vectors are opposite to the spanwise components of the injectant velocity (vortices L0-L4). Consequently, higher Stanton numbers are generally present over larger portions of the test surface with vortices R0-R4 than with vortices L0-L4.
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Siw, Sin Chien, Minking K. Chyu, Tom I. P. Shih, and Mary Anne Alvin. "Effects of Pin Detached Space on Heat Transfer and From Pin Fin Arrays." In ASME Turbo Expo 2010: Power for Land, Sea, and Air. ASMEDC, 2010. http://dx.doi.org/10.1115/gt2010-23227.
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Heat transfer and pressure characteristics in a rectangular channel with pin-fin arrays of partial detachment from one of the endwalls have been experimentally studied. The overall channel geometry (W = 101.6 mm, E = 25.4 mm) simulates an internal cooling passage of wide aspect ratio (4:1) in a gas turbine airfoil. With a given pin diameter, D = 6.35 mm = 1/4 E, three different pin-fin height-to-diameter ratios, H/D = 4, 3, and 2, were examined. Each of these three cases corresponds to a specific pin array geometry of detachment spacing (C) between the pin-tip and one of the endwalls, i.e. C/D = 0, 1, 2, respectively. The Reynolds number, based on the hydraulic diameter of the un-obstructed cross-section and the mean bulk velocity, ranges from 10,000 to 25,000. The experiment employs a hybrid technique based on transient liquid crystal imaging to obtain distributions of the local heat transfer coefficient over all of the participating surfaces, including the endwalls and all the pin elements. Experimental results reveal that the presence of a detached space between the pin-tip and the endwall have a significant effect on the convective heat transfer and pressure loss in the channel. The presence of pin-to-endwall spacing promotes wall-flow interaction, generates additional separated shear layers, and augments turbulent transport. In general, an increase in detached spacing, or C/D leads to lower heat transfer enhancement and pressure drop. However, C/D = 1, i.e. H/D = 3, of a staggered array configuration exhibits the highest heat transfer enhancement, followed by the cases of C/D = 0 and C/D = 2, i.e. H/D = 4 or 2, respectively.
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Hoang, Huy Trong, and Hamid R. Rahai. "Numerical and Experimental Investigations of a Turbulent Jet From a Round Ribbed Tube." In ASME 2002 Joint U.S.-European Fluids Engineering Division Conference. ASMEDC, 2002. http://dx.doi.org/10.1115/fedsm2002-31274.
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Results of numerical and experimental investigations of turbulent jet from a round ribbed tube are presented. The round ribbed tube is a coil-inserted tube. The ratio of the coil wire diameter to the tube inside diameter, d/D, is 0.1 and the ratio of the coil pitch spacing to the tube inside diameter, p/D, is 1.2. The coil is placed inside the tube such that it terminates at the tube outlet. The standard k-e turbulence model along with the control volume method is used in the numerical calculations. The numerical results provided more insights into the flow characteristics in the radial planes. Results show that the coil inserts generates a weak swirl at the tube outlet that dissipates at an approximate distance of X/D = 1 where at this location the generated free vortices off the coil become the main mechanism behind the entrainment and mixing process. Comparisons of the numerical and experimental results show over estimation of the results by the numerical method.