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Book Flow and Heat Transfer Characteristics of Impinging Circular Synthetic Jets

Download or read book Flow and Heat Transfer Characteristics of Impinging Circular Synthetic Jets written by Meng Li and published by . This book was released on 2008 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Book Synthetic Jet Impingement Heat Transfer from a Circular Cylinder

Download or read book Synthetic Jet Impingement Heat Transfer from a Circular Cylinder written by Krishan Gopal and published by . This book was released on 2020 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: The last decade has seen a dramatic rise in the research on synthetic jet (SJ) impingement cooling and heat transfer. This is primarily due to the many advantages of a SJ that include its low cost, simple structure, light weight, ease of installation and ability to be miniaturised using MEMs technology, making it a very promising alternative to other technologies in use. Consequently, a large body of literature exists on the impingement of SJ normally on a heated flat surface. The demand for cooling technologies however is not limited to target objects having flat surfaces only. Real applications can present a whole range of geometrical situations, with curved surfaces, and tight spaces with bounding walls. In spite of this, there exists very little research and information beyond the SJ impinging on flat surfaces in unconfined environments. An obvious deviation from a flat surface is a surface with curvature. For the specific situation of a circular cylinder, very few studies, if any, have been carried out in the past for analysing the heat transfer characteristics of SJ impingement. This research work was therefore aimed at investigating the flow and heat transfer characteristics of a slot synthetic jet (SJ) impinging on a circular cylinder. Specifically, it focussed on the influence of the geometric arrangements and flow conditions on the flow dynamics of the slot SJ, flow characteristics associated with the SJ impingement on a circular cylinder and the resulting thermal behaviour of the SJ. A bench-top synthetic jet actuator driven by a magnetic shaker via a loudspeaker diaphragm was utilised for the study. The SJ was generated from a slot of dimensions w = 6.4 mm x h = 160 mm (aspect ratio h/w of 25), with a jet Reynolds number of 2,400-3,900 (based on the slot width). To help understand the characteristics of the impingement fluid dynamics and heat transfer, a detailed investigation of the SJ flow field (in the absence of the cylinder) was first carried out. In this regard, an important aspect of the research was aimed at generating detailed understanding of the SJ flow-field characteristics in a bounded region. In a number of generic situations, this work is of high importance as the SJ could potentially be deployed for cooling applications in constrained environments. To attain a constrained environment, two parallel sidewalls were mounted along the shorter side of the slot extending in the streamwise direction to constrain the flow along the slot span. Hot-wire anemometry was used to explore the flowfield characteristics of the SJ ensuing in both a free (i.e. without sidewalls) and the constrained environment. To establish the flow and thermal characteristics of the SJ impingement, two instrumented aluminium cylinders of diameter, D of 19 mm, having a curvature ratio D/w of 3 were fabricated. The first was equipped for unsteady surface pressure measurements, while the second with a uniform surface temperature for heat transfer analysis. The cylinders were traversed along the jet centreline over non-dimensional distances from the slot of H/w = 5-50, corresponding to the SJ jet near-field through the developing region to the fully developed region. In addition, smoke flow visualizations were conducted to gain insights into the flow dynamics associated with the SJ flow-field with and without sidewalls, and SJ impinging on the cylinder. The experimental investigation for the SJ with and without sidewalls revealed that the presence of the sidewalls strongly influences the SJ flow-field. For instance, jet spreading rate reduced by almost 31.5 % with a corresponding rise in the statistically two-dimensional region in the slot downstream with the inclusion of the sidewalls. In addition, the phenomenon of axisswitching was found to be absent in the SJ flow-field in the presence of the sidewalls. Other jet properties such as the turbulence intensity, skewness, and flatness factors further revealed the differences in the flow-field of the two configurations. Furthermore, the experimental results for the SJ impinging on a circular cylinder showed that the flow-field behaviour differs significantly from that of a cylinder in uniform flow and is largely affected by the jet-cylinder separation distance and the operating environment i.e., free or constrained. For instance, the plots of the pressure distribution and normalized standard deviation of the fluctuating pressure around the cylinder surface revealed higher flow fluctuations associated with SJ impingement. The flow visualization and the hot wire measurements further unveiled that there was no obvious vortex shedding that occurs in the cylinder wake; instead evidence for vortex dipoles rising from the cylinder surface was found, on either side of the cylinder. Under uniform cylinder surface temperature conditions, the thermal performance of SJ impingement was found to be governed by the Reynolds number, jet cylinder separation distance and the excitation frequency, as might be expected from the literature on SJ impingement on flat surfaces. The SJ was found to perform better in the constrained environment, attributed to relatively higher flow fluctuations developed by the complex interaction of the vortex with the sidewall boundary layer and the cylinder. Almost 12% higher average heat transfer was observed in the case of the constrained environment over the range of parameters employed in the current work. Moreover, a strong dependence of heat transfer on the jet cylinder separation distance was also found. In contrast to the SJ impinging on flat target surfaces where the maximum heat transfer was attained in the intermediate field, at H/w = 14 to 18, for SJ impingement on the circular cylinder however, this was consistently attained in the near field i.e., H/w = 5. Also, the thermal performance as a function of the flow Reynolds number was found comparable to the uniform flow case, when the Reynolds number was based on the approach flow velocity (i.e. local velocity based on the cylinder location) instead of the velocity at the slot exit. The present study revealed for the first time, the flow and heat transfer behaviour of the SJ impinging on a circular cylinder in free and constrained environments. The results of the study may serve as a guide for SJ based solutions for various heating or cooling applications.

Book Flow and Heat Transfer of Impinging Synthetic Jets

Download or read book Flow and Heat Transfer of Impinging Synthetic Jets written by Arnau Miró Jané and published by . This book was released on 2019 with total page 129 pages. Available in PDF, EPUB and Kindle. Book excerpt: Synthetic jets are produced by the oscillatory movement of a membrane inside a cavity, causing fluid to enter and leave through a small orifice. This results in a net jet that is able to transfer kinetic energy and momentum to a fluid medium without the need of an external fluid source. This is why synthetic jets are interesting and will have key roles in a wide range of relevant applications such as active flow control, thermal cooling or fuel mixing. From the phenomenological point of view, synthetic jets are formed by elaborate flow patterns given their non-linear nature and, under certain conditions, unstable complex flows can be observed. The present dissertation is focused on the investigation of the fluid flow and thermal performance of synthetic jets. Two different synthetic jet actuator geometries (i.e., slotted and circular) are studied. The jets in both configurations are confined by two parallel isothermal plates with an imposed temperature difference, and impinge into a heated plate located at a certain distance from the actuator orifice. The unsteady three-dimensional Navier-Stokes equations are solved for a range of Reynolds numbers using time-accurate numerical simulations. Moreover, a detailed model of the actuator that uses Arbitrary Lagrangian-Eulerian (ALE) formulation to account for the movement of the actuator membrane is developed. This model, based on the governing numbers of the flow, is used to conduct the numerical analyses. The flows obtained in both configurations are noticeably different and three-dimensional for almost all the Reynolds numbers considered. The jet in the slotted configuration is formed by a pair of vortices that undergo turbulent transition and eventually coalesce into the jet. The external flow is dominated by two major recirculation structures that find their counterparts inside the actuator cavity. A new vortical structure, observed in confined slotted jets, appears as an interaction of the synthetic jet flow with the bottom wall and results in a change on the jet's heat transfer mechanisms. On the other hand, the jet in the circular configuration presents three different flow regions that have been identified according to the literature: the main vortex ring, the trailing jet and the potential core. In this case, the external flow is dominated by the main vortex ring and the trailing jet, thus presenting a different morphology and heat transfer behavior than the slotted configuration. A detailed analysis of the vortex trajectories has shown that the advected vortices on the circular configuration reach the impingement before their slotted counterparts. Distributions of turbulent kinetic energy at the expulsion and vortex swirl and shear strength have revealed that the flow on the circular jet is mostly concentrated near the jet centerline, while it is more spread for the slotted configuration. For these reasons, at the same jet ejection velocity and actuator geometry, synthetic jet formation on the circular configuration can occur at higher frequencies than on the slotted configuration. The analysis of the synthetic jet outlet temperature has shown that assuming a uniform profile is reasonable if the Reynolds number is high enough. Moreover, the outlet jet temperature is significantly higher than the cold plate temperature. The two configurations present different impinging behaviors due to the differences on the flow. Heat transfer analysis on the hot wall has revealed that the circular configuration reaches a higher heat transfer peak than the slotted configuration, however, heat transfer decays faster in the circular configuration when moving away from the jet centerline. Eventually, correlations for the heat transfer at the hot wall and the outlet temperature with the Reynolds number are proposed. They can be useful to include the cavity effects when using simplified models that do not account for actuator cavity.

Book Mechanical Measurements

Download or read book Mechanical Measurements written by S.P. Venkateshan and published by Springer Nature. This book was released on 2021-07-01 with total page 560 pages. Available in PDF, EPUB and Kindle. Book excerpt: p="" This book focuses both on the basics and more complex topics in mechanical measurements such as measurement errors & statistical analysis of data, regression analysis, heat flux, measurement of pressure, and radiation properties of surfaces. End of chapter problems, solved illustrations, and exercise problems are presented throughout the book to augment learning. It is a useful reference for students in both undergraduate and postgraduate programs. ^

Book Flow Control Techniques and Applications

Download or read book Flow Control Techniques and Applications written by Jinjun Wang and published by Cambridge University Press. This book was released on 2019 with total page 293 pages. Available in PDF, EPUB and Kindle. Book excerpt: Master the theory, applications and control mechanisms of flow control techniques.

Book Local Heat transfer Characteristics of a Row of Circular Air Jets Impinging on a Concave Semicylindrical Surface

Download or read book Local Heat transfer Characteristics of a Row of Circular Air Jets Impinging on a Concave Semicylindrical Surface written by John N. B. Livingood and published by . This book was released on 1973 with total page 36 pages. Available in PDF, EPUB and Kindle. Book excerpt: An experimental study was made of the local heat-transfer characteristics of air jets impinging on the concave side of a right circular semicylinder. A correlation was developed for expressing individual and combined effects of a number of dimensionless variables on the normalized Nusselt number distributions. Results of the present study are in good agreement with those of other investigators.

Book Investigation of Synthetic Jets Heat Transfer and Flow Field

Download or read book Investigation of Synthetic Jets Heat Transfer and Flow Field written by Carlo Salvatore Greco and published by Youcanprint. This book was released on 2015-04-30 with total page 187 pages. Available in PDF, EPUB and Kindle. Book excerpt: Synthetic jets are devices able to “synthetize” a jet from the ambient in which they are embedded through a simple membrane oscillation inside a cavity with an orifice. Such features make them high reliable, silent and easy to be miniaturized. For these reasons, they are widely investigated as electronic cooling devices. The present research is focused on the design and analysis of a different type of synthetic jet device compared to its single classical configuration. Such a device his experimentally characterized through the study of its free and impinging flow field and the evaluation of its heat transfer performance.

Book Flow and Heat Transfer Characteristics of an Impinging Jet with Crossflow

Download or read book Flow and Heat Transfer Characteristics of an Impinging Jet with Crossflow written by Brian Chee Yuen Cheong and published by . This book was released on 2002 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Book Jet Array Impingement with Crossflow Correlation of Streamwise Resolved Flow and Heat Transfer Distributions

Download or read book Jet Array Impingement with Crossflow Correlation of Streamwise Resolved Flow and Heat Transfer Distributions written by L. W. Florschuetz and published by . This book was released on 1981 with total page 68 pages. Available in PDF, EPUB and Kindle. Book excerpt: Correlations for heat transfer coefficients for jets of circular offices and impinging on a surface parallel to the jet orifice plate are presented. The air, following impingement, is constrained to exit in a single direction along the channel formed by the jet orifice plate and the heat transfer (impingement) surface. The downstream jets are subjected to a crossflow originating from the upstream jets. Impingement surface heat transfer coefficients resolved to one streamwise jet orifice spacing, averaged across the channel span, are correlated with the associated individual spanwise orifice row jet and crossflow velocities, and with the geometric parameters. (NTRL site)

Book Synthetic Jets

    Synthetic Jets

    Book Details:
  • Author : Kamran Mohseni
  • Publisher : CRC Press
  • Release : 2014-09-17
  • ISBN : 1439868115
  • Pages : 378 pages

Download or read book Synthetic Jets written by Kamran Mohseni and published by CRC Press. This book was released on 2014-09-17 with total page 378 pages. Available in PDF, EPUB and Kindle. Book excerpt: Compiles Information from a Multitude of SourcesSynthetic jets have been used in numerous applications, and are part of an emergent field. Accumulating information from hundreds of journal articles and conference papers, Synthetic Jets: Fundamentals and Applications brings together in one book the fundamentals and applications of fluidic actuators.

Book A Study on Flow and Heat Transfer Characteristics of Geometrically Innovative Impinging Jets

Download or read book A Study on Flow and Heat Transfer Characteristics of Geometrically Innovative Impinging Jets written by Kazuyoshi Nakabe and published by . This book was released on 1998 with total page 6 pages. Available in PDF, EPUB and Kindle. Book excerpt: It was found in the case of the former nozzle that main and secondary peaks of the Nusselt number distributions around the stagnation region were merged into a single peak as the extension collor length was increased, regardless of the oscilllating frequency. The latter case was found to enhance heat transfer from a spanwisely much wider area, compared with the case of the conventional impinging jet nozzle normal to the target wall. The enhanced area of heat transfer corresponds very well to the behaviors of the longitudinal vortices. [Authors' abstract].