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Nanofluid in Heat Exchanges for Mechanical Systems: Numerical Simulation shows how the finite volume method is used to simulate various applications of heat exchanges. Heat transfer enhancement methods are introduced in detail, along with a hydrothermal analysis and second law approaches for heat exchanges. The melting process in heat exchanges is also covered, as is the influence of variable magnetic fields on the performance of heat exchange. This is an important reference source for materials scientists and mechanical engineers who are looking to understand the main ways that nanofluid flow is simulated and applied in industry. Provides detailed coverage of major models used in nanofluid analysis, including the finite volume method, governing equations for turbulent flow, and equations of nanofluid in presence of variable magnetic field Offers detailed coverage of swirling flow devices and melting processes Assesses which models should be applied in which situations
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.
Featuring contributions by leading researchers in the field, Nanoparticle Heat Transfer and Fluid Flow explores heat transfer and fluid flow processes in nanomaterials and nanofluids, which are becoming increasingly important across the engineering disciplines. The book covers a wide range, from biomedical and energy conversion applications to mate
Nanofluids are solid-liquid composite material consisting of solid nanoparticles suspended in liquid with enhanced thermal properties. This book introduces basic fluid mechanics, conduction and convection in fluids, along with nanomaterials for nanofluids, property characterization, and outline applications of nanofluids in solar technology, machining and other special applications. Recent experiments on nanofluids have indicated significant increase in thermal conductivity compared with liquids without nanoparticles or larger particles, strong temperature dependence of thermal conductivity, and significant increase in critical heat flux in boiling heat transfer, all of which are covered in the book. Key Features Exclusive title focusing on niche engineering applications of nanofluids Contains high technical content especially in the areas of magnetic nanofluids and dilute oxide based nanofluids Feature examples from research applications such as solar technology and heat pipes Addresses heat transfer and thermodynamic features such as efficiency and work with mathematical rigor Focused in content with precise technical definitions and treatment
ABSTRACT: The flow structure and convective heat transfer behavior of a free liquid jet ejecting from a round nozzle impinging vertically on a hemispherical solid plate and a slot nozzle impinging vertically on a cylindrical curved plate have been studied using a numerical analysis approach. The simulation model incorporated the entire fluid region and the solid hemisphere or curved plate. Solution was done for both isothermal and constant heat flux boundary conditions at the inner surface of the hemispherical plate and the constant heat flux boundary condition at the inner surface of the cylindrical shaped plate. Computations for the round nozzle impinging jet on the hemispherical plate and cylindrical plate were done for jet Reynolds number (ReJ) ranging from 500 to 2000, dimensionless nozzle to target spacing ratio (β) from 0.75 to 3, and for various dimensionless plate thicknesses to diameter nozzle ratio (b/dn) from 0.083-1.5. Also, computations for the slot nozzle impinging jet on the cylindrical plate were done for inner plate radius of curvature to nozzle diameter ratio (Ri/dn) of 4.16-16.66, plate thickness to nozzle diameter ratio (b/dn) of 0.08-1.0, and different nozzle diameters (dn), Results are presented for dimensionless solid-fluid interface temperature, dimensionless maximum temperature in the solid, local and average Nusselt numbers using the following fluids: water (H2O), flouroinert (FC-77), and oil (MIL-7808) and the following solid materials: aluminum, copper, Constantan, silver, and silicon. Materials with higher thermal conductivity maintained a more uniform temperature distribution at the solid-fluid interface. A higher Reynolds number increased the Nusselt number over the entire solid-fluid interface. Local and average Nusselt number and heat transfer coefficient distributions showed a strong dependence on the impingement velocity or Reynolds number. As the velocity increases, the local Nusselt number increases over the entire solid-fluid interface. Decreasing the nozzle to target spacing favors the increasing of the Nusselt number. Increasing the nozzle diameter decreases the temperature at the curved plate outer surface and increases the local Nusselt number. Similarly, local and average Nusselt number was enhanced by decreasing plate thickness. Numerical simulation results are validated by comparing with experimental measurements and related correlations.
Heat Transfer Enhancement Using Nanofluid Flow in Microchannels: Simulation of Heat and Mass Transfer focuses on the numerical simulation of passive techniques, and also covers the applications of external forces on heat transfer enhancement of nanofluids in microchannels. Economic and environmental incentives have increased efforts to reduce energy consumption. Heat transfer enhancement, augmentation, or intensification are the terms that many scientists employ in their efforts in energy consumption reduction. These can be divided into (a) active techniques which require external forces such as magnetic force, and (b) passive techniques which do not require external forces, including geometry refinement and fluid additives. - Gives readers the knowledge they need to be able to simulate nanofluids in a wide range of microchannels and optimise their heat transfer characteristics - Contains real-life examples, mathematical procedures, numerical algorithms, and codes to allow readers to easily reproduce the methodologies covered, and to understand how they can be applied in practice - Presents novel applications for heat exchange systems, such as entropy generation minimization and figures of merit, allowing readers to optimize the techniques they use - Focuses on the numerical simulation of passive techniques, and also covers the applications of external forces on heat transfer enhancement of nanofluids in microchannels
Applications of Nanofluid for Heat Transfer Enhancement explores recent progress in computational fluid dynamic and nonlinear science and its applications to nanofluid flow and heat transfer. The opening chapters explain governing equations and then move on to discussions of free and forced convection heat transfers of nanofluids. Next, the effect of nanofluid in the presence of an electric field, magnetic field, and thermal radiation are investigated, with final sections devoted to nanofluid flow in porous media and application of nanofluid for solidification. The models discussed in the book have applications in various fields, including mathematics, physics, information science, biology, medicine, engineering, nanotechnology, and materials science. - Presents the latest information on nanofluid free and force convection heat transfer, of nanofluid in the presence of thermal radiation, and nanofluid in the presence of an electric field - Provides an understanding of the fundamentals in new numerical and analytical methods - Includes codes for each modeling method discussed, along with advice on how to best apply them