Download or read book Direct Numerical Simulations of Three dimensional Flow and Augmented Heat Transfer in a Symmetrically Grooved Channel with Constant Temperature Walls written by Robert J. Faulkner and published by . This book was released on 1997 with total page 216 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Proceedings of the ASME Heat Transfer Division 2000 written by Jong H. Kim and published by . This book was released on 2000 with total page 426 pages. Available in PDF, EPUB and Kindle. Book excerpt: Technical papers from the November 2000 ASME Heat Transfer Division congress and exposition comprise 31 sessions, including transport phenomena in fuel cell systems, radiation heat transfer in energy systems, heat transfer in microgravity systems, cryogenic heat transfer, innovative heat transfer vi

Download or read book Journal of Heat Transfer written by and published by . This book was released on 2002 with total page 416 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Predicting Turbulent Convective Heat Transfer in Three Dimensional Duct Flows written by and published by . This book was released on 1999 with total page 26 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Numerical Simulations of Steady Low Reynolds number Flows and Enhanced Heat Transfer in Wavy Plate fin Passages written by and published by . This book was released on 2005 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Extended or finned surfaces are widely used in compact heat exchangers to reduce the thermal resistance of air- or gas-side flows. Besides increasing the effective heat transfer surface area, geometrically modified finned surfaces also improve the heat transfer coefficient by altering the flow field. Wavy plate-fin surfaces have such properties and promote relatively high thermal-hydraulic performance. They are also attractive for their simplicity of manufacture and ease of use in compact heat exchangers. The current study numerically investigates the fluid flow and enhanced convection heat transfer in two-dimensional and three-dimensional wavy plate-fin passages with sinusoidal wall corrugations in the low Reynolds number regime. Constant property, periodically fully developed, and laminar or low Reynolds number forced convection are considered. The governing equations of continuity, momentum, and energy are solved computationally using finite-volume techniques. The solution procedure is based on the SIMPLE algorithm and a non-orthogonal, non-uniform grid. The influences of fin geometry (fin spacing, fin height, fin amplitude and fin length) on the enhanced heat transfer and fluid flow behaviors are investigated. The simulation results for the velocity and temperature distributions, isothermal Fanning friction f, and Colburn factor j are presented and discussed. The complex flow patterns in the wavy-fin channel are characterized by re-circulating and/or helical swirl flows with periodic flow separation and reattachment. Two flow regimes can be classified based on these results, namely, (1) low-Re streamline-flow regime where viscous forces dominate, and (2) high-Re swirl-flow regime characterized by flow recirculation and/or helical vortices. Heat transfer enhancement is observed in the swirl flow regime along with an increased pressure drop penalty, as a consequence of the periodic thermal boundary-layer thinning, strong flow mixing, and periodic generation and dissipation of vortices or re-circulating cells. In the streamline-flow regime, the flow and heat transfer behavior are similar to that in straight flow channel, though an enhanced performance is obtained. Also, results of flow visualization experiment for a two-dimensional wavy flow channel are shown to agree well with the numerical results. Finally, the computational methodology is extended to illustrate the flow behaviors in out-of-phase wavy flow passages.

Download or read book Applied Mechanics Reviews written by and published by . This book was released on 1988 with total page 384 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Study of Wall bounded Turbulent Heat Transfer and Flow Dynamics at Transcritical Conditions written by Jack Guo and published by . This book was released on 2023 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: Transcritical fluid conditions, at pressures above the thermodynamic critical pressure, present a thermodynamic regime with fluid behaviors that differ significantly from those at more commonly-encountered subcritical pressures. In engineering settings, increasing societal demands for higher power and energy efficiencies necessitate the increasing relevance of transcritical operating conditions. In the context of these current trends, a wide range of technological sectors such as energy generation, propulsion, and chemical processing are increasingly utilizing turbulent fluid flows at transcritical conditions. Despite the relevance and prevalence of transcritical flows at turbulent conditions in the presence of walls, the details of the flow and heat transfer have not been thoroughly investigated. For such flows, enhanced fluctuations, steep gradients, and intensified heat transfer are key characteristics -- the combination of these features create a challenging physical environment to be studied. Particularly, the structure of the turbulent thermal boundary layer under realistic density gradients and heating conditions remains poorly understood. Statistical descriptions of the temperature field in such flows are inconsistently provided using existing models; because an accurate description of the temperature statistics are crucial towards understanding the heat transfer, this lack of understanding and the associated inability to predict the near-wall temperature present a critical gap in knowledge. To address this issue, this thesis discusses the design, computational generation, results, and analysis of a set of direct numerical simulations of fully developed transcritical turbulent channel flow cases. Six cases are chosen to sample the parameter space, ranging from the symmetric wall temperatures case (without significant convective wall heat flux) up to several strongly heated cases (with significant convective wall heat flux). The pressure and temperature conditions in the current study cause density changes of a factor of up to order 20 between the hot and cold walls. The resulting transcritical turbulent flow displays a number of distinguishing characteristics when compared to flows at classical (constant-property + ideal gas) thermodynamic conditions. Many fundamental results from classical turbulence theory (specifically scalings and quantitative predictions of engineering parameters) have been shown to be invalid or have become points of contention in the community. Because of this, we present and discuss flow features of the turbulent cases in the current investigation. As a consequence of the proximity of the Widom line to the hot wall, a central theme that is observed is the presence of significant asymmetries in the momentum and thermal field features when comparing regions near the cold wall and near the hot wall. These observations serve to inform general insights into the understanding and modeling of transcritical wall-bounded turbulence. Previous transformations that attempt to collapse the near-wall mean temperature profiles are examined. By addressing model deficiencies in capturing the transcritical thermal boundary layer by these past works, we formulate and propose an improved mean temperature transformation. The viscous sublayer behavior of the mean temperature has been well characterized and collapsed in the literature; however, the behavior further from the wall in the logarithmic region has not. Because computational cost limitations for practical engineering applications necessitate a wall model from the wall up through a portion of the log region, accurate predictive understanding of the temperature behavior is critical to correctly capture the wall heat transfer in such computations (as a thermal analogy to the log-layer mismatch problem). Our proposed transformation is shown to perform well in collapsing the slope of the logarithmic region to a single universal value with reduced uncertainty. Appropriate considerations for real fluid effects that involve strong variations in thermodynamic quantities are included; as a result, the transformation handles well the steep gradients and large relative fluctuation magnitudes presented by cases with strong wall heat transfer. We borrow from the established procedure of past transformations by separating the transformed profile into the Prandtl-number-dependent and non-Prandtl-number-dependent components. As an extension to improve the utility of our transformation, we then propose a predictive framework that models each component analytically, such that the entire near-wall mean temperature profile can be predicted using only input parameters. The final combination of the transformation and the extended framework thus provides a tool towards the development of more accurate reduced-order models for wall-bounded transcritical turbulence.

Download or read book Direct Numerical Simulation of Strained Three dimensional Wall bounded Flows written by Gary N. Coleman and published by . This book was released on 1996 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Direct Numerical Simulation of Turbulent Flow and Heat Transfer in a Square Duct at Low Reynolds Number written by M. Piller and published by . This book was released on 2001 with total page 8 pages. Available in PDF, EPUB and Kindle. Book excerpt: In this paper, we present the results from Direct Numerical Simulations of turbulent, incompressible flow through a square duct, with an imposed temperature difference between two opposite walls, while the other two walls are assumed perfectly insulated. The mean flow is sustained by an imposed, mean pressure gradient. The most interesting feature, characterizing this geometry, consists in the presence of turbulence-sustained mean secondary motions in the cross-flow plane. In this study, we focus on weak turbulence, in that the Reynolds number, based on bulk velocity and hydraulic diameter, is about 4450. Our results indicate that secondary motions do not affect dramatically the global parameters, like friction factor and Nusselt number, in comparison with the plane-channel flow. This issue is investigated by looking at the distribution of the various contributions to the total heat flux, with particular attention to the mean convective term, which does not appear in the plane channel flow.

Download or read book Numerical Study of Three Dimensional Incompressible Flow and Heat Transfer Over a Stationary and Moving and Rotating Sphere in a Pipe written by Nader Shahcheraghi and published by . This book was released on 1996 with total page 264 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Simulation of Three dimensional Laminar Flow and Heat Transfer in an Array of Parallel Microchannels written by Justin Dale Mlcak and published by . This book was released on 2010 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Heat transfer and fluid flow are studied numerically for a repeating microchannel array with water as the circulating fluid. Generalized transport equations are discretized and solved in three dimensions for velocities, pressure, and temperature. The SIMPLE algorithm is used to link pressure and velocity fields, and a thermally repeated boundary condition is applied along the repeating direction to model the repeating nature of the geometry. The computational domain includes solid silicon and fluid regions. The fluid region consists of a microchannel with a hydraulic diameter of 85.58[mu]m. Independent parameters that were varied in this study are channel aspect ratio and Reynolds number. The aspect ratios range from 0.10 to 1.0 and Reynolds number ranges from 50 to 400. A constant heat flux of 90 W/cm2 is applied to the northern face of the computational domain, which simulates thermal energy generation from an integrated circuit. A simplified model is validated against analytical fully developed flow results and a grid independence study is performed for the complete model. The numerical results for apparent friction coefficient and convective thermal resistance at the channel inlet and exit for the 0.317 aspect ratio are compared with the experimental data. The numerical results closely match the experimental data. This close matching lends credibility to this method for predicting flows and temperatures of water and the silicon substrate in microchannels. Apparent friction coefficients linearly increase with Reynolds number, which is explained by increased entry length for higher Reynolds number flows. The mean temperature of water in the microchannels also linearly increases with channel length after a short thermal entry region. Inlet and outlet thermal resistance values monotonically decrease with increasing Reynolds number and increase with increasing aspect ratio. Thermal and friction coefficient results for large aspect ratios (1 and 0.75) do not differ significantly, but results for small aspect ratios (0.1 and 0.25) notably differ from results of other aspect ratios.

Download or read book International Aerospace Abstracts written by and published by . This book was released on 1996 with total page 944 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Convection Heat Transfer in Three Dimensional Turbulent Separated written by and published by . This book was released on 2007 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: The measurements and the simulation of convective heat transfer in separated flow have been a challenge to researchers for many years. Measurements have been limited to two-dimensional flow and simulations failed to predict accurately turbulent heat transfer in the separated and reattached flow region (prediction are higher than measurements by more than 50%). A coordinated experimental and numerical effort has been initiated under this grant for examining the momentum and thermal transport in three-dimensional separated and reattached flow in an effort to provide new measurements that can be used for benchmarking and for improving the simulation capabilities of 3-D convection in separated/reattached flow regime. High-resolution and non-invasive measurements techniques are developed and employed in this study to quantify the magnitude and the behavior of the three velocity components and the resulting convective heat transfer. In addition, simulation capabilities are developed and employed for improving the simulation of 3-D convective separated/reattached flow. Such basic measurements and simulation capabilities are needed for improving the design and performance evaluation of complex (3-D) heat exchanging equipment. Three-dimensional (3-D) convective air flow adjacent to backward-facing step in rectangular channel is selected for the experimental component of this study. This geometry is simple but it exhibits all the complexities that appear in any other separated/reattached flow, thus making the results generated in this study applicable to any other separated and reattached flow. Boundary conditions, inflow, outflow, and wall thermal treatment in this geometry can be well measured and controlled. The geometry can be constructed with optical access for non-intrusive measurements of the flow and thermal fields. A three-component laser Doppler velocimeter (LDV) is employed to measure simultaneously the three-velocity components and their turbulent fluctuations. Infrared thermography is utilized to measure the wall temperature and that information is used to determine the local convective heat transfer coefficient. FLUENT - CFD code is used as the platform in the simulation effort and User Defined Functions are developed for incorporating advanced turbulence models into this simulation code. Predictions of 3-D turbulent convection in separated flow, using the developed simulation capabilities under this grant, compared well with measured results. Results from the above research can be found in the seventeen refereed journal articles, and thirteen refereed publications and presentations in conference proceedings that have been published by the PI during the this grant period. The research effort is still going on and several publications are being prepared for reporting recent results.

Download or read book Numerical Simualtion of Mixed Convection Over a Three dimensional Horizontal Backward facing Step written by Juan Gabriel Barbosa Saldana and published by . This book was released on 2005 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: A FORTRAN code was developed to numerically simulate the mixed convective flow over a three-dimensional horizontal backward-facing step. The momentum and energy equations under the assumption of the Boussinesq approximation were discretized by means of a finite volume technique. The SIMPLE algorithm scheme was applied to link the pressure and velocity fields inside the domain while an OpenMP parallel implementation was proposed to improve the numerical performance and to accelerate the numerical solution. The heating process corresponds to a channel heated from below at constant temperature keeping insulated all the other channel walls. In addition, the back-step was considered as a thermally conducting block and its influence in the heating process was explored by holding different solid to fluid thermal conductivity ratios. The effects over the velocity and temperature distribution of buoyancy forces, acting perpendicular to the mainstream flow, are studied for three different Richardson numbers Ri=3, 2, and 1 and the results are compared against those of pure forced convection Ri=0. In these simulations the Reynolds number is fixed at 200 while the bottom wall temperature is adjusted to fulfill the conditions for the different Ri. Under this assumption, as Ri increases the buoyancy effects are the dominant effects in the mixed convective process. The numerical results indicate that the velocity field and the temperature distribution for pure forced convection are highly distorted if compared with the mixedconvective flow. If the Ri parameter is increased, then the primary re-circulation zone is reduced. Similarly, as the buoyancy forces become predominant in the flow, the convective rolls, in the form of spiral-flow structures, become curlier and then higher velocity components are found inside the domain. The temperature field distribution showed that as the Ri is increased a thicker layer of high temperature flow is located at the channel's top wall as a result of the higher rates of low-density flow moving to the top wall. The flow is ascending by the channel sidewalls, while descending by the channel span-wise central plane. The parallel numerical strategy is presented and some results for the performance of the OpenMP implementation are included. In this sense, linear speedup was obtained when using 16 possessors in parallel.

Download or read book Numerical Simulation of Unsteady Three Dimensional Fluid Flow and Heat Transfer Occurring in Open Channel Forehearths written by Yun Shang Lin and published by . This book was released on 1985 with total page 268 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Gas Turbine Heat Transfer and Cooling Technology Second Edition written by Je-Chin Han and published by CRC Press. This book was released on 2012-11-27 with total page 892 pages. Available in PDF, EPUB and Kindle. Book excerpt: A comprehensive reference for engineers and researchers, Gas Turbine Heat Transfer and Cooling Technology, Second Edition has been completely revised and updated to reflect advances in the field made during the past ten years. The second edition retains the format that made the first edition so popular and adds new information mainly based on selected published papers in the open literature. See What’s New in the Second Edition: State-of-the-art cooling technologies such as advanced turbine blade film cooling and internal cooling Modern experimental methods for gas turbine heat transfer and cooling research Advanced computational models for gas turbine heat transfer and cooling performance predictions Suggestions for future research in this critical technology The book discusses the need for turbine cooling, gas turbine heat-transfer problems, and cooling methodology and covers turbine rotor and stator heat-transfer issues, including endwall and blade tip regions under engine conditions, as well as under simulated engine conditions. It then examines turbine rotor and stator blade film cooling and discusses the unsteady high free-stream turbulence effect on simulated cascade airfoils. From here, the book explores impingement cooling, rib-turbulent cooling, pin-fin cooling, and compound and new cooling techniques. It also highlights the effect of rotation on rotor coolant passage heat transfer. Coverage of experimental methods includes heat-transfer and mass-transfer techniques, liquid crystal thermography, optical techniques, as well as flow and thermal measurement techniques. The book concludes with discussions of governing equations and turbulence models and their applications for predicting turbine blade heat transfer and film cooling, and turbine blade internal cooling.

Download or read book Modelling of Convective Heat and Mass Transfer in Rotating Flows written by Igor V. Shevchuk and published by Springer. This book was released on 2015-07-24 with total page 253 pages. Available in PDF, EPUB and Kindle. Book excerpt: This monograph presents results of the analytical and numerical modeling of convective heat and mass transfer in different rotating flows caused by (i) system rotation, (ii) swirl flows due to swirl generators, and (iii) surface curvature in turns and bends. Volume forces (i.e. centrifugal and Coriolis forces), which influence the flow pattern, emerge in all of these rotating flows. The main part of this work deals with rotating flows caused by system rotation, which includes several rotating-disk configurations and straight pipes rotating about a parallel axis. Swirl flows are studied in some of the configurations mentioned above. Curvilinear flows are investigated in different geometries of two-pass ribbed and smooth channels with 180° bends. The author demonstrates that the complex phenomena of fluid flow and convective heat transfer in rotating flows can be successfully simulated using not only the universal CFD methodology, but in certain cases by means of the integral methods, self-similar and analytical solutions. The book will be a valuable read for research experts and practitioners in the field of heat and mass transfer.