Application of the method of fundamental solutions and the radial basis functions for laminar flow and heat transfer in internally corrugated tubes

Paper presented to the 10th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Florida, 14-16 July 2014.Heat transfer characteristics for a laminar fully developed flow in an internally corrugated circular tube with axially uniform heat flux with peripherally uniform temperature are obtained using the method of fundamental solution and the radial basis functions. The internal shape of the tube is modelled by cosine function. The nonlinear governing equation of temperature field problem was converted into the hierarchy of non-homogenous problems using the Picard iteration method. The non-homogenous part of the equation was interpolated using the radial basis functions. On each iteration step the solution of the governing equation consists of general solution as linear combination of fundamental solutions and particular solution. Boundary conditions were satisfied using the boundary collocation method. The results of the numerical experiments, that are velocity profiles, temperature field, friction factor, Nusselt number, errors of method were presented.dc201

A quick review of the applications of artificial neural networks (ANN) in the modelling of thermal systems

Thermal systems play a main role in many industrial sectors. This study is an elucidation of the utilization of artificial neural networks (ANNs) in the modelling of thermal systems. The focus is on various heat transfer applications like steady and dynamic thermal problems, heat exchangers, gas-solid fluidized beds, and others. Solving problems related to thermal systems using a traditional or classical approach often results to near feasible solutions. As a result of the stochastic nature of datasets, using the classical models to advance exclusive designs from the experimental dataset is often a function of trial and error. Conventional correlations or fundamental equations will not proffer satisfactory solutions as they are in most cases suitable and applicable to the problems from where they are generated. A preferable option is the application of computational intelligence techniques focused on the artificial neural network model with different structures and configurations for effective analysis of the experimental dataset. The main aim of current study is to review research work related to artificial neural network techniques and the contemporary improvements in the use of these modelling techniques, its up-and-coming application in addressing variability of heat transfer problems. Published research works presented in this paper, show that problems solved using the ANN model with regression analysis produced good solutions. Limitations of the classical and computational intelligence models have been exposed and recommendations have been made which focused on creative algorithms and hybrid models for future modelling of thermal systems.http://www.etasr.com/index.php/ETASR/indexdm2022Mechanical and Aeronautical Engineerin

EXPERIMENTAL AND CFD INVESTIGATION OF SOLAR CENTRAL RECEIVER TUBES

Lower electricity cost corresponds to high efficiency, which in turn corresponds to high operating temperatures in Concentrated Solar Power technology. Central receiver of such system constitutes 15% of the cost and plays an important role in achieving high operating temperatures. Central receiver systems are composed of tubes with heat transfer fluid flowing inside them that transports heat from radiation on the outer wall of tubes. Circular cross-sectional tubes are conventionally used for this application, but many different variable geometry tubes have been proposed for better heat transfer. Numerous experiments have shown the enhanced heat transfer behavior of different corrugated tubes. This work proposes a tube of new cross-sectional geometry and performs experiment using water as heat transfer fluid. The experiment is conducted on four different samples of corrugated tubes adopted from literature and compared to a circular tube and a new proposed tube. The experimental and CFD results are compared and reported. It is found that the new tube design can be used for such heat transfer applications but is not an ideal option. Meanwhile, corrugated tubes have higher heat transfer than circular tube, but not without the addition of extra material and pressure drop. If the material is to be kept similar for all tubes, circular tube is found to be the best option for central receiver systems

Efficient simulation of flow and heat transfer in arbitrarily shaped pipes

The transport of fluids through pipes is a very common application. Corrugated pipes have characteristics such as local stiffness and flexibility that makes them convenient in several application areas such as offshore LNG (Liquefied Natural Gas) transfer, cryogenic engineering, domestic appliances, etc. Nonetheless, the introduction of pipes with corrugated walls increases the difficulty of simulating flow and heat transfer in these type of pipes. The present thesis addresses the development of efficient models and numerical methods for simulating fluid flow and heat transfer in arbitrarily shaped pipes. The presented work combines both, numerical and analytical techniques with this goal in mind. We start by providing a general framework to the governing equations of fluid flow and heat transfer. We present the Boussinesq approximation and on basis we derive the governing equations for isothermal flow and non-isothermal flow. In the case of non-isothermal flow, we consider the limiting cases of forced and natural convection. We put special attention to the computation of the losses of mechanical energy and derive integral expressions for the friction factor (for periodic corrugated pipes) and for the loss coefficient (for arbitrary conduits). In the case of isothermal laminar flow we develop a very efficient analytical formula for computing the friction factor in slowly varying pipes. For non-slowly varying geometries we present an efficient numerical model which uses a periodicity decomposition in order to reduce the numerical domain to just one period. We use the numerical model for systematically evaluating the accuracy of the analytical formula. Based on the presented models, we also address the problem of wall-shape design. For the problem of non-isothermal laminar flow we consider two limiting cases, namely forced and natural convection. In the case of forced convection, we consider the problem of constant prescribed heat flux at the walls. As in the case of isothermal flow, we use periodicity decomposition for reducing the computational domain. For natural convection, first we take a more practically oriented approach and concentrate on an industrial application involving a cryogenic storage tank featuring a thermosyphon loop. We present a numerical model to simulate the involved phenomena. With this numerical model, we show that it is possible to optimize the wall-shape of the thermosyphon. However the computational cost of such a numerical model are considerable. This happens mainly because the problem does not allow for a periodicity decomposition and the whole extension of the domain needs to be considered. In addition, the corrugations introduce multiple scales which further increase the computational requirements for handling this problem. We provide a more efficient alternative for simulating natural convection by using the method of homogenization. The homogenization method allows us to replace the boundary conditions on a complex boundary by certain effective boundary condition on a homogenized (much simpler) boundary. This is advantageous from a computational point of view, the generation of an adequate mesh becomes straight forward and it is also easier to numerically solve the equations. At the same time, the effects of wall-shape are kept via the effective boundary conditions. The homogenized model is able to handle developing flows and can capture boundary layers. The homogenized model accurately predicts local and averaged quantities in a fraction of the costs of the direct numerical approach. We continue with the case of isothermal turbulent flow. We first present the (RANS) Reynolds averaged Navier-Stokes equations. On this framework, we introduce two turbulence models, the two-equation k-epsilon model and the algebraic LVEL model. We validate both models with experimental data and provide a comparison between both models

The promise of nanofluids: A bibliometric journey through advanced heat transfer fluids in heat exchanger tubes

© 2024 The Author(s). Published by Elsevier B.V. This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY), https://creativecommons.org/licenses/by/4.0/Thermal management is a critical challenge in advanced systems such as electric vehicles (EVs), electronic components, and photoelectric modules. Thermal alleviation is carried out through the cooling systems in which the coolant and the heat exchangers are the key components. The study examines recent literature on nanofluids and heat exchanger tubes along with state-of-the-art concepts being tested for heat transfer intensification. The performance of nanofluids in several common heat transfer tubes’ geometries/configurations and the effectiveness of novel heat transfer augmentation mechanisms are presented. Promising results have been reported, showing improved heat transfer parameters with the use of nanofluids and intensification mechanisms like turbulators, fins, grooves, and variations in temperature and flow velocity. These mechanisms enhance dispersion stability, achieve a more uniform temperature distribution, and reduce the boundary layer thickness, resulting in lower tube wall temperatures. Moreover, introducing flow pulsations and magnetic effects further enhances particle mobility and heat exchange. However, there are limitations, such as increased frictional losses and pressure drop due to magnetic effects. The combination of nanofluids, novel heat exchanger tube geometries, and turbulators holds great promise for highly efficient cooling systems in the future. The study also presents a bibliometric analysis that offers valuable insights into the impact and visibility of research in the integration of nanofluids into heat transfer systems. These insights aid in identifying emerging trends and advancing the field towards more efficient and compact systems, paving the way for future advancements.Peer reviewe

Computational Heat Transfer and Fluid Mechanics

With the advances in high-speed computer technology, complex heat transfer and fluid flow problems can be solved computationally with high accuracy. Computational modeling techniques have found a wide range of applications in diverse fields of mechanical, aerospace, energy, environmental engineering, as well as numerous industrial systems. Computational modeling has also been used extensively for performance optimization of a variety of engineering designs. The purpose of this book is to present recent advances, as well as up-to-date progress in all areas of innovative computational heat transfer and fluid mechanics, including both fundamental and practical applications. The scope of the present book includes single and multiphase flows, laminar and turbulent flows, heat and mass transfer, energy storage, heat exchangers, respiratory flows and heat transfer, biomedical applications, porous media, and optimization. In addition, this book provides guidelines for engineers and researchers in computational modeling and simulations in fluid mechanics and heat transfer

Technology of forced flow and once-through boiling: A survey

Representative boiling heat transfer and pressure drop information obtained primarily from past NASA and AEC programs is presented which is applicable to forced flow and once-through boiler systems. The forced convection boiler has a number of advantages: little possibility of flow mal-distribution; heat transfer characteristics are usually consistent; and conductances are predictable, so that higher heat fluxes may be employed with safety (which leads to more compact, lighter weight equipment). It was found that in gas-fired systems particularly, the controlling heat transfer resistance may be on the hot side, so that increased fluxes would require extended surfaces. If in a power generation system the working fluid is very expensive, a forced flow boiler can be designed especially for small holdup volume. If the fluid is temperature sensitive, the boiling side wall temperatures can be tailored to maintain maximum heat transfer rates without overheating the fluid. The forced flow and once-through configurations may be the only type which can satisfy a specific need (such as the automotive Rankine cycle power plant design having a very short time-response boiler)