Purpose This paper aims to study, experimentally validate and select the main physical and numerical parameters of influence in computational numerical simulations to evaluate mean heat flux by natural convection on square flat plates. Design/methodology/approach Several numerical models were built to study the influence of physical and numerical parameters about the predictions of the natural convection heat transfer rates on the surface of a flat plate with aspect ratio = 1, in isothermal conditions, turbulent regime and using the free and open-source software OpenFOAM®. The studied parameters were: boundary conditions (using or not using wall functions in properties ε, κ, νt and ω), degree of mesh refinement, refinement layers and turbulence models [κ – ε and κ – ω Shear Stress Transport (SST)]. From the comparison of the values of the mean Nusselt number, obtained from numerical simulations and literature experimental results, the authors evaluated the precision of the studied parameters, validating and selecting the most appropriate to the analyzed problem situation. Findings The validation and agreement of the numerical results could be proven with excellent precision from experimental references of the technical scientific literature. More refined meshes with refinement layers were not suitable for the studies developed. The κ – ε and κ – ω SST turbulence models, in meshes without refinement layers, proved to be equivalent. Whether or not to use wall functions in turbulent boundary conditions proved to be irrelevant as to the accuracy of results for the problem situation studied. Practical implications Use of the physical and numerical parameters is studied and validated for various applications in natural convection heat transfer of technology and industry areas. Social implications Use of free and open-source software as a research tool in the Computational Fluid Dynamics (CFD) area, especially in conditions without large financial resources or state-of-the-art infrastructure. Originality/value To the best of the authors’ knowledge, this work is yet not available in existing literature.
Laminar forced convection inside a square cavity with inlet and outlet ports was numerically analyzed. The positions of the inlet and outlet ports were fixed and the ports sizes were equal 25% of the side wall. The influence of the Reynolds and Prandtl numbers on the flow and temperature fields inside the cavity was verified for nine cases, with Re = 50, 100 and 500 and Pr = 0.7, 3 and 5. The heat transfer process in the cavity was analyzed from obtained values for the average Nusselt number and the local Nusselt number on the walls. The open source computer package OpenFOAM® was used for simulations considering a two-dimensional flow. For all tested Prandtl numbers, there is a growth in the rotating vortex regions as Reynolds number is increases. The temperature fields are directly related to the presence of the rotating vortices and the temperature gradient is more noticeable at the interface sections of the throughflow stream with the neighboring vortices and the next to the walls for greater Reynolds and Prandtl numbers. It was verified that the local Nusselt number on the walls varies radically with minimum and maximum points and it is dependent on the flow and temperature fields adjacent to the respective wall. The results for average Nusselt number per wall indicated that the bottom wall is the most susceptible to variations in its average Nusselt number and that the top wall present higher values of this parameter for all tested cases. Finally, the average Nusselt number was increased with increasing the Reynolds and Prandtl numbers indicating the enhanced thermal exchange.
Natural convection is present in the most different Thermal Engineering systems, such as solar collectors, electric furnaces, electronic equipment cooling, lubrication, thermal comfort projects in buildings, etc. In the last decade, the number of research on natural convection heat transfer has increased considerably, especially in the areas of physical-numerical modeling and validation, experimental construction and efficiency optimization of thermal systems, and related technologies. This work presents an experimental methodology for studying natural convection on flat and corrugated plates. The design and construction stages of the experimental apparatus, data processing and analysis, physical-mathematical modeling and uncertainty analysis were extensively explored. The applications and extensions of the proposed methodology were discussed in the numerical-experimental validation of physical-numerical modeling methodologies, design and optimization of the experimental apparatus and also of measuring instruments and, finally, in sensitivity analysis studies to reduce the propagation of uncertainties. The limitations of the proposed methodology were discussed, pointing out suggestions for future work.
Because of the better flexibility in warming and high production, the continuous furnace tunnel is the better option to the processing of industrialized food products. This study presents a numerical investigation of the effects of RANS turbulence modeling on the main parameters of the air flow inside a continuous oven with indirect heating - velocities, temperatures, streamlines and heat flows by convection and radiation. The geometry and operating conditions used for constructing the model, setting the mesh and initial and boundary conditions were obtained based on values of operating ovens. Modeling consider the hypothesis of air as an ideal gas, incompressible and Newtonian; the equations of continuity, momentum balance and energy in turbulent regime; closing model of two equations κ- ε and radiation model viewFactor. Utilized the free open source software OpenFOAM® for device modeling. The Rayleigh Number of the cavity was used to evaluate the treatment indicated to turbulence. Considering the results obtained, the inclusion of model κ- ε stabilized the velocity fields and temperatures around the average value. In relation to the heat exchanges involved, heat flow by convection on the mat showed negligible compared to the effects of radiation. Due to the discrepancy between the orders of magnitude of convection and radiation, it's difficult the precise evaluation of the first, because small fluctuations in temperature and velocity affect considerably and induce oscillations in their behavior. However, the radiation model attained good approximation the most relevant exchanges, showing a good chance their application in practical cases.
Purpose The purpose of this study is to analyze the influence of the main physical–numerical parameters in the computational evaluation of natural convection heat transfer rates in isothermal flat square plates in the laminar regime. Moreover by experimentally validate the results of the numerical models and define the best parameter settings for the problem situation studied. Design/methodology/approach The present work is an extension of the study by Verderio Junior et al. (2021), differing in the modeling, results analysis and conclusions for the laminar flow regime with Rade=1×105. The analysis of the influence and precision of the physical–numerical parameters: boundary conditions, degree of mesh refinement, refinement layers and κ – ω SST and κ – ε turbulence models, occurred from the results from 48 numerical models, which were simulated using the OpenFOAM® software. Comparing the experimental mean Nusselt number with the numerical values obtained in the simulations and the analysis of the relative errors were used in the evaluation of the advantages, restrictions and selection of the most adequate parameters to the studied problem situation. Findings The numerical results of the simulations were validated, with excellent precision, from the experimental reference by Kitamura et al. (2015). The application of the κ – ω SST and κ – ε turbulence models and the boundary conditions (with and without wall functions) were also physically validated. The use of the κ – ω SST and κ – ε turbulence models, in terms of cost-benefit and precision, proved to be inefficient in the problem situation studied. Simulations without turbulence models proved to be the best option for the physical model for the studies developed. The use of refinement layers, especially in applications with wall functions and turbulence models, proved unfeasible. Practical implications Use of the physical–numerical parameters studied and validated, and application of the modeling and analysis methodology developed in projects and optimizations of natural convection thermal systems in a laminar flow regime. Just like, reduce costs and the dependence on the construction of experimental apparatus to obtain experimental results and in the numerical-experimental validation process. Social implications Exclusive use of free and open-source computational tools as an alternative to feasible research in the computational fluid dynamics area in conditions of budget constraints and lack of higher value-added infrastructure, with applicability in the academic and industrial areas. Originality/value The results and discussions presented are original and new for the applied study of laminar natural convection in isothermal flat plate, with analysis and validation of the main physical and numerical influence parameters.
Natural convection heat transfer is present in the most diverse applications of Thermal Engineering, such as in electronic equipment, transmission lines, cooling coils, biological systems, etc. The correct physical-mathematical modeling of this phenomenon is crucial in the applied understanding of its fundamentals and the design of thermal systems and related technologies. Dimensionless analyses can be applied in the study of flows to reduce geometric and experimental dependence and facilitate the modeling process and understanding of the main influence physical parameters; besides being used in creating models and prototypes. This work presents a methodology for dimensionless physical-mathematical modeling of natural convection turbulent flows over isothermal plates, located in an “infinite” open environment. A consolidated dimensionless physical-mathematical model was defined for the studied problem situation. The physical influence of the dimensionless numbers of Grashof, Prandtl, and Turbulent Prandtl was demonstrated. The use of the Theory of Dimensional Analysis and Similarity and its application as a tool and numerical device in the process of building and simplifying CFD simulations were discussed.
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