Convective heat transfer enhancement in low Reynolds number flows with wavy walls

The present work reports the analysis of combining low Reynolds number flows and channels with wall corrugation and the corresponding thermal exchange intensification achieved. The proposed model involves axial heat diffusion along the fluid and adiabatic regions both upstream and downstream to the corrugated heat transfer section, in light of the lower values of Reynolds numbers (and consequently Peclet numbers) that can be encountered in the present class of problems. Aimed at developing a fast and reliable methodology for optimization purposes, the related laminar velocity field is obtained by an approximate analytical solution valid for smooth corrugations and low Reynolds numbers, typical for instance of micro-channel configurations, locally satisfying the continuity equation. A hybrid numerical-analytical solution methodology for the energy equation is proposed, based on the Generalized Integral Transform Technique (GITT) in partial transformation mode for a transient formulation. The hybrid approach is first demonstrated for the case of a smooth parallel-plates channel situation, and the importance of axial heat conduction along the fluid is then illustrated. Heat transfer enhancement is analyzed in terms of the local Nusselt number and dimensionless bulk temperature along the heat transfer section. An illustrative sinusoidal corrugation shape is adopted and the influence of Reynolds number and corrugation geometric parameters is then discussed.Indisponível

Integral transform solution for hyperbolic heat conduction in a finite slab

An analytical integral transformation of the thermal wave propagation problem in a finite slab is obtained through the generalized integral transform technique (GITT). The use of the GITT approach in the analysis of the hyperbolic heat conduction equation leads to a coupled system of second order ordinary differential equations in the time variable. The resulting transformed ODE system is then numerically solved by Gear's method for stiff initial value problems. Numerical results are presented for the local and average temperatures with different Biot numbers and dimensionless thermal relaxation times, permitting a critical evaluation of the technique performance. A comparison is also performed with previously reported results in the literature for special cases and with those produced through the application of the Laplace transform method (LTM), and the finite volume-Gear method (FVGM).Indisponível

Laminar flow and convective heat transfer of non-Newtonian fluids in doubly connected ducts

A hybrid numerical–analytical solution based on the Generalized Integral Transform Technique (GITT) is obtained for laminar heat and fluid flow of power-law non-Newtonian fluids inside doubly connected ducts. The mathematical formulation is constructed in the cylindrical coordinates system in such a way that the solid surfaces are described in terms of internal and external radii as functions of the angular coordinate, thus avoiding discontinuities in the boundary conditions. An annular doubly connected duct of arbitrary geometric configuration is considered for the analysis of the fully developed velocity field, as well as for the temperature field under thermally developing flow with boundary conditions of prescribed wall temperature. For illustration purposes, the case of eccentric annular ducts is more closely analyzed in order to demonstrate the ability of the GITT approach in dealing with such class of problems. Numerical results for the velocity field, the product of the Fanning friction factor-Reynolds number, temperature field and Nusselt numbers were produced for different values of the governing parameters, i.e., eccentricity, radii ratio and power-law indices. Such results were examined against previously reported ones, providing critical comparisons in order to illustrate the adequacy of the employed integral transform approach.Indisponível

The UNIT algorithm for solving one-dimensional convection-diffusion problems via integral transforms

A unified approach for solving convection-diffusion problems using the Generalized Integral Transform Technique (GITT) was advanced and coined as the UNIT (UNified Integral Transforms) algorithm, as implied by the acronym. The unified manner through which problems are tackled in the UNIT framework allows users that are less familiar with the GITT to employ the technique for solving a variety of partial-differential problems. This paper consolidates this approach in solving general transient one-dimensional problems. Different integration alternatives for calculating coefficients arising from integral transformation are discussed. Besides presenting the proposed algorithm, aspects related to computational implementation are also explored. Finally, benchmark results of different types of problems are calculated with a UNIT-based implementation and compared with previously obtained results.Indisponíve

Integral transforms solution for flow development in wavy wall ducts

Purpose – The purpose of this paper is to provide an analysis of two‐dimensional laminar flow in the entrance region of wavy wall ducts as obtained from the solution of the steady Navier‐Stokes equations for incompressible flow. Design/methodology/approach – The study is undertaken by application of the generalized integral transform technique in the solution of the steady Navier‐Stokes equations for incompressible flow. The streamfunction‐only formulation is adopted, and a general filtering solution that adapts to the irregular contour is proposed to enhance the convergence behavior of the eigenfunction expansion. Findings – A few representative cases are considered more closely in order to report some numerical results illustrating the eigenfunction expansions convergence behavior. The product friction factor‐Reynolds number is also computed and compared against results from discrete methods available in the literature for different Reynolds numbers and amplitudes of the wavy channel. Research limitations/implications – The proposed methodology is fairly general in the analysis of different channel profiles, though the reported results are limited to the wavy channel configuration. Future work should also extend the analysis to geometries represented in the cylindrical coordinates with longitudinally variable radius. Practical implications – The error‐controlled converged results provide reliable benchmark results for the validation of numerical results from computational codes that address the solution of the Navier‐Stokes equations in irregular geometries. Originality/value – Although the hybrid methodology is already known in the literature, the results here presented are original and further challenges application of the integral transform method in the solution of the Navier‐Stokes equations.Indisponível

Unified Integral Transforms Algorithm for Solving Multidimensional Nonlinear Convection-Diffusion Problems

The present work summarizes the theory and describes the algorithm related to an open-source mixed symbolic-numerical computational code named unified integral transforms (UNIT) that provides a computational environment for finding hybrid numerical-analytical solutions of linear and nonlinear partial differential systems via integral transforms. The reported research was performed by employing the well-established methodology known as the generalized integral transform technique (GITT), together with the symbolic and numerical computation tools provided by the Mathematica system. The main purpose of this study is to illustrate the robust precision-controlled simulation of multidimensional nonlinear transient convection-diffusion problems, while providing a brief introduction of this open source implementation. Test cases are selected based on nonlinear multidimensional formulations of Burgers’ equation, with the establishment of reference results for specific numerical values of the governing parameters. Special aspects in the computational behavior of the algorithm are then discussed, demonstrating the implemented possibilities within the present version of the UNIT code, including the proposition of a progressive filtering strategy and a combined criteria reordering scheme, not previously discussed in related works, both aimed at convergence acceleration of the eigenfunction expansions.Indisponível

Maturity Assessment in Public Institutions Using Management and Monitoring Network Free Software / Avaliação da Maturidade em Instituições Públicas Utilizando Software Gratuito de Gestão e Monitorização de Redes

In this case study, the ABNT ISO/IEC 14598-6 tool was used to measure the quality of the ZABBIX software applied in the IT area, of a federal research and teaching institute, regarding the network asset management and monitoring system, based on free software. This system was adopted due to the great relevance of modern network monitoring. This ISO tool, based on the international software quality measurement standards, was applied to verify the user's perception of the ZABBIX system, obtaining as a result of the evaluation an approval in all software attributes evaluated. The implementation of the solution brought real gains in quality, management, security, performance and savings in institutional resources

Integral transform solution of the Navier–Stokes equations in full cylindrical regions with streamfunction formulation

A hybrid numerical–analytical solution based on the generalized integral transform technique is proposed to handle the two‐dimensional Navier–Stokes equations in cylindrical coordinates, expressed in terms of the streamfunction‐only formulation. The proposed methodology is illustrated in solving steady‐state incompressible laminar flow of Newtonian fluids in the developing region of a circular tube. The flow modeling also considers two limiting inlet conditions, namely, uniform velocity profile representing a parallel flow, and zero vorticity that characterizes irrotational inlet flow. The integral transform analysis for such a full cylindrical region brings up singularities at the channel centerline, and, as previously described in a work dealing with the boundary‐layer formulation, a way to alleviate this difficulty is to adopt a recently introduced fourth‐order eigenvalue problem as the basis for the eigenfunction expansion. A thorough convergence analysis of the proposed expansion is then undertaken, for different values of Reynolds number, and a set of reference results for the velocity distributions and friction factors are then presented in tabular and graphical forms.Indisponível

An Analysis of Heat Conduction Models for Nanofluids

The mechanism of heat transfer intensification recently brought about by nanofluids is analyzed in this article, in the light of the non-Fourier dual-phase-lagging heat conduction model. The physical problem involves an annular geometry filled with a nanofluid, such as typically used for measurements of the thermal conductivity with Blackwell's line heat source probe. The mathematical formulation for this problem is analytically solved with the classical integral transform technique, thus providing benchmark results for the temperature predicted with the dual-phase-lagging model. Different test cases are examined in this work, involving nanofluids and probe sizes of practical interest. The effects of the relaxation times on the temperature at the surface of the probe are also examined. The results obtained with the dual-phase-lagging model are critically compared to those obtained with the classical parabolic model, showing that the increase in the thermal conductivity of nanofluids measured with the line heat source probe cannot be attributed to hyperbolic effects.Indisponível

Estudo da incorporação de material laterítico ferroaluminoso na taxa de queima de compósito de matriz termofixa

Os compósitos são versáteis e podem ser aplicados em diversos setores dependendo das necessidades exigidas e de suas características, de modo a conciliar fatores como segurança, meio ambiente e economia. Os materiais lateríticos estão presentes em grande parte do território nacional e podem apresentar teores elevados de óxi-hidróxidos de ferro e alumínio, podendo influenciar significativamente nas propriedades térmicas de compósitos poliméricos. O material utilizado no trabalho é originário da Serra do Piriá, localizada no município de Vizeu, Estado do Pará. O trabalho consistiu na caracterização deste material e produção de compósitos utilizando o mesmo como carga, em uma matriz de poliéster isoftálico, os quais foram testados através de ensaios de flamabilidade. Foram realizadas análises de granulometria a laser, espectroscopia de fluorescência de raios-X (FRX), infravermelho por transformada de Fourier (FTIR), termogravimetria (TG) e calorimetria exploratória diferencial (DSC). Os compósitos foram fabricados segundo processo hand lay-up em molde fechado, com compressão de 2,7 toneladas por 20 minutos. As frações volumétricas utilizadas para a fabricação dos compósitos foram de 10, 20 e 30 % e os ensaios de flamabilidade foram conduzidos segundo a norma ASTM D 635-03. Como resultados, o material apresentou diâmetro médio igual a 23,5 μm, constituído por 61,13 % de Fe2O3 e 18,63 % de Al2O3, ratificando a presença destes óxidos, bandas características a 3448 cm1 indicam a presença de cátions trivalentes de Al3+ ou Fe3+. Quanto ao comportamento calorimétrico, o mesmo apresentou transformações de fases em uma faixa de temperatura adequada ao retardo de chamas, com perda de massa significativa a partir de aproximadamente 270 ºC. Nos compósitos com 30 % de material laterítico a propagação de chamas reduziu-se em 69,86 % com relação a matriz de poliéster, o que viabiliza o estudo de sua aplicação em compósitos.Palavras-chave: Laterita, Ferro, Alumínio, Caracterização.