bluuebunny/crossref_metadata_2025 huggingface dataset:
TWO-DIMENSIONAL COMPUTATIONAL MODELING OF THE SOIL THERMAL BEHAVIOR DUE TO THE INCIDENCE OF SOLAR RADIATION
Authors: Brum R. S. , Isoldi L. A. , Dos Santos E. D. , Vaz J. , Rocha L. A. O.
Published: November 2018

Nowadays, there is a focus on finding sustainable energy sources, as well as, alternatives to rationalize the use of electrical energy. In this sense, the employment of Earth-Air Heat Exchangers (EAHE) is one technique which allows the reduction of energy consumption for climatization of buildings environments. The present study shows the evaluation of a numerical method to estimate the ground thermal potential, allowing its applicability for future thermal design of EAHE. The soil domain is considered twodimensional and a transient solution for the thermal behavior of the soil is obtained. Moreover, a soil surface temperature distribution equation based on experimental data is employed to define the domain boundary conditions. The simulations are performed with a numerical method based on the finite volume method, more precisely using the software FLUENT®. The results presented an excellent agreement with analytical solutions showing the validity and effectiveness of the computational model for prediction of the soil behavior. The numerical results were also confronted with experimental ones predicted into literature and show a good agreement, with a deviation lower than 14%. The main difference is attributed to the duct presence which is taken into account only for the experimental study.
A PROPOSED MATHEMATICAL MODEL FOR THE VELOCITY PROFILE INTERNALLY TO A CONICAL DIFFUSER
Authors: Barbosa D. L. M. , Vaz D. A. T. D. R. , Vaz J. R. P. , Figueiredo S. W. O. , Da Silva M. O. , Blanco C. J. C. , Mesquita A. L. A.
Published: November 2018

The use of diffusers around of the horizontal-axis wind turbines have been widely studied, since the diffuser provides an improvement in the turbine power coefficient. These diffusers are often called Diffuser Augmented Wind Turbines (DAWT’s). The DAWT’s have the feature to make efficiency exceeding the Betz limit (maximum energy flow extracted = 59.26%), due to the increasing of the internal mass flow by influence of the diffuser presence. Thus, the present work proposed a mathematical model describing the behavior of the velocity profile internally to a diffuser according to the characteristics of flow and geometry of a conical diffuser. The model results were compared with experimental data and showed good agreement.
NUMERICAL SIMULATION OF AIRFOILS APPLIED TO UAVs
Authors: P. Corrêa P. C. , Barcelos M. N. D.
Published: November 2018

This essay aims the process optimization when referred to aeronautical projects. By using mesh generators softwares and simulations made in CFD, the article employs numerical techniques to simulate airfoils and shows that is possible to extract accurated and conservative outcomes when compared to wind tunnel results. The test cases studied were based on the Selig 1223 type of airfoil and developed into the ANSYS platform, whereas by using the ICEM mesh tool, structured meshs were generated and imported to the CFX enviroment, where they could be simulated and analyzed.
CONSTRUCTAL DESIGN OF A X-SHAPED CAVITY COOLED BY CONVECTION
Authors: Link F. B. , Rocha L. A. O. , Dos Santos E. D. , Isoldi L. A.
Published: November 2018

This paper applies Constructal design to study the geometry of a X-shaped cavity that penetrates into a solid conductive wall. The objective is minimizing the dimensionless maximal excess of temperature between the solid body and the cavity. There is uniform heat generation on the solid body. The cavity surfaces are cooled by convection heat transfer while the solid body is subjected to adiabatic conditions on its outer surfaces. The total volume and the cavity volume are fixed, but the lengths and thickness of the X-shaped cavity can vary. The emerged optimal configurations and performance are reported. The effect of the area fraction φ which denotes the ratio between the cavity area and the total area of the geometry, and the ratio between the length and thickness of the branch cavity, H1/L1, on the dimensionless maximal excess of temperature is numerically investigated. The results show that the dimensionless maximal excess of temperature θmax,min decreases approximately 60% when the cavity fraction increases from φ = 0.05 to 0.25. The results also show that the X-shaped cavity performs approximately 45% better when compared to a C-shaped cavity under the same thermal conditions. The optimal X-shaped cavity is also in accordance with the optimal distribution of imperfections principle.
EXPERIMENTAL ANALYSIS OF PRESSURE DROP IN SINGLE AND TWO PHASE IN MINI CHANNELS
Authors: Oliveira J. D. , Copetti J. B. , Dias I. C. , Macagnan M. H.
Published: November 2018

Evaporators with mini and micro channels are one of the main focuses in the design and development of equipment applied to compact refrigeration systems. The objective of this work is to investigate pressure drop of natural refrigerant, isobutane (R-600a), in the single-phase flow through two small tubes, with 1.0 mm and 2.6 mm of internal diameter. Also, the pressure drop was analyzed in the boiling flow in a 2.6 mm internal diameter tube. The experimental tests included mass velocities of 188, 240, 280 and 370 kg/(m²s), heat fluxes in the range from 0 to 134 kW/m² and boiling flow the saturation temperature of 22 ºC and vapor quality up to 0.8. It was possible to observe the significant influence of the diameter and mass velocity on the total pressure drop and the frictional pressure drop, respectively. The experimental frictional pressure drop in flow boiling in 2.6 mm of internal diameter was compared with four different correlations in literature.
EXPERIMENTAL STUDY OF TERNARY FUEL BLENDS ON AN ASTM-CFR-CETANE ENGINE
Authors: Rocha H. L. , Pinto N. R. , Colaço M. J. , Leiroz A. J. K.
Published: November 2018

This work analyses how ternary blends of biodiesel, anhydrous and hydrous ethanol, and diesel, in different proportions, behave regarding fuel emissions and combustion parameters. The determination of their cetane number, using an ASTM-CFR cetane research engine is also investigated. The base fuels used were 99,9% pure anhydrous ethanol, commercial diesel, which contains 5% of biodiesel in volume, biodiesel from soybean oil, and hydrous ethanol with 7% of water, in volume. The fuel blends werespecified after a careful bibliography research. Five volume fractions of biodiesel (5, 10, 20, 60 and 100%, in volume) and four of ethanol (0, 5, 8 and 15%, also in volume) were used in this study. All blends have endured a mixture stability test prior to being burned, the ones with clear visual phase separation being eventually rejected. The results for the cetane number presented a clear decrease in its value as ethanol was added. Some blends with high ethanol content failed to provide the minimum cetane number for use in compression ignition engines according to the present Brazilian regulations. Concerning the emissions tests, carbon dioxide emissions showed a decreasing trend as the quantity of added ethanol raised. Carbon monoxide emissions, however, showed the opposite trend. The nitrogen oxides emissions presented an increase as more biodiesel was added to the blend. The conclusions as to the impact of changing ethanol’s volume in the blends were discussed taking in consideration important operational remarks. A final analysis was proposed in order to compare anhydrous and hydrous ethanol. A clear reduction in nitrogen oxides and carbon dioxide emissions was observed, with an almost identical value for the carbon monoxide emissions. Cetane number for the hydrous ethanol blend, however, suffered a decrease compared to the same blend with anhydrous ethanol.
THE ELASTO-VISCOPLASTIC-TIME-DEPENDENT NATURE OF WAXY CRUDE OILS
Authors: Tarcha B. A. , Forte B. P. P. , Soares E. J. , Thompson R. L.
Published: November 2018

Production in reservoirs located in deep and ultra-deep water that contain waxy crude oils faces a huge obstacle imposed by the low temperatures of the environment. When the waxy crude oil is subjected to a temperature below the Gelation Temperature, as in the case investigated in the present work, it exhibits a variety of non-Newtonian features: elasticity, plasticity, viscous effects, and time-dependency, which renders to this material a highly complex behavior. A crucial feature that is frequently ignored when the determination of the yield stress is being carried out is the timedependency nature of these materials. We demonstrate that this character has a significant impact on the measurement of the yield stress and, therefore, values obtained from a protocol that neglects time-dependency can be substantially different from a more careful procedure.
EXPERIMENTAL ANALYSIS OF AN S809 AIRFOIL
Authors: Gomes A. O. , Brito R. F. , Rosa H. M. P. , Campos J. C. C. , Tibiriça A. M. B. , Treto P. C.
Published: November 2018

This paper looks into the aerodynamic behavior of an S809 airfoil commonly utilized in wind turbines. Tests were carried out to measure drag coefficient profiles under high speed flows of up to 14 m/s, with Reynolds numbers ranging between approximately Re = 11,400 and Re = 135,400. The prototype was fabricated on a fused deposition modeling machine with ABS Plus thermoplastic. Several tests were carried out in a wind tunnel. Angles of attack ranging from 0° to 20° were tested in increments of two degrees in both the clockwise (leading edge above trailing edge) and counterclockwise directions (leading edge below trailing edge). Drag coefficient versus Reynolds number curves were obtained for the aforementioned angles. The airfoil drag coefficient was found to decrease as the Reynolds number increased for all the angles of attack analyzed. Airfoil dynamic stall was determined (maximum lift coefficient). In the tests, dynamic stall occurred at approximately 16° clockwise. This value is in agreement with the literature.
VORTEX FORMATION IN INCOMPRESSIBLE AXISYMMETRIC FREE JETS
Authors: Del Rio E. R. V. , Woiski E. R. , Gasche J. J. , Mansur S. S. , Vieira E. D. R.
Published: November 2018

Free jets have been utilized extensively in many industrial applications. In general jet fluid discharging from a nozzle develops flow oscillations in the shear layer. The oscillations will roll up to eventually become toroidal vortices which increase in size with the axial distance from the nozzle. In the present work, flow visualization as well as hot-film anemometry have been employed in order to study incompressible axisymmetric free jet in moderate Reynolds numbers up to 20,000. The injection of liquid dye or micro particles associated with a laser sheet turns possible to visualize the shear layers and, consequently, the vortex formation. Hot-film measurements into the jet allow determining the flow velocity profile. Flow visualization is a qualitative tool which a broad view of the flow topology. On the other hand, hot-film anemometry is a precise quantitative tool but measurement in only one location at a time. The association of flow visualization and hot-film anemometry shows very adequate for free jet studies.
NUMERICAL INVESTIGATION OF HEAT TRANSFER IN A TURBULENT FLOW IN CHANNELS WITH GAP
Authors: Souza S. I. S. , Martins H. A. , Goulart J. N. V.
Published: November 2018

Turbulent flow in channels with gap is still a challenge for engineering. The velocity fluctuations and the appearance of coherent structures have been playing a major role in forced convective heat transfer process between the warm tube walls and the cooling fluid. In this paper numerical simulation of non-isothermal turbulent flow in a rectangular channel containing only one tube was performed. Unsteady Reynolds Navier-Stokes along with the energy equation were applied to model the problem. In order to overcome the closure problem the turbulence was modeled applying SAS model. The simulated geometry consists of a heated cylindrical tube, placed 10 mm from the bottom wall of the rectangular duct. The fluid flows externally to the heated tube along the mainstream direction. The channel’s length was based on the tube diameter, yielding L/D equal 80.
EDITORIAL
Authors: Mariano A. B.
Published: November 2018

The need for diversification of the global energy grid is present in the speeches of most governments, the motivation of scientists and the perception of a growing segment of the population. Even so, the dependence on non-renewable fuels, such as fossil fuels, has been increasing progressively due to the rapid global growth, rising consumption and increasing purchasing power of the population. Besides searching global solutions to resolve the energy quest, efforts must be directed to short-term actions, taking advantage of the available scientific and technological knowledge to improve the performance of existing systems and in use today. Improving the efficiency of cooling systems, which are responsible for much of the world electricity consumption through intelligent control of compressors can reduce up to 50% electricity consumption, and thus provide economic and strategic advantages to countries that encourage this type of initiative. Likewise, the reduction of electricity for domestic heating or showering can be obtained by waste heat recovery, solar heating or the use of heat pumps with immersed condensers, among others, contributing to the reduction of electric energy consumption. A challenge to be overcome is the popularization of such technologies in the form of final product at affordable costs. Also, for popular use, it is the important the interest of nation leaders in order to drive the use of those technologies through tax incentives and public policies. Other advances could be achieved by the use and improvement of biotechnological processes, coupling the treatment of emissions and effluents to the production of biofuels, as well as high aggregated value products. Through exergy analysis, thermoeconomics, mathematical modeling, simulation and optimization, thermal engineering is able to contribute to the efficient coupling of such different biotechnological processes and contribute to decreasing dependence on fossil fuels.
USING BEM TO PREDICT THE EFFECTIVE THERMAL CONDUCTIVITY FOR HETEROGENEOUS MATERIALS
Authors: Oberg M. B. A. M. , Anflor C. T. M. , Goulart J. N. V.
Published: November 2018

This work presents a study on the effective thermal conductivity in material with heterogeneous composition in two dimensions. The Boundary Elements Method (BEM) is used to solve the steady state potential equations. The sub regions technique was implemented in order to take into account the effects of these inclusions inside the domain. In the numerical implementation, the inclusions are randomly generated in a Representative Volume Element (RVE) domain. The Average Field Theory is used to predict the effective properties (macroscopic) of the material with heterogeneous composition. The material is characterized by a specified volume fraction as well as the inclusion’s size. The samples are composed of square domains with defined number of randomly distributed inclusions and submitted to a condition of unidirectional heat conduction. Each set of samples is analyzed several times in order to guarantee statistical stability of the result.
COMPUTATIONAL MODELING APPLIED TO THE STUDY OF THERMAL BUCKLING OF COLUMNS
Authors: Michaello R. Da S. , Helbig D. , Rocha L. A. O. , Real M. V. , Dos Santos E. D. , Isoldi L. A.
Published: November 2018

Buckling is an instability phenomenon that can happen in slender structural components when subjected to a compressive axial load. This phenomenon can occur due to an externally applied force, which when exceed a certain limit, called critical load, will promote the mechanical buckling on the structural member. Another buckling possibility happens to statically indeterminate structural elements when submitted to a positive temperature variation. As the axial displacements are restricted, if the temperature gradient is larger than the critical temperature variation, it will be generated a compressive axial load higher than the critical load of the structural component and the thermal buckling will occur. In this context, the present work presents a computational model to solve the thermal buckling problem of columns. A thin shell finite element, called SHELL93, was adopted for the computational domain discretization. It was employed a solution involving homogeneous algebraic equations, where the critical temperature variation is determined by the smallest eigenvalue and the buckled configuration is defined by its associated eigenvector. A case study was performed considering a steel column with three different support conditions at its ends: fixed-fixed, fixed-pinned, and pinned-pinned. The numerical results obtained for the critical temperature variation showed a maximum absolute difference around 2% when compared to the analytical solutions. Moreover, the buckled shape of the column, for each case, was defined in agreement with the configurations found in literature. Therefore, the computational model was verified, i.e., it is able to satisfactorily predict the mechanical behavior of the thermal buckling of columns. So, it is possible to use this numerical model in practical situations that do not have an analytical solution, as is the case of the thermal buckling of columns with cutouts.
EXPERIMENTAL VALIDATION OF A DYNAMIC MODEL FOR A RESIDENTIAL HEAT PUMP WITH IMMERSED CONDENSER
Authors: Nunes R. O. , Faria R. N. , Koury R. N. N. , Machado L. , Huebner R.
Published: November 2018

This work describes the validation of a dynamic model for a vapor compression residential heat pump with an immersed condenser. A detailed description of the modelling methodology for each component (compressor, capillary tube, evaporator, and immersed condenser) and the solution methodology employed in the complete heat pump system are presented. The main contribution of this work is in the dynamic modeling of the thermal processes occurring within the heat exchangers. Instabilities of the solutions for the heat exchangers are minimized by considering spatially and temporal varying errors. Another contribution of the model is the investigation of the temperature distribution inside the water storage tank, which highlights the possibility of using immersed condensers for this purpose without significant thermal stratification in the tank. Simulation results and experimental results are compared for transient operations using multivariate profiles of temperature, pressure and mass flow rates in heat exchangers during the water heating process.
CFD NUMERICAL ANALYSIS OF A PROPOSED CHANGE IN THE CHANNEL GEOMETRY DOWNSTREAM OF A REVERSED TAINTER GATE
Authors: Corte M. D. , Oliveski R. C. , Marques M. G. , Dai Pra M.
Published: November 2018

Reversed Tainter gates are often used to control flow in the filling and emptying locks navigation systems of high fall. High speeds and pressure fluctuations may occur in the flow downstream of these gates, the flow cavitation may occur, damaging the structure. One way proposed to mitigate this problem is through geometric changes in the channel downstream of the gate. In this study was analyzed using CFD the effect of an expansion in the roof and the base of the conduit, followed by a straight section and a subsequent contraction until returning to the original geometry. It was observed that the pressure at the base of the conduit increases with the modification, however peaks of positive and negative pressures occur due to the shape change of the geometry of the corners not be smooth. The size of recirculation downstream of the gate increases with the geometrical alteration, increasing the distance required for pressure recovery.
AN APPROACH FOR THE OPTIMUM HYDRODYNAMIC DESIGN OF HYDROKINETIC TURBINE BLADES
Authors: Shinomiya L. D. , Vaz J. R. P. , Mesquita A. L. A. , De Oliveira T. F. , Brasil Jr A. C. P. , Silva P. A. S. F.
Published: November 2018

This work aims to develop a simple and efficient mathematical model applied to optimization of horizontal-axis hydrokinetic turbine blades considering the cavitation effect. The approach uses the pressure minimum coefficient as a criterion for the cavitation limit on the flow around the hydrokinetic blades. The methodology corrects the chord and twist angle at each blade section by a modification on the local thrust coefficient in order to takes into account the cavitation on the rotor shape. The optimization is based on the Blade Element Theory (BET), which is a well known method applied to design and performance analysis of wind and hydrokinetic turbines, which usually present good agreement with experimental data. The results are compared with data obtained from hydrokinetic turbines designed by the classical Glauert's optimization. The present method yields good behavior, and can be used as an alternative tool in efficient hydrokinetic turbine designs.
EVALUATION OF THE COMBUSTION PROCESS OF COFFEE HUSK SAMPLES IN A DROP TUBE FURNACE (DTF)
Authors: Cruz G. , Crnkovic P. M.
Published: November 2018

Thermal conversion processes that use coffee husk are an alternative to solve the environmental problems of disposal and waste burning in open places and avoid greenhouse gases emissions. The present study evaluates in natura coffee husk samples and residues obtained from a combustion process in a Drop Tube Furnace (DTF). Such an evaluation consists in understanding the efficiency of the burning process, therefore the activation energies (Ea) of the combustion process for both samples were determined. The isoconversional kinetic method (Model Free Kinetics) was used for the determination of the Ea values of the samples. The Ea values of the main stages of the combustion process (devolatilization and carbonization) for both samples were compared. Thermogravimetric (TG) and Derivative Thermogravimetric (DTG) data at five heating rates (10, 15, 20, 25 and 30 oC min-1) were used for the determination of hemicellulose, cellulose and residual lignin. SEM (Scanning Electronic Microscopy) images and EDS (Energy Dispersive Spectroscopy) analysis were applied as complementary techniques in the combustion process. The results show that for both samples the Ea values were higher for the carbonization step than for devolatilization. The Ea values for the stages of devolatilization and carbonization for the residues were 33 and 15% lower than those for the in natura coffee husk samples. The lower Ea values in both steps for the residues are indicative of a reduction in the complexity of the reaction mechanism, which can be a parameter for the evaluation of the biomass combustion process. According to the SEM images, the residues showed exploded surfaces caused by the combustion process, whereas in the in natura samples a denser and robust structure was observed. The ash formed after the combustion process in the thermobalance was also evaluated by SEM and EDS analyses and showed a more homogenous structure with tiny particles in comparison with the in natura coffee husk samples. The EDS analysis confirmed the presence of precursor elements in the samples, such as potassium and other inorganic materials, which were intensified after the combustion process.
MATHEMATICAL MODELING OF LEACHING PROCESS OF RED MUD IN ORDER TO OBTAIN THE KINETICS PARAMETERS
Authors: Dos Passos K. L. M. , Viegas B. M. , Macêdo E. N. , Souza J. A. S. , Magalhães E. M.
Published: November 2018

The use of the waste of the Bayer process, red mud, is due to its chemical and mineralogical composition that shows a material rich in oxides of iron, titanium and aluminum. Some studies conducted show that this waste can be applied as a source of alternative raw material for concentration and subsequent recovery of titanium compounds from an iron leaching process, which is present in higher amounts, about 30% by weight. To obtain a greater understanding about the leaching kinetics, the information of the kinetic data of this process is very important. In this context, the main objective of this work is the development of a mathematical model that is able to fit the experimental data (conversion / extraction iron, titanium and aluminum) of the leaching process by which is possible to obtain the main kinetic parameters such as the activation energy and the velocity of chemical reactions as well as the controlling step of the process. The development of the mathematical model was based on the model of core decreasing. The obtained model system of ordinary differential equations was able to fit the experimental data obtained from the leaching process, enabling the determination of the controlling step, the rate constants and the activation energies of the leaching process.
THERMAL PERFORMANCE OF THERMOSYPHON FOR DIFFERENT WORKING FLUIDS
Authors: Russo G. M. , Krambeck L. , Nishida F. B. , Santos P. H. D. , Alves T. Antonini
Published: November 2018

In this paper, an experimental investigation was performed of the thermal performance of different working fluids in thermosyphons that can be used in thermal control of electronic equipment. The working fluids were considered acetone, water, ethanol, and methanol. The thermosyphon are manufactured of copper with an outer diameter of 9.45 mm, an inner diameter of 7.75 mm, a total length of 200 mm, whereas an evaporator of 80 mm length, an adiabatic region of 20 mm in length and a condenser of 100 mm in length. They were loaded with 1.39 ml of the working fluid, corresponding to a filling ratio of 40% of the evaporator volume. Experimental tests were performed in a vertical position considering thermal loads between 5W and 25W. The thermosyphons operated satisfactorily in all the tests. The operating temperature distribution as a function of time and the heat resistance behavior as a function of power dissipation have been presented for each analyzed working fluid. These results indicated that acetone is the working fluid that has the best thermal performance.
REVIEW OF NUMERICAL SCHEMES AND BOUNDARY CONDITIONS APPLIED TO WAVE PROPAGATION PROBLEMS
Authors: Almeida Odenir De
Published: November 2018

As a review framework, the present study describes the application and performance of different numerical schemes for Computational Aeroacoustics (CAA) of simple wave propagation problems. The current approach aims to simulate pulse propagation on the near field by the use of different spatial and temporal numerical schemes for the full and Linearized Euler Equations (LEE) in a dimensional and dimensionless formulation. Comparisons of processing time, residual error and quality of results are present and discussed shedding light to the relevant parameters which play important role in aeroacoustics. The investigation is focused on different Gaussian pulse propagation cases in unbounded and bounded domains which is solved by using optimized spatial and temporal schemes for reducing dissipative and dispersive errors. The numerical results are compared with the exact analytical solutions when available, showing good agreement.
THE ONSET OF DOUBLE-DIFFUSIVE CONVECTION IN A LAYER OF NANOFLUID UNDER ROTATION
Authors: Rana G. C. , Thakur R. C.
Published: November 2018

Double-diffusive convection in a horizontal layer of nanofluid under rotation heated from below is studied. The nanofluid describes the effects of thermophoresis and Brownian diffusion. Based upon perturbations and linear stability theory, the normal mode analysis method is applied to obtain the dispersion relation characterizing the effect of different parameters when both the boundaries are free. Due to thermal expansion, the nanofluid at the bottom will be lighter than the fluid at the top. Thus, this is a top heavy arrangement which is potentially unstable. In this paper we discuss the influences of various non-dimensional parameters such as rotation, solute gradient, thermo- nanofluid Lewis number, thermo-solutal Lewis number, Soret and Dufour parameter on the stability of stationary convection for the case of free-free boundaries. It is observed that rotation and solute gradient have stabilizing influence on the system. Rotation and solute gradient play important role in the thermal convection of fluid layer and has applications in rotating machineries such as nuclear reactors, petroleum industry, biomechanics etc. and solute gradient finds applications in geophysics, food processing, soil sciences, oil reservoir modeling, oceanography etc. A very good agreement is found between the present paper and earlier published results.
HYDROGEN PRODUCED BY SOLAR ENERGY AND THEIR USE AS CLEAN FUEL FOR POWER GENERATION IN A COMBINED CYCLE POWER PLANT
Authors: Restrepo J. C. , Venturini O. J. , Silva E. E. , Cortabarria L. A.
Published: November 2018

The solar energy is one of the most promising energy sources expected for the future, due at their huge potential and the wide availability around the world. However, nowadays this important source of energy is not being harnessed or even addressed in their full potential. According to the last statements, it is important to develop solar energy conversion systems of high efficiency, as well as spreading its use in other forms besides the traditional systems of electric power generation or heating systems. For this reason, in this paper, it is explored the production of hydrogen through solar energy utilization, and the later electrical energy production by burning the produced hydrogen in a combined cycle power plant. The process was modelled for 3 MWe of electricity generation, and using the organic Rankine cycle. The main process for producing hydrogen from water using solar energy is based on a two steps redox thermochemical cycle, which has a theoretical conversion efficiencies of 54% at 1600 K. It is expected that this paper could contributed to the development of ways to enable a better integration of the solar energy with the current electricity generation technologies, as well as to incentive the use of the hydrogen as a clean fuel.
EDITORIAL
Authors: Yang Sam
Published: November 2018

The editorial of Engenharia Térmica of this issue continues the discussion on scientific research needs in vital areas in which thermal engineering has important participation. The main goal is to motivate the readers, within their specialties, to identify possible subjects for their future research. Extensive research efforts have been devoted to the development of high performance heat sinks, and numerous geometric designs and fin arrangements as well as materials have been proposed to achieve higher heat dissipation rates. Previous studies have deduced different fin geometries and arrangements based on minimum entropy generation or maximum heat transfer rate, subject to various constraints such as available space, material, or cost. Consequently, many fin shapes and arrangements exist in literature ranging from elliptical cylinders to rhombus, and from pin to flared fin, respectively. According to the literature review, however, helical fins have not yet been explored as an alternative design owing to its complex geometry that restricts the analysis to 3D space. Therefore, a 3D helical fin model still needs to be developed to investigate its feasibility and performance as an alternative fin design. In addition, a helical fin arrangements optimization study shall be conducted for minimum pressure drop and maximum heat transfer. The mission of Engenharia Térmica is to document the scientific progress in areas related to thermal engineering (e.g., energy, oil and renewable fuels). We are confident that we will continue to receive articles’ submissions that contribute to the progress of science.
SOCIO-ECONOMIC PERFORMANCE OF A SOLAR FLAT PLATE COLLECTOR BASED IN A HEAT PUMP WATER HEATING SYSTEM IN THE BRAZILIAN SOUTHEAST
Authors: Rodríguez O. R. S. , Koury R. N. N. , Maia A. A. T.
Published: November 2018

By increasing renewable energy demand, the use of solar energy has been widely investigated over the recent years. Brazil is a privileged country in terms of the levels of receivable solar radiation in almost all over its territory. However, as there are days when there is a deficit in solar energy, because the day be cloudy or rainy days, and for this reason, solar collectors need a support to contribute to the water heating to the desired temperature. In this work, an experimental study of a heat pump operated with R-134a, as an ancillary equipment for a solar water heating system in Belo Horizonte city has been accomplished. For this project, is used a set of electrical resistances for by a power control step, simulate historical annual values of solar radiation. In the results, it was observed that is achieved through the collection of solar energy the temperature of 45°C in the reservoir only in January, and the other eleven months is necessary to use the heat pump to achieve reach that temperature. With the heat pump operating in conditions similar to real conditions gave an average annual consumption of 137.65 kWh and a cost of R$ 60.61.
EXPERIMENTAL EVALUATION OF THE AERODYNAMIC PERFORMANCE OF SMALL WIND TURBINES CONFECTIONED IN 3D PROTOTYPING
Authors: Garré S. O. , Paula A. V. , Luz J. L. R. , Vecina T. D. J. , Petry A. P.
Published: November 2018

This paper presents the experimental evaluation of the aerodynamic performance of two small wind turbines models with five blades in the Aerodynamic Tunnel Professor Debi Pada Sadhu. The models were confectioned on a reduced scale using 3D prototyping, the first one was designed using the blade element method, assuming the power coefficient of Betz, named Optimal Blade Betz (OBB) and the second is modified from the first one, named Optimal Blade Betz Modified (OBBM). The velocity distribution in the cross section of the tunnel was determined with the aid of a Pitot tube before the evaluation of the equipment. With the known tunnel velocity profile, the static torque of the prototypes were determined with the use of a digital torquemeter coupled to the machine axis, which recorded the readings for the speed range of 1 m/s to 9.88 m/s. Also with the torquemeter, were evaluated the influence of the angular position of the blades in the measured torque. The blades were designed allowing vary their angular position in the hub, thus changing the angle of attack, and by consequence, the torque produced. A photo tachometer was employed to measure the rotation of the model in free spin. With the experimental data, the curves of static torque and angular velocity were determined as a function of incident speed. Through experimental determination of the incident velocity profile and the velocity profile in the aerodynamic wake of each turbine, the variation of the amount of momentum of the outflow was evaluated, and so the power extracted by the rotor in free rotation. This study aims to contribute to the design of a real small wind turbine, informing the aerodynamic characteristics of the equipment that can be constructed with this layout. The experimental results demonstrate good approximation for torque and power to the results obtained by evaluation by element of the blade method. The turbine constructed with Optimal Betz Blades presented static torque 17.8% higher than constructed with the Modified Blades and extracted 22% more power from the air outflow.
SOLUTION OF 1D AND 2D POISSON'S EQUATION BY USING WAVELET SCALING FUNCTIONS
Authors: Burgos R. B. , Peixoto H. F. C.
Published: November 2018

The use of multiresolution techniques and wavelets has become increasingly popular in the development of numerical schemes for the solution of partial differential equations (PDEs). Therefore, the use of wavelet scaling functions as a basis in computational analysis holds some promise due to their compact support, orthogonality and localization properties. Daubechies and Deslauriers-Dubuc functions have been successfully used as basis functions in several schemes like the Wavelet- Galerkin Method (WGM) and the Wavelet Finite Element Method (WFEM). Another possible advantage of their use is the fact that the calculation of integrals of inner products of wavelet scaling functions and their derivatives can be made by solving a linear system of equations, thus avoiding the problem of using approximations by some numerical method. These inner products were defined as connection coefficients and they are employed in the calculation of stiffness matrices and load vectors. In this work, some mathematical foundations regarding wavelet scaling functions, their derivatives and connection coefficients are reviewed. A scheme based on the Galerkin Method is proposed for the direct solution of Poisson's equation (potential problems) in a meshless formulation using interpolating wavelet scaling functions (Interpolets). The applicability of the proposed method and some convergence issues are illustrated by means of a few examples.
GEOMETRICAL OPTIMIZATION OF MIXED CONVECTIVE FLOWS OVER TRIANGULAR ARRANGEMENT OF CYLINDERS
Authors: Barros G. M. , Pereira M. Dos S. , Carmo D. M. do , Cemin R. , Isoldi L. A. , Rocha L. A. O. , Santos E. D. dos
Published: November 2018

The present study consists on the numerical evaluation of a triangular arrangement of circular cylinders submitted to transient, two-dimensional, incompressible, laminar and mixed convective flows. The geometrical evaluation is performed by means of Constructal Design. For all simulations it is considered Reynolds and Prandtl numbers of ReD = 100 and Pr = 0.71. Moreover, three different values of Richardson number are investigated: Ri = 0.1 (which represents flows dominated by forced convective), 1.0 (which represents an equilibrium between forced and natural driven forces) and 10.0 (which represents flows with dominance of natural convective). The conservation equations of mass, momentum and energy are solved with the use of Finite Volume Method (FVM). The buoyancy forces are tackled with the Boussinesq approximation. The area occupied by the triangular arrangement of cylinders is a geometric constraint of the problem and the cylinders have the same diameter. The main purpose is to evaluate the effect of Richardson number over the drag coefficient (CD) and Nusselt number (NuD) between the cylinders and the surrounding flow, as well as, over the optimal ratio ST/D (ratio between transversal pitch and the cylinder) for two different values of the ratio SL/D = 1.5 and 2.5 (ratio between longitudinal pitch and the cylinders diameter). Results showed that the effect of ST/D over drag coefficient and Nusselt number is strongly affected by the magnitude of Richardson number. Concerning the Nusselt number, for Ri = 0.1 the optimal geometry which maximizes the NuD is reached for the highest magnitude of ST/D, while for Ri = 10.0 an intermediate optimal ratio of ST/D maximizes the NuD. The Richardson magnitudes also have large influence over the fluid dynamic and thermal behavior of fluid flow for all evaluated geometries. An increase in the ratio SL/D improved the heat exchange of the flow, but decreased the fluid dynamic performance.
DIFFERENTIAL EVOLUTION ALGORITHM APPLIED IN A NUMERICAL COST OPTIMIZATION DESIGN OF A SHELL AND-TUBE HEAT EXCHANGER
Authors: Martinez L. C. , Mariani V. C. , Coelho L. S. , Segundo E. H. V.
Published: November 2018

Shell-and-tube heat exchangers are the most common heat exchangers that can be found in several industrial applications. The reduction of the investment cost and the operation of this equipment it’s one of main industrial designers and entrepreneurs aim. With the intention of reducing total costs of a shell-and-tube heat exchangers, as proposed by Caputo et al. (2008), employed in this present study the optimization technique called Differential Evolution (DE), which basically consists in a calculation mechanism, supported on operators of “crossing” and “mutation” differential, through mathematical and heuristics arguments that indicate your adequacy for function optimization. This study is defined as a mono-objective optimization problem and the total cost of a shell-and-tube heat exchanger is the objective function. To this, it was taken as a design variable intern diameter tube, the outer diameter of the shell and the spacing between baffles or deflectors. The results reached in this work were compared with the same problem when used GA (Genetics Algorithms), PSO (Particle Swarm Optimization), QPSO (Quantum Particle Swarm Optimization) and QPSOZ (Quantum Particle Swarm Optimization by Zaslavskii). Regarding the literature, the capital investment in the heat exchange reduces corresponding in 15.2% and consequently the depreciation charge of the equipment decrease approximately 12.5%. In general, the total cost of the shell-and-tube heat exchange in analysis, presented a reduction of 15%, showing the potential of applied method in this study, the technique DE.
AN APPROACH TO OPTIMISE THE SELECTION OF LNG CARRIERS’ PROPULSION SYSTEM
Authors: Marques C. H. , Belchior C. R. P. , Caprace J. -D.
Published: November 2018

Marine transport of natural gas, mostly in its liquid phase, is of growing importance in the global energy markets. The fleet of liquefied natural gas carriers is thereby increasing and being upgraded to enhance its performance. Since there is no well-defined procedure about how to perform the selection of the propulsion system considering the peculiarities of this kind of vessel, this work intend to fill this gap. In other words, the present article aims to propose an approach so that one can perform the optimised selection of liquefied natural gas carriers’ propulsion system mainly concerning financial aspects. Firstly, some fundamentals about liquefied natural gas and its transport are presented followed by reasons why the traditional steam turbine propulsion plant was abandoned and dual- fuel diesel engines have been applied instead. Then, a list of criteria is discussed and studies that inspired this work are summarised. A case study of a ship with cargo capacity of 174,000 m3 operating between Lake Charles and Tokyo Bay via Panama Canal is selected. Owing to this route and environmental rules, the ship has to travel at three different levels of service speed unlike ordinary ones, which usually keep a steady speed throughout voyage. Maximising the net present value of the project is the objective function that is intended to be achieved by optimising eleven variables regarding synthesis, design and operation of the propulsion system. Finally, it is suggested that this work may assist marine engineers and ship-owners to design and outline the operation of liquefied natural gas carriers.
SEMI-ANALYTICAL SOLUTION OF THE HEAT CONDUCTION IN A PLATE WITH HEAT GENERATION
Authors: Silva L. C. da , Chalhub D. J. N. M. , Calil A. L. O. , Moura R. S. de
Published: November 2018

In the present work, a formulation for the solution of the two-dimensional steady state heat conduction with heat generation is presented. The classical integral transform technique (CITT) is used to solve the problem in a semi- analytical manner. CITT deals with expansions of the sought solution in terms of infinite orthogonal basis of eigenfunctions, keeping the solution process always within a continuous domain. For the particular problem, the resulting system is composed of a set of uncoupled differential equations which can be solved analytically. However, a truncation error is involved since the infinite series must be truncated to obtain numerical results. For comparison and validation purposes, the second order central finite difference method (FDM) is also implemented. The convergence analysis showed that CITT has a greater performance having no difficulties to obtain accurate results with very few terms in the solution summation. The FDM had convergence troubles specially for the positions near the center and for high concentration of heat generation in the center of the plate.
ANALYSIS OF LAMINAR FORCED CONVECTION INSIDE A SQUARE VENTILATED CAVITY USING THE OPENFOAM®
Authors: Mioralli P. C. , Scalon V. L. , Avallone E. , Verdério Jr S. A.
Published: November 2018

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.
EDITORIAL
Authors: Balmant W.
Published: November 2018

There is currently a strong UN and IPCC-led campaign promoting the rejection of oil-derived fuels because of the risk of global warming. However, global demand for oil does not decline, but tends to increase to 100 million barrels per day in 2018 according to the International Energy Agency (IEA). This clearly demonstrates that a speech is not enough, but new sources of energy are needed that can unequivocally replace oil from a technical and economic point of view. In this context, one of the possible solutions is the introduction of biorefineries, which have the capacity to process biomass from different sources, generating several products and fuels derived from biomass. An example of biorefinery is the production of ethanol from sugarcane bagasse, where all sugarcane biomass is harvested for ethanol generation. However, the processes involving biorefineries are still in laboratory or pilot scale, because these processes are not yet economically feasible. One of the crucial bottlenecks of a biorefinery is the energy cost of the processes involved, which is often greater than the energy gain obtained. One way to reduce the energy costs of these processes is thermodynamic optimization. For this, mathematical models are needed that are capable of describing all the processes that occur within a biorefinery. Unfortunately, there is no such tool available, which makes thermodynamic optimization of biorefinery impossible. However, for oil refining, this tool is already available even in the form of commercial software such as Aspen Plus, after all petroleum refining is an industry more than a hundred years old and so the exploitation of oil is so profitable. If biorefineries want to compete with the oil industry, it is necessary to develop simulation tools that can be used for thermodynamic optimization, so that the processes of a biorefinery become economically feasible.