Listagem por temas:
Escolhendo um título você terá acesso ao arquivo original em Post-Script.
COB47 ANÁLISE NUMÉRICO-EXPERIMENTAL DA DISTRIBUIÇÃO DE TEMPERATURA EM UM RESERVATÓRIO DE ÁGUA QUENTE / NUMERICAL-EXPERIMENTAL ANALYSIS OF TEMPERATURE DISTRIBUTION IN A HOT WATER STORAGE TANK
Rejane de-Césaro-Oliveski, Arno Krenzinger, Horácio A . Vielmo & César W. M. Prieb
PROMEC - Programa de Pós-Graduação em Engenharia Mecânica - UFRGS -Porto Alegre
Rua Sarmento Leito, 425 - CEP 90.050-170 R. S., Brasil - E-mail:decesaro@vortex.ufrgs.br
This work presents a numeric-experimental analysis of temperature and velocity fields inside a hot water reservoir in transient conditions. Initially the tank is at an uniform temperature and thereafter subject to a slow cooling at ambient temperature. A finite volumes method is applied in order to perform this analysis, with a bidimensional model in cylindrical coordinates. The program is continuously fed by 14 polynomials, which prescribe the tank wall temperature. These polynomials vary with the tank height and have time as argument. They were originated from experimental tests on a tank with an aspect ratio (height/diameter) close to unity. The temperatures of the walls and the center were measured by means of iron-constantan thermocouples. Errors caused by contact resistance and by the thermocouples themselves were also analyzed, with satisfactory results. Numerical tests show an excellent agreement between theoretical and experimental results.
Keywords: Análise numérico-experimental, armazenamento de calor, energia solar, convecção transiente / Numerical-experimental analysis, heat storage, solar energy, transient convection.
COB506 MODELO PARA SINTETIZAÇÃO DE DADOS DE RADIAÇÃOSOLAR EM SEQÜÊNCIAS COM INTERVALOS DE 5 MINUTOS / METHOD FOR SOLAR RADIATION DATA SYNTHESIZING IN SEQUENCES WITH INTERVALS OF 5 MINUTES.
Arno Krenzinger
Departamento de Engenharia de Materiais / Grupo de Estudos Térmicos e Energéticos - PROMEC / Universidade Federal do Rio Grande do Sul, Rua Sarmento Leite, 425/208 CEP:90.050-170 Porto Alegre RS
This work presents a method to generate sequences of solar radiation data in intervals of 5 minutes with the use of a computer program. The data are generated starting from information of hourly horizontal global solar radiation values, date and local latitude. The method was developed with exclusive interest in simulations of solar systems being more important for photovoltaic applications than for water-heating simulating. It is very important that the frequency and the intensity of variation of the radiation have some similarity with measured data. The effort was concentrated in finding a simple method, that didn't demand many input data but that could correspond to a behavior waited as typical in most of the places. The results were compared with measured data and there was obtained very good agreement.
Keywords: Energia Solar, Radiação Solar, Seqüências de Dados, Simulação de Sistemas Solares
Solar Energy, Solar Radiation, Meteorologic Data Sequences, Solar Systems Simulation
COB735 VENTILAÇÃO NATURAL INDUZIDA POR ENERGIA SOLAR : ANÁLISE TEÓRICA E EXPERIMENTAL / SOLAR ENERGY INDUCED NATURAL VENTILATION : THEORETICAL AND EXPERIMENTAL ANALYSIS
Lurdes Zunino & Alcir de Faro Orlando .
Departamento de Engenharia Mecânica, PUC-Rio, R. Marquês de S. Vicente 225, Rio de Janeiro
CEP 22453-900, Brasil, e-mail afo@mec.puc-rio.br
The influence of different architectural elements on the performance of a solar energy induced natural ventilation system has been experimentally studied. It is basically composed of a chimney, a solar energy air collector and architectural elements on the top of the chimney to protect it from outside. A vertical screen, placed between the chimney top and its horizontal cover was found to be the most effective element, as far as the air flow is concerned. A venetian blind was found to have the best performance when its slats are set inclined 60o to the chimney wall, upwards. The cover was necessary to induce a higher natural ventilation. The design of the collector entrance was found to be important for better performance. Finally, a simulation procedure was used to predict the natural ventilation device under different insolation levels.
Keywords: Natural Ventilation, Solar Energy, Chimney effect, Air Collector / Ventilação Natural, Energia Solar, Efeito Chaminé, Coletor para Ar.
COB780 ESTUDO DO ESCOAMENTO LAMINAR EM SISTEMAS AERO-SOLARES / LAMINAR FLOW ANALYSIS OF SOLAR-AIR SYSTEMS
Marco A. dos S. Bernardes, Márcio Fonte-Boa Cortez, Ramón M. Valle.
Departamento de Engenharia Mecânica, Universidade Federal de Minas Gerais
Av. Antônio Carlos, 6627, CEP: 31270-901, Belo Horizonte-MG, BRASIL - E-mail: marco@oraculo.lcc.ufmg.br
Solar Chimneys are devices used to convert solar energy into thermal and electrical energy. These devices are built with a transparent radial canopy covering the ground and a chimney positioned at its center. In the present work, the thermal hydrodynamic behavior of air in free convection in a Solar Chimney was theoretically analyzed to verify the geometrical and operational effects. The mathematical model formulation was performed considering laminar flow and prescribed boundary conditions. The visualization of the flow and the temperature profiles were allowed by the use of Finite Volume with Generalized Coordinates. Geometrical variations were introduced in a basic configuration to verify the system performance under variations of geometrical parameters. Three geometrical parameters were evaluated throughout simulation: the canopy/ground distance, the canopy/chimney connection shape and the chimney shape and cross section. The results indicated that the best performance was achieved with curved canopy/chimney connection shape and chimney conic shaped.
Keywords: Chaminé Solar, Volumes Finitos em Coordenadas Generalizadas, Convecção Natural, Energia Solar, Fontes Alternativas de Energia / Solar Chimney, Finite Volume Method with Generalized Coordinates, Free Convection, Solar Energy, Renewable Energy Sources.
COB884 THERMAL EFFICIENCY OF A SOLAR COOKING SYSTEM WITH STORAGE / EFICIÊNCIA TÉRMICA DE UM SISTEMA DE FOGÃO SOLAR COM ARMAZENAMENTO DE CALOR
Maria Eugênia Vieira, Carlos Antônio Silva Gomes & Raimundo Nonato Pereira Teixeira
Laboratório de Energia Solar Aplicada, Centro de Tecnologia, Bloco 710, Universidade Federal do Ceará
CEP 60455-760 Fortaleza, Ceara, Brazil -E-mail: eugenia@les.ufc.br, carlos@les.ufc.br, nonato@les.ufc.br
The thermal performance of a solar natural circulation heating system that uses an oil as the working fluid, a flat plate solar collector, and a storage tank has been studied for the ambient conditions in Fortaleza. To determine the system efficiency, each component is modeled separately. To estimate the total mass flow rate through the collector, the total frictional pressure drop is set equal to the pressure gain due to the difference in density in the two vertical portions of the circuit. In the analysis, the flow was considered laminar because of the low velocities expected. The results show the numerical values for total mass flow rate through the circuit and castor oil presented the best performance, that is the highest values for collector heat removal factor, when compared to cotton and soy oil.
Keywords: Solar cooker, flat plate collector / Fogão solar, coletor de placa plana
COB885 ANALYTICAL AND EXPERIMENTAL STUDY OF A STILL TYPE SOLAR DISTILLER / ESTUDO ANALÍTICO E EXPERIMENTAL DE UM DESSALINIZADOR SOLAR DE TANQUE
Maria Eugênia Vieira, Claudia Alves de Lima & Lecimara Duque Estrada
Laboratório de Energia Solar Aplicada, Centro de Tecnologia, Universidade Federal do Ceará
CEP 60.455-760 Fortaleza - Ce- Brazil - E-mail: eugenia@les.ufc.br
This work presents a procedure to estimate the thermal efficiency of a still type solar distiller to produce potable water from salty water. At present, the general model is based on the simultaneous solution of the energy balance equations for the water in the tank and the transparent cover. These equations are written as functions of the thermal variables, the ambient variables such as the intensity of solar radiation, ambient temperature, wind speed, and the construction materials and dimensions of the distiller. This numerical model allows the simulation of the thermal performance of the solar distiller so that more units may be developed and built taking into consideration the local ambient variables and resources. The thermal efficiency is calculated as the ratio of the energy used in the evaporation process to the total incident solar radiation.
Keywords: Solar tank, distiller, desalination / tanque solar, destilador, dessalinizador
COB887 THERMAL ANALYSIS OF AN EVACUATED TUBE SOLAR COLLECTOR IN FORCED AND NATURAL CIRCULATION FLOW / ANÁLISES TÉRMICAS DE UM COLETOR SOLAR DE TUBO EVACUADO EM ESCOAMENTO NATURAL E FORÇADO
Maria Eugênia Vieira, Heloisa Beatriz Cordeiro Moreira & Gleidson Santos do Nascimento
Laboratório de Energia Solar Aplicada, Centro de Tecnologia, Bloco 710, Campus do Pici - UFC
CEP 60455-760 - Fortaleza , Brazil - E-mail: eugenia@ufc.br / heloisa@les.ufc.br
An evacuated tube solar collector is a heat exchanger that converts radiant solar energy into heat. It is made of an absorber plate placed in a glass tube. The space inside the tube is evacuated to a pressure of 10-04 to 10-06 Torr. The evacuation reduces convection losses from the plate, which may be coated with a selective surface. This work presents a numerical model to determine the thermal efficiency of this collector operating in forced and natural circulation flows. In forced flow, the energy balance equations for the absorber plate and the glass tube are used to estimate the collector heat removal factor. In natural circulation, with water vapor as the working fluid, a model developed for a solar thermal siphon circuit is used. The thermal efficiency values found for both operations under the ambient conditions in Fortaleza were high and indicated the possibility of applications in solar refrigeration systems.
Keywords: Evacuated tube, solar collector, solar heat pipe / Tubo Evacuado, coletor solar, tubo de calor solar
COB1453 ANÁLISE TEÓRICO-EXPERIMENTAL DE UM LEITO DE PEDRAS DE GRÊS-DO-PARÁ PARA FINS DE SECAGEM/ THEORETICAL-EXPERIMENTAL ANALYSIS OF A STONE BED ABSORBER WITH GRÊS-DO-PARÁ FOR DRYING PURPOSES
Fábio Nogueira Batista e Severiano da Silva Lima Filho
Departamento de Engenharia Mecânica - Universidade Federal do Pará – UFPA
CEP 66075-900 Belém do Pará, Brasil – E-Mail: slima@amazon.com.br
This work presents a numerical and experimental study to evaluate some parameters of the heat transfer in a stone bed solar collector - The outlet temperature and humidity. The numerical analysis is based on the equations obtained by the energy balance using the concept of lumped formulation and fourth order Runge-Kutta´s method applied to this non-linear case. The results are then compared to an experiment and were considered satisfactory for design purposes.
Keywords: Drying sistem, solar energy, stone bed absorber, Runge-Kutta ´s method, lumped formulation.