ENCIT2012-080 IMPROVED MODEL FOR SOLAR CHIMNEY ANALYSIS - PDF
Christian Scapulatempo Strobel, UFPR, Brazil
Luís Mauro Moura, Viviana Cocco Mariani, PUCPR, Brazil
Abstract: Solar chimneys are power generation plants which use the energy from the sun to promote airflow, and the kinetic energy is harnessed by turbines located at the base of the chimney which convert it into electrical energy. In this paper are proposed new approaches improving the mathematical models presented in the literature. The new approaches proposed include the influence of the multiple reflections of solar radiation on glazing collector and on glazing/ground interface in order to improve the accuracy of the total temperature increase by the system. Four models are analised, and the reasons for the difference among the models are highlighted. The proposed model in this study leads to an error of only 1.0\% when compared to experimental data of Manzanares.
Keywords:Solar chimney; Solar energy; Renewable energy,; Heat transfer; Solar tower.
Presentation Schedule: Tuesday, 16:20-16:40. Session: ETS1-2. Presenter: Luis Mauro Moura.
ENCIT2012-077 TWO-DIMENSIONAL COMPUTATIONAL MODELING OF THE SOIL THERMAL BEHAVIOR DUE TO THE INCIDENCE OF SOLAR RADIATION - PDF
Ruth da Silva Brum, Elizaldo Domingues dos Santos, Joaquim Vaz, Liércio André Isoldi, FURG, Brazil
Luiz Alberto Oliveira Rocha, UFRGS, Brazil
Abstract: Nowadays, there is a great concern to find sustainable and energy saving thermal comfort technologies for buildings. The Earth-Air Heat Exchangers (EAHE) are among the air conditioning techniques that meet these conditions. This work presents a transient two-dimensional model to assess numerically the soil thermal behavior, i.e., the soil thermal potential aiming to help the design of EAHE. The incidence of the solar radiation was considered by a soil surface temperature distribution equation based on experimental data. This equation was employed as a boundary condition in the numerical model. The FLUENT package, that is a Computational Fluid Dynamics (CFD) commercial code, was used. The preliminary results present an excellent agreement with analytical solutions and experimental data showing the validity and effectiveness of the 2D developed computational model.
Keywords:Soil Thermal Potential; Earth-Air Heat Exchangers (EAHE); Computational Modeling; FLUENT.
Presentation Schedule: Wednesday, 10:00-10:20. Session: ETS2. Presenter: Ruth da Silva Brum.
ENCIT2012-079 RADIATIVE HEAT TRANSFER CONSIDERING THE EFFECT OF MULTIPLE REFLECTIONS IN SOLAR COLLECTORS - PDF
Christian Scapulatempo Strobel, UFPR, Brazil
Luís Mauro Moura, Viviana Cocco Mariani, PUCPR, Brazil
Abstract: In greenhouse structures, given the major role played by glazing systems with regard to losing and gains of energy in the system, an accurate prediction of the radiative heat transfer through the glazing material and in the interface between cover and ground, it is of great importance in energy simulations involving solar radiation. Note that the solar radiation is not only a function of the extinction coefficient (consequently the transmission coefficient), but also depends on the multiple reflections inside the glazing and between the glazing and its neighborhood. Then the objective of this study is to incorporate multiple reflections in the glazing and its neighborhood analyzing its influence on radiative heat transfer. In this paper, results show that the methods available in literature that use only the multiple reflections on the glass cover can receive 13\% less energy, while methods that consider only the transmission coefficient receives approximately 17.5 \% more energy than the proposed method in this study, depending on the quality of the glass and the neighborhood reflectance.
Keywords:Solar radiation; Solar collector; Greenhouse; Multiple reflections; Glazing; Heat transfer.
Presentation Schedule: Monday, 16:20-16:40. Session: ETS1-1. Presenter: Luis Mauro Moura.
ENCIT2012-395 A MATHEMATICAL MODEL FOR THE VELOCITY PROFILE INTERNALLY TO A CONICAL DIFFUSER - PDF
Disterfano Lima Martins Barbosa, Jerson Rogério Pinheiro Vaz, Déborah Aline Tavares Dias do Rio Vaz, Sávio Wesley Oliveira Figueiredo, Marcelo Oliveira da Silva, Claudio José Cavalcante Blanco, UFPA, Brazil
Abstract: The use of diffusers around of the horizontal-axis wind turbines have been widely studied, since the diffuser causes an improvement in the power coefficient of a turbine and 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. Thus, in the present study shows 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 results are compared with experimental data and show good agreement.
Keywords:DAWTs; Diffuser; Renewable energy.
Presentation Schedule: Wednesday, 09:40-10:00. Session: ETS2. Presenter: Marcelo Oliveira da Silva.
ENCIT2012-334 EXPERIMENTAL-THEORETICAL ANALYSIS OF SOLAR DRYERS WITH INFRARED THERMOGRAPHY AND INTEGRAL TRANSFORMS - PDF
Ivana Fernandes Sousa, Renato Machado Cotta, Carolina Palma Naveira-Cotta, UFRJ, Brazil
Mohammed Lachi, Mourad Rebay, Université de Reims, France
Abstract: The present work deals with conjugated natural convection-conduction heat transfer in inclined plane solar collectors as employed in small scale agricultural solar dryers, according to a constructive model proposed by the Instituto Agronômico do Paraná (IAPAR). The experimental analysis is performed by employing a combination of thermocouples, fluxmeters and infrared thermography. A classical lumped-differential model for heat conduction along the plate length is combined with available correlations for local Nusselt numbers along the natural convection boundary layer over the inclined plate to simplify the heat transfer analysis of the metallic collector plate. The resulting transient one-dimensional model is solved by Integral Transforms (UNIT code) and critically compared with the experimental results. The proposed model is simple enough but requires experimental information on the temperatures of the glass cover and on the incident radiation heat flux. Therefore a second model is also proposed coupling the heat conduction equation in the cover glass, again applying concentrated parameters in the transverse direction but now not requiring experimental data input, which is finally validated by the experimental results. The coupled model is found to be more adequate in predicting the heat transfer phenomena along the plate length, allowing for the selection of basic parameters such as collector length and thickness and inclination angle.
Keywords:solar collector; natural convection; infrared thermography; integral transforms; conjugated problem.
Presentation Schedule: Wednesday, 10:20-10:40. Session: ETS2. Presenter: Ivana Fernandes Sousa.