Modelagem e simulação de sistemas de injeção de gás ozônio para fumigação de grãos de milho (Zea mays L.) utilizando a mecânica dos fluidos computacional

• Ano de defesa: 2009
• Autor(a) principal: Pereira Júnior, João Rodrigues
• Orientador(a): Martins, Márcio Arêdes
• Banca de defesa: Campos, Júlio César Costa , Coimbra, Jane Sélia dos Reis , Martins, José Helvécio , Figueiredo, Kátia Cecília de Souza
• Tipo de documento: Dissertação
• Tipo de acesso: Acesso aberto
• Idioma: por
• Instituição de defesa: Universidade Federal de Viçosa
• Programa de Pós-Graduação: Mestrado em Engenharia Agrícola
• Departamento: Construções rurais e ambiência; Energia na agricultura; Mecanização agrícola; Processamento de produ
• País: BR
• Palavras-chave em Português: CFD; Ozônio; Fumigação; Modelagem; Milho
• Palavras-chave em Inglês: CFD; Ozone; Fumigation; Modeling; Corn
• Área do conhecimento CNPq: CNPQ::CIENCIAS AGRARIAS::ENGENHARIA AGRICOLA
• Link de acesso: http://locus.ufv.br/handle/123456789/3544

The national crop production of grains from 2007 to 2008 was the largest in the history of Brazil, reaching 143.87 million of tons. Among this amount, maize grains respond for 40.7% (58.58 million of tons). The pest control in stored grains is carried out mainly by fumigation with fosfine. It is verified in literature that some insects has been developed resistance to fosfine, and there is no practical fumigant available. The ozone gas is a strong oxidant and it consists on a new technology with great potential for pest control in stored grains. Due to the size of the Brazilian structures for grain storage, experimental tests with alternative fumigants are essentially costly, so the computational fluid mechanics (CFD) arises as a powerful tool for prediction and design injection systems for ozone gas. The aim of this study was the modeling and simulation of injection systems for ozone gas for maize grains stored in a commercial bin using the CFD technique applied to porous media. Two one-dimensional cases of mass transport by convection-diffusion and diffusion-reaction, in which the exact solutions were known, were employed to validate the CFD model. The effects of Péclet number and Thiele modulus on the mass transfer along the porous media were investigated. It was verified that for smaller Péclet numbers the gradient concentration tend to be smooth and constant along the porous media, and when the Péclet number increase, a mesh refinement should be made near the outlet. When the Thiele modulus increases, the concentration gradient for the ozone gas also increases due to its fast consumption by reaction when compared to the axial diffusion transport. The Thiele modulus for the ozone is 41, which means that the decomposition rate is greater than the diffusion rate in the grains mass. Thus, different from the application of fumigants such as the fosfine, the ozone should be injected by convection into the grains mass. For the convectiondiffusion- reaction transport of ozone gas in porous media, the decomposition and saturation kinetics were modeled and used in the CFD model. The ozone gas transport in the model was used to simulate the ozone gas in a fixed bed and the concentration profile was compared to experimental data reported by Kells et al. (2001). The simulation results show good agreement to experimental results and the associated error norm was low. Therefore, the proposed CFD model can be used for simulation of gas ozone injection systems in maize grains. The performance of two injection systems of ozone gas was compared using CFD simulation in a commercial storage bin. Two injection systems were simulated: injection at the base of the silo and using probes. A minimum injection rate of 1.27 kg s-1 and 9.50 kg s-1, for injection at the base and by probes, respectively, was required to reach 50 ppm of ozone in more than 95% of the grain mass. Thus, the injection by the base of the bin is more efficient since it require a smaller mass flow. The proposed model for the ozone transport in porous media is valid and it can be used in other studies of injection systems of ozone in stored grains.