| As an important strategic resource of our nation, grain always attract much attention of people. Grain storage is particularly important at present stage. Due to storing the big amount of grain and long storing period, large warehouse is the main type for grain storage in our country. In order to overcome the difficulties during out-put and in-put of warehouse, Academy of State Administration of has reformed warehouse ventilation significantly. The ventilation mode has been changed from traditional vertical positive pressure model to horizontal negative pressure model, which can achieve the goal of duct on to the wall, vacating ground and machinery operation conveniently. Simultaneously, based on horizontal ventilation system, the technology of Controlled Atmosphere Storage of Grain with N2 has been developed and it can help to pollution-free green grain storage.The research method of stored grain ecosystem mainly include theoretical parameters analysis with medium and small scale test and real scale store system demonstration before. Time consuming of the former one is shorter, but there is a certain difference with the actual situation. The latter one’s results are real, but it need long time to be verified, and the cost is high. With the rapid development of computer technology, simulation technology has attracted more and more attention, and it can solve the problem costing less time and giving more accurate results.Based on previous work of mechanical ventilation theory and technology, the theoretical basis of porous media and computational fluid dynamics (CFD), this research analyzes the diffusion law of nitrogen concentration inside bulk grain which got via numerical simulation, after that suggestions are put forward for improvement of ventilation. The simulation data was verified by field trial, taking nitrogen filling technology used in national grain reserves large warehouse as an example.The present work summarizes research achievements of domestic and overseas researc hers in Controlled Atmosphere Storage of Grain, and introduces the horizontal ventilation system with nitrogen gas filling. The tests were conducted in a new warehouse with that system, and the measured data was sorted and analyzed.This thesis selects symmetry plane in the direction of length of warehouse as the calculation region, establishes a two-dimensional model,and then simulates the process of nitrogen filling.Comparing simulation results with experimental data, the validity of numeri-cal model has been confirmed. On this basis, three-dimensional models of real grain wareh-ouses are established. With those numerical models, simulations are conducted, accordin g which the filling processes was optimized. Then the basic law of nitrogen concentration and uniformity inside the grain is discussed.Studies results have shown that the established numerical model can reproduce the different stages of filling process in bulk grain, and the correctness and accuracy of method has been confirmed via comparing simulation results with experimental data. The proposed optimization of filling nitrogen, based on the analysis of simulation results, can realize the effect of low-oxygen and nitrogen-rich as well as energy saving. As a result of using nitrogen filling process with horizontal ventilation system, the nitrogen concentration inside the entire bulk grain is very uniform, which can help to provide a hypoxia green storage environment. With the rapid development of CFD, computer simulation technology has been introduc ed into the traditional field of grain storage. This technology can analyze the effectiven ess of existing process of grain storage, give some comprehensive guidance to optimiza tion of ventilation system and grain storage technology. The result of this research hav e important theoretical and guiding significance for improving the quality and security of grain storage, and it also can improve the economic benefit of grain enterprises and ensure the sustainable development of national food strategy. |
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