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首页> 美国政府科技报告 >Mathematical Modelling of Transport Precesses and Degradation Reaction in Piles of Forest Fuel Material. Part 2
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Mathematical Modelling of Transport Precesses and Degradation Reaction in Piles of Forest Fuel Material. Part 2

机译：森林燃料材料桩运输过程及降解反应的数学模型。第2部分

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The measurements show that the permeability is less than 2 x 10/sup -9/ m/sup 2/ in compacted chipped logging residues and the permeability decreases moderately due to compression of the material caused by the weight of the material above the measuring point. In piles with compacted oak chips and uncompacted chipped logging residues the permeability is a factor 10 higher than for the compacted logging residues and the measurements were influenced by turbulence in the air flow. Air flow due to natural convection is calculated. Temperature profile and air permeability experimentally determined in a pile with compacted logging residues were used in the calculations. The results show that air flows into the pile through the lower part of the lateral surface. The air principally flows out from the pile through the flat top. A value of about 0.1-0.2 m/sup 3//m/sup 2/ and h is obtained for the air flow rate near the lateral surface. Heat and oxygen transport caused by natural convection is calculated for a stream tube through a section of the pile. The equations are solved for steady state conditions. The results show that the most important factors are the maximum degradation rate and the relationship between degradation rate and temperature. The oxygen concentration in the pile is also determined by the heat losses to the surroundings. The model is one-dimensional. This model gives qualitative knowledge of the relationship between temperature and oxygen concentration for different values of some parameters. For a quantitative description of these relationships a two-dimensional model, taking into account oxygen diffusion in the center of the pile and heat losses to the surroundings, is needed. Secondly, the model is steady-state. It does not consider the initial period when the temperature in the pile is increased from the initial value to the steady-state value. (ERA citation 12:030288)

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