【摘要】 蚯蚓粪是有机固体废弃物经蚯蚓过腹处理后排出的特殊物料,由于含水率高达40%～60%的同时又能够保持散体细小颗粒的状态,导致流动性参数难以通过常规测试手段得到。为给蚯蚓粪收集、分离、运输等不同阶段机械化作业提供有效的运动摩擦参数,探究含水率变化对蚯蚓粪颗粒流动性参数的影响。研究通过堆积角试验与离散元仿真(Discrete element method,DEM)堆积角虚拟试验相结合的方法,从数值上量化分析了基于牛粪转化后不同含水率25%～65%蚯蚓粪物料的滚动摩擦参数与物料黏结能力。结果表明,显著影响蚯蚓粪堆积角的因素为蚯蚓粪-蚯蚓粪滚动摩擦系数,蚯蚓粪-不锈钢滚动摩擦系数,蚯蚓粪的JKR表面能(Johnson Kendall Roberts surface energy)。随着含水率的增加,蚯蚓粪-蚯蚓粪的滚动摩擦系数由0.135下降至0.110,蚯蚓粪-不锈钢滚动摩擦系数由0.116下降至0.102,两者呈现小幅度下降,内摩擦角由45.81°降至26.10°,而JKR表面能由0.179 J/m~2增加至0.345 J/m~2,增幅显著。含水率低于50%时,随着含水率增加,物料滚动摩擦系数减小,内摩擦角减小,一定程度上有利于物料滚动流动;含水率超过50%时,由于表面能增高,内聚力增大,蚯蚓粪物料之间易发生物料黏结团聚,一定程度上又会阻碍蚯蚓粪的翻滚运动。更多还原

【Abstract】 The earthworm processing of waste is recognized as a very sustainable approach for management of organic wastes. The vermicompost resulted from this procession has been proved to be practical and useful in farming, substrate nursery, gas absorbent etc. However, this technology has been widely adopted to treat different organic waste material. Most of scientific investigation in vermicompost concentrates on its nutrient characteristics and microorganism rather than physical properties. The flow ability is key factor for the mechanized operation of vermicomposting. The basic parameters like rolling friction coefficient and surface energy are needed for the equipment design, material calculation, and vermicompost product manufacture. The moisture content of vermicompost can reach 40%-50% under natural condition, even with high moisture content, the vermicompost can still keep the granular condition. Flow parameters, such as friction coefficient, cannot simply test though the normal physical method. In order to provide the quantized flow parameters of vermicompost for mechanization, in this study, vermicompost transformed from pure cow dung by the worm procession was used. The experiments were undertaken in condition of different moisture contents, changing from 25%-65%. The friction coefficient and surface energy were investigated by the method of pile angle simulation and calibration using discrete element method(DEM). First, Plackett-Burman(PB) design was conducted to select the impacted physical frictional parameter factors that have significant influence on pile angle. Then, the steep climbing test was conducted to shorten the parameter ranges from the maximum range of PB design. According to the result of steep climbing test, the response surface methodology(RSM) was carried out to build the model which can reflect the relationship between pile angle and friction coefficients. Besides, for explaining the flow ability of vermicompost in further, the direct shearing test was applied to calculate the internal frictional angle of vermicompost with different moisture contents. The results of experiment indicated that three key factors vermicompost-vermicompost rolling friction coefficient, vermicompost-steel rolling friction coefficient and Johnson Kendall Roberts surface bonding energy(JKR surface energy), significantly affected the pile angle(P<0.05). With the rising of moisture content from 25% to 65%, the vermicompost-vermicompost rolling friction coefficient dropped from 0.135 to 0.110, the vermicompost-steel rolling friction coefficient dropped from 0.116 to 0.102. From the result, the surface energy was the most impact factor in three factors, which changed from 0.179 to 0.345 J/m2. The few rise of moisture content can improve the flow ability of vermicompost significantly under low moisture content condition. When the moisture content was over 50%, the surface energy and the cohesion force were increased, which would restrict the flow movement of vermicompost to some extent. The study is expected to provide numerical parameter reference for the practical application and development of mechanization.更多还原