抗结块硝酸铵的制备及性能测试

硝酸铵是一种极易溶于水的无机盐,由于它来源广、成本低以及具有低爆轰性和燃烧时无烟或少烟的特性,因而不仅被作为农用肥料和化工原料,而且还被作为固体推进剂和工业炸药的主要氧化剂.但是,由于硝酸铵具有多晶性,常压下,它有5种热力学稳定的晶体结构[1].每种晶体仅在一定的温度范围内存在,当温度发生变化时,各种晶体之间可以发生转变.当硝酸铵从一种晶体向另一种晶体转变时会伴随着热量、比容、热容和熵等物理参数的突然变化,同时还会引起硝酸铵晶体之间的内凝聚力发生变化,从而导致了硝酸铵易结块性的性质.     

颗粒运动的声信号分析与气固流化床流化质量的判断

根据颗粒碰撞流化床反应器壁面产生声信号的机理,结合频谱分析以及颗粒温度理论,获得了气固流化床颗粒温度与声信号平均能量以及表观气速的关系,由此得到了不同气速下主流区和滞流区颗粒温度的计算公式．由于颗粒温度的大小体现了体系中颗粒运动的活跃程度,由此提出了临界颗粒温度的概念,进而得到了气固流化床良好流化的判据,即当T^＊≥T^＊cr时,床内颗粒具有一定的活跃程度,整床流化质量良好,没有出现团聚结块的流化床故障．基于判据,得到了流化床良好流化的临界操作气速．由此获得了一种简单快捷、实时在线的流化床反应器流化状态检测的方法,对工业上生产监控和操作优化具有重要的指导意义．     

An experimental and numerical study of packing,compression, and caking behaviour of detergent powders

This paper presents an experimental and numerical study of the packing, compression, and caking behaviour of spray dried detergent(SDD) powders with a two-fold aim: an experimental process of observation and evaluation of the packing, compression and caking behaviour of SDD powders, and a numerical approach based on discrete element modelling(DEM). The mechanical properties, including the stress–strain response and the corresponding porosity change as a function of consolidation stress in a confined cylinder, the stress–strain response during unconfined shearing and the cake strength as a function of consolidation stress, were evaluated and compared for different SDD powders using an extended uniaxial tester(Edinburgh Powder Tester – EPT). The experiments using EPT showed excellent reproducibility in the measurement of packing, compression and caking behaviour and were therefore very useful for describing the handling characteristics of these powdered products including screening new products and different formulations. It was found that the sample with higher moisture had lower bulk porosity but higher compressibility and cake strength. The porosity, compressibility and cake strength were found to vary across different size fractions of the same sample. The larger sieve-cut samples had higher initial bulk porosity, compressibility and cake strength. It is revealed that moisture plays a significant role in packing, compression, and shearing behaviour of the powder. Three-dimensional DEM modelling using a recently developed elasto-plastic adhesive-frictional contact model showed that the contact model is able to capture the detergent behaviour reasonably well and can be used to model complex processes involving these powders.     

减少结块的球形氯化钠晶体

 物理学有时也能解决简单的日常问题,比如如何防止普通的盐结块。在盐的储存过程中,这一问题尤其突出,专家认为这是由于氯化钠晶体互相接触后发生粘连造成的。阿马尔·巴拉(AmarBallabh)与印度古杰拉特邦中央盐水和海洋化学研究所(CentralSalt&MarineChemicalsResearchInstitute)和班加罗尔市印度利华研究中心、印度联合利华研究中心的同行发现,向普通盐水中加入少量甘氨酸,析出的盐结晶将是正十二面体,而不是正方体。这种形状几乎为球形,减少了盐晶体的接触面积;不但能减少盐结块,还可改善盐水的流量特性。