侧压式安装振动筛筛网动力学仿真分析

为了研究在电动机激振作用下侧压式安装的筛网的动态响应特性,在Recur Dyn软件中建立了三电动机双轨迹振动筛的多刚体仿真模型,基于有限元多柔体动力学(MFBD)技术,在刚体模型的基础上建立了刚柔耦合多体动力学模型,通过对其仿真分析,得到筛网在处于不同安装条件下的振动与力学特性,分析结果表明:刚柔耦合模型能够更加准确地反映振动筛的抛掷指数,该仿真方法能够为筛网的结构设计、安装方法以及疲劳损伤的评估等提供数据参考;侧压式安装的筛网,相对筛箱的振幅较螺栓绷紧式、楔形块压紧式要小,但是压紧力对筛网振动和受力影响过大。     

基于大型直剪试验的土石混合体颗粒破碎特征研究

土石混合体剪切时存在细观上的颗粒破碎现象,并对其宏观力学性质产生影响。基于此,以4种含水率的土石混合体为研究对象,通过室内大型直剪试验和筛分试验,分析土石混合体剪切后的颗粒破碎特征,并建立细观颗粒破碎与宏观力学性质的联系,从而加深对宏观力学性质的认识。研究结果表明:土石混合体剪切后的颗粒破碎较明显,可分为完全剪断型、表面破裂型和表面研磨型3类;颗粒破碎细观上表现为粗粒组含量降低、细粒组含量增加、中等粒组含量波动变化,统计上表现为级配曲线上移,宏观上表现为低含水率出现应变软化破坏、高含水率出现应变硬化破坏、中等含水率出现塑性应变破坏、剪应力–剪切位移曲线"跳跃"和强度非线性特征,本质上是颗粒间接触力作用产生应力集中的结果;颗粒相对破碎率随着含水率的降低或法向压力的增大而增大;黏聚力和内摩擦角均随着含水率的增大而呈幂函数规律降低。     

不同方法测试粒度分布的比较研究

介绍了不同原理仪器粒度测试结果间存在差异的原因以及对测试结果准确性应如何评价。用筛分法和激光法对氧化铝样品进行测试对比,初步分析结果间的差异。结果表明,筛分法和激光法测试粒度分布在质量(体积)累积分布达到50%时,测试结果相差最小,不同的粒度组成、颗粒的形状都会造成两种方法测试结果的差异。     

Shape-size sieving of trans- and cis-piperylene isomers with gallate-based metal-organic frameworks

The isolation of C₅ diolefins, mainly consisting of trans-piperylene, cis-piperylene, and isoprene, is a challenging task and requires complex and energy-intensive separation schemes. Particularly, the segregation of trans/cis-piperylene is the most challenging operation for geometric isomers. Here, we report an isostructural family of metal-organic frameworks, Mg-, Co-, and Ni-gallate, which are perfectly suitable for the precise matching of trans-piperylene molecules while excluding the slightly large cis-piperylene molecules, contributing to remarkable separation of trans/cis-piperylene via shape-size sieving. Significantly, Mg-gallate exhibits high affinity for trans-piperylene, leading to an outstanding trans/cis-piperylene uptake selectivity of 4.22 (298 K, 0.1 bar) in adsorption isotherms. This excellent separation performance is further attested by single-crystal x-ray diffraction of Ni-gallate loaded with trans-piperylene isomer. In breakthrough tests, M-gallate materials not only display excellent separation performance of trans- and cis-piperylene but also can accomplish complete segregation of the ternary mixture (trans-piperylene/cis-piperylene/isoprene) into individual compounds combined with zeolite 5A.     

Comparison of breakage behavior between the sieving crusher and ordinary teeth roll crushers

Comparison of breakage behavior of coals is conducted between the industrial sieving crusher (SC) and ordinary teeth roll crushers in different breakage flow sheets. Two types of coals, about 10 tons, are used for each comparison, and consumed energy and size distribution of products are analyzed. Due to differences in roll rotation rate and teeth distribution on roll, breakage product of SC shows the lower yield of +50 mm particles and ?6 mm fines, and the higher content of ?50 + 6 mm progenies. SC also indicates the advantage of saving energy if compared with that of single tooth roll crusher and double teeth roll crusher (DTRC). On the other hand, the combined flow sheet of classification and breakage is compared with the single utilization of a SC. The ?50 mm particles in the feed are removed by hand sieving and +50 mm particles are broken by DTRC. As a comparison, raw coal without any pretreatment is fed to a SC. Results indicate that the decrease of coal mass to DTRC can reduce the consumed breakage time and energy, but products of SC have a higher yield of ?50 + 6 mm particles. Parallel tests show the small standard deviations. In summary, experimental results of this paper are reliable, and SC shows advantages in breakage efficiency and saving energy, which is a benefit for the breakage of coarse particles.     

Hydrogen Isotope Separation in Confined Nanospaces: Carbons,Zeolites, Metal–Organic Frameworks,and Covalent Organic Frameworks

One of the greatest challenges of modern separation technology is separating isotope mixtures in high purity. The separation of hydrogen isotopes can create immense economic value by producing valuable deuterium (D) and tritium (T), which are irreplaceable for various industrial and scientific applications. However, current separation methods suffer from low separation efficiency owing to the similar chemical properties of isotopes; thus, high‐purity isotopes are not easily achieved. Recently, nanoporous materials have been proposed as promising candidates and are supported by a newly proposed separation mechanism, i.e., quantum effects. Herein, the fundamentals of the quantum sieving effect of hydrogen isotopes in nanoporous materials are discussed, which are mainly kinetic quantum sieving and chemical‐affinity quantum sieving, including the recent advances in the analytical techniques. As examples of nanoporous materials, carbons, zeolites, metal–organic frameworks, and covalent organic frameworks are addressed from computational and experimental standpoints. Understanding the quantum sieving effect in nanospaces and the tailoring of porous materials based on it will open up new opportunities to develop a highly efficient and advanced isotope separation systems.     

细度对挤压麦麸理化特性及其全麦粉加工品质特性的影响

以挤压麦麸(粗麸、细麸、胚芽、次粉混合料)为原料,研究筛分细度(粒径44.15~198.48μm)对挤压麦麸的理化特性及其全麦粉加工品质特性的影响。结果表明:随着筛分目数的增加,挤压麦麸的粒径范围分布变窄;筛分细度对其戊聚糖、阿魏酸含量的影响较大;对其持水性、溶胀性的影响较小,对全麦粉的糊化特性、粉质特性的影响较小;挤压处理麦麸混合料可获得较均一的麦麸产品。     

Alkali-induced sieving effect in Ni on silica catalysts

It is suggested that the addition of potassium nitrate to a Ni/SiO₂ precursor results, after reduction, in a blocking of nickel particles by a K-containing compound. The potassium film is supposed to act as a molecular sieve: it is permeable to a small molecule (H₂) and inhibits the access of large molecules to the nickel.