新型双级旋流管空气滤效率研究

为了研究双级旋流管空气滤的适宜滤清效率,对双级旋流管空气滤进行了仿真分析和试验研究,试验结果表明:双级旋流管空气滤的重量效率达到98%以上,对10μm以上粒子的分离效率达到90%以上,与仿真结果相差13%.仿真和试验结果证明新型双级旋流管空气滤能够满足压气机前端对进气过滤重量效率要求,可在此基础上进一步研究旋流管空气滤适宜滤清效率.

电动多旋翼植保无人机升力特性综合测评方法

升力特性是电动多旋翼植保无人机性能测试的重要参数之一。为了实现对电动多旋翼植保无人机升力特性的性能检测,针对不同型号、不同规格的电动多旋翼植保无人机在评价过程中存在无统一的评价指标问题,该文提出了一种半系留式电动多旋翼植保无人机升力特性的测试与评价方法,包括性能检测平台、升力特性测试方法及指标、升力特性的评价方法。为了验证方法的可行性,对3种不同机型(分别为四旋翼机型Ⅰ、六旋翼机型Ⅱ、八旋翼机型Ⅲ)进行了升力特性指标的性能测试试验。试验结果表明:3种机型在功率载荷、重量效率、热效比等方面有较大差异,功率载荷最好的机型Ⅲ比最差的机型Ⅰ大7.6 m N/W,重量效率最好的机型Ⅰ比最差的机型Ⅱ大0.33,热效比最好的机型Ⅲ比最差的机型Ⅱ大10.5 N/℃,反映出3种机型在设计过程中整个动力系统效率、机型整体结构和材料选择上的差异,从而在整机作业性能上表现出差异。在上述指标测试的基础上,结合无人机动力系统数学模型,提出了运用功率载荷、重量效率和热效比进行电动多旋翼植保无人机升力特性综合评价的评分方法,对上述3种机型进行综合评分的结果为:机型Ⅲ>机型Ⅰ>机型Ⅱ,该结果表明所提出的评价方法能有效对不同类型电动多旋翼植保无人机的升力特性进行综合评判。该文所给出的测试与评价方法,不仅能用于电动多旋翼植保无人机性能的评测,还能为机型性能的进一步改进提供参考。

论包装在现代物流中重要作用

现代物流定义及演变 在全球化经济竞争日益激烈的今天,物流问题愈加受到人们的重视.物流是一个十分现代化的概念,它对国际商务活动的影响越来越明显,物流公司已经成为新经济社会的焦点.最初,人们把物流称为"Physical Distribution",主要侧重于商品物质的移动作用,即发生在商品流通领域中存在一定劳动组织条件下,实现从供应方朝着需求方的商品实体的定向移动.在这种情况下,在商业物流或销售物流过程中,包装已在保护产品和方便运输中发挥出巨大作用.但随着社会的进步,经济的发展和人们生活质量的提高,物流一词在概念上也发生了很大变化.

Luminescent Efficiency in Single-layer Organic Electrophosphorescent Devices

Based on the charge injection and recombination processes and the triplet-triplet annihilation process, a model to calculate the electroluminescent(EL) efficiency is presented. The influences of the applied electric field on the injection efficiency, recombination efficiency and electroluminescent efficiency are discussed. It is found that: (1) The injection efficiency is increasing while the recombination efficiency is decreasing with the applied electric field increasing. (2) The EL efficiency is enhanced at low electric field slowly but is decreasing at high electric field with the increase of applied voltage. (3) The EL efficiency is decreasing with the increase of the host-guest molecular distance (R). So, it is concluded that the EL efficiency in single-layer organic electrophosphorescent devices is dominated by injection efficiency at lower electric field and recombination efficiency at higher electric field.

Mathematical modeling and analysis of thermodynamic processes in a twin-rotor piston engine

In order to study the major performance indicators of the twin-rotor piston engine(TRPE), Matlab/simulink was used to simulate the mathematical models of its thermodynamic processes. With consideration of the characteristics of the working processes in the TRPE, corresponding differential equations were established and then simplified by period features of the TRPE. Finally, the major boundary conditions were figured out. The changing trends of mass, pressure and temperature of working fuel in the working chamber during a complete engine cycle were presented. The simulation results are consistent with the trends of an actual working cycle in the TRPE, which indicates that the method of simulation is feasible. As the pressure in the working chamber is calculated, all the performance parameters of the TRPE can be obtained. The major performance indicators, such as the indicated mean effective pressure, power to weight ratio and the volume power, are also acquired. Compared with three different types of conventional engines, the TRPE has a bigger utilization ratio of cylinder volume, a higher power to weight ratio and a more compact structure. This indicates that TRPE is superior to conventional engines.

Effect of Vacuum Cooling on Shelf Life of Organic Chayote Shoot （Sechium edule Sm.）

The effect of vacuum cooling on shelf life of organic chayote was investigated. Vacuum cooling processes of organic chayote shoot packed in perforated polyethylene package using different vacuum pressure reserving operation modes were experimented. The holding final pressures for vacuum-cooled organic cilantro packed in holed polyethylene bags were set at two different levels, namely at 10 and 11 millibar. The pressures were experimented with 3 levels of reserving time of 3, 4 and 5 minutes. The weight loss percentage of chayote shoot during precooling to the temperature of 8 ~ 1 ~C using reserving pressure of 10 milibars for 3, 4, and 5 minutes were 0.5, 0.7, and 0.9, respectively. For the weight loss percentage during precooling using reserving pressure of 11 milibars for 3, 4, and 5 minutes were 0.4, 0.5, and 0.5, respectively. The optimum parameter for vacuum cooling process of organic chayote shoot at the initial temperature of 19-23 ℃to 8 ±1 ℃was the reserving pressure of 11 mbar with reserving time of 5 minutes. The precooled organic chayote shoot was then stored at 8 ℃ for quality analysis. The results showed that vacuum cooling had no effect on the change of color, chlorophyll a, b and total chlorophyll. However, precooled organic chayote shoots showed better appearance than non-precooled vegetables. Vacuum cooling can reduce weight loss percentage. The amount of total soluble solids in organic chayote shoots increased with storage time. Precooled organic chayote shoot had longer shelf life of 8 days compared to normal storage life of 5 days.