Two Phase Pressure Drop Performance of Refrigerant in a Small Horizontal Smooth Tube with 2.5 mm inside Diameter

Two-phase flow pressure drop measurements were made during the phase change heat transfer process of R22 in a small horizontal smooth tube with 2.5 mm inside diameter. Conclusions can be drawn that the quality corresponding to the pressure gradient peak value of small tubes became higher than that of large tubes. The effect of quality to pressure drop becomes weak as the mass flux increases. The experiment data were compared with the predicated values of the state-of-the-art correlations from the open literature. The comparisons between the data and the predictions indicate that most of the state-of-the-art correlations fails to predict the experimental data.Chisholm model shows a relatively better predictive ability than the other empirical correlations although it has a mean deviation of 26.7%. But the predicated values of Chisholm model are lower by 50% than the experimental data when the quality becomes larger.     

加速度计灵敏度校准方法的研究

加速度计已在汽车检测技术中得到广泛应用,加速度计灵敏度校准也愈发重要。通过对传统加速度计灵敏度的标定方法———背靠背方法的分析,提出了一种较为准确的加速度计灵敏度替代校准方法,比较了两种校准方法的优势,并解决了测试系统的安装及数据采集的技巧问题。     

基于滞留费用及时效性的空车调配优化模型

针对我国铁路空车需求量总体上大于供应量,以及时效性考虑不足的现状,考虑到空车(或以重代空的车)过早或过晚到达都会给铁路运输企业带来额外的费用,而且在空车总体供应量大于需求量的前提下,充分考虑车种代用和满足重点货物、重点客户对空车的需求条件。在此基础上,建立在区段空车运输能力约束条件下基于滞留费用及时效性的空车调配综合优化模型。     

Role of the Railways in the Future of Air Transport

Abstract

The role of the railways in the air transport industry is usually limited to provision of access to airports. However, the development of high-speed rail networks and the congestion and environmental problems faced by the air transport industry suggest the railways could have a greater role in working with the airlines to provide an integrated transport service for medium-distance journeys (up to 800 km). Many air journeys involve two flights and a transfer at a hub airport. The alternative being investigated here would replace air journeys by a rail journey and a flight, and a transfer between them at the hub airport. Such integration could offer a positive alternative to aircraft on some routes and lead to railway journeys to airports becoming part of air transport services, and not only to provide access to them. Integration could therefore provide a better use of available air capacity rather than duplicating some high-speed rail routes and services.     

R407C取代R22的工况计算及分析

围绕制冷剂发展历程和制冷剂技术更新进行了讨论.着重介绍制冷剂R407C替换制冷剂R22的工况计算,基于生产实践提出了制冷剂替换对系统的影响以及系统需要做出的改变.     

一种实用的配电网潮流算法

目前matlab潮流计算程序多是基于输电网开发,而对配电网中潮流计算程序较少开发。配电网由于其特有的辐射性、R／X较大、节点较多的特性,导致用于输电网的潮流计算方法由于收敛性问题并不适用于配电网系统中。针对辐射性配电网的特点,开发了用于配电网潮流计算的matlab程序,该程序采用新的支路选择方法,无需对网络进行复杂的编号,并通过算例验证了程序的正确性。     

Some remarks on the TKIP key mixing function of IEEE 802.11i

Temporal key integrity protocol (TKIP) is a sub-protocol of IEEE 802.11i. TKIP remedies some security flaws in wired equivalent privacy (WEP) protocol. TKIP adds four new algorithms to WEP: a message integrity code (MIC) called Michael, an initialization vector (IV) sequencing discipline, a key mixing function and a re-keying mechanism. The key mixing function, also called temporal key hash, de-correlates the IVs from weak keys. Some cryptographic properties of the substitution box (S-box) used in the key mixing function are investigated in this paper, such as regularity, avalanche effect, differ uniform and linear structure. Moen et al pointed out that there existed a temporal key recovery attack in TKIP key mixing function. In this paper a method is proposed to defend against the attack, and the resulting effect on performance is discussed.     

Theoretical method for predicting the weight reduction rate of a box-type car body for rolling stock by material substitution design

In this paper, a theoretical approach is suggested for predicting the structural performances and weight reduction rate of a car body with a box-type section when its material is substituted with a lightweight material for weight saving. For the material substitution design of a car body for rolling stock, bending, axial, and twisting deformations should be considered at constant stiffness and strength conditions. To compare the weight reduction effects on different material applications, some new indices were derived from a structural performance point of view. The derived indices provide good measures to estimate weight reduction by material substitution design and can be effectively applied to the conceptual design of a car body.     

A New Experimental Rig of Testing Flow Boiling Heat Transfer of Refrigerant and Lubricant Mixture

This paper proposed a new experimental rig of testing flow boiling heat transfer of refrigerant and lubricant oil mixture. The quantity of oil in the test section can be controlled and regulated conveniently and accurately by connecting separate lubricant oil circuit with test section in parallel. It was built up by retrofitting a multiple air-conditioner and installing three oil-separators in serials at the compressor outlet. And so the lubricant oil in the discharged refrigerant gas of compressor can be removed completely. The refrigerant flow rate through test section can be bypassed by the by-path circuit of indoor unit. This experimental rig has advantages such as on-line and continuous oil injection, short time of obtaining stability, flexible operation, simple control, which lead to high efficiency in the research of flow boiling heat transfer of refrigerant and lubricant oil mixture.     

行政法意义上的非政府组织

非政府组织在行政管理学上有较多的研究,在行政法学上却少有论述,随着政治体制改革的深化,许多管理职能将由政府部门交由非政府组织行使,在这种情况下,我们必须从行政法的角度来研究权力转移的方式和条件,为这种权力转移提供法学依据.