Numerical Analysis of Heat Transfer and Nanofluid Flow in a Triangular Duct with Vortex Generator: Two‐Phase Model

Laminar forced convection heat transfer and nanofluids flow in an equilateral triangular channel using a delta‐winglet pair of vortex generators is numerically studied. Three nanofluids, namely; Al₂O₃, CuO, and SiO₂ nanoparticles suspended in an ethylene glycol base fluid are examined. A two‐phase mixture model is considered to simulate the governing equations of mass, momentum and energy for both phases and solved using the finite volume method (FVM). Constant and temperature dependent properties methods are assumed. The single‐phase model is considered here for comparison. The nanoparticle concentration is assumed to be 1% and 4% and Reynolds number is ranged from 100 to 800. The results show that the heat transfer enhancement by a using vortex generator and nanofluids is greater than the case of vortex generator and base fluid only, and the latest case provided higher enhancement of heat transfer compared to the case of a base fluid flowing in a plain duct. Considering the nanofluid as two separated phases is more reasonable than assuming the nanofluid as a homogeneous single phase. Temperature dependent properties model provided higher heat transfer and lower shear stress than the constant properties model.     

新型多功能漏电保护器芯片的设计

利用数模混合信号CMOS工艺实现了一种新型漏电开关保护器芯片.与传统的模拟电路保护芯片相比,这一芯片充分利用了数字电路带来的好处:降低了功耗,采用"定时延"方法大大提高了保护控制的精度,集成了电源的过压、过载保护功能以及自动重合闸功能,提供了适应不同应用环境的可编程性,同时对每一个输入的漏电信号都进行有效性检测,减小漏电保护器的误触发率,提高了抗干扰能力.     

水幕抑制油气泄漏扩散及爆炸传播规律研究

采用数值模拟方法,以油罐泄漏的油气为研究对象,分析水幕抑制油气泄漏扩散及爆炸事故的演变规律。容积为5 000 m3油罐泄漏的油气以0.25 m/s的速率释放600 s时,距泄漏源4 m处体积分数达到1.6%,超过油气爆炸下限。水幕喷射80 s时水幕后方区域油气体积分数低于爆炸下限的1/2,喷射250 s时仅泄漏源周边油气达到爆炸下限;无水幕时,监测点爆炸超压峰值为10.2 kPa,温度峰值为2 360 K;添加1道水幕后,爆炸超压峰值下降到2.8 kPa,温度峰值下降到1 813 K;水幕数目分别为1、2、3、4时,爆炸超压峰值分别为2.80、1.42、1.30、1.10 kPa,温度峰值分别为1 813、1 210、993、382 K。水幕数量为4道时,抑制高温峰值效果明显。     

一种低功耗高性能的滑动Cache方案

Cache存储器的功耗占整个芯片功耗的主要部分．针对不同类型的应用程序对指令和数据Cache的容量实时需求不同,一种滑动Cache组织方案被提出．它均衡考虑指令和数据Cache需求,动态地调整一级Cache的容量和配置,消除了Cache中闲置部分产生的功耗．SPEC95仿真结果表明,采用滑动Cache结构不但降低了一级Cache的动态和静态泄漏功耗,而且还降低了整个处理器的动态功耗,提高了性能．滑动Cache比两种传统Cache结构和DRI结构的一级Cache平均动态功耗分别降低21．3％,19．52％和20．62％．采用滑动Cache结构与采用两种传统Cache结构和DRI结构相比,处理器平均动态功耗分别降低了8．84％,8．23％和10．31％,平均能量延迟乘积提高了12．25％,7．02％和13．39％．     

Magnetization reversal in asymmetric trilayer dots: effect of the interlayer magnetostatic coupling

The spin structure and magnetization reversal in Co/insulator/Fe trilayer nanodots are investigated by micromagnetic simulations. The vortex and C-state are found and the magnetization reversal is dominated by the shape asymmetry of the dots, which is produced by cutting off a fraction of the circular dot. The vortex chirality is thus controlled by the magnetic field direction. On the other hand, the magnetostatic interaction between the top and bottom magnetic layers has interesting influence on the dot reversal process, where the magnetocrystalline anisotropy direction of the Co layer is allowed to vary within the layer plane. The combined effect of these two aspects is discussed on the base of dot coercivity, remanent magnetization, vortex nucleation and annihilation, and the bias of the Fe layer hysteresis loop. While leading to a new S-state in circle dots, the interlayer interaction facilitates the formation of C-state in asymmetric dots, which reduces the vortex nucleation field. The bias effect of all dots is decreased with the deviation of the Co layer easy axis from the field direction. Unlike the circle and semicircle dots, the field range of the vortex state in other asymmetric dots increases with the angle between the cutting direction and the Co layer anisotropy. Additionally, vortex ranges in less asymmetric dots even larger than that in the circle dots are evidenced unexpectedly. Therefore, the control of the vortex chirality and enhancement of the vortex range are found simultaneously.     

循环水单级双吸泵轴承箱油封改造

介绍循环水泵驱动端轴承箱漏油现象,结合经验将原环形沟槽结构羊毛毡油封改为凹凸密封结构无骨架油封,彻底解决漏油现象,对油封的维修更换简化工序、缩短时间.     

储罐罐底板漏磁检测仪的研制

在研究漏磁场原理的基础上，设计了一种罐底板漏磁检测仪。该仪器对罐底板的检测不受表面油污和其它非导磁材料影响，具有速度快、性能可靠、操作方便等特点，是全面检测整个罐底板的有效手段。     

AV90-2轴流压缩机漏油问题的分析研究

对NF-6风洞AV90-2轴流压缩机漏油问题进行了分析研究,提出采用磁力完全密封零重力油封技术的密封环对压缩机轴进行密封处理,并在轴承座内侧迷宫槽1/5长度截面处通入高压气流,形成一个高压气流区,阻挡润滑油泄漏,从而实现密封.测试结果表明:采用密封环和提供高压气方式对轴流压缩机具有很好的密封作用,能够成功运用于解决轴流压缩机漏油问题.     

Vortex wake transit time measurements for flow metering

A method of flow measurement is described based on using a vortex wake as a flow tracer shed from a low-blockage-ratio bluff body, the velocity of which is measured by cross-correlation. Preliminary comparisons are made between measurement iof the vortex shedding frequency and the vortex wake transit time between the two ultrasonic beams to determine the flow rates. Whilst preliminary results are confined to a 50 mm diameter sensing head, there is no upper limit to pipe size using the same suitably extended bluff body.     

盐穴地下储气库密封性的测试与评价

对盐穴储气库系统密封性的测试与评价方法进行了详细介绍。测试方法选取原则、测试相关计算方法以及测试标准为储气库密封性测试的工程设计提供了详实的理论基础。