增压汽油发动机冷却系统Flowmaster模拟分析研究

由于原机型冷却系统管路设计的结构较为复杂,需要对冷却系统管路布置进行重新设计,本文主要针对这种改进后的冷却系统管路设计结构进行计算分析.利用Flowmaster软件建立了发动机冷却系统1D的模拟仿真模型.着重分析计算两种方案的流量、压力分布和流经元件的温度升高等情况.通过分析对比,确定方案1冷却液流量分布更均衡,能满足各元件的冷却需求,采用方案1作为冷却系统的结构改进方案.     

超超临界660 MW机组给水泵再循环阀的优化改造

给水泵再循环阀一旦出现了严重内漏,会使给水泵失去流量调节功能,严重影响机组安全经济运行.本文针对某超超临界660 MW机组给水泵再循环阀故障进行分析,提出了利用国产部件对此类进口再循环阀进行优化改造的方法:在阀芯上加节流槽、迷宫式笼套阀套和镶嵌式节流装置等结构部件,使再循环阀实现了调节平稳、关断严密的良好控制效果.实际多台机组再循环阀,在改造后的整个检修周期内均未再出现内漏情况.该改造方法具有一定的推广应用价值.     

给水泵迷宫式密封装置密封水流量的测量及改进

针对国内部分给水泵采用迷宫式密封装置的状况,对当前密封水流量的测量方法及其缺点进行了阐述.提出了密封水流量测量的改进方案,为方便、准确地测量迷宫式密封装置的密封水流量提供了参考.     

150t提钒转炉底吹元件布置物理模拟研究

通过水力学模拟实验,在1∶6的物理模型上,对承钢150t提钒转炉的底吹元件布置进行优化,运用测电导率法测定了7种不同底吹元件布置方案转炉熔池的混匀时间.实验结果表明:方案3熔池混匀时间最短,为最佳底吹元件布置方案；在本试验条件下,枪位在225 mm,顶吹气体流量为81～83.3 m3/h.,底吹气体流量为1.8 m3/...     

水源热泵变流量节能技术实践研究

对某宾馆传热空调系统进行了水水热泵采暖方案的变流量改造设计。通过计算机技术、变频调速技术、自动控制技术的应用,实现对供热空调系统动态热负荷变化过程的跟踪优化,调节循环水泵运行参数,实现空调系统在大温差、小流量、恒温、节能的工况下运行。经测试,系统运行正常,简单可靠,经济性好。     

作用面积形状与布管方式对自喷系统能耗影响

自动喷水灭火系统设计时为满足规范的要求,往往存在设计压力、流量过剩的情况,造成了能量的极大浪费.对此,本文通过自动喷水灭火系统设计中最不利点处作用面积不同形状与管道布置方式对自动喷水灭火系统流量和压力的影响进行计算,可以从中得出最为节能的最不利点处作用面积形状与管道布置方式,这样可降低系统的设计压力、流量,达到降低喷淋系统能耗的目的,也验证了“喷规”第9.1.2条的合理性.     

竖轴潮流能水轮机群数值模拟研究

为了实现竖轴潮流能水轮机群的优化布置,基于CFD方法分别对单排和双排水轮机群进行数值模拟。对于单排水轮机群排布,水轮机只有相互十分靠近时其输出效率才会得到显著提升,而相邻水轮机相对旋转方向对机群的效率无影响。对于双排水轮机群排布,下游水轮机会使上游水轮机的尾流变窄、流速加快,但对上游水轮机的效率无影响。合理选择上游水轮机的间距可提高下游水轮机的效率,优化的双排水轮机群排布方案大幅提升了整个机群的效率。     

基于碰撞水舌入水分布形态的泄洪布置优化方法及应用

鉴于挑流水舌碰撞效果关系到水垫塘消能效率且其碰撞入水形态复杂难以测量的问题,根据挑流水舌的形态特点,提出应用二维高斯函数表示挑流水舌碰撞后入水流量分布形态规律。应用该方法计算了白鹤滩水电站泄洪水舌落水分布情况,并针对局部流量集中的现象优化了泄洪孔口布置,改善了泄洪流量空间分配。物理模型试验证明,水垫塘动水压力分布形式与所提算法计算结果较为吻合,且优化后的泄洪孔口布置方案有效降低了水垫塘动水冲击压力,可用于指导泄洪消能布置的设计。     

迷宫式气封热稳定性的简便评定法

在迷宫式气封中,由于转子-静子的干扰引起摩擦而产生的热量,部分被传导给转子和静子.部分通过对流由冷却空气带走,少量被辐射散出.热弹性随着转子和静子的温度上升而改变.如果由于状况变化而使得转子-静子的干扰消失,则热量就停止产生.另一方面,如果干扰加剧,则发热也增加,系统趋向不稳定并导致损坏.原则上,迷宫式气封的稳定性现象是热弹性的.本文完全着重于热的影响,文中规定了一个比较简单的准则,以供设计师快速检查迷宫式气封的热稳定性.在稳态和非稳态设计中都用了所规定的准则并且该准则成功地预示出稳定和非稳定状态.所讨论的一些影响参数为设计师提供了取得一种能稳定运行的迷宫式气封配置的指南.     

温室空气-土壤换热系统的数值模拟

该文用FLUENT5.4软件对空气－土壤换热器（SHESS）进行三维动态模拟计算。研究了换热器进出口温度随时间的变化、温度和压力在换热器中的分布。,要用双排管布置，可以保证所有管内的流量均匀分布；采用压头150Pa的排风扇可以保证管内空气流速在最佳范围之内。空气－土壤换热器在华南地区冬季气温回暖期间对温室有明显的降温效果。     

Enhancement of condensate water quantity and coefficient of performance of an air conditioning system: An experimental study

The objective of the present work is to increase the quantity of condensate water from atmospheric air during the air conditioning (A/C) process by using two techniques: increasing moisture content in atmospheric air by adding steam and passing compressed air instead of atmospheric air, respectively. The experiment was performed with both capillary valve and thermostatic expansion valve operations for assessing the volume flow rates (VFRs) of condensate and coefficient of performance (COP) concerning the air A/C arrangement. The control valve operated for the steam supply case was at half valve opening and one-fourth opening, respectively. The R-22 refrigerant was used in this study. From this study, it was perceived that the condensate water quantity was increased by adding the moisture to the inlet air for the A/C system simultaneously with the usage of compressed air. Furthermore, the COP of the system was also compared to normal atmospheric air admission conditions. The compressed air and steam admission to the A/C system has shown a tremendous increase in COP together with the VFR of the system rather than atmospheric air admission conditions.     

Performance of thermostatic and electronic valves controlling the compressor capacity

The performance of the energy consumption of an electronic valve and a classical thermostatic valve has been compared when these expansion valves are adopted in a vapour compression plant subjected to a cold store. The main aim is to verify experimentally which type of expansion valve would be preferable from energy point of view when a classical thermostat or a fuzzy logic algorithm are used as the control system for the refrigeration capacity. The fuzzy logic‐based control is able to modulate continuously the compressor speed through an inverter. The results show that with a fuzzy algorithm, the thermostatic expansion valve allows an energy saving of about 8% in comparison with the electronic valve. When on–off control is used, the electric energy consumption obtained both with the electronic valve and with the thermostatic valve is comparable. Copyright © 2006 John Wiley & Sons, Ltd.     

一种新型水滴迷宫式调节阀流场特性研究

针对超(超)临界工况下调节阀压降大、流速高的特点,以传统迷宫碟片式调节阀为基础,提出一种新型水滴迷宫式碟片调节阀。利用Fluent软件进行数值模拟,研究阀门在不同开度下的流通性能及不同水滴级数对阀门降压控速能力的影响。研究表明,新结构碟片流通性能良好,可以满足阀门工作条件要求,增加水滴级数会降低阀门流通性能;随着水滴级数的增加,各级水滴间的压降和阀内流速均呈现减小的趋势,五级水滴介质平均压降为5.08MPa,比二级水滴降低了6.26 MPa;最大速度为108m/s,降低了40%;碟片流道出口处存在气蚀现象,水滴级数的增加可减小气蚀区域。     

套筒结构对阀门节流特性影响机理分析

为研究套筒结构对汽轮机高压旁路阀节流特性影响机理,利用SST湍流模型对阀门内流道进行数值模拟,对比迷宫弯折型、条形孔型和圆柱直孔型3种套筒结构与同一套筒不同盘片对阀门节流特性影响。结果表明:3种套筒结构中迷宫弯折型套筒对阀门内汽流的降压、降速能力最强,其引起汽流滞止量最少,进入套筒内流道汽流碰撞损失最少;套筒各盘片的节流特性不同,越靠近套筒上方的盘片对汽流降压能力越强,越靠近套筒下方的盘片对汽流降速能力越强;阀门开度不同时同一盘片对阀门的节流特性影响也不同,但相对来说影响较小。     

Performance of a residential heat pump operating in the cooling mode with single faults imposed

The system behavior of a R410A residential unitary split heat pump operating in the cooling mode was investigated. Seven artificial faults were implemented: compressor/reversing valve leakage, improper outdoor air flow, improper indoor air flow, liquid line restriction, refrigerant undercharge, refrigerant overcharge, and presence of non-condensable gas in the refrigerant. This study monitored eight fault detection features and identified the most sensitive features for each fault. The effect of the various fault levels on energy efficiency ratio (EER) was also estimated. Since the studied system employed a thermostatic expansion valve (TXV) as an expansion device, it could adapt to some faults making the fault less detectable. The distinctiveness of the fault depended on the TXV status (fully open or not).     

Comparison of expansion valve performance

This paper compares the performance of a thermostatic expansion valve, thermoelectric expanison valve, solenoid expansion valve and a motorized type operating as part of an extensively controlled and instrumented refrigeration system. It will be shown that the solenoid expansion valve provides the best contol.     

Synchronization of self-sustained thermostatic oscillations in a thermal-hydraulic network

Flow and temperature oscillations occur under normal conditions in a thermal system with thermostatic control. We present experimental results of the synchronization of multiple oscillators in the secondaries of a thermal-hydraulic network. The test facility is composed of three secondary loops with heat exchangers that exchange heat with a primary heating loop on one side and a primary cooling loop on the other. A thermostatic controller senses the temperature at the outlet of a heat exchanger and modulates the flow rate in that loop. The flow valve is partially closed if the temperature goes above an upper limit and is completely opened if it falls below a lower limit. As a consequence a self-sustained flow and temperature oscillation is set up in that secondary. The frequency of the oscillation depends on the dead-band between the upper and lower temperature limits. Coupled oscillators are set up by the simultaneous action of multiple controllers on different branches. Frequency locking, phase synchronization as well as phase slips are observed to occur due to thermal-hydraulic coupling between the controllers. The phenomenon is a function of the detuning between them which is altered by changing the dead-band of the controllers.     

Effects of air flow maldistribution on refrigeration system dynamics of air source heat pump chiller under frosting conditions

The effects of air flow maldistribution on the performance of an air source heat pump chiller under frosting conditions were investigated experimentally. The results indicated that air flow maldistribution was the dominant factor leading to hunting of the thermostatic expansion valve for medium and/or large size finned tube evaporators. With air flow maldistribution degree (AMD) increasing, frost occurred earlier, and the frost layer grew faster. The operating characteristics became lower when AMD was increased. We found such phenomenon seemed to be related to both the difference of refrigerant outlet superheat and the frosting velocity. In the hunting stage, the frost block effect became the main factor degrading the refrigeration system performance. With AMD increasing, the heat pump system pertinent performance data (suction pressure, evaporation temperature, discharge pressure, refrigerant outlet temperature, etc.) were degraded more dramatically.     

Experimental evaluation of electronic and thermostatic expansion valves performances using R22 and R407C

An experimental study to evaluate the energetic performances in steady-state and in transient operating modes of an electronic and thermostatic expansion valve is presented. Both valves have been assembled to feed an air cooled evaporator connected to an experimental vapour compression plant with a water cooled condenser operating with a semihermetic compressor. The performances of the valves have been examined at different conditions when the experimental plant works with R22 and with a substitute as the non-azeotropic blend R407C that is chlorine free. Indeed the HCFC designated as R22 contains chlorine that is harmful for the ozone layer and must be replaced in the future. The final results of this study show an overall better performance of the electronic expansion valve compared with the thermostatic expansion valve under transient conditions while in steady-state conditions both the valves are equal in performance. These results apply to both R22 and R407C.     

An experimental evaluation of the vapour compression plant performances in presence of R407C leaks using an electronic expansion valve

Chlorofluorocarbons and hydrofluorocarbons (HFCs) used as working fluids in the vapour compression plants, have to be replaced by new substances because of their ozone depletion potential. Zeotropic mixture of HFCs refrigerants that are environment-friendly substances are often employed. The zeotropic mixtures with a large glide temperature could cause problems in the refrigeration control system when a leak occurs because their composition modifies. This paper presents a comparison of the energetic performances, in presence of leaks, when a thermostatic valve and an electronic expansion valve are used in a refrigeration plant, working with the zeotropic mixture designated as R407C (R32/R125/R134a 23/25/52% in mass)—this is the most suitable substitute of the HCFC22. The vapour leaks are simulated at the inlet of the evaporator and at the liquid receiver. Experimental results show that a good adaptability to mixture leaks is related to the electronic expansion valve, while better energetic performances are obtained using the thermostatic expansion valve as long as it is usable.