新型集成开关电容DC─DC变换器及其计算机仿真

本文介绍了一种新型ＤＣ─ＤＣ变换器，它具有损耗低、不采用功率电感性元件、体积小、重量轻的优点，非常适合于制作为混合功率集成电路。与一般开关电容变换器相比，它还具有直接反馈控制、电压和电流调整范围宽、对器件参数要求不高、集成后成品率高的优点。文中给出了利用ＳＰＩＣＥ仿真的电路模型和仿真结果。     

Towards zero carbon design in offices: Integrating smart facades,ventilation, and surface heating and cooling

This paper discusses an overall strategy for reducing energy demand in non-domestic buildings, mainly focusing on office developments. It considers four areas: reducing internal heat loads; addressing passive design through the building construction; using efficient and responsive HVAC systems and focusing on chilled (heated) surface systems; integrating renewable energy supply systems into the building design. The impact on energy use and carbon dioxide emissions will be discussed. The paper will draw from a range of design projects carried out in Europe, where this integrated approach has been applied, and then explore the benefits in relation to applications in the Middle East and China. Energy modeling results, to inform the design process will be presented, using energy simulation for three case study locations, in Zurich, the Chongqing and Abu Dhabi.     

新型耐温耐压多层结构管道及其壁温计算

为降低高温高压流体管道的制造成本,遵循耐温与耐压分离的原则,提出了一种耐温耐压的多层管道结构,并建立了计算该管道壁温的热力学模型,探讨了不同内管道外径时遮热管壁温、遮热管外半径和热流功率与遮热管数量的关系.结果表明:在内管道壁温为700℃时,随着遮热管数量的增加,外管道壁温迅速下降,最终可降至350℃以下,完全可以使用普通的钢材来制造耐压管道,大大降低了管道的制造成本.     

100t复吹转炉底枪位置的设计与应用

基于水模拟实验优化后的6种底枪布置方案(对称布置A1,A2,A3和A4,以及非对称布置B1和B2),利用FLUENT软件对转炉熔池流场进行了三相流模拟,对底枪位置进一步优化,以确定最佳底吹方案。模拟结果表明,方案A2和B2的转炉熔池搅拌效果明显优于其他底枪布置方案;但由于前者的侵蚀面积小于后者,且熔池平均速度大于后者,确定采用A2底枪布置方式。工业试验表明,平均冶炼时间为14.8 min,终点含碳量满足钢种需求,脱磷率达96%以上,设计方案为转炉冶炼提供了良好的动力学条件。     

连续管水力喷射压裂机理与试验研究

面对我国日益增加的"多井低产"问题,连续管水力喷射压裂技术作为一项能够有效提高单井产量的新技术而备受关注。依托国家863计划的重点课题,探索了连续管水力喷射压裂机理;基于孔内压力分布的数值模拟,验证了水力射流射入孔内的增压作用与水力封隔作用导致孔内压力升高的作用机理,分析了主要参数对孔内压力分布的影响;以连续管管径为重要特征参数,提出了连续管水力喷射压裂3种作业方式。基于试验研究,验证了连续管水力喷射压裂机理和数值模拟计算结果,认为在相同喷嘴压降下,孔内压力随着围压增加近似于呈线性增大;在井眼垂深较大、地层破裂压力较高时,推荐使用高一些的喷嘴压降,以获得更好的增压作用与水力封隔效果;对于连续管水力喷射压裂,通常采用管径不小于50·8mm(2英寸)的连续管。     

Direct numerical simulation of nonpremixed flame-wall interactions

The objective of the present study is to use detailed numerical modeling to obtain basic information on the interaction of nonpremixed flames with cold wall surfaces. The questions of turbulent fuel-air-temperature mixing, flame extinction, and wall-surface heat transfer are studied using direct numerical simulation (DNS). The DNS configuration corresponds to an ethylene-air diffusion flame stabilized in the near-wall region of a chemically inert solid surface. Simulations are performed with adiabatic or isothermal wall boundary conditions and with different turbulence intensities. The simulations feature flame extinction events resulting from excessive wall cooling and convective heat transfer rates up to 90 kW/m². The structure of the simulated wall flames is studied in terms of a classical mass-mixing variable, the fuel-air based mixture fraction, and a less familiar heat loss variable, the excess enthalpy variable, introduced to provide a measure of nonadiabatic behavior due to wall cooling. In addition to the flame structure, extinction events are also studied in detail and a modified flame extinction criterion that combines the concepts of mixture fraction and excess enthalpy is proposed and then tested against the DNS data.     

Numerical investigation of boiling flow of nitrogen in a vertical tube using the two-fluid model

The two-fluid model has been extensively used in modeling boiling flow of water, however, there are few equivalent studies of boiling flow of cryogenic liquids. In the present study, the two-fluid model which is basically included in the CFX code was modified by incorporating new closure correlations, then boiling flow of liquid nitrogen in a vertical tube was numerically simulated using the basic model and the modified model, respectively. Comparison with experimental data shows that the modified model is satisfactorily improved in accuracy. This study demonstrated that the following parameters and models are important for accurate prediction: the lift force, the bubble diameter distribution and the active site density, among which, the active site density has the most significant effect.     

Conjugate natural convection heat transfer in an inclined square cavity containing a conducting block

The present work is concerned with computation of natural convection flow in a square enclosure with a centered internal conducting square block both of which are given an inclination angle. Finite volume method through the concepts of staggered grid and SIMPLE algorithm have been applied. Deferred QUICK scheme has been used to discretize the convective fluxes and central difference for diffusive fluxes. The problem of conjugate natural convection has been taken up for validating the code. The abrupt variation in the properties at the solid/fluid interface are taken care of with the harmonic mean formulation. Solution has been performed in the computational domain as a whole with proper treatment at the solid/fluid interface. Computations have been performed for Ra = 10³–10⁶, angle of inclination varying from 15° to 90° in steps of 15° and ratio of solid to fluid thermal conductivities of 0.2 and 5.0. Results are presented in terms of streamlines, isotherms, local and average Nusselt number.     

基于Matlab/Simulink的单轴燃气轮机动态仿真

本文利用Matlab/Simulink对某型单轴燃气轮机系统进行了仿真,并采用了自适应控制与常规的PID控制相结合的方法对转速控制器进行了建模分析,不仅系统的响应时间缩短,而且系统超调量大幅度减小,为燃气轮机的转速控制提供了一种新的思路。     

汽车发动机冷却系仿真优选方法的研究

介绍了汽车发动机冷却系散热器、风扇和水泵的仿真优选方法。建立了散热器性能计算模型,提出了散热器优选的方法。通过收集不同结构形式的风扇和水泵的试验数据,建立风扇性能数据库,应用相似理论,对风扇和水泵进行优选,给出了应用实例。