柴油机喷雾火焰撞壁瞬时传热特性仿真研究北大核心CSCD

使用CONVERGE发动机仿真软件,基于流固耦合建立了撞壁喷雾火焰瞬时传热仿真模型,并利用试验数据对仿真模型进行了标定。利用该模型探究了撞壁距离、喷射压力及环境氧体积分数对喷雾火焰撞壁瞬时传热特性的影响。仿真计算结果表明:撞壁距离的变化对壁面传热的影响不大,喷射压力升高及环境氧体积分数的增加都会使喷雾火焰撞壁瞬时壁面传热损失升高。     

大容量超超临界锅炉水冷壁壁温特性研究

采用区域法建立二维小区计算模型,分别得到不同计算条件下烟气侧、工质侧以及二者耦合传热下模型截面上壁温分布规律,并与实测数据进行比较。结果表明:3种计算条件下耦合迭代模型计算的平均误差分别为2.66%、2.11%和2.38%,均远小于炉内辐射传热模型和管内换热模型的计算平均误差,表明耦合传热计算模型具有较好的准确性和适用性。     

超临界CO2锅炉气冷壁壁温及炉内烟温分布

为了从超临界CO₂锅炉实验数据中挖掘出更多的参数信息,应用固体导热计算、工质管路分配计算、炉膛辐射传热仿真等研究方法对气冷壁及其内、外部热边界进行求解,基于DO模型、支持向量机提出了一种气冷壁壁温和炉内烟温预测模型,并根据实验数据进行了计算。该算法的数据源为运行监测数据,可以实现炉内烟气温度分布、壁温及热负荷等物理量的在线求解。研究结果表明：气冷壁导热计算获得的管壁特定点温度与工质温度温差拟合公式准确性高,相关性在0.99以上;气冷壁壁温与外部热边界求解计算中获得热负荷波动情况一致;烟温预测模型的有效性在传热数据库测试中得到验证,其最大相对误差不超过8.5%。     

槽式太阳能聚光集热器传热数学模型研究

为了计算分析槽式太阳能集热器的传热特性,将金属吸热管表面的热流密度不均匀特性考虑在内,建立了一种传热数学模型;该模型将金属吸热管管壁所能接受到的热流密度简化为矩形分布,考虑了管壁的周向和径向导热。本文以Dudley的试验数据为依据对其进行计算验证,同时也进行了不均匀热流边界条件下槽式太阳能吸热管的管内流动模拟研究。计算结果和模拟结果都与文献提供的数据有较好的吻合度,集热器出口流体温度和效率与试验数据的最大相对误差分别为0.91%和4.79%。该传热数学模型可用于槽式太阳能集热器传热热性的计算分析。     

6110A柴油机绝热性能的预测

本文建立了计算直喷式柴油机气缸内热力过程、气缸周壁传热和气缸盖排气道传热的数学模型,并编制了计算机程序。采用解析法处理气缸周壁传热,特别是应用二维解析法建立活塞顶传热,将气缸周璧传热计算与柴油机气缸内热力过程计算相结合,互为边界条件,因此能模拟计算绝热机工作过程。在几种气缸周壁绝热层布置形式下,以6110A柴油机为例进行了非增压、增压和增压带动力涡轮在标定工况下的模拟计算,并分析了绝热对发动机性能,燃烧过程以及热平衡的影响。为研制绝热发动机提供了预测数据。     

大功率汽轮机快速冷却时汽缸壁温度的计算方法

本文提出一种汽轮机快速冷却时汽缸壁温度的计算方法,将汽缸当成一个圆筒,求出当量厚度,根据双层汽缸内,外缸不同的传热条件更出汽缸的传热微分方程,其解与实测结果能较好吻合,可用来计算停机后快速冷却时汽缸温度的变化。     

Calculation on Water Wall Temperature in the Furnace of a 1000 MW Ultra-supercritical Tower Boiler

以某电厂1 000 MW超超临界塔式锅炉为研究对象,在一维分区的计算基础上,对炉内主燃烧区域进行分区,在满足工程需要的基础上简化了辐射传热模型和管内换热模型,对炉内主燃烧区进行变工况研究得出水冷壁壁温分布,并且与实测数据进行比较验证.结果表明：水冷壁壁温沿炉膛高度方向呈现双峰,沿炉膛宽度方向则呈中间高两边低的趋势;随着负荷降低,水冷壁壁温降低;模型计算数据与实测数据相比,均方根误差最大为5.38%;该模型可以预测水冷壁壁温分布,为锅炉设计和实际运行提拱技术支持.     

1000MW超超临界塔式锅炉炉内水冷壁壁温计算研究

以某电厂1 000 MW超超临界塔式锅炉为研究对象,在一维分区的计算基础上,对炉内主燃烧区域进行分区,在满足工程需要的基础上简化了辐射传热模型和管内换热模型,对炉内主燃烧区进行变工况研究得出水冷壁壁温分布,并且与实测数据进行比较验证.结果表明:水冷壁壁温沿炉膛高度方向呈现双峰,沿炉膛宽度方向则呈中间高两边低的趋势;随着负荷降低,水冷壁壁温降低;模型计算数据与实测数据相比,均方根误差最大为5.38%;该模型可以预测水冷壁壁温分布,为锅炉设计和实际运行提拱技术支持.     

HCCI发动机多区燃烧模型的比较研究

多区模型作为现阶段均质压燃（HCCI）发动机高效准确的数值模型得到了世界范围的广泛关注。讨论了不同子模型对多区模型预测性能的影响。以实验为基准,比较了多区模型中区间划分、缸壁传热模型、区间热量交换模型、区间质量交换模型和边界层模型对HCCI发动机燃烧和排放模拟结果的影响,全部计算均基于异辛烷的详细化学动力学机理。结果表明：在区间划分时对温度较低的区域细化可以提高排放的计算效果,而对高温区域的细化对计算结果影响不大;改进的Woschni传热模型更准确地模拟了缸壁的传热过程;区间的质量和热量交换对计算结果影响显著,特别是质量交换模型的加入使CO排放的预测与实验值更为接近;而边界层厚度模型对整个结果影响不大。     

双层壁冷却结构综合冷却效率和相对压力损失多目标优化

在典型燃烧室工作环境下,针对特定双层壁冷却结构,以综合冷却效率和相对压力损失为优化目标,采用径向基神经网络构建数学模型,通过遗传优化算法实现多目标优化,旨在提高其气动和传热性能。在给定的双层壁冷却结构参数范围内,优化后双层壁冷却结构的最大综合冷却效率为0.89,而相对压力损失可降至0.17%。     

应用CFD软件模拟双层通风幕墙节能性对比——在强制通风且有热对流情况下

应用CFD软件对双层通风幕墙的内流场进行了分析研究,得到了包括内流场图、温度分布图、出风口流速表和温度表等参数,通过改变双层通风幕墙的间距,考察幕墙间距对幕墙整体节能性能的影响并提出改进意见。     

被动蒸发冷却技术在双层皮玻璃幕墙的应用

双层皮玻璃幕墙较之传统幕墙更好地为建筑提供夏季隔热和冬季保温。本文提出将被动蒸发冷却技术应用于双层皮玻璃幕墙结构,通过在双层皮玻璃幕墙内设置水被动冷却蒸发系统,当夹层温度过高时水自动喷出或流出,达到降低夹层温度、提高隔热性能的目的,以提高双层皮玻璃幕墙对夏季炎热气候的适应性。     

夏热冬冷地区"双层皮"玻璃幕墙节能技术研究

玻璃幕墙是影响到建筑能耗的关键部位。本文分析了传统玻璃幕墙的弊端;通过玻璃幕墙的耗能计算公式说明影响玻璃幕墙耗能的相关因素;阐述了适合夏热冬冷地区的节能型玻璃幕墙—“双层皮”玻璃幕墙的构造和节能原理;通过实验验证了“双层皮”玻璃幕墙比传统的“单层皮”玻璃幕墙具有更佳的热工性能,其节能效果与通风和遮阳构造设计等有关。     

The performance simulation of all-glass vacuum tubes with coaxial fluid conduit

A numerical investigation has been carried out for a solar system, which consists of all-glass (double skin) solar vacuum tubes. Water is heated as it flows through the coaxial fluid conduit inserted in each tube. The space between the exterior of the fluid conduit and the glass tube is filled with antifreeze solution. This is to facilitate heat transfer from the solar heated absorber surface to water and to prevent the functional problems due to freezing in frigid weather conditions. Results show good agreement when compared with other experimental data demonstrating the reliability of the present model. The one-dimensional numerical model could be used efficiently in designing all-glass solar collector tubes with different geometrical parameters other than those considered in the present analysis.     

Non-uniform double slot injection (suction) on a forced flow over a slender cylinder

A general analysis has been developed to investigate the influence of non-uniform double slot injection (suction) on the steady non-similar incompressible laminar boundary layer flow over a slender cylinder, where the slender cylinder is inline with the flow. Non-similar solutions are obtained starting from the origin of the stream-wise coordinate along the stream-wise direction by using an implicit finite difference scheme in combination with the quasilinearization technique. Numerical results are reported to display the effects of non-uniform double slot injection/suction on skin friction coefficient and heat transfer rate at the wall. Further, the effects of viscous dissipation and Prandtl number on velocity and temperature profile, and skin friction and heat transfer co-efficients are also presented in this paper.     

A three-dimensional performance analysis of all-glass vacuum tubes with coaxial fluid conduit

The thermal performance of a solar system composed of parallel, all-glass (double skin) vacuum tubes has been investigated by using a three-dimensional analytical model. Each vacuum tube is equipped with a coaxial fluid conduit for water to flow through and collect the sun's thermal energy. The space between the exterior of the fluid conduit and the glass tube is filled with antifreeze solution to facilitate heat transfer from the solar heated absorber surface to water and to prevent the functional problems due to freezing in frigid weather conditions. Different from one-dimensional analytical models, the three-dimensional model considered in the present analysis enables the prediction of spatial variation of water temperatures as it flows through the coaxial conduit. This is quite useful in extracting major variables for the operation of the solar system using all-glass vacuum tubes as considered in the present investigation.     

Shock wave boundary layer interactions in hypersonic flows over a double wedge geometry by using conjugate heat transfer

Shock wave boundary layer interaction phenomena play a critical role in the design of supersonic and hypersonic vehicles. Consequently, this paper mainly focuses on hypersonic flow over a double wedge model, flow fields around concave corners are relatively complicated, and produce several classical viscous flow features depending on the combination of the first and second wedge, and the important characteristic phenomena are mainly the shock‐boundary layer and shock‐shock interaction. For these interactions, aerodynamic heating and pressure loads increase greatly when interactions are present. The conjugate heat transfer (CHT) technique is expected to exactly predict the separation bubble length, heat flux, skin friction coefficient, and pressure distributions in double wedge studies in hypersonic applications. In the present CHT studies, the different wall materials used are thermal insulation, Macor, and SiC, it is clearly shown that while using Macor and thermal insulctation wall material in CHT studies, the interface temperature, skin friction coefficient, heat flux distribution along the length change significantly with increase in simulation time. In comparing the CHT results with the fluid flow solver with the wall, considering isothermal and adiabatic boundary results, it is clearly indicated that the fluid flow solver results are either underpredicting or overpredicting the interface properties, but CHT studies give an accurate prediction of the separation length and interface properties.     

Thermal transmittance of multiple glazing: computational fluid dynamics prediction

Computational fluid dynamics (CFD) is applied for predicting the convective heat transfer coefficient, thermal resistance and thermal transmittance for a double glazing unit. The predicted thermal resistance of glazing is compared with reference data and good agreement is achieved. The convective heat transfer coefficient and thermal transmittance vary with the air space width and the temperature difference across glazing. The CFD technique can be used to gain insight into multiple glazing performance and also optimise the design and operation of novel multiple glazing systems such as air flow windows or double skin facades in terms of energy efficiency and thermal comfort.     

Mixed convection flow over a vertical cone with double dispersion and chemical reaction effects

This contribution brings mixed convection flow across a vertical cone in the presence of double dispersion and chemical reaction effects. The model of the problem is designed mathematically in the forms of governing equations; it is nondimensionalized for ease of numerical computations and the gained nonsimilarity equations are solved numerically throughout the detailed numerical technique. The outcomes are summarized in graphical and numerical forms to illustrate the impacts of governing parameters Prandtl number, Schmidt number, buoyancy ratio, thermal dispersion, chemical reaction, solutal dispersion, and buoyancy parameters at various streamwise spots of velocity, temperature, and concentration profiles. Moreover, skin friction, heat, and mass transfer rates are tabulated. To establish the exactness of the adopted numerical technique, residual analysis study also portrayed; we made a comparison with prior published outcomes and found them to be in great consent.     

双超模型在吕梁市圪洞流域山洪模拟中的应用

为分析双超模型在圪洞流域洪水模拟中的适用性,利用流域内1966~2012年14场代表性降雨对模型参数进行率定和验证,并利用洪峰流量相对误差、径流深相对误差、确定性系数及峰现时差四个指标评价了双超模型的模拟精度,之后探讨了不同土地利用下模型主要敏感参数的取值。结果表明,双超模型在圪洞流域的适用性良好,山洪预报结果基本能够满足实际应用的要求;不同土地利用类型下,土壤水分最大吸力、土壤饱和时的渗透力等模型主要参数排序由小到大均为建设用地、草地、林地、耕地。研究结果为双超模型在黄土丘陵沟壑区的应用提供了借鉴。