地源热泵U型埋管土壤温度场数值模拟

结合相关文献给出原始地温计算式,针对垂直U型埋管换热器建立瞬态传热模型,采用控制容积法对方程进行离散,对换热器周围土壤温度场进行数值模拟.对模拟结果进行分析获得地下埋管换热器的传热特性与土壤温度变化规律,并通过实验数据验证模拟结果的正确性.     

U型垂直埋管周围土壤温度场的数值模拟

针对土壤源热泵地下垂直U型埋管，建立周围土壤的非稳态温度场的数学模型，并利用MATLAB软件进行求解。通过对夏季制冷工况的模拟，其结果与实测值非常吻合，并得到土壤温度沿径向、纵向的变化规律及埋管的热作用半径的变化规律，为U型垂直埋管的埋深及间距设计提供参考。     

翅片空冷器内外侧流体流动数值模拟与特性研究

翅片空冷器在电站中发挥着重要作用,其冷却方式采取空气为冷却介质,取代了传统的水冷却介质。因空气冷凝器暴露在空气中,与周围空气是进行热交换,其环境风场则会对空冷器运行产生较大影响。应用FLUENT软件,对翅片空冷器内外侧流体流动数值进行模拟与特性研究。在分析翅片空冷器内外侧流体流动数值特性的基础上,提出研究结论。     

进口流体温度对U型地埋管换热器换热性能的影响

利用土壤源热泵的热传递模型,模拟分析了在夏季运行工况时不同进口流体温度下井群换热器的换热规律,探讨了不同进口流体温度对换热器换热性能的影响,得出了不同进口流体温度下井群换热器换热量的计算方法,为工程实际提供了理论依据。     

无机膜管气体除尘流场分布的数值模拟

先进的多孔无机膜管为高温、高腐蚀烟气净化提供了一种切实可行的新型技术路线,但装置的设计还存在很多急需解决的问题.利用Gambit软件建立了无机膜管二维几何模型,采用FLUENT软件中混合模型对无机膜管过滤瞬间的速度和压力场进行数值模拟.结果表明,通过膜管的压强降分布均匀,并且压强降损失主要发生在膜管的多孔过滤介质中.该模型可以用来分析预报无机膜过滤器内的气体流动情况,并可以为无机膜管收尘装置的优化设计提供理论依据.     

封闭腔内纳米流体自然对流换热的数值模拟

采用数值模拟方式研究充满了纳米流体的封闭腔内的稳态自然对流。重点分析了纳米颗粒的体积分数,Ra数以及不同类型纳米颗粒对自然对流换热特性的影响。数值模拟结果表明:在纯水中加入纳米颗粒可以显著提高基液的自然对流换热特性;对于给定的Ra数下,随着纳米流体的体积分数增大,纳米流体换热效果显著增强;对于给定的体积分数下,随着Ra数增大,纳米流体的换热强度也随之增大,并且换热机理由热传导为主变为热对流为主;通过Ag,Cu,CuO和Al2O3四种纳米颗粒的对流换热效果比较分析得出,金属Ag和Cu纳米颗粒比金属氧化物CuO和Al2O3的纳米颗粒制备的纳米流体的对流换热效果更好。     

“U”形管内油-冰两相流冲蚀特性数值模拟分析

本文针对燃油管路上游冰晶脱落对下游“U”形管的冲蚀特性进行了数值模拟分析,并建立油冰两相流冲蚀DPM模型。比较考虑升力和不考虑升力的计算结果后发现,考虑升力时计算出的冲蚀速率是不考虑升力时的2～3倍,说明升力在“U”形管内的冲蚀过程中具有重要作用,不可被忽略。通过分析“U”形管弯头内的流场细节,分析了萨夫曼升力和马格努斯升力对冰晶输运特性的作用机制。在此基础上,进一步分析了燃油流速对冰晶冲蚀的影响,发现弯头的最大冲蚀速率与流量近似呈线性关系,而下游直管段呈指数关系,并初步提出了预测方法。     

脉冲管制冷机交变流动动态特性数值研究：第二部分：数值模拟结果

第一部分给出了脉冲管制冷机数值模拟的基本方程和改进的数值计算方法。这一部分采用第一部分的方法对脉冲管制冷机的内部交变流动，换热以及制冷过程进行了详尽的数值模拟研究，得到了脉冲管制冷要内部各参数的动态变化，分析了各动态参数变化对制冷机整机性能的影响，并与实验结果进行了比较，数值模拟分析与实验结果符合良好，     

不同强化管传热特性的数值模拟与实验研究

对横纹槽管、缩放管和螺旋槽管在夹套间进行了传热特性实验,研究了传热效率指标随雷诺数的变化规律.运用FLUENT软件,采用二维轴对称方法和k-ε模型对夹套间流体流动传热进行了数值模拟,并将模拟结果与实验结果进行对比.从场协同的角度研究了速度场与温度场夹角对传热膜系数的影响.     

U型节流阀流场特性的数值和试验研究

液压控制阀的调压精度和工作稳定性依赖于流道内部流场特性的深入研究。基于Schnerr-Sauer空化模型和标准k-ε湍流模型,开展了双U型节流阀内空化流场仿真计算。搭建了可视化试验台,通过高速相机捕捉了透明节流阀内的空化形态流场。通过对双U型节流阀内部流场特性及影响因素的试验和数值分析可知：节流口为主要压降区,由收缩流变为扩散流,是空化发生的主要区域。节流槽出口处的空泡群狭长型,且与出口截面呈一定角度、稳定存在。随着进出口压差的减小,双U型节流阀节流口空化强度进一步缩小,且向节流口萎缩。随着开度的增大,空泡团由团状逐渐收缩为细长状,空化区域及空化强度均呈现先增强再减弱的趋势。此外,一级槽的深度也是影响双U型节流阀内部空化流场的重要因素。一级槽深度减小时,节流槽内阻力增加,压力恢复加快,空化区域及空化强度亦逐渐减弱。随着一级槽深度值减小,高速流范围变小,空化面积亦减小。合理控制双U型节流槽深度,可以有效抑制空化发生程度。     

低温冷箱跑冷损失及其对内部换热器温度分布的影响

以中国先进研究堆(CARR)的冷中子源项目为背景,建立了低温换热器与冷箱换热的物理模型,并通过对换热器内部冷热流体之间的传热以及换热器与冷箱、管道、支架之间辐射换热的耦合计算,得出冷箱和换热器的辐射热流密度,以及辐射跑冷对冷箱内部换热器温度分布的影响.辐射跑冷导致换热器温度变化最高达4 K.采用铝箔包裹换热器和管道的隔热方法,可以大幅度减小辐射跑冷量.计算表明,运用该方法后辐射对换热器温度的影响最大不超过0.4 K,结果能够满足使用要求.     

仿树叶型混合元件湍流特性的数值模拟

为提高选择性催化还原系统中催化剂与烟气的混合效率,减小组件的布置深度,采用FLUENT模拟了三种仿树叶型混合元件的速度场和湍流场.结果表明,三种仿树叶型混合元件对流体的混合都能起到作用,其中柳叶形叶片产生的湍动能值最高,松叶形叶片产生的湍动能值最小;柳叶截面的速度云图变化最大,枫叶其次,松叶变化最小.     

Numerical investigation of energy and Reynolds stress distribution for a turbulent flow in an orifice

The turbulent heavy water and light water flows through an orifice, which characterize different reactor systems in nuclear power plants, are studied. The aim was to reveal the influence of process fluid on the turbulence parameters by considering heavy water and light water flows under the unique flow accelerated corrosion (FAC) conditions. The heavy water and light water are referenced based on their density values. The change in density values may have an effect on the flow dynamics and hence on FAC. These effects are brought out in this study and they can be extended to other cases for example, the change in the density of light water due to the chemical additions for controlling the pH values. The flow details at the downstream of orifice were studied extensively with the aid of computational modelling for different Reynolds numbers. Also structural development of the entire vortical flow field which could immensely enhance the knowledge about vortical structures occurring in the recirculation regions at the upstream and downstream of orifice is investigated. This study has been started with the exploration of flow topology of the velocity field by checking the topological consistency. The kinetic energy and dissipation rate were predicted by the modelling of turbulence using the Realizable k–ɛ model. Also the Reynolds stresses were calculated using the Reynolds stress model. The recirculation region showed maximum value for these parameters near the center line of the elliptic point, but for the dissipation rate this maximum value is observed at the wall. The maximum values of kinetic energy and wall shear stress are observed at the periphery of the orifice in comparison with that of the recirculation region. The predicted turbulent parameters have higher values in the recirculation region for heavy water flow and at the periphery of the orifice for light water flow with respect to each other flows. Also, the Sh distribution has been analyzed to estimate the FAC rate along the solid surface. The predicted peak values of these parameters will help to locate the locations which are susceptible to FAC.     

HTR-PM蒸汽发生器入口结构对流量分配影响的数值研究

针对高温气冷堆核电站示范工程(HTR-PM)蒸汽发生器实验模型的一回路流量分配进行了数值模拟研究.用Gambit前处理软件建立了数值计算模型并进行网格化处理,通过Fluent流体力学计算软件对没有遮流板和添加不同角度遮流板情况下换热组件出口流量分配均匀性进行模拟分析,结果表明垂直角度的遮流板能够最优地改善流量分配均匀性...     

Numerical investigation of the effect of a recess on the characteristics of a pulsating gas flow

A supersonic flow past a recess with pressure fluctuations in the separation zone is simulated numerically. The effect of the gasdynamic and geometric parameters determining the flow in the recess on the character of the pressure fuctuations is studied. Different shapes of the recess are considered. To simulate flow in the recess kinetically consistent difference schemes that have proved themselves good in describing complex flows are used. Obtained results of numerical calculations are compared with experimental data. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 71, No. 3, pp. 477–483, May–June, 1998.     

空分设备冷箱内配管优化设计

随着空分设备向大型化、多样化发展,冷箱内部管道不断增多,配管难度也越来越高。对冷箱内配管进行优化设计,以提高空分设备运行的安全性和经济性。文章从单元设备、阀门及冷箱板开孔位置布置,与单元设备相连管道布置,换热器热端管道布置,水平管道敷设和排放管道引出方式等10方面,介绍杭氧对冷箱内配管所做的优化设计,旨在提高空分设备的经济性和运行安全性。     

Numerical and experimental investigation on temperature distribution of the discontinuous welding

The main objective of this study is to generate new understanding and improve computer methods for calculating the thermal cycles and temperature distribution of 5A06 aluminum alloy structure during discontinuous welding. Predicting the thermal cycle also provides an estimate of the weld penetration and weld width. The submodeling technique was used to save computing time and improve calculation accuracy. The arc heat input was applied in the weld zone using different forms of surface, volumetric and combined heat flux distribution functions. In order to validate the thermal simulation model, temperature distribution at the weld backside was precisely measured by infrared thermography during the welding process. The simulation results showed that the model is quite sensitive to the energy distribution during the welding process, the effects of the pre-heating and re-heating are significant. The present simulation model can be used as a proper tool to investigate the effect of different metal inertia gas (MIG) process parameters.     

Numerical investigation of fatigue characteristics of concrete pavement

In concrete pavements, fatigue is one of the major causes of distress. Repeated loads result in the formation of cracks. The propagation of these cracks cause internal progressive damage within the structure, which ultimately leads to failure of the pavement due to fatigue. This paper presents a theoretical investigation of crack propagation within concrete pavement and its fatigue characteristics under cyclic loading. A numerical fatigue performance model has been developed for this purpose. The model is based on fictitious crack approach for the propagation of cracks and stress degradation approach for estimating the bridging stress under cyclic loading. Using the numerical model, a parametric study has been performed for a typical concrete pavement to evaluate its fatigue characteristics for different foundation strengths. The method can be used for prediction of crack propagation in concrete pavement under cyclic loading and gives an estimate of the incremental damage or the entire crack history of the pavement.     

Experimental investigation of frost formation on a horizontal cold cylinder under cross flow

In the present work, frost formation on a horizontal cold cylinder was investigated experimentally. An apparatus was designed and carried out on a physical model which was included an air tunnel and a cold cylinder exposed to humid air flow. It was found that the frost layers formed on the front and rear surfaces of the cylinder were thicker than the top surfaces where the flow separation was nearly or wholly initiated. The effects of air flow parameters such as flow Reynolds number, entrained air temperature, absolute air humidity and temperature of cylinder surface on the frost thickness and density formed over the cylinder were studied. In this paper, the dew point temperature of the inlet air was above the freezing point and also the earlier transition time was investigated.