Effects of Solid Matrix and Porosity of Porous Medium on Heat Transfer of Marangoni Boundary Layer Flow Saturated with Power-Law Nanofluids

The effect of the solid matrix and porosity of the porous medium are first introduced to the study of power-law nanofluids, and the Marangoni boundary layer flow with heat generation is investigated. Two cases of solid matrix of porous medium including glass balls and aluminum foam are considered. The governing partial differential equations are simplified by dimensionless variables and similarity transformations, and are solved numerically by using a shooting method with the fourth-fifth-order Runge-Kutta integration technique. It is indicated that the increase of the porosity leads to the enhancement of heat transfer in the surface of the Marangoni boundary layer flow.

MHD Heat and Mass Transfer of an Oscillatory Flow over a Vertical Permeable Plate in a Porous Medium with Chemical Reaction

The problem of magneto-hydro-dynamic (MHD) mass and heat transfer of an oscillatory fluid in two-dimensional viscous, electrically conducting over an infinite vertical permeable moving plate in a saturated porous medium with the presence of a transverse magnetic field and chemical reaction is analytically presented. The governing equations, momentum, energy, and concentration are solved. Various flow parameters effects on velocity, temperature and concentration fields are discussed. It is found that, the fluid velocity increases with increasing both the permeability and chemical reaction parameters. While, it increases with decreasing the magnetic field parameter. Furthermore, the concentration increases with increasing chemical reaction parameters.

An Investigation into the Effect of Porous Medium on Performance of Heat Exchanger

In this paper, a detailed numerical investigation of two-dimensional laminar forced convection in a porous channel with inlet and outlet slot is presented. A uniform heat flux is applied on one wall of channel and another wall is isolated. The flow in the porous medium is modeled using the Brinkman-Forchheimer-extended Darcy model in which the inertia and boundary effects are taken into consideration and thermal dispersion effects are not included in the energy equation. Parametric studies are conducted to evaluate the effects of particle diameter, Reynolds number on the heat transfer and friction factor. Nusselt number and friction factor are developed for efficient design of a porous heat exchanger based on the present configuration. In order to solve this problem Fluent software was used.

Piezoelectric Power Harvesting Process via Phase Changes of Low-Boiling-Point Medium Together with Water for Recovering Low-Temperature Heats

Low-temperature thermal energy conversions down to exergy zero to electric power must contribute energy sustainability. That is to say, reinforcements of power harvesting technologies from extremely low temperatures less than 373 K might be at least one of minimum roles for the current generations. Then, piezoelectric power harvesting process for recovering low-temperature heats was invented by using a unique biphasic operating medium of an underlying water-insoluble/low-boiling-point medium (i.e. NOVEC manufactured by 3M Japan Ltd.) in small quantity and upper-layered water in large quantity. The higher piezoelectric power harvesting densities were naturally revealed with an increase in heating temperatures. Excessive cooling of the operating medium deteriorated the power harvesting efficiency. The denser operating medium was surpassingly helpful to the higher piezoelectric power harvesting density. Concretely, only about 5% density increase of main operating medium (i.e. water with dissolving alum at 0.10 mol/dm3) came to the champion piezoelectric power harvesting density of 92.6 pW/dm2 in this study, which was about 1.4 times compared to that with the original biphasic medium of pure water together with a small quantity of NOVEC.

介质物态变化对超低温阀门降温效果的影响

深入研究超低温阀门的关键技术,对提高我国特种阀门技术具有深远影响。在仿真模拟超低温阀门温度分布时,采用的分析方式忽略了低温介质吸收热量发生相变后,所产生的低温气体与阀门之间的热量传递。为此,以Class300-DN65超低温截止阀为例,研究了稳态工作过程中介质物态变化及相变产生的低温气体对阀门降温效果的影响。首先,对绝热状态下介质流动的过程进行了计算流体动力学(CFD)仿真模拟,并建立了其传热学模型,以解释热量的传递过程;然后,研究了发生热量传递时阀盖内部间隙、以及阀体内流场介质物态分布规律;最后,根据稳态流-热耦合分析了阀门的温度分布情况。研究结果表明:由液化天然气闪蒸以及汽化产生的低温气体会在阀盖内部空腔底部流动,不断与阀盖、阀杆对流换热,从而对其进行降温。未考虑低温气体对阀门结构温度场的影响时,填料函底部温度为10.6℃;考虑低温气体时,填料函底部温度仅为-0.2℃。因此,设计超低温阀门时需要考虑低温气体对阀门的降温效果,否则容易导致密封失效。

Further Stabilization and Power Density Improvement of Stack-Type Thermoelectric Power Generating Module with Biphasic Medium by Using Various Flexible Metals as Electrodes

In order to realize further stability of a stack-type thermoelectric power generating module (i.e. no electrical connections inside), flexible materials of metal springs and/or rods having restoring forces were installed between lower-temperature-sides of thermoelectric elements. These flexible materials were expected to play three important roles of interpolating different thermal expansions of the module components, enlarging heat removal area and penetration of any media through themselves. Then, a low-boiling-point medium (i.e. NOVEC manufactured by 3M Japan Ltd.) was also applied for a high-speed direct heat removal via its phase change from the lower-temperature-sides of the thermoelectric elements in the proposing stack-type thermoelectric power generating module. No electrical disconnections inside the module were confirmed for more than 9 years of use, indicating further module stability. The power generating density was improved to about 120 mW·m-2 with SUS304 springs having 0.7 mm diameter. Increasing power generating density can be expected in terms of suitable selection of flexible metal with high Vickers hardness, cavities control on the spring surface, more vigorous multiphase flow with adding powders to the medium and optimization of the module configurations according to numerical simulations.

分数阶Maxwell纳米流体二阶滑移流动与热传递分析

在考虑二阶滑移边界的影响下,对多孔介质中垂直拉伸板引起的分数阶Maxwell纳米流体流动与热传递特性开展分析研究。利用分数阶剪切应力和分数阶Cattaneo热通量模型构建二维边界层控制方程,采用有限差分和L1算法进行数值求解。对不同物理参数下的速度、温度、平均表面摩擦系数和平均Nusselt数的变化趋势进行图形化分析。研究结果表明,牛顿流体的流动性能和热传递优于粘弹性流体;速度分数阶导数参数和温度松弛时间会恶化对流和热传递,而温度分数阶导数参数和速度松弛时间则促进对流和热传递;滑移参数降低了流体初始速度,一阶滑移参数对流动和热传递的影响大于二阶滑移参数;流动和热传递对各物理参数的敏感度随该物理参数的增大而下降。

中国地下含水层跨季节储热可行性分析

主要介绍了地下储热的常见方式及其优缺点,并针对国内地区的气候、地理、水文等因素对地下含水层跨季节储热工程的可行性进行分析,包括地下含水层跨季节储热的基本原理和结构,所需的地理地质条件及水文条件,地下含水层跨季节储热的物理过程及基本数学模型。结合国内有供暖需求地区的供暖现状,对该工程应用于国内供暖工程的可行性进行分析,给出了未来中国在清洁供暖领域的一个发展方向。

考虑电网调峰的中频加热炉综合调控技术研究

由于中频加热炉加热方式以燃气或燃油为主,浪费资源,同时对环境造成一定的污染,为此提出一种考虑电网调峰的中频加热炉综合调控技术。在考虑电网调峰的基础上,构建中频加热炉的数学模型,并分析其能量流向;对模型中的光伏电、热泵、水套炉、电锅炉以及热储能部分结构构建数学模型,分析其固定成本和维护费用;从经济性和削峰填谷两方面提出对中频加热炉的综合调控策略。通过与未应用调控技术的其他方案相比,实验结果表明,所研究中频加热炉综合调控技术展现出了明显的优势,调控方式更加灵活,减少热能的浪费,同时可以更好地观测负荷变化,实现精准削峰填谷。

太阳能集热组合墙系统的耦合传热与流动分析

针对太阳能集热组合墙系统,分析了太阳辐射及环境温度变化时,组合墙内传热与流动变化。太阳能集热组合墙系统中,多孔介质起半透明隔热体和蓄热体的作用。多孔介质的空隙率、粒径大小对系统的采暖效果影响较大。

多孔介质太阳能集热组合墙的耦合传热与流动分析

针对接触型和分隔型多孔介质太阳能集热组合墙系统,分析了太阳辐射及环境温度变化时,组合墙内传热与流动变化。多孔介质太阳能集热组合墙中,多孔介质起半透明隔热体和蓄热体的作用。多孔介质集热层的孔隙率、粒径、材料热导率和多孔介质集热层在组合墙中的位置对系统的采暖效果影响较大。

内蒙古阿尔山温泉热结构

首先通过对阿尔山温泉区的热源研究 ,确定阿尔山温泉为中低温对流型地热系统。继而在对温泉区进行地球物理、地球化学综合勘探的基础上 ,研究阿尔山地热区的热储温度、温泉水循环深度、水热资源规模及温泉在阿尔山地堑中的空间展布 ,最后根据各种研究方法所获得的数据建立了阿尔山温泉概念性地热系统模型。

600MW机组凝汽器壳侧数值模拟与应用

采用多孔介质模型数值研究了仿生双连树型管束及双峰型管束凝汽器壳侧的流动与传热特性。数模拟结果表明,仿生双连树型管束比双峰型管束的向心流动更明显,涡流更少且影响范围更小,空气聚集减弱,传热系数更为均匀。在600MW热负荷的设计工况下,HEI标准的设计背压应为4.9kPa,双峰型管束和仿生双连树型管束的数值模拟计算背压分别为5.37kPa和4.67kPa。邹县5号机组的工程试验测量仿生双连树型管束的背压为4.77kPa,与数值模拟结果相近,验证了数值模拟方法的可靠性。数值模拟和工程实践都验证了仿生双连树型管束具有显著的节能效果。

保护渣对结晶器热流的影响

分析了5种中碳钢保护渣对结晶器热流的影响,结晶器热流过大或热流稳定性越差时连铸坯表面纵裂出现的几率越大。对渣膜取样研究表明,保护渣对结晶器热流的控制是通过渣膜结构来实现的,要得到控制热流好的渣膜结构必须保证渣膜的高结晶率,找出了适合邯钢中碳钢连铸坯的保护渣组成。

纳米流体作为柴油机冷却系传热介质的数值模拟

应用Cu-水纳米流体作为柴油机冷却系传热介质,利用CFD方法对质量浓度为0.5%,1%,3%和5%的Cu-水纳米流体在柴油机冷却水套内的流动和换热过程进行三维数值模拟.并采用湍流随机跟踪方法,对固液两相流离散项纳米粒子的运动进行轨迹追踪,得到了不同质量浓度纳米流体Cu粒子在柴油机水套内的浓度场分布、速度场分布、内能变化、停留时间、换热总量以及水套进、出口之间的压降变化计算结果表明,以Cu-水纳米流体作为传热介质可以显著提高柴油机的散热性能,随着纳米粒子浓度的增加,柴油机散热能力增强,水泵功率损失小范围增加,Cu粒子在水套内的平均停留时间与其浓度相关性不明显,换热效率与纳米流体的流速相关性不明显.

热管换热器流动与传热的CFD模拟及试验

根据热管换热器结构特点及传热特性,建立了热管换热器壳程流动与传热的三维物理模型。模型中引入了多孔介质模型中的分布阻力和分布热源的概念,通过CFD计算软件模拟研究了热管换热器压力降与温度场分布,模拟研究结果与试验结果吻合良好,为热管换热器的进一步理论研究和推广应用提供了依据。

多组分合成气强化换热器壳程传热的数值模拟

采用多孔介质模型对ASPEN软件设计的高压多组分合成气换热器进行了三维数值模拟,分析了不同的几何结构对壳程流体的传热和压降的影响规律。分析结果表明,采用ASPEN软件设计的换热器具有较好的流动和换热特性;多孔介质模型可用于模拟净燃气过热器壳程流体的流动和换热;在其它参数不变情况下换热器折流板的圆缺度由20%减至15%对壳程流体的换热影响不大,但增加了壳程流体的压降。

LNG缠绕管式换热器试验研究中的热物性计算方法

在基本负荷型的LNG工厂中,多股流缠绕管式换热器是应用最广泛的主低温换热器,多组分介质在管程和壳程的传热与流动特性是主低温换热器试验研究的关键,而混合介质的热物性(密度、动力黏度、导热系数、比热容)对试验研究的影响较大。为此,在考虑了压力对气态混合物热物性计算影响的情况下,对气态和液态混合介质的4种基本热物性的计算方法进行了提炼、集成,并将计算结果与HYSYS的计算结果进行了比较,结果表明:相关的热物性计算方法是可行的,计算误差均控制在工程允许范围内。该计算方法为国内开发大型冷塔提供了技术支撑,有助于早日实现LNG缠绕管式换热器冷塔的国产化。

简易试验沙槽地下水流分异模拟试验

以简易试验沙槽模拟为研究手段,GMS软件模拟为辅助验证,研究排泄条件、介质结构、局部热源对地下水流系统的影响。试验发现:排泄点的增加导致地下水流系统由简单向复杂转变;弱透水或隔水介质的加入,使地下水流形态发生巨变,循环可由潜循环向深循环转变;热源仅在其附近一定范围内引起流线偏移,温度的升高导致流体渗流速度加快。

天然气加热炉的发展现状与改进探索

作为一种特殊的炉型形式,天然气加热炉采用中间载热介质间接加热的方式,是天然气生产、输送和应用中的主要耗能设备。为了节能降耗、提高加热效率,必须结合工程实际的需要,优化加热炉的结构,设计制造出高效节能的天然气加热炉。为此,分析了天然气加热炉传热的薄弱环节及其强化措施,针对天然气加热炉大筒体内换热面的常规布置形式存在的缺陷,提出了旋转加热和冷却受热面以及在受热面之间加装导流板两种简单而有效的天然气加热炉改良结构,使中间载热介质形成整体有组织的顺畅流动并强化传热,从而达到节能降耗和提高天然气加热炉效率的目的。以上两项技术已获得国家专利授权。