槽式太阳能集热器聚光面能流分布及传热特性

本文运用蒙特卡罗光线追踪法模拟了LS-2型槽式太阳能集热系统的聚光特性,并以此为边界条件,进一步研究传热工质为THERMINOL55合成导热油时该集热器内管壁和管内流体的温度分布特性和传热特性。结果表明,管壁和管内流体温度分布十分不均匀。并考察了不同导热油以及导热油的流速对传热效率的影响工质流速对管壁温度分布影响较大,当太阳直射辐照为1000 W/m^2,导热油入口温度为160℃,流速为0.05 m/s时,吸热管圆周方向最大温差为235℃左右,当流速增加到0.05 m/s时,最大温差减小到142℃左右。     

A computational investigation of particle distribution and deposition in a 90° bend incorporating a particle–wall model

This paper investigates the particle flow movement and deposition in a 90° bend after a straight duct, utilizing the Lagrangian particle-tracking model incorporated with a particle–wall collision model. Particle turbulent dispersion is introduced by employing the ‘eddy lifetime’ model, and particle deposition velocity in the bend is proposed by counting the number of deposited trajectories in a time period. The developed models are validated for both airflow and particle flow by previous experimental data. Particle distribution and deposition behavior at five size groups (1, 3, 5, 9, and 16 μm) are investigated. The simulation results show that, compared with traditional ‘Trap’ model, the particle–wall collision model postpones the emergence and slows the increase of the ‘particle free zone’ as the particle diameter increases. Particle deposition velocity in the duct bend is also generally predicted by the proposed estimation equation under the simulated conditions. This reveals that adopting the particle–wall collision model obtains a reasonable prediction of particle distribution and deposition in the duct bend. This work will benefit the understanding and application of microparticle flow in curved duct systems.     

氧化沟弯道的污泥沉积分析与水力计算

针对氧化沟弯道水流流态复杂的特点,分析了弯道横向环流和水流流速在弯道的重新分布对污泥沉积的影响,借助ANSYS FLOTRAN模块对设置偏置导流墙前、后的水流流速分布情况进行了模拟比较,探讨了偏置导流墙减少污泥沉积的机理,并研究了氧化沟弯道局部阻力和边墙超高的计算方法,从而为导流墙的设计提供参考。     

天然气高压管道弯管壁厚的计算

通过对GB50251--2003《输气管道工程设计规范》、GB50028--2006（城镇燃气设计规范》中关于弯管的相关要求、壁厚增大系数、壁厚减薄率等参数进行分析,确定弯管壁厚的计算方法。     

Useful solar gains through a glazed south-facing wall in the U.K. climate

A glass skin attached to a southfacing wall may serve to direct a sizeable fraction of the solar gain absorbed at the outer surface of the wall to the wall interior. The heat flow may help to make good ventilation heat losses, and conduction losses to other parts of the building. A wall of high thermal resistance tends to restrict this flow, but it also restricts the outward flow of heat. For given conditions there may be an optimum thickness. Tables are presented giving the heat needs for an unglazed wall, and for a wall with one or two glass skins attached to it. The variation in heat need with choice of month, ventilation loss and comfort temperature is shown as a function of the wall resistance. The results are based on weather data for the north Wirral, U.K. 53.4° N.     

地下洞室多孔墙体热湿传递的数值模拟

提出了一种以温度与相对湿度为驱动势的多孔墙体热湿耦合传递的数学模型,该模型同时考虑了水蒸气与毛细孔内液态水的传递。采用控制容积法将理论方程组离散并编制了计算程序,对深埋地下洞室的墙体进行了热湿传递的数值模拟,得到了墙体温度、相对湿度、热流率、湿流率的变化规律。结果表明,墙体传热过程趋于稳定的时间远小于传湿过程。     

天然气高压管道弯管壁厚减薄率的确定

对天然气高压管道弯管壁厚减薄率的计算公式进行了理论推导,计算结果与相关规范和工程技术规格书的指标一致,工程实践证明推导的弯管壁厚减薄率计算公式行之有效。     

Two-dimensional steady-state temperature distributions and heat flows in square corners

The Schwartz-Christoffel transformation is applied to the case of symmetrical and asymmetrical square corners, with solid walls and isothermal surfaces. The steady-state patterns of temperature distribution and of heat flow lines are shown. The distribution of heat flow intensity along the inside surfaces is illustrated for a range of wall thickness ratios. The Finite Element Method is applied to obtain the components of the maximum intensity occurring at the point where the two inside surfaces meet, and the results are tabulated for a range of wall thickness ratios. The total rate of heat flow for various cases is compared with that obtained from an analytical expression derived by Carslaw and Jaeger. (Conduction of Heat in Solids, 2nd edn, p. 454). This is an approximate expression, asymptotically correct at points distant from the corner, but involving some error near to the corner. A simple graphical procedure is demonstrated, which now permits the total heat flow to be calculated at any distance from the inside corner. Additionally, a method is shown for finding the distance from the corner at which the analytical equation applies within a given error.     

Firefighter Nozzle Reaction

Nozzle reaction and hose tension are analyzed using conservation of fluid momentum and assuming steady, inviscid flow and a flexible hose in frictionless contact with the ground. An expression that is independent of the bend angle is derived for the hose tension. If this tension is exceeded owing to anchor forces, the hose becomes straight. The nozzle reaction is found to equal the jet momentum flow rate, and it does not change when an elbow connects the hose to the nozzle. A forward force must be exerted by a firefighter or another anchor that matches the forward force that the jet would exert on a perpendicular wall. Three reaction expressions are derived, allowing it to be determined in terms of hose diameter, jet diameter, flow rate, and static pressure upstream of the nozzle. The nozzle reaction predictions used by the fire service are 56% to 90% of those obtained here for typical firefighting hand lines. Sharing these findings with the fire protection community can improve the safety of firefighters.     

A parametric study of Trombe walls for passive cooling of buildings

Air movement in a naturally-ventilated room can be induced through the use of a solar chimney or Trombe wall. In this work Trombe walls were studied for summer cooling of buildings. Ventilation rates resulting from natural cooling were predicted using the CFD (computational fluid dynamics) technique. The renoramlization group (RNG) k-ε turbulence model was used for the prediction of buoyant air flow and flow rate in enclosures with Trombe wall geometries. The CFD program was validated against experimental data from the literature and very good agreement between the prediction and measurement was achieved. The predicted ventilation rate increased with the wall temperature and heat gain. The effects of the distance between the wall and glazing, wall height, glazing type and wall insulation were also investigated. It was shown that in order to maximize the ventilation rate, the interior surface of a Trombe wall should be insulated for summer cooling. This would also prevent undesirable overheating of room air due to convection and radiation heat transfer from the wall.     

热传导与墙材厚度之间的关系

本文分析了墙体厚度与热传导之间的关系,热传导与优化的墙体厚度之间的关系是一个非线性函数,函数形式为x=a+bk+ck2。这个公式对于估计墙体的优化厚度,减少穿过墙体的热量是很有用的。     

逆流管式换热器动态特性的模拟计算

逆流管式换热器的动态特性计算，间壁两侧按分布参数考虑，导出的动态数学模型，用有限差分隐式（Ｗｅｎｄｒｏｆｆ格式）法进行数值计算，得出套管换热器不同热流温度、热流流量对冷热流温度时间和换热器管子轴向分布的影响。     

环形狭缝通道内流固耦合传热特性的数值分析

建立了流固耦合传热的数值分析模型,求解得到了流固耦合传热性能如温度、传热系数、摩擦系数、汽相体积分数沿换热元件轴向变化的分布。结果表明：随着质量流量的增加传热性能有被强化的趋势;相变之前,传热性能与热流密度的无关,相变之后,传热性能被强化,但趋势逐渐放缓;热流密度越大,质量流量越小,相变点越靠前。     

Impact of computational domain on the prediction of buoyancy-driven ventilation cooling

Traditional solar heated cavity structures such as solar chimneys make use of the stored solar energy in the interior wall to enhance natural ventilation of buildings but integration of photovoltaic devices into the exterior wall of such a structure can result in different proportions of heat distribution on both interior and exterior walls. This paper presents results of CFD simulation of the buoyancy-driven airflow and heat transfer in vertical cavities of different heights and widths with different total heat fluxes and wall heat distributions for ventilation cooling. Two sizes of computational domain were used for simulation – a small domain same as the physical size of a cavity and a large extended domain that is much larger than the cavity. The predicted natural ventilation rate and heat transfer coefficient have been found to depend on not only the cavity size and the quantity and proportion of heat distribution on the cavity walls but also the domain size. The difference in the predicted ventilation rate or heat transfer coefficient using the small and large domains is generally larger for wider cavities where heat distribution on two vertical walls is highly asymmetrical; incoming air would be distorted from symmetrical distribution across the inlet opening; and/or significant reverse flow would occur at the outlet opening. The difference in the heat transfer coefficient is generally less than that in the ventilation rate. In addition, a cavity with symmetrical heating has a higher ventilation rate but lower heat transfer coefficient than does an asymmetrically heated cavity.     

混凝土砌块墙体检测中的几个问题

墙体主体传热系数通常使用热流计进行测量.本文分析了热流计的使用条件,提出对于砌块墙体等表面温度分布不均匀的墙体,不适宜使用热流计测量其主体传热系数的观点.而后以混凝土砌块墙体为例,分别模拟了不同室外温度时,不保温、外保温和内保温3种情况下,墙体内外表面温度分布的情况.并针对保温墙体改变其保温层厚度.得出墙体内外表面温度及温差变化的趋势,进而得到应将热流计粘贴在保温层一侧对保温墙体进行检测的结论.模拟结果还显示,当室外温度大于0℃时,对于保温层厚度大于70 mm的内保温墙体,也可将热流计贴在不保温的一侧进行检测.     

刻楞式胶合木别墅外墙保温性能测试分析

采用热流计法对牡丹江某刻楞式胶合木别墅外墙的保温性能进行检测。通过对室内外温度、墙体热流检测数据的测试,计算得出实测传热系数。将实测传热系数与PKPM软件计算值进行对比,发现实测传热系数比软件计算值高3.3%。进行墙体热成像分析后,找出数据差异原因,并提出改进措施。     

弯道水流的紊动特性

针对弯道水流的紊流现象,应用声学多普勒测速仪,对弯道概化模型进行施测,并对弯道水流的紊动特性进行了研究,得到关于弯道水流紊动强度和雷诺应力方面的成果,为其进一步的研究提供了理论基础。     

太阳集热墙通道中气流速度场与温度场的协同性探讨

为了有效提高太阳能的热利用率,本文运用对流换热场协同理论对太阳集热墙通道中的气流速度场和温度场进行了研究,探讨了通道内温度梯度的方向和气流速度比(u/v)对场协同角及对流换热贡献率的影响规律。研究得出:太阳集热墙通道中的场协同性主要取决于集热墙板的形状和通道中气流的输运工况,改善集热墙板的形状可形成有益于对流换热的温度梯度方向角(θ);当θ一定时(θ≠0°),随着气流速度比的增加,对换热的贡献亦增加,且θ越大,效果越明显。由此提出了优化太阳集热墙集热板的思路,设计了一种带孔折型集热板的太阳墙系统并进行了实验验证。     

太阳能烟囱自然通风的一维稳态模型

太阳能烟囱是一种利用太阳能加热来强化自然通风的技术.在前人简化模型的基础上,考虑了玻璃盖板和集热墙的导热热阻的影响,建立了一个修正的太阳能烟囱自然通风的一维稳态数学模型.并利用此模型,对太阳能烟囱内的空气平均温度、集热墙温度、空气流量以及集热效率等进行了模拟计算和讨论.模型计算结果与相关实验数据及前人的简化模型进行了对...     

Locating Outfalls on Meandering Channels to Optimise Transverse Mixing

Many sources of river pollution approximate steady-state conditions and, under such conditions, the rate of transverse mixing is critical in determining the impact of pollutants. Results are presented from transverse-mixing experiments which were carried out on a large-scale laboratory channel with meander planform geometry of natural cross-section, generated by flow over a mobile bed. Dye-tracer measurements below three point sources within one cross-section are presented and compared, together with hydrodynamic measurements. The results show the importance of locating outfalls to maximise mixing rates, hence minimising pollution impact (depending on the environmental need). A release on the outside of a bend is shown to result in a faster rate of transverse mixing than a release on the inside of a bend.