新型太阳能聚焦器焦面能流分布仿真

考虑太阳光不平行度,应用蒙特卡洛光线跟踪法及光线的镜面反射定律,并采用数值模拟的方法分析了焦面位置误差、指向误差等对一种新型展开式太阳能聚焦器焦面光斑形状及能流分布的影响。结果表明:焦面位置误差绝对值越大,焦面光斑半径越大,焦面能流峰值越小;焦面误差绝对值相同时,焦面光斑形状及能流分布几乎一样;指向误差越大,光斑越偏离焦面中心,并且光斑由圆形逐渐演变成椭圆形,光斑长短径之比越大。结论可以为该新型空间太阳能聚焦吸热系统的设计提供参考依据。     

空间太阳能热动力发电系统10kW聚能器焦平面热流分布计算

考虑了表面形状误差、指向误差、不同的半张角、太阳表面亮度不均匀对聚能器焦平面热流分布的影响，该算法是一种较为全面、可靠的计算焦平面热流分布算法。以10kW太阳能动力系统为例，介绍了采取该算法计算的聚能器焦平面的热流分布。     

碟式太阳能光热转化单元热损失数值分析

以某碟式太阳能光热转化单元为例,基于集热器尺寸误差、几何结构和运行工况参数,建立了碟式太阳能光热转化单元热损失以及热效率数学模型,开展了碟式太阳能光热转化单元热损失及热效率的定性分析和定量计算。结果表明:各种热损失中,聚光器光学损失Qopt、吸热器再辐射热损失Qrad、反射热损失Qref占总损失的比例相对较大,光学损失Qopt最为显著,达到为58.27%;集热器光学误差δ、采光口直径Dap是影响光热转化单元热损失及热效率的关键因素;降低光学误差δ,减小集热器采光口直径Dap,可有效降低单元热损失值,提高热效率。     

基于小型发电机的碟式太阳能热发电技术研究进展

阐述了碟式太阳能热发电系统的发展历程和特点，介绍了碟式热发电的基本原理，着重分析了碟式热发电所涉及的关键技术，包括Stirling发电机、Brayton发电机、碟式聚光镜和受热器。通过对关键技术的分析，指出提高碟式聚光镜系统的稳定性和降低成本两个方面是当前技术开发的重点。同时提出了发展中国碟式太阳能热力发电技术所需技术开发过程的建议。     

碟式斯特林太阳能发电系统最新进展

太阳能热发电技术中最具发展潜力的是碟式太阳能高温发电技术,尤其是近几年碟式斯特林太阳能发电技术更是令世界瞩目,它具有光电转换效率高、耗水量低、发电方式灵活及可逐步规模化等特点。目前,国内外碟式斯特林太阳能发电系统的研制方兴未艾,国外太阳能斯特林发电机制作及测试技术已趋于成熟,正处于中试和大规模推广阶段。国外主要的碟式斯特林发电系统包括SES公司的SunCatcher单元、Cleanergy公司的Eurodish单元、Infinia公司的PowerDish单元等。国内碟式斯特林太阳能热发电技术研究取得了一些成绩,但总体来说,目前还未获得实质性的进展,相关研究尚处于初级阶段。碟式斯特林太阳能发电系统的核心部件是太阳能斯特林发电机,其某些关键部件的研发难度较大,如高温太阳能吸收器、高效回热器、工质密封、功率和转速控制等。要攻克这些关键技术,需要国内外相关部门的大力支持。我国科研工作者应通过各种形式与国外斯特林发电机制造商及科研机构进行技术合作,逐渐掌握此项技术;或者借鉴国外的研制经验自主研发,然后通过示范推广,建设大型碟式斯特林太阳能发电厂。     

碟式太阳能发电在分布式能源系统中的应用

碟式太阳能发电系统具有单机容量小,排布灵活,余热可综合利用等特点,是一种较适合与分布式能源系统结合的太阳能利用类型。对碟式太阳能发电技术进行逐一分析,总结了在分布式能源站中应用碟式太阳能所面临的诸多问题。结合实例,详细介绍华电电力科学研究院有限公司一套25 kW的碟式太阳能发电系统运行情况,提出系统的改进和提升方向。     

太阳光不平行度对太阳能聚集性能影响的数值研究

对大型对日定向的碟式太阳能反射聚集器,通过数值模拟研究了太阳光不平行度与定向跟踪精度对聚光性能的影响。通过建立锥形光束的概率模型,采用蒙特卡洛法直接模拟了太阳光经碟式反射聚集器后在焦平面上产生的能流分布。比较了不同定向跟踪精度下,不同口径比的反射聚集器对太阳光与平行光的聚集性能差别。     

专利信息

专利信息一神手动跟踪太阳能聚能器本实用新型为一种手动跟踪太阳能聚能器，它是一种太阳能转换装置，可用于各种工业及民用太阳能采集装置中，如太阳能热水以及太阳能发电设备。本发明使反射镜的跟踪运动变为直线运动，可以大大减小跟踪装置结构体积，无平衡问题。本实用...     

采用真空柱状接收器的碟式集热器光热特性研究

提出利用柱状真空管作为碟式太阳能聚光系统的接收器,强化碟式抛物面太阳能聚光器的接收效率、降低系统对跟踪精度的要求,进而降低整个系统的工程造价,实现系统低成本运行。对系统结构进行光学和传热性能分析,给出几何聚光比随接收器几何参数的变化规律。结果表明,接收器在跟踪误差为0.5°时,几何聚光比仍可达到理想情况时的80%。结合传热学计算和Tracepro光学仿真,得到接收器热损失系数随接收表面温度,以及局部能量聚光随跟踪误差的变化规律,为此类碟式太阳能聚光集热器的优化设计提供依据。     

碟式太阳能聚光器跟踪系统研究(上)

介绍了太阳能热发电系统中太阳能聚光器跟踪系统的跟踪控制方式、控制结构及其研究动态,探讨了碟式太阳能聚光器跟踪系统的研究关键,对研究开发碟式太阳能热发电系统具有积极意义。     

The influence of size-distribution parameters on the evaporation of polydisperse dilute sprays

An analytical study has been performed of both diffusion-controlled and radiation-controlled (opaque droplets) evaporation of single-component polydisperse sprays. The overall evaporation characteristics of sprays of different initial size distributions were found to be correlated best by their initial Sauter mean diameter. In the case of diffusion-controlled evaporation, the representation of a polydisperse spray by a monodisperse spray of droplet size equal to the initial Sauter mean diameter of the polydisperse spray is a good assumption during the early stages of evaporation. When 40% of the volume of droplets has evaporated, the error of the monodisperse model reaches 20%. On the other hand, in the case of radiationcontrolled evaporation, the monodisperse spray model yields good results for most of the period of evaporation of the spray.     

3D CFD simulation and experimental validation of particle-to-fluid heat transfer in a randomly packed bed of cylindrical particles

The heat transfer characteristics of solid cylinders in a bed with tube-to-particle diameter ratio equal to 2, by the presence of contact points between the cylinders were investigated numerically. Three-dimensional CFD simulation of air flow through two different arrangements of particles in this randomly packed bed have been carried out by the standard κ–ε turbulence model with the use of FEMLAB (Multiphysics in MATLAB) software version 2.3. The simulation results were validated by naphthalene sublimation mass transfer experiments. From mass and heat transfer analogy, the Nusselt numbers for each cylindrical particle in bed were found from the corresponding Sherwood numbers. It is shown that the CFD simulation results can predict the heat transfer characteristics, with an acceptable average error compared to experimental values.     

Assessment of dimensionless CHF correlations for subcooled flow boiling in microgravity and Earth gravity

A comprehensive review and analysis of prior subcooled flow boiling CHF correlations was conducted to identify those correlations that provide the most accurate predictions for dielectric working fluids and small rectangular flow passages found in electronics cooling applications in both microgravity and Earth gravity. Since most prior correlations were derived from water databases, only those with dimensionless form were deemed potentially suitable for other working fluids. Only a small fraction of these dimensionless correlations were found to tackle other fluids and more complicated flow and heating configurations with acceptable accuracy. These correlations were ranked relative to mean error, mean absolute error, and root mean square error. Better predictions where achieved when correlations were based on the heated diameter rather than the hydraulic diameter because of the ability of the former to better describe vapor development in subcooled flow. Two previous correlations by Hall and Mudawar provided the best overall CHF predictions for both microgravity and Earth gravity.     

Heat Transfer Correlations for Single-Phase Flow,Condensation, and Boiling in Microfin Tubes

Experimental single-phase, condensation and flow boiling heat transfer data from the literature and our previous studies were collected to evaluate existing heat transfer correlations for microfin tubes of different geometries. The Ravigururajan and Bergles correlation modified by using the hydraulic diameter proposed by Li et al. (2012) can predict single-phase heat transfer data relatively well. Among the four reviewed condensation heat transfer correlations, the Yu and Koyama (1998) correlation presents the best prediction. However, all the four condensation correlations are prone to overpredict the carbon dioxide data. For flow boiling in microfin tubes, the general semiempirical correlation developed by Wu et al. (2013), applicable for intermittent and annular flow patterns, is the most reliable predictive method among the five evaluated correlations. It can predict 90% of the overall 754 data points within a ±30% error band, with a mean absolute deviation and a standard deviation equal to 18.2% and 21.9%, respectively, covering pure halogenated refrigerants, near azeotropic refrigerant mixtures, and carbon dioxide with the following applicable range: fin root diameter 2.1 to 14.8 mm, mass flux 100 to 800 kg/m²s, heat flux 4.5 to 59 kW/m², and reduced pressure 0.07 to 0.7.     

A numerical investigation of evaporation characteristics of a fuel droplet suspended from a thermocouple

Numerical simulations of combined natural convection–conduction in a droplet of n-dodecane suspended from a thermocouple were carried out, taking into consideration evaporation, and the effect of thermocouple diameter on the evaporation characteristics was investigated. The calculated temperature history of the droplet is in good agreement with experimental results; both show that the rate of heating decreases with increasing thermocouple diameter. The maximum error in temperature due to the thermocouple increases linearly with increasing thermocouple diameter. Thus, in investigations involving a droplet suspended from a thermocouple, it is preferable to use a thermocouple with the smallest possible diameter.     

Effects of an agglomerate size distribution on the PEFC agglomerate model

The agglomerate model of a polymer electrolyte fuel cell (PEFC) electrode typically assumes a single, representative agglomerate diameter, while in reality there is a distribution of agglomerate sizes. Here, we analyze how the agglomerate model's predictions are affected by incorporating an agglomerate diameter distribution. Our analysis shows that the diameter distribution causes the agglomerate model predictions to differ by as much as 70% when compared to even reasonable single agglomerate diameter choices. The error in the model's predictions is highly sensitive to both agglomerate diameter and overpotential. Even the agglomerate diameter that gives the lowest maximum error in our results, 115 nm, errs by as much as 15% at certain overpotentials.     

铁道车辆轮径测量仪

车轮直径和车轮圆度误差是评价车轮磨耗的关键参数之一。研制了一种新型的机械电子式轮径测量装置——WD-A铁道车辆轮径测量仪,可以测量轮径和车轮圆度误差。其机械部分可绕车轮转动,实现车轮滚动圆上多点的测量;数据采集部分集成了DSP、蓝牙等技术,PDA（掌上电脑）数据处理和界面显示。该仪器在实际测试中,操作方便,人机界面友好。直径测量,单点重复偏差〈0．05mm,区段测量偏差〈0．4mm,采用最小区域搜索的圆度误差〈0．05mm。     

用等径孔桥集箱强度计算程序计算不等径孔桥

对引进的CE公司集箱强度计算程序进行了改进,论述了用现行的等径孔桥集箱强度计算程序计算不等径孔桥的原理、方法和步骤。这一方法的提出,进一步扩大了现行计算机程序的使用功能,更好地满足了工程设计的需要。     

CFD simulation and experimental validation for wall effects on heat transfer of finite cylindrical catalyst

In this paper, heat transfer of single cylindrical particle affected by wall has been investigated numerically and experimentally for Reynolds number range 2000 to 6000. The heat transfer in two different orientations, axial and cross flow over the particle has been considered in simulation with MultiPhysics Software FEMLAB version 2.3. The heat and mass transfer analogy technique has been applied for validation of the simulation results. The coated particle with naphthalene was sublimated to obtain the corresponding Sherwood numbers. The results show that the CFD model can predict the particle-to-fluid heat transfer for two situations due to trivial error (an average error of 6%) compared to experimental values. Influence of wall on heat transfer of particle in seven different bed-to-cylinder diameter ratio (N = 1.66, 2.65, 2.75, 5, 6.66, 12, and 18) have been discussed in different velocities. According to obtaining results, with increasing the bed-to-cylinder diameter ratio over the 12 wall have no significant consequence on Nusselt number. Due to this fact, a CFD based correlation has been proposed to consider the wall effects on particle-to-fluid Nusselt number with an average error of 2.19%.     

Effect of crossflow regulation by varying jet diameters in streamwise direction on jet impingement heat transfer under maximum crossflow condition

Jet impingement heat transfer has been studied numerically for a maximum crossflow condition using a 3?×?9 array of jets. Five-hole configurations have been studied for jet average Reynolds numbers ranging from 10,000 to 20,000. Crossflow has been mitigated by varying the jet diameters in the streamwise direction to reduce the impact of crossflow on downstream jet impingement. The design criteria for all five configurations were to keep the average of the jet diameters equal to the constant jet diameter configuration (baseline). It has been found that the configuration with increasing and then decreasing jet diameters provided higher levels of heat transfer with more uniform cooling when compared to the traditional constant diameter configuration and other configurations.