夏季晴天不同土壤湿度条件的绿洲辐射特征

利用2005年在甘肃省金塔绿洲开展的"绿洲系统能量与水分循环过程观测试验"所取得的资料,分析了夏季晴天金塔绿洲不同土壤湿度条件下的辐射收支特征。结果表明:向下短波辐射不受土壤湿度的影响;当植被处于同一生长期,土壤湿度越大,向上的辐射就越小,净辐射就越大;当空气中的水汽含量相差不大时,土壤较湿润则大气逆辐射白天较小,夜晚较大。但当水汽含量差别较大时,水汽含水量起主要影响作用,空气越湿润,大气逆辐射越小。     

中国可能太阳总辐射的气候计算及其分布特征

本文利用以乌克兰英采夫法确定的可能太阳总辐射辐照度(日平均通量密度)资料,着重分析了使用以公式为基础的理论方法问题,用迭代法解出系数并研究了它的变化特征,建立了它与水汽压的经验关系,检验了它对理论公式的灵敏度和用其反演可能太阳总辐射辐照度的相对误差。结果表明,可能太阳总辐射的理论公式对系数f变化的反应是不太灵敏的,利用水汽压资料算出f值,就可相当精确地反演得到全国各地的可能太阳总辐射。对全国71个日射站可能太阳总辐射的反演表明,它与实测值的平均相对误差仅为4.5％。在此基础上还计算了全国240个站各月的可能太阳总辐射辐照度,并详细地讨论了其时空分布特点。     

青藏高原有效辐射参数化

利用1982年8月~1983年7月青藏高原地面辐射平衡资料及五道梁能量平衡观测站的辐射观测资料,将水汽压、云量及气压作为独立的影响因子,同时引入了气温、地面温度、水汽压、云量、气压的平均量,给出了青藏高原地区地面有效辐射的参数化形式,与其它的参数化方案作了对比,该文的参数化方案计算误差小,计算结果较好。     

影响地面太阳辐射及其谱分布的因子分析

针对目前全球变暗(明)的热点问题,利用一个高光谱分辨率的辐射传输模式,计算了全球42种大气下到达地面的太阳辐射通量及其在近红外、可见和紫外各光谱区间的比例,详细分析了大气内部因子(水汽和臭氧、云和气溶胶等)以及外部因子(太阳天顶角和地表反照率)对它们的影响.结果表明:中低云对地面太阳辐射通量及其谱分布有很大影响,高云的影响很小.水汽和臭氧的敏感性试验表明,水汽对地面近红外辐射的影响较大,而臭氧对可见和紫外辐射的影响较大.气溶胶对地面太阳辐射的影响仅次于大气的吸收作用,是不容忽视的.此外,太阳天顶角和地表反照率都会对地面太阳辐射通量及其谱分布产生重要影响.     

填料塔内相变凝结促进燃烧源超细颗粒的脱除

在填料塔洗涤器中,利用蒸汽相变原理进行了促进燃烧源超细颗粒凝结长大并高效脱除的实验研究,通过调节进口烟气含湿量及进口烟气与洗涤水的温差建立微粒凝结长大所需的过饱和水汽环境.研究了细颗粒粒径分布、进口烟气与洗涤水的温差、蒸汽添加量和液气比等对脱除效率的影响.结果表明:使烟气在填料塔内达到过饱和状态可高效脱除燃烧源超细颗粒,脱除效率随气液温差、液气比的增大而提高.在蒸汽添加量为0.08 kg/m3、气液温差为50 °C时,燃煤超细颗粒脱除效率达到81%;在相同气液温差下,增大进口烟气含湿量,可显著提高超细颗粒的脱除效率.     

用Lowtran 7进行分光辐射的计算研究(Ⅰ)--不同波段分光总日射比例份额的计算研究

利用Lowtran 7所能提供的计算参数,分别计算了小于400nm(紫外辐射)、400～700nm (光合有效辐射)和大于700nm(红外辐射)3个波段的总日射占全波段总日射的比例,并研究了不同太阳高度角、不同气溶胶、不同海拔高度以及大气中不同水汽和气溶胶含量对上述比例的影响.以前实测中发现的光合有效辐射所占比例有随地理纬度减少而略有增长的趋势得到了合理的论证;而理论模式的计算结果与我们的实测季节过完全一致,则证明所用方法是合理和可行的.     

福建省太阳总辐射和地面辐射平衡的分布

首先利用福州市的辐射观测资料，建立计算太阳总辐射的经验公式，并计算福建省各市、县的太阳总辐射的年、月平均辐照度。然后利用地区代表站的地面反射率，求得福建省各月、年地面所吸收的太阳辐射能的分布。再利用地面温度、气温、水汽压和总云量，计算得出福建省各地的地面有效辐射的月、年平均辐照度。最后得出福建省各月、年地面辐射平衡的分布。     

水的相变过程中辐射机理研究

水的相变过程会出现异常辐射现象,在短波范围内其辐射强度比普朗克辐射强度强4倍左右,这与常规的热辐射不同,称为相变辐射。针对水在凝结过程中所释放的异常辐射现象做了机理性研究,并将热力学、分子理论与所发现的实验数据相结合,提出一个新的机理来解释这一现象。研究结果表明,相变辐射的产生可能与水分子氢键的形成过程相关,辐射的波长段所具有的能量值与氢键形成时所释放的能量值较为接近,且水分子密度越高相变辐射强度越强;水分子内振动能级的跃迁与相变辐射能存在很大的联系,振动能级的跃迁伴随着光子的释放,并与在其他已发表文献中所发现的相变辐射能有着较为匹配的能量值。研究结果为进一步探讨相变辐射提供了理论基础。     

用Lowtran 7进行分光辐射的计算研究(Ⅱ)——UVB测量仪的校准方法及影响UVB的环境因子

太阳的紫外光辐射能量随波长变化极大，与室内紫外标准灯的光谱存在着相当大的差异，如何将室内紫外标准光源标定出的工波段紫外辐射表灵敏度校正到太阳到紫外辐射的灵敏度，是观测和标定工作中必须解决的问题。该文提出了通过太阳紫外光谱测量与模式计算相结合的方法，并利用Lowtran7模式软件所能提供的计算参数，分别计算了3个紫外波段（UV－A，UV－B和UV－C）的辐照度，研究了不同太阳高度角，不同气溶胶，不同海拔高度以及大气中不同水汽和气溶胶含量对3个紫外波辐照度的影响；并以Eppley实验室制造的TUVR宽带紫外辐射表测量的紫外辐照度为例，证明了此类辐射表的测量值，并非就是紫外辐射的总量，而是其中的一部分，其所占比例随大气条件变化而改变。此外通过，证实了在紫外辐射中以散射辐射为主的情况。     

凝结理论在汽轮机设计中应用的探讨

本文在总结西安交通大学湿蒸汽研究小组近年来部分研究成果的基础上，提出自发凝结和非均质凝结流动理论应用于蒸汽透平设计的两条技术途径。通过对自发凝结和非均质凝结进行对比，指出非均质凝结优于自发凝结的原因在于非均质改变了凝结模式。基于物理学中对带电微粒表面张力特性的研究成果，进一步提出利用电场影响凝结过程，在纯净水蒸汽中实现与非均质凝结类似过程的设想。     

Phase-transition radiation in vapor condensation process

Energy release by radiative relaxation during water vapor condensation is considered to be responsible for phase-transition radiation in the water vapor condensation process. A two-level transition model is proposed to explain the radiative transfer mechanism for condensation radiation of water vapor. The absorption coefficient due to condensation radiation and the associated optical properties are defined in the radiative transfer equation. The spectral profile of the source function of vapor condensation radiation is examined and agreement with the experimental characteristic wavelength of condensation radiation is found.     

超音速分离管中水蒸气凝结相变的数值研究

基于超音速分离管中混合气体流动属于伴随凝结相变的可压缩、跨音速的特点,建立了考虑传质效应与非平衡凝结过程的数学模型,并采用数值方法对伴随水蒸气凝结的超音速分离管中的流动进行分析研究。以空气、水蒸气及液态水为流动介质,采用两相流动中的VOF模型结合凝结相变模型以及组分传输模型,研究不同进出口参数及不同水蒸气含量对凝结流场的影响。研究结果表明,所建立的分离管内部非平衡凝结相变模型可以较好的再现超音速流中的凝结成核及液滴生长过程;数值计算结果表明,入口压力、温度及水蒸气含量对分离管内流动凝结过程有直接且重要的影响。因此在进行超音速分离管设计时,考虑温度压力参数的同时,考虑水蒸气含量对分离管性能的影响也是非常重要的。     

Steady and unsteady 3D non-isothermal modeling of PEM fuel cells with the effect of non-equilibrium phase transfer

A 3D model that fully couples multi-species and multi-phase transport, electrochemical kinetics, and heat transfer processes has been developed. The non-equilibrium membrane water absorption/desorption processes along with non-equilibrium condensation/evaporation processes have been investigated utilizing this comprehensive model. In addition, the fallacious assumption that water is produced in vapor phase during the half cell electrochemical reaction is addressed for the first time. The difference and relationship of the cell output current density among three water production mechanisms are exhibited to show the potential error induced by vapor or liquid production assumptions. The present model is capable of predicting transient phenomena within the cell as well. Our results show that compared to the liquid production modeling the dynamic response of PEM fuel cells in vapor production modeling is significantly overestimated owing to the sluggish condensation process.     

The impact of thermal conductivity and diffusion rates on water vapor transport through gas diffusion layers

Proper water management in a hydrogen-fueled polymer electrolyte membrane (PEM) fuel cell is critical for performance and durability. A mathematical model has been developed to elucidate the effect of thermal conductivity and water vapor diffusion coefficient in the gas diffusion layers (GDLs). The fraction of product water removed in the vapor phase through the GDL as a function of GDL properties/set of material and component parameters and operating conditions has been calculated. The current model enables identification of conditions wherein condensation occurs in each GDL component. The model predicts the temperature gradient across various components of a PEM fuel cell, providing insight into the overall mechanism of water transport in a given cell design. The water condensation conditions and transport mode in the GDL components depend on the combination of water vapor diffusion coefficients and thermal conductivities of the GDL components. Different types of GDLs and water transport scenarios are defined in this work, based on water condensation in the GDL and fraction of water that the GDL removes through the vapor phase, respectively.     

An experimental study on vapor condensation of wet flue gas in a plastic heat exchanger

An experimental system investigating condensation heat transfer of wet flue gas was set up, and the heat transfer performance of vapor‐gas mixture with vapor condensation was discussed. The experimental results of laminar flow in a plastic longitudinal spiral plate heat exchanger were obtained and are in good agreement with the modified classical film model. It is shown that the plastic air preheater can avoid acid corrosion in the low‐temperature field for the boiler using fuel containing sulfur and recover latent heat of the water vapor of the wet flue gas. Also some SO₂ was scrubbed during the vapor condensing process in the heat exchanger. © 2001 Scripta Technica, Heat Trans Asian Res, 30(7): 571–580, 2001     

Thermodynamic analysis of the effects of atmospheric conditions on the performance of a precooled gas turbine fueled with liquid hydrogen

The effects of varying atmospheric conditions such as temperature, humidity and pressure on the performance of a precooled gas turbine cycle fueled with liquid hydrogen are analyzed. Since the hydrogen temperature at the precooler inlet is very low, the condensation and freezing of water vapor contained in suction air is supposed to occur within the precooler. Due to the condensation of water vapor, the precooling process requires more cryogenic hydrogen. Therefore, the temperature-drop ratio of suction air ? within the precooler decreases. Thermodynamic analysis has revealed that the thermal efficiency and specific output per unit mass flow rate considerably decrease with the increase of humidity ψ, the performance degradation of gas turbine due to atmospheric temperature rise is augmented with the increase of humidity. The humidity ratio between precooler inlet and outlet is also made clear.     

一种改进的太阳能吸附式空气取水器

介绍了一种透光良好、冷凝迅速、吸附彻底、集热高效的太阳能吸附式空气取水器。冷凝罩在上布置, 便于和空气分层的水蒸气及时冷凝;冷凝罩夹层内所填相变材料的蓄冷,加速冷凝过程。透光罩在下布置,避 免了水蒸气在其内表面的凝结,以维持原有透光率。金属网球既可对吸附床内的吸附剂导热、均温,从而提高 集热效率;又可在吸附床内均布气道,加速吸,脱附过程。解决了沙漠地区的淡水补给问题,避免了淡水运输的 困难。     

径向错列翅片管内凝结对流换热数值模拟分析

采用数值模拟方法,对径向错列翅片管内含不凝结气体水蒸气的凝结对流换热及阻力特性进行了综合分析。将编写的自定义函数(UDF)导入ANSYS FLUENT软件,对新型强化管传热性能和阻力性能进行了数值模拟,并根据管长方向壁面上蒸汽质量分数的变化情况,讨论分析了凝结过程中翅片管传热性能的变化规律。分析结果表明:与光管相比,内翅片管的强化传热效果随翅数增多、翅片换热接触面积增大而更加显著;另一方面,翅片管的流动阻力相应增大,对管路换热产生不良影响。在所研究翅型范围内16翅y=2x~2型翅片管综合强化换热效果更优;此外随着换热过程的持续,蒸汽凝结逐渐放缓;入口速度增大导致水蒸气凝结不充分,对换热效果的提升有一定制约。     

Rate of growth of drops during condensationVitesse de croissance de gouttes pendant la condensationWachstumsrate von tropfen während der kondensationCкopocть pocтa кaпeль пpи кoндeнcaции

The growth of drops during condensation in direct contact between liquid drops and vapor was studied. An approximate correlation for this process was obtained from theoretical considerations. Experimental investigation of condensation of steam on water drops of three different diameters and with different initial subcooling of drops below the saturation temperature of steam was performed. High speed photography was used to analyse the growth of drops during condensation.     

Extensive study on laminar free film condensation from vapor–gas mixture

The dimensionless velocity component method was successfully applied in a depth investigation of laminar free film condensation from a vapor–gas mixture, and the complete similarity transformation of its system of governing partial differential equations was conducted. The set of dimensionless variables of the transformed mathematical model greatly facilitates the analysis and calculation of the velocity, temperature and concentration fields, and heat and mass transfer of the film condensation from the vapor–gas mixture. Meanwhile, three difficult points of analysis related to the reliable analysis and calculation of heat and mass transfer for the film condensation from the vapor–gas mixture were overcome. They include: (i) correct determination of the interfacial vapor condensate saturated temperature; (ii) reliable treatment of the concentration-dependent densities of vapor–gas mixture, and (iii) rigorously satisfying the whole set of physical matching conditions at the liquid–vapor interface. Furthermore, the critical bulk vapor mass fraction for condensation was proposed, and evaluated for the film condensation from the water vapor–air mixture, and the useful methods in treatment of temperature-dependent physical properties of liquids and gases were applied. With these elements in place, the reliable results on analysis and calculation of heat and mass transfer of the film condensation from the vapor–gas mixture were achieved.The laminar free film condensation of water vapor in the presence of air was taken as an example for the numerical calculation. It was confirmed that the presence of the non-condensable gas is a decisive factor in decreasing the heat and mass transfer of the film condensation. It was demonstrated that an increase of the bulk gas mass fraction has the following impacts: an expedited decline in the interfacial vapor condensate saturation temperature; an expedited decrease in the condensate liquid film thickness, the condensate liquid velocity, and the condensate heat and mass transfer. It was found that an increase of the wall temperature will increase the negative effect of the non-condensable gas on heat and mass transfer of the film condensation from the vapor–gas mixture.