PAG润滑油对超临界CO_2换热性能影响的研究

综述了润滑油在气冷器中对超临界CO_2换热特性影响的国内外研究现状,进行了润滑油对超临界CO_2换热性能影响的实验研究,以实验装置为物理原型建立了换热模型,编写了模拟程序,并根据实验得到的结果验证了模拟程序,模拟得出:随着CO_2压力增大,油膜增厚,换热系数反而也增大;随着CO_2质量流量增大,局部换热系数增大。可通过在管道内促进形成无源扰动、管道中设置扰流原件,设计气冷器时适当缩小后半段CO_2换热管管径等方法强化换热。     

双面纵向波纹管强化冷凝换热的研究

本文对六种不同波距与波深比(p/e)的余弦型纵向波纹管的冷凝换热进行了实验研究和理论分析.在本实验的条件下,波纹管的平均冷凝换热系数是光管的4～7.5倍.在2.79≤D/e≤9.85的范围内,强化效果随p/e值的减小而增大.根据大量的实验数据得到波纹管的平均冷凝换热系数随冷凝液膜Re数和p/e的变化关系.运用数值方法,结合实验,从理论上分析计算了余弦型波纹管的冷凝换热系数.计算值与实验结果和国外的研究结果吻合较好.     

CO2—润滑油水平光滑管内流动沸腾换热特性

对适用于二氧化碳制冷系统的润滑油进行比选。建立R744(二氧化碳工质)-润滑油(PAG油)混合物(以下简称混合物)水平光滑管内流动沸腾换热特性实验系统,研究在不同工质干度下PAG油质量分数对混合物水平光滑管内流动沸腾换热系数的影响。将实验结果与计算结果(采用经典水平光滑管内流动沸腾换热关联式)进行比较,筛选出适于计算混合物水平光滑管内流动沸腾换热系数的经典换热关联式。     

混凝土表面自然对流换热系数的实验研究

提出了空气—混凝土表面在自然状态下对流换热系数的实验方案。采用混凝土空心圆管试件,从圆管内部加热,试件混凝土内部布置18个热电偶测点测读温度场。利用专门设计制作的实验装置,可全自动控制加热过程并自动记录实验数据。进行了5个混凝土试件实验,并设定不同的圆管内部加热温度进行了多次测读,结果具有很好的一致性。实验结果表明,空气—混凝土表面对流换热系数在自然状态下基本为一常数,不随表面温度的变化而改变。实验所得到的自然对流换热系数,可用于混凝土结构温度效应计算。     

污水源热泵污水侧流化除垢与强化换热性能

由小尺度污物引起的污垢等问题成为污水源热泵推广应用的瓶颈,该文首先探讨污水取水换热过程中污垢的形成机理;进而将液固循环流化床技术引入污水源热泵污水侧的防、除垢应用中,考虑碰撞应力以接触面中心呈对称分布的特点,对已有碰撞应力模型进行修正,并以垢层所受到的剥离力(液固两相流对垢层的剪应力与固体粒子对垢层的碰撞应力)来探讨液固循环流化床的防、除垢机理;最后进行液固循环流化床换热器防、除垢特性的实验研究。研究结果表明循环流化床换热技术可有效解决污水中小尺度污物所引起的污垢等问题。     

流体流速对钛板板式换热器总换热系数的影响

利用实验数据对钛板板式换热器总换热系数与流速之间的关系式进行拟合,计算分析流速对总换热系数的影响。一级侧(热流体)或二次侧(冷流体)流速增大时,换热器总换热系数随之增大。设定一级侧流体流速不变,二级侧流体流速越高,通过增大流速强化传热的作用越弱。     

竖直平板上蒸汽层流膜状冷凝换热特性的数值模拟研究

采用ANSYS FLUENT软件,基于VOF模型对蒸汽在竖直平板上的层流膜状冷凝换热过程进行数值模拟研究。以S.K.Park蒸汽实验为经典算例验证数值模拟计算模型的准确性与可靠度,并基于该实验的几何模型,研究不同蒸汽流速、壁温及壁面接触角(亦表面张力)下的冷凝过程。通过分析相应的冷凝水量、传质速度及局部换热系数的分布云图,得到蒸汽在竖直平板上冷凝换热系数与蒸汽流速、壁温及壁面接触角的变化规律。     

涡轮动叶顶部换热的萘升华模拟实验研究

为了研究叶顶形状对涡轮动叶顶部上换热特性的影响,在低速涡轮实验台上采用萘升华技术对2种叶顶(平叶顶和凹槽叶顶)的换热系数进行了实验测量。同时为增加实验的可信性,将该测试方法在吹风平板上进行了验证。实验结果表明:萘升华法可以较准确地获得平板上的换热趋势,可以用于测量涡轮叶顶壁面的换热特性;采用凹槽结构将影响叶顶的泄露流动,从而改变叶顶局部区域的换热分布。实验测量结果能为涡轮动叶顶部换热的研究提供一定的参考。     

中深层无干扰地热能量交换装置优化研究

以西咸新区沣西新城无干扰地热能供暖项目(三期)一标段枫溪美郡工程为依托,在分析地热能交换原理的基础上,对中深层无干扰地热能能量交换装置从取热装置、换热管安装装置优化展开研究.采用优化后的门式支架换热管安装装置,与传统安装方式相较,提高了中深层无干扰地热能地热井内HDPE换热管安装质量、安装效率.具有显著的经济性和社会效...     

螺旋扭带阻垢强化换热装置工程应用的测试研究

将螺旋扭带式的阻垢强化换热装置进行了开利和约克中央空调冷水机组的工程实际应用,设计了该装置工程应用的分析测试方法,详细测试了安装装置前后的主机组运行情况,并对测试结果进行了对比分析.结果表明:安装阻垢强化换热装置能实现阻垢和强化换热的功能,不会对主机正常运行产生影响,可以提高主机的制冷效率(COP值)达15％以上,实现...     

循环流化床一体化污泥焚烧工程的调试及分析

为探索采用焚烧工艺处理污水厂剩余污泥的可行性,在杭州市七格污水处理厂建设了规模为100 t/d的污泥焚烧处理示范工程,并进行了冷、热态调试。冷态调试结果表明,系统关键设备如干污泥螺旋输送机、焚烧炉、复合干化器等的测试数据与设计值吻合。热态调试结果显示,复合干化器内温度均匀,含水率为79%～80%的湿污泥在复合干化器内破碎和干燥程度良好,干污泥颗粒最大直径为3 mm5,0%的切割粒径为0.32 mm。干污泥即时进入循环流化床焚烧炉焚烧,焚烧温度为860℃。可见,采用循环流化床一体化焚烧技术处理污泥在工程上是可行的。     

Heat sink elimination and optimisation by natural convection method

ABSTRACT

All electrical and electronic components in a circuit generate a certain amount of heat when the circuit is energised by a power supply. The heat energy thus generated must be dissipated properly to maintain the surface temperature within the threshold limit to avoid early breakdown of the components. Due to miniaturisation the effective surface area for convective heat transfer gets reduced, to agitate the heat transfer rate power operated fan is required. In the present work, we have adopted a novel design of double side cross section, natural convection heat sink which has more efficiency, effectiveness and heat transfer rate compared to single side cross section of the heat sink for a given size.     

沸腾态传热的实验研究

对悬浮沸腾态的传热进行了实验研究。分别对管道和旋风筒的传热、分解炉的传热和沸腾床的传热进行了实验，对传热系数，速度和温度的关系进行了测试，从而得出了相关的结论。     

Heat flux through a geothermally heated fluidized bed at the bottom of a lake

Heat fluxes and the underground inflow through a natural fluidized bed within the main sub-basin of Lake Banyoles are studied and parameterized. In the upper part of this fluidized bed, at a depth of about 30 m, the vertical gradients of particle concentration and temperature are very sharply located within an interface a few centimeters thick. Within this interface (lutocline), the depths where the temperature and the concentration gradients are maximum match exactly. On the other hand, the lutocline determines a flat, horizontal surface dividing the water column into a hot, turbid medium at the bottom and clear, colder, bulk water above. Through this interface the flow regime also varies from being laminar just below it, to turbulent due to convective processes developing above it. More precisely, in studied main sub-basin a buoyant plume develops above the lutocline, as a result of the heat flux, and affects the lake's water quality due to particles dragged along by it. In this paper it is proposed to determine the temperature at the depth of maximum gradient within the interface by means of measured temperature profiles, and consider the stationary heat transport equation in the laminar region below it, in order to obtain the water velocity and the heat flux. Heat flux parameterization is given based on a large number of thermal high-resolution profiles, covering six campaigns in different years and seasons. Furthermore, and in consideration of the fact that high-resolution thermal profiles are not always available, some alternative parameterizations for the heat flux are presented based only on the temperature of the fluidized bed and that of the lower hypolimnion.     

Φ2.4×18m回转烘干系统高产运行技术措施

文章详细介绍了回转烘干机和配套设备,根据流体力学、传热传质学的基本规律,建立烘干数字化模型,在线检测烘干物料的水份、温度、供热能力等,获得最佳的物料烘干效果。     

流化床气固传热特性的研究

在对流化床气固传热合理简化的基础上，依据稳态工况活动段区温度分布求取有效气固传热系数。实验结果和前人经验式预测值吻合，从而论证计算有效传热系数的可行性。     

砂子基底正庚烷流淌火特性及传热分析

摘 要：在砂子基底上进行了未点燃正庚烷的蔓延实验和点燃正庚烷的燃烧实验,研究砂子粒径对正庚烷蔓延和燃烧特性的影响。分析了蔓延距离、火焰前锋、燃烧速率,探究了传热过程对流淌火特性的影响。结果表明,由于砂子的吸附能力随着砂子粒径增大而减小,未点燃的正庚烷在蔓延阶段,其流淌蔓延距离和速度随着砂子粒径增大而增大,且小于无砂工况。随着砂子粒径的增大,正庚烷稳定燃烧阶段火焰前锋先增大后减小、稳定燃烧速率先减小后增大。传热分析表明,当砂子粒径从0.25 mm增大为4 mm时,热传导反馈的减小是引起燃烧速率减小的主要原因;而当砂子粒径进一步增大为8 mm时,热辐射反馈的增大导致了燃烧速率的增大。最后得出砂子的吸附能力是影响蔓延阶段的主要因素,热反馈是影响稳定燃烧阶段的主要影响因素,0.25 mm细砂更适用于流淌火的阻挡扑灭。     

搅拌造粒型回转式污泥直接干化试验研究

自行设计了搅拌造粒型回转式污泥直接干燥机,并研究了污泥和烟气的流向、干燥机筒体转速、干燥机倾角、搅拌轴转速等运行参数对干燥机性能和干化效果的影响。结果表明,采用此干燥机干化城市污泥时,逆流方式优于顺流方式,2.5°倾角优于5°倾角,固定倾角下存在最佳筒体转速,搅拌轴转速越高则对干燥越有利。根据试验数据,对反映干燥机性能的两个重要参数——蒸发强度A和蒸发系数α进行了探讨,发现干燥机的运行参数对二者均有一定影响,其中对A的影响较大、对α的影响较小。     

A convective model for laboratory fires with well-ordered vertically-oriented fuel beds

Several studies in the literature explore the connection between rate of spread (ROS) and wind in wildland fires. These studies show very different positions about the role of radiation and convection as heat transfer mechanisms. In the case when the fuel bed is well-ordered and vertically-oriented, there seems to be a consensus leading to suggest that convective heating is the dominant heat transfer mode in that case. The purpose of this work is to propose a convective semi-physical model for the behaviour of the rate of spread in wind, when the fuel bed is vertically-oriented. Due to a specific fuel bed arrangement, flame radiation –i.e. radiation from the part of the flame above the vegetal stratum– is neglected. Only horizontal radiation from the fuel burning particles area and convective heating are taken into account. Convective heat transfer is assumed to be the primary heat transfer mechanism. The proposed model is confronted to 172 laboratory fires with a wide range of fuel characteristics. The predicted results are also compared with two simplified models from the literature. Statistical tools are used to check the agreement between the predicted ROS and the observed one where a strong agreement is generally observed, irrespective of fuel bed characteristics.