侧风作用下火电厂冷却塔性能的实验研究

冷却塔是火电厂重要设备之一,冷却塔冷却性能的优劣直接影响机组效率与安全.通过建立火电厂冷却水系统实验平台,研究了侧风作用下冷却塔的冷却性能.研究发现:随着环境侧风的增加,冷却温差和效率呈先减小后增大的趋势,拐点风速值为0.8m/s;迎风面的进塔风速随之变大,背风面的通风量减小;并采用弗劳德准则数分析了环境侧风对冷却塔性能的影响.     

环境侧风对300MW火电机组冷却塔影响的数值模拟

以300MW机组双曲线自然通风冷却塔为研究对象,采用Fluent软件对冷却塔进行了三维数值模拟,分析了变工况下环境侧风对冷却塔冷却性能的影响、环境侧风对冷却塔进风口速度场的影响。研究发现:随着侧风风速的增加,冷却温差先减小后增大,出塔水温先增大后减小;并且,环境侧风的存在会扰乱冷却塔进风口流场,其临界风速值为6m/s。     

侧风环境下湿式冷却塔性能参数变化规律的试验研究

外界侧风在很大程度上影响自然通风逆流湿式冷却塔的传热传质性能,根据相似理论,通过热态模型试验,以冷却数和刘易斯数为出发点,研究了外界侧风对冷却塔传热传质性能的影响.研究发现:冷却数和刘易斯数随着外界侧风的变化呈现先减小后增大的趋势,拐点风速值为0.4 m/s;当外界侧风风速小于0.7 ～0.8m/s时,侧风的存在严重恶...     

侧风对太阳能增强型冷却塔排热量影响的数值模拟与分析

以一种新型空气冷却系统——太阳能增强型冷却塔为研究对象,通过数值模拟,研究侧风风速对其内部空气动力场、速度场和冷却性能的影响,并与自然通风干式冷却塔进行对比分析,同时对3种典型防风装置及其耦合方式的防风效果进行研究。结果表明:低风速下太阳能增强型冷却塔对侧风的敏感程度低于自然通风干式冷却塔,当风速超过7 m/s后则反之;导流板和挡风板在不同的侧风条件下各具优势;综合考虑导流板与120°分布挡风板的耦合方式是最为有效的防风措施,排热量最大可提高10.6%。     

火电厂循环水冷却塔冷却性能的实验研究

电厂循环水冷却系统的冷却性能直接关系到电厂的安全、经济和稳定运行。因此,对循环水冷却系统冷却塔性能的研究具有重要的工程价值和现实意义。分析研究了循环水温、循环水量和环境参数对于冷却塔性能的影响,在其它条件不变的情况下,当循环水量增加时,塔内风速增加,出塔水温升高;当进塔水温升高时,进塔水温的变化对出塔水温的影响并不大;风机的开度增大,冷却塔出口水温降低;环境空气的温度升高,出塔水温升高,冷却效率降低。     

逆流湿式冷却塔内不锈钢填料热力性能的试验研究

逆流湿式冷却塔是工业生产中普遍使用的换热设备,填料热力性能优劣直接影响到冷却塔热力性能优劣。为研究不锈钢填料的热力性能,搭建了逆流湿式冷却塔实验台,对比分析了S波、人字波和V波三种不锈钢填料与S波PVC填料随进塔水温的热力性能变化规律,以及研究了S波不锈钢填料随淋水密度的热力性能,结果表明:不锈钢填料的热力性能比常用PVC填料好,S波、人字波和V波不锈钢填料与S波PVC填料的冷却塔进出水温差和总换热量均随进塔水温的增大而增大,而冷却塔的冷却效率随进塔水温的升高先增大后减小,进塔水温在37.5～38.5℃时,冷却塔的冷却效率达到最大;且S波不锈钢填料冷却塔进出水温差、冷却塔的冷却效率及总换热量随淋水密度的增大而减小。优化填料波纹形状以及材料均有助于提高冷却塔的热力性能。     

旋流导风板湿式冷却塔填料区热力性能的数值研究

针对环境侧风对湿式冷却塔填料区传热传质性能的重要影响,基于ANSYS FLUENT软件对600 MW机组湿式冷却塔内的流场进行数值模拟,研究了加装旋流型导风板对填料区热力性能的影响,并对比分析了不同旋流叶片弧度(φ=0、π/12、π/6、π/4)对填料区热力性能的优化程度。结果表明:当侧风风速从0m/s增至4 m/s时,填料区的传质传热能力恶化,4 m/s时取得填料区传质传热系数极小值;加装旋流型导风板后,4 m/s时的传质系数相较于无侧风时平均降低了27.92%,传热系数相较于无侧风时平均降低了24.44%;ψ=π/6的旋流型导风板的优化效果最佳,在侧风风速为4和6 m/s时,传质系数较之于无导风板工况分别提升了4.37%和11.27%,传热系数较之于无导风板工况分别提升了19.76%和26.93%;当侧风风速为4 m/s时,冷却效率系数与冷却数均最低,这与冷却塔的传热传质性能有关,加装π/6的旋流型导风板,在侧风风速为4 m/s时,两系数较之无导风板工况分别提升了10.32%和53.81%。     

喷水预冷特性对蒸发冷却性能影响的数值模拟

为改善间接空冷塔在夏季高温环境下的冷却性能,提高火电厂整体效率,基于计算流体力学建立了空冷单元喷水预冷系统的数学模型,分析了喷水预冷特性对空冷塔某一扇区的影响,分别计算了环境特性和喷嘴特征等因素对冷却效率、有效冷却区域的温降和面积的影响。结果表明：随着流动距离的增加,冷却效率逐渐提高;环境风速和空气相对湿度降低以及风温、张角、喷嘴质量流量和喷嘴间距增大均会使冷却效率提高;液滴随空气流动逐渐蒸发,有效冷却区域的面积沿流动方向逐渐增大;有效温降沿着流动方向先因液滴的蒸发而增加,而后因冷却空气与周围空气的传热传质而减小。     

菲涅尔聚光PV/T系统热电输出特性分析

基于螺旋式微通道冷却的菲涅尔聚光PV/T系统性能进行研究,分析太阳直射辐照度(DNI,G)、冷却水流速及入射角对其热电性能的影响。结果表明,增大冷却水流速可提高PV/T系统的光电转换效率,但当流速大于某一值后,系统光电转换效率基本保持不变;光热转换效率随流速的增大呈先增后减的趋势,且随着G的增大光热转换效率逐渐升高,当G为1000 W/m~2,冷却水流速为3.8 m/s时,系统光热转换效率可达43%;当G在200~1000 W/m~2范围时,光电光热综合效率最大值为79.55%,DNI对其影响较小;入射角的增大对系统能量转化与利用均产生不利影响,为保证系统高效运行入射角应控制在0.3°以内;同时,对菲涅尔聚光PV/T系统的输出性能进行试验测试,结果表明,呼和浩特冬季一日内,系统峰值功率13.89 W出现在G最大时,但光电转换效率最大值26%出现在G突降时刻。     

复合角对曲壁多斜孔冷却特性的影响

在燃烧室曲壁中,采用复合角分别为0°、30°和65°的多斜孔冷却结构,数值模拟和实验研究了吹风比为3.5时的流场和气膜冷却效率的分布规律。结果表明:相比无复合角模型,引入复合角后,气膜出流的展向扩散增强,气膜在相邻列之间搭接较好,冷却效率提高,同时气膜高度方向扩散减弱,减少了与高温主流的掺混,使气膜覆盖长度增加;当复合角从30°增大为65°时,冷却效率略有提升,流量系数随复合角的增大先增大后减小。     

闭式冷却塔内冷却盘管传热热阻分析

通过对闭式冷却塔内冷却盘管各热阻的数量级分析,认为在实际计算中,管壁导热热阻比其它热阻小一个数量级,计算中可忽略,但其余热阻均不可忽略。影响盘管总热阻大小的因素很多,从数学上分析了各热阻对总热阻的影响,找出影响盘管总热阻的主次因素,为冷却盘管的研究、设计及运行管理提供参考。     

System analysis in a European perspective of new industrial cooling supply in a CHP system

In the municipality of Södertälje two large industries use much of the electricity, district heating (DH) and chilled water in the area. The Södertälje energy system is not isolated, however, but is connected to the DH systems of southern and central Stockholm, and a change in the Södertälje energy system will also influence the connected energy systems in Stockholm. The cooling demand in Södertälje is currently covered by lake water cooling and compression chillers, but in order to reduce the use of electricity, conversion to absorption cooling or increased lake water cooling can be considered. The large combined heat and power (CHP) plant in Södertälje is not used to its full potential today, but investment in absorption cooling and/or a cold condenser unit integrated with the CHP plant could increase the plant’s operation hours. In this paper the system effects of introducing new industrial cooling supply in Södertälje has been investigated through optimizations of a model including both the industries and the district heating supply in Södertälje and Stockholm. The results show that, independently of whether condensing power production is feasible in the CHP plant or not, investments in both increased lake water cooling and absorption cooling are profitable. A sensitivity analysis of how energy market prices affect the results shows that even though the system cost will change depending on energy market prices, the optimum cooling technology mix will remain the same. However, a sensitivity analysis of the transfer DH capacity between the Södertälje and Stockholm energy systems shows that if the transfer DH capacity is increased, absorption cooling will be less profitable since more heat can be sold from Södertälje to Stockholm while at the same time reducing the use of fuel resources.     

具有新型双层壁结构的透平叶片流热耦合研究

多通道壁面射流冷却结构是一种新型的燃气透平动叶内部冷却结构,具有消耗冷气少、压力损失小等优点。本文构建了简化的壁面射流冷却叶片与GE-E3冷却结构叶片模型,采用流热耦合方法对比研究了其流动与换热特性。结果表明,壁面射流冷却通道内的狭小空间抑制了横流的产生,冷气在冷却通道中形成了流向涡;前缘冷气流道中的大量冷气流经吸力侧冷却区,并从出口压力更小、面积更大的尾缘排出,使得前缘气膜孔出流的冷气流量和动量较小,冷气在叶片外表面的气膜覆盖特性更好;离心力的影响导致前缘冷气流道中叶根处的压力较低,叶根附近的气膜孔出现燃气主流入侵现象。相比于GE-E3叶片,壁面射流冷却叶片的前缘温度和温度梯度都较小,因此多通道壁面射流冷却在前缘具有更优异的冷却特性。     

平板气膜冷却孔下游湍流场的试验研究

利用二维粒子图像测速（PIV）技术,在吹风比为0.5和1.0、雷诺数为480时,对平板直冷却孔和弯曲冷却孔下游湍流场的流动结构进行了测量,得到了中心截面及射流下游4个流向横截面上的平均速度、涡量分布以及烟雾显示照片,并分析了弯曲冷却孔通道对下游涡结构沿流向演化过程的影响.结果表明：冷却孔射流具有较低的射流轨迹,可以增强气膜的贴附效果,有利于提高冷却效率;弯曲冷却孔能为气膜提供较强的横向动量,使其具有较高的横向扩展能力,从而改善气膜的侧向覆盖效果.     

一种多孔介质蒸发冷却中冷器性能的初步研究

文中简介蒸发冷却中冷器的原理和结构,并通过风洞实验检验各种填料的阻力特性和降温特性,选取合适的填料介质试验。结果表明：蒸发冷却式中冷器原理简单,将其替换原有中冷器应用是可行的,可用于柴油机、燃气轮机进口及ICR船用燃气轮机上。     

The cooling performance of a radiator based roof component

Energy conservation in buildings is becoming an issue of great importance. Space cooling is getting important in most countries and different techniques have been developed one of which is radiative cooling. A prototype roof component, exploiting radiative cooling, was built and tested in the outdoor test facilities of the Centre of Renewable Energy Sources in Greece. The component comprises a radiator, which is utilizing water as the fluid medium and its cooling performance was investigated. This paper presents the construction of the component, the experimental set-up and the results taken during the monitoring procedure.     

Cooled soil as a cooling source for buildings

Two approaches have been tested by the author for cooling soil in a given location to temperatures well below the “normal” temperatures in that location. The first approach has been tested in Sde Boqer Campus, in the Israeli Negev desert. The soil was covered with a layer of pebbles, about 10 cm. thick, and watered in the mornings. Substantial cooling of the soil was achieved. This cooling system was tested in test cells in Sde Boqer, Israel, and in a full scale room in Riyadh, Saudi Arabia, and has provided effective cooling. The second approach was tested at A&M University in Tallahassee, Florida. Temperature measurements were taken of moist soil under a wooden shack on stilts raised about 60 cm above the ground. Thus the soil under it was permanently shaded. The cooled soil temperatures were below the outdoors’ minimum temperatures, even during the peak of the summer, providing a potential heat sink for cooling buildings. The thermal performance of an earth covered building in the Negev arid region of Israel is also summarized.     

Numerical analysis of a cool-thermal storage system with a thermal conductivity enhancer operating under a freezing condition

Enhancing the cooling process of water in a cool-thermal storage system is investigated in this paper. The system is utilized to cool air during on-peak power consumption hours to save energy. The system consists of parallel plates filled with water and triangular corrugated fins. A finite element model for the system is used to predict the cooling time of water for different water's initial temperatures, and also to study the effect of fins design on the cooling process. The result indicates that the aspect ratio of the triangular fin has a significant effect the cooling process of water, and cooling rate increases for the aspect ratio greater or less than 0.75. Temperature contours, average water temperature, and Nusselt number are presented for the cooling process.     

Energy consumption of a residential building: comparison of conventional and RES-based systems

The energy needs of a typical one-family house in the Thessaloniki area for heating, cooling and domestic hot water production are calculated. The calculations are based on the typical average daily consumption of hot water and on the degree-day method for heating and cooling. The results are finally translated into thermal energy consumption, assuming the typical Greek situation (heating with diesel oil boilers and conventional radiators, cooling with local air-to-air split-type heat pumps and hot water production with electric heaters). The same energy needs are assumed to be covered by a vertical closed loop ground heat exchanger combined with a water-to-water heat pump system with fan-coils for heating and cooling and a thermosyphonic solar system for domestic hot water production. The ground heat exchanger/heat pump system efficiency is determined using data from an existing and continuously monitored similar system installed in the broader area of Thessaloniki. The solar system load coverage is calculated using the f-chart method. The energy consumption of the renewable energy systems is calculated and compared to that of the conventional system. The results prove that significant energy savings can be achieved.     

Analysis of a passive cooled building for the semiarid climate

The quasi-steady-state analysis of a hostel building for semiarid climatic conditions has been presented by incorporating the effectiveness of various cooling approaches in the analysis. The effect of intermittent use of an exhaust chimney, opening of windows and a desert cooler has also been incorporated in the analysis to study its performance. It is observed that there is an appreciable reduction in the room temperature by intermittent use of various cooling approaches.