共查询到20条相似文献,搜索用时 171 毫秒
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目前对直接空冷凝汽器积灰现象所做研究不多,且多数忽略了流道截面尺寸及空气流量的变化进行研究,近期发现此结论与凝汽器清洗前后现场监测数据不符.积灰不仅影响换热系数,对管外空气的流量的影响亦不容忽视,在考虑到积灰后流道截面尺寸及管外空气流量变化的条件下,对积灰凝汽器管外空气流动与换热进行了综合计算及分析.结果表明:直接空冷凝汽器积灰后,换热系数有所升高,冷却空气量明显减少,冷却空气流量的减少是导致凝汽器性能降低的根本原因;夏季凝汽器积灰对机组背压影响较大,需严防凝汽器积灰;积灰后出口空气温度升高,实时监测出口空气温度可以作为监测凝汽器局部积灰的一种有效手段. 相似文献
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自然通风直接空冷系统凝汽器单元"Λ"型布局和传统翅片结构使得冷却空气流过翅片管束时发生严重转向,从而显著影响空冷凝汽器的流动传热性能。提出了一种新型翅片管束,其翅片通道与基管椭圆长轴方向呈一定夹角,使翅片通道方向与塔浮升力方向平行。通过CFD数值模拟和实验验证,获得了采用新型倾斜翅片管束的自然通风空冷凝汽器的空气流场和温度场,计算得到了不同环境风速下空冷凝汽器总换热量的变化规律,并与现有翅片管束的空冷凝汽器性能进行了对比。研究结果表明,采用倾斜翅片空冷凝汽器可以显著改善自然通风直接空冷系统热力性能,降低机组背压,提高空冷机组运行的经济性。 相似文献
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空冷岛运行优化中,需要将汽轮机、空冷凝汽器及空冷岛风机的特性综合起来进行分析。在综合直接空冷机组冷端各个组成部分,包括空冷凝汽器、低压缸至空冷凝汽器之间排汽管道及空冷岛风机特性的基础上,建立汽轮机排汽背压与空冷岛风机转速的特性关系,为空冷岛运行优化计算创造了条件。 相似文献
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以汽轮机变工况为基础,综合考虑多种因素,结合1000MW空冷机组热力系统运行参数,应用弗留格尔公式计算了不同机组负荷下汽轮机排汽量的变化情况以及机组的背压对汽轮机功率的影响特性。根据空冷凝汽器的变工况分析,确定了不同环境温度时汽轮机排汽背压与空冷风机所消耗功率的对应关系。通过优化分析,计算了机组运行的最佳背压。编程开发了计算机应用软件,并进一步根据风机的运行原理实现了机组的不同运行状态下通过采集当时的运行参数给出最经济风机运行转速的功能,实现了对机组运行人员的在线指导。该软件在宁夏灵武发电厂4号机得到实际应用,结果表明该系统应用效果良好,具有重要的实际意义。 相似文献
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直接空冷机组具有明显的节水效果,但也存在诸如汽轮机的运行背压高且变幅大、直接空冷凝汽器的冷却性能受环境、风和砂尘的影响大、直接空冷凝汽器冬季运行时容易发生冻结、凝结水溶氧超标以及热污染等运行方面的问题,针对这些现象及原因进行了分析,并提出对策。 相似文献
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For an air-cooled steam condenser (ACSC), environmental wind can cause a large flow rate reduction in the axial fans mainly near the windward side of the air-cooled platform due to cross-flow effects, resulting in a heat transfer reduction. This leads to an increase of turbine back pressure, and occasional turbine trips occur under extremely gusty conditions. A new method is proposed in this paper to remove the strong wind effect by adding deflecting plates under the air-cooled platform, which contributes to forming a uniform air mass flow rate in the axial fans by leading enough cooling air to the fans in the upwind region. Numerical simulation is made of the thermal-flow characteristics and heat transfer performance of the improved ACSC with deflectors. A heat exchanger model is used for simulating the flow and heat transfer in the ACSC, in which the heat exchanger is simplified to a porous medium and all flow losses are taken into account by a viscous and an inertial loss coefficient. A fan model is used for reaching the flow condition at the heat exchanger inlet with the actual performance curves of the fan. It is found that the improved ACSC with deflector shows a significant enhancement in both the cooling air mass flow rate and the heat rejection rate compared with the conventional ACSC. The higher the wind speed is, the larger the heat transfer enhancement of the improved ACSC is. The effect of the plate inclination is also investigated, and the inclination angle of 45° is found to be the optimum value for the arrangement of the deflector. 相似文献
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为了研究不可凝气体(non-condensable gases, NCG)对火电与光热发电机组上广泛使用的大扁管空冷凝汽器性能的影响,以工程机组凝汽器上普遍应用的通流面积220 mm×20 mm的大扁管为研究对象,针对汽轮机典型工况下的实际蒸汽流量,基于Lee相变方程、VOF方法以及组分扩散模型,对蒸汽与NCG混合气体管内两相流凝结换热进行数学建模与数值计算。结果表明:由于大扁管的狭窄通流几何结构与高蒸汽流量,NCG对管内蒸汽凝结的抑制效果要远低于预期;当入口空气质量分数按2%增加时,凝结管凝结换热系数仅下降2%左右,这与NCG导致低流量圆管凝结性能急剧下降的结论不同;空气正常泄漏不会导致空冷凝汽器性能下降而影响发电机组效率。 相似文献
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The effect of the cooling water flow path on the flow and heat transfer in a double tube-pass condenser for a 660 MW power plant unit was numerically investigated based on a porous medium model. The results were used to analyze the streamline, velocity, air mass fraction and heat transfer coefficient distributions. The simulations indicate that the cooling water flow path is important in large condensers. For the original tube arrangement, the heat transfer with the lower-upper cooling water flow path is better than that with the upper-lower cooling water flow path. The reason is that the steam cannot flow into the internal of upper tube bundle and the air fractions are higher in the upper tube bundle with the upper-lower cooling water flow path. An improvement tube arrangement was developed for the upper-lower cooling water flow path which reduced the back pressure by 0.47 kPa compared to the original scheme. Thus, the results show that the tube arrangements should differ for different cooling water flow paths and the condenser heat transfer can be improved for the upper-lower cooling water flow path by modifying the tube arrangement. 相似文献
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Experimental investigation is conducted to study the performance of evaporative condensers/coolers. The analysis includes development of correlations for the external heat transfer coefficient and the system efficiency. The evaporative condenser includes two finned-tube heat exchangers. The system is designed to allow for operation of a single condenser, two condensers in parallel, and two condensers in series. The analysis is performed as a function of the water-to-air mass flow rate ratio (L/G) and the steam temperature. Also, comparison is made between the performance of the evaporative condenser and same device as an air-cooled condenser. Analysis of the collected data shows that the system efficiency increases at lower L/G ratios and higher steam temperatures. The system efficiency for various configurations for the evaporative condenser varies between 97% and 99%. Lower efficiencies are obtained for the air-cooled condenser, with values between 88% and 92%. The highest efficiency is found for the two condensers in series, followed by two condensers in parallel and then the single condenser. The parallel condenser configuration can handle a larger amount of inlet steam and can provide the required system efficiency and degree of subcooling. The correlation for the system efficiency gives a simple tool for preliminary system design. The correlation developed for the external heat transfer coefficient is found to be consistent with the available literature data. 相似文献
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L.J. Yang X.Z. Du Y.P. Yang 《International Journal of Heat and Mass Transfer》2011,54(15-16):3109-3119
Ambient winds may lead to poor fan performance, exhaust air recirculation and mal-distribution of the air across the tube bundles of the air-cooled condensers in a power plant. Investigations of the impacts of the ambient winds on the air-cooled condensers are key area of focus. Based on a representative 2 × 600 MW direct dry cooling power plant, the physical and mathematical models of the air-side fluid and heat flow in the air-cooled condensers at various ambient wind speeds and directions are set up by introducing the radiator model to the fin-tube bundles. The volumetric flow rate, inlet air temperature and heat rejection for different air-cooled condensers as a whole, condenser cells and fin-tube bundles are obtained by using CFD simulation. The results show that the thermo-flow performances for the air-cooled condenser as a whole, condenser cells and heat exchanger bundles vary widely in space. The thermal performances of the air-cooled condensers, condenser cells and fin-tube bundles at the downstream are generally superior to those at the upwind. It is of use for the upwind fan regulations and the A-frame condenser cell geometric optimization to investigate the space characteristics of the thermal performance for the air-cooled condensers in a power plant. 相似文献
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William A. Davies III 《传热工程》2020,41(22):1843-1855
Abstract The effect of airflow profile and condensation pressure on the performance of air-cooled condensers is investigated experimentally. Two large, flattened-tube air-cooled steam condensers are studied. The tube lengths are 10.7 and 5.7?m, with inner dimensions of 216?×?16?mm and aluminum fins on each side of the elongated-slot cross sections. Capacity and pressure drop are measured and discussed here. All tests are performed with a horizontal tube and co-current vapor and condensate flow. Four different profiles of cross-flowing air are tested: uniform air flowing upwards, uniform air flowing downwards, and two profiles of non-uniform air flowing upwards. For the 10.7?m tube, reversing airflow direction from upwards to downwards is found to significantly increase condenser capacity. Also for the 10.7?m tube, a favorable non-uniform air-velocity profile is shown to increase capacity in comparison to a uniform air-velocity profile. Both of these performance increases are shown to be the result of matching regions of maximum heat transfer coefficient on the air and steam sides. For the 5.7?m tube, a non-uniform airflow profile is shown to have no effect on capacity. Reducing condensation pressure is shown to decrease condenser capacity for both condenser tubes. 相似文献