Influence of Different Vortex Generators on Heat Transfer in Direct Air-Cooled Condensers

通过数值模拟研究了矩形小翼、三角小翼、梯形小翼、柱面梯形翼、柱面三角翼和柱面矩形翼等6种涡流发生器分别安装于直接空冷凝汽器单排蛇形翅片扁管中的压降和换热性能。Re数在600~1800范围内,涡流发生器采用相同高宽比、尾高、攻角以及安装位置。结果表明：矩形小翼的换热及压降增大最多,Re=1729时,相比平直翅片分别增加了14.27%和18.32%。Re=1 729时,柱面梯形翼的压力损失比矩形小翼少4.7%,换热低1.5%。当以（j/j0）/（f/f0）1/3作为综合换热性能评价标准时,柱面梯形翼的综合换热性能最好。另外,考察了柱面梯形翼倾角的影响（0°、6°、12°、20°、24°和26°）,相同工况下,倾角为12°的柱面梯形翼换热最好（较平直翅片增强4.29%~14.1%）、压降最小（增大7.5%~12.8%）且综合换热性能最好。柱面梯形翼因其迎流面积与斜边长度的匹配以及流线型柱面,具有良好的强化传热效果以及较小的压降。

Calculation of the Choked Back Pressure for Steam Turbines with Air Cooled Condensers

The choked back pressure characteristic of the steam turbine unit with air cooled condenser is very different with the unit with wet cooling technology, and the understanding of the choked back pressure performance change with operation load is important to guide the economic operation of the unit. One simplified Variable Operation Condition Analysis Method was put forward for calculation of the unit output-turbine back pressure characteristics. Based on this method, the choked back pressure for each operation load can be determined. An example was given for a super-critical, regenerative single-shaft, 2-casing with 2-exhaust steam turbine generation unit with air cooled condenser. The calculation result was provided and compared with the result of the unit with wet cooling technology.

Transient Heat Transfer Study of Direct Contact Condensation of Steam in Spray Cooling Water

We conducted a transient experimental investigation of steam–water direct contact condensation in the absence of noncondensible gas in a laboratory-scale column with the inner diameter of 325 mm and the height of 1045 mm. We applied a new analysis method for the steam state equation to analyze the molar quantity change in steam over the course of the experiment and determined the transient steam variation. We also investigated the influence of flow rates and temperatures ofcooling water on the efficiency ofsteam condensation. Our experimental results show that appropriate increasing of the cooling water flow rate can significantly accelerate the steam condensation. We achieved a rapid increase in the total volumetric heat transfer coefficient by increasing the flow rate of cooling water, which indicated a higher thermal convection between the steam and the cooling water with higher flow rates. We found that the temperature ofcooling water did not play an important role on steam condensation. This method was confirmed to be effective for rapid recovering ofsteam.

Performance Analysis of Automated Control System for Condenser Water Treatment Unit

The air conditioning system in the Umm Al-Qura University (Albdiya Campus) was conceived to be a district cooling by a remote chilled water plant. Recently, there are two chilled water plants in the university installed strategically to provide chilled water to all the academic and administrative buildings of the university through distribution network with total capacity approximately of 12,000 tons of refrigeration. The plants were built based on cooling towers with open water cycle as heat rejection system. Water treatment chemicals has been used to protect the cooling systems from corrosion, scaling and microbiological fouling accompanied with dissolved and suspended water impurities. Different methods are being used to determine and control the treatment chemical concentrations and system performance indicators. Traditional chemical controller has drawback of indirect measurements and set points. The purpose of this paper is to present a solution to overcome the problems of traditional and conventional chemical treatment and control sys-tems. Central cooling plant number (1) assigned to perform experimental setup using new chemical treatment technology. Advanced automatic chemical treatment controller installed on condensers (1, 2 and 3), and certain key performance indicators were selected and monitored such as chemical and water consumption, power, energy saving, and maintaining system integrity and efficiency. Satisfactory results were obtained in terms of performance and cost of operation.

Measurement Methodology for Monitoring Fouling Resistance in Condenser of Chiller

This paper established an on-line monitoring model for fouling resistance of cooling water based on heat transfer theory,which was mainly applied to the fouling resistance test for condenser of chiller in operation,and the test requirements were presented.It proves that the load ratio of chiller has big influence on the test result,and the best load ratio for test is the range of 80%～100%.A case has been executed to validate the model's feasibility.

Effect of Non-Condensable Gas Leakage on Long Term Cooling Performance of Loop Thermosyphon

We have developed a loop thermosyphon for cooling electronic devices. The cooling performance of a thermosyphon deteriorates with an increasing amount of non-condensable gas (NCG). Design of a thermosyphon must consider NCG to provide guaranteed performance for a long time. In this study, the heat transfer performance of a thermosyphon was measured while changing the amount of NCG. The resultant performances were expressed as approximations. These approximations enabled us to predict the total thermal resistance of the thermosyphon by the amount of NCG and input heating. Then, using the known leakage in the thermosyphon and the amount of dissolved NCG in the water, we can predict the amount of NCG and the total thermal resistance of the thermosyphon after ten years. Although there is a slight leakage in the thermosyphon, we are able to design a thermosyphon with a guaranteed level of cooling performance for a long time using the proposed design method.

Thermodynamic Simulation of CCP in Air-Cooled Heat Pump Unit with HFCs and CO₂Trans-Critical

The exergy analysis and finite time thermodynamic methods had been employed to analyze the compound condensation process (CCP). It was based on the air-cooling heat pump unit. The cooling capacity of the chiller unit is about 1 kW, and the work refrigerant is R22/R407C/R410A/CO2. The MATLAB/SIMULINK software was employed to build the simulation model. The thermodynamic simulation model is significant for the optimization of parameters of the unit, such as condensation and evaporation temperature and mass flow of the sanitary hot water and size of hot water storage tank. The COP of the CCP of R410A system is about 3% - 5% higher than the CCP of the R22 system, while CCP of the R407C system is a little lower than the CCP of R22 system. And the CCP of CO2 trans-critical system has advantage in the hot supply mode. The simulation method provided a theoretical reference for developing the production of CCP with substitute refrigerant R407C/R410A/CO2.

The Experimental Investigation of Recirculation of Air-Cooled System for a Large Power Plant

The paper introduces thermal buoyancy effects to experimental investigation of wind tunnel simulation on direct air-cooled condenser for a large power plant. In order to get thermal flow field of air-cooled tower, PIV experiments are carried out and recirculation ratio of each condition is calculated. Results show that the thermal flow field of the cooling tower has great influence on the recirculation under the cooling tower. Ameliorating the thermal flow field of the cooling tower can reduce the recirculation under the cooling tower and improve the efficiency of air-cooled condenser also.

Effect of Temperature Differentials on Condensers of Split-Type Air Conditioners in Apartment Buildings

Analyzing the effects of heat rejection from condensers of split-type air-conditioning units at lower-floors of MLABs （multi-level apartment buildings）, using field measurements to monitor environmental conditions and condenser operation, revealed increases in the inlet air temperature at the condensers at the upper floors, which in turn increased the power and energy requirements for these units and decreased their cooling capacities. Results indicated that a decrease of up to 16,000 tons in cooling capacity and an increase of up to 67.2 MW in the national peak load demand might be reached for a 4 ℃ temperature differential for Kuwait conditions. It is recommended that the condensers be placed in the wind pathway to minimize the impact of heat rejection and stack effect and to optimize the operation of split-type air-conditioning units, and that other factors regarding installation setup and location are investigated.

厂区布置对钢塔自然通风空冷凝汽器性能的影响

利用计算传热学(NHT)软件FLUENT,在自然通风状态下,对2×350MW机组钢结构外覆铝板冷却塔及直接空冷凝汽器(DACC)的流动和换热性能进行了数值模拟、分析和研究。确定了考核工况,不同环境风向下,周边建筑物对DACC和钢塔性能的影响。结果表明,两机一塔水平矩形布置方式下,平行于A列的来风对钢塔通风和DACC换热有负面影响。不考虑风向频率时,各风向下周边建筑物对DACC总体换热影响约为2.4%。在电厂总平面布置时,应尽量使厂区主导风向避开不利风向,汽机房空冷塔间距还需综合其它因素确定。

自然通风湿式冷却塔节水方案的数值研究

为降低自然通风湿式冷却塔的耗水量,本文采用一种可用于回收其蒸发损失的空气冷凝器结构,并通过数值模拟方法对其节水特性展开研究。首先基于空气运动控制方程和水蒸气冷凝模型,建立了用于分析空气冷凝器节水特性的数学模型,其次分析了冷却空气流速、空气冷凝器的结构尺寸和材质等因素对该冷凝器节水特性的影响。研究结果表明:空气冷凝器的单位面积节水量随着冷却空气流速以及冷凝器宽度的增大而增大,但随着冷凝器长度和高度的增大而减小;空气冷凝器的材质和壁厚对其单位面积节水量没有显著影响,空气冷凝器可采用重量轻和成本低的薄壁PVC来加工制造。

2023年中南某市夏季公共场所嗜肺军团菌污染状况

目的了解2023年中南某市三类公共场所嗜肺军团菌污染状况,分析健康风险。方法于2023年7月采取非随机抽样方法在在中南某市三类公共场所采集集中空调水样、室内空气样本,以及公共设施物体表面样本进行检测和分析。采用培养法对集中空调冷却水和冷凝水嗜肺军团菌进行检测;采用荧光定量PCR对室内空气以及物体表面嗜肺军团菌进行检测。利用Fisher确切概率法用于评估水样类型、场所类型与健康风险等级的相关性。结果调查中共采集集中空调水样24份、室内空气样本213份以及公共设施物体表面样本282份。培养法检测结果显示,集中空调水样的总体阳性率为37.5%,其中冷却水的阳性率为55.6%(5/9),冷凝水的阳性率为26.7%(4/15)。其中,地铁站的集中空调水样阳性率为27.3%(3/11),宾馆的阳性率为66.7%(6/9),火车站水样中未检测出嗜肺军团菌(0/4)。风险分析发现,冷却水的高风险率为55.6%(5/9),冷凝水的高风险率为20.0%(3/15);地铁和宾馆水样的高风险率分别为27.3%(3/11)和55.6%(5/9)。荧光定量PCR结果显示,公共场所的室内空气和物体表面的检测结果均为阴性,中高风险率为0%。结论三类公共场所中,地铁和宾馆嗜肺军团菌阳性率较高,冷却水和冷凝水中均有较高检出率。

大型冷凝式消雾节水冷却塔性能试验研究

为研究获得菱形模块消雾节水冷却塔的消雾节水和节能特性,对某设计循环水量为5000 m^(3)/h的菱形消雾节水冷却塔的消雾性能、节水性能和节能性能进行了试验研究。建立了冷却塔消雾节水节能性能评价模型,通过现场试验获得冷却塔消雾节水和节能特性参数及其变化规律。结果表明:消雾节水冷却塔设计出塔空气相对湿度为85%,实测出塔相对湿度为82.28%,消雾指数为1.03,符合“零雾型”消雾冷却塔的要求。经菱形消雾冷凝模块换热后的冷凝水量为14.19 m^(3)/h,冷却塔节水率为25.3%,冷凝节水效果好。单塔年总节能收益约40万元,整体年节能收益达240万元,菱形消雾节水冷却塔具有良好的经济效益及环保效益。

Predicting moisture condensation risk on the radiant cooling floor of an office using integration of a genetic algorithm-back-propagation neural network with sensitivity analysis

Pre-dehumidification time(τ_(pre))and pre-dehumidification energy consumption(E_(pre))play important roles in preventing the condensation of moisture on the floors of rooms that use a radiant floor cooling(RFC)system.However,there are few theoretical or experimental studies that focus on these two important quantities.In this study,an artificial neural network(ANN)was used to predict condensation risk for the integration of RFC systems with mixed ventilation(MV),stratum ventilation(SV),and displacement ventilation(DV)systems.A genetic algorithm-back-propagation(GA-BP)neural network model was established to predict τ_(pre) and E_(pre).Both training data and validation data were obtained from tests in a computational fluid dynamics(CFD)simulation.The results show that the established GA-BP model can predict τ_(pre) and E_(pre) well.The coefficient of determination(R^(2))of τ_(pre) and of E_(pre) were,respectively,0.973 and 0.956.For an RFC system integrated with an MV,SV,or DV system,the lowest values of τ_(pre) and E_(pre) were with the DV system,23.1 s and 0.237 kWh,respectively,for a 67.5 m^(3) room.Therefore,the best pre-dehumidification effect was with integration of the DV and RFC systems.This study showed that an ANN-based method can be used for predictive control for condensation prevention in RFC systems.It also provides a novel and effective method by which to assess the pre-dehumidification control of radiant floor surfaces.

精馏装置塔顶冷凝器冷却水的优化——以化工生产技术国赛装置为例

许多人操作国赛精馏装置时并没有认真分析不同阶段冷却水的用量,要么放弃冷却水的评分直接全程最大流量,要么就是大范围调节冷却水流量,导致冷凝器没有正常运行。通过实际操作国赛规定精馏装置,动态分析不同阶段冷却水的流量和确定塔顶冷凝器冷却水的最佳出口温度,从而降低冷却水的用量,使得装置评分更高,操作更简单。

热湿气候下蒸发冷却式冷凝器系统的节能特性对比研究

为评估和提高蒸发冷却式冷凝器系统(MVC-EC)在热湿气候条件下的应用潜力,提出了一种结构优化的两级蒸发冷却式双冷凝器系统(MVC-TSEC),并基于详细的能耗分析模型进行了性能对比研究。首先,建立了各系统中所有组件的分布式参数模型,并进行了实验数据验证。其次,分析了室外空气温度和相对湿度及房间显冷负荷对2种系统COP和节能率的影响。最后,评估了2种系统在典型热湿城市的节能潜力。结果显示:相较于MVC-EC系统,MVC-TSEC系统在高温、中高湿度和高负荷工况下具有更好的节能优势,节能率约提高4.3%~10.9%,并且可提高制冷剂系统适应温度约0.8~1.9℃;在广州市和长沙市夏季6—8月,MVC-TSEC系统的节能率分别为12.7%和21.1%,高于MVC-EC系统(8.5%和14.9%)。

基于外部冷却模块和内部凝雾模块的高位收水机械通风冷却塔性能对比研究

为了控制雾羽和节约水资源,搭建了高位收水机械通风冷却塔热态实验系统,分别对外部冷却模块(干湿联合冷却塔)和内部凝雾模块(凝雾式冷却塔)的消雾、节水及热力性能进行对比分析,研究了环境温度、循环水进水温度及循环水量对冷却塔性能的影响。结果表明:干湿联合冷却塔和凝雾式冷却塔均具有消雾和节水能力,但实现二者的消雾和节水是以降低冷却塔冷却性能为代价的;与原塔相比,干湿联合冷却塔和凝雾式冷却塔的循环水温降约降低了1.5 K;干湿联合冷却塔和凝雾式冷却塔的消雾和节水性能受运行参数的影响很大,且凝雾式冷却塔的节水量和节水率高于干湿联合冷却塔。

辐射供冷的节能性、舒适性和防结露研究

辐射供冷具有优越的节能性和舒适性,但冷辐射板易结露的问题,制约了供冷量的提升,限制了辐射供冷系统的应用场所和地区。因此,冷辐射板的防结露是辐射供冷系统的关键问题。通过文献总结,探讨辐射板的节能性和舒适性,从改进冷辐射板结构防结露、独立送风防结露、调节供水防结露、疏导结露四个方面,探究冷辐射板防结露目前的研究进展,以及不同防结露措施的优势和有待改进的地方,为辐射板防结露的发展提供有益的参考。

电容去离子技术用于模拟调相机转子冷却水处理的研究

电容去离子(CDI)技术是一种新型高效的水处理技术,具有低能耗、高效率、低成本、绿色无污染、电极可再生等优势。配制CuSO_(4)溶液模拟转子冷却水,通过溶液电导率、Cu^(2+)去除率、能耗、循环稳定性等系列指标,探讨基于活性炭电极的CDI技术处理调相机转子冷却水的应用可行性。实验结果表明,经CDI处理后,模拟转子冷却水电导率可低至4.1μS/cm,Cu^(2+)去除率为100%,出水透明纯净且无机械杂质,符合《发电机内冷水处理导则》(DL/T1039—2016)中规定的水质控制标准。采用SEM、XPS等表征了吸附Cu^(2+)后的活性炭电极,结果表明碳材料上出现铜元素。通过吸附动力学模型进一步对电吸附机理进行讨论分析,结果表明,吸附行为更符合伪一级动力学模型,推测电极对Cu^(2+)的吸附主要为物理吸附机制。