Performance criterion of an indirect dry air‐cooled condenser for small modular reactor based on pressure transition temperature

In terms of reducing the environmental pollution caused by effluent water from typical condensers and the water dependency of small modular reactors, indirect dry air‐cooled condensers (IDACs) are being considered an ultimate heat sink. While the performance of air‐cooled heat exchangers has been investigated thoroughly for decades, evaluations of the condenser performance rely primarily on empirical data. Thus, a method for precisely determining the performance of the IDAC under various environmental and thermal‐hydraulic conditions has not yet been understood. The objective of this study is to experimentally investigate the critical parameter that initiates the deterioration of the condenser performance by varying the cooling duty and water velocity. The investigation is also extended to a parametric study of the air‐cooling conditions using a best‐estimate thermal hydraulic analysis code called multi‐dimensional analysis of reactor safety (MARS‐KS) to suggest a method for designing an IDAC system. Results showed that, for a given cooling duty and water velocity, the condenser exhibited an insufficient performance above a certain cooling water temperature. The temperature was defined as the pressure transition temperature (PTT) that initiates the increase in pressure inside the condenser. The calculation results of MARS‐KS were analysed based on the PTT and was used to suggest methods for designing an appropriate IDAC for the cooling duty and environmental conditions of given target site.     

Numerical investigation on the flow field of an axial flow fan in a direct air‐cooled condenser for a large power plant

The flow field of an axial fan in a direct air‐cooled condenser for a large power plant is modeled numerically. In order to improve the efficiency of heat exchange of the air‐cooled condenser, methods of increasing the rotational velocity of the fan and laying out the guide blade at the outlet of the fan are adopted. Results show that increasing the rotational velocity of the fan can effectively increase the flux of the fan, and can improve the efficiency of an air‐cooled condenser; laying out the guide blade at the fan outlet can ameliorate the flow field in an A‐flame. This causes the rotational kinetic energy to change into static pressure at the fan outlet, so the ability of the heat exchange of the air‐cooled condenser is improved. © 2012 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley Online Library (wileyonlinelibrary.com/journal/htj). DOI 10.1002/htj.21027     

Design and characterization of a cylindrical,water‐cooled heat sink for thermoelectric air‐conditioners

Thermoelectric air‐conditioners (TEACs) are becoming much concerned due to their many advantages, but the low COPs limit their broad applications. The two key factors to raise the COPs of TEACs are both the improvement of thermoelectric materials and the optimum design of hot side heat sinks. This paper provides a thermoelectric air‐conditioning system with a water‐cooled sleeve heat sink in the hot side of the thermoelectric pellets, and compares the overall heat transfer rates q_t, the total heat resistances R_t between the water‐cooled and air‐cooled heat sinks as well as the optimum fin length, the optimum fluid flow velocity and the optimum fin gap distance. The simulation results show that the overall heat transfer rate of water‐cooled heat sink is more than 20 times that of air‐cooled heat sink under the other same circumstances, as a result of the improvement of heat sink, the optimum COP of the thermoelectric air‐conditioning system with the water‐cooled heat sink proximately doubles that with the air‐cooled heat sink. This novel system could be simply installed and applied all the year round for cooling in summer and heating in winter. Copyright © 2005 John Wiley & Sons, Ltd.     

Effect of pre‐cooling of inlet air to condensers of air‐conditioning units

Energy conservation and increase in performance of air‐conditioning systems could be achieved by pre‐cooling the air intake of the condensers. This paper experiments three different methods of pre‐cooling the condenser air; the cooling pad (CP) setup, the cooling mesh (CM) setup and the shading setup. The CP and CM setups are two different methods of evaporatively cooling the air. The three methods have been applied to three identical, 2.8 tons, split air‐conditioning units during the peak summer time period in Kuwait, under ambient temperatures ranging from 39 to 45°C. The results yielded a drop in the power consumption ranging from 8.1 to 20.5% and an increase in the cooling load ranging from 6.4 to 7.8% by using the CP and CM setups, which, in turn, resulted in an increase in the coefficient of performance (COP) of the units by 36–59%. The shading setup has resulted in an increase of power consumption due to air trapped below the shaded area, which resulted in heat being generated. Copyright © 2005 John Wiley & Sons, Ltd.     

An experimental study on multi‐purpose desiccant integrated vapor‐compression air‐conditioning system

In this paper, a multi‐purpose hybrid desiccant integrated vapor‐compression air‐conditioning system of a small capacity is experimentally investigated. The system, referred as hybrid desiccant‐assisted air conditioner (HDAC), is designed to meet the cooling load of spaces having large latent heat portions and at the same time to extract water from atmospheric air. The system is mainly consisted of a liquid‐desiccant dehumidification unit integrated with a vapor‐compression system (VCS). The dehumidification unit uses lithium chloride (LiCl) solution as the working material. The effect of different parameters, such as desiccant solution flow rate, process airflow rate, evaporator and condenser temperatures, strong solution concentration and regeneration temperature on the performance of the system, is studied. This system has a water recovery rate of 6.7 l/h TR (1.91 l/h kW) of pure water at typical north Egyptian climate (20–30°C dry bulb and 35–45% relative humidity). The HDAC system has a COP as high as 3.8 (an improvement of about 68% over the conventional VCS). The system offers a total cooling capacity of about 1.75 TR (6.15 kW) using a 0.75 TR (2.6 kW) VCS unit. Finally, the proposed system is found to have a payback time of about 10 months without any considerable extra capital cost compared with the known split air‐conditioning system. The results emphasize the potential benefits of the HDAC system. Copyright © 2010 John Wiley & Sons, Ltd.     

火电站直接空冷凝汽器积灰监测

火电站直接空冷凝汽器积灰是影响传热性能的重要因素,研究直接空冷凝汽器积灰对传热性能的影响规律并提出监测措施具有重要意义。通过分析汽轮机背压与汽轮机排汽量、冷却空气流量、凝汽器传热系数、凝汽器总传热面积以及环境温度之间的关系,得到了空冷凝汽器在维持汽轮机排汽量和冷却空气量不变时,汽轮机背压和传热系数之间的关系以及凝汽器积灰对汽轮机背压的影响。研究表明:凝汽器积灰会导致凝汽器传热系数降低,汽轮机背压升高,机组运行经济性下降。设计工况下,当蛇形翅片扁平管结构凝汽器积灰厚度达到1.2 mm时,汽轮机背压将增加50%左右。通过监测空冷机组运行过程中汽轮机背压的变化,可预报积灰的程度,为直接空冷凝汽器清洗提供一定的理论依据。     

Conservation of energy estimated by second law analysis of a power-consuming process

A refrigeration system removing heat from a cold storage is analyzed to determine exergetic losses of the thermodynamic cycle and the power needed for the flows of the refrigerant and the media transferring heat at a specified temperature. How much the overall power consumption of the system can be decreased by lowering the condensing temperature, by either increasing the external heat transfer at the condenser or by lowering the inlet temperature of the heat exchanging media, is investigated. The latter depends on the relative humidity of the air. The performance of air, water and evaporative-cooled condensers are evaluated as a function of relative humidity of the ambient air. It is shown that the evaporative condenser operates at the lowest condensing temperature and, therefore, the least power consumption of the total system is achieved. Wetting the condenser with water requires only 1% of the overall power consumption but reduces the consumption by 30% as compared with the air-cooled condenser. Precooling the air by a water spray before it enters an air-cooled condenser is of benefit only at relative humidities of 65% or less. At other state conditions of the air, a higher power consumption will result. Lowering the temperature of the surroundings lowers P_rev and the second law efficiency must be properly defined so that, for cases of lowest power consumption, highest values of the efficiency will be obtained. Means for the design of least power-consuming air-conditioners are briefly stated, as well as the advantages of evaporative condensers for fog-free operation.     

600MW直接空冷机组主要技术经济指标分析

以内蒙古某发电有限公司600MW等级直接空冷机组为例,对供电煤耗率、厂用电率、汽轮机热耗、真空度、节水量等5个方面的指标进行分析,初步指出影响以上技术经济指标的因素,并结合直接空冷系统的特点提出初步的防治措施,以提高直接空冷机组运行经济性。     

不可凝气体对大扁管空冷凝汽器性能的影响分析

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。     

Improved condenser design and condenser-fan operation for air-cooled chillers

Air-cooled chillers traditionally operate under head pressure control via staging constant-speed condenser fans. This causes a significant drop in their coefficient of performance (COP) at part load or low outdoor temperatures. This paper describes how the COP of these chillers can be improved by a new condenser design, using evaporative pre-coolers and variable-speed fans. A thermodynamic model for an air-cooled screw-chiller was developed, within which the condenser component considers empirical equations showing the effectiveness of an evaporative pre-cooler in lowering the outdoor temperature in the heat-rejection process. The condenser component also contains an algorithm to determine the number and speed of the condenser fans staged at any given set point of condensing temperature. It is found that the chiller’s COP can be maximized by adjusting the set point based on any given chiller load and wet-bulb temperature of the outdoor air. A 5.6–113.4% increase in chiller COP can be achieved from the new condenser design and condenser fan operation. This provides important insights into how to develop more energy-efficient air-cooled chillers.     

包覆吸水膜的管式蒸发散热器性能的实验研究

应用间接蒸发散热的原理,在空调冷凝器表面包覆吸水膜,利用水蒸发带走热量.这样蒸发面积达到了最大值,并且能够通过毛细力自动补充蒸发的水分.空调冷凝器中热工质的温度和热容比间接散热器中的一次空气大,能够提高蒸发表面温度,提高蒸发量,进而提高散热效率.通过对通有热水的表面覆盖吸水纸膜的单铜管的实验研究,得出了该方式的传热系数以及水膜的,导热系数,证明了该散热方式较空调冷凝器空气强制对流和其它蒸发散热方式的优势.     

包覆吸水膜的管式蒸发散热器性能的实验研究

应用间接蒸发散热的原理,在空调冷凝器表面包覆吸水膜,利用水蒸发带走热量.这样蒸发面积达到了最大值,并且能够通过毛细力自动补充蒸发的水分.空调冷凝器中热工质的温度和热容比间接散热器中的一次空气大,能够提高蒸发表面温度,提高蒸发量,进而提高散热效率.通过对通有热水的表面覆盖吸水纸膜的单铜管的实验研究,得出了该方式的传热系数以及水膜的导热系数,证明了该散热方式较空调冷凝器空气强制对流和其它蒸发散热方式的优势.     

Experimental and theoretical study of waste heat recovery from a refrigeration system using a finned helical coil heat exchanger

This paper is an experimental and theoretical study that aimed at conserving energy by utilizing the waste heat generated from a refrigeration system by calculating the range of condensation after the compression stage for the refrigerant (R410A). A helical coil tube‐shell heat exchanger was designed as a heat recovery unit to use the waste heat from an air conditioner 1TR (split type) in the outdoor unit between the compressor and the condenser to produce hot water and increase the coefficient of performance (COP) of the refrigeration cycle. Two experimental types of the helical coil heat exchanger (conventional and finned) were used in attempts to induce absorption of the rejected heat into tap water. The increase in the COP ranges from 12.5% to 40%, an increase in the water outlet temperatures difference reaches 12°C. A cost–benefit analysis in terms of the net present value and the payback period (PP) has been performed. From the analysis, it has been observed that the use of the designed heat recovery unit will save electrical consumption to produce the required hot water with a PP of about 11.7 months for the conventional heat exchanger and 17.5 months for the finned helical coil heat exchanger.     

Numerical Simulation of the Performance of a Capillary Thermal Driven Ejector Refrigerator

A capillary driven ejector refrigerator is a new refrigeration system that can use solar energy and other low-grade heat sources. In this paper, the performance of the refrigeration system is simulated numerically by use of an iteration algorithm and block exchanging technology for all unit models. The flow and heat transfer characteristics in a solar collector, generator, ejector, condenser, and evaporator are analyzed and calculated. The results show that when the generating temperature is higher than 75–80°C and the environmental temperature is lower than 35°C, the system can work normally; the coefficient of performance of this refrigeration system is in the range of 0.05–0.15 by use of water as a refrigerant. The cooling capacity and COP increase with an increasing generative temperature and decreasing condensing pressure.     

Rotational speed adjustment of axial flow fans to maximize net power output for direct dry cooling power generating units

The power consumption of axial flow fans may account for more than 1% of the rated power output of the power generating unit, so it is of benefit to the energy efficiency of the power generating unit to propose an operation adjustment approach to axial flow fans. On the basis of representative 2 × 600 MW direct dry cooling generating units, a computational model of air‐side flow and heat transfer of an air‐cooled condenser (ACC) combined with exhaust steam condensation is developed, by which the airflow rate, inlet air temperature of ACCs, the power consumption of axial flow fans, turbine backpressure, and net power output of power generating units at various wind speeds and in various wind directions are obtained. The results show that the net power output in the presence of winds always decreases when the rational speeds of the first upwind row axial flow fans increase from the rated speed of 79 rpm by 10% to 86.9 rpm. However, the net power output will increase in various wind directions if the rational speeds of all the fans except the upwind first row fans increase to 86.9 rpm. This can contribute to the optimal operation of the ACC by rotational speed adjustment of axial flow fans.     

1000MW直接空冷机组汽泵冷凝采用蒸发式冷凝器的探讨

在分析蒸发式冷凝器工作原理的基础上,对1 000MW超超临界直接空冷机组汽动给水泵小汽轮机冷凝采用蒸发式冷凝器的可行性进行了系统分析,对分别采用蒸发式冷凝器和带湿冷塔的湿式循环冷却系统的用水特性及经济性进行了对比,并介绍了蒸发式冷凝器在国外火电厂的应用情况.研究表明,蒸发式冷凝器与带湿冷塔的湿式循环冷却系统相比,具有节能、节水、运行费用低和投资少等诸多优点,特别适合于强调节能和节水的空冷式发电机组汽泵的冷凝,在我国推广这项技术十分必要.该文为蒸发式冷凝器在国内火电厂中的应用推广提供参考.     

Improved energy performance of air cooled centrifugal chillers with variable chilled water flow

This paper considers how to apply optimum condensing temperature control and variable chilled water flow to increase the coefficient of performance (COP) of air cooled centrifugal chillers. A thermodynamic model for the chillers was developed and validated using a wide range of operating data and specifications. The model considers real process phenomena, including capacity control by the inlet guide vanes of the compressor and an algorithm to determine the number and speed of condenser fans staged based on a set point of condensing temperature. Based on the validated model, it was found that optimizing the control of condensing temperature and varying the evaporator’s chilled water flow rate enable the COP to increase by 0.8–191.7%, depending on the load and ambient conditions. A cooling load profile of an office building in a subtropical climate was considered to assess the potential electricity savings resulting from the increased chiller COP and optimum staging of chillers and pumps. There is 16.3–21.0% reduction in the annual electricity consumption of the building’s chiller plant. The results of this paper provide useful information on how to implement a low energy chiller plant.     

冬季自然通风状态下直接空冷凝汽器的性能

直接空冷电厂的安全运行与空冷凝汽器在冬季自然通风条件下的换热性能有着密切的联系.依托实际工程项目,确定了某135MW直接空冷凝汽器(ACC)冬季自然通风下的热压.利用计算传热学(NHT)软件FLUENT,对不同迎面风速下,直接空冷凝汽器双排管换热元件的冬季性能进行了数值模拟、分析和研究.根据空气的作用压力与流经空冷凝汽器时所产生阻力之间的对应关系,确定了冬季自然通风状态下空冷凝汽器性能.它为直接空冷系统的优化设计提供帮助.     

Performance of sub‐cooled PEMFCs

Numerical simulations of a proton exchange membrane fuel cell were carried out for various temperatures ranging from well below the freezing temperature of water to a moderate ambient temperature, and also for various inlet temperatures, to investigate its performance. A three‐dimensional serpentine flow field was used to determine the cell behavior temperature conditions. The saturation of liquid water was considered for various ambient temperatures in order to obtain realistic estimates of cell performance, with special emphasis placed on sub‐cooled temperatures. Results show that both the ambient and the inlet temperature have strong influences on cell performance, although the inlet temperature has much more important influence than the ambient temperature. In addition, liquid water saturation is enhanced at higher inlet temperatures. Moreover, for sub‐cooled ambient temperatures the liquid saturation level is higher in the shoulder region near the inlet section than in the outlet section; this trend is reversed for higher ambient temperatures. There is a high probability that operation of the cell at sub‐cooled temperatures and higher inlet temperatures will result in the formation of ice throughout the system, which may further degrade the cell performance. The model was validated by comparison of predicted polarization curves with those found in the literature. Copyright © 2010 John Wiley & Sons, Ltd.     

Coupling of an innovative small PWR and advanced sodium‐cooled fast reactor for incineration of TRU from once‐through PWRs

In the nuclear industry, safely managing spent fuels discharged from PWRs (pressurized water reactors) is an ongoing challenge. In this paper, a synergistic coupling of innovative small long‐cycle PWRs and advanced sodium‐cooled fast reactors is considered to reduce the accumulated TRUs (transuranics) by transmuting them with electricity production. In the coupling strategy, the innovative small PWRs employing UO₂–ThO₂ and fully ceramic micro‐encapsulated fuels are used to deeply burn TRUs from commercial PWRs, while advanced SFRs (sodium‐cooled fast reactors) with actinide recycling are designed to further transmute the TRUs discharged from innovative small PWRs. This work focuses on the core physics analysis of new SFR burner cores using different TRU feeds discharged from small PWRs. Additionally, quasi‐static reactivity balance analyses are performed to understand the safety of the SFR burner cores. The mass flows of TRUs in the nuclear park, which is composed of PWRs, small long‐cycle PWRs, and SFR burners, are analyzed to evaluate TRU inventory reduction. The results of this study show that the advanced SFR burners with all the TRU feed types discharged from the small long‐cycle PWRs have a high TRU consumption rate. They satisfy all of the conditions for self‐controllability under unprotected accidents with a reasonable number of control rods. This coupling strategy requires ~35% less power in conjunction with the advanced SFR burners in the nuclear park and increases the support ratio of SFR burners by ~42% than does the coupling of commercial PWRs and SFR burners. Copyright © 2015 John Wiley & Sons, Ltd.