Evaporative Cooling Applied in Thermal Power Plants:A Review of the State-ofthe-Art and Typical Case Studies

A review is conducted about the application of the evaporative cooling technology in thermal power plants.Different case studies are considered,namely,evaporative air conditioners,evaporative cooling in direct air-cooled systems,gas turbine inlet cooling,wet cooling towers,and hybrid cooling towers with a crosswind effect.Some effort is provided to describe the advantages related to direct evaporative cooling when it is applied in thermal power plants and illustrate the research gaps,which have not been filled yet.In particular,typical case studies are intentionally used to compare the cooling performances when direct evaporative cooling is implemented in different types of cooling towers,including the natural draft wet cooling tower(NDWCT)and the pre-cooled natural draft dry cooling tower(NDDCT).It is shown that the NDWCT provides the best cooling performance in terms of power station cooling,followed by the pre-cooled NDDCT,and the NDDCT;moreover,the evaporative pre-cooling is able to enhance the cooling performance of NDDCT.Besides,on a yearly basis,better NDDCT cooling performances can be obtained by means of a spray-based pre-cooling approach with respect to wet media pre-cooling.Therefore,the use of nozzle spray is suggested for improvement in the performance of indirect/direct air-cooling systems with controlled water consumption.

Experimental Study of Air Conditioning Unit of Evaporative Cooling Assisted Mechanical Refrigeration

The evaporative cooling,which assists the refrigeration machinery air-conditioning systems test-rig,has been designed.Its structure and working principle were described,and the performance test was conducted and analyzed.The test shows that making full use of the evaporative cooling "free cooling" in Spring and Autumn seasons can fully meet the requirements of air-conditioned comfort through the switch of the function in different seasons.Taking into account the evaporative cooling fan and pump energy consumption,compared with the traditional mechanical refrigeration system,more than 80 percent of energy can be saved,and the energy efficiency ratio of the Unit(EER)is as high as 7.63.Using the two stages of indirect evaporative cooling to pre-cool the new wind in summer,under the conditions of the same air supply temperature requirements,0.83 kg/s chilled water saved can be equivalent to the traditional mechanical refrigeration system,and when the new wind ratio up to 50 percent,more than 10 percent load was reduced in mechanical refrigeration system.The overall EER increased about 35 percent.

Stark-potential evaporative cooling of polar molecules in a novel optical-access opened electrostatic trap

We propose a novel optical-access opened electrostatic trap to study the Stark-potential evaporative cooling of polar molecules by using two charged disk electrodes with a central hole of radius r0 = 1.5 mm, and derive a set of new analytical equations to calculate the spatial distributions of the electrostatic field in the above charged-disk layout. Afterwards, we calculate the electric-field distributions of our electrostatic trap and the Stark potential for cold ND3 molecules, and analyze the dependences of both the electric field and the Stark potential on the geometric parameters of our charged-disk scheme, and find an optimal condition to form a desirable trap with the same trap depth in the x, y, and z directions. Also, we propose a desirable scheme to realize an efficient loading of cold polar molecules in the weak-field-seeking states, and investigate the dependences of the loading efficiency on both the initial forward velocity of the incident molecular beam and the loading time by Monte Carlo simulations. Our study shows that the maximal loading efficiency of our trap scheme can reach about 95%, and the corresponding temperature of the trapped cold molecules is about 28.8 inK. Finally, we study the Stark-potential evaporative cooling for cold polar molecules in our trap by the Monte Carlo method, and find that our simulated evaporative cooling results are consistent with our developed analytical model based on trapping-potential evaporative cooling.

A Mathematical Model of an Evaporative Cooling Pad Using Sintered Nigerian Clay

Overtime, reduction in the amount of heat generated in engineering systems in operations have been of great concern and have continuously been under study. It is in line with the above that this research work developed a mathematical model of an evaporative cooling pad using sintered Nigerian clay. A physical model of the evaporative cooling phenomenon was developed followed by the derivation of the governing equations describing the energy and mass transfer for the clay model from the laws of conservation of continuum mechanics. A set of reasonable and appropriate as-sumptions were imposed upon the physical model. Constitutive relationships were also developed for further analysis of the developed equations. The finite element model of numerical methods was used to analyse the energy transfer governing equations which resulted in the determination of the temperature of the exposed boundary surface at any given time, t2 after the commencement of the evaporative cooling processes. In this paper, it was found out that surface temperature differences could be as much as 6?C in the first cycle of evaporative cooling with the potential of further reduction. Further, an equation for the prediction of the effectiveness of an evaporative cooling system using clay modeled cooling pads was developed. The findings in this research work can be applied in the design, construction and maintenance of evaporative coolers used to dissipate waste heat when a large amount of natural water is not readily available or if for environmental and safety reasons the large water body can no longer absorb waste heat.

Collision of cold CaF molecules: Towards evaporative cooling

Long range intermolecular interaction potential surface of CaF(~2∑^+) was simulated by employing the MOLPRO program and using the RCCSD(T)/def2-TZVP theory. The predicted data were further fitted to obtain the collision crosssection. The elastic collision cross-section of CaF at the temperature around 2 mK is as high as 6.5 × 10^(-9) cm^2 and the collision rate is over 4.1 × 10~6 Hz. Additionally, we found that an orientation electric field will simplify the intermolecular interaction potential function from quaternary into ternary and the collision cross-section will be raised by about three orders. All-optical evaporative cooling of cold CaF is discussed in the conclusion.

Surface-induced evaporative cooling

The effects of surface-induced evaporative cooling on an atom chip are investigated. The evolutions of temperature, number and phase-space density of the atom cloud are measured when the atom cloud is brought close to the surface. Rapid decrease of the temperature and number of the atoms is found when the atom-surface distance is 〈 100 ttm. A gain of about a factor of five on the phase-space density is obtained. It is found that the efficiency of the surface-induced evaporative cooling depends on the atom-surface distance and the shape of the evaporative trap. When the atoms are moved very close to the surface, severe heating is observed, which dominates when the holding time is 〉 8 ms. It is important that the surface-induced evaporative cooling offers novel possibilities for the realization of a continuous condensation, where a spatially varying evaporative cooling is required.

Experimental investigation of evaporative cooling mixture of bosonic ^(87)Rb and fermionic ^(40)K atoms with microwave and radio frequency radiation

We investigate sympathetic cooling fermions 40K by evaporatively cooling bosonic 87Rb atoms in a magnetic trap with microwave and radio frequency induced evaporations in detail. The mixture of bosonic and fermionic atoms is prepared in their polarized spin states IF = 9/2, mF = 9/2） for 40K and IF = 2, mF=2〉 for 87Rb, which is trapped in Quadrupole-Ioffe-Configuration trap. Comparing microwave with radio frequency evaporatively cooling bosonic STRb atoms with sympathetically cooling Fermi gas 40K, we find that the presence of rubidium atoms in the [2, 1} Zeeman states, which are generated in the evaporative process, gives rise to a significant loss of 40K due to inelastic collisions. Thus, the rubidium atoms populated in the [2, 1} Zeeman states should be removed in order to effectively perform sympathetically cooling 40K with the evaporatively cooled STRb atoms.

Light-induced evaporative cooling in a magneto-optical trap

This paper presents an experimental demonstration of light-induced evaporative cooling in a magneto-optical trap. An additional laser is used to interact with atoms at the edge of the atomic cloud in the trap. These atoms get an additional force and evaporated away from the trap by both the magnetic field and laser fields. The remaining atoms have lower kinetic energy and thus are cooled. It reports the measurements on the temperature and atomic number after the evaporative cooling with different parameters including the distance between the laser and the centre of the atomic cloud, the detuning, the intensity. The results show that the light-induced evaporative cooling is a way to generate an ultra-cold atom source.

Modeling and numerical analysis of evaporative condensing regenerator

A two-dimensional steady state model was developed and solved numerically to predict the performance of evaporative condensing regenerator.Two-dimensional parameter distributions of air,solution and refrigerant were calculated by the mathematical model.The solution content first increases and then decreases along the solution flow direction.At y/Hr=0.98(where Hr is the height of regenerator),air humidity increases from 1.99% to 2.348% firstly and then decreases.The experimental results were used to validate mathematical model.It is indicated that the simulation results agree with experimental data well.The results not only show that the mathematical model can be used to predict the performance of regenerator,but also has great value in the design and improvement of evaporative condensing regenerator.

The Effects of Evaporative Cooling on Folliculogenesis and Ovarian Hormones during the Estrous Cycle of Dairy Holstein Cows during the Summer Months in Saudi Arabia

Heat stress is identified as a major cause of lower productive and reproductive performance in animal farming. This situation is more common in Saudi Arabia than in other countries because of extremely high ambient temperatures experienced during the summers. The evaporative cooling cow group had significantly increased serum E2 concentrations on days 7 and 14 - 19 of their estrous cycles, and significantly decreased serum P4 concentrations on days 7 - 18 of their estrous cycles. Evaporative cooling plus shade lowered ambient temperatures (41.80 ± 0.74 versus 47.40?C ± 0.84?C) have increased the relative humidity (0.33 ± 0.01 versus 0.24 ± 0.01) and decreased the temperature humidity index (80.24 ± 0.60 versus 84.77 ± 0.68) when compared with shade alone. However, cows under shade alone, compared to cows under evaporative cooling with shade, had a larger number of small (10.04 ± 0.54 versus 4.72 ± 0.58), medium (2.80 ± 0.21 versus 1.79 ± 0.17), and large follicles (6.82 ± 0.28 versus 5.66 ± 0.22). These results demonstrated that while evaporative cooling had positive effects on dairy cows in this experiment, changes could have been more profound, if installations of curtains and fans were implemented, which might need further investigation.

Modeling and Simulation of Evaporative Cooling System in Controlled Environment Greenhouse

Greenhouses are used for the main purpose of improving the environmental conditions in which plants are grown. There are many parameters can affect the growing of plants inside greenhouse, such as air temperature and relative humidity. The adjustment of these parameters is achieved by selecting appropriate control actions. This work proposes a controlling technique for greenhouse indoor temperature and relative humidity. The proposed greenhouse cooling system temperature controller is designed to adjust the air volume flow rate in pad-fan cooling system to fix the greenhouse indoor temperature at 20?C and 70% relative humidity. The designed control technique is realized to ensure the required and continuous operation of the greenhouse. Moreover, this work present, a complete mathematical modeling and simulation of cooling system is introduced. In addition, a computer model based on MATLAB SIMULINK software has been used to predict the temperature and relative humidity profiles inside the greenhouse. The results are realized the requirements of the greenhouse cooling system environment.

Observation of Atomic Dynamic Behaviors in the Evaporative Cooling by In-Situ Imaging the Plugged Hole of Ultracold Atoms

We experimentally observe the dynamic evolution of atoms in the evaporative cooling, by in-situ imaging the plugged hole of ultracold atoms. Ultracold rubidium atoms confined in a magnetic trap are plugged using a blue-detuned laser beam with a waist of 20 m at a wavelength of 767 nm. We probe the variation of the atomic temperature and width versus the radio frequency in the evaporative cooling. Both the behaviors are in good agreement with the calculation of the trapping potential dressed by the rf signal above the threshold temperature,while deviating from the calculation near the phase transition. To accurately obtain the atomic width, we use the plugged hole as the reference to optimize the optical imaging system by precisely minimizing the artificial structures due to the defocus effect.

Experimental Study on the Thermal Performances of a Tube-Type Indirect Evaporative Cooler

The so-called indirect evaporative cooling technology is widely used in air conditioning applications.The thermal characterization of tube-type indirect evaporative coolers,however,still presents challenges which need to be addressed to make this technology more reliable and easy to implement.This experimental study deals with the performances of a tube-type indirect evaporative cooler based on an aluminum tube with a 10 mm diameter.In particular,the required tests were carried out considering a range of dry-bulb temperatures between 16℃ and 18℃ and a temperature difference between the wet-bulb and dry-bulb temperature of 2℃∼4℃.The integrated convective heat transfer coefficient inside the tube in the drenching condition has been found to lie in the range between 36.10 and 437.4(W/(m^(2)⋅K)).

管式蒸发冷却下LiCl-CaCl_(2)混合溶液降膜除湿特性分析

针对绝热型溶液除湿器性能低下的问题,设计了一种管式蒸发冷却型溶液除湿器,并采用具有较高经济性的LiCl-CaCl_(2)混合溶液作为除湿剂.基于理论模型,数值模拟了混合溶液中LiCl、CaCl_(2)两组分混合质量比、溶液参数和空气参数对蒸发冷却及绝热工况下除湿器热湿传递特性的影响.结果表明,除湿器在蒸发冷却工况下的单位面积除湿率高于绝热工况,最高可提升41.5%,且溶液中LiCl质量分数越小,其性能优势越显著.蒸发冷却除湿优势受溶液温度影响显著,单位面积除湿率与除湿空气流量呈正相关,与溶液流量呈负相关.不同的LiCl-CaCl_(2)混合质量比下蒸发冷却除湿特性主要受溶液温度影响,且在溶液温度较低时降低LiCl质量分数对除湿性能影响较小.2种运行工况下空气流量对除湿器单位面积除湿率的正向提升率可达136.9%~168.1%,而溶液流量对其影响较弱.

动车检查库不同通风系统降温效果对比研究

基于实测数据开展了不同通风系统对夏热冬冷地区动车检查库降温效果的对比研究。结果表明:屋顶机械排风系统设计换气次数宜为2~4 h^(-1);直接蒸发冷却送风系统换气次数宜为3~4 h^(-1);诱导通风系统推荐采用中部送风、两侧排风的系统形式,机械送排风换气次数宜为2 h^(-1);各通风方案在推荐设计值下都能满足湿球黑球温度限值30℃的舒适性要求;综合对比各方案,机械排风系统造价最低,诱导通风系统效果最好,蒸发冷却送风系统适合于改善局部热环境。

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%)。

电子束设备蒸镀铝膜工艺的研究

利用电子束蒸镀设备沉积高质量铝膜是薄膜工艺的一个难题。为此,提出一种采用改造的三氧化二铝坩埚作为蒸镀铝膜的衬锅,通过三次添加物料预熔再蒸镀来沉积铝膜的方法,研究了不同蒸镀速度对铝膜电阻率、晶粒形貌和成分组成的影响。结果表明:凸起状的熔融铝液面能有效增大其与坩埚壁的接触角,基本消除铝膜中的三氧化二铝杂质;随着蒸镀速度的增加,铝膜晶粒尺寸逐渐增大,而平均电阻率呈下降趋势;采用本方法能够制备出纯度99.9%,电阻率最低为3.4×10^(-6)Ω·cm的铝膜。

通信机楼绿色节能改造及运行能效优化研究

本文以北京某大型通信机楼的空调系统节能改造为例,分析了间接蒸发冷却系统与水氟换热技术在机房空调节能改造方面的优势,并且对其实际运行期的节能表现开展了量化分析。结果显示,该系统在保障机房温湿度环境稳定的同时,提高了能效比,降低了运行费用,展示了显著的节能减碳潜力。研究成果可为数据中心和通信机房的节能改造提供有价值的参考。

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。

R1234yf在板式蒸发冷凝器中换热过程的数值模拟

通过建立板式蒸发冷凝器的二维数学模型,模拟了新型制冷剂R1234yf在板式蒸发冷凝器的换热过程,总结了冷却水温度、空气含湿量、制冷剂温度在板式蒸发冷凝器中的分布规律,并分析了冷凝温度、降膜雷诺数及空气湿球温度对板式蒸发冷凝器中换热的影响。研究表明:板式蒸发冷凝器的换热能力随冷凝温度升高而增大,随空气湿球温度升高而减小,随着降膜雷诺数的升高先增大后减小。冷凝温度从41℃变化到45℃时,板式蒸发冷凝器的热流密度增加了16.2%;湿球温度从21℃升高到26℃时,板式蒸发冷凝器的热流密度降低了14.6%;在不同冷凝温度下降膜雷诺数由60变化到120,板式蒸发冷凝器的热流密度最大变化率为6.06%。