Recent researches in indirect evaporative cooler V: relative thermal performance of buildings coupled to direct and indirect evaporative cooler

A mathematical model has been developed to evaluate the relative thermal performance of a building coupled with an indirect or direct evaporative cooler. Using periodic analysis for taking into account thermal storage of building envelope, explicit expressions have been obtained for room air temperature and room air humidity. For comparing their performance under different climatic conditions, numerical calculations have been made taking meteorological parameters for a typical day for Delhi (composite climate), Jodhpur (hot-dry climate) and Madras (hot-humid climate). It is found that the indirect evaporative cooler is a more effective and energy efficient system than the air-conditioner; it can hence be commercially used for computer and electronic exchange applications as well as for human comfort in a variety of climatic conditions, whereas direct evaporative cooler has limited use (only in hot-dry and composite climates). © 1997 by John Wiley & Sons, Ltd.     

穿片式气体冷却器特点及其影响因素分析

为满足不同容量的汽轮发电机通风冷却系统的需要,必须采用不同形式的翅片式气体冷却器,以进一步改善冷却器的传热与阻力性能。介绍了目前常用的不同翅片形式的穿片式气体冷却器的结构特点,分析了影响穿片式气体冷却器传热和阻力特性的主要因素,以期为穿片式气体冷却嚣的结构与性能优化提供参考。     

板式间接蒸发冷却器热工特性的实验研究

对自行研制设计的间接蒸发冷却换热试件开展了实验,研究了影响换热器换热性能的因素。结果表明：板式间接蒸发冷却器换热效率随二次空气入口的速度升高、一次空气入口的温度、二次空气入口的湿球温度升高而变大,随一次空气入口的速度变大而变小。实验结果对于深入认识间接蒸发冷却器的换热机理及开展换热器的优化设计有着很大的指导意义。     

Performance evaluations of refrigeration systems with air‐cooled,water‐cooled and evaporative condensers

This paper compares the performance characteristics of refrigeration systems employing three types of condensers, namely the air‐cooled, the water‐cooled and the evaporative condensers. Experimental studies were conducted in the same vapour‐compression refrigeration unit operating with a different condenser in each test. It was found that the system with water‐cooled condenser had a higher refrigeration capacity by 2.9–14.4%, and a higher COP by 1.5–10.2% than the one with evaporative condenser. However, the refrigeration capacity and COP of the unit with evaporative condenser were higher than those of the one with air‐cooled condenser by 31.0 and 14.3%, respectively. Copyright © 2004 John Wiley & Sons, Ltd.     

Influence of gas velocity on particulate fouling of exhaust gas recirculation coolers

The objective of this research is to study the influence of gas flow velocity on particulate fouling of exhaust gas recirculation (EGR) coolers. An experimental setup has been designed and constructed to simulate particulate fouling in EGR coolers in diesel engines. The setup consists of soot generator, gas/particle flow heater, testing section for EGR coolers and finally an exhaust system. Two sets of fouling experiments have been performed with and without water injection, and the gas velocity in each set has varied between 30, 70 and 120 m/s. The concentration of soot particles in the gas flow is 100 mg/m³, and the average diameter of the particles is 130 nm with a standard deviation of 55 nm. It has been found that the thermal resistance and thickness of the fouling layer and the fouling rate decrease as the gas velocity in the EGR cooler increases. If EGR coolers are operated with a gas velocity, which is just lower than the critical flow velocity for the largest particle in the flow, quick deterioration of the thermal performance of the heat exchanger will nevertheless occur. This strongly indicates that the gas velocity should exceed a certain critical flow velocity in order to prevent particulate fouling. In addition, the presence of water vapour in the gas flow improves the thermal performance of the cooler and decreases the fouling rate, and its influence decreases as the gas velocity increases.     

冷冻水冷器水垢影响电费水费损失的评估

介绍了冷冻系统水冷器污垢影响的对比试验实测和评估,粗略计算了水垢 造成我国冷冻水冷器运行电费水费的损失每年高达３０亿元．因此,建议重视自动 清洗技术的应用。     

The impact of fouling on performance evaluation of multi-zone feedwater heaters

A numerical method for analyzing closed system feedwater heaters is presented. A general approach to determine area allocations among the desuperheating, condensing and subcooling zones under a known set of operating conditions is presented for a feedwater heater in a steam power plant. A significant amount of heat duty is handled by the condensing zone, whereas the subcooling zone handles a least amount of heat duty which essentially vanishes at low steam pressures. Fluids mass flow rates and accordingly the overall heat transfer coefficients have significant effects on the areas needed for desuperheating, condensing and subcooling in a feedwater heater. Two fouling models are considered to examine their effect on the heat exchanger performance. Insignificant changes were noticed when comparing the heat transfer rate and outlet temperature results of both the models. It is found that heat duty of the heat exchanger decreases by 2.7% in 3 years when we use the recommended fouling resistance, while the outlet shell-side fluid temperature increased by 6.3%.     

蒸发式冷凝器用于火电厂冷却系统中的可行性分析

概述了火电厂冷却系统的特点，介绍了蒸发式冷凝器的工作原理，基于朗肯循环详细分析了蒸发式冷凝器用在火电厂冷却系统中所具有的优点，从而提出了在我国运用这项技术的必要性，并通过两个实例说明蒸发式冷凝器用于火电厂的冷却系统是可行的。     

Effects of acoustic barriers and crosswind on the operating performance of evaporative cooling tower groups

Most evaporative cooling towers are arranged on building roof due to the limitation of space and noise, and acoustic barriers are always installed around cooling towers in practical applications. The existence of acoustic barriers and crosswind may affect the recirculation phenomenon which is directly related to the operating performance of cooling towers. In this study, a physical and mathematical computation model is proposed to research the crosswind and distance between acoustic barriers and inlet of cooling towers. Both sensible and latent heat are considered in this research. The reflux flow rate and performance ratio are obtained to evaluate the recirculation and operating performance, respectively. The results show that the higher the crosswind velocity, the larger the reflux flow rate, and the lower the performance ratio of cooling tower groups. For high crosswind velocity, the presence of acoustic barriers is useful to inhibit reflux and improve operating performance, especially for ICE cooling tower groups. In addition, the optimum values are recommended for LiBr/ICE cooling tower groups in the research cases The variation of reflux flow rate and performance ratio with the acoustic barriers’ distance presents a parabolic tendency.     

Recent research on an indirect evaporative cooler (IEC) Part 2: thermal performance of a non-conditioned building coupled with an IEC

The thermal performance of a non-conditioned building fitted with an indirect evaporative cooler (IEC) has been investigated in terms of hourly, monthly and seasonal discomfort index. The effect of various design parameters of the IEC on the discomfort index has been investigated for three different climatic areas of India, i.e. hot–dry, warm, humid and composite. The analysis has shown that the IEC is effective for creating thermal comfort conditions in buildings in dry–hot and composite climates. © 1997 by John Wiley & Sons, Ltd.     

Theoretical and testing performance of an innovative indirect evaporative chiller

An indirect evaporative chiller is a device used to produce chilled water at a temperature between the wet bulb temperature and dew point of the outdoor air, which can be used in building HVAC systems. This article presents a theoretical analysis and practical performance of an innovative indirect evaporative chiller. First, the process of the indirect evaporative chiller is introduced; then, the matching characteristics of the process are presented and analyzed. It can be shown that the process that produces cold water by using dry air is a nearly-reversible process, so the ideal produced chilled water temperature of the indirect evaporative chiller can be set close to the dew point temperature of the chiller’s inlet air. After the indirect evaporative chiller was designed, simulations were done to analyze the output water temperature, the cooling efficiency relative to the inlet dew point temperature, and the COP that the chiller can performance. The first installation of the indirect evaporative chiller of this kind has been run for 5 years in a building in the city of Shihezi. The tested output water temperature of the chiller is around 14–20 °C, which is just in between of the outdoor wet bulb temperature and dew point. The tested COP_r,s of the developed indirect evaporative chiller reaches 9.1. Compared with ordinary air conditioning systems, the indirect evaporative chiller can save more than 40% in energy consumption due to the fact that the only energy consumed is from pumps and fans. An added bonus is that the indirect evaporative chiller uses no CFCs that pollute to the aerosphere. The tested internal parameters, such as the water–air flow rate ratio and heat transfer area for each heat transfer process inside the chiller, were analyzed and compared with designed values. The tested indoor air conditions, with a room temperature of 23–27 °C and relative humidity of 50–70%, proved that the developed practical indirect evaporative chiller successfully satisfy the indoor air conditioning load for the demo building. The indirect evaporative chiller has a potentially wide application in dry regions, especially for large scale commercial buildings. Finally, this paper presented the geographic regions suitable for the technology worldwide.     

Recent researches in indirect evaporative cooler III: optimization of the cooling potential of a room–coupled indirect evaporative cooler

A mathematical model based on heat transfer principles, for characterizing the cooling performance of a room coupled indirect evaporative cooler (tube type) has been developed. Two dimensionless parameters, i.e. environment factor, ϕ and cooling factor, CF have been defined to characterize the performance of IEC coupled with a room. The optimum values of these parameters have been obtained for different environmental and thermal load conditions. In addition to this, a linear relationship has been obtained for the optimum size of a cooler to remove maximum heat from a room of given size. © 1998 John Wiley & Sons, Ltd.     

甲醇汽车燃油箱蒸发物吸附装置性能的研究

通过对甲醇汽车燃油箱蒸发物的测量,得到M85燃料与汽油的昼fq换气损失分别为6．62g和11．4g。又通过甲醇燃料箱蒸发物吸附装置性能试验,测得活性碳罐对汽油(M0)的工作能力高于对甲醇燃料(M100、M85)的工作能力。试验结果表明,在正常条件下．油箱体积相同时,汽油箱燃油蒸发物吸附装置基本上适用于甲醇汽车。如果碳罐扩容28％,就能达到与汽油相同的吸附效果。     

Study on constant stress: Accelerated life tests of fouling thermal resistance

To shorten the time of fouling tests, fouling life was defined. The statistical analysis method for type II‐censored exponential life data under constant‐stress accelerated life testing models and the accelerated coefficients a and b were obtained. By using an accelerated model, the estimators of the fouling life under usual stress could be obtained. A computing example was given. Results indicated that it is credible and feasible to perform accelerated life tests of asymptotic fouling thermal resistance, and will be of important value to experimental research of fouling. © 2006 Wiley Periodicals, Inc. Heat Trans Asian Res, 35(2): 110–114, 2006; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.20105     

Effect of fractional condensers on characteristics,compounds distribution and phenols selection of bio-oil from pine sawdust fast pyrolysis

Bio-oil is a multicomponent mixture of more than 400 types of organic compounds, with high water content. Fractionation of bio-oil may be a more efficient approach for primary separation of bio-oil. In this work, to better understand the effect of fractional condensers on bio-oil yield, physicochemical characteristics, compounds distribution and phenols selection during biomass fast pyrolysis process, a semi-automatic controlled fluidized bed reactor biomass fast pyrolysis system with four-stage condensers was developed. Average temperatures of Condensers 1, 2, 3, 4 were 32.39 °C, 26.74 °C, 24.06 °C and 23.68 °C, respectively. And the bio-oil yields of Condenser 1, 2, 3, and 4 were 26.82%, 7.31%, 1.48% and 9.69%, respectively. Bio-oil collected from Condenser 4 had the lowest water content (9.68 wt%), the lowest acidity (pH = 3.67), and the highest HHV (29.2 MJ/kg). The highest relative contents of compounds collected from Condenser 1, 2, 3 and 4 were 1-(4-hydroxy-3-methoxyphenyl)-2-Propanone (6.95%), trans-Isoeugenol (6.63%), Creosol (5.28%), and trans-Isoeugenol (6.69%), respectively. Fractional condensers affected the compounds distribution, but it has a stronger effect on relative heavy compounds (molar mass > 250) and a weaker effect on relative light compounds (molar mass < 200). Fractional condensers were more conducive to the selection of phenols with relative yield of more than 30%. Phenols, acids and furfurans tended to distribute at higher temperature, while alcohols, ethers and hydrocarbons tended to distribute at relative lower temperature, but the difference was small. The research has provided a reference for the production of bio-oil.     

Effect of buckling on the cooling performance of free-standing planar thermoelectric coolers

This article investigates the effect of buckling on the cooling performance of planar thermoelectric (TE) coolers (TECs). The TEC is made up of n-type and p-type TE elements with large length-to-thickness ratio. Each TE element is modeled as a fixed–fixed thin plate. Theoretical model for the solutions of temperature and electric potential fields of the TE element after buckling is established. The corresponding coefficient of performance (COP) that indicates the cooling performance of TEC is also given. Influence of Seebeck coefficient, thermal conductivity, temperature difference, and the ratio of length-to-thickness on the cooling performance are discussed. It is found that buckling of TEC will reduce its cooling performance. A bigger Seebeck coefficient and smaller thermal conductivity can both improve the value of COP. It is also found that there is no maximum COP when the temperature difference across the TEC is zero. However, the effect of buckling on the cooling performance of TEC can be ignored if the TEC achieves the maximum COP. The peak value of COP is independent of the ratio of length-to-thickness of the TEC. An optimized value of the electric current corresponding to the maximum COP of the TEC is obtained.     

燃气轮机进气喷雾蒸发冷却的经济性分析

以轮南燃气轮机电站喷雾蒸发冷却器为例,分析了在不同气候条件下蒸发冷却器运行的经济性。结果表明,对于联网运行机组,蒸发冷却器的投运可提高燃气轮机出力,从而获得经济效益,在高温干燥地区尤为突出,且机组在保持T5温度(燃气轮机第三级透平喷嘴入口处温度)不变的情况下投运所带来的经济效益更为明显。     

粉末活性炭控制一体式膜生物反应器膜污染的作用

投加粉末活性炭以减缓膜生物反应器膜污染,延长反应器工作周期,降低膜反应器电耗。试验结果表明:投加80~100目活性炭,可减缓膜污染速度,平均膜比通量比对照反应器提高3.82×10-6m3/(m2.m.s);投加200~300目活性炭,由于粒径过小,会造成严重膜污染,反应器膜比通量下降速度较对照反应器更快;投加40~60目活性炭,由于粒径过大,活性炭会在反应器内沉淀,很难有效控制膜污染。投加粉末活性炭时,膜生物反应器具有比普通膜生物反应器更稳定的出水水质,COD、BOD5分别提高3.1%、2.4%。     

Performance evaluation and comparison of multistage indirect evaporative cooling systems in two operation modes

The evaporative cooling technique is an efficient approach for cooling application. This study aims to establish a performance evaluation method to advance the appropriate design for multistage indirect evaporative cooling systems. A mathematical formulation has been developed for the indirect evaporative cooler (IEC). After the validation, the mathematical model was used to analyze the evaluation criteria by considering the simultaneous influence of the cooling effectiveness, the pressure drop, and the cooling capacity of the multistage IEC operating in two modes. The Mode-1 IEC is a conventional counterflow unit, while the Mode-2 IEC employs a regenerative M-cycle arrangement. The IECs are operated in a tandem arrangement. The multistage system is capable of improving the cooling performance and reducing the outlet air temperature. In addition, the multistage system displays a higher pressure drop resulting in a lager consumption of fan power. The analysis of performance evaluation criteria indicates that the appropriate maximum stage is suggested to be three-stage and two-stage for the Mode-1 and the Mode-2 IEC, respectively.