一种基于太阳能与蒸发冷却的新型新风处理机组

新风负荷约占空调能耗的30％,减少新风处理能耗对降低空调能耗有重要作用.本文提出了一种将太阳能空气集热器与间接蒸发冷却器相结合的新型新风处理机组,夏季采用间接蒸发冷却器对新风预冷,喷淋水以循环水为主,利用冷凝水作为其补充水,降低了喷淋水的水温,并利用室内排风作为间接蒸发冷却器的二次空气,提高了换热效率;冬季采用太阳能空气集热器对新风预热,并利用间接蒸发冷却器作为一次空气与二次空气的显热换热器来承担部分冬季新风负荷,从而大大减少了新风处理机组的能耗.能耗计算分析结果表明,与传统新风处理机组相比,新型新风处理机组夏季节能36.9％,冬季节能64.0％,静态投资回收期为3.7年,动态投资回收期为4.7年.     

CFD方法与间接蒸发冷却换热器的三维数值模拟

采用计算流体力学(CFD)和数值传热学方法,对间接蒸发冷却器内流体流动与热质交换过程进行简化和假设,建立了换热器内三维层流流动与传热的数学物理模型。采用交错网格离散化非线性控制方程组,编制了三维simple算法程序。对间接蒸发冷却器内的流场、温度场及浓度场进行数值模拟研究,得到换热器内的流体流动状态和热流分布,并分析了通道宽度变化对换热器内流体流动与换热的影响。     

土壤空气换热器换热特性的模拟研究

文章针对日光温室环境下土壤空气换热器的换热特性进行了研究。首先通过监测土壤空气换热器沿程空气温度的全天变化,分析了试验工况下土壤空气换热器的动态换热过程及系统性能变化规律。研究结果表明,在试验工况下,土壤空气换热器系统的性能系数(COP)可高达24.1。在此基础上,通过建立土壤空气换热器的非稳态换热模型,模拟研究不同的入口风速对土壤空气换热器换热性能的影响。研究结果表明,当换热管入口空气温度相同时,随着入口风速的增加,土壤空气换热器进出口空气温度差逐渐减小,出口处空气温度与土壤温度差值逐渐增大,这意味着土壤空气换热器有效换热长度逐渐变长。在此过程中,土壤空气换热器系统的换热量和COP随着入口空气风速的增加呈现出先增后减的规律。通过模拟结果可知,当入口风速达到5.5 m/s时,土壤空气换热器系统的换热量与COP均达到最大值。     

间接蒸发冷却板式换热器的(火用)效率分析

在考虑壁面两侧空气温度实际变化的前提下,对间接蒸发冷却传热过程中影响yong效率的主要因素,如一次空气进口温度、一、二次空气流速之比,二次空气相对湿度,一、二次通道宽度之比以及壁面润湿率进行了分析研究,为实际换热器设计提供理论依据。     

基于场协同原理的微通道熔盐换热器传热强化

微通道换热器具有换热性能好、结构紧凑的优点，但在换热器中，熔盐侧的流动换热性能较差。为解决上述问题，运用场协同原理对翼型微通道熔盐换热器进行强化，并对其进行数值分析。该文以60%硝酸钠和40%硝酸钾混合而成的二元硝酸盐（太阳盐，Solar Salt）作为热侧流体，计算出局部场协同角分布，分析入口流速和入口温度对速度场和温度场场协同性的影响，并对局部场协同性较差的位置进行强化。结果表明，入口流量在0.005～0.013 kg/s(Re=2810～7307)范围内，翼型微通道换热器的场协同性随入口流量和入口温度的增加而变差。强化后的换热器其熔盐侧全场场协同角下降约3.73°，综合换热性能（PEC）提升2.25%。     

满液型海水淡化蒸发器的换热特性研究

海水淡化装置，太阳能或余热吸收式制冷机中的蒸发换热器目前使用管排外降膜式蒸发方式。如将传热管束紧凑排列置于饱和状态液体中则变为满液式蒸发换热器，利用传热管束间受限空间内早期沸腾强化换热机理，将中小热负荷条件下的自然对流换热转化为核沸腾换热，在间隙尺寸适宜时，其换热性能可能优于降膜式蒸发换热器。该研究以盐水为实验工质，对紧凑传热管束受限空间的沸腾换热进行了实验研究，确认了满液式蒸发换热器也具有很好的换热性能，在中小热负荷条件下甚至超过降膜式蒸发换热器。     

蒸发式换热器结构及热工水力特性计算分析

为了使设计的蒸发式换热器安全高效,讨论其计算原理和完善其设计流程意义重大。本文针对核电实验应用的蒸发式热交换器,由中国原子能科学研究院提供设计参数,采用热工水力分析和强度校核,通过制定和完善设计步骤和计算流程,最终计算得到换热器换热面积,设计裕量和一次侧阻力,同时通过作图阐明了系统特性参数如总传热系数、一次侧进出口温度,二次侧压力等随负荷的变化规律。计算结果均达到工程实际的要求,分析结果表明功率负荷的增加伴随着一次侧温度的提高和二次侧压力的降低,堵管使总传热系数减小,二次侧压力降低。研究提出了高效、安全、节能的设计方案,并为工程上蒸发式换热器设计提供了有价值的参考。     

板管式间接蒸发冷却换热器的设计分析

介绍一种结构具有代表性的间接蒸发冷却换热器——板管式间接蒸发冷却换热器,并从芯体结构、材料的选择、芯体的换热计算和各功能部件的设计计算等方面进行详细设计分析。     

单元式露点蒸发冷却装置的实验研究

本研究设计了一台由干、湿通道相结合的单元式露点蒸发冷却装置,通过实验研究了蒸发冷却装置在空气经过一级冷却的模式1和经过二级冷却的模式2两种运行模式下,不同空气入口参数时的换热效果。实验结果表明,空气的入口温度越高,换热效果越好;低湿度时空气的进出口温差比高湿度时大,但其湿球效率和露点效率反而较低,这说明2种效率并不适用于不同湿度间的冷却效果对比;模式2运行时的换热效果比模式1好。与已有研究成果对比表明,该单元式露点蒸发冷却装置的湿球效率和露点效率分别可以达到120%和88%,为露点蒸发冷却装置的优化设计提供理论依据和优化方向。     

百叶窗板翅式换热器换热与阻力性能数值模拟研究

为了解决百叶窗板翅式换热器的内部性能优化问题,通过对层流稳态下换热器燃气侧的典型流动换热单元进行建模及流动换热分析,得到了单元体内部速度、流线及温度的分布特性,并通过对换热系数、科尔本传热因子、进出口单位压降、范宁摩擦系数的比较,获得了不同燃气入口速度下翅片间距及翅片角度对换热器换热性能及流动阻力的影响。结果表明:在百叶窗翅片角度及其他尺寸参数不变时,当百叶窗间距为0. 7 mm时其换热性能最优,阻力随间距增大而减小;在翅片间距等参数不变而角度变化时,换热性能与阻力均随角度增大而增大,当百叶窗角度从15°增加至30°时,换热性能的增加幅度较为明显。     

An indirect evaporative chiller

A novel indirect evaporative chiller driven by outdoor dry air to produce cold water as the cooling source for air conditioning systems is introduced, and the principle and the structure of the chiller is presented. The cold water can be produced almost reversibly under ideal working conditions, with its temperature infinitely close to the dew point temperature of the inlet air. The key components of the chiller are an air cooler and a padding tower. To improve the heat transfer performance inside the chiller, a quasi-countercurrent air cooler was designed; a subsection linear method was used for the mathematical model of the padding tower. The first indirect evaporative chiller, designed and developed in 2005, has been in use in Kairui Building, a big hotel in Shihezi, Xinjiang Autonomous Region. The tested temperature of the water produced is below the wet bulb temperature of outdoor air and reached the average value of the dew point temperature and the wet bulb temperature of outdoor air. As the running components are only pumps and fans, the COP (cooling energy for room divided by power cost) of this chiller is high, and the drier the outdoor air, the higher COP the chiller obtained. Since no CFCs are used in this chiller, it would not cause any pollution to the aerosphere. Finally, the application prospect of the indirect evaporative chiller in the world is presented.     

The impact of fouling on performance evaluation of evaporative coolers and condensers

Fouling of evaporative cooler and condenser tubes is one of the most important factors affecting their thermal performance, which reduces effectiveness and heat transfer capability with time. In this paper, the experimental data on fouling reported in the literature are used to develop a fouling model for this class of heat exchangers. The model predicts the decrease in heat transfer rate with the growth of fouling. A detailed model of evaporative coolers and condensers, in conjunction with the fouling model, is used to study the effect of fouling on the thermal performance of these heat exchangers at different air inlet wet bulb temperatures. The results demonstrate that fouling of tubes reduces gains in performance resulting from decreasing values of air inlet wet bulb temperature. It is found that the maximum decrease in effectiveness due to fouling is about 55 and 78% for the evaporative coolers and condensers, respectively, investigated in this study. For the evaporative cooler, the value of process fluid outlet temperature T_p,out varies by 0.66% only at the clean condition for the ambient wet bulb temperatures considered. Copyright © 2005 John Wiley & Sons, Ltd.     

Indirect evaporative cooling of air to a sub-wet bulb temperature

Indirect evaporative cooling is a sustainable method for cooling of air. The main constraint that limits the wide use of evaporative coolers is the ultimate temperature of the process, which is the wet bulb temperature of ambient air. In this paper, a method is presented to produce air at a sub-wet bulb temperature by indirect evaporative cooling, without using a vapour compression machine. The main idea consists of manipulating the air flow inside the cooler by branching the working air from the product air, which is indirectly pre-cooled, before it is finally cooled and delivered. A model for the heat and mass transfer process is developed. Four types of coolers are studied: three two-stage coolers (a counter flow, a parallel flow and a combined parallel-regenerative flow) and a single-stage counter flow regenerative cooler.It is concluded that the proposed method for indirect evaporative cooling is capable of cooling air to temperatures lower than the ambient wet bulb temperature. The ultimate temperature for such a process is the dew point temperature of the ambient air. The wet bulb cooling effectiveness (E_wb) for the examples studied is 1.26, 1.09 and 1.31 for the two-stage counter flow, parallel flow and combined parallel-regenerative cooler, respectively, and it is 1.16 for the single-stage counter flow regenerative cooler. Such a method extends the potential of useful utilisation of evaporative coolers for cooling of buildings as well as other industrial applications.     

Going below the wet-bulb temperature by indirect evaporative cooling: Analysis using a modified ε-NTU method

The objective of this paper is to study a method to achieve sub-wet bulb temperature by indirect evaporative cooling of air (without using a vapor compression machine). For this purpose, an analytical model is developed based on the effectiveness-NTU method (ε-NTU). The main idea for achieving a sub-wet bulb temperature by indirect evaporative cooling of air is by indirectly pre-cooling the working air before it enters the wet passage. It is shown that a modified analytical model for indirect evaporative coolers could be based on the ε-NTU method for sensible heat exchangers when proper adjustments are made by redefining the potential gradients, transfer coefficient, heat capacity rate parameters and assuming a linear saturation temperature-enthalpy relation of air. This modified model is used to find the performance of a regenerative indirect evaporative cooler. The model results show very good agreement with results from experimental measurements and a numerical model.     

An experimental study of a cross-flow type plate heat exchanger for dehumidification/cooling

The thermal and dehumidification behaviour of a standard cross-flow type plate heat exchanger, intended for use as a dehumidifier/cooler, has been investigated both experimentally and numerically. Three sets of experiments have been carried out where air is blown into the primary and secondary sides of the exchanger, while water and liquid desiccant were being sprayed in a counter flow arrangement. The first set represents the indirect evaporative cooling of the primary stream by the secondary air stream. The second set is with liquid desiccant only and no indirect evaporative cooling. In the third set of experiments the primary air stream is indirectly evaporatively cooled by the secondary air stream and dehumidified by the liquid desiccant sprayed into the primary side of the exchanger. The above experiments indicate that the heat exchanger performs well when used with liquid desiccant. Furthermore, for an exchanger angle of 45°, there is an optimum value of air mass flow rate at which the effectiveness and dehumidification efficiency of the plate heat exchanger are maxima. To investigate the effect of the ambient air conditions on the PHE performance, further experiments were carried out using a heater element and a humidifier. The results show that under laboratory conditions the exchanger effectiveness and dehumidification efficiency increase with increasing primary air inlet temperature and humidity ratio. The experimental results were used to validate a computer model developed for the cross-flow type plate heat exchanger/dehumidifier. Comparison indicates that the numerical results are in good agreement with the experiments.     

Modelling and performance analysis of a cross-flow type plate heat exchanger for dehumidification/cooling

This paper describes the performance analysis of a cross-flow type plate heat exchanger for use as a liquid desiccant absorber (dehumidifier) and indirect evaporative cooler. The proposed absorber can be described as a direct contact, cross-flow, heat and mass exchanger, with the flow passages separated from each other by thin plastic plates. One air stream (primary air) is sprayed by liquid desiccant solution, while the other stream (secondary air) is evaporatively cooled by a water spray. Each thin plate, besides separating the water/air passage from the solution/air passage, also provides the contact area for heat and mass transfer between the fluids flowing in each passage. A parametric study for the primary air stream at 33°C, 0.0171 kg/kg humidity ratio and secondary air stream at 27°C and 0.010 kg/kg humidity ratio using calcium chloride solution was performed in this study. The results showed a strong dependence on the heat and mass transfer area, solution concentration and ratio of secondary to primary air mass flow rates. However, negligible differences were found between the performance of a counter flow and a parallel flow arrangement. The results demonstrate that the proposed absorber will not offset both the latent and sensible load of the primary air and, therefore, an auxiliary cooler or more dehumidification/indirect evaporative cooling stages will generally be required to meet the sensible and latent load in a typical comfort application.     

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.     

Maisotsenko循环在燃气轮机进气冷却中的应用研究

采用基于Maisotsenko循环的露点间接蒸发式冷却作为进气冷却的手段,研究了不同环境条件下其对燃气轮机性能的提升效果。建立了针对某9E级燃气轮机的热力循环过程的计算模型,并利用该热力模型分析了进气温度变化对燃机出力的影响。基于Maisotsenko循环的原理,以温降为指标对露点间接蒸发冷却器的性能进行了分析。以功率和效率作为指标,对燃气轮机性能随环境条件的变化情况做了数值模拟,对露点蒸发式冷却与无进气冷却、直接喷雾式冷却对燃机性能的影响进行了计算分析。结果表明,在高温低湿度的条件下,露点间接蒸发式冷却能有效提升燃机性能。     

Modelling of a direct evaporative air cooler using artificial neural network

This paper proposes the use of artificial neural networks (ANNs) to predict various performance parameters of a direct evaporative air cooler. For this aim, an experimental evaporative cooler was operated at steady‐state conditions, while varying the dry bulb temperature and relative humidity of the entering air along with the flow rates of air and water streams. Using some of the experimental data for training, a three‐layer feed‐forward ANN model based on back propagation algorithm was developed. This model was used for predicting various performance parameters of the cooler, namely the dry bulb temperature and relative humidity of the leaving air, mass flow rate of the water evaporated into the air stream, sensible cooling rate, and effectiveness of the cooler. Then, the performance of the ANN predictions was tested by applying a set of new experimental data. The predictions usually agreed well with the experimental values with correlation coefficients in the range of 0.969–0.993, mean relative errors in the range of 0.66–4.04%, and very low root mean square errors. This study reveals that, as an alternative to classical modelling techniques, the ANN approach can be used successfully for predicting the performance of direct evaporative air coolers. Copyright © 2007 John Wiley & Sons, Ltd.